Transmitter multiplexing system in UHF mobile radio

At a base station of a UHF mobile radio telephone system in a large city, many transmitters are used. In such a case it is not practical to use an individual antenna for each transmitter from the viewpoint of system economy and interference. Common use of one antenna for many radio-frequency channels is suitable and transmitter multiplexing devices should be used for this purpose. A transmitter multiplexer has been developed which can be used for multiplexing more than twelve 100-W transmitters in the 450-MHz band with a channel spacing of 150 kHz. The multiplexer consists of circulators, cavity resonators, and junction boxes. The principal features of this multiplexer are H
101
mode cavity resonators which are ultrastable with respect to the variation of environment conditions such as temperature and humidity. The resonators are temperature compensated to maintain the variation of resonant frequency within 5 kHz at the ambient temperature variation of 40°C. The voltage standing-wave ratio (VSWR) of the multiplexer, looking from the transmitter side, is less than 2.0 and the insertion loss is less than 3 dB at the operating frequency. Design objectives, over-all performance, and characteristics of cavity resonators and circulators are also presented.