Design and Tolerance Analysis of Cascaded Broadband Contiguous Microwave Diplexers

This work presents the realization of two broadband contiguous diplexers in suspended stripline technology in the frequency range DC-7.5-11 GHz and DC-11-17 GHz. Limitations due to manufacturing tolerances and anisotropic dielectric properties of the substrate are discussed and taken into account for resimulation and redesign. A proper T-junction is introduced, which allows optimum adjustment of both low-pass filter and high-pass filter with respect to each other. The presented design operates without any additional annulling network which could limit the diplexers' operation bandwidth and introduce additional channel insertion loss. The realized diplexer features a return loss of more than 15 dB with very low channel insertion losses of typically less than 1 dB. For achieving an optimal compatibility with external circuits, a broadband suspended stripline to coax transition was designed. The feasibility of cascading both diplexers to a triplexer is investigated.