If a four-port network is terminated by arbitrary impedances, the conventional methods for even- and/or odd-mode excitation analyses are not available because no symmetry planes exist. Under these conditions, two types of new design equations for asymmetric 3-dB branch-line hybrids are reported. To make sure that the derived design equations are correct and adaptable, simulations were performed under assumed ideal conditions for one type of asymmetric 3-dB branch-line hybrid and a uniplanar branch-line hybrid terminated by 50 Ω, 41.6 Ω, 55.6 Ω and 62.5 Ω was fabricated and measured for another type of asymmetric 3-dB branch-line hybrid.

This letter proposes a wideband compact DC block design technique. This DC block has a wide pass-band and wide stop-band and transforms termination impedances. It comprises a pair of coupled lines on a defected ground structure (DGS) with capacitor loading. A periodic DGS pattern increases coupling, and, consequently, a wideband DC block design is allowed with a microstrip process on a high dielectric low height substrate. A DC block with equal termination impedances of 50,$Omega$ and another that transforms 50 into 30,$Omega$ are fabricated. The measured fractional bandwidths are 48% and 47%. The size of the DC block is 16.8$ imes$ 15,mm$^2(0.057lambda_0 imes 0.051lambda_0)$.