Phase-control system for telecommunications signals received by an adaptive antenna

In a receiving station having an adaptive receiving antenna, a phasing system comprises a plurality of reception paths receiving telecommunications signals derived from the same useful signal combined in transmission with a disturbing signal having a frequency band outside the frequency band of the useful signal, via a plurality of primary sources of the receiving antenna. The phasing system includes a narrowband filtering circuit for filtering the overall telecommunications signal in one of the reception paths to derive a reference signal undisturbed by the disturbing signal and solely dependent on the useful signal. In phasing circuits respectively assigned to the reception paths, the useful signal alone is set to a phase as close as possible to the phase of the reference signal in order to obtain, after signal summing at outputs of the phasing circuits, a maximum power using signal mixed with an attenuated scrambling signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the utilization of an adaptive 
receiving antenna in a receiving station to receive a useful 
telecommunications signal transmitted by a transmitting station and 
combined during transmission with a disturbing signal. 
2. Description of the Prior Art 
It is known in the prior art in the radar field to use an adaptive 
receiving antenna including a plurality of primary sources feeding a 
plurality of corresponding reception paths. Due to the distances between 
the various primary sources on the antenna, the telecommunications signals 
picked up by the primary sources are relatively out-of-phase and must be 
matched in phase by comparison with a reference phase in order to sum the 
received signals into a received signal having a maximum power. Since 
transmitting and receiving "stations" of a radar are close together, the 
reference phase is that of the useful transmitted signal which has the 
same waveform, to within amplitude, as the received signal. 
However, in telecommunications systems involving distant transmitting and 
receiving stations, the receiving station does not know the exact 
frequency of the transmitted useful signal. Indeed, in the 
telecommunications field, the nature of the received signal is never 
completely known a priori, since the purpose of a transmission is 
precisely to send information from a transmitting station to a receiving 
station in the form of a sequential modification of the transmitted 
telecommunications signal i.e., the useful signal. 
Moreover, the useful signal received at the receiving station can be 
degraded by at least one disturbing signal located outside the frequency 
band of the transmitted signal, in accordance with the standard 
radiofrequency scheme. Hereafter, in the present specification and claims, 
such a signal that is located in a frequency band outside of the frequency 
band of the transmitted useful signal and which arrives at a receiving 
antenna from a direction different from the direction of the useful 
signal, to degrade the useful transmitter signal received at the receiving 
station, is referred to as a disturbing signal. To process the useful 
signal emitted by the transmitting station and received together with the 
disturbing signal at the receiving station, it is necessary to attenuate 
or even eliminate the disturbing signal in the receiving station. 
OBJECT OF THE INVENTION 
The main object of this invention is to provide a system for phasing 
telecommunicatons signals, wherein the phasing of the useful transmitted 
signal included among the various telecommunications signals received by 
the primary sources of the receiving antenna is obtained by means of a 
reference signal which depends only on the useful signal and is 
independent of the disturbing signal. 
SUMMARY OF THE INVENTION 
Accordingly, there is provided a phase-control system included in a 
receiving station for phasing telecommunications signals derived from a 
single useful signal transmitted by a transmitting antenna to a receiving 
antenna and combined with a disturbing signal having a frequency band at 
least partly different from a frequency band of the useful signal. The 
telecommunications signals are respectively fed to a plurality of 
reception paths by a plurality of receiving antenna primary sources via a 
plurality of frequency transposing and preamplifying means. The 
phase-control system comprises filtering means coupled to one of the 
reception paths for filtering within a narrow frequency band the 
telecommunications signal fed to the channel to derive a reference signal 
undisturbed by the disturbing signal. The narrowband is within the 
frequency band of the useful signal and outside the frequency band of the 
disturbing signal. The phase-control system further comprises, in each of 
the reception paths, a phasing means for comparing the phases of the 
telecommunications signal, derived from the transposing and amplifying 
means in the path with a phase of the reference signal in order to set the 
phase of the useful signal included in the telecommunications signal to a 
phase as near as possible to, i.e., approximately equal to, that of the 
reference signal. 
