An Ultrawideband GaAs MMIC Microstrip Directional Coupler With High Directivity and Very Flat Coupling

By introducing an adaptive lumped bridged-T amplitude equalizer into the microstrip directional coupler, this article realizes a 2.2 mm $\times1.3$ mm ultrawideband GaAs monolithic microwave integrated circuit (MMIC) directional coupler with high directivity and very flat coupling by using the GaAs integrated passive device (IPD) process. The experimental results show that the proposed directional coupler exhibits more comprehensive radio frequency (RF) performance than the reported directional couplers due to the use of an adaptive bridged-T amplitude equalizer. In the ultrawide working frequency range from 2 to 20 GHz, the insertion loss of the coupler is less than 1.5 dB, the return loss is better than −20 dB, the coupling flatness is within ±0.3 dB, the isolation is higher than 40 dB, and the directivity is more than 20 dB, which are basically consistent with theoretical predictions. The microstrip directional coupler using the adaptive bridged-T amplitude equalizer shows great potential in the high-performance broadband communication system.