WO2021028732A1

WO2021028732A1 - Method of automatic adjustment of a tunable passive antenna and a tuning unit, and apparatus for radio communication using this method

Info

Publication number: WO2021028732A1
Application number: PCT/IB2020/055006
Authority: WO
Inventors: Frederic Broyde; Evelyne Clavelier
Original assignee: Tekcem
Priority date: 2019-08-13
Filing date: 2020-05-27
Publication date: 2021-02-18
Also published as: FR3099969A1; FR3099969B1

Abstract

The invention relates to a method for automatically adjusting one or more tunable passive antennas and a single-input-port and single-output-port tuning unit. The invention also relates to an apparatus for radio communication using this method, for instance a radio transceiver.An apparatus for radio communication of the invention comprises: a tunable passive antenna (1); a single-input-port and single-output-port tuning unit (4) having an input port and an output port; a feeder (2); a sensing unit (3); a transmission and signal processing unit (8) which applies an excitation to the input port through the sensing unit, which delivers one or more "antenna adjustment instructions", and which delivers "tuning unit adjustment instructions"; and a control unit (6) which delivers one or more "antenna control signals" and one or more "tuning control signals".

Description

Method of automatic adjustment of a tunable passive antenna and a tuning unit, and apparatus for radio communication using this method FIELD OF THE INVENTION The invention relates to a method for automatically adjusting one or more tunable passive antennas and a single-input-port and single-output-port tuning unit, for instance a tunable passive antenna and a single-input-port and single-output-port tuning unit of a radio transmitter. The invention also relates to an apparatus for radio communication using this method, for instance a radio transceiver. The French patent application No. FR1909176 of 13 August 2019, entitled “Procédé pour réglage automatique d’une antenne passive accordable et d’une unité d’accord, et appareil pour communication radio utilisant ce procédé” is incorporated by reference. PRIOR ART In what follows, in line with the “IEC multilingual dictionary of electricity” edited by the Bureau Central de la Commission Electrotechnique Internationale in 1983, “open-loop control” means control which does not utilize a measurement of the controlled variable, and “closed-loop control” (which is also referred to as “feedback control”) means control in which the control action is made to depend on a measurement of the controlled variable. A tunable passive antenna comprises at least one antenna control device having at least one parameter having an effect on one or more characteristics of said tunable passive antenna, said at least one parameter being adjustable, for instance by electrical means. Adjusting a tunable passive antenna means adjusting at least one said at least one parameter. Each of said one or more characteristics may for instance be an electrical characteristic such as an impedance at a specified frequency, or an electromagnetic characteristic such as a directivity pattern at a specified frequency. A tunable passive antenna may also be referred to as “reconfigurable antenna”. Some authors consider three classes of tunable passive antennas: polarization-agile antennas, pattern-reconfigurable antennas and frequency-agile antennas. The state of the art regarding frequency-agile antennas is for instance described in the article of A. Petosa entitled “An Overview of Tuning Techniques for Frequency-Agile Antennas”, published in IEEE Antennas and Propagation Magazine, vol. 54, No. 5, in October 2012. As explained in this article, many different types of antenna control device may be used to control one or more characteristics of a tunable passive antenna. An antenna control device may for instance be: - an electrically controlled switch or change-over switch, in which case a parameter of the antenna control device having an effect on one or more characteristics of the tunable passive antenna may be the state of the switch or change-over switch; - an adjustable impedance device, in which case a parameter of the antenna control device having an effect on one or more characteristics of the tunable passive antenna may be the reactance or the impedance of the adjustable impedance device at a specified frequency; or - an actuator arranged to produce a mechanical deformation of the tunable passive antenna, in which case a parameter of the antenna control device having an effect on one or more characteristics of the tunable passive antenna may be a length of the deformation. If an antenna control device is an electrically controlled switch or change-over switch, it may for instance be an electro-mechanical relay, or a microelectromechanical switch (MEMS switch), or a circuit using one or more PIN diodes or one or more insulated-gate field-effect transistors (MOSFETs) as switching devices. An adjustable impedance device is a component comprising two terminals which substantially behave as the terminals of a passive linear two-terminal circuit element, and which are consequently characterized by an impedance which may depend on frequency, this impedance being adjustable. An adjustable impedance device having a reactance which is adjustable by electrical means may be such that it only provides, at a given frequency, a finite set of reactance values, this characteristic being for instance obtained if the adjustable impedance device is: - a network comprising a plurality of capacitors or open-circuited stubs and one or more electrically controlled switches or change-over switches, such as electro-mechanical relays, or microelectromechanical switches, or PIN diodes or insulated-gate field-effect transistors, used to cause different capacitors or open-circuited stubs of the network to contribute to the reactance; or - a network comprising a plurality of coils or short-circuited stubs and one or more electrically controlled switches or change-over switches used to cause different coils or short-circuited stubs of the network to contribute to the reactance. An adjustable impedance device having a reactance which is adjustable by electrical means may be such that it provides, at a given frequency, a continuous set of reactance values, this characteristic being for instance achievable if the adjustable impedance device is based on the use of a variable capacitance diode; or a MOS varactor; or a microelectromechanical varactor (MEMS varactor); or a ferroelectric varactor. Many methods exist for automatically adjusting one or more tunable passive antennas. Some of these methods are applicable to a radio transmitter, for instance the method disclosed in the patent of the United States of America No. 5,225,847 entitled “Automatic antenna tuning system”. Some of these methods are applicable to a radio receiver, for instance the method disclosed in the patent of the United States of America No.7,463,870 entitled “Receiver circuit and control method”. A method for automatically adjusting a tunable passive antenna, applicable to a radio transmitter, is implemented in the automatic antenna system shown in Figure 1. This automatic antenna system is similar to the one disclosed in said patent of the United States of America No. 5,225,847. The automatic antenna system shown in Fig. 1 has a user port (31), the user port presenting, at a given frequency, an impedance referred to as “the impedance presented by the user port”, the automatic antenna system comprising: a tunable passive antenna (1), the tunable passive antenna comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said tunable passive antenna, said at least one antenna control device parameter being adjustable by electrical means; a sensing unit (3) delivering two “sensing unit output signals”, each of the sensing unit output signals being determined by one electrical variable sensed (or measured) at the user port; a feeder (2) having a first end coupled to a signal port of the tunable passive antenna, the feeder having a second end coupled to the user port, through the sensing unit; a signal processing unit (5), the signal processing unit estimating q real quantities depending on the impedance presented by the user port, where q is an integer greater than or equal to 1, using the sensing unit output signals caused by an excitation applied to the user port, the signal processing unit delivering an “adjustment instruction” as a function of said q real quantities depending on the impedance presented by the user port; and a control unit (6), the control unit receiving the adjustment instruction from the signal processing unit, the control unit delivering “control signals”, the control signals being determined as a function of the adjustment instruction, each of the one or more antenna control device parameters being mainly determined by at least one of the control signals. Unfortunately, it was found that a tunable passive antenna often only provides a poor tuning capability, so that it is often not possible to obtain that the automatic antenna system shown in Fig. 1 can sufficiently reduce or cancel any variation in the impedance presented by the user port, caused by a variation in a frequency of operation, and/or caused by the well-known user interaction. This problem is solved in a first method for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit, applicable to a radio transmitter, which is implemented in the automatic antenna system shown in Figure 2. This method is similar to the one disclosed in the ninth embodiment of the patent of the United States of America No.9,680,510, entitled “radio communication using tunable antennas and an antenna tuning apparatus”. The automatic antenna system shown in Fig.2 has a user port (31), the user port presenting, at a given frequency, an impedance referred to as “the impedance presented by the user port”, the automatic antenna system comprising: a tunable passive antenna (1), the tunable passive antenna comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said tunable passive antenna, said at least one antenna control device parameter being adjustable by electrical means; a sensing unit (3) delivering two “sensing unit output signals”, each of the sensing unit output signals being determined by one electrical variable sensed (or measured) at the user port; a single-input-port and single-output-port tuning unit (4) having an input port and an output port, the input port being coupled to the user port through the sensing unit, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at said given frequency, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a feeder (2) having a first end coupled to a signal port of the tunable passive antenna, the feeder having a second end coupled to the output port; a signal processing unit (5), the signal processing unit estimating q real quantities depending on the impedance presented by the user port, where q is an integer greater than or equal to 1, using the sensing unit output signals caused by an excitation applied to the user port, the signal processing unit delivering an “adjustment instruction” as a function of said q real quantities depending on the impedance presented by the user port; and a control unit (6), the control unit receiving the adjustment instruction from the signal processing unit, the control unit delivering “control signals”, the control signals being determined as a function of the adjustment instruction, the reactance of each of the one or more adjustable impedance devices of the tuning unit being mainly determined by at least one of the control signals, each of the one or more antenna control device parameters being mainly determined by at least one of the control signals. The method for automatically adjusting a tunable passive antenna, and the first method for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit use closed-loop control to adjust the single-input-port and single-output-port tuning unit. They typically provide either an accurate but slow automatic tuning requiring many iterations, or a fast but inaccurate automatic tuning requiring few iterations. Two other methods for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit, disclosed in the patent of the United States of America No. 9,960,491, entitled “Method for automatic adjustment of a tunable passive antenna and a tuning unit, and apparatus for radio communication using this method”, and in the patent of the United States of America No. 10,008,777, entitled “Method for automatically adjusting a tunable passive antenna and a tuning unit, and apparatus for radio communication using this method”, are applicable to a radio transmitter. An automatic antenna system implementing one of these two other methods is shown in Figure 3. The automatic antenna system shown in Fig.3 has a user port (31), the automatic antenna system comprising: a tunable passive antenna (1), the tunable passive antenna comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said tunable passive antenna, said at least one antenna control device parameter being adjustable by electrical means; a single-input-port and single-output-port tuning unit (4) having an input port and an output port, the input port being directly coupled to the user port, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at a given frequency, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a sensing unit (3) delivering two “sensing unit output signals”, each of the sensing unit output signals being determined by one electrical variable sensed (or measured) at the output port; a feeder (2) having a first end which is directly coupled to a signal port of the tunable passive antenna, the feeder having a second end which is indirectly coupled to the output port, through the sensing unit; a signal processing unit (5), the signal processing unit estimating q real quantities depending on an impedance seen by the output port, where q is an integer greater than or equal to 1, using the sensing unit output signals caused by an excitation applied to the user port, the signal processing unit delivering an “adjustment instruction” as a function of said q real quantities depending on an impedance seen by the output port; and a control unit (6), the control unit receiving the adjustment instruction from the signal processing unit, the control unit delivering “control signals”, the control signals being determined as a function of the adjustment instruction, the reactance of each of the one or more adjustable impedance devices of the tuning unit being mainly determined by at least one of the control signals, each of the one or more antenna control device parameters being mainly determined by at least one of the control signals. Said two other methods for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit use open-loop control to adjust the single-input-port and single-output-port tuning unit, so that they may be fast, but they are typically inaccurate. Thus, the prior art does not teach a fast and accurate method for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit. SUMMARY OF THE INVENTION The purpose of the invention is a method for automatically adjusting one or more tunable passive antennas and a single-input-port and single-output-port tuning unit, without the above- mentioned limitations of known techniques, and also an apparatus for radio communication using this method. In what follows, X and Y being different quantities or variables, performing an action as a function of X does not preclude the possibility of performing this action as a function of Y. In what follows, “having an influence” and “having an effect” have the same meaning. In what follows, “coupled”, when applied to two ports (in the meaning of circuit theory), may indicate that the ports are directly coupled, in which case each terminal of one of the ports is connected to (or, equivalently, in electrical contact with) one and only one of the terminals of the other port, and/or that the ports are indirectly coupled, in which case an electrical interaction different from direct coupling exists between the ports, for instance through one or more components. The method of the invention is a method for automatically adjusting one or more tunable passive antennas and a single-input-port and single-output-port tuning unit, the single-input-port and single-output-port tuning unit having an input port and an output port, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at a given frequency, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being mainly determined by one or more “tuning control signals”, the one or more tunable passive antennas and the single-input-port and single-output-port tuning unit being parts of an apparatus for radio communication, the apparatus for radio communication allowing, at the given frequency, a transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas, the method comprising the steps of: selecting a frequency referred to as the “selected frequency”; generating one or more “antenna control signals”, each of the one or more tunable passive antennas comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said each of the one or more tunable passive antennas, said at least one antenna control device parameter being adjustable by electrical means, said at least one antenna control device parameter being mainly determined by at least one of the one or more antenna control signals; applying an excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency; generating, for each of the one or more tuning control signals, an initial value of said each of the one or more tuning control signals, the initial value of said each of the one or more tuning control signals being determined as a function of one or more “initial tuning unit adjustment instructions”; sensing one or more electrical variables at the input port, to obtain one or more “sensing unit output signals”, each of the one or more sensing unit output signals being mainly determined by at least one of the one or more electrical variables sensed at the input port; estimating q tuning parameters by utilizing the one or more sensing unit output signals, where q is an integer greater than or equal to one, each of the one or more tuning parameters being a quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while each said initial value is generated; and generating, for at least one of the one or more tuning control signals, at least one subsequent value of said at least one of the one or more tuning control signals, as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters. Each of the q tuning parameters may for instance be substantially proportional to the absolute value, or the phase, or the real part, or the imaginary part of said impedance presented by the input port, or of the inverse of said impedance presented by the input port (this inverse being an admittance presented by the input port), or of a voltage reflection coefficient at the input port, defined as being equal to (Z_UI - Z_O ) (Z_UI + Z_O )^S1, where Z_O is a reference impedance, and where Z_UI is said impedance presented by the input port. It is for instance possible that the q tuning parameters are sufficient