Wideband and Miniaturized Forward-Wave Directional Coupler Using Periodical Parallel Plates and Vertical Meander Lines

A wideband and miniaturized forward-wave directional coupler using periodical loaded <italic>LC</italic> network is proposed in this brief. The loaded <italic>LC</italic> network consists of parallel plates and vertical meander lines. The coupler is designed with impedance matching, and a large phase difference with a small variation between the even and odd modes within a wide frequency range. These propagation characteristics are calculated and predicted by a unit cell using Bloch-Floquet theorem. Finally, a prototype is fabricated by low-temperature co-fired ceramic (LTCC) technology. The electric length of the proposed coupler is 1.52 ${\boldsymbol{\lambda }}$ <italic>g</italic>. The operating bandwidth of the coupling level of 1.5 dB is from 5.5 to 9 GHz, and its fractional bandwidth is 48.28x0025;. Good agreement is achieved between the simulated and measured results.