Because of the narrowband filtering of one of the telecommunications 
signals to derive the reference signal, a reference phase is supplied that 
depends only on the useful signal transmitted by the transmitting antenna. 
In each of the phasing means, a correlation between the reference signal 
and the received telecommunications signal enables detection of phase 
mismatches between the useful signal component in the telecommunications 
signal and the reference signal and correction solely of the phase of the 
useful signal. In signals leaving the phasing means to be summed, the 
useful signal is put into phase, whereas the scrambling signal, not being 
phase matched, is attenuated. 
Such phase control of the useful signal in each of the reception paths or 
channels is obtained by correlating means for comparing the phase of the 
reference signal with the phase of the useful signal component in the 
respective telecommunications signal using in-phase and quadrature 
component signals relative to said respective telecommunications signal to 
derive two analog control signals, by means for attenuating the in-phase 
and quadrature component signals on the basis of the sign and amplitude of 
the two analog phase control signals so as to substantially phase the 
useful signal with the reference signal, and by means for summing 
attenuated component signals leaving the attenuation means. 
According to another feature of this invention, the phase control signals 
for each reception path drive a variable-gain amplifier in the reception 
path so as to amplify the telecommunications signal in the path only 
according to the level of the useful signal which has been so detected in 
the path phasing means. Thus, as opposed to the prior art variable-gain 
amplifier circuits where the gain varies as a function of the detected 
envelope of the telecommunications signal, or otherwise stated, as a 
function of the combined useful and scrambling signals, an amplifier gain 
control according to the invention depends only upon the useful signal. 
Specifically, when the useful signal is weak in comparison with the 
disturbing signal, the gain control according to the prior art amplifies 
the telecommunications signal based upon the level of the disturbing 
signal, but the gain control according to the invention amplifies the 
telecommunications signal based upon the level of the useful signal, thus 
enabling it to be suitably detected for phasing. 
According to yet another feature of this invention, the phase control 
signals for any two reception paths are processed in calculating means to 
establish the angular position of the transmitting antenna with respect to 
the receiving antenna. As will be explained hereinafter, this enables the 
particular orientation of the receiving antenna to be slaved to the 
position of the transmitting antenna for the purpose of receiving a 
highest possible power of useful signal, when the transmitting station is 
mobile, for example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 are only shown in detail two of several reception paths V.sub.a, 
V.sub.b, . . . of a receiving station receiving via an adaptive antenna a 
useful telecommunications signal, a telephone signal for instance, 
transmitted by a transmitting station. It is remembered that an adaptive 
antenna includes a group of two or more primary sources, or elements such 
as dipoles, receiving a useful signal SU, with relative phase shifts such 
as .PSI..sub.a and .PSI..sub.b for two channels or paths V.sub.a and 
V.sub.b illustrated in FIG. 1. It is assumed throughout the following that 
the primary sources also receive a disturbing signal SB characterized by a 
frequency spectrum outside the frequency band of the useful signal SU and 
arriving from a direction different from than the useful signal direction 
between the transmitting and receiving stations. The useful signal SU may 
for example be a frequency-modulated signal or a phase-modulated signal, 
i.e., an angle modulated signal, having a carrier modulated by either a 
digital signal or an analog signal. The signal carrier has a frequency 
lying for example in the range of 1 to 10 GHz. 
The term "reception path" used herein shall be understood to mean a 
combination of circuits for amplifying and transforming signals received 
by a primary source of the receiving antenna. 
Each reception path V.sub.a, V.sub.b, . . . comprises identical input 
circuits 2.sub.a, 2.sub.b, . . . receiving, via an associated primary 
source 3.sub.a, 3.sub.b, . . . of the adaptive receiving antenna, a 
telecommunications signal corresponding to a combination of the useful 
signal SU phase-shifted by .PSI..sub.a, .PSI..sub.b, . . . with the 
disturbing signal. The useful signal and the scrambling signal are 
subjected to same conventional transformations in the input circuits. In 
input circuits 2.sub.a, 2.sub.b, . . . , the received signal is subjected 
to one or two frequency transpositions and a preamplification to produce a 
signal SU.sub.a +SB.sub.a, SU.sub.b +SB.sub.b, . . . transposed to an 
intermediate frequency IF, generally equal to 70 MHz. The preamplification 
may be carried out after one or both frequency transpositions, by means of 
an automatic gain control (AGC) circuit which detects an IF signal 
envelope and compares it with a reference voltage in order to preamplify 
the received signal as a whole, i.e. the useful signal mixed with the 
scrambling signal. 
