WO2022259057A1 - Antenna tuner, and tunable antenna comprising this antenna tuner - Google Patents

Antenna tuner, and tunable antenna comprising this antenna tuner Download PDF

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Publication number
WO2022259057A1
WO2022259057A1 PCT/IB2022/054346 IB2022054346W WO2022259057A1 WO 2022259057 A1 WO2022259057 A1 WO 2022259057A1 IB 2022054346 W IB2022054346 W IB 2022054346W WO 2022259057 A1 WO2022259057 A1 WO 2022259057A1
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Prior art keywords
terminal
winding
antenna
port
coupled
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PCT/IB2022/054346
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French (fr)
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Frédéric Broyde
Evelyne Clavelier
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Tekcem
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Publication of WO2022259057A1 publication Critical patent/WO2022259057A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/02—Transmitters
    • H04B1/04—Circuits
    • H04B1/0458—Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole
    • H01Q9/20—Two collinear substantially straight active elements; Substantially straight single active elements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/18—Input circuits, e.g. for coupling to an antenna or a transmission line
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/38—Impedance-matching networks

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Details Of Aerials (AREA)
  • Support Of Aerials (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)

Abstract

The invention relates to an antenna tuner, this antenna tuner being particularly suitable for radio communications utilizing an electrically short dipole antenna. The invention also relates to a tunable antenna comprising this antenna tuner. An antenna tuner of the invention comprises : an antenna port (1) having a first terminal (11) and a second terminal (12); a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a wanted mutual induction existing between the first winding and the second winding, a wanted mutual induction existing between the third winding and the second winding; a variable inductor (5); and a user port (7) having a first terminal (71) and a second terminal (72).

Description

Antenna tuner, and tunable antenna comprising this antenna tuner
FIELD OF THE INVENTION
The invention relates to an antenna tuner, this antenna tuner being particularly suitable for radio communications utilizing an electrically short dipole antenna. The invention also relates to a tunable antenna comprising this antenna tuner.
The French patent application No. FR2106199 of 11 June 2021, entitled “Accordeur d’antenne, et antenne accordable comportant cet accordeur d’antenne” is incorporated by reference.
PRIOR ART
In what follows, “coupled” always refers to an electrical coupling. When applied to two items such as terminals, conductors, nodes, etc, “coupled” may indicate that the items are directly coupled, that is to say connected (or, equivalently, in electrical contact) to one another, and/or that the items are indirectly coupled, in which case an electrical interaction different from direct coupling exists between the items, for instance through one or more components. When applied to two multi-terminal items, such as ports, connectors, etc, “coupled” may indicate that the items are directly coupled, in which case each terminal of one of the items is directly coupled to one and only one of the terminals of the other item, and/or that the items are indirectly coupled, in which case an electrical interaction different from direct coupling exists between the terminals of the items, for instance through one or more components. In what follows, in line with circuit theory, a port has exactly two terminals.
Tuning an impedance means obtaining that an impedance presented by an input port of a device approximates a wanted impedance, and simultaneously offering an ideally lossless, or nearly lossless, transfer of power from the input port to an output port of the device, in a context where the impedance seen by the output port may vary. Thus, if a signal generator presenting an impedance equal to the complex conjugate of the wanted impedance is connected to the input port, it will deliver a maximum power to the input port, this maximum power being referred to as “available power”, and the output port will deliver a power near this maximum power.
In what follows, “antenna tuner” always refers to an antenna tuner having a single antenna port and a single user port (the user port being sometimes also referred to as “radio port”). The antenna port is intended to be directly or indirectly coupled to a signal port of an antenna. The user port is intended to be used for transmitting and/or receiving radio signals, through the antenna tuner and the antenna. To this end, the user port is typically directly or indirectly coupled to a port of a radio transmitter, or of a radio receiver, or of a radio transceiver. An antenna tuner behaves, at any frequency in a given frequency band, with respect to its antenna port and its user port, substantially as a passive linear 2-port device. Here, “passive” is used in the meaning of circuit theory, so that the antenna tuner does not provide amplification. An antenna tuner comprises one or more adjustable impedance devices each having an adjustable reactance. Adjusting an antenna tuner means adjusting the reactance of one or more of its adjustable impedance devices. An antenna tuner maybe used for tuning an impedance. To tune an impedance, the antenna tuner must be properly adjusted, that is to say, the reactances of its adjustable impedance devices must be properly adjusted.
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. For instance, an adjustable impedance device may be adjustable by mechanical means, for instance by utilizing a mechanical power provided by an operator. For instance, an adjustable impedance device may be adjustable by electrical means.