to allow a determination of said impedance presented by the input port. The given frequency and the selected frequency may for instance be frequencies greater than or equal to 150 kHz. The specialist understands that an impedance seen by the output port is a complex number, and that an impedance presented by the input port is a complex number. We will use Z_Sant to denote the impedance seen by the output port, and Z_U to denote the impedance presented by the input port. The impedances Z_Sant and Z_U depend on the frequency. Moreover, Z_U also depends on the one or more tuning control signals, so that the wording “impedance presented by the input port while each said initial value is generated” has a clear meaning. Each of the one or more tunable passive antennas has a port, referred to as the “signal port” of the tunable passive antenna, which can be used to receive and/or to emit electromagnetic waves. Each of the one or more tunable passive antennas comprises at least one antenna control device, which may comprise one or more terminals used for other electrical connections. It is assumed that each of the one or more tunable passive antennas behaves, at the given frequency, with respect to its signal port, substantially as a passive antenna, that is to say as an antenna which is linear and does not use an amplifier for amplifying signals received by the antenna or signals emitted by the antenna. Let N be the number of the one or more tunable passive antennas. As a consequence of linearity, and considering only, for each of the one or more tunable passive antennas, its signal port, it is possible to define: if N is equal to one, an impedance presented by the one or more tunable passive antennas; and if N is greater than or equal to two, an impedance matrix presented by the one or more tunable passive antennas, this impedance matrix being of size N by N. As said above in the prior art section, each of said one or more characteristics may for instance be an electrical characteristic such as an impedance at a specified frequency, or an electromagnetic characteristic such as a directivity pattern at a specified frequency. It is said above that the apparatus for radio communication allows, at the given frequency, a transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas. In other words, the apparatus for radio communication is such that, if a power is received by the input port at the given frequency, a part of said power received by the input port is transferred to an electromagnetic field radiated by the one or more tunable passive antennas at the given frequency, so that a power of the electromagnetic field radiated by the one or more tunable passive antennas at the given frequency is equal to said part of said power received by the input port. For instance, the specialist knows that a power of the electromagnetic field radiated by the one or more tunable passive antennas (average radiated power) can be computed as the flux of the real part of a complex Poynting vector of the electromagnetic field radiated by the one or more tunable passive antennas, through a closed surface containing the one or more tunable passive antennas. To obtain that the apparatus for radio communication allows, at the given frequency, a transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas, at least one of the one or more tunable passive antennas may for instance be coupled, directly or indirectly, to the output port. More precisely, for at least one of the one or more tunable passive antennas, the signal port of the tunable passive antenna may for instance be coupled, directly or indirectly, to the output port. For instance, an indirect coupling may be a coupling through a feeder. For suitable values of the one or more tuning control signals and of the one or more antenna control signals, said transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas may for instance be a transfer of power with small or negligible or zero losses, this characteristic being preferred. The specialist understands that the one or more antenna control signals have an effect on each of the one or more antenna control device parameters, so that they may have an influence on the impedance seen by the output port, and on the impedance presented by the input port. In the previous sentence, “each of the one or more antenna control device parameters” clearly means “each said at least one antenna control device parameter of each said at least one antenna control device of each of the one or more tunable passive antennas”. For instance, it is possible that open-loop control is utilized to generate each of the one or more antenna control signals. Equivalently, it is for instance possible that an open-loop control scheme is utilized to generate each of the one or more antenna control signals. This possible characteristic will be explained below in the presentations of the fourth embodiment and of the eleventh embodiment. It is for instance possible that at least one of the one or more subsequent values is generated by utilizing a numerical model, as explained below in the fourth embodiment. An apparatus implementing the method of the invention is an apparatus for radio communication comprising: one or more tunable passive antennas, each of the one or more tunable passive antennas comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said each of the one or more tunable passive antennas, said at least one antenna control device parameter being adjustable by electrical means; a single-input-port and single-output-port tuning unit having an input port and an output port, the apparatus for radio communication allowing, at a given frequency, a transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at the given frequency, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a sensing unit, the sensing unit delivering one or more “sensing unit output signals”, each of the one or more sensing unit output signals being mainly determined by one or more electrical variables sensed at the input port; a transmission and signal processing unit, the transmission and signal processing unit selecting a frequency referred to as the “selected frequency”, the transmission and signal processing unit delivering one or more “antenna adjustment instructions”, the transmission and signal processing unit delivering “tuning unit adjustment instructions”, at least one of the tuning unit adjustment instructions being an “initial tuning unit adjustment instruction”, at least one of the tuning unit adjustment instructions being a “subsequent tuning unit adjustment instruction”; and a control unit, the control unit delivering one or more “antenna control signals” to the one or more tunable passive antennas, each of the one or more antenna control signals being determined as a function of at least one of the one or more antenna adjustment instructions, each of the one or more antenna control device parameters being mainly determined by at least one of the one or more antenna control signals, the control unit delivering one or more “tuning control signals”, the control unit generating, for each of the one or more tuning control signals, one or more values of said each of the one or more tuning control signals, each of said one or more values of said each of the one or more tuning control signals being determined as a function of at least one of the tuning unit adjustment instructions, the reactance of each of the one or more adjustable impedance devices of the tuning unit being mainly determined by at least one of the one or more tuning control signals; the apparatus for radio communication being characterized in that: the transmission and signal processing unit is used to apply an excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency; for each of the one or more tuning control signals, said one or more values of said each of the one or more tuning control signals comprise an initial value determined as a function of one or more of the one or more initial tuning unit adjustment instructions; the transmission and signal processing unit estimates q tuning parameters by utilizing the one or more sensing unit output signals, where q is an integer greater than or equal to one, each of the one or more tuning parameters being a quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while each said initial value is generated; and at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters. In the previous sentence, “each of the one or more antenna control device parameters” clearly means “each said at least one antenna control device parameter of each said at least one antenna control device of each of the one or more tunable passive antennas”. For instance, each of said electrical variables may be a voltage, or an incident voltage, or a reflected voltage, or a current, or an incident current, or a reflected current. For instance, it is possible that the control unit is such that: for each of the one or more tuning control signals, the initial value of said each of the one or more tuning control signals is determined as a function of one of the one or more initial tuning unit adjustment instructions; and for one or more of the one or more tuning control signals, said one or more values of each said one or more of the one or more tuning control signals comprise at least one subsequent value determined as a function of one of the one or more subsequent tuning unit adjustment instructions. In this case, it is for instance possible to say that the control unit generates: for each of the one or more tuning control signals, an initial value determined as a function of one of the one or more initial tuning unit adjustment instructions; and, for at least one of the one or more tuning control signals, at least one subsequent value determined as a function of one of the one or more subsequent tuning unit adjustment instructions. In this case, it is for instance possible to say that at least one subsequent value of said at least one of the one or more tuning control signals is generated as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters. As explained above, it is for instance possible that at least one of the one or more tunable passive antennas is coupled, directly or indirectly, to the output port. As explained above, it is for instance possible that, for at least one of the one or more tunable passive antennas, the signal port of the tunable passive antenna is coupled, directly or indirectly, to the output port. Thus, it is for instance possible that said transfer of power (from the input port to an electromagnetic field radiated by the one or more tunable passive antennas) takes place through the single-input-port and single-output-port tuning unit. It is for instance possible that the integer p is greater than or equal to 2. It is for instance possible that the integer q is greater than or equal to 2. It is for instance possible that the output port is, at a given time, directly or indirectly coupled to one and only one of the one or more tunable passive antennas. It is for instance possible that the input port is coupled, directly or indirectly, to a port of the transmission and signal processing unit, said port of the transmission and signal processing unit delivering the excitation. For instance, it is possible that the reactance of any one of the one or more adjustable impedance devices of the tuning unit has an influence on an impedance presented by the input port. It is for instance possible that at least one of the one or more subsequent tuning unit adjustment instructions is determined by utilizing a numerical model, as explained below in the fourth embodiment. The specialist understands that the apparatus for radio communication of the invention is adaptive in the sense that the reactances of the one or more adjustable impedance devices of the tuning unit are varied with time as a function of the one or more sensing unit output signals, which are each mainly determined by one or more electrical variables. BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and characteristics will appear more clearly from the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the accompanying drawings in which: - Figure 1 shows a block diagram of an automatic antenna system, and has already been discussed in the section dedicated to the presentation of the prior art; - Figure 2 shows a block diagram of an automatic antenna system, and has already been discussed in the section dedicated to the presentation of the prior art; - Figure 3 shows a block diagram of an automatic antenna system, and has already been discussed in the section dedicated to the presentation of the prior art; - Figure 4 shows a block diagram of an apparatus for radio communication of the invention (first embodiment); - Figure 5 shows a flowchart implemented in an apparatus for radio communication of the invention (fourth embodiment); - Figure 6 shows a schematic diagram of a single-input-port and single-output-port tuning unit, which may be used in the apparatus for radio communication shown in Fig.4 (fifth embodiment); - Figure 7 shows a schematic diagram of a single-input-port and single-output-port tuning unit, which may be used in the apparatus for radio communication shown in Fig.4 (sixth embodiment); - Figure 8 shows a flowchart implemented in an apparatus for radio communication of the invention (seventh embodiment); - Figure 9 shows a first tunable passive antenna, which comprises a single antenna control device (eighth embodiment); - Figure 10 shows a second tunable passive antenna, which comprises three antenna control devices (ninth embodiment); - Figure 11 shows a third tunable passive antenna, which comprises a single antenna control device (tenth embodiment); - Figure 12 shows a block diagram of an apparatus for radio communication of the invention (eleventh embodiment); - Figure 13 shows a back view of a mobile phone (twelfth embodiment); - Figure 14 shows a first typical use configuration (right hand and head configuration); - Figure 15 shows a second typical use configuration (two hands configuration); - Figure 16 shows a third typical use configuration (right hand only configuration); - Figure 17 shows a block diagram of an apparatus for radio communication of the invention (thirteenth embodiment). First embodiment. As a first embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 4 the block diagram of an apparatus for radio communication comprising: a tunable passive antenna (1), the tunable passive antenna comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said tunable passive antenna, said at least one antenna control device parameter being adjustable by electrical means; a single-input-port and single-output-port tuning unit (4) having an input port and an output port, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at a given frequency greater than or equal to 30 MHz, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a feeder (2), the feeder having a first end which is directly coupled to a signal port of the tunable passive antenna, the feeder having a second end which is directly coupled to the output port; a sensing unit (3), the sensing unit delivering two “sensing unit output signals”, each of the sensing unit output signals being mainly determined by one or more electrical variables sensed (or measured) at the input port; a transmission and signal processing unit (8), the transmission and signal processing unit selecting a frequency referred to as the “selected frequency”, the transmission and signal processing unit delivering one or more “antenna adjustment instructions”, the transmission and signal processing unit applying an excitation to the input port through the sensing unit, the excitation having a carrier frequency which is equal to the selected frequency, the transmission and signal processing unit delivering “tuning unit adjustment instructions”, at least one of the tuning unit adjustment instructions being an “initial tuning unit adjustment instruction”, at least one of the tuning unit adjustment instructions being a “subsequent tuning unit adjustment instruction”; and a control unit (6), the control unit receiving the one or more antenna adjustment instructions, the control unit delivering one or more “antenna control signals” to the tunable passive antenna, each of the one or more antenna control signals being determined as a function of at least one of the one or more antenna adjustment instructions, each of the one or more antenna control device parameters being mainly determined by at least one of the one or more antenna control signals, the control unit receiving the tuning unit adjustment instructions, the control unit delivering one or more “tuning control signals” to the single-input-port and single-output-port tuning unit, the control unit generating, for each of the one or more tuning control signals, one or more values of said each of the one or more tuning control signals, each of said one or more values of said each of the one or more tuning control signals being determined as a function of at least one of the tuning unit adjustment instructions, the reactance of each of the one or more adjustable impedance devices of the tuning unit being mainly determined by at least one of the one or more tuning control signals; wherein: for each of the one or more tuning control signals, said one or more values of said each of the one or more tuning control signals comprise an initial value determined as a function of one or more of the one or more initial tuning unit adjustment instructions; the transmission and signal processing unit estimates q tuning parameters, where q is an integer greater than or equal to one, by utilizing the sensing unit output signals, each of the one or more tuning parameters being a quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while each said initial value is generated; and at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters. The tunable passive antenna is coupled to the output port. More precisely, the signal port of the tunable passive antenna is indirectly coupled to the output port, through the feeder. Moreover, the output port is coupled to the tunable passive antenna. More precisely, the output port is indirectly coupled to the signal port of the tunable passive antenna, through the feeder. The q tuning parameters are sufficient to allow a determination of an impedance presented by the input port. The wording “are sufficient to allow a determination of an impedance presented by the input port” does not imply that an impedance presented by the input port is determined, but it is possible that an impedance presented by the input port is determined. Since, in the two previous sentences, “impedance” means “complex impedance”, the requirement “the q tuning parameters are sufficient to allow a determination of an impedance presented by the input port” is equivalent to “the q tuning parameters are sufficient to allow a determination of a real part and an imaginary part of an impedance presented by the input port”. The wording “are sufficient to allow a determination of a real part and an imaginary part of an impedance presented by the input port” does not imply that the real part and the imaginary part of an impedance