A Miniaturized 3 dB 90 $^{\circ}$ Hybrid Coupler Using Coupled-Line Section With Spurious Rejection

In this letter, a novel miniaturization method for 3 dB 90 $^{\circ}$ hybrid coupler is proposed. The proposed structure is composed of a conventional structure with a coupled line section inserted in the low impedance section. The proposed coupler occupies an area of only 9.6% compared to a conventional branch-line coupler, and reveals comparable $S$ -parameter characteristics in the operation band. Furthermore, the proposed structure demonstrates a harmonic suppression property due to the a periodicity at odd order harmonics.