A compact 90° coupler using CMOS-compatible technology

In this paper, the design and implementation of a compact 90° coupler on a glass substrate is presented. The process provides a low-loss substrate to reduce substrate losses, and three thick metal layers to reduce conductor losses. Therefore, peak-Q factors of capacitors and inductors on the substrate can reach 90 and 30 at least, respectively. Benefiting by these superior passive components, the 5.2-GHz coupler demonstrates a compact design with low insertion losses. The insertion losses are less than 0.97 dB, and the phase difference between in-phase/quadrature outputs is 88.2°. Moreover, the return loss and isolation is 20.2 dB and 22.5 dB, respectively. The chip size including all testing pads is 2.26 × 1.4 mm².