A novel C-band hole-coupled bandpass filter with metallized post (or via-hole) arrays directly embedded in middle of the microstrip line is presented in this letter. The proposed filter removes via-hole arrays embedded along waveguide section from the half-mode substrate integrated waveguide filter, while the new concept simplifies the structure of previous filter. Simulated and experimental results show that the proposed filter of this paper has good performances of low insertion loss, return loss, and better rejection characteristics. The insertion loss of measured four-pole filter is about 0.8 dB, and the return loss is better than À25 dB in the whole passband. Keeping the advantages of excellent performances, the proposed filter can be constructed more conveniently and is suitable for low-cost planar circuit.ABSTRACT: This article presents a design for wideband bandpass filters using a microstrip cavity coupler. The broadband nature of the cavity-coupled designs is fully exploited for this application. Two additional circuits are introduced to improve the stopband performance of the cavity-coupled bandpass filter. A prototype design example is presented with its center frequency located at 6.28 GHz. The design has the merits of wide bandwith of more than 140%, flat group delay within the passband, good insertion/return loss, and stopband attenuation of nearly 30 dB up to 30 GHz. The validity of the simulation results is verified experimentally.

A microstrip bandpass filter implemented with slow‐wave open‐loop resonators is described in this article. The slow‐wave open‐loop resonators make the filter compact and allow the implementation of positive and negative inter‐resonator couplings. Implementation of the positive and negative couplings is used to introduce a pair of finite frequency transmission‐zeros in the filter response. The two zeros are designed to be close to the passband, thus improving the selectivity of the filter. As an example, a fourth‐order cross‐coupled filter is fabricated. The experimental results are demonstrated and discussed. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1057–1060, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24232