A Millimeter Wave, Two-Pole, Circular-Electric Mode, Channel-Dropping Filter Structure

The TEoi circular-electric mode in round waveguide lias considerable attention due to its low-loss characteristic. The of multiplexing in communication systems using this mode approached by Marcatili. 1 His scheme used low-loss, TE 0 s 2261 received problem was first circular- 2262 T H E BELL SYSTEM TECHNICAL J O U R N A L , DECEMBER lOG? electric mode resonators* to realize channel-dropping filters having single-pole, maximally flat responses. Interest in channel-dropping filters with multiple-pole responses was stimulated by recent advances in the repeater art. An all solid-state repeater having a 51.7 GHz carrier and operating at a bit rate of 306 megabits per second has been constructed. 2 The repeater performance is such that a 15-mile repeater spacing could be achieved using propagation in the T E 0 i circularelectric mode in two-inch i.d. round guide. Since high bit rates imply increased bandwidth, multiple-pole filters are required to maximize usable channel capacity. A design procedure has been developed for diplexers having a twopole, maximally flat amplitude response. Section II describes the structure. Section I I I presents some preliminary considerations involving arrays of such structures. Section IV outlines the design procedure. Experimental results are presented in Section V. The major theoretical contribution of this work lies in relating the parameters of the structure to the elements of a low-pass prototype network. This extension of Marcatili's work makes it possible to utilize mode-conversion resonators in multiple-pole filter structures.