presented by the input port are determined, but it is possible that the real part and the imaginary part of an impedance presented by the input port are determined. The information carried by the sensing unit output signals must be sufficient to allow the signal processing unit to estimate the q tuning parameters. The sensing unit (3) may for instance be such that the two sensing unit output signals delivered by the sensing unit comprise: a first sensing unit output signal proportional to a first electrical variable, the first electrical variable being a voltage across the input port; and a second sensing unit output signal proportional to a second electrical variable, the second electrical variable being a current flowing in the input port. Said voltage across the input port may be a complex voltage and said current flowing in the input port may be a complex current. Alternatively, the sensing unit (3) may for instance be such that the two sensing unit output signals delivered by the sensing unit comprise: a first sensing unit output signal proportional to a first electrical variable, the first electrical variable being an incident voltage (which may also be referred to as “forward voltage”) at the input port; and a second sensing unit output signal proportional to a second electrical variable, the second electrical variable being a reflected voltage at the input port. Said incident voltage at the input port may be a complex incident voltage and said reflected voltage at the input port may be a complex reflected voltage. The input port is indirectly coupled to a port of the transmission and signal processing unit (8), through the sensing unit, said port of the transmission and signal processing unit delivering the excitation. Each of the one or more antenna adjustment instructions and each of the tuning unit adjustment instructions may be of any type of digital message. The one or more antenna adjustment instructions and the tuning unit adjustment instructions are delivered during one or more adjustment sequences. Two different adjustment sequences are described below, in the fourth embodiment and in the seventh embodiment. The duration of an adjustment sequence is less than 100 microseconds. For instance, it is possible that the excitation is an unmodulated carrier, the carrier frequency of the excitation being the frequency of said carrier. For instance, it is possible that the excitation is an amplitude modulated carrier, the carrier frequency of the excitation being the frequency of said carrier. For instance, it is possible that the excitation is a frequency modulated carrier, the carrier frequency of the excitation being the frequency of said carrier. For instance, as explained in the presentation of the third embodiment, it is possible that the excitation is a bandpass signal, the carrier frequency of the excitation being a carrier frequency of said bandpass signal. The value of the selected frequency lies in a “set of possible values of the selected frequency”, which comprises several elements. For instance, it is possible that the selected frequency may take on any value lying in the set of possible values of the selected frequency. Thus, it is possible that the carrier frequency of the excitation may take on any value selected in the set of possible values of the selected frequency. The specialist understands that, to estimate the q tuning parameters, it is necessary to use sensing unit output signals, each of which is mainly determined by one or more electrical variables sensed at the input port while the excitation is applied, and while, for each of the one or more tuning control signals, the initial value of said each of the one or more tuning control signals is generated. The single-input-port and single-output-port tuning unit is such that it can provide, at said given frequency, for suitable values of the one or more tuning control signals, a low-loss transfer of power from the input port to the output port, and a low-loss transfer of power from the output port to the input port. The output port being indirectly coupled to the tunable passive antenna, the specialist sees that the apparatus for radio communication allows, at the given frequency, a transfer of power from the input port to an electromagnetic field radiated by the tunable passive antenna. Thus, the apparatus for radio communication is such that, if a power is received by the input port at the given frequency, a part of said power received by the input port is transferred to an electromagnetic field radiated by the tunable passive antenna at the given frequency, so that a power of the electromagnetic field radiated by the tunable passive antenna at the given frequency is equal to said part of said power received by the input port. The apparatus for radio communication also allows, at the given frequency, a transfer of power from an electromagnetic field incident on the tunable passive antenna to the input port. Additionally, the single-input-port and single-output-port tuning unit and the tunable passive antenna are such that, at said given frequency, for suitable values of the one or more tuning control signals and of the one or more antenna control signals, a low-loss transfer of power from the input port to an electromagnetic field radiated by the tunable passive antenna can be obtained (for radio emission), and a low-loss transfer of power from an electromagnetic field incident on the tunable passive antenna to the input port can be obtained (for radio reception). Thus, it is possible to say that the apparatus for radio communication allows, at the given frequency, for suitable values of the one or more tuning control signals and of the one or more antenna control signals, a low-loss transfer of power from the input port to an electromagnetic field radiated by the tunable passive antenna, and a low-loss transfer of power from an electromagnetic field incident on the tunable passive antenna to the input port. The suitable values of the one or more tuning control signals and of the one or more antenna control signals are provided automatically. Thus, the specialist understands that any small variation in the impedance seen by the output port can be at least partially compensated with a new automatic adjustment of the one or more adjustable impedance devices of the tuning unit. The specialist understands that, following an approach similar to the one used in section II of the article of F. Broydé and E. Clavelier entitled “Some Properties of Multiple-Antenna-Port and Multiple-User-Port Antenna Tuners”, published in IEEE Trans. on Circuits and Systems — I: Regular Papers, Vol.62, No. 2, pp. 423-432, in February 2015, a numerical model of the single-input-port and single-output-port tuning unit and of the control unit may be put in the form of a mapping denoted by g_CU and defined by g_CU ( f, Z_Sant , t_C ) = Z_U (1) where f is the frequency and where t_C is the applicable tuning unit adjustment instruction, t_C lying in a set of possible tuning unit adjustment instructions, this set being denoted by T_C . Experimental results have shown that temperature often also influences Z_U , and that a cause of this influence is typically the temperature dependence of the reactance and of the resistance of some types of adjustable impedance devices. If one or more such adjustable impedance devices are used among the one or more adjustable impedance devices of the tuning unit, then the mapping g_CU is only a coarse numerical model of the single-input-port and single-output- port tuning unit and of the control unit. Let a_T be a real vector of temperatures, which is sufficient to characterize the effects of temperature on Z_U . The entries of a_T may for instance be one or more temperatures of the one or more adjustable impedance devices of the tuning unit. An accurate numerical model of the single-input-port and single-output-port tuning unit and of the control unit may be put in the form of a mapping denoted by g_U and defined by g_U ( f, Z_Sant , t_C , a_T ) = Z_U (2) which applies to any normal thermal environment of the single-input-port and single-output-port tuning unit and of the control unit, that is to say, to any combination of ambient temperature, temperature gradient, nearby heat sources, etc, which may occur under any normal operating conditions of the single-input-port and single-output-port tuning unit and of the control unit. The mapping g_CU is a model of the single-input-port and single-output-port tuning unit and of the control unit. This model takes into account the influences of the frequency, of the impedance seen by the output port, and of the applicable tuning unit adjustment instruction, on an impedance presented by the input port. The mapping g_U is another model of the single-input-port and single-output-port tuning unit and of the control unit, applicable to any normal thermal environment of the single-input-port and single-output-port tuning unit and of the control unit. This model takes into account the influences of the frequency, of the impedance seen by the output port, of the applicable tuning unit adjustment instruction and of one or more temperatures at one or more locations, on an impedance presented by the input port. The specialist understands that Z_Sant is independent of the variable t_C , whereas equations (1) and (2) shows that Z_U depends on the variable t_C . Since each of the one or more tuning parameters is a quantity depending on an impedance presented by the input port while each said initial value is generated, it follows that the apparatus for radio communication uses a closed- loop control scheme to determine the one or more subsequent tuning unit adjustment instructions. The apparatus for radio communication is a portable radio transceiver, so that the transmission and signal processing unit (8) also performs functions which have not been mentioned above, and which are well known to specialists. For instance, the apparatus for radio communication can be a user equipment (UE) of an LTE-advanced wireless network, or of a 5G New Radio wireless network. The specialist understands that Z_Sant depends on the frequency and on the electromagnetic characteristics of the volume surrounding the tunable passive antenna. In particular, the body of the user has an effect on Z_Sant , and Z_Sant depends on the position of the body of the user. This is referred to as “user interaction”, or “hand effect” or “finger effect”. The specialist understands that the apparatus for radio communication may automatically compensate a variation in Z_Sant caused by a variation in a frequency of operation, and/or automatically compensate the user interaction. In order to respond to variations in the electromagnetic characteristics of the volume surrounding the tunable passive antenna and/or in the frequency of operation, a new adjustment sequence starts shortly after each change of the frequency of operation, and no later than 10 milliseconds after the beginning of the previous adjustment sequence. Second embodiment. The second embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this second embodiment. The excitation applied to the input port may for instance comprise a sinusoidal signal at said given frequency, for instance a sinusoidal current at said given frequency applied to the input port. The excitation applied to the input port may for instance comprise a sinusoidal signal at a frequency different from said given frequency, or a non-sinusoidal signal. The transmission and signal processing unit is used to apply the excitation to the input port. For instance, the excitation may consist of a voltage applied to the input port, or consist of a current applied to the input port. In this second embodiment, q = 2 and the q tuning parameters fully determine an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while, for each of the one or more tuning control signals, the initial value of said each of the one or more tuning control signals is generated. Also, the two sensing unit output signals are proportional to a complex voltage across the input port and to a complex current flowing in the input port, respectively, as explained above. The transmission and signal processing unit (8) can clearly use the sensing unit output signals caused by the excitation applied to the input port, to compute Z_U . Thus, said q tuning parameters may consist of a real number proportional to the real part of Z_U , and of a real number proportional to the imaginary part of Z_U . Third embodiment. The third embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this third embodiment. In this third embodiment, the excitation is a bandpass signal. This type of signal is sometimes improperly referred to as “passband signal” or “narrow-band signal” (in French: “signal à bande étroite”). A bandpass signal is any real signal s(t), where t denotes the time, such that the spectrum of s(t) is included in a frequency interval [f_C S W/2, f_C + W/2], where f_C is a frequency referred to as “carrier frequency” and where W is a frequency referred to as “bandwidth”, which satisfies W < 2 f_C . Thus, the Fourier transform of s(t), denoted by S( f ), is non-negligible only in the frequency intervals [Sf_C S W/2, Sf_C + W/2] and [f_C S W/2, f_C + W/2]. The complex envelope of the real signal s(t), also referred to as “complex baseband equivalent” or “baseband-equivalent signal”, is a complex signal s_B(t) whose Fourier transform S_B ( f ) is non-negligible only in the frequency interval [S W/2, W/2] and satisfies S_B ( f ) = k S( f_C + f ) in this interval, where k is a real constant which is chosen equal to the square root of 2 by some authors. The real part of s_B(t) is referred to as the in-phase component, and the imaginary part of s_B(t) is referred to as the quadrature component. The specialist knows that the bandpass signal s(t) may for instance be obtained: - as the result of a phase and amplitude modulation of a single carrier at the frequency f_C ; - as a linear combination of a first signal and a second signal, the first signal being the product of the in-phase component and a first sinusoidal carrier of frequency f_C , the second signal being the product of the quadrature component and a second sinusoidal carrier of frequency f_C , the second sinusoidal carrier being 90° out of phase with respect to the first sinusoidal carrier; - in other ways, for instance without using any carrier, for instance using directly a filtered output of a digital-to-analog converter. The frequency interval [f_C S W/2, f_C + W/2] is a passband of the bandpass signal. From the definitions, it is clear that, for a given bandpass signal, several choices of carrier frequency f_C and of bandwidth W are possible, so that the passband of the bandpass signal is not uniquely defined. However, any passband of the bandpass signal must contain any frequency at which the spectrum of s(t) is not negligible. The complex envelope of the real signal s(t) clearly depends on the choice of a carrier frequency f_C . However, for a given carrier frequency, the complex envelope of the real signal s(t) is uniquely defined, for a given choice of the real constant k. The excitation applied to the input port is a bandpass signal having a passband which contains said given frequency. Said given frequency being considered as a carrier frequency, the excitation has one and only one complex envelope (or complex baseband equivalent). For instance, if we use t to denote time, the excitation may consist of a current i(t), of complex envelope i_E (t), applied to the input port. It is possible to show that, if the bandwidth of the complex envelope of the excitation is sufficiently narrow, then any voltage or current measured at the input port and caused by the excitation is a bandpass signal whose complex envelope is proportional to the complex envelope of the excitation, the coefficient of proportionality being complex and time-independent. The specialist sees that it is possible to obtain q = 2 tuning parameters which fully determine an impedance presented by the input port, each of the tuning parameters being a real quantity depending on said impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while, for each of the one or more tuning control signals, the initial value of said each of the one or more tuning control signals is generated. More precisely, in a first example of signal processing, we assume that, while the one or more initial values are generated, the excitation consists of a current i(t), of complex envelope i_E (t), applied to the input port. The excitation causes a voltage across the input port, of complex envelope v_E (t). As explained above, if the bandwidth of the complex envelope i_E (t) is sufficiently narrow, v_E (t) is proportional to i_E (t), and we have v_E (t) = Z_U i_E (t) (3) The specialist understands how the sensing unit output signals can be processed to obtain i_E (t) and v_E (t). For instance, let us assume that the sensing unit delivers: a first sensing unit output signal proportional to the voltage across the input port; and a second sensing unit output signal proportional to the current flowing in the input port. The transmission and signal processing unit may for instance perform an in-phase/quadrature (I/Q) demodulation (homodyne reception) of these sensing unit output signals, to obtain four analog signals: the real part of v_E (t); the imaginary part of v_E (t); the real part of i_E (t); and the imaginary part of i_E (t). These analog signals may then be converted into digital signals and further processed in the digital domain, to estimate Z_U and/or its inverse Y_U , using equation (3). This first example of signal processing shows that the excitation can be used to estimate any quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while the one or more initial values are generated. Said q tuning parameters may for instance consist of a real number proportional to the real part of Y_U , and of a real number proportional to the imaginary part of Y_U . Said q tuning parameters may for instance consist of a real number proportional to the absolute value of Y_U , and of a real number proportional to the argument of Y_U . In a second example of signal processing, we assume that, while the one or more initial values are generated, the excitation consists of a voltage v(t), of complex envelope v_E (t), applied to the input port. The excitation causes a current flowing in the input port, of complex envelope i_E (t). As explained above, if the bandwidth of the complex envelope v_E (t) is sufficiently narrow, v_E (t) is proportional to i_E (t), and equation (3) is satisfied. For instance, let us assume that the sensing unit delivers: a first sensing unit output signal proportional to the voltage across the input port; and a second sensing unit output signal proportional to the current flowing in the input port. The transmission and signal processing unit may for instance perform a down- conversion of the sensing unit output signals, followed by an in-phase/quadrature (I/Q) demodulation (heterodyne reception), to obtain four analog signals: the real part of v_E (t); the imaginary part of v_E (t); the real part of i_E (t); and the imaginary part of i_E (t). These analog