A triple-passband, dual-stopband filter consisting of six cascaded singlets is introduced in substrate integrated waveguide (SIW) technology. Each singlet produces one independent transmission zero (TZ). Four of six TZs are placed within the filter passband, producing three passbands separated by two stopbands. The corresponding coupling matrix is synthesized based on a combination of well-known analytic and optimization methods. The SIW filter is designed for stopbands centered at 10.25 and 11.23 GHz, and passbands at 9.72, 10.76, and 11.76 GHz. The prototype is fabricated and measured. Good agreement between simulated and measured results is achieved. Index Terms-Bandpass filter (BPF), coupling matrix, dual-bandstop filter, nonresonating node (NRN), substrate integrated waveguide (SIW).

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A new design for a cylindrical dielectric resonator antenna (DRA) with a capability of switching between circular, linear horizontal and linear vertical polarizations is introduced. The DRA, operating at the center frequency of 3.25 GHz, is fed by a microstrip line through two dog-bone slots. In this design, only two PIN diodes are employed as switching elements which significantly decreases the complexity of DC biasing circuits compared to existing designs. The PIN diodes are embedded in transformers connected to the feeding microstrip lines. This technique conveniently allows to make compensations for parasitic effects of the PIN diodes junction capacitors on the antenna matching bandwidth. The circular, linear horizontal and linear vertical polarizations have a bandwidth of 22%, 17% and 18%, respectively. The 3-dB axial ratio bandwidth for the circular polarization is 12%. The measured results obtained from prototyped antenna agree well with simulated results of the designed antenna system, which confirms the validity of the design process.

A new K-band triple-stopband filter in substrate integrated waveguide (SIW) technology is introduced. The filter consists of six rectangular cavities resonating in their fundamental mode. Main and cross couplings between resonators are used to design a filter with six transmission zeros, separating three stopbands and four passbands. A corresponding coupling matrix is presented. The initial filter covers an overall bandwidth of 4.50 GHz at center frequency of 19.50 GHz. The three stopbands are located at 17.6, 19.56, and 21.34 GHz with bandwidths of 0.92 GHz, 0.82 GHz, and 0.85 GHz, respectively. The two passbands located between the three stopbands have center frequencies of 18.70 and 20.56 GHz with corresponding bandwidths of 0.97 GHz and 0.88 GHz, respectively. The filter is prototyped and measured. Good agreement between simulated and measured results proves the reliability and robustness of the design method.