A Network for Combining Radio Systems at 4, 6 and 11 kmc

Development of the broadband horn reflector antenna has -permitted the simultaneous radiation and reception of radio signals on different frequencies in the three common-carrier bands in which the Bell System has developed radio relay systems. A necessary adjunct to the antenna is a network to combine or separate the common carrier bands and also to combine or separate the two polarizations of any one band. The particular form of the network that is described ivas designed to meet strict system requirements on impedance match, insertion loss and cross-coupling between ports. Microwave radio relay systems have been developed for Bell Telephone System toll transmission in the common carrier frequency bands of 3700 to 4200 mc, 5925 to (>425 mc and 10,700 to 11,700 mc. There will be many routes where two, or all three, of these radio systems will be in use simultaneously. On such routes, a common antenna1 at the top of the station tower will transmit or receive all three frequency bands. The broadband antennas will operate with both polarizations of the radio waves, and the feed line will be a 3-inch circular copper waveguide (WC 281). The 3-inch waveguide is capable of supporting three modes in the 4-kmc frequency range and 22 modes in the 11-kmc frequency range. With the possibility of so many propagating modes, small discontinuities in the internal dimensions of the waveguide may cause undesirable mode conversion with associated transmission loss or reflection of signal energy.