Design of multi‐band bandpass filters based on stub loaded stepped‐impedance resonator with defected microstrip structure

Abstract

The design of multi‐band bandpass filters (BPFs) employing stub loaded stepped‐impedance resonator with defected microstrip structure (SL‐SIR‐DMS) is presented in this study for the first time. The proposed SL‐SIR‐DMS is created by embedding DMS on the low‐impedance line of the SL‐SIR. It is found that different defected structures can lead to different frequency responses. In addition, by using DMS, tri‐band and even quad‐band responses can be easily achieved without increasing the resonator size. As verification, one tri‐band SL‐SIR‐DMS and one quad‐band SL‐SIR‐DMS are designed and analysed using even/odd‐mode method. Subsequently, one tri‐band BPF and one quad‐band BPF have been developed with pseudo‐interdigital coupling to realise good out‐of‐band performance. The predicted results are compared with measured ones and good agreement is achieved. Compared with BPFs using only SL‐SIR, the proposed filters with DMS are more compact due to the slow‐wave characteristic. Compared with the BPFs using defected ground structure to improve the stopband performance, the proposed ones can realise comparable wide stopbands but maintaining the signal integrity on the ground plane for packaging purpose.

Analysis of four‐stage stepped‐impedance resonators and their application to quad‐band microstrip bandpass filter

“…However, this kind of BPFs is often hard to realize higher order responses and always suffers a large circuit size because of the inevitable great