An antenna tuner is also referred to as “matching circuit”, “coupler”, “antenna coupler”, “coupling circuit”, etc. Unfortunately, these alternative appellations do not mention or suggest the essential characteristic of being adjustable. In the section “Coupling the Transmitter to the Line” (pages 88 to 99) of chapter 3 of the book entitled The A. R. R. L. Antenna Book, 8th edition, published by The American Radio Relay League in 1956, several matching circuits are for instance described, these matching circuits being in fact antenna tuners because they include a variable capacitor and/or a variable inductor. In chapter 6 (pages 182 to 186) of the same book (The A. R. R. L. Antenna Book, 8th edition), several couplers, antenna couplers, and coupling circuits are for instance described, these devices being in fact antenna tuners because they include a variable capacitor and/or a variable inductor. More information on antenna tuners can be found in the book of J.R. Hallas entitled The ARRL Guide to Antenna Tuners, published by The American Radio Relay League in 2012.
A first prior art antenna tuner, suitable for being used with a balanced antenna, is shown in Fig. 1 and comprises: an antenna port (1) having a first terminal (11) and a second terminal (12); a first variable capacitor (31) having a first terminal and a second terminal, the first terminal of the first variable capacitor being coupled to the first terminal of the antenna port, the second terminal of the first variable capacitor being coupled to the second terminal of the antenna port; a coil (2), the coil having a first winding (21) and a second winding (22), a wanted mutual induction existing between the first winding and the second winding, the first winding having a first terminal and a second terminal, the first terminal of the first winding being coupled to the first terminal of the first variable capacitor, the second terminal of the first winding being coupled to the second terminal of the first variable capacitor, the second winding having a first terminal and a second terminal; a second variable capacitor (32) having a first terminal and a second terminal, the first terminal of the second variable capacitor being coupled to the second terminal of the second winding; a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being coupled to the second terminal of the second variable capacitor.
A second prior art antenna tuner, suitable for being used with a balanced antenna, is shown in Fig. 2 and comprises: an antenna port (1) having a first terminal (11) and a second terminal (12); a first variable capacitor (33) having a first terminal and a second terminal, the first terminal of the first variable capacitor being coupled to the first terminal of the antenna port; a second variable capacitor (34) having a first terminal and a second terminal, the first terminal of the second variable capacitor being coupled to the second terminal of the antenna port; a coil (2), the coil having a first winding (21) and a second winding (22), a wanted mutual induction existing between the first winding and the second winding, the first winding having a first terminal and a second terminal, the first terminal of the first winding being coupled to the second terminal of the first variable capacitor, the second terminal of the first winding being coupled to the second terminal of the second variable capacitor, the second winding having a first terminal and a second terminal; a third variable capacitor (35) having a first terminal and a second terminal, the first terminal of the third variable capacitor being coupled to the second terminal of the second winding; a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being coupled to the second terminal of the third variable capacitor.
The specialist understands the difference between a wanted mutual induction and an unwanted mutual induction. The effect of an unwanted mutual induction is often referred to as “stray mutual inductance”. The specialist understands why mutual induction is wanted between the windings of the coils considered in the first prior art antenna tuner shown in Fig. 1, and in the second prior art antenna tuner shown in Fig. 2.
The specialist understands why the first prior art antenna tuner is suitable for being used with a balanced antenna, in particular if the stray capacitances of the first variable capacitor shown in Fig. 1 are well balanced. The specialist understands why, if the first variable capacitor and the second variable capacitor shown in Fig. 2 are identical and identically tuned, the second prior art antenna tuner is suitable for being used with a balanced antenna.
Unfortunately, the prior art antenna tuners do not give good results when they are used with an electrically short center-fed dipole antenna (which is a balanced antenna), in cases where the antenna port sees a negative reactance. This is because, in these cases, these antenna tuners have large losses and/or provide a very narrow bandwidth.
SUMMARY OF THE INVENTION
The purpose of the invention is an antenna tuner suitable for being used with a balanced antenna, without the above-mentioned limitations of known techniques, and also a tunable antenna comprising this antenna tuner.
An antenna tuner of the invention comprises: an antenna port having a first terminal and a second terminal; a coil, the coil having a first winding, a second winding and a third winding, a wanted mutual induction existing between the first winding and the second winding, a wanted mutual induction existing between the third winding and the second winding, the first winding having a first terminal and a second terminal, the second winding having a first terminal and a second terminal, the third winding having a first terminal and a second terminal, the first terminal of the first winding being coupled to the first terminal of the antenna port, the second terminal of the third winding being coupled to the second terminal of the antenna port; a variable inductor having a first terminal and a second terminal, the first terminal of the variable inductor being coupled to the second terminal of the first winding, the second terminal of the variable inductor being coupled to the first terminal of the third winding; and a user port having a first terminal and a second terminal, the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being coupled to the second terminal of the second winding.