After going through the input circuits 2.sub.a, 2.sub.b, . . . , the signal 
SU.sub.a +SB.sub.a, SU.sub.b +SB.sub.b, . . . in the respective reception 
path V.sub.a, V.sub.b, . . . is subjected to certain transformations in a 
respective phasing circuit 1.sub.a, l.sub.b, . . . , as explained 
hereinafter, in order to sum in phase the signals received at the 
frequency of the useful signal alone, and thus recover a maximum of energy 
of the useful signal and attenuate to a large extent the disturbing 
signal. Besides this, a small part of the received signal energy is taken 
from one of the reception paths, such as path V.sub.b, to derive a 
reference signal SR that is used specifically to find the in-phase sum of 
the signals at the useful frequency. 
In accordance with the invention, the reference signal SR is obtained in a 
filtering circuit 4. A main function of circuit 4 is narrowband filtering 
of the SU.sub.b +SB.sub.b signal in path 1.sub.b. An input of filtering 
circuit 4 is coupled to reception path 1.sub.b via a coupler 40. Coupler 
40 is interconnected between output 20.sub.b of input circuits 2.sub.b and 
input 10E.sub.b of a power divider 10 included in phasing circuit 1.sub.b. 
Filtering circuit 4 comprises from an input connected to coupler 40, 
circuits connected in series such as a bandpass filter 41, an amplifier 
42, an amplitude limiter 43 and a low-pass filter 44. Bandpass filter 41 
is a narrowband filter which takes out a narrowband of the frequency range 
of the useful signal SU carried in the overall signal SU.sub.b +SB.sub.b. 
This narrowband is outside the frequency band of the disturbing signal SB 
to produce a reference signal SR undisturbed by the disturbing signal. 
The signal produced by an output of the filter 44 is not degraded by the 
disturbing signal and serves as reference signal SR according to the 
invention, to phase together the useful signals SU.sub.a, SU.sub.b, . . . 
in the reception paths V.sub.a, V.sub.b, . . . The signal SR is 
distributed to all the paths V.sub.a, V.sub.b, . . . by a common power 
divider 45 having an input connected to the output of the low-pass filter 
44 and outputs connected respectively to inputs of dual-output power 
dividers included in phasing circuits 1.sub.a, 1.sub.b, . . . such as 
power divider 14 in circuit 1.sub.a in FIG. 1. 
The phasing circuits 1.sub.a, 1.sub.b. . . in all of the paths V.sub.a, 
V.sub.b. . . of the receiving station being identical, only circuit 
1.sub.a in reception path V.sub.a is hereinafter described with reference 
to FIG. 1. 
The phasing circuit 1.sub.a comprises two quasi-identical main sub-paths. 
The two main sub-paths each are divided into two quasi-identical secondary 
sub-paths to divide the overall SU.sub.a +SB.sub.a signal into four 
component signals in quadrature pairs and act upon the amplitude of the 
four component signals to obtain a useful signal SU.sub.a phase as close 
as possible to phase .PSI..sub.R of the reference signal SR. This breaking 
down of path 1.sub.a into four sub-paths enables phasing of the signal SU 
in all four quadrants (0, .pi./2), (.pi./2, .pi.), (.pi., 3.pi./2) and 
(3.pi./2, 2.pi.) of the phase diagram, regardless of the phase difference 
.PSI..sub.R -.PSI..sub.a between signal SU.sub.a and reference signal SR. 
