A.R. Tuzbekov, B.H. Golberg

This paper describes an orthomode waveguide transducer of small longitudinal dimension for satellite communication systems of Ku-band. The reception is provided at one linear polarization within frequency band of 11,95 to 12,75 GHz. The transmission is provided at another linear polarization orthogonal to the first one within frequency band of 13,75 to 14,50 GHz. The transducer is made of two polarization T-junctions connected in series and turned at 90 degrees with respect to each other around their common longitudinal axis. It is provided with a shorting plug in the axial channel and has longitudinal dimension of 60,5 mm. The axial channel cross-section shape is oval. The dimension of its major axis determined by the diameter of the feed input channel is 17,5 mm. The dimension of the minor axis of the oval is selected to be 12.5 mm. The waveguide cut-off frequency in this case is 9.8 GHz at the reception mode. It slightly differs from the cut-off frequency 10 GHz of the dominant mode of the feed input channel. The cut-off frequency 13.1 GHz of the mode at the transmission polarization is located between the reception and transmission bands. The cut-off frequency 15.3 GHz of the E01 mode of the oval waveguide exceeds the upper frequency of the transmission band by 5.5%. The axial channel of the device is equipped by a single-step transition to the input circular waveguide of the feed. The side channels of the T-junctions are made of standard rectangular waveguides of cross-section 7,2 x 3,4 mm2. The standard side flanges of the indicated waveguides are spaced 27 mm apart from the longitudinal transducer axis. They overlap each other more than by half in the longitudinal projection. The side channel of the T-junction nearest to the feed operates in the transmission mode, while the other T-junction operates in the reception one. Both side channels have oval diaphragms in the place of the junction with the axial waveguide. The oval diaphragms of the reception and transmission channels are placed asymmetrically at maximum distance along the device longitudinal axis. The shorting-plug is provided by two mutually perpendicular conducting plates. One of them is arranged in parallel to the conducting plate of the transmission channel. This additional plate removes resonant frequencies stipulated by the small longitudinal dimension of the main plate of the transmission channel from the operating bands. The second plate provides matching of the reception channel. The orthomode transducer is a part of the monoblock unit in the feed device. The longitudinal dimensions of the feed and monoblock are 18,5 mm and 79 mm, respectively. The overall transversal dimensions of the transducer do not exceed those of the feed. The maximum level of the reflected modes in the transmission channels over a batch of the monoblocks are minus 25,7 to 28,3 dB. Similar maximum levels for the reception channels are in the limits of minus 20,4 to 23,7 dB. The minimum values of isolation between the standard rectangular waveguide channels of reception and transmission over a batch of the monoblocks are 36 to 38 dB in the transmission band and 38 to 40 dB in the reception band. The maximum attenuation over a batch of the devices is 0,04 to 0,06 dB in the transmission channels and 0,11 to 0,15 in the reception channels. The maximum cross-polar levels in the input feed channel over a batch of the devices are 38 to 40 dB in the reception band and 38 to 42 dB in the transmission band.