E-plane circulators for integrated millimetric sub-systems

The modules, which are broadly described as E-plane sub-systems, use a number of transmission media, all of which can be housed in a rectangular waveguide cross section which is split across the E-plane. The emphasis at GEC-Marconi Research Centre has been on fin-line as the most commonly used medium for components incorporating semiconductor devices, with microstrip, suspended substrate and waveguide as other possibilities, to be used when appropriate. Both isolators and circulators are needed, isolators for the output of oscillators or in various other positions, and circulators most commonly for transmit-receive duplexers. Since the reason for integrating components is to produce a cheap and compact sub-system, the ferrite components must be easy to assemble and test. Their situation between other components, with the ports often accessible only by devious means, add further design constraints. The initial components were designed for the 26.5 to 40 GHz frequency range with further extension to the 60 GHz and 94 GHz bands planned (and now almost completed). Thus only design approaches which could be extended to higher frequencies were chosen. In this paper the design options will be reviewed, the development of the circulator outlined and millimetric sub-systems which use the circulators and iso-circulators described