US3747101A - High performance radio navigation stationcus - Google Patents

Abstract

A radio-navigation station allowing, in particular, the introduction of a wide-base system in a pre-existing station with a single antenna radiating a rotating cardioid radiation pattern, without replacement of the transmitting and receiving equipment. A plurality of such antennas are used each one being successively connected, for a predetermined duration, to the receiver in the case of a direction-finding station and to the transmitter in the case of a radio-beacon.

Description

0 ilnited States Patent 1 [111 3,747,101 Becavin July 17, 1973 1 111011 PERFoRMANCE 2,465,384 3/1949 Marchand 343/118 x 2,994,081 7/1961 Jordan et al.... 343/123 X RADIO NAVHGATION STATIONQUS 3,047,864 7/1962 Byatt 33/118 X [75] Inventor: Henri G. Becnvin, Paris, France [73] Assignee: Thomson-CSF, Paris, France Primary Examiner Benjamin Ah Borcheh [22] Filed: June 30, 1971 Assistant Examiner-Richard E. Berger pp No: 158,486 Attorney-Cushman, Darby & Cushman [30] Foreign Application Priority Data [57] ABSTRACT July 17, 1970 France 7026432 May 18, 1971 France 7117978 A radio-navigation station allowing, in particular, the July 17, 1970 France 7026433 introduction of a wide-base system in a pre-existing sta- May 18, 1971 France 71 17979 tion with a single antenna radiating a rotating cardioid radiation pattern, without replacement of the transmit- [52] [1.8. Ci. 343/106 R, 343/118 ting and receiving equipment. [51] Int. Cl. G018 1/54 A plurality of Such antennas are used each one-being [58] Field of Search 343/118, 106 R successively connected, for a predetermined duration to the receiver in the case of a direction-finding station [56] References Cited and to the transmitter in the case of a radio-beacon.

UNITED STATES PATENTS 3,144,649 8/1964 Steiner 343/118 X '7 (Iiaims, 4 Drawing Figures O O g\ *5 Race/yin 3%;???" 42 f 45 a 7 Clark L 4 1o PATENTEUJUL 1 7191s SHEEI 1 OF 4 Receiying dev/ce Clock geuerator Conlrol signal Pmmwwm' 3,747,101.

mm 0F 4 Switching device I07 I k I Genera tons,

The present invention relates to radio-navigation, i.e., direction-finding or beacon stations, and more particularly to wide-base stations that is to say those in which the receiving or transmitting points are distributed over a curve or a surface the dimensions of which are at least comparable with the operation wavelength.

One of the essential causes of inaccuracy in radionavigation information stems from the station environment which can disturb the propagation of electromagnetic waves through creating supplementary paths.

Among the known wide-base stations, some require an important number of fixed antennas to produce a high-directivity lobe whose displacement is obtained either through using several groups of antennas which are fed in turn, or through varying the feeding of a single antenna group. Other ones (Doppler effect antennas) use a single antenna the radiation diagram of which is fixed relatively to the antenna, but the antenna being moved by mechanical means.

All these devices yield an appreciable reduction in the errors.

' However, where the problem is 'to improve an existing small-base station, the introduction therein of a wide base requires a replacement of all the transmitting and receiving equipment.

The present invention overcomes this drawback, in the very common case of a pre-existing station using a single antenna with a rotating horizontal cardioid radiation pattern, through making it possible to introduce therein a wide base without any change in the transmitters and receivers.

According to the invention, there is provided a radionavigation station comprising a plurality of antennas with a rotating cardioid radiation pattern, an amplitude modulation transmitting or receiving device, and switching means for successively connecting said device to each of said antennas for a predetermined duration.

The invention will be better understood and other of its features rendered apparent, with the help of the description and the attached drawings in which FIG. I schematically shows an embodiment of a radio D.F. station in accordance with the invention;

FIGS. 2 and3 are explanatory diagrams;

FIG. 4 schematically shows an embodiment of a radio-beacon station in accordance with the invention.

Before describing the station shown in FIG. l, the operation of a direction-finding station using a single antenna with a cardioid cardoid radiation pattern will be briefly recalled.

The high frequency wave received from an aircraft to be localized is amplitude modulated at the rotation frequency F of the pattern, which frequency is generally comprised between 25 and 100 c/s the modulation low frequency signal is detected in an AM receiver; it is thereafter compared in phase with a reference signal which is synchronous with the rotation of the pattern. The phase of the modulation signal relatively to the reference signal, which hereinafter will be more briefly referred to as the phase of the low frequency signal, indicates the azimuth of the aircraft, which information is given to the observer by an indicator system.

