DISPOSITIF DE CORRECTION AUTOMATIQUE DE L'EFFET DE DEPOLARISATION DES ONDES ELECTROMAGNETIQUES

DEVICE FOR AUTOMATICALLY CORRECTING THE DEPOLARIZING EFFECT OF ELECTROMAGNETIC WAVES

Abrégé anglais

ABSTRACT OF THE DISCLOSURE:
A device for automatically correcting the depolarizing
effect of circularly polarized electromagnetic waves in trans-
mission systems of the type employing two distinct receiving
and transmitting frequency bands, each of which has a double
crossed circular polarization and wherein two "beacon" signals
of distinct frequencies are allocated to the receiving band. A
separating unit separates the signals of the two bands and a
correcting unit corrects the interference effects due to de-
polarization of the receiving band signal. A conversion-
separation unit transforms the two circular cross-polarizations
of the receiving band signals into two linear cross-polarizations
according to two orthogonal components (namely D and S) and
those of the beacon signals into two linear cross-polarizations
according to two orthogonal components (namely B and C). A
pair of separating units which separate the components of the
beacon signals (B and C) from the components of the receiving
band signals (D and S) and two pairs of filters are tuned to
the frequencies f1 and f2 of the two beacon signals, the inputs
of these filters being connected to the output of the separating
units which further separate each of the components B and C
into the non-depolarized beacon signals and to the depolarized
beacon signals. A processing unit is connected to the outputs of
the two pairs of filters, this unit processing the non-depolar-
ized and depolarized signals and emitting four output signals
each of which controls an adjusting element for adjusting the
correcting unit.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A device for automatically correcting a depo-
larization effect of polarized electromagnetic waves in
transmitting systems of the type using two frequency bands which
are distinct at receiving side and transmission side, each
having a double polarization and wherein two beacon
signals at frequency f1 and f2 are allocated to the receiving
band, comprising in combination;
- a separating unit for separating the signals included
in the two bands;
- a correcting unit connected to the separating unit
for correcting interference effects due to the depolarization of
the signal receiving band;
- a conversion-separation unit connected to the dor-
recting unit and which transforms the two polariza-
tions of the receiving band into two polarizations
according to orthogonal components and the two,
polarizations of the beacon signal into two polar-
izations according to two further orthogonal components;
- a pair of separating means each connected to one
output of said conversion-separation unit separating the or-
thogonal components of the beacon signals from the orthogonal
components of the receiving band;
- two pairs of filters tuned to the frequencies f1
and f2, the inputs of which are connected to the output of said
separating means,for separating each of the beacon signal com-
ponents into components due to non-depolarized beacon signals,
respectively, and into components due to depolarized beacon
signals;

- a processing unit connected to the outputs of the
two pairs of said filters, for processing said non-depolarized
and depolarized signals, said processing unit issuing four output
signals for adjusting said correcting unit.
2. A device as claimed in claim 1, characterized in
that the correcting unit comprises two differential attenuators,
the differential attenuation planes of which are at a predeter-
mined angle therebetween, and two differential phase shifters
the differential phase displacement planes of which are at a pre-
determined angle therebetween.
3. A device as claimed in claim 2, characterized in
that said two angles are equal to one another and of 45°.
4. A device as claimed in claim 2, characterized in
that the processing unit comprises:
- two phase shifters which cause an adjustable phase
displacement of the signal from one pair of said filters;
- two further phase shifters which phase shift by 90
two fractions of the signals from said phase shifters;
- four coherent detectors respectively connected to
said pairs of filters, to said phase shifters and said further
phase shifters;
- a summing circuit and a substracting circuit each
receiving a signal from the first and third coherent detectors;
and
- a further summing circuit and a further substracting
circuit, receiving a signal from the second and fourth coherent
detectors.

Description

~o695~9
~ he present invention relates to a device for automatic-
ally correcting the depolarizing effect of polarized
electromagnetic waves in transmission systems of the type em-
ployir~ two distinct receiving and transmitting frequency bands
each of which has a dou~le polarization and
wherein two "beacon" signals of distinct freguencies are allocated
to the receiving band.
Systems of this type are, for example, those used for
telecommunicating via satellite ~here, by using a double crossed
polarization (such as circular polarization), it is possible to
transmit an amount of information~ the engaged band being equal~
twice as much with respect to the simple polarization.
In this case it is necessary, however, to avoid inter-
ference phenomena among signals of the two polarizations.
One source of interference is the depolarization of the
electromagnetic wave. ~his term generally indicates the phase
di~placement and the attenuation undergone by one of the two
polarizations, throughout the transmission means, with respect to
the other. In these conditions, undesired components of electro-
magnetic field according to the two polarizations are generated.These components cause interference between signals of the two
polarizations and also attenuation as well as degradation of the
signal-noise ratio.
One of the main causes of this phenomenon~ which may
be described as an anisotropy of the transmitting means, resides
in the atmospheric disturbances which, due to their irregular
character, make it difficult to eliminate interference pheno~ena.
~ wo methods are known for correcting depolarization:
one method being the so-called "cancellation" method and the
other being the so-called "recovery" method.
~ he first method takes ad~anta~e of a portion of the
energy corresponding to the de5ired polarization to eliminate
.' ~
. . . - ~ ,

