DE2535536A1 - CIRCUIT ARRANGEMENT FOR THE AUTOMATIC CORRECTION OF THE DEPOLARIZATION OF ELECTROMAGNETIC WAVES - Google Patents

Description

9602-7 5 / H / Ro.

_D B 332 Dr.'Jnri, -.mat Sonrmrfd

Italian note, no. 26166 A / 74 ^L '"' ■ ■ ·

from August 9, 1974 Γ \: .. ■. . -. \ _:

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Societä Italiana Telecomunicazioni

Siemens s.p.a. Piazzale Zavattari, 12, Milan / Italy

Circuit arrangement for automatic correction the depolarization of electromagnetic waves.

The invention relates to a circuit arrangement according to the preamble of claim 1.

Such systems can be found, for example, in satellite communication systems Application with which using a double (e.g. circular) cross polarization With the same tape load, twice the amount of messages can be transmitted than with a single polarization. Here, however, interference phenomena between the signals with the two polarizations must be avoided will. One cause of this interference is the so-called depolarization of the electromagnetic wave. Herewith one generally denotes the phase shift and attenuation caused by the transmission medium, which one of the two polarizations compared to the other polarization. This creates unwanted components of the electromagnetic field according to the two polarizations. These components lead to interference between the Signals with the two polarizations and consequently to one

609809/0738

Attenuation and a deterioration in the signal-to-noise ratio. One of the main causes of this phenomenon, which is schematically due to an anisotropy of the transmission medium is traceable, lies in the weather influences, the irregularity of which suppresses the interference phenomena difficult.

There are two known methods of correcting depolarization: the so-called deletion method and the so-called Recovery procedure.

In the cancellation process, a part of the energy belonging to the desired polarization is used to partially or completely eliminate the interference components appearing in the undesired cross-polarization. In this case, however, the useful signal is attenuated at one point on the signal transmission path (radio frequency part) at which a The smallest possible loss of energy should be aimed for.

The recovery method, on the other hand, sees a reconversion of the converted according to the undesired cross-polarization Energy share according to the desired polarization before, but is so far only for linear cross-polarization has been applied.

The invention is based on the object of an arrangement for equalization which operates according to the recovery method or to create correction of the depolarization, which is suitable on the one hand for circular polarization, on the other hand in broadband transmission s systems and a correction in the entire frequency band using only two im Beacon signals lying in the same frequency band are guaranteed. Furthermore, the arrangement should be simplified accordingly also be applicable in the case of a linear polarization.

The invention solves this problem by the arrangement characterized in claim 1.

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A particular advantage of the invention is that the arrangement without mechanical actuators for the to be equalized Received signals.

The invention is described in more detail below using a preferred exemplary embodiment, its circuit details can be found in the drawing. Show:

1 shows a schematic representation of the arrangement, and FIG. 2 shows a detailed block diagram of the arrangement.

The antenna AN is used for both reception and transmission and therefore works with the following signals: (a) dem Signal of the received band with double circular polarization, for example an opposing band frequency of 4 GHz and can have a bandwidth of 500 MHz; (b) the two beacon signals with the frequencies f. and f ~, which, likewise with double circular polarization, within the frequency band of the received signal lie; and (c) the transmitted signal (transmission band), for example at 6 GHz.

The separation unit DG has the task of the two signal bands to separate while avoiding interference, so that the reception correction unit CRR only the signals according to (a) and (b) receives.

The reception correction unit CRR is used to equalize the depolarized signals. It consists in a preferred embodiment according to Figure 2 consists of two differential attenuators A ₁ and A _2, the differential-attenuation planes include an angle of 45 ° with one another, and two differential phase shifters 0 ₂ ^{un (^} 0i 'eieren differential phase planes. also enclose an angle of 45 ° with each other. This angle value, as will be described below, is an optimal value for the mode of operation of the arrangement, but it is not mandatory to select it Exclusion of orthogonality), in which case only the

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2 b 3 5 5 3 6

The speed at which the system processes the Makes corrections. By these four actuators, which are controlled in the manner described below, the Amplitude of the interference signal (compared to the useful signal, the attenuation of which is negligibly small) at the output the reception correction unit reduced to a minimum.

The converter and separation unit DPR converts the circular cross polarizations into linear cross polarizations, so that at the output of this unit two linear orthogonal polarizations, one of which is a component with D resulting from the conversion of the right-handed circular polarization and the other from the conversion of the left-handed polarization Component resulting from circular polarization is denoted by S, and two further linear orthogonal polarization components B, C appear, which arise from the conversion of the beacon signals. Since the beacon signals also suffer from depolarization phenomena, components B and C are not only due to the right-handed and left-handed circular polarizations of the original beacon signals, but also have components that originate from the anisotropy of the transmission medium. These components are now separated on the basis of the different frequencies of the beacon signals, specifically with the aid of the filters F ₁ and F _{1 'tuned to the frequency f 1 and the filters F 2} and F, ¹ tuned to the frequency f ". In the block diagram according to FIG. 2, the converter and isolation unit DPR contains a converter OTM in the form of a so-called "ortho-mode transducer" and two low-noise amplifiers Gl, G2, which are the first amplifiers on the signal path. As can be seen, the recovery of the depolarized components takes place in the radio-frequency position. This results in a considerable improvement in the signal-to-noise ratio. With the aid of the separation units SP ₁ and SP ₂ , the linear polarization components D, S and B, C are separated from one another.

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The components D, S are fed to the receiving devices RC and RC ₂ , respectively.

In Fig. 2, the circuit blocks labeled M and M- represent two frequency converters. When frequencies f. And f ₂ are mentioned below, the frequencies obtained by converting the beacon signals are meant (it is a common measure to improve the system). Two light couplers are designated with C and C _2. D and D ₂ represent two separating circles.

With further reference to the block diagram according to FIG. 2, the evaluation unit ELS connected to the filter will now be described. The signals coming from the filters F. and F ₂ are passed through the phase shifter SF. and SF- a further phase shift so that the appropriate phase relationships between the components of the useful signals and the components of the interference signals come about. If V and H denote the useful signals with the frequencies f. And f ~ and with ν and h the interference signals with the frequencies f. And f2, the following applies:

<x) the output signal of the phase shifter SF. is proportional to j V (frequency f.);

ß) the output signal of the phase shifter SF ₂ is proportional to j H (frequency f ₂ );

γ) the output signal of the filter F ₂ 'is proportional to H. {a, - D ₁ - (a ₂ Jf ₂ - b ₂ S ₂ ) + j [a ₂ - b ₂ + Ca ₁ ^ ₁ - b ^)] (frequency f ₂ );

δ) the output signal of the filter F ₁ ¹ is proportional to V - Ja ₂ - b ₂ - Ca ₁ ^ ₁ - bj-9 ^) + j Ca ₁ - b _± + (a ₂ i ₂ - bi ^}] (frequency f,).

/ Γι 1

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Here: b .. and b mean the differential damping caused by the damping elements A and A _? be evoked; a, and a ₂ the differential attenuations which are caused by the free space in two planes which are orthogonal _{to the attenuation planes of the attenuators A. and A 2;} IjC and SC the differential phase shifts caused by the phase shifters 0 and 0 ₂ , respectively; and ^, and ^ - the differential phase shifts caused by the free space in two planes which are orthogonal _{to the phase shift planes of the phase shifters 0, and 0 2.}

The signals mentioned are fed to four coherent detectors T, U, X and Y via the four power dividers S ₁ , S ', S ₂ , S ₂ ¹ and the phase shifters Q and Q _{2, which cause a phase shift of 90 °.} The output signals from these detectors are DC signals proportional to

H- | a ₂ - b ₂ + U ₁ ^ ₁ - b ^) I for T, H- Ia ₁ - b _x - (a ₂ ? ₂ - b ₂ ^) I for U, V · l ^a 2 ~ ^b 2 ~ (^ ¹ - ^b i ^ i> I for-X or V- Ia ₁ - Yes ₁ + Ca ₂ ^ ₂ - Ta ₇ ^ ₇ ) | for Y.

These signals are then fed to adding circuits J _{1 and E 2} or subtracting circuits A 1 and Δ ₂ via the power dividers B ₁ , E ₁ , B ₃ , E _2. How easy it is to prove mathematically is

the output signal of the adder circuit J \ _{proportional to (a - b 2} ),

the output of the adder circuit JT ₃ to Ca ₁ - b.,) proportional,

the output signal of the subtracting circuit A ₁ to

(a ^ y ^, -bj ^ O proportional, and

the output signal of the subtracting circuit Δ ₂ to

* ^a 2 ^ 2 ~ ^b 2 ^ 2 ^ proportional.

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Since these signals are proportional to the differences between the interference effects of the transmission medium and the equalizations or corrections effected by the actuators, one can conclude that these differences can be made as small as desired at the output of the reception correction unit CRR. The system is therefore "convergent" and able to correct the depolarization effectively, even if the signals mentioned contain, strictly speaking, small additional components which can be attributed to interference phenomena among the signals themselves. The output signals of the adding and subtracting circuits JT. , £ ", Δ. , Δ- control the correction of the attenuators or phase shifters A ~, A ₁ , ⁰ I ' ⁰ 2 ·

Assuming that the disruptive influence of the transmission medium on the transmission frequency band has the same effects as on the reception frequency band, the same signals are also _{supplied to corresponding equalization or correction elements for the transmission signal (attenuators A 4} and A ^, phase shifters 0 ₃ and 0) . The signals are taken over by the takeover circuits designated in FIG. 2 with H 1, H, K ₁ , K 3. The mixer circuit in the transmitting section is designated with DPT, to which the signals coming _{from the transmitting devices TR 1} and TR _{2 are fed.}

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Claims (4)

2 b 3 5 5 3 ß - 8 claims Circuit arrangement for the automatic correction of the depolarization of circularly polarized electromagnetic waves in transmission systems with two different frequency bands for reception and transmission, each of which has a double circular cross polarization, with two beacon signals with the frequencies f a correction unit (CRR) for equalizing the interferences caused by depolarization of the reception band signal with a separation unit (DG) for separating the signals of the two frequency bands connected converter and separation unit (DPR) is provided, which the two circular cross polarizations of the reception band Signals into two linear cross polarizations according to two orthogonal components (D, S) and the two circular cross polarizations of the beacon signals also into two linear cross polarizations according to two orthogonal components (B, C) converts that with the outputs of two Tre nneinheiten (sp., SP ₂₎ which of the beacon signals from the components (D, S) of the receiving band signals separate the components (B, C), f two pairs of the frequencies and f _2, the beacon signals matched filters (F ,, F ₃ ¹ ; F ', F ₂ ) are connected, which break down each of the components (B, C) of the beacon signals into useful components that are due to non-depolarized beacon signals and into interference components that are due to depolarized beacon signals, and that An evaluation unit (ELS) is connected to the outputs of the two filter pairs, which evaluates the useful and interference components and generates four signals, each of which controls an actuator of the correction unit (CRR) and is only dependent on the depolarization that it over able to correct the actuator assigned to it in the correction unit (CRR). 60980 9/0736 2 b 3 5 5 3 6 2.) Circuit arrangement according to claim 1, characterized in that the correction unit (CRR) of two differential attenuators (A., A -) / their differential attenuation planes enclose a predetermined angle with each other, and of two differential phase shifters (0 ₁ , 0 ~) whose differential phase planes enclose a further predetermined angle with one another is formed. 3.) Circuit arrangement according to claim 2, characterized characterized in that the values of the two predetermined angles are equal to each other and amount to 45 °. 4.) Circuit arrangement according to one of the preceding claims, characterized in that the evaluation unit (ELS) contains two first phase shifters (SF, SF_) which cause a controllable phase shift of the signal coming from the filters (F ,, F “) for the beacon signal , furthermore two further phase shifters (Q., Q ₂ ) f shift the two signal components of the signals coming from the first phase shifters (SF ₁ , SF ") by 90 °, four coherent detectors (T, U, X, Y), the each pick up the signals coming from the corresponding filters and phase shifters (from F ₂ ¹ and Q ₂ , or from F ₃ ¹ and SF ₂ , or from SF and F ₁ ', or from Q. and F. ^{1) and four} generate corresponding de signals, an adding circuit (] [.) and a subtracting circuit (Δ.), each of which is supplied with the signals generated by the first and third coherent detectors (T, X), and an adding circuit (J ₂ ) and a subtracting circuit (Δ ₂ ), each of which the second and fourth coherent detector (U, Y) receives generated signals. 603809/0736 Empty soap