Monolithic GaAs interdigitated couplers

This paper described the design, fabrication, and performance of two monolithic GaAs C-band 90° interdigitated couplers with 50- and 25-ω impedances, respectively. A comparison of the performance of these two couplers show that the 25-ω coupler has the advantages of lower loss and higer fabrication yield. the balanced amplifier configuration using 25-ω couplers will require a fewer member of elements in the input-output matching circuit of the FET amplifier. The fewer number of matching elements results in great savings in the GaAs real estate for microwave monolithic integrated circuits (MIMIC's). Both the couplers have been fabricated on a 0.1-mm-thick GaAs SI substrate. The measured results agree quite well with calculated results. The losses of the 50- and 25-ω couplers are 0.5 and 0.3 dB, respectively, over the 4-8-GHz frequency band.