simulated and tested, and the results are presented graphically. The considered structure resonates at two closely spaced frequencies lying in the median band for the WiMax communication systems approved by IEEE 802.16 Working Group. The impedance bandwidth of proposed arrangement of patches is improved significantly without loosing circular polarization characteristics or compactness of the patch geometry. The measured impedance bandwidth of proposed arrangement is nearly 12%, and simulated axial ratio bandwidths at the two frequencies are 1.74% and 0.8%. The measured radiation patterns of proposed arrangement in the entire bandwidth range are identical in shape and directed normal to patch geometry. The results obtained with proposed geometry suggest that this compact size antenna with little more improvements may be proved a useful geometry for modern communication systems. ACKNOWLEDGMENTSAuthors express their sincere thanks to DIT, New Delhi for supporting the research work. Authors are also thankful to Mr. S. Srinivasan and Dr. S. Pal, ISRO Satellite Center, Bangalore for their help in carrying out the measurements.ABSTRACT: A bandpass filter in substrate integrated waveguide (SIW) technology is designed with its suitable excitation. Sensitivity analysis of the SIW filter electrical response toward the number and positions of metallic via holes are performed using wave concept iterative procedure. It leads to a reduction of the number of vias with identical performance of the filter.