This article presents a cross-coupled folded substrate integrated waveguide (FSIW) cavity bandpass filter. A novel type of negative coupling between FSIW cavities has been investigated and demonstrated. A prototype of four-pole FSIW cavity bandpass filter has been designed, fabricated with multilayer standard printed circuit board process. The filter has good selectivity which is demonstrated by the measured results, indicating 7.5% bandwidth and more than 14-dB return loss, with good agreement obtained when compared with the simulated ones. In addition, the rejection band of this filter is quite wide, implying good harmonic rejection. Figure 8 (a) Narrowband result. (b) Wideband result of the bandpass filter. (c) Photograph of the fabricated bandpass filter. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]ABSTRACT: A compacted CMOS K-band bandpass filter incorporating meandering thin film microstrip and defective uniplanar compact photonic bandgap (UC-PBG) slow-wave structures for size reduction are presented. Benefited from the multilayer metal technology of the standard 0.18-m CMOS process, meandering thin film microstrip and broadside-coupled structures with large coupling degree are properly constructed to realize bandpass filters with small insertion loss. The slow-wave effect of UC-PBG structure is investigated and a center frequency drop of 14% is achieved by the use of UC-PBG ground. A 3.6-dB loss 18-GHz filter with two transmission poles has been designed and implemented in standard 0.18-m CMOS technology and only with an area of 0.34 mm 2 .

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