High selectivity wideband BPF with very wide stopband characteristic

Abstract

This paper describes the design and evaluation of a highly selective wideband microstrip bandpass filter with a near brick‐shaped transmission response and a very wide stopband characteristic. The proposed filter structure excites multimode resonances that combine to realize a wideband filter response and excited too are transmission zeros that create a highly selective filter with wideband suppression in the upper and lower stopbands. The filter configuration comprises electromagnetically coupled resonators that are stub loaded. The input and output feedlines are interdigitally coupled to the resonators. Measured results confirm the low‐loss and via‐free wideband filter exhibits an elliptical response with a wide stopband with a rejection greater than 30 dB. The selectivity factor and stopband performance of the proposed filter is better than that obtained with the high‐temperature superconductor (HTS) filters. Design of the filter is relatively simple and easy to manufacture using standard PCB technology. There is good correlation between the simulation and measured results. The proposed wideband bandpass filter is suitable for applications in high interference environments and cognitive radio systems.

Multi‐spurious harmonics suppression in folded hairpin line bandpass filter by meander spur‐line

“…In Table 2, the parameters are f 0 = center frequency (GHz), FBW = Fractional bandwidth (%), IL = Insertion loss (dB), RL = Return loss (dB), SRL = Stopband rejection level (dB), SBW = Stopband bandwidth (GHz), and size in terms of λ g λ g . It has been noted that there has been an improvement in the stopband rejection level for the proposed filters than 5‐7,12‐15,18 . Moreover, an improvement of stopband rejection bandwidth has been obtained for this work compared to References 6,10,12‐14,18.…”

“…Moreover, an improvement of stopband rejection bandwidth has been obtained for this work compared to References 6,10,12‐14,18. The proposed filters have acquired less circuit size than 6,9,12‐15,18 . Since this work is an extension of Reference 18, from Table 2 it has been further revealed that the proposed filters have exhibited significant improvement over those of Reference 18 with respect to narrow passband by 50% (from 8% to 4%), compactness by 12.44% (overall circuit area from 305.93 mm 2 to 267.85 mm 2 ), stopband rejection level by 11.11% (from 36 dB to 40 dB) and stopband rejection bandwidth by 33.33% (from 3 f 0 to 4 f 0 ).…”

“…It has been noted that there has been an improvement in the stopband rejection level for the proposed filters than 5‐7,12‐15,18 . Moreover, an improvement of stopband rejection bandwidth has been obtained for this work compared to References 6,10,12‐14,18. The proposed filters have acquired less circuit size than 6,9,12‐15,18 .…”

“…However, most of the studies in References 5‐11 have been performed for conventional hairpin‐line filters, acquiring large circuit areas, and hence, their applications become restricted in modern wireless communication systems where compact‐sized filters are essential. Very recently, compact wideband bandpass filters with high selectivity and wide stopband have been proposed in References 12‐15. In Reference 12, a microstrip‐slotline bandpass filter has been designed by cascading two back‐to‐back microstrip‐to‐microstrip vertical transitions and a rejection level of 20.63 dB up to 3.86 f 0 has been reported.…”

“…In Reference 12, a microstrip‐slotline bandpass filter has been designed by cascading two back‐to‐back microstrip‐to‐microstrip vertical transitions and a rejection level of 20.63 dB up to 3.86 f 0 has been reported. As an alternative approach, electromagnetically coupled resonators loaded with stubs and interdigital coupled input and output feed lines have been utilized in Reference 13 to design a wideband filter with the center frequency of 8.04 GHz and 3 dB bandwidth of 40.3%. Accordingly, a wide rejection level of more than 30 dB up to 2.49 f 0 has been obtained.…”