Novel tight coupling and high directivity λ /4 partially-narrowed and slotted coupled line and its application

A new λ/4 microstrip coupled line (MSCL) partially-narrowed and slotted the other part to obtain both tight coupling beyond machining limitations and high directivity is proposed. And a multi-element broadband coupler using the proposed MSCL as the tightest coupling element is presented. A multi-element 10 dB coupler is designed, and the performances, which are -10.3±0.9dB coupling and greater than 20dB isolation over 162% of the bandwidth.