In what follows, in line with the “IEC multilingual dictionary of electricity” edited by the Bureau Central de la Commission Electrotechnique Internationale in 1983 , a tap is a connection made at some intermediate point in a winding. It is possible that said first winding comprises one or more taps. It is possible that said second winding comprises one or more taps. It is possible that said third winding comprises one or more taps.
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 schematic diagram of a first antenna tuner suitable for being used with a balanced antenna, and has already been discussed in the section dedicated to the presentation of the prior art; Figure 2 shows a schematic diagram of a second antenna tuner suitable for being used with a balanced antenna, and has already been discussed in the section dedicated to the presentation of the prior art;
Figure 3 shows a schematic diagram of an antenna tuner of the invention (first embodiment);
Figure 4 shows a schematic diagram of an antenna tuner of the invention (first embodiment);
Figure 5 shows a schematic diagram of an antenna tuner of the invention (second embodiment);
Figure 6 shows a schematic diagram of an antenna tuner of the invention (third embodiment); and
Figure 7 shows a schematic diagram of a tunable antenna comprising an antenna tuner of the invention (fourth embodiment).
DETAILED DESCRIPTION OF SOME EMBODIMENTS First embodiment.
As a first embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 3 the schematic diagram of an antenna tuner comprising: an antenna port (1) having a first terminal (11) and a second terminal (12); a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a wanted mutual induction existing between the first winding and the second winding, a wanted mutual induction existing between the third winding and the second winding, the first winding having a first terminal and a second terminal, the second winding having a first terminal and a second terminal, the third winding having a first terminal and a second terminal, the first terminal of the first winding being directly coupled to the first terminal of the antenna port, the second terminal of the third winding being directly coupled to the second terminal of the antenna port; a variable inductor (5) having a first terminal and a second terminal, the first terminal of the variable inductor being directly coupled to the second terminal of the first winding, the second terminal of the variable inductor being directly coupled to the first terminal of the third winding; and a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being directly coupled to the first terminal of the second winding, the second terminal of the user port being directly coupled to the second terminal of the second winding.
The variable inductor is an adjustable impedance device, and the variable inductor is adjustable by mechanical means, by utilizing a mechanical power provided by an operator. It is possible that the variable inductor can provide, at a given frequency, a continuous set of reactance values. For instance, the variable inductor may in this case be a plunger core coil, or a variometer, or a roller inductor, etc.
Alternatively, it is possible that the variable inductor can only provide, at a given frequency, a finite set of reactance values. For instance, the variable inductor may in this case be a network comprising a plurality of windings and/or short-circuited stubs and one or more mechanically controlled switches or change-over switches, used to cause different windings or short-circuited stubs of the network to contribute to the reactance.
The coil is a high-frequency transformer. If the user port is coupled, directly or indirectly, to an output port of a radio transmitter, and if the antenna port is coupled, directly or indirectly, to a signal port of an antenna used for emission, we see that the second winding is a primary of this high-frequency transformer, and that the first winding and the third winding form a secondary of this high-frequency transformer.
The specialist understands that a common-mode current is prevented from flowing out of the antenna port, because the antenna port is electrically isolated from the primary. Thus, the specialist understands that the antenna tuner shown in Fig. 3 is suitable for being used with a balanced antenna coupled to the antenna port, in particular if: a self-inductance of the first winding is substantially equal to a self-inductance of the third winding; a mutual inductance between the first winding and the second winding is substantially equal to a mutual inductance between the third winding and the second winding; the stray capacitances of the first winding and of the third winding are sufficiently small and/or well balanced; and the stray capacitances of the variable inductor are sufficiently small and/or well balanced.
Let us now consider a dipole antenna, which is a balanced antenna. At any frequency in a given frequency band, this dipole antenna is electrically short, that is to say, the length of the dipole antenna is much less than the half of the wavelength in vacuum that corresponds to said frequency in a given frequency band. Consequently, this antenna presents, at said frequency in a given frequency band, a reactance which is negative and a resistance which is positive and much less than the opposite of the reactance. If the dipole antenna is directly coupled to the antenna port, or if the dipole antenna is indirectly coupled to the antenna port, through a sufficiently short transmission line, then it is possible that an assumption relating to the impedance seen by the antenna port is satisfied, the assumption relating to the impedance seen by the antenna port being: at any frequency in the given frequency band, the antenna port sees a negative reactance and a resistance which is positive and less than the opposite of the negative reactance, an absolute value of the negative reactance being less than or equal to 500 ohms.