Circuit 1.sub.a comprises an input circuit consisting of a balanced power 
divider 10 receiving, via an input 10E.sub.a, the signal SU.sub.a 
+SB.sub.a supplied by an output 20.sub.a of the input circuits 2.sub.a, 
and producing two signals S.sub.1 and S.sub.2 having a same amplitude but 
a relative phase shift of .pi./2 at two outputs 10S.sub.1 and 10S.sub.2 
which constitute respective inputs of the two main sub-paths. Signal 
S.sub.1 leaving output 10S.sub.1 is in phase with the overal SU.sub.a 
+SB.sub.a signal. Signal S.sub.2 leaving output 10S.sub.2 is phase shifted 
by .pi./2 with respect to signal SU.sub.a +SB.sub.a and signal S.sub.1 by 
means of a .pi./2 phase-shifter included in the power divider 10. 
The signals S.sub.1 and S.sub.2 are each separated into two identical 
signals S.sub.1 ' and S.sub.2 ' thanks to balanced power dividers 11.sub.1 
and 11.sub.2. Two signals S.sub.1 ' and S.sub.2 ' are applied to first 
inputs 12E.sub.1 and 12E.sub.2 of correlators 12.sub.1 and 12.sub.2, and 
two other signals S.sub.1 ' and S.sub.2 ' are applied to inputs 13E.sub.1 
and 13E.sub.2 of balanced power dividers 13.sub.1 and 13.sub.2 each having 
a .pi. phase shifter respectively. Outputs 13S.sub.1 and 13S.sub.3 of 
divider 13.sub.1 constitute inputs of the two secondary sub-paths of the 
first main sub-path and supply signals s.sub.1 and s.sub.3 having equal 
amplitudes but phase shifted by 0 and .pi. respectively with respect to 
signal SU.sub.a +SB.sub.a at input 10E.sub.a. Inputs of the two secondary 
sub-paths of the second main sub-path are provided by outputs 13S.sub.2 
and 13S.sub.4 of the power divider 13.sub.2 which supply signals s.sub.2 
and s.sub.4 having equal amplitudes but phase shifted by .pi./2 and 
3.pi./2 respectively with respect to signal SU.sub.a +SB.sub.a at input 
10E.sub.a. 
Two outputs of the power divider 14 in circuit 1.sub.a feed the reference 
signal to second inputs 12R.sub.1 and 12R.sub.2 of correlators 12.sub.1 
and 12.sub.2. Reference signal SR is compared with the 0 and .pi./2 
phase-shifted signals S.sub.1 ' and S.sub.2 ' in the correlators 12.sub.1 
and 12.sub.2. Signals delivered by outputs 12S.sub.1 and 12S.sub.2 of 
correlators 12.sub.1 and 12.sub.2 are strictly a function of the relative 
phase between the SU.sub.a +SB.sub.a signal in path V.sub.a and the 
reference signal SR, taken at the frequency of the useful signal. Products 
of the comparisons made with the disturbing signal SB.sub.a are finally 
completely eliminated by means of integrators 15.sub.1 and 15.sub.2 which 
are connected to outputs 12S.sub.1 and 12S.sub.2 of correlators 12.sub.1 
and 12.sub.2 and which supply analog phase control signals 
.DELTA..PSI..sub.1 and .DELTA..PSI..sub.2. Integrators 15.sub.1 and 
15.sub.2 have integration time constants allowing only low-frequency 
components to pass, coming from the correlation of the SU.sub.a and SR 
signals, while higher frequency components resulting from the correlation 
of the SB.sub.a and SR signals having different frequencies are notably 
attenuated. Signals .DELTA..PSI..sub.1 and .DELTA..PSI..sub.2 have 
non-zero amplitudes only for frequency components of the reference signal 
SR also appearing in signals S.sub.1 and S.sub.2, i.e. in signal SU.sub.a. 
Typically, the time constants of the integrators 15.sub.1 and 15.sub.2 are 
on the order of 1 to 10 ms for a narrow frequency band of the reference 
signal SR of about 1 MHz obtained by filtering a useful signal SU having a 
useful frequency band of 10 MHz. 
