Transponder and antenna-design problems at millimeter wavelengths for 20-30 GHz communications satellites

The Japanese medium capacity Communication Satellite (CS) includes two C-band transponder channels in the 4-6 GHz range, and six K-band transponder channels in the 18-30 GHz range. Each of these channels is 200 MHz wide and the design of these channels was specifically directed toward optimal transmission of 100 Mbps BPSK digital carriers. This satellite is a spinner satellite using a bus derived from the NATO satellite. The difficulties encountered in providing the actual hardware realization of this satellite due to extreme problems related to mechanical assembly and tolerance and to antenna pattern, channel bandwidth, and loss/power sensitivity which are not encountered at much lower frequencies of 4/6 GHz and 11/14 GHz but which are indigenous to the millimeter wave frequencies of 20 and 30 GHz are emphasized. The problems in packaging and integration of the 20-30 GHz portion of the transponder and the 18-28 GHz portion of the antenna feed involving shortest length and therefore lowest loss connections in extremely confined spaces, within the satellite structure are discussed.