Said high-frequency transformer has a coefficient of coupling between its primary and its secondary, this coefficient of coupling being less than 8/10. The assumption relating to the impedance seen by the antenna port being satisfied, and the antenna tuner being used at a frequency in the given frequency band, the specialist understands that the variable inductor must be adjusted in such a way that said frequency in the given frequency band is close to a resonant frequency, the resonant frequency corresponding to a resonance involving: firstly, an impedance seen by the antenna port, this impedance having a negative imaginary part (reactance); and secondly an impedance presented by the first winding connected in series with the variable inductor connected in series with the third winding, this impedance having a positive imaginary part (reactance).
The assumption relating to the impedance seen by the antenna port being satisfied, the coil is proportioned such that, at any frequency in the given frequency band, it is possible to adjust the variable inductor to obtain that the second winding presents a positive conductance and negative susceptance, the positive conductance being close to a wanted positive conductance, the negative susceptance being suitable for being easily canceled by utilizing a capacitance connected in parallel with the second winding.
Thus, it is possible that, as shown in Figure 4, the antenna tuner further comprises an adjustable capacitance device (36) having a first terminal and a second terminal, the first terminal of the adjustable capacitance device being coupled to the first terminal of the second winding, the second terminal of the adjustable capacitance device being coupled to the second terminal of the second winding. We see that the adjustable capacitance device is connected in parallel with the user port, and is connected in parallel with the second winding. In Figure 4, the second terminal of the user port is grounded, because the user port corresponds to a coaxial connector, the internal conductor of the coaxial connector being the first terminal of the user port, the external conductor of the coaxial connector being the second terminal of the user port.
The adjustable capacitance device is an adjustable impedance device, and the adjustable capacitance device is adjustable by mechanical means.
It is possible that the adjustable capacitance device can provide, at a given frequency, a continuous set of reactance values. For instance, the adjustable capacitance device may in this case be a variable capacitor.
Alternatively, it is possible that the adjustable capacitance device can only provide, at a given frequency, a finite set of reactance values. For instance, the adjustable capacitance device may in this case be a network comprising a plurality of capacitors or open-circuited stubs and one or more mechanically controlled switches or change-over switches, used to cause different capacitors or open-circuited stubs of the network to contribute to the reactance.
At any frequency in the given frequency band, it is possible to adjust the adjustable capacitance device such that its positive susceptance is close to the opposite of said negative susceptance. For instance, said wanted positive conductance may be independent of the frequency and equal to 20 millisiemens. In this case, at any frequency in the given frequency band, it is possible to adjust the variable inductor and the adjustable capacitance device such that the user port presents a conductance close to the wanted positive conductance and a susceptance substantially equal to zero, consequently such that the user port presents an impedance close to 50 ohms. The assumption relating to the impedance seen by the antenna port being satisfied, the specialist understands that, in the prior art antenna tuners shown in Fig. 1 and Fig. 2, some variable capacitors (31) (33) (34) make the quality factor seen by the first winding (21) larger than the quality factor seen by the antenna port. The specialist understands that, for this reason, these antenna tuners have large losses and/or provide a very narrow bandwidth. In contrast, according to the invention, the assembly formed by the secondary of the high-frequency transformer and the variable inductor sees a quality factor equal to the quality factor seen by the antenna port, so that losses can be smaller and the bandwidth wider.
Thus, the invention solves the problem of obtaining an antenna tuner that is suitable for being used with a balanced antenna, and which gives good results when it is used with an electrically short dipole antenna, in cases where the antenna port sees a negative reactance.
Second embodiment (best mode).
Asa second embodiment of a device of the invention, given by way of non-limiting example and best mode of carrying out the invention, we have represented in Figure 5 the schematic diagram of an antenna tuner comprising: an antenna port (1) having a first terminal (11) and a second terminal (12); a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a mutual induction existing between the first winding and the second winding, a mutual induction existing between the third winding and the second winding, the first winding having a first terminal and a second terminal, the second winding having a first terminal and a second terminal, the third winding having a first terminal and a second terminal, the first terminal of the first winding being coupled to the first terminal of the antenna port, the second terminal of the third winding being coupled to the second terminal of the antenna port; a variable inductor (5) having a first terminal and a second terminal, the first terminal of the variable inductor being coupled to the second terminal of the first winding, the second terminal of the variable inductor being coupled to the first terminal of the third winding; an adjustable capacitance device (37) having a first terminal and a second terminal, the first terminal of the adjustable capacitance device being coupled to the second terminal of the second winding, the second terminal of the adjustable capacitance device being grounded; and a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being indirectly coupled to the second terminal of the second winding, through the adjustable capacitance device. The variable inductor is an adjustable impedance device, and the variable inductor is adjustable by electrical means. However, the circuits and the control links needed to determine the reactance of the variable inductor are not shown in Fig. 5.
