Analysis and design of Kemp-type 3-dB quadrature couplers

An analysis is presented of the 3-dB quadrature coupler of Kemp et al. (Electron Lett., vol.19, p.197-9, March 1983), and a table of element values is given. It is shown that the Kemp approach overcomes the tight coupling problem associated with the method of E.G. Cristal and L. Young (IEEE Trans. Microwave Theory Tech., vol.13, no.9, p.544-58, 1965), but there is a severe bandwidth contraction penalty. It is also shown that the use of interconnection lines sufficiently long to reduce cross-coupling causes an unacceptable degradation in coupling performance. Although the technique provides a useful increase in bandwidth over that obtainable from a single-section coupler, it is suggested that the tandem multisection method is more suitable for decade bandwidths