signals may then be converted into digital signals and further processed in the digital domain, as above. In a third example of signal processing, we assume that, while the one or more initial values are generated, the excitation causes a voltage across the input port, of complex envelope v_E (t), and causes a current flowing in the input port, of complex envelope i_E (t). As explained above, if the bandwidth of the complex envelope of the excitation is sufficiently narrow, v_E (t) is proportional to i_E (t), and equation (3) is satisfied. For instance, let us assume that the sensing unit delivers: a first sensing unit output signal proportional to an incident voltage at the input port, of complex envelope v_IE (t); and a second sensing unit output signal proportional to a reflected voltage at the input port, of complex envelope v_RE (t). The transmission and signal processing unit may for instance perform a down-conversion of the sensing unit output signals, followed by a conversion into digital signals using bandpass sampling, and by a digital quadrature demodulation, to obtain four digital signals: the samples of the real part of v_IE (t); the samples of the imaginary part of v_IE (t); the samples of the real part of v_RE (t); and the samples of the imaginary part of v_RE (t). The specialist understands how these digital signals may then be further processed in the digital domain, to estimate any quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while the one or more initial values are generated. Fourth embodiment (best mode). The fourth embodiment of a device of the invention, given by way of non-limiting example and best mode of carrying out the invention, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this fourth embodiment. A flowchart of one of the one or more adjustment sequences used in this fourth embodiment is shown in Figure 5. In addition to the begin symbol (801) and the end symbol (809), said flowchart comprises: a process “choosing the selected frequency” (802), in which the transmission and signal processing unit chooses the selected frequency, from the set of possible values of the selected frequency; a process “delivering antenna control signals to the tunable passive antenna” (803), in which the transmission and signal processing unit delivers one or more of the one or more antenna adjustment instructions, and in which the control unit delivers said one or more antenna control signals to the tunable passive antenna, each of said one or more of the one or more antenna adjustment instructions being determined as a function of the selected frequency; a process “start applying the excitation” (804), in which the transmission and signal processing unit starts to apply, through the sensing unit, the excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency, so that the sensing unit becomes able to deliver sensing unit output signals such that each of the sensing unit output signals is determined by an electrical variable sensed at the input port while the excitation is applied; a process “initial values of the tuning control signals” (805), in which the transmission and signal processing unit delivers an initial tuning unit adjustment instruction, and in which, for each of the one or more tuning control signals, the control unit begins to generate a value of said each of the one or more tuning control signals, said value being referred to as initial value, said initial value being determined as a function of the initial tuning unit adjustment instruction, and only as a function of the initial tuning unit adjustment instruction; a process “impedance presented by the input port” (806), in which the transmission and signal processing unit estimates q = 2 tuning parameters, which fully determine an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port after the end of the process “delivering antenna control signals to the tunable passive antenna” (803) and while each said initial value is generated, said tuning parameters being for instance estimated by utilizing one of the signal processing techniques explained in the third embodiment; a process “subsequent values of the tuning control signals” (807), in which the transmission and signal processing unit delivers a subsequent tuning unit adjustment instruction, and in which, for each of the one or more tuning control signals, the control unit begins to generate a value of said each of the one or more tuning control signals, said value being referred to as subsequent value, said subsequent value being determined as a function of said subsequent tuning unit adjustment instruction, and only as a function of said subsequent tuning unit adjustment instruction; and a process “stop applying the excitation” (808), in which the transmission and signal processing unit stops applying the excitation to the input port. Each of the one or more antenna control signals has no influence on the selected frequency. Each of the one or more antenna adjustment instructions has no influence on the selected frequency. Each of said one or more of the one or more antenna adjustment instructions being determined as a function of the selected frequency, and only as a function of the selected frequency, it is clear that open-loop control is utilized to generate each of the one or more antenna control signals. In this fourth embodiment, the one or more antenna adjustment instructions and the one or more antenna control signals are such that: at the end of the process “delivering antenna control signals to the tunable passive antenna” (803), the impedance seen by the output port approximates a specified impedance, which may depend on frequency; and each said antenna control device parameter of each said antenna control device of the tunable passive antenna has a value which does not change from the end of the process “delivering antenna control signals to the tunable passive antenna” (803) to the end of said one of the one or more adjustment sequences. To obtain that, at the end of the process “delivering antenna control signals to the tunable passive antenna” (803), the impedance seen by the output port approximates the specified impedance, the transmission and signal processing unit uses an algorithm to determine and deliver the one or more antenna adjustment instructions. The algorithm uses the selected frequency and some properties of the tunable passive antenna. For instance, the algorithm may be based on a formula allowing one to estimate Z_Sant in an assumed use configuration, as a function of the selected frequency and of each said antenna control device parameter of each said antenna control device of the tunable passive antenna, the formula being possibly used to compute, for the assumed use configuration, an optimal value of each said antenna control device parameter of each said antenna control device of the tunable passive antenna, at the selected frequency. For instance, the algorithm may be based on one or more formulas allowing one to estimate, in an assumed use configuration, an optimal value of each said antenna control device parameter of each said antenna control device of the tunable passive antenna, as a function of the selected frequency. The specialist knows how to write such an algorithm, and he understands that such an algorithm cannot take into account the variations of Z_Sant caused by variations in the electromagnetic characteristics of the volume surrounding the tunable passive antenna. Moreover, as said above in the prior art section, a tunable passive antenna often only provides a poor tuning capability. Consequently, at the end of the process “delivering antenna control signals to the tunable passive antenna” (803), the impedance seen by the output port typically only very coarsely approximates the specified impedance. The single-input-port and single-output-port tuning unit has a full tuning capability, the definition of which is given in section III of said article entitled “Some Properties of Multiple- Antenna-Port and Multiple-User-Port Antenna Tuners”. Thus, the specialist understands that any small variation in the impedance seen by the output port can be completely compensated with a new adjustment of the one or more adjustable impedance devices of the tuning unit. In this fourth embodiment, p is greater than or equal to 2 because, as explained in said article entitled “Some Properties of Multiple-Antenna-Port and Multiple-User-Port Antenna Tuners”, this is necessary to obtain a full tuning capability. Said one of the one or more adjustment sequences is intended to be such that, at the end of said one of the one or more adjustment sequences, the impedance presented by the input port is close, or as close as possible, to a wanted impedance, denoted by Z_W , said wanted impedance being possibly dependent on the selected frequency. We need to clarify the meaning of “close, or as close as possible, to the wanted impedance Z_W ”. Let us consider the absolute value of the image of an impedance Z under a function denoted by h, the function being a complex function of a complex variable, the function being continuous where it is defined and such that h(Z_W ) = 0. For instance, the function may be defined by h(Z ) = Z - Z_W (4) in which case the image of Z under the function is a difference of impedances, or by h(Z ) = Z ^-1 - Z_W ^-1 (5) in which case the image of Z under the function is a difference of admittances, or by h(Z ) = (Z - Z_W ) (Z + Z_W )^-1 (6) in which case the image of Z under the function is a voltage reflection coefficient. We say that Z is close to the wanted impedance if and only if the absolute value of h(Z ) is close to zero; we say that Z is coarsely close to the wanted impedance if and only if the absolute value of h(Z ) is coarsely close to zero; we say that Z is as close as possible to the wanted impedance if and only if the absolute value of h(Z ) is as close as possible to zero; we say that Z is very close to the wanted impedance if and only if the absolute value of h(Z ) is very close to zero; etc. In the process “initial values of the tuning control signals” (805), the initial tuning unit adjustment instruction is determined as a function of the selected frequency. For instance, in the process “initial values of the tuning control signals” (805), it is possible that the transmission and signal processing unit uses a lookup table (also spelled “look-up table”) to determine and deliver the initial tuning unit adjustment instruction, as a function of the selected frequency. The specialist knows how to build and use such a lookup table, and he understands that such a lookup table cannot take into account the variations of Z_Sant caused by variations in the electromagnetic characteristics of the volume surrounding the tunable passive antenna. Consequently, in this case, at the end of the process “initial values of the tuning control signals” (805), it is very likely that the impedance presented by the input port is only very coarsely close to the wanted impedance Z_W . For instance, in the process “initial values of the tuning control signals” (805), it is possible that the transmission and signal processing unit first determines if an earlier adjustment sequence (that is to say, an adjustment sequence which was completed before the beginning of said one of the one or more adjustment sequences), which used the same selected frequency as said one of the one or more adjustment sequences, has its subsequent tuning unit adjustment instruction stored in memory, in which case this subsequent tuning unit adjustment instruction stored in memory is used to determine and deliver the initial tuning unit adjustment instruction, whereas, in the opposite case, a lookup table is used to determine and deliver the initial tuning unit adjustment instruction, as a function of the selected frequency (as explained above). The specialist understands that a subsequent tuning unit adjustment instruction of an earlier adjustment sequence cannot take into account the current variations of Z_Sant caused by variations in the electromagnetic characteristics of the volume surrounding the tunable passive antenna, so that, at the end of the process “initial values of the tuning control signals” (805), it is likely that the impedance presented by the input port is only coarsely close to the wanted impedance Z_W . We are now going to explain how, by utilizing a numerical model, the process “subsequent values of the tuning control signals” (807) provides an impedance presented by the input port, denoted by Z_U , which is very close, or as close as possible, to the wanted impedance Z_W . Here, the numerical model is the model of the single-input-port and single-output-port tuning unit and of the control unit defined above by equation (2). We assume that the transmission and signal processing unit knows the mapping g_U , for instance based on one or more equations and/or on one or more suitable lookup tables. The process “subsequent values of the tuning control signals” (807) utilizes the q tuning parameters to determine a value of Z_U , said value of Z_U being denoted by Z_UI and being an impedance presented by the input port while the one or more initial values are generated. The process “subsequent values of the tuning control signals” (807) then utilizes the selected frequency (which is a quantity determined by the selected frequency), denoted by f_C , and the initial tuning unit adjustment instruction (which is a variable determined by the initial tuning unit adjustment instruction), denoted by t_CI , to solve the equation g_U ( f_C , Z_Sant , t_CI , a_T ) = Z_UI (7) with respect to the unknown Z_Sant . When this is done, Z_Sant has been computed, and the process “subsequent values of the tuning control signals” (807) may use an algorithm to find a subsequent tuning unit adjustment instruction, denoted by t_CS , such that the impedance presented by the input port Z_U , given by g_U ( f_C , Z_Sant , t_CS , a_T ) = Z_U (8) is very close, or as close as possible, to the wanted impedance Z_W . Said one of the one or more adjustment sequences uses the model of the single-input-port and single-output-port tuning unit and of the control unit twice, the first time when it uses equation (7) and the second time when it uses equation (8). The explanations provided below in the presentations of the fourteenth and fifteenth embodiments show that this characteristic is such that the unavoidable inaccuracies in the model of the single-input-port and single-output-port tuning unit and of the control unit have a reduced effect on the accuracy of the resulting Z_U . Thus, said one of the one or more adjustment sequences is accurate. We see that, according to our explanations, the transmission and signal processing unit can determine a subsequent tuning unit adjustment instruction such that Z_U is very close, or as close as possible, to Z_W , by utilizing a numerical model of the single-input-port and single-output-port tuning unit and of the control unit, and as a function of: (a) one or more quantities determined by the selected frequency; (b) one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and (c) the q tuning parameters. To compensate the effects of temperature, the subsequent tuning unit adjustment instruction (and, consequently, the subsequent values of the one or more tuning control signals) may also be determined as a function of: (d) one or more temperature signals each mainly determined by one or more temperatures measured at one or more locations in the single-input-port and single-output-port tuning unit; and/or (e) one or more temperature signals each mainly determined by one or more temperatures measured at one or more locations in the control unit; and/or (f) information on one or more other temperatures measured at one or more other locations in the apparatus for radio communication. The specialist understands that, in the steps of the process “subsequent values of the tuning control signals” (807), the combined use of the data (a), (b) and (c), and possibly of the data (d), (e) and (f), has allowed the transmission and signal processing unit to compute Z_Sant by utilizing equation (7), and to determine afterwards the subsequent tuning unit adjustment instruction by utilizing an algorithm based on equation (8), so that each of the one or more tuning control signals can directly vary from its initial value to its subsequent value, the subsequent values of the one or more tuning control signals being such that Z_U is very close, or as close as possible, to Z_W . Thus, said one of the one or more adjustment sequences is very fast. Consequently, we see that the invention overcomes the limitations of prior art, because it provides a fast and accurate method for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit. The specialist understands that the invention is completely different from the method for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit mentioned above in the “prior art” section and corresponding to the system shown in Fig. 2, because the invention is characterized in that at least one subsequent tuning unit adjustment instruction is determined as a function of the data (a), (b) and (c), which allows the transmission and signal processing unit to utilize a numerical model of the single-input-port and single-output-port tuning unit and of the control unit twice, to obtain a fast and accurate method for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit. The specialist understands that the invention is completely different from the methods for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit mentioned above in the “prior art” section and corresponding to the system shown in Fig.3, because the invention is not based on the use of electrical variables sensed at the output port. Moreover, the specialist understands that there is an interaction between the process “delivering antenna control signals to the tunable passive antenna” (803) and the subsequent processes of said one of the one or more adjustment sequences, and of next adjustment sequences, this interaction improving speed and accuracy. The specialist also understands that the invention provides a much broader tuning range than an automatic tuning system which would comprise the single-input-port and single-output-port tuning unit, but no tunable passive antenna. Fifth embodiment. The fifth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4 and to the flowchart shown in Figure 5, and all explanations provided for the first embodiment and for the fourth embodiment are applicable to this fifth embodiment. Additionally, we have represented in Figure 6 the single-input-port and single-output-port tuning unit (4) used in this fifth embodiment. This single-input-port and single-output-port tuning unit comprises: an output port (401) having two terminals (4011) (4012), the output port being single- ended; an input port (402) having two terminals (4021) (4022), the input port being single-ended; one of the one or more adjustable impedance devices of the tuning unit (403), presenting a negative reactance and having a terminal connected to a terminal of the output port; one of the one or more adjustable impedance devices of the tuning unit (404), presenting a negative