Monolithic GaAs Interdigitated Couplers

This paper deseribes the design, fabrication, and performance of two monolithic GaAs C-band 90° interdlgitiited couplers with 50- and 25-Omega impedances, respectively. A comparison of the performance of´ these two couplers shows that the 25-Omega coupler has the advantages of lower loss and bigher fabrication yield. The bafanced amplifier configuration rising 25-Omega couplers will require, a fewer number of elements in the input-output matching circuit of the FET amplifier. The fewer number of matcfdng elements results in great savings in the GaAs real estate for microwave monolithic intergrated circuits (MMIC´s). Both the couplers have been fabricated on a 0.1-mm-thick GaAs S1 substrate. The measured results agree quite well with calculated results. The losses of the 50- and 25-Omega couplers are 0.5 and 0.3 dB, respectively, over the 4-8-GHz frequency band.