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.