reactance and having a terminal connected to a terminal of the input port; and a coil (405). Each of the one or more adjustable impedance devices of the tuning unit (403) (404) is adjustable by electrical means, but the circuits and the control links needed to adjust the reactance of each of the one or more adjustable impedance devices of the tuning unit are not shown in Fig.6. The specialist understands that, at a frequency at which the single-input-port and single-output-port tuning unit is intended to operate, the reactance of any one of the one or more adjustable impedance devices of the tuning unit has an influence on an impedance presented by the input port. The specialist understands that we may use: Z₄₀₃( f_C , t_C , a_T ) to denote an impedance of one of the one or more adjustable impedance devices of the tuning unit (403), presenting a negative reactance and having a terminal connected to a terminal of the output port; Y₄₀₅( f_C , a_T ) to denote an admittance of the coil (405); and Z₄₀₄( f_C , t_C , a_T ) to denote an impedance of one of the one or more adjustable impedance devices of the tuning unit (404), presenting a negative reactance and having a terminal connected to a terminal of the input port. The specialist understands that we obtain g_U ( f, Z_Sant , t_C , a_T ) = ((Z_Sant + Z₄₀₃( f_C , t_C , a_T ))^S1 + Y₄₀₅( f_C , a_T ))^S1 + Z₄₀₄( f_C , t_C , a_T ) (9) The transmission and signal processing unit knows said numerical model of the single-input-port and single-output-port tuning unit and of the control unit, which comprises equation (9) relating to the mapping g_U , a lookup table describing Z₄₀₃( f_C , t_C , a_T ), a lookup table describing Y₄₀₅( f_C , a_T ), and a lookup table describing Z₄₀₄( f_C , t_C , a_T ). Thus, the solution of equation (7) with respect to the unknown Z_Sant is given by Z_Sant = ((Z_UI S Z₄₀₄( f_C , t_CI , a_T ))^S1 S Y₄₀₅( f_C , a_T ))^S1 S Z₄₀₃( f_C , t_CI , a_T ) (10) so that it is computed quickly and accurately by the transmission and signal processing unit. We note that such a computation does not exist in any of the methods for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit mentioned above in the “prior art” section. Sixth embodiment. The sixth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4 and to the flowchart shown in Figure 5, and all explanations provided for the first embodiment and for the fourth embodiment are applicable to this sixth embodiment. In this sixth embodiment, the excitation is a signal which is used for wireless communication by the apparatus for radio communication. We have represented in Figure 7 the single-input-port and single-output-port tuning unit (4) used in this sixth embodiment. This single-input-port and single-output-port tuning unit comprises: an output port (401) having two terminals (4011) (4012), the output port being single- ended; an input port (402) having two terminals (4021) (4022), the input port being single-ended; one of the one or more adjustable impedance devices of the tuning unit (406), presenting a positive reactance; one of the one or more adjustable impedance devices of the tuning unit (407), presenting a negative reactance and being connected in parallel with the output port; one of the one or more adjustable impedance devices of the tuning unit (408), presenting a negative reactance and being connected in parallel with the input port; and an electromagnetic screen (48), which is grounded. Each of the one or more adjustable impedance devices of the tuning unit (406) (407) (408) is adjustable by electrical means, but the circuits and the control links needed to adjust the reactance of each of the one or more adjustable impedance devices of the tuning unit are not shown in Fig.7. The specialist understands that the single-input-port and single-output-port tuning unit is such that, at said given frequency, if an impedance seen by the output port is equal to a given impedance, then the reactance of any one of the one or more adjustable impedance devices of the tuning unit has an influence on an impedance presented by the input port. Experimental results have shown that the electromagnetic characteristics of the volume surrounding the single-input-port and single-output-port tuning unit often influence the characteristics of the single-input-port and single-output-port tuning unit. The specialist understands that this phenomenon may be detrimental, because the process “subsequent values of the tuning control signals” (807) utilizes a numerical model of the single-input-port and single-output-port tuning unit and of the control unit, which ignores this phenomenon. Experimental results have shown that this phenomenon may be mitigated by reducing the variable electromagnetic field produced by the single-input-port and single-output-port tuning unit outside the single-input-port and single-output-port tuning unit. In Fig.7, an appropriate reduction of this electromagnetic field is provided by the electromagnetic screen (48), which may also be referred to as electromagnetic shield, and which is connected to a ground plane of the printed circuit board on which the single-input-port and single-output-port tuning unit is built. In this sixth embodiment, the number of the one or more adjustable impedance devices of the tuning unit is equal to 3. Thus, it is possible that the number of the one or more adjustable impedance devices of the tuning unit is greater than or equal to 3. The specialist understands that we may use: Y₄₀₇( f_C , t_C , a_T ) to denote an admittance of one of the one or more adjustable impedance devices of the tuning unit (407), presenting a negative reactance and being connected in parallel with the output port; Z₄₀₆( f_C , t_C , a_T ) to denote an impedance of one of the one or more adjustable impedance devices of the tuning unit (406), presenting a positive reactance; and Y₄₀₈( f_C , t_C , a_T ) to denote an admittance of one of the one or more adjustable impedance devices of the tuning unit (408), presenting a negative reactance and being connected in parallel with the input port. The specialist understands that we obtain g_U ( f, Z_Sant , t_C , a_T ) = (((Z_Sant ^-1 +Y₄₀₇( f_C , t_C , a_T )) ^-1 + Z₄₀₆( f_C , t_C , a_T )) ^-1 + Y₄₀₈( f_C , t_C , a_T )) ^-1 (11) The transmission and signal processing unit knows said numerical model of the single-input-port and single-output-port tuning unit and of the control unit, which comprises equation (11) relating to the mapping g_U , a lookup table describing Y₄₀₇( f_C , t_C , a_T ), a lookup table describing Z₄₀₆( f_C , t_C , a_T ), and a lookup table describing Y₄₀₈( f_C , t_C , a_T ). Thus, the solution of equation (7) with respect to the unknown Z_Sant is given by Z_Sant = (((Z_UI ^-1 - Y₄₀₈( f_C , t_C , a_T )) ^-1 - Z₄₀₆( f_C , t_C , a_T )) ^-1 S Y₄₀₇( f_C , t_C , a_T )) ^-1 (12) so that it is computed quickly and accurately by the transmission and signal processing unit. We note that such a computation does not exist in any of the methods for automatically adjusting a tunable passive antenna and a single-input-port and single-output-port tuning unit mentioned above in the “prior art” section. To find a subsequent tuning unit adjustment instruction t_CS such that the impedance presented by the input port Z_U given by equation (8) is as close as possible to the wanted impedance Z_W (in which case Z_U is very close to Z_W , because the single-input-port and single-output-port tuning unit has a full tuning capability), the transmission and signal processing unit uses an algorithm. A first possible algorithm may for instance use the formulas shown in Section VI of said article entitled “Some Properties of Multiple-Antenna-Port and Multiple-User-Port Antenna Tuners”. This first possible algorithm does not take the losses in the single-input-port and single-output-port tuning unit into account. A second possible algorithm may for instance use the iterative computation technique presented in Section 4 or Appendix C of the article of F. Broydé and E. Clavelier entitled “A Tuning Computation Technique for a Multiple-Antenna-Port and Multiple-User-Port Antenna Tuner”, published in International Journal of Antennas and Propagation, in 2016. This second possible algorithm is more accurate than the first possible algorithm, because it takes the losses in the single-input-port and single-output-port tuning unit into account. The specialist knows how to write such an algorithm, which uses said lookup tables. We see that the algorithm can be such that the adjustment of the single-input-port and single-output-port tuning unit is always optimal or almost optimal, in spite of the losses in the single-input-port and single-output-port tuning unit. In the fifth embodiment and the sixth embodiment, the input port and the output port are single-ended. This is not at all a characteristic of the invention. According to the invention, it is possible that the input port and/or the output port are single-ended, and it is possible that the input port and/or the output port are balanced or symmetrical. For instance, a single-input-port and single-output-port tuning unit may comprise the circuit shown in Fig.7 and a transformer, to obtain a balanced input port or a balanced output port. Such a transformer is often referred to as a balun. For instance, a single-input-port and single-output-port tuning unit may comprise the circuit shown in Fig.7 and two baluns, to obtain a balanced input port and a balanced output port. Seventh embodiment. The seventh embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4 and all explanations provided for the first embodiment are applicable to this seventh embodiment. In this seventh embodiment, the excitation is applied continuously, so that the sensing unit can continuously deliver the sensing unit output signals caused by said excitation. A flowchart of one of the one or more adjustment sequences used in this seventh embodiment is shown in Figure 8. Before said one of the one or more adjustment sequences, the transmission and signal processing unit has chosen the selected frequency, from the set of possible values of the selected frequency. The excitation has, during said one of the one or more adjustment sequences, a carrier frequency which is equal to the selected frequency. In addition to the begin symbol (801) and the end symbol (809), said flowchart comprises: a process “delivering antenna control signals to the tunable passive antenna” (803), in which the transmission and signal processing unit delivers one or more of the one or more antenna adjustment instructions, and in which the control unit delivers said one or more antenna control signals to the tunable passive antenna, each of said one or more of the one or more antenna adjustment instructions being determined as a function of the selected frequency; a process “initial values of the tuning control signals” (805), in which the transmission and signal processing unit delivers an initial tuning unit adjustment instruction, and in which, for each of the one or more tuning control signals, the control unit begins to generate a value of said each of the one or more tuning control signals, said value being referred to as initial value, said initial value being determined as a function of the initial tuning unit adjustment instruction, and only as a function of the initial tuning unit adjustment instruction; a process “initialization” (810), in which a requirement is defined; a process “impedance presented by the input port” (806), in which the transmission and signal processing unit estimates q = 2 tuning parameters, which fully determine an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port after the end of the process “delivering antenna control signals to the tunable passive antenna” (803) and while the one or more initial values are generated; a process “subsequent values of the tuning control signals” (807), in which the transmission and signal processing unit delivers a subsequent tuning unit adjustment instruction by utilizing a numerical model, and in which, for each of the one or more tuning control signals, the control unit begins to generate a value of said each of the one or more tuning control signals, said value being referred to as subsequent value, said subsequent value being determined as a function of said subsequent tuning unit adjustment instruction, and only as a function of said subsequent tuning unit adjustment instruction; a process (811) in which a test value is determined; a decision (812) used to reach the end symbol (809) if the test value satisfies the requirement (which corresponds to a termination criterion); and a process “prepare the iteration” (813), in which the transmission and signal processing unit decides that the latest subsequent tuning unit adjustment instruction becomes, for the next processes, the initial tuning unit adjustment instruction, and decides that, for each of the one or more tuning control signals, the subsequent value of said each of the one or more tuning control signals, which was determined as a function of said latest subsequent tuning unit adjustment instruction, becomes, for the next processes, the initial value of said each of the one or more tuning control signals. To obtain that, at the end of the process “delivering antenna control signals to the tunable passive antenna” (803), the impedance seen by the output port approximates a specified impedance, the transmission and signal processing unit uses a lookup table to determine and deliver the one or more antenna adjustment instructions, as a function of the selected frequency. The specialist knows how to build and use such a lookup table, and he understands that such a lookup table cannot take into account the variations of Z_Sant caused by variations in the electromagnetic characteristics of the volume surrounding the tunable passive antenna. Moreover, as said above in the prior art section, a tunable passive antenna often only provides a poor tuning capability. Consequently, at the end of the process “delivering antenna control signals to the tunable passive antenna” (803), the impedance seen by the output port typically only very coarsely approximates the specified impedance. The decision (812) is such that, during said one of the one or more adjustment sequences, the process “impedance presented by the input port” (806) and the process “subsequent values of the tuning control signals” (807) are performed at least two times, for instance two times, or for instance three times. The numerical model comprises a numerical model of the single-input-port and single-output-port tuning unit and of the control unit. The explanations provided below in the presentations of the fourteenth, sixteenth and seventeenth embodiments show that, in the case where the numerical model is not accurate, said one of the one or more adjustment sequences is accurate, because the process “impedance presented by the input port” (806) and the process “subsequent values of the tuning control signals” (807) are performed at least two times. Eighth embodiment. The eighth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this eighth embodiment. The tunable passive antenna (1) used in this eighth embodiment is shown in Figure 9. The tunable passive antenna shown in Figure 9 comprises a planar metallic structure (111) built above a ground plane (115), the signal port of the tunable passive antenna (116) where an unbalanced feeder is connected to the metallic structure, and an antenna control device (112). The metallic structure is slotted and such that, if the antenna control device was not present, the tunable passive antenna would be an example of a planar inverted-F antenna, also referred to as PIFA. The antenna control device is a MEMS switch comprising a first terminal (113) connected to the metallic structure (111) at a first side of the slot, and a second terminal (114) connected to the metallic structure (111) at a second side of the slot. The specialist understands that the self-impedance of the tunable passive antenna, in a given test configuration and at the given frequency, is a characteristic of the tunable passive antenna which may be varied using said antenna control device, so that this characteristic is controlled by utilizing said antenna control device. The state of the MEMS switch (on or off) is an antenna control device parameter of the antenna control device. This antenna control device parameter has an influence on said characteristic. This antenna control device parameter is adjustable by electrical means, but the circuits and the control links needed to determine the state of the antenna control device are not shown in Figure 9. Ninth embodiment. The ninth embodiment of an apparatus of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this ninth embodiment. The tunable passive antenna (1) used in this ninth embodiment is shown in Figure 10. The tunable passive antenna shown in Figure 10 comprises a planar metallic structure (111) built above a ground plane (115), the signal port of the tunable passive antenna (116) where an unbalanced feeder is connected to a metallic strip (117) lying between the ground plane and the metallic structure, and three antenna control devices (112). Each of the antenna control devices is an adjustable impedance device having a reactance at the given frequency, comprising a first terminal (113) connected to the metallic structure (111), and a second terminal (114) connected to the ground plane (115). The specialist understands that the self-impedance of the tunable passive antenna, in a given test configuration and at the given frequency, is a characteristic of the tunable passive antenna which may be varied using said antenna control devices, so that this characteristic is controlled by utilizing said antenna control devices. Each of the antenna control devices has a reactance at the given frequency, this reactance being an antenna control device parameter of said each of the antenna control devices, this antenna control device parameter having an influence on said characteristic. This antenna control device parameter of said each of the antenna control devices is adjustable by electrical means, but the circuits and the control links needed to determine the reactance of each of the antenna control devices are not shown in Figure 10. Tenth embodiment. The tenth embodiment of an apparatus of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this tenth embodiment. The tunable passive antenna (1) used in this tenth embodiment is shown in Figure 11. The tunable passive antenna shown in Figure 11 comprises a main antenna (121), a parasitic antenna (122), the signal port of the tunable passive antenna (127) where an unbalanced feeder (128) is connected to the main antenna and to ground (126), and an antenna control device (123). The antenna control device is an adjustable impedance device having a reactance at the given frequency, comprising a first terminal (124) connected to the parasitic antenna (122), and a second terminal (125) connected to ground (126). The specialist understands that the directivity pattern of the tunable passive antenna, in a given test configuration and at the given frequency, is a characteristic of the tunable