The four-port couplers are the fundamental building blocks of large-scale passive beam-forming network design. They find application in the design of antenna feed networks, power combiners and dividers, balanced mixers and amplifiers. Conventional branch-line couplers (BLCs) were designed for quadrature-phase imbalance using four quarter-wavelength transmission lines (TLs). On the other hand, conventional rat-race couplers (RRCs) are designed for in-phased/out-of-phased imbalance using six identical quarter-wavelength TLs. To obtain a non-quadrature phase-shift, external phase shifters are required. Recently, BLCs with inherent non-quadrature phase imbalance properties have received attention among microwave researchers. There are several types of implementation such as lumped, distributed, and mixed with different topologies, that have been proposed by several researchers. It is quite challenging for young researchers to extract all possible design data from the design equations and simulate them to understand their figure of merits. This motivates the author to provide solutions for non-quadrature unequal power division BLCs.