In order to obtain a rotating cardioid diagram, it is possible, in particular, to use an antenna comprising a centre dipole feeding the receiver, which centre dipole is surrounded by N reflector dipoles located at the apices ofa regular polygon with N sides, and one of which only is used at any one time, the others being then detuned. Through using all the reflectors successively, there is obtained an N position rotating radiation pattern and the corresponding detected signal is filtered to be converted into a sinusoidal waveform, the phase of which is compared with that of the reference signal.

The direction-finding station shown in FIG. 1 comprises n six antennas, 1 to 6 of the above described type. Each of those antennas thus comprises a centre dipole, such as the dipole 11 of the antenna 1 and N 6 reflector dipoles, such as the dipole 12 of the antenna 1 N being in this example equal to n but this equality not being in the least necessary.

The antennas 1 4 and 6 are located at the apices of an equilateral triangle inscribed .in a circle of centre 0. and the radius 2A, where A is the operation wavelength.

The antennas 2 3 and 5 are each located at the centre of respective sides of the triangles.

The antennas 2, 3 and 6 are thus located on a circle concentris with the one just described but of radius X.

Moreover, the height of the antennas above the ground is advantageously chosen in such fashion as to cancel the field reflected by the ground, in the direction of the other antennas.

A receiving device 8 identical to that which is used in the stations with a single antenna, comprises the receiver proper, the phase comparator and the indicator system. A clock It) delivers at its output 41 pulses I the recurrence frequency of which isf= 1/9, where 9 is the duration for which a dipole reflector is placed in the resonance condition, and, by means of a frequency divider incorporated therein, delivers at its outputs 42 and 43 pulses J the recurrence frequency of which is the rotation frequency F of the cardioid radiation patterns. A generator 7 provides the control signals for placing the reflector dipoles in the resonance state and receives to this end the pulses I A switching device 9 receives the pulses J from the output 42 of the clock ill).

The pulses J delivered at the output 43 of the clock are supplied to the receiving device 8 for the generation of the phase reference signal.

The diode of each one of the reflectors is connected In a first embodiment, each antenna is successively made operative for a duration T equal to the period of rotation of the radiation pattern, while the reflectors thereof are successively put in the resonance state for a duration 9 T/N. In that case f= NF.

By means of the synchronizing pulses l the generator 7 delivers at N outputs, grouped in a single cable in the Figure, N series of pulses S the series S,(i 1,2 N) being affected to the dipoles whose position number is i in each of the antennas. The pulses of each series have a duration T/N and a period T the pulses of the series S, being shifted by G relatively to the pulses of the series S The'switching device 9 by means of the pulses J the frequency of which is F effects in the course of a cycle of duration n T the following operations In the course of the j'(j=l,2 n) time interval of duration T the switching device 9 directs the N series S, respectively to the corresponding reflectors of the j" antenna at the same time as it places the center dipole of this antenna in the resonance state and connects it to the receiving device 8 the synchronization of the rotation of the radiation pattern with the phase reference signal being ensured by means of the pulses J The low frequency signal forming the envelope of the signal received by the receiver presents in the course of a complete cycle of duration n T successively the following phases (relatively to the phase reference signal) P AP P AP P AP, where AP, is the error affecting the j" antenna; this signal is averaged by the low frequency filtering of the receiver and by the indicator system following the phase comparator, the indicator system thus delivering an information corresponding to the phase P AP, where AP AP,+AP AP,,)/n which on an average considerably decreases the final phase error.

The averaged errors are essentially those resulting from the creation of reflected rays from the environment, these rays arriving at the antenna at a different angle to the principal ray.

Calculation shows that under certain conditions this mean error is substantially less than that encountered with a single antenna, the ratio K between the two errors being as small as U10 and even less.

In FIG. 2 the value of this factor K as a function of the angle a between the direction of the reflected parasitic ray and the principal ray, when an antenna is assumed to rapidly and successively occupy all the points on a surface or a curve, has been illustrated, under the assumption that a as well as the amplitude A of the reflected signal, remains the same for each of these points.

A curve has been plotted making the assumption that the antennas are distributed upon the surface of a circle of radius equal to twice the wavelength of the high-frequency signal being received. The curve 21 assumes distribution on a circumference of the same radius and the curve 22 on two circumferences of respective radii equal to said wavelength and to twice said wavelength.