The two phase control signals .DELTA..PSI..sub.1 and .DELTA..PSI..sub.2 are 
respectively inverted in amplitude inverters 151.sub.1 and 151.sub.2, then 
are amplified in amplifiers 152.sub.1 and 152.sub.2 to feed control inputs 
C.sub.1 and C.sub.2 of analog multipliers 16.sub.1 16.sub.2. In addition, 
signals .DELTA..PSI..sub.1 and .DELTA..PSI..sub.2 are respectively applied 
to control inputs C.sub.3 and C.sub.4 and of second analog multipliers 
16.sub.3 and 16.sub.4 via amplifiers 152.sub.3 and 152.sub.4. Inverters 
151.sub.1 and 151.sub.2 and amplifiers 152.sub.3 to 152.sub.4 thus 
determine the signs and amplitudes of the control signals 
.DELTA..PSI..sub.1 and .DELTA..PSI..sub.2. The analog multipliers 16.sub.1 
and 16.sub.4 can be PIN-diode controlled attenuators and constitute the 
secondary sub-paths receiving component signals s.sub.1 to s.sub.4 phase 
shifted by 0, .pi./2, .pi.and 3.pi./2 with respect to signal SU.sub.a 
+SB.sub. a at the input 10E.sub.a, respectively. The signals 
.DELTA..PSI..sub.1, .DELTA..PSI..sub.2, -.DELTA..PSI..sub.1 and 
-.DELTA..PSI..sub.2 respectively delivered by the amplifiers 152.sub.1 to 
152.sub.4 are used to control the phase of the various component signals 
s.sub.1 to s.sub.4 in path V.sub.a, by acting on the amplitude of the two 
component signals S.sub.1 ' and S.sub.2 ' differing in phase by .pi./2, by 
means of the attenuators 16.sub.1 to 16.sub.4 which are voltage controlled 
according to the positive amplitudes of the respective control signals 
-.DELTA..PSI..sub.1, -.DELTA..PSI..sub.2, .DELTA..PSI..sub.1 and 
.DELTA..PSI..sub.2. 
For example, to vary the phase of signal SU.sub.a in the first phase 
quadrant from 0 to .pi./2, the amplitudes of the quadrature component 
signals s.sub.1 and s.sub.2 are adjusted by the attenuators 16.sub.1 and 
16.sub.2. To vary the phase of signal SU.sub.a in the second phase 
quadrant from .pi./2 to .pi., it is necessary act on the amplitudes of 
other quadrature component signals, i.e. on the amplitude of quadrature 
component signal S.sub.2 corresponding to signal s.sub.2 and the amplitude 
of phase component signal S.sub.1, having shifted its phase by .pi. to 
produce signal s.sub.3 ; thereafter, the signal SU.sub.a phase shifting 
between .pi./2 and .pi. is obtained by means of the attenuators 16.sub.2 
and 16.sub.3. Likewise, the phase shifts of signal SU.sub.a in the third 
quadrant from .pi. to 3.pi./2 and the fourth quadrant from 3.pi./2 to .pi. 
are achieved respectively by the attenuators 16.sub.3 and 16.sub. 4 and 
attenuators 16.sub.4 and 16.sub.1, respectively. 
The two pairs of phased signals leaving attenuators 16.sub.1 to 16.sub.4 
are mixed in two-input summing circuits 17.sub.1 and 17.sub.2, and then in 
an output summing circuit 18 having two inputs connected to outputs of 
summing circuits 17.sub.1 and 17.sub.2. Output 18S.sub.a of circuit 18 in 
circuit 1.sub.a thus supplies a signal including the useful signal 
SU.sub.a and having a phase substantially equal to the reference phase 
.PSI..sub.R and a maximum power, and the scrambling signal SB.sub.a not 
having been shifted back into phase. 
The phased useful signals SU.sub.a, SU.sub.b, . . . and the scrambling 
signals SB.sub.a, SB.sub.b, . . . not having been shifted back into phase, 
supplied by outputs 18S.sub.a, 18S.sub.b, . . . of summing circuits 18 in 
all the phasing circuits 1.sub.a, 1.sub.b, . . . are mixed in a common 
summing circuit 5. An output 5S of circuit 5 supplies a useful signal SU 
having a maximum power and considerable unscrambled, i.e. mixed with a 
weak or diminished disturbing signal in comparison with the scrambling 
signal picked up by the receiving antenna. 