10695~39
the interference ~hich depends upon the ~ndesired cro~s-polariza-
tion. ~his method reduces or eliminates interference by "can-
celling" the interference component, but, by doing so, it also
attemlates the useful signal at places where it would be desir-
able to reduce any energy loss (radio frequency section) to a
min~mum. ;
~he ~recoveryl' method instead comprises transforming
again, according to the desired polarization, the energy fraction
which Wa8 transformed accordi~g to the undesired cros~-polariza-
tion but was used only for linear cross-polarizations up to now.
The object of the present invention is to pro~ide a
depolarization correction de~ice of the "recovery" type for
polarizations, ~herein no mechanical members are provided to
correct the received signals, said de~ice being designed to be
used in wide-band transmitting syste~s and to effect a correction
throughout the whole band by making use of.two beacon signals
allocated with~n th~s band, only.
~he in~ention is characterizea in that it comprises,
~n combination, the following eleme~ts:
20 - a separating unit separating signals of the two bands;
- a correcting unit correcting the interference effect~
due to depolarization of the receiving band signal;
- a conversion-separation unit which transforms the two
polarizations of the receiving band signal~ into two polarizations
according to two orthogonal components (namely D and S) and those
of the beacon signals ~nto two polarizations according to two
orthogonal components (n~mely B and C);
- a pair of ~urther separating units which separate
the components of the beacon ~ignals (B and C) from the compo-
- , . . . .

~695~39
nents of the receiving band signals (D and S);
-two pairs of filters tuned to the frequencies f1 and
f2 f the two beacon signals, the inputs of these filters being
connected to the output of the separating units v~hich further
æeparate each of the components ~ and C into the components Bu
and Bi and Cu and Ci respectively due to the non-depolarized
beacon signals (Bu and Cu) and to the depolarized beacon signals
(~i and Ci);
- a processing ~nit connected to the outputs of the
two pairs of filters, said unit processing the signals Bu, Cu~
Bi and Ci and emitting four output signals each of which controls
an adjusting element for adjusting the correcting unit and depends
only upon the effect of the depolarization that it can correct
through the correct element associated therewith in the correction
unit.
A preferred embodiment of the present invention will
be hereinafter described with reference to the accompanying
drawings, in which:
~ igure 1 is a block diagram of the present invention;
and
~ igure 2 is a detailed block diagram of a detailed em-
bodiment of the present invention.
~ he antenna A~ is used for receiving and tranæmitting
and deals with the following signals:
a) the receiving band signal with a double circular
polarization (which, for example, may have a counterband fre-
guency of 4 GHz and band amplitude of 500 ~Iz);
b) the two beacon signals of freguency f1 and f2
(internal to the receiving si~nal bard and also ha~ing a double
oircular polarization);
c) ths transmission band signal (for example, of 6 GHz)
from the transmitter.

1069589
~ he separating unit DG is intended to separate the two
signal bands without interferences and then the block ~RR will
rece:ive only signals aocording to paragraphs a) and b) above.
The receiving correction unit CRR, one embodIment of
which is shown in Figure 2, corrects the depolarized signals.
In the embodiment shown in Figure 2, it comprises two differential
attenuators A1 and A2 whose differential attenuation planes are
at an angle of 45 with respect to one another and two differ-
ential phase shifters ~ 2 and ~ 1 whose differential phase d~s-
placement planes are at an angle of 45 with respect to oneanother As will be explained below, this angle is an optimum
value for the operation of the device but is not binding since
it i~ possible to use various angles (other than right angles) by
reducing only the rate at which the system carries out the cor-
reotions.
~ he ~our ad~usting elements controlled in a way which
wiii be explained below, operate in such a way that at the out-
put of the correction unit the intensity of the interference
signal (as far as the useful signal is concexned ~hose atten-
uations are negligible) is at a minimum.
~ he block DPR transforms the cross-circulax polariza-
tion into cross-linear polarizations and as a result two orthogo-
nal linear polarizations (which are indicated by D= when obtained
by the conversion of the right-hand circular polarization and by
S- when obtained from the conversion of the left-hand circular
polarization~ occur at the output of this element and two
orthogonal linear polarizations from the conversions of the bea-
con signals (B and C).
Since also beacon signals undergo depolarization ef-
3o fects the components of B and C will not only be duc to theright-hand and left-hand circular polarizations of the original
beacon signals~ but will contain components due to the anisot-
.. ~,. :,
;. . .