It is possible that the variable inductor can provide, at a given frequency, a continuous set of reactance values. For instance, the variable inductor may in this case be a motorized variometer, or a motorized roller inductor, etc.
Alternatively, it is possible that the variable inductor can only provide, at a given frequency, a finite set of reactance values. For instance, the variable inductor may in this case be a network comprising a plurality of windings and/or short-circuited stubs and one or more electrically controlled switches or change-over switches, such as electro-mechanical relays or microelectromechanical switches, used to cause different windings or short-circuited stubs of the network to contribute to the reactance.
The adjustable capacitance device is an adjustable impedance device, and the adjustable capacitance device is adjustable by electrical means. However, the circuits and the control links needed to determine the reactance of the adjustable capacitance device are not shown in Fig. 5.
It is possible that the adjustable capacitance device can provide, at a given frequency, a continuous set of reactance values. For instance, the adjustable capacitance device may in this case be a motorized variable capacitor, or (for a sufficiently low power) an adjustable impedance device based on the use of a variable capacitance diode; or a MOS varactor; or a microelectromechanical varactor (MEMS varactor); or a ferroelectric varactor.
Alternatively, it is possible that the adjustable capacitance device can only provide, at a given frequency, a finite set of reactance values. For instance, the adjustable capacitance device may in this case be 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, used to cause different capacitors or open-circuited stubs of the network to contribute to the reactance.
We see that the adjustable capacitance device is connected in series with the second winding.
The coil is characterized by: a self-inductance of the first winding, denoted by LE x ; a self- inductance of the second winding, denoted by LE 2 ; a self-inductance of the third winding, denoted by LE3 ; a mutual inductance between the first winding and the second winding, denoted by ME 12 and which is equal to a mutual inductance between the second winding and the first winding; a mutual inductance between the first winding and the third winding, denoted by ME 13 and which is equal to a mutual inductance between the third winding and the first winding; and a mutual inductance between the second winding and the third winding, denoted by ME 23 and which is equal to a mutual inductance between the third winding and the second winding.
The coil is a high-frequency transformer. If the user port is coupled, directly or indirectly, to an output port of a radio transmitter, and if the antenna port is coupled, directly or indirectly, to a signal port of an antenna used for emission, we see that the second winding is a primary of this high-frequency transformer, and that the first winding and the third winding form a secondary of this high-frequency transformer. The high-frequency transformer is characterized by: a self-inductance of the primary, denoted by LTl ; a self-inductance of the secondary, denoted by LT2 ; and a mutual inductance between the primary and the secondary, denoted by MT n and which is equal to a mutual inductance between the secondary and the primary. The specialist understands that:
LT l is equal to LE 2 ;
LT2 is equal to LE l + LE3 + 2 ME 13 ; and
MT n is equal to ME 12 + ME23 .
The specialist understands that a common-mode current cannot flow out of the antenna port, because the antenna port is electrically isolated from the primary and from the ground. Thus, the specialist understands that the antenna tuner shown in Fig. 5 is suitable for being used with a balanced antenna coupled to the antenna port, in particular if:
LE I is substantially equal to LE3 ;
ME 12 is substantially equal to ME23 ; the stray capacitances of the first winding and of the third winding are sufficiently small and/or well balanced; and the stray capacitances of the variable inductor are sufficiently small and/or well balanced.
A given frequency band is the 80-meter band of the amateur service in ITU region 1, that is from 3.5 MHz to 3.8 MHz. Let us consider a center-fed dipole antenna, which is a balanced antenna, having a total length equal to about 16.55 meters. At any frequency in the given frequency band, this dipole antenna is electrically short, that is to say, the length of the dipole antenna is much less than the half of the wavelength in vacuum that corresponds to said frequency in the given frequency band. Consequently, this antenna presents, at said frequency in the given frequency band, a reactance which is negative and a resistance which is positive and much less than the opposite of the reactance. This dipole antenna is indirectly coupled to the antenna port, through a ladder line (also called “open-wire line”) of length equal to about 7.89 meters. Measurements show that at any frequency in the given frequency band, the antenna port sees a negative reactance and a resistance which is positive and less than 7 ohms, an absolute value of the negative reactance being less than 350 ohms and greater than 250 ohms. More precisely, the antenna port sees an impedance of about 3.8 - j 330 ohms at 3.50 MHz, an impedance of about 4.6 -j 296 ohms at 3.65 MHz, and an impedance of about 5.6 -j 263 ohms at 3.80 MHz.