passive antenna which may be varied using said antenna control device, so that this characteristic is controlled by utilizing said antenna control device. The reactance of the antenna control device at the given frequency is an antenna control device parameter of said antenna control device. This antenna control device parameter has an influence on said characteristic. This antenna control device parameter is adjustable by electrical means, but the circuits and the control links needed to determine the reactance of the antenna control device are not shown in Figure 11. However, the specialist understands that this antenna control device parameter also has an influence on the self-impedance of the tunable passive antenna, so that the self-impedance of the tunable passive antenna, in a given test configuration and at the given frequency, is also a characteristic of the tunable passive antenna which may be varied using said antenna control device. The tunable passive antenna could also comprise other parasitic antennas each coupled to an antenna control device. Eleventh embodiment. As an eleventh embodiment of the invention, given by way of non-limiting example, we have represented in Figure 12 the block diagram of an apparatus for radio communication comprising: a localization sensor unit (7), the localization sensor unit estimating one or more “localization variables”, each of the one or more localization variables depending on a distance between a part of a human body and a zone of the apparatus for radio communication; a tunable passive antenna (1) comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter having an effect on one or more characteristics of said tunable passive antenna, said at least one antenna control device parameter being adjustable by electrical means; a feeder (2); a single-input-port and single-output-port tuning unit (4), having an input port and an output port, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at a given frequency greater than or equal to 300 MHz, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a sensing unit (3), the sensing unit delivering one or more “sensing unit output signals”, each of the one or more sensing unit output signals being determined by an electrical variable sensed at the input port; a transmission and signal processing unit (8), the transmission and signal processing unit selecting a frequency referred to as the “selected frequency”, the transmission and signal processing unit delivering one or more “antenna adjustment instructions”, the transmission and signal processing unit delivering “tuning unit adjustment instructions”, at least one of the tuning unit adjustment instructions being an “initial tuning unit adjustment instruction”, at least one of the tuning unit adjustment instructions being a “subsequent tuning unit adjustment instruction”; and a control unit (6), the control unit delivering one or more “antenna control signals” to the tunable passive antenna, each of the one or more antenna control signals being determined as a function of at least one of the one or more antenna adjustment instructions, each of the one or more antenna control device parameters being determined by at least one of the one or more antenna control signals, the control unit delivering one or more “tuning control signals”, the control unit generating, for each of the one or more tuning control signals, one or more values of said each of the one or more tuning control signals, each of said one or more values of said each of the one or more tuning control signals being determined as a function of at least one of the tuning unit adjustment instructions, the reactance of each of the one or more adjustable impedance devices of the tuning unit being determined by at least one of the one or more tuning control signals; the apparatus for radio communication being characterized in that: at least one of the one or more antenna adjustment instructions is determined as a function of one or more quantities depending on the selected frequency, and as a function of one or more of the one or more localization variables; at least one of the one or more initial tuning unit adjustment instructions is determined as a function of one or more quantities depending on the selected frequency, and as a function of one or more of the one or more localization variables; the transmission and signal processing unit applies, through the sensing unit, an excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency; for each of the one or more tuning control signals, said one or more values of said each of the one or more tuning control signals comprise an initial value determined as a function of one or more of the one or more initial tuning unit adjustment instructions; the transmission and signal processing unit estimates q tuning parameters by utilizing the one or more sensing unit output signals, where q is an integer greater than or equal to two, each of the tuning parameters being a real quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while each said initial value is generated; and at least one of the one or more subsequent tuning unit adjustment instructions is determined by utilizing a numerical model, as a function of: one or more quantities depending on the selected frequency; one or more variables depending on one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters. It is possible that at least one of the one or more localization variables is an output of a sensor responsive to a pressure exerted by a part of a human body. Thus, it is possible that at least one of the one or more localization variables is the output of a circuit comprising a switch using a single pressure non-locking mechanical system, the state of which changes while a sufficient pressure is exerted by a part of a human body. It is also possible that at least one of the one or more localization variables is the output of a circuit comprising another type of electromechanical sensor responsive to a pressure exerted by a part of a human body, for instance a microelectromechanical sensor (MEMS sensor). It is possible that at least one of the one or more localization variables is an output of a proximity sensor, such as a proximity sensor dedicated to the detection of a human body. Such a proximity sensor may for instance be a capacitive proximity sensor, or an infrared proximity sensor using reflected light intensity measurements, or an infrared proximity sensor using time- of-flight measurements, which are well known to specialists. It is possible that the set of the possible values of at least one of the one or more localization variables is a finite set. It is possible that at least one of the one or more localization variables is a binary variable, that is to say such that the set of the possible values of said at least one of the one or more localization variables has exactly two elements. For instance, a capacitive proximity sensor dedicated to the detection of a human body (for instance the device SX9300 of Semtech) can be used to obtain a binary variable, which indicates whether or not a human body has been detected near a zone of the apparatus for radio communication. It is possible that the set of the possible values of any one of the one or more localization variables is a finite set. However, it is possible that the set of the possible values of at least one of the one or more localization variables is an infinite set, and it is possible that the set of the possible values of at least one of the one or more localization variables is a continuous set. It is possible that the set of the possible values of at least one of the one or more localization variables has at least three elements. For instance, an infrared proximity sensor using time-of- flight measurements and dedicated to the assessment of the distance to a human body (for instance the device VL6180 of STMicroelectronics) can be used to obtain a localization variable such that the set of the possible values of the localization variable has three or more elements, one of the values meaning that no human body has been detected, each of the other values corresponding to a different distance between a zone of the apparatus for radio communication and the nearest detected part of a human body. It is possible that the set of the possible values of any one of the one or more localization variables has at least three elements. It is possible that at least one of the one or more localization variables is an output of a sensor which is not dedicated to human detection. For instance, it is possible that at least one of the one or more localization variables is determined by a change of state of a switch of a keypad or keyboard, which is indicative of the position of a human finger. For instance, it is possible that at least one of the one or more localization variables is determined by a change of state of an output of a touchscreen, which is indicative of the position of a human finger. Such a touchscreen may use any one of the available technologies, such as a resistive touchscreen, a capacitive touchscreen or a surface acoustic wave touchscreen, etc. It is said above that each of the one or more localization variables depends on the distance between a part of a human body and a zone of the apparatus for radio communication. This must be interpreted as meaning: each of the one or more localization variables is such that there exists at least one configuration in which the distance between a part of a human body and a zone of the apparatus for radio communication has an effect on said each of the one or more localization variables. However, it is possible that there exist one or more configurations in which the distance between a part of a human body and a zone of the apparatus for radio communication has no effect on said each of the one or more localization variables. For instance, the distance between a part of a human body and a zone of the apparatus for radio communication has no effect on a switch, in a configuration in which no force is directly or indirectly exerted by the human body on the switch. For instance, the distance between a part of a human body and a zone of the apparatus for radio communication has no effect on a proximity sensor if the human body is out of the proximity sensor’s range. It is possible that one of the one or more antenna adjustment instructions and one of the one or more initial tuning unit adjustment instructions are combined into a single instruction delivered by the transmission and signal processing unit. Thus, it is possible that an instruction delivered by the transmission and signal processing unit is both one of the one or more antenna adjustment instructions and one of the one or more initial tuning unit adjustment instructions. Each of the one or more antenna control signals has no influence on the selected frequency and on the one or more localization variables. Each of the one or more antenna adjustment instructions has no influence on the selected frequency and on the one or more localization variables. Since each of the one or more antenna adjustment instructions is determined as a function of the selected frequency and of the one or more localization variables, and only as a function of the selected frequency and of the one or more localization variables, it is clear that open-loop control is utilized to generate each of the one or more antenna control signals. Twelfth embodiment. The twelfth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Fig. 12, and all explanations provided for the eleventh embodiment are applicable to this twelfth embodiment. Moreover, in this twelfth embodiment, the apparatus for radio communication is a mobile phone, and the localization sensor unit comprises 4 proximity sensors. Figure 13 is a drawing of a back view of the mobile phone (800). Figure 13 shows: a point (71) where the first of the 4 proximity sensors is located; a point (72) where the second of the 4 proximity sensors is located; a point (73) where the third of the 4 proximity sensors is located; and a point (74) where the fourth of the 4 proximity sensors is located. A finite set of typical use configurations is defined. For instance, Figure 14 shows a first typical use configuration, which may be referred to as the “right hand and head configuration”; Figure 15 shows a second typical use configuration, which may be referred to as the “two hands configuration”; and Figure 16 shows a third typical use configuration, which may be referred to as the “right hand only configuration”. In Fig.14, Fig.15 and Fig.16, the mobile phone (800) is held by a user. More precisely, the user holds the mobile phone close to his head using his right hand in Fig.14; the user holds the mobile phone far from his head using both hands in Fig. 15; and the user holds the mobile phone far from his head using his right hand only in Fig.16. In an actual use configuration, the localization variables assessed by the 4 proximity sensors are used to determine the typical use configuration which is the closest to the actual use configuration. Said at least one of the one or more antenna adjustment instructions and said at least one of the one or more initial tuning unit adjustment instructions are determined from a set of pre-defined instructions that are stored in a lookup table realized in the transmission and signal processing unit, based on the closest typical use configuration and on the selected frequency. The specialist understands how to build and use such a lookup table. The specialist understands the advantage of defining and using a set of typical use configurations, which must be sufficiently large to cover all relevant cases, and sufficiently small to avoid an excessively large lookup table. It has been shown that, to obtain a good accuracy of said at least one of the one or more antenna adjustment instructions and said at least one of the one or more initial tuning unit adjustment instructions, more than two typical use configurations must be defined, and a single localization variable cannot be used to determine a closest typical use configuration. Consequently, in this twelfth embodiment, it is important that a plurality of localization variables is estimated. Additionally, to be able to determine a closest typical use configuration, it is necessary to use localization variables depending on the distance between a part of a human body and different zones of the apparatus for radio communication. More precisely, it is necessary that there exist two of the localization variables, denoted by A and B, the localization variable A depending on the distance between a part of a human body and a zone X of the apparatus for radio communication, the localization variable B depending on the distance between a part of a human body and a zone Y of the apparatus for radio communication, such that X or Y are distinct, or preferably such that X and Y have an empty intersection. In this twelfth embodiment, this result is obtained by utilizing a localization sensor unit comprising a plurality of proximity sensors, located at different places in the apparatus for radio communication, as shown in Fig. 13. Thirteenth embodiment. As an thirteenth embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 17 the block diagram of an apparatus for radio communication comprising: N = 4 tunable passive antennas (1), each of the tunable passive antennas comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said each of the tunable passive antennas, said at least one antenna control device parameter being adjustable by electrical means; a switching unit (9), the switching unit comprising N antenna ports each coupled to one and only one of the tunable passive antennas through a feeder (2), the switching unit comprising an antenna array port, the switching unit operating in an active configuration determined by one or more “configuration instructions”, the active configuration being one of a plurality of allowed configurations, the switching unit providing, in any one of the allowed configurations, for signals in a given frequency band, a bidirectional path between the antenna array port and one and only one of the antenna ports; a single-input-port and single-output-port tuning unit (4) having an input port and an output port, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as “the one or more adjustable impedance devices of the tuning unit” and being such that, at a given frequency in the given frequency band, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a sensing unit (3), the sensing unit delivering one or more “sensing unit output signals”, each of the one or more sensing unit output signals being mainly determined by one or more electrical variables sensed (or measured) at the input port; a transmission and signal processing unit (8), the transmission and signal processing unit selecting a frequency referred to as the “selected frequency”, the transmission and signal processing unit delivering one or more “antenna adjustment instructions”, the transmission and signal processing unit delivering the one or more configuration instructions, the transmission and signal processing unit delivering “tuning unit adjustment instructions”, at least one of the tuning unit adjustment instructions being an “initial tuning unit adjustment instruction”, at least one of the tuning unit adjustment instructions being a “subsequent tuning unit adjustment instruction”; and a control unit (6), the control unit delivering one or more “antenna control signals” to the tunable passive antennas, each of the one or more antenna control signals being determined as a function of at least one of the one or more antenna adjustment instructions, each said at least one antenna control device parameter of each said at least one antenna control device of each of the tunable passive antennas being mainly determined by at least one of the one or more antenna control signals, the control unit delivering one or more “tuning control signals”, the control unit generating, for each of the one or more tuning control signals, one or more values of said each of the one or more tuning control signals, each of said one or more values of said each of the one or more tuning control signals being determined as a function of at least one of the tuning unit adjustment instructions, the reactance of each of the one or more adjustable impedance devices of the tuning unit being mainly determined by at least one value of at least one of the one or more tuning control signals; the apparatus for radio communication being characterized in that: the transmission and signal processing unit is used to apply an excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency; for each of the one or more tuning control signals, said one or more values of said each of the one or more tuning control signals comprise an initial value determined as a function of one or more of the one or more initial tuning unit adjustment instructions; the transmission and signal processing unit estimates q tuning parameters by utilizing the one or more sensing unit output signals, where q is an integer greater than or equal to one, each of the one or more tuning parameters being a quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while