1~)695~3~
ropy of the means. These components are separated precisely onaccount of the different frequencies of the beacon signals
thro~h filters ~1 and F1~ t~ned to the frequency fl and filters
~2 and ~2~ tuncd to the frequency f2. The diagram sholvn in
~igure 2~ the block D~R comprises an ortho-mode transducers and
two loyJ-noise amplifiers which are the first amplifiers met by
the signal. As one may realise, the recovery of the depolarized
components occurs at a radio frequency and this substantially
improves the signal-noise ratio.
The linear polarizations D ans S (and B and ~) which
are then applied (D and S)respectively to the receiving assemblies
RC1 and RC2 are separated by the séparators SP1 and SP20
In Figure 2~ the blocks indicated by M1 and M2 show two
frequency converters but Y~ shall continue to refer to frequencies
f1 and f2 ~rhich should be understood as the fxequencies obtained
through conversion from thé beacon signals, since thi~ does not
modify the philosophy of the system nor the practical conclu-
sions, this being a conventional technical solution provided to
improve the system. C1 and C2 are two directive couplers and
blocks D1 and D2 indicate t~ separators.
With reference now to the diagram shoY~ in Figure 2,
the processing unit ~S will be described.
The signals from ~1 and ~2 are further phase-shifted
through the phase shifters S~1 and S~2 and this in order to ob-
tain suitable phase relationships between the components of the
useful signals and those of the interference signals.
By indicating at V and H the useful signals at frequen-
¢ies f1 and f2, respec~ively, and at v and h the interference
si~nals at frequencies f1 and f2, respectively, there occurs that:
a) -the output signal from S~1 is proportional to j V
(fr~uency f1); !
~) the output signal from S~2 is proportional to j H
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~069589
(fre~uency f2);
r) the output si~nal from ~2' is proportional to:
H , ~a1 - b1 - ~a2~2 ~ b2~2) ~ jra2 b2 + a1~ }
(frequency -~2);
~) the output signal from ~1~ is proportional to:
~ 2 2 ( 1~1 b1~ Ca1 - b1 ~ (a2~2 ~ b ~ )]}
(frequency f1); .
where:
b1 and b2 are the differential attenuations introduced by the
attenuators A1 and A2, respectively;
a1 and a2 are the differential attenuations introduced by the
free space according to two planes at right angles to the atten-
uation planes of the attenuators A1 and A2, respectively; ~r1
and ~2 are the differential phase displacements introduced by
the pha~e shifters ~ and ~ ~ respectively;
~1 and ~ are the differential phase displacements introduced
by the free space along planes at right angles to the differential
phase displacement planes of phase shifters ~ and ~ , respec-
tively.
By means of the four power dividers S1, S1~, S2, S2~
and the phase shifters Q1 and Q2 (which effect a phase displace-
ment of 90), said signals are sent to four coherent detectors
indicated by T, U, X, Y.
The output signals from said detectors are proportional
continuous signals, respectively: - _ ~ to H . ra2 ~ b2 ~ (a1 ~1 b1 1)~ ;
- U to H . ra1 ~ b1 ~ (a2 ~ 2 b2~2)~;
- X to V ~a2 b2 (a1 ~ 1 1 1) ;
_ Y to V . [a1 ~ b1 + (a2 ~2 b2 2)~; .
~0 Subsequently, through the power dividers ~1~ E1~ ~2~ E2'
said signals are applied to summing blocks ~1 and ~2 and to the
subtracting bloaks ~1 and ~2.

~069589
As may easily be analytically verified~ the output
signals have the following properties:-
- the output signal from ~1 is proportional to (a2 - b2)
- the output signal from ~2 is proportional to (a2 - b1)
- the output signal from ~1 is proportional to
(a1q~1 -b1~91');
- the output signal from ~2 is proportional to
(a2~2 ~ b2er2)
Since these signals are proportional to the differences
between the disturbance effects of the transmitting means and to
the corrections made by the adjusting members, the differences
at the output of the correcting system (CRR) can be small at
will. The system is then convergent and can then efficiently
correct the depolaxization even if in the strict sense said
signals contain even small contributions due to interference
phenomena among them.
The output signals fro~ ~ 2~ 2 are t
to control the corrections of elements A2, A1, ~ , ~ , respec-
tively.
Moreover, on the ground of the hypothesis that the
disturbance introduced by the transmitting means results in
effects on the transmitted frequency band proportional to those
occurring on the received band, the same signals are applied
also to corresponding correcting elements for the transmitted
.- signal (attenuators A4 and A3, phase shifters ~ and ~ ). The
signals are withdrawn by means of blocks indicated by H1, H2,
K1, K2 in Figure 2. DPT indicates the conversion-mixing unit
of the transmitting part which receives signals from the trans-
mitting assemblies TR1 and TR2.
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