The improvement thus obtained is a really major one, in the order of 8 times (K 0.125) on average, but this is a theoretical result since it assumes the use of an infinite number of antennas.

In FIG. 3 the value of this same factor is illustrated as a function of the angle a for the case where the number of antennas is finite. The curve 32 relates to an array of six antennas in accordance with FIG. 1 and the curve 31 corresponds to the case where the radius of the external circle passing through three antennas 1, 4, 6 is equal to only 1.6 times the wavelength.

It will be seen that a gain of 3 (K 0.33) can on an average be obtained with this design.

In practice, the reflected rays come from specific directions due to the presence of large-sized obstacles such as hangers and hills, and it is therefore possible by appropriate orientation of the antenna system to obtain much better real improvement factors, better than five for example.

The same applies to the kinds of antennas used, which may be of any known type producing a radiation pattern in the form of a rotating cardioid.

The described device assumes however that the inertia of the indicator system does not allow it to follow fluctuations of frequency PM l/nT which may lead to limit n or to eliminate particular indicator systems.

It is possible to avoid such limitations through effecting the switching operations so that all the antennas are successively made operative in the course of a time interval n9 shorter than nT and increasing thus the frequency f of the fluctuations to a value 1 /n9 sufficiently high for ensuring the entire elimination of the fluctuations by the filtering in the low frequency stages of the receiver.

With the antenna system of FIG. 1 the switching operation may for example be effected in the following way.

A whole cycle has a duration T divided in N time intervals of duration T/N in the course of which one and the same position of the rotating radiation pattern is used successively for each of the antennas.

The fundamental frequency of the fluctuations is then NF (instead of Flu) and the filtering of the low frequency stages of the receiver will suffice to eliminate those fluctuations, whatever the indicator system may be.

In that case, the clock 10 delivers at its output 41 pulses with the frequency nNF and at its output 42 pulses with the frequency NF The generator 7 delivers at n separate outputs n series U,( 1,2 n) of pulses of duration 9 T/n with the period T/N the pulses of the series U, being shifted by G relatively to those of the series U The pulses of the n series U, are respectively used by switching device 9 to place in the resonance state the center dipoles of the n antennas respectively, to connect those dipoles to the receiver, and to place in the resonance state one of the reflectors.

The reflector used for each antenna is successively the reflector with position number 1 (in the first time interval of duration T/N of each cycle), then the reflector with position number 2 and so on, the necessary switching being effected in the switching device 9 by means of the pulses of frequency NF.

FIG. 4 shows a radio-beacon station according to the invention.

The operation mode of a radio-beacon using a single antenna with a rotating cardioid diagram will first be briefly recalled. Such a diagram may be obtained for example through using a complex antenna, comprising two crossed dipoles and an omnidirectional antenna.

The latter is fed by a first HF signal amplitude modulated by a subcarrier which is itself frequency modulated by the phase reference signal at the frequency F the frequency of which is generally of the order of 30 Hz; the two dipoles respectively receive two other HF signals, having the same angular frequency a) and the same HF phase as the first one, and having respectively the form sin 21rFt sin wt and cos 21rFt sin wt.

The first signal is radiated according to an omnidirectional pattern, and the subcarrier thereof supplies the phase reference; the combination of the two other radiated HF signals gives a rotating radiation pattern at the frequency F which combined with the omnidirectional pattern gives the cardioid pattern.

Reverting to FIG. 4 six antennas Hill to 106 are respectively located in relation to one another like the six antennas l to 6 of FIG. ll each of those antennas is schematically represented by two crossed dipoles.

Conventional signal generators 108, 109, 110 respectively deliver the HF signal for the omnidirectional antennas (not shown in the figure) and the two signals which are modulated in phase quadrature. A switching device 107 fed by the three signal generators is connected to the antennas 1100 to 106 by means of cables 171 to 176 respectively.

Each of these cables comprise three transmission lines respectively delivering the three HF signals to the antennas.

This system may be operated in the two ways indicated for the direction-finding station.

In a first embodiment, the n antennas are successively fed, each for a duration T l/F through the switching device 107 which receives, to this end, by means of a connection not shown in the Figure, a signal at the frequency F of the modulating signal, a complete cycle of operation having the duration nT.