the one of more initial values are generated; and at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters. Since said at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of one or more quantities determined by the selected frequency, it is possible to say that said at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of the selected frequency. Since said at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions, it is possible to say that said at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of one or more of the one or more initial tuning unit adjustment instructions. The switching unit operates (or is used) in an active configuration determined by the one or more configuration instructions, the active configuration being one of a plurality of allowed configurations, the switching unit providing, in any one of the allowed configurations, for signals in the given frequency band, a path between the antenna array port and one of the antenna ports. Thus, the switching unit operates in an active configuration which is one of the allowed configurations, and each allowed configuration corresponds to a selection of an antenna port among the N antenna ports. It is also possible to say that the switching unit operates in an active configuration corresponding to a selection of an antenna port among the N antenna ports. Each allowed configuration corresponds to a selection of an antenna port among the N antenna ports, the switching unit providing, for signals in the given frequency band, a path between the antenna array port and the selected antenna port. This path may preferably be a low loss path for signals in the given frequency band. The specialist understands that a suitable switching unit may comprise one or more electrically controlled switches and/or change-over switches. In this case, one or more of said one or more electrically controlled switches and/or change-over switches may for instance be an electro-mechanical relay, or a microelectromechanical switch, or a circuit using one or more PIN diodes and/or one or more insulated-gate field-effect transistors as switching devices. In this thirteenth embodiment, it is not possible to say that, for each of the tunable passive antennas, a signal port of the tunable passive antenna is coupled, directly or indirectly, to the output port. However, in this thirteenth embodiment, the output port is, at a given time, coupled to one and only one of the N tunable passive antennas. Or, more precisely, the output port is, at any given time except during a change of active configuration, indirectly coupled to a signal port of one and only one of the N tunable passive antennas, through the switching unit and one and only one of the feeders. The output port being directly coupled to the antenna array port, the specialist sees that the apparatus for radio communication allows, at the given frequency, a transfer of power from the input port to an electromagnetic field radiated by the tunable passive antennas. Thus, the apparatus for radio communication is such that, if a power is received by the input port at the given frequency, a part of said power received by the input port is transferred to an electromagnetic field radiated by the tunable passive antennas at the given frequency, so that a power of the electromagnetic field radiated by the tunable passive antennas at the given frequency is equal to said part of said power received by the input port. The apparatus for radio communication also allows, at the given frequency, a transfer of power from an electromagnetic field incident on the tunable passive antennas to the input port. Additionally, the single-input-port and single-output-port tuning unit and the tunable passive antennas are such that, at said given frequency, for suitable values of the one or more tuning control signals and of the one or more antenna control signals, a low-loss transfer of power from the input port to an electromagnetic field radiated by the tunable passive antennas can be obtained (for radio emission), and a low-loss transfer of power from an electromagnetic field incident on the tunable passive antennas to the input port can be obtained (for radio reception). The apparatus for radio communication is a radio transmitter or a radio transceiver, so that the transmission and signal processing unit (8) also performs functions which have not been mentioned above, and which are well known to specialists. The given frequency band only contains frequencies greater than or equal to 300 MHz. For instance, each of the one or more configuration instructions may be determined as a function of: one or more localization variables, defined as in the eleventh embodiment; a frequency used for radio communication with the tunable passive antennas; one or more additional variables, each of the additional variables lying in a set of additional variables, the elements of the set of additional variables comprising: communication type variables which indicate whether a radio communication session is a voice communication session, a data communication session or another type of communication session; a speakerphone mode activation indicator; a speaker activation indicator; variables obtained using one or more accelerometers; user identity variables which depend on the identity of the current user; reception quality variables; and emission quality variables. The elements of said set of additional variables may further comprise one or more variables which are different from the localization variables and which characterize the grip with which a user is holding the apparatus for radio communication. Each of the one or more configuration instructions may for instance be determined using a lookup table. Each of the one or more configuration instructions may be of any type of digital message. Each of the one or more antenna adjustment instructions and each of the tuning unit adjustment instructions may be of any type of digital message. The one or more configuration instructions, the one or more antenna adjustment instructions and the tuning unit adjustment instructions are delivered during several adjustment sequences. The transmission and signal processing unit begins an adjustment sequence when one or more configuration instructions are delivered. The transmission and signal processing unit ends the adjustment sequence when the last tuning unit adjustment instruction of the adjustment sequence has been delivered. The duration of an adjustment sequence is less than 100 microseconds. In order to respond to variations in the electromagnetic characteristics of the volume surrounding the tunable passive antennas and/or in the frequency of operation, adjustment sequences may take place repeatedly. For instance, a new adjustment sequence may start periodically, for instance every 10 milliseconds. Outside the adjustment sequences, the transmission and signal processing unit uses the one or more sensing unit output signals to estimate one or more quantities each depending on a power received by the input port. For instance, such quantities each depending on a power received by the input port may be used to control the power received by the input port, by varying a power delivered to the input port. Fourteenth embodiment. The fourteenth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this fourteenth embodiment. As in the fourth embodiment, an adjustment sequence is intended to be such that, at the end of said adjustment sequence, the impedance presented by the input port is close to a wanted impedance, denoted by Z_W . The transmission and signal processing unit knows an approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit, this approximate numerical model corresponding to a mapping denoted by g_AU , such that g_AU ( f, Z_Sant , t_C , a_T ) + d_AU ( f, Z_Sant , t_C , a_T ) = Z_U (13) where the mapping d_AU represents the error of the approximate numerical model, and is not known to the transmission and signal processing unit. We use f_C to denote the selected frequency. An adjustment sequence comprises the following steps: an antenna adjustment instruction is delivered by the transmission and signal processing unit; an initial tuning unit adjustment instruction t_CI is delivered by the transmission and signal processing unit; the transmission and signal processing unit estimates q tuning parameters, which provide a measurement Z_UIM of Z_UI , where Z_UI is the value of Z_U at f_C while t_CI is applicable; and a subsequent tuning unit adjustment instruction t_CS is computed as explained below, and delivered by the transmission and signal processing unit. While t_CI is applicable, (that is while, for each of the one or more tuning control signals, the control unit generates a value determined as a function of t_CI ), we have g_AU ( f_C , Z_Sant , t_CI , a_T ) + d_AU ( f_C , Z_Sant , t_CI , a_T ) = Z_UI (14) Let a_TM be an estimated value of a_T , for instance obtained using one or more temperature signals. The transmission and signal processing unit solves the equation g_AU ( f_C , Z_SantE , t_CI , a_TM ) = Z_UIM (15) with respect to the unknown Z_SantE , to obtain an estimated value Z_SantE of Z_Sant . Thus, we have Z_UI – Z_UIM = g_AU ( f_C , Z_Sant , t_CI , a_T ) – g_AU ( f_C , Z_SantE , t_CI , a_TM ) + d_AU ( f_C , Z_Sant , t_CI , a_T ) (16) Z_SantE and a_TM are used by a suitable algorithm, to obtain t_CS such that g_AU ( f_C , Z_SantE , t_CS , a_TM ) is as close as possible to the wanted impedance Z_W . We may write g_AU ( f_C , Z_SantE , t_CS , a_TM ) + d_QCL2 ( f_C , Z_SantE , t_CS , a_TM ) = Z_W (17) where the mapping d_QCL2 represents a quantization error which is known to the transmission and signal processing unit, but which cannot be avoided because there is no t_C in T_C such that g_AU ( f_C , Z_SantE , t_CS , a_TM ) is closer to Z_W . The resulting value of Z_U at f_C while t_CS is applicable (that is while, for each of the one or more tuning control signals, the control unit generates a value determined as a function of t_CS ) is given by g_AU ( f_C , Z_Sant , t_CS , a_T ) + d_AU ( f_C , Z_Sant , t_CS , a_T ) = Z_U (18) Thus, the error of the adjustment sequence while t_CS is applicable is given by Z_U – Z_W = g_AU ( f_C , Z_Sant , t_CS , a_T ) – g_AU ( f_C , Z_SantE , t_CS , a_TM ) + d_AU ( f_C , Z_Sant , t_CS , a_T ) – d_QCL2 ( f_C , Z_SantE , t_CS , a_TM ) (19) Let us use D_AU to denote the mapping such that D_AU ( f_C , Z_Sant , Z_SantE , t_CS , t_CI , a_T , a_TM ) = g_AU ( f_C , Z_Sant , t_CS , a_T ) – g_AU ( f_C , Z_SantE , t_CS , a_TM ) + d_AU ( f_C , Z_Sant , t_CS , a_T ) – [g_AU ( f_C , Z_Sant , t_CI , a_T ) – g_AU ( f_C , Z_SantE , t_CI , a_TM ) + d_AU ( f_C , Z_Sant , t_CI , a_T )] (20) For any values of f_C , Z_Sant , Z_SantE , t_CI , a_T and a_TM , we have D_AU ( f_C , Z_Sant , Z_SantE , t_CI , t_CI , a_T , a_TM ) = 0 (21) It follows from equation (16) and equation (20) that Z_UI – Z_UIM + D_AU ( f_C , Z_Sant , Z_SantE , t_CS , t_CI , a_T , a_TM ) = g_AU ( f_C , Z_Sant , t_CS , a_T ) – g_AU ( f_C , Z_SantE , t_CS , a_TM ) + d_AU ( f_C , Z_Sant , t_CS , a_T ) (22) Substituting equation (22) in equation (19), we can write that the error of the adjustment sequence while t_CS is applicable is given by Z_U – Z_W = Z_UI – Z_UIM + D_AU ( f_C , Z_Sant , Z_SantE , t_CS , t_CI , a_T , a_TM ) – d_QCL2 ( f_C , Z_SantE , t_CS , a_TM ) (23) By equation (15), Z_SantE may be regarded as a function of f_C , t_CI , a_TM and Z_UIM . Thus, by equation (17), t_CS may be regarded as a function of f_C , t_CI , a_TM , Z_UIM and Z_W . Thus, by equation (20), D_AU ( f_C , Z_Sant , Z_SantE , t_CS , t_CI , a_T , a_TM ) may be regarded as a function of f_C , Z_Sant , t_CI , a_T , a_TM , Z_UIM and Z_W . Thus, we can define a mapping E_AU such that E_AU ( f_C , Z_Sant , t_CI , a_T , a_TM , Z_UIM , Z_W ) = D_AU ( f_C , Z_Sant , Z_SantE , t_CS , t_CI , a_T , a_TM ) (24) If Z_UIM = Z_W the transmission and signal processing unit believes that it has reached Z_W , so that t_CS = t_CI . Thus, using equation (21) and equation (24), we obtain that, for any values of f_C , Z_Sant , t_CI , a_T , a_TM and Z_W , we have E_AU ( f_C , Z_Sant , t_CI , a_T , a_TM , Z_W , Z_W ) = 0 (25) With respect to the variable Z_UIM of equation (24), the mapping E_AU is probably neither smooth nor continuous, because of the quantization error and possibly other reasons. However, the single-input-port and single-output-port tuning unit, the control unit, and the transmission and signal processing unit are such that, with respect to the variable Z_UIM , the mapping E_AU may approximately be considered as continuous. Thus, by equation (25), if Z_UIM is sufficiently close to Z_W , then E_AU ( f_C , Z_Sant , t_CI , a_T , a_TM , Z_UIM , Z_W ) is close to zero and D_AU ( f_C , Z_Sant , Z_SantE , t_CS , t_CI , a_T , a_TM ) is close to zero. Thus, by equation (23), if Z_UIM is sufficiently close to Z_W , the error of the adjustment sequence while t_CS is applicable satisfies Z_U – Z_W ! Z_UI – Z_UIM – d_QCL2 ( f_C , Z_SantE , t_CS , a_TM ) (26) According to equation (26), the error of the adjustment sequence while t_CS is applicable is almost equal to the measurement error Z_UI – Z_UIM less the quantization error. If we compare equation (26) to equation (23), we observe that a cancellation of errors has occurred. Also, the error given by equation (26) is to a large extent independent of the accuracy of the approximate numerical model. The adjustment sequence described above uses the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit twice, the first time when it solves equation (15) to obtain Z_SantE , and the second time when said suitable algorithm is used to obtain t_CS such that g_AU ( f_C , Z_SantE , t_CS , a_TM ) is as close as possible to the wanted impedance Z_W . We have shown that, provided Z_UIM is sufficiently close to Z_W , the inaccuracies in the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit have a reduced effect on the accuracy of the resulting Z_U . Thus, if Z_UIM is sufficiently close to Z_W , the adjustment sequence described above is accurate. It is important to note that this adjustment sequence does not use any known value of the reactance of any one of the one or more adjustable impedance devices of the tuning unit, to obtain the estimated value Z_SantE of Z_Sant . If this was the case, the adjustment sequence would not use an approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit twice, and the above-mentioned cancellation of error would not occur, so that the accuracy of the resulting Z_U would be degraded. Fifteenth embodiment. The fifteenth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment and for the fourteenth embodiment are applicable to this fifteenth embodiment. In this fifteenth embodiment, the apparatus for radio communication is such that, in an adjustment sequence, Z_UIM is sufficiently close to Z_W to obtain that the error of the adjustment sequence while t_CS is applicable satisfies equation (26). For the reasons provided in the presentation of the fourteenth embodiment, we can say that the adjustment sequence uses the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit twice, and that this characteristic is used to obtain that the inaccuracies in the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit have a reduced effect on the accuracy of the resulting Z_U . Thus, said adjustment sequence is accurate. Sixteenth embodiment. The sixteenth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment and for the fourteenth embodiment are applicable to this sixteenth embodiment. In this sixteenth embodiment, the apparatus for radio communication is such that a first adjustment sequence has used a Z_UIM which need not be sufficiently close to Z_W to obtain that the error of the first adjustment sequence while its t_CS is applicable satisfies equation (26). At the end of the first adjustment sequence, the error is given by equation (23). This first adjustment sequence is quickly followed by a second adjustment sequence, such that the subsequent tuning unit adjustment instruction of the first adjustment sequence is the initial tuning unit adjustment instruction of the second adjustment sequence. In this sixteenth embodiment, the apparatus for radio communication is such that the second adjustment sequence uses an initial tuning unit adjustment instruction such that Z_UIM is sufficiently close to Z_W to obtain that the error of the second adjustment sequence while its t_CS is applicable satisfies equation (26). For the reasons provided in the presentation of the fourteenth embodiment, we can say that the inaccuracies in the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit have a reduced effect on the accuracy of the resulting Z_U at the end of the second adjustment sequence. Thus, the combination of the first adjustment sequence and of the second adjustment sequence is accurate, because, in this combination, the transmission and signal processing unit estimates the tuning parameters twice, and delivers a subsequent tuning unit adjustment instruction twice (so that the combination of the first adjustment sequence and of the second adjustment sequence uses the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit four times). Seventeenth embodiment. The seventeenth embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the apparatus for radio communication shown in Figure 4, and all explanations provided for the first embodiment are applicable to this seventeenth embodiment. An adjustment sequence of this seventeenth embodiment comprises the first adjustment sequence of the sixteenth embodiment and the second adjustment sequence of the sixteenth embodiment. For the reasons provided in the presentation of the sixteenth embodiment, we can say that the inaccuracies in the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit have a reduced effect on the accuracy of the resulting Z_U at the end of the adjustment sequence. Thus, the adjustment sequence is accurate, because, in the adjustment sequence, the transmission and signal processing unit estimates the tuning parameters twice, and delivers a subsequent tuning unit adjustment instruction twice (so that the adjustment sequence uses the approximate numerical model of the single-input-port and single-output-port tuning unit and of the control unit four times). INDICATIONS ON INDUSTRIAL APPLICATIONS The method of the invention is suitable for optimally, automatically and quickly adjusting one or more tunable passive antennas and a single-input-port and single-output-port tuning unit. The apparatus for radio communication of the invention can optimally, automatically and quickly adjust its one or more tunable passive antennas and its single-input-port and single-output-port tuning unit. The apparatus for radio communication of the invention may for instance be a radio receiver, a radio transmitter, or a radio transceiver. The invention is particularly suitable for mobile radio transmitters and mobile radio transceivers, for instance those used in portable radiotelephones or portable computers, which may be subject to fast variations in the electromagnetic characteristics of the medium surrounding the one or more tunable passive antennas being used for radio communication.

