A Miniaturized 90° Hybrid Coupler Utilizing Slow Wave Effects With a Hybrid Approach

A 90° hybrid coupler is one of the essential components widely used in various RF applications. The arms of the conventional branch line 90° hybrid coupler typically require a $\lambda $ /4 length. In applications operating at low frequencies in the megahertz range or those demanding extremely small form factors, miniaturization becomes even more critical. In this letter, we present a 90° hybrid coupler using a hybrid approach to achieve miniaturization by combining meander lines and discontinuity lines. The proposed 90° hybrid coupler is validated via simulation and measurement, where the results show that the size of the proposed coupler is less than $0.1\lambda $ in both the width and length, indicating a size reduction of 95.1%.