MMIC GaAs X-Band Isolator with Enhanced Power Transmission Response

This paper discusses the RF design and characterization of an X-band MMIC isolator. It is based on a directional coupler and a non-reciprocal RF signal path that comprises a gain stage and two transmission line elements for phase control. In this manner, enhanced power transmission is obtained in the forward direction and isolation in the reverse one. The operating principles and RF design trade-offs (isolation, gain, matching) of the isolator are presented through circuit-based analysis. For proof-of-concept demonstration purposes, a prototype was designed at X-band and manufactured with a commercial MMIC GaAs process. Its RF measured performance is summarized as follows: center frequency: 9.4 GHz, maximum gain = 9.3 dB, maximum isolation = 27.7 dB, and 3 dB passband bandwidth with > 23 dB of isolation= 1.61 GHz.