Claims

CLAIMS 1. A method for automatically adjusting one or more tunable passive antennas (1) and a single-input-port and single-output-port tuning unit (4), the single-input-port and single-output-port tuning unit having an input port and an output port, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at a given frequency, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being mainly determined by one or more “tuning control signals”, the one or more tunable passive antennas and the single-input-port and single-output-port tuning unit being parts of an apparatus for radio communication, the apparatus for radio communication allowing, at the given frequency, a transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas, the method comprising the steps of: selecting a frequency referred to as the “selected frequency”; generating one or more “antenna control signals”, each of the one or more tunable passive antennas comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said each of the one or more tunable passive antennas, said at least one antenna control device parameter being adjustable by electrical means, said at least one antenna control device parameter being mainly determined by at least one of the one or more antenna control signals; applying an excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency; generating, for each of the one or more tuning control signals, an initial value of said each of the one or more tuning control signals, the initial value of said each of the one or more tuning control signals being determined as a function of one or more “initial tuning unit adjustment instructions”; sensing one or more electrical variables at the input port, to obtain one or more “sensing unit output signals”, each of the one or more sensing unit output signals being mainly determined by at least one of the one or more electrical variables sensed at the input port; estimating q tuning parameters by utilizing the one or more sensing unit output signals, where q is an integer greater than or equal to one, each of the one or more tuning parameters being a quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while each said initial value is generated; and generating, for at least one of the one or more tuning control signals, at least one subsequent value of said at least one of the one or more tuning control signals, as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters.

2. The method of claim 1, wherein at least one of the one or more subsequent values is generated by utilizing a numerical model.

3. The method of any one of the previous claims, wherein the q tuning parameters are sufficient to allow a determination of a real part of said impedance presented by the input port, and of an imaginary part of said impedance presented by the input port.

4. The method of any one of the previous claims, wherein a value of the selected frequency lies in a “set of possible values of the selected frequency”, which comprises several elements, and wherein the selected frequency may take on any value selected in the set of possible values of the selected frequency.

5. The method of any one of the previous claims, wherein at least one of the one or more initial tuning unit adjustment instructions is determined as a function of one or more quantities depending on the selected frequency.

6. The method of any one of the previous claims, wherein the output port is, at a given time, directly or indirectly coupled to one and only one of the one or more tunable passive antennas.

7. The method of any one of the previous claims, wherein p is greater than or equal to two, and wherein q is greater than or equal to two.

8. The method of any one of the previous claims, wherein the reactance of any one of the one or more adjustable impedance devices of the tuning unit has an influence on an impedance presented by the input port.

9. The method of any one of the previous claims, wherein at least one of the one or more initial tuning unit adjustment instructions is determined as a function of one or more localization variables, each of the one or more localization variables depending on a distance between a part of a human body and a zone of the apparatus for radio communication.

10. An apparatus for radio communication comprising: one or more tunable passive antennas (1), each of the one or more tunable passive antennas comprising at least one antenna control device, said at least one antenna control device having at least one antenna control device parameter, said at least one antenna control device parameter having an effect on one or more characteristics of said each of the one or more tunable passive antennas, said at least one antenna control device parameter being adjustable by electrical means; a single-input-port and single-output-port tuning unit (4) having an input port and an output port, the apparatus for radio communication allowing, at a given frequency, a transfer of power from the input port to an electromagnetic field radiated by the one or more tunable passive antennas, the single-input-port and single-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to one, the p adjustable impedance devices being referred to as the “one or more adjustable impedance devices of the tuning unit” and being such that, at the given frequency, each of the one or more adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the one or more adjustable impedance devices of the tuning unit being adjustable by electrical means; a sensing unit (3), the sensing unit delivering one or more “sensing unit output signals”, each of the one or more sensing unit output signals being mainly determined by one or more electrical variables sensed at the input port; a transmission and signal processing unit (8), the transmission and signal processing unit selecting a frequency referred to as the “selected frequency”, the transmission and signal processing unit delivering one or more “antenna adjustment instructions”, the transmission and signal processing unit delivering “tuning unit adjustment instructions”, at least one of the tuning unit adjustment instructions being an “initial tuning unit adjustment instruction”, at least one of the tuning unit adjustment instructions being a “subsequent tuning unit adjustment instruction”; and a control unit (6), the control unit delivering one or more “antenna control signals” to the one or more tunable passive antennas, each of the one or more antenna control signals being determined as a function of at least one of the one or more antenna adjustment instructions, each said at least one antenna control device parameter of each said at least one antenna control device of each of the one or more tunable passive antennas being mainly determined by at least one of the one or more antenna control signals, the control unit delivering one or more “tuning control signals”, the control unit generating, for each of the one or more tuning control signals, one or more values of said each of the one or more tuning control signals, each of said one or more values of said each of the one or more tuning control signals being determined as a function of at least one of the tuning unit adjustment instructions, the reactance of each of the one or more adjustable impedance devices of the tuning unit being mainly determined by at least one of the one or more tuning control signals; the apparatus for radio communication being characterized in that: the transmission and signal processing unit is used to apply an excitation to the input port, the excitation having a carrier frequency which is equal to the selected frequency; for each of the one or more tuning control signals, said one or more values of said each of the one or more tuning control signals comprise an initial value determined as a function of one or more of the one or more initial tuning unit adjustment instructions; the transmission and signal processing unit estimates q tuning parameters by utilizing the one or more sensing unit output signals, where q is an integer greater than or equal to one, each of the one or more tuning parameters being a quantity depending on an impedance presented by the input port, said impedance presented by the input port being an impedance presented by the input port while each said initial value is generated; and at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of: one or more quantities determined by the selected frequency; one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and the q tuning parameters.

11. The apparatus for radio communication of claim 10, wherein at least one of the one or more subsequent tuning unit adjustment instructions is determined by utilizing a numerical model.

12. The apparatus for radio communication of any one of the claims 10 or 11, wherein the q tuning parameters are sufficient to allow a determination of a real part of said impedance presented by the input port, and of an imaginary part of said impedance presented by the input port.

13. The apparatus for radio communication of any one of the claims 10 to 12, wherein a value of the selected frequency lies in a “set of possible values of the selected frequency”, which comprises several elements, and wherein the selected frequency may take on any value selected in the set of possible values of the selected frequency.

14. The apparatus for radio communication of any one of the claims 10 to 13, wherein at least one of the one or more initial tuning unit adjustment instructions is determined as a function of one or more quantities depending on the selected frequency.

15. The apparatus for radio communication of any one of the claims 10 to 14, wherein the one or more sensing unit output signals delivered by the sensing unit comprise: a first sensing unit output signal proportional to a first electrical variable, the first electrical variable being a voltage across the input port; and a second sensing unit output signal proportional to a second electrical variable, the second electrical variable being a current flowing in the input port.

16. The apparatus for radio communication of any one of the claims 10 to 14, wherein the one or more sensing unit output signals delivered by the sensing unit comprise: a first sensing unit output signal proportional to a first electrical variable, the first electrical variable being an incident voltage at the input port; and a second sensing unit output signal proportional to a second electrical variable, the second electrical variable being a reflected voltage at the input port.

17. The apparatus for radio communication of any one of the claims 10 to 16, wherein the output port is, at a given time, directly or indirectly coupled to one and only one of the one or more tunable passive antennas.

18. The apparatus for radio communication of any one of the claims 10 to 17, wherein p is greater than or equal to two, and wherein q is greater than or equal to two.

19. The apparatus for radio communication of any one of the claims 10 to 18, wherein the reactance of any one of the one or more adjustable impedance devices of the tuning unit has an influence on an impedance presented by the input port.

20. The apparatus for radio communication of any one of the claims 10 to 19, wherein at least one of the one or more initial tuning unit adjustment instructions is determined as a function of one or more localization variables, each of the one or more localization variables depending on a distance between a part of a human body and a zone of the apparatus for radio communication.