Modified vertically installed planar couplers for ultrabroadband multisection quadrature hybrid

Abstract

In this letter, we describe a five-section ultrabroadband 1-9 GHz microstrip quadrature hybrid (90 degrees, - 3 dB coupler), which uses two types of modified vertically installed planar (VIP) couplers and is suitable for conventional printed circuit board realization. The modified VIP couplers provide not only a way to implement tight coupling value with reduced modal phase velocity difference but also a layout flexibility to minimize the discontinuity between sections. An experimental circuit is designed and fabricated with a passband ripple of +/- 0.5 dB, a return loss of less than -20 dB, and an isolation of better than 20 dB over the frequency of 1-9 GHz. Very good agreement between the simulated and measured results is obtained.