In accordance with another embodiment of the invention, the coupling 
circuit 40 associated with the filtering circuit 4 can be replaced by a 
coupling circuit interconnected with one of the outputs of the phasing 
circuits, such as output 18S.sub.a or 18S.sub.b of circuit 1.sub.a or 
1.sub.b, or interconnected with the output 5S of the common summing 
circuit 5, without altering the phasing principle according to the 
invention. 
In accordance with a first application of the phasing circuits according to 
the invention, the phase control signals .DELTA..PSI..sub.1 and 
.DELTA..PSI..sub.2 in each reception path are used to control a 
preamplification of the useful signal leaving the input circuits in the 
path. As shown in FIG. 2, with reference to reception path V.sub.a for 
example, a useful signal preamplification circuit 6.sub.a is provided 
between the output 20.sub.a of the input circuits 2.sub.a and the input 
10E.sub.a of the power divider 10 in the phasing circuit 1.sub.a. Circuit 
6.sub.a includes a variable-gain amplifier 60 and a follower-amplifier 61 
series-connected between the terminals 20.sub.a and 10E.sub.a. 
Amplifier 60 has a gain controlled by an analog signal V.sub.R -.rho..sub.a 
derived by a gain control circuit 7.sub.a. Circuit 7.sub.a comprises four 
diodes 70.sub.1, 70.sub.2, 70.sub.3 and 70.sub.4 having anodes 
respectively connected to the outputs of inverters 151.sub.1 and 151.sub.2 
and to the outputs of integrators 15.sub.1 and 15.sub.2, and a voltage 
comparator 71. An inverse input 71 of comparator 71 is connected to 
cathodes of diodes 70.sub.1 to 70.sub.4 and receives a voltage 
proportional to a signal .rho..sub.a having the greatest amplitude of all 
the signals derived from integrators 15.sub.1 and 15.sub.2 and inverters 
151.sub.1 and 151.sub.2, i.e. a voltage proportional to the amplitude of 
the phase control signals .DELTA..PSI..sub.1 and .DELTA..PSI..sub.2 and so 
varying with the amplitude of the useful signal SU.sub.a. The signal 
.rho..sub.a is compared with a reference voltage V.sub.R applied to a 
direct input 71.sub.+ of the comparator 71 after suitable adjustment by 
means of a potentiometer 72. An output 71S of the comparator 71 thus 
supplies the control signal V.sub.R -.rho..sub.a which is applied to a 
gain control input 60C of amplifier 60 to control the preamplification of 
the signal SU.sub.a +SB.sub.a, not on the basis of an envelope of the 
signal SU.sub.a +SB.sub.a dependent on the amplitude of the scrambling 
signal SB.sub.a but rather on the basis of the envelope of the useful 
signal SU.sub.a. In fact, the signal .rho..sub.a is directly dependent on 
the coincidence of the received signal SU.sub.a +SB.sub.a and the 
reference signal SR in correlators 12.sub.1 and 12.sub.2, which reference 
signal SR is independent of the scrambling signal SB.sub.a. The scrambling 
signal SB.sub.a is also amplified by amplifier 60, but is amplified as a 
dependent of the useful signal amplitude rather than as a dependent of the 
combined useful signal and scrambling signal amplitudes. 
