AN MMIC-COMPATIBLE TIGHTLY COUPLED-LINE STRUCTURE USING EMBEDDED MICROSTRIP

This paper presents a highly manufacturable coupled line structure for MMIC's which uses embedded microstrip to achieve tight coupling and e mploys the process steps necessary to make metal-insulator-metal (MIM) capacitors. Passive circuits demonstrated using this technique includ e a single-section 5-21 GHz broadband 3 dB coupler fabricated on both 75 and 125 mum thick GaAs substrates and a 6-15 GHz 90-degrees Schiffm an section fabricated on a 125 mum thick GaAs substrate. The coupler a nd the Schiffinan section use tight (2 dB) to extremely tight (0.7 dB) coupling factors, respectively. Additionally, two single-section 2-7 GHz couplers are compared, one having a crossover and one without. Thi s is the first time that a coupler has achieved such a wide bandwidth on thin GaAs substrates. Complete test data are presented, including t he amplitude, isolation, and phase response of the couplers and the ph ase and amplitude response of the Schiffman sections.