Series feedback integrated active microstrip antenna synthesis and characterisation

A methodology for the optimal design of a FET based integrated active microstrip antenna is demonstrated; the electrical characteristics of the antenna are also discussed. The antenna consists of a rectangular microstrip patch peripherally loaded with a single GaAs MESFET. The microstrip patch acts as both the radiating element and the optimal FET drain load impedance required for oscillator synthesis. The active patch element operates as a series feedback oscillator and the microstrip patch is resonated in its fundamental mode. An NEC 71084 packaged FET is used as the active device in the patch element which itself is constructed on RT-Duroid 5880 material. The element has a free running frequency of 9.625 GHz (at 3 V) and exhibits excellent electrical characteristics. Experimental results are presented for the frequency pushing characteristics of the element which are nearly linear. The active element is capable of producing an output power level of 8 mW with 10% efficiency at 2.3 V, and has an external Q factor of 32.