In accordance with a second application of the phasing circuits according 
to the invention, the phase control signals for any two reception paths, 
such as paths V.sub.a and V.sub.b, are utilized to determine an angular 
position of the antenna in the transmitting station in relation to the 
antenna of the receiving station. As shown in FIG. 2, the receiving 
station comprises a computer 8 having two first inputs 8E.sub.a1 and 
8E.sub.a2 respectively connected to the outputs of the integrators 
15.sub.1 and 15.sub.2 in phasing circuit 1.sub.a and two second inputs 
8E.sub.b1 and 8E.sub.b2 respectively connected to the outputs of 
corresponding integrators 15.sub.1 and 15.sub.2 in circuit 1.sub.b. The 
first inputs and second inputs of the computer 8 receive signals related 
to the phases .PSI..sub.R -.PSI..sub.a and .PSI..sub.R -.PSI..sub.a 
+.pi./2, and .PSI..sub.R -.PSI..sub.b and .PSI..sub.R -.PSI..sub.b 
+.pi./2, and therefore actually pairs of signals having a relative phase 
.PSI..sub.b -.PSI..sub.a. 
Computations handled by the computer 8 consist particularly in computing 
the relative phase angle .PSI..sub.b -.PSI..sub.a. For this purpose the 
computer is provided with a first tangent calculating circuit 81.sub.a for 
calculating tan(.PSI..sub.R -.PSI..sub.a) based upon the phase signals 
.PSI..sub.R -.PSI..sub.a and .PSI..sub.R -.PSI..sub.a +.pi./2, i.e. based 
upon cos(.PSI..sub.R -.PSI..sub.a) and sin(.PSI..sub.R -.PSI..sub.a), a 
second tangent calculating circuit 81.sub.b for calculating 
tan(.PSI..sub.R -.PSI..sub.b) based upon the phase signals .PSI..sub.R 
-.PSI..sub.b and .PSI..sub.R -.PSI..sub.b +.pi./2, i.e. based upon 
cos(.PSI..sub.R -.PSI..sub.a) and sin(.PSI..sub.R -.PSI..sub.a), two 
antitangent calculating circuits 82.sub.a and 82.sub.b for calculating 
.PSI..sub.R -.PSI..sub.a and .PSI..sub.R -.PSI..sub.b based upon the 
signals tan(.PSI..sub.R -.PSI..sub.a ) and tan(.PSI..sub.R -.PSI..sub.b) 
and a subtractor 83 for calculating .PSI..sub.b -.PSI..sub.a based upon 
signals .PSI..sub.R -.PSI..sub.a and .PSI..sub.R -.PSI..sub.b. 
Using 2d to designate the distance between the two primary sources 3.sub.a 
and 3.sub.b of the receiving antenna respectively assigned to the paths 
V.sub.a and V.sub.b, .lambda. to designate the wavelength of the 
transmission carrier and .theta. the angle between the direction from the 
transmitting antenna to the receiving antenna and the mid-perpendicular to 
the segment joining the two sources 3.sub.a and 3.sub.b, it is known that 
the difference .PSI..sub.b -.PSI..sub.a is given by the following 
relation: 
EQU .PSI..sub.b -.PSI..sub.a =2.pi.. (2d/.lambda.).sin .theta.. 
From this relation the angle .theta. can be found: 
EQU .theta.=sin.sup.-l ((.PSI..sub.b -.PSI..sub.a)..lambda./(4.pi.d)). 
The computer 8 then includes a directional angle computing circuit 84 which 
computes according to the above mentioned relation the angle .theta. as a 
function of .PSI..sub.b -.PSI..sub.a established by subtractor 83. 
Advantageously, the distance 2d between the two selected sources 3.sub.a 
and 3.sub.b is small, so as to resolve the indeterminacy of the 
computation of angle .theta. to within k.pi., where k is an integer. 
Based on the value of .theta., a known servocontrol means (not shown in the 
drawings) is used to control the relative position of the receiving 
antenna in relation to the direction of the antennas in order to receive 
the greatest possible power of useful signal SU. The servocontrol means 
thus enables the receiving antenna to be suitably pointed at the 
transmitting antenna when one of the antennas if movable with respect to 
the other. Such an angular correction is thus carried out every time a 
direction-finding or "goniometric" operation is required to ensure 
adequate reception of telecommunications signals, such as in the case of 
aircraft navigation and landing radio aids, earth station tracking of a 
satellite, or the orientating of a receiving antenna in a fixed broadcast 
station with respect to a mobile broadcasting station aboard a vehicle.