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 LC network is proposed in this brief. The loaded LC 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 λg. The operating bandwidth of the coupling level of 1.5 dB is from 5.5 to 9 GHz, and its fractional bandwidth is 48.28%. Good agreement is achieved between the simulated and measured results.