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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $</tex-math> </inline-formula>/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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.1\lambda $</tex-math> </inline-formula> in both the width and length, indicating a size reduction of 95.1%.