The coil is proportioned such that, at any frequency in the given frequency band, it is possible to adjust the variable inductor to obtain that the second winding presents a positive resistance and a positive reactance, the positive resistance being close to a wanted positive resistance, the positive reactance being such that it is possible to adjust the adjustable capacitance device such that its negative reactance is close to the opposite of said positive reactance. For instance, said wanted positive resistance may be independent of the frequency and equal to 50 ohms. In this case, at any frequency in the given frequency band, it is possible to adjust the variable inductor and the adjustable capacitance device such that the user port presents a resistance close to the wanted positive resistance and a reactance substantially equal to zero, consequently such that the user port presents an impedance close to 50 ohms.
In this case, a possible proportioning leads to a self-inductance LTl equal to 3.50 pH; a self- inductance LT2 equal to 6.80 pH, and a mutual inductance MTn equal to 1.40 pH.
If we assume that the coil, the variable inductor and the adjustable capacitance device are lossless, we get the following results for the antenna tuner of this second embodiment: to obtain that the user port presents an impedance close to 50 ohms at 3.50 MHz, it is sufficient that the inductance of the variable inductor is close to 7.85 pH and that the capacitance of the adjustable capacitance device is close to 256 pF, values for which we obtain a bandwidth of about 16.0 kHz for a standing-wave ratio (SWR) less than 2; to obtain that the user port presents an impedance close to 50 ohms at 3.65 MHz, it is sufficient that the inductance of the variable inductor is close to 5.72 pH and that the capacitance of the adjustable capacitance device is close to 251 pF, values for which we obtain a bandwidth of about 21.1 kHz for a SWR less than 2; and to obtain that the user port presents an impedance close to 50 ohms at 3.80 MHz, it is sufficient that the inductance of the variable inductor is close to 3.82 pH and that the capacitance of the adjustable capacitance device is close to 246 pF, values for which we obtain a bandwidth of about 27.4 kHz for a SWR less than 2.
In contrast, using the antenna tuners shown in Fig. 1 and Fig. 2, if we assume that the coils and the variable capacitors are lossless, the bandwidths obtained at the same frequencies, for a SWR less than 2, are narrower.
If we assume that the coil and the variable inductor have a quality factor of 120, and that the adjustable capacitance device is lossless, we get the following results for the antenna tuner of this second embodiment: to obtain that the user port presents an impedance close to 50 ohms at 3.50 MHz, it is sufficient that the inductance of the variable inductor is close to 7.78 pH and that the capacitance of the adjustable capacitance device is close to 311 pF, values for which we obtain a bandwidth of about 27.8 kHz for a SWR less than 2, and a power loss of about 2.38 dB at 3.50 MHz; to obtain that the user port presents an impedance close to 50 ohms at 3.65 MHz, it is sufficient that the inductance of the variable inductor is close to 5.66 pH and that the capacitance of the adjustable capacitance device is close to 291 pF, values for which we obtain a bandwidth of about 32.5 kHz for a SWR less than 2, and a power loss of about 1.87 dB at 3.65 MHz; and to obtain that the user port presents an impedance close to 50 ohms at 3.80 MHz, it is sufficient that the inductance of the variable inductor is close to 3.77 pH and that the capacitance of the adjustable capacitance device is close to 275 pF, values for which we obtain a bandwidth of about 38.4 kHz for a SWR less than 2, and a power loss of about 1.45 dB at 3.80 MHz.
In contrast, using the antenna tuners shown in Fig. 1 and Fig. 2, if we assume that the coils have a quality factor of 120 and that the variable capacitors are lossless, the power losses obtained at the same frequencies are greater.
We see that, according to the invention, losses can be smaller and the bandwidth wider than the ones obtained by utilizing the antenna tuners shown in Fig. 1 and Fig. 2. This is because, according to the invention, the assembly formed by the secondary of the high-frequency transformer and the variable inductor sees a quality factor which is not increased by a parallel capacitance (present in the antenna tuner shown in Fig. 1) or by one or more series capacitances (present in the antenna tuner shown in Fig. 2), so that this quality factor is equal to the quality factor seen by the antenna port.
Thus, the invention solves the problem of obtaining an antenna tuner that is suitable for being used with a balanced antenna, and which gives good results when it is used with an electrically short dipole antenna, in cases where the antenna port sees a negative reactance.
