Some Recent Advancements in Hybrid MICs

This paper describes some circuit design features of MIC sub-systems utilising hybrid-open microstrip techniques which give improved performance, particularly where military environments necessitate a wide operating temperature range and compactness is of prime importance. The design and performance of a J (Ku)-band radar duplexer-receiver MIC sub-system is described to illustrate the points of interest. Emphasis is placed on the influence of v.s.w.r. and isolation characteristics resulting from the performance of non-reciprocal circuit functions, microstrip launchers and the propagation of box modes, on the overall operation of the sub-system. Particular attention is given to the temperature characteristics of microstrip circulators, and novel techniques are described which compensate for the reversible temperature coefficient properties of the samarium-cobalt magnetic material used to bias the ferrite devices. Design features are also described which reduce degradation in circuit isolation due to radiation from the microsttrip and are compatible with small size and low weight requirements.