W‐band power amplifier using broadband impedance‐transforming coupled line couplers

In this letter, a compact and broadband impedance-transforming 90° hybrid is proposed, where two coupled lines with different characteristic impedances are cascaded to transform 50 to 25 Ω. The designed 50–25 Ω transforming coupler on a GaAs substrate shows a measured insertion loss of 1.1 dB with a return loss of 29.0 dB at 77 GHz. The insertion loss is lower than 2.0 dB in the range from 30 to 97 GHz. The proposed impedance-transforming couplers are used in the design of a W-band balanced power amplifier (PA) with a port impedance of 25 Ω, which allows the compact and broadband design of matching circuits in the PA. The PA fabricated by a 0.15-μm GaAs pHEMT process shows a small-signal gain of 13.3 dB at 79.5 GHz with a 3-dB bandwidth of 21.4% (from 72 to 89 GHz). The measured output power is as high as 16.7 dBm at 75 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:803–806, 2015