In a second embodiment, the n antennas are successively made operative for a duration 9 T/p smaller than T The number p must be so chosen that the fundamental and harmonic frequencies generated by the switching of the antennas should lie not only outside the low frequency band used for the determination of the azimuth, but also outside the low frequency bands used (by means of auxiliary modulation of the HF signals) for additional information (identification of the beacon, telephony). On the other hand, a choice of an integer for the value ofp simplifies the switching. The device 107 receives then a signal at the frequency pF from which the frequency F of the modulating signal is advantageously derived by frequency division.

Relatively to the usual operation with a single antenna the aircraft receivers are not in the least affected by the new structure of the beacon.

' As concerns the averaging of the errors, the considerations made in the case of a direction-finding station also apply in this case.

The triangular arrangement shown in FIGS. l and 4 and the spacings indicated are of course only one of the numerous arrangements which are possible; a diamond-shaped arrangement in particular brings a gain of better than ten if the parasitic ray is located in a narrow sector making an angle of 1 10 with the main effective signal. The choice of the arrangement is a function of the special features of the site where the antenna is to be installed. In the case ofa well defined and localized obstacle, it may be advantageous to use a linear arrangement of the antennas, for example, normally to the direction of the obstacle.

The same applies to the kinds of antennas used, which may be of any known type producing a radiation pattern in the form of a rotating cardioid.

It is very clear from the foregoing that the radionavigation station in accordance with the invention makes it possible to obtain performance characteristics which are at least as good as those of Doppler stations, and it has the advantage over these latter of much greater simplicity, much lower cost and, above all, of being able to be developed readily from existing stations having only one antenna.

What is claimed is ll. A radio-navigation station comprising a plurality of antennas each with a rotating cardioid radiation pattern, the radiation patterns of said antennas having a common rotation period T an amplitude modulation device, and switching means for successively connecting said device to each of said antennas for a predetermined duration.

2. A radio-navigation station as claimed in claim 1, wherein said predetermined duration is equal to the rotation period T of said radiation patterns.

3. A radio-navigation station as claimed in claim 1, wherein said predetermined duration is shorter than the rotation period T of said radiation patterns.

4. A radio-navigation station as claimed in claim 1 for transmitting direction-indicating signals, said amplitude-modulation device being a transmitting device.

5. A radio-navigation station as claimed in claim 1 for receiving direction-indicating signals, said amplitude-modulation device being a receiving device.

6. A radio-navigation station as claimed in claim 5, wherein said rotating radiation patterns being patterns with N discrete positions, said predetermined duration is equal to T/(n.l\l)n being the number of antennas. I

7. A radio-navigation station as claimed in claim 5, wherein each of said antennas comprises a vertical centre dipole and several peripheral vertical dipoles located at the apices of a regular polygon, each of said dipoles being interrupted by a diode, the conduction of which places said dipoles in the resonance state relatively to the operation wavelength, said switching means ensuring in addition the control of said diodes so that only the center dipole and one of the peripheral dipoles of the antenna being connected to said device is placed in the resonance state.

Claims (7)

1. A radio-navigation station comprising a plurality of antennas each with a rotating cardioid radiation pattern, the radiation patterns of said antennas having a common rotation period T , an amplitude modulation device, and switching means for successively connecting said device to each of said antennas for a predetermined duration.

2. A radio-navigation station as claimed in claim 1, wherein said predetermined duration is equal to the rotation period T of said radiation patterns.

3. A radio-navigation station as claimed in claim 1, wherein said predetermined duration is shorter than the rotation period T of said radiation patterns.

4. A radio-navigation station as claimed in claim 1 , for transmitting direction-indicating signals, said amplitude-modulation device being a transmitting device.

5. A radio-navigation station as claimed in claim 1 , for receiving direction-indicating signals, said amplitude-modulation device being a receiving device.

6. A radio-navigation station as claimed in claim 5, wherein said rotating radiation patterns being patterns with N discrete positions, said predetermined duration is equal to T/(n.N)n being the number of antennas.

7. A radio-navigation station as claimed in claim 5, wherein each of said antennas comprises a vertical centre dipole and several peripheral vertical dipoles located at the apices of a regular polygon, each of said dipoles being interrupted by a diode, the conduction of which places said dipoles in the resonance state relatively to the operation wavelength, said switching means ensuring in addition the control of said diodes so that only the center dipole and one of the peripheral dipoles of the antenna being connected to said device is placed in the resonance state.

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