Miniaturised dual‐band rat‐race coupler with harmonic suppression using synthetic transmission line

Abstract

A dual‐band 90° unit module with harmonic suppression (HS) is proposed. This unit module consists of a pair of back‐to‐back stepped impedance sections and an open stub. The unit module is realised by synthetic transmission lines, and it is successfully implemented into a novel miniature dual‐band (2.45/5.8‐GHz) rat‐race coupler with HS (suppression level ≥16 dB, 6.8–13 GHz). Compared with traditional 1.5 λ microstrip ring hybrid, the proposed dual‐band rat‐race with HS only occupies 13.84% of its area.