Frequency-Flexible High Selectivity Multichannel Filtering Crossover Based on Slow-Wave Substrate Integrated Waveguide

A slow-wave substrate integrated waveguide multichannel filtering crossover has been presented in this article, for the advantages of smaller overall circuit size, high selectivity, and improved bandwidth. Pleated uniform impedance microstrip line is combined with the SIW structure, to increase the path travelled by the signal, and achieve the slow-wave effect. The E-field modes utilized in the designed cavities are TE $_{102}$ and TE $_{201}$ modes. The strategic alignment of the feedlines on to the cavities in orthogonal orientation, aided better isolation control. To achieve transmission zeroes for high selectivity, a uniform impedance concentric transition structure has been embedded on the main cavities. For validation, four-and six-channel bandpass filtering crossovers have been fabricated and measured. Both the measured and simulated results have been compared and discussed. The performances exhibited good insertion and return losses, while high isolation levels and frequency selectivity have also been achieved. In all, two transmission zeroes have been achieved with one each located at both the lower and upper frequency cutoffs. There is a very good agreement of the compared results. The overall circuit size achieved a reduction greater than 50%.