Patent GB-1504899-A (GB)
Title: Apparatuses for automatically correcting for the depolarizing effect in electromagnetic waves
IPC: H04B7/00
Filed: 1975-08-11
Abstract: 1504899 Radio telecommunication systems SOC ITALIANA TELECOMUNICAZIONI SIEMENS SpA 11 Aug 1975 [9 Aug 1974] 33338/75 Headings H4L and H4M Apparatus for automatically correcting for depolarization of radio waves in a system using distinct frequency bands for transmission and reception each band having double polarization, e.g. opposed circular polarizations, and additionally using two beacon signals one of each polarization and having different frequencies f 1 , f 2  in the reception band, comprises a band separating unit DG, Fig. 2a, for separating transmitted and received signals, a receiver correction unit CRR for correcting for mutual interference between the received signals with the different polarizations due to depolarization during transmission, a conversion-separation unit DPR arranged to transform the different polarizations into two orthogonal linear polarizations, the beacon signals being similarly transformed, first and second separating units SP 1 , SP 2  respectively arranged to separate the beacon signals from other received signals, first and second pairs of filters, Fig. 2b, F 1 , F 2 <SP>1</SP> and F 1 <SP>1</SP>, F 2  respectively, a respective filter of each pair being tuned to pass a respective one of the two beacon signals, the pairs being connected respectively to the outputs of SP 1  and SP 2 , and a processing unit ELS connected to the outputs of the filters, and arranged to pass four output signals to the receiver correction unit CRR to control correcting elements A 1 , A 2 , # 1 , # 2  therein. Four more output signals pass from ELS to a transmitter correction unit CRT, the control signals produced from the beacon signals being applied to both receiver and transmitter on the assumption that depolarization effects are the same on both bands, separate transmitters TR 1 , TR 2  and separate receivers RC 1 , RC 2  being provided for the two different polarizations of the signals. Since the differently polarized beacon signals have different frequencies f 1 , f 2 , in the absence of depolarization the f 1  signal would be directed by ortho-mode transducer OTM of unit DPR to SP 1 , and then by filter F 1  to phase shifter SF 1  of ELS. (M 1 , M 2  are frequency converters, and the filters are tuned to the converted frequencies corresponding to f 1  and f 2 .) In the presence of depolarization a component of the f 2  signal may be produced with the polarization appropriate to SP 1 , and this is passed to power divider S,' of ELS by filter F 2 <SP>1</SP>; similarly a component of the f 1  signal with the polarization appropriate to SP 2  is passed to power divider S 2 <SP>1</SP> of ELS by filter F,'. Processing unit ELS further comprises phase shifters Q 1 , Q 2 , coherent detectors T, U, X, Y, adders # 1 , # 2  and subtracters # 1 , # 2  arranged to produce the required control signals according to mathematical formulµ given in the Specification. The correcting elements of CRR comprise, in the embodiment described, differential attenuators A 1 , A 2  whose planes of differential attenuation are at 45 degrees to each other, and differential phase shifters # 1 , # 2  whose planes of differential phase displacement are at 45 degrees to each other; angles other than 45 degrees (apart from 90 degrees) may be used.