The variable inductor and the adjustable capacitance device being adjustable by electrical means, the antenna tuner can be a part of an automatic antenna tuner, for instance an automatic antenna tuner implementing any one of the control schemes presented in the article of F. Broyde and E. Clavelier entitled “A Typology of Antenna Tuner Control Schemes, for One or More Antennas”, published in Excem Research Papers in Electronics and Electromagnetics, number 1, doi: 10.5281/zenodo.3902749, in June 2020. For instance, the automatic antenna tuner could implement the method disclosed in the French patent number 1800872, entitled “Precede pour reglage automatique d’une unite d’ accord, et appareil pour communication radio utilisant ce precede” and in the international application number PCT/IB2019/056447 of 29 July 2019 (WO 2020/035756), entitled “Method for automatic adjustment of a tuning unit, and apparatus for radio communication using this method”.
Third embodiment.
As a third embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 6 the schematic diagram of an antenna tuner comprising: an antenna port (1) having a first terminal (11) and a second terminal (12); a 2-pole 3-throw rotary switch (6) comprising a first single-pole 3-throw switch (61) and a second single-pole 3-throw switch (63); a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a mutual induction existing between the first winding and the second winding, a mutual induction existing between the third winding and the second winding, the first winding having a first end, a first tap, a second tap and a second end, the first winding having a first terminal and a second terminal, the first terminal of the first winding being selected by the first single-pole 3 -throw switch among the first end of the first winding, the first tap of the first winding and the second tap of the first winding, the second terminal of the first winding being the second end of the first winding, the second winding having a first terminal and a second terminal, the third winding having a first end, a first tap, a second tap and a second end, the third winding having a first terminal and a second terminal, the first terminal of the third winding being the second end of the third winding, the second terminal of the third winding being selected by the second single-pole 3-throw switch among the first end of the third winding, the first tap of the third winding and the second tap of the third winding, the first terminal of the first winding being coupled to the first terminal of the antenna port, the second terminal of the third winding being coupled to the second terminal of the antenna port; a variable inductor (5) having a first terminal and a second terminal, the first terminal of the variable inductor being coupled to the second terminal of the first winding, the second terminal of the variable inductor being coupled to the first terminal of the third winding; an adjustable capacitance device (38) having a first terminal and a second terminal, the first terminal of the adjustable capacitance device being coupled to the first terminal of the second winding; and a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being indirectly coupled to the first terminal of the second winding, through the adjustable capacitance device, the second terminal of the user port being coupled to the second terminal of the second winding.
The specialist understands that the 2-pole 3-throw rotary switch, the variable inductor and the adjustable capacitance device can be used to adjust the antenna tuner over a broad frequency range.
Fourth embodiment.
As a fourth embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 7 the schematic diagram of a tunable antenna comprising an antenna tuner of the invention. The tunable antenna comprises: a passive antenna (8) having a signal port (83); an antenna port (1) having a first terminal (11) and a second terminal (12), the antenna port being coupled to the signal port; a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a wanted mutual induction existing between the first winding and the second winding, a wanted mutual induction existing between the third winding and the second winding, the first winding having a first terminal and a second terminal, the second winding having a first terminal and a second terminal, the third winding having a first terminal and a second terminal, the first terminal of the first winding being directly coupled to the first terminal of the antenna port, the second terminal of the third winding being directly coupled to the second terminal of the antenna port; a variable inductor (5) having a first terminal and a second terminal, the first terminal of the variable inductor being directly coupled to the second terminal of the first winding, the second terminal of the variable inductor being directly coupled to the first terminal of the third winding; and a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being coupled to the second terminal of the second winding.
The passive antenna (8) has a first conductor (81) and a second conductor (82). For instance, it is possible that a length of the first conductor is close to a length of the second conductor, and that the passive antenna is a balanced antenna. For instance, it is possible that the passive antenna is a center-fed dipole antenna.
The signal port (83) has a first terminal (831) and a second terminal (832). The signal port is used to receive and/or to emit electromagnetic waves, through the passive antenna.
The tunable antenna further comprises a feeder (9) having a first end and a second end, the first end being coupled to the signal port. The antenna port is coupled to the second end of the feeder, so that the antenna port is indirectly coupled to the signal port, through the feeder. Alternatively, the antenna port could be directly coupled to the signal port.
For instance, il est possible that the feeder is a balanced transmission line. For instance, for frequencies less than 200 MHz, it is possible that the feeder is of the type called “air-insulated line” or “ladder line”, or of the “window line” type, or of the “twin lead” type. For instance, for frequencies greater than 100 MHz, it is possible that the first conductor, the second conductor and the feeder are built on or in a printed circuit board.
It is possible that the tunable antenna further comprises an adjustable capacitance device, the adjustable capacitance device being connected in parallel with the second winding, or in series with the second winding.
INDICATIONS ON INDUSTRIAL APPLICATIONS
The antenna tuner of the invention is suitable for radio communication in a given frequency band, by utilizing a balanced antenna presenting a negative reactance in the given frequency band, for instance an electrically short dipole antenna. The tunable antenna of the invention is suitable for radio communication in a frequency band where it is electrically short. The tunable antenna of the invention is therefore compact, and it is inexpensive.

Claims

1. An antenna tuner comprising: an antenna port (1) having a first terminal (11) and a second terminal (12); a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a wanted mutual induction existing between the first winding and the second winding, a wanted mutual induction existing between the third winding and the second winding, the first winding having a first terminal and a second terminal, the second winding having a first terminal and a second terminal, the third winding having a first terminal and a second terminal, the first terminal of the first winding being coupled to the first terminal of the antenna port, the second terminal of the third winding being coupled to the second terminal of the antenna port; a variable inductor (5) having a first terminal and a second terminal, the first terminal of the variable inductor being coupled to the second terminal of the first winding, the second terminal of the variable inductor being coupled to the first terminal of the third winding; and a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being coupled to the second terminal of the second winding.
2. The antenna tuner of claim 1 , further comprising an adjustable capacitance device (36), the adjustable capacitance device being connected in parallel with the second winding.
3. The antenna tuner of claim 1 , further comprising an adjustable capacitance device (37), the adjustable capacitance device being connected in series with the second winding.
4. The antenna tuner of any one of the previous claims, wherein the first winding comprises one or more taps, and wherein the third winding comprises one or more taps.
5. The antenna tuner of any one of the previous claims, wherein the second winding comprises one or more taps.
6. A tunable antenna comprising: a passive antenna (8) having a signal port (83); an antenna port (1) having a first terminal (11) and a second terminal (12), the antenna port being coupled to the signal port; a coil (4), the coil having a first winding (41), a second winding (42) and a third winding (43), a wanted mutual induction existing between the first winding and the second winding, a wanted mutual induction existing between the third winding and the second winding, the first winding having a first terminal and a second terminal, the second winding having a first terminal and a second terminal, the third winding having a first terminal and a second terminal, the first terminal of the first winding being coupled to the first terminal of the antenna port, the second terminal of the third winding being coupled to the second terminal of the antenna port; a variable inductor (5) having a first terminal and a second terminal, the first terminal of the variable inductor being coupled to the second terminal of the first winding, the second terminal of the variable inductor being coupled to the first terminal of the third winding; and a user port (7) having a first terminal (71) and a second terminal (72), the first terminal of the user port being coupled to the first terminal of the second winding, the second terminal of the user port being coupled to the second terminal of the second winding.
7. The tunable antenna of claim 6, further comprising an adjustable capacitance device, the adjustable capacitance device being connected in parallel with the second winding.
8. The tunable antenna of claim 6, further comprising an adjustable capacitance device, the adjustable capacitance device being connected in series with the second winding.
9. The tunable antenna of any one of the claims 6 to 8, wherein the first winding comprises one or more taps, and wherein the third winding comprises one or more taps.
10. The tunable antenna of any one of the claims 6 to 9, wherein the second winding comprises one or more taps.
PCT/IB2022/054346 2021-06-11 2022-05-10 Antenna tuner, and tunable antenna comprising this antenna tuner WO2022259057A1 (en)

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FR2106199A5 (en) 1970-08-31 1972-04-28 Illinois Tool Works
WO2019056447A1 (en) 2017-09-20 2019-03-28 武汉华星光电半导体显示技术有限公司 Array substrate and manufacturing method therefor
WO2020035756A1 (en) 2018-08-16 2020-02-20 Tekcem Method for automatic adjustment of a tuning unit, and apparatus for radio communication using this method
US20210041515A1 (en) * 2019-08-07 2021-02-11 Raytheon Company Tuning networks for single loop resonators

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FR2106199A5 (en) 1970-08-31 1972-04-28 Illinois Tool Works
WO2019056447A1 (en) 2017-09-20 2019-03-28 武汉华星光电半导体显示技术有限公司 Array substrate and manufacturing method therefor
WO2020035756A1 (en) 2018-08-16 2020-02-20 Tekcem Method for automatic adjustment of a tuning unit, and apparatus for radio communication using this method
US20210041515A1 (en) * 2019-08-07 2021-02-11 Raytheon Company Tuning networks for single loop resonators

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ANONYMOUS: "Antenna tuner - Wikipedia", 3 June 2021 (2021-06-03), XP055895036, Retrieved from the Internet <URL:https://en.wikipedia.org/w/index.php?title=Antenna_tuner&oldid=1026726650> [retrieved on 20220224] *
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