Patent GB-1506889-A (GB)
Title: Apparatuses for automatically correcting depolarization effects on electro-magnetic waves in radio frequency connections using double polarization
IPC: H04J11/00
Filed: 1975-09-03
Abstract: 1506889 Radio communications TELESPAZIO SpA PER LE COMUNICAZIONI SPAZIALI and GTE TELECOMUNICAZIONI SpA and SOC ITALIANA TELECOMUNICAZIONI SIEMENS SpA 3 Sept 1975 [3 Sept 1974] 36328/75 Headings H4L and H4M An apparatus for automatically correcting depolarization effects on radio waves in a system using separate bands for reception and transmission, e.g. a satellite system using about 4 and 6 GHz respectively, each band being divided into pairs of channels having the same frequency and crossed polarizations and the reception band including two beacon signals having different frequencies and the said polarizations, comprises an R.F. compensation unit CLB, Fig. 3, providing regeneration of energy lost to the opposite polarization, a processing unit ELT generating control signals depending on the depolarization interference for predistorting in a unit PRE signals to be transmitted by a transmitter CLT, and a channel-by-channel blanking unit CCA for cancelling any remaining interference between the channels of each pair before reception at a receiver CLR. The two crossed polarizations may be either vertical and horizontal, or right and left hand circular, or elliptical. The beacon signals ("band" beacons) (F1a, F2b), Fig. 1 (not shown), may be supplemented by "channel" beacon signals (fia, fib, fja, fjb), the band beacon signals being transmitted by the satellite, and the channel beacon signals being transmitted from an earth station. Compensation unit CLB comprises a unit CRT which may include differential phase shifters and attenuators controlled by unit ELT, a separator SP1 for the two polarizations, and a measuring and stabilizing unit UMS shown in detail in Fig. 4. The portion of unit UMS to the left of line rr equalizes in phase and amplitude the signals of the two polarizations by means of differential. phase shifter SF1' and variable gain amplifier AM5. Mixers Ml, M2 and local oscillator OL change the frequencies to I.F. values. The right hand portion of unit UMS separates the frequencies corresponding to the two band beacon signals, coherent detectors X4, X5 receiving via point m one beacon signal (F1a) in the correct polarization (a) and via point n depolarized interference arising from the same signal. Coherent detectors X6, X7 receive the corresponding components of the other beacon signal (F2b). The channel-by-channel blanking unit CCA may comprise, Fig. 5, separation networks DIS1, DIS2 for separating the signals in the channels of the reception band, and then for each pair of channels a blanking unit UC followed by a measuring and control unit MC. Coherent detectors X8 and X9 receive from point c one channel beacon signal (fja) in the correct polarization (a) and from point d depolarized interference arising from the same signal. Coherent detectors X 10, X11 receive the corresponding components of the other channel beacon signal in the reception band (fjb). Outputs 1, 2,3,4 of these detectors are connected to corresponding control inputs 1, 2, 3, 4 of units T1, T2, T3, T4 each comprising adjustable attenuators and phase shifters. The outputs of T1, T2 and T3, T4 are coupled in adders #1, #2 respectively and used to cancel the interfering signal in the respective channel. In another embodiment of the blanking unit CCA, Fig. 6 (not shown), channel beacon signals are not used, but the information signals in each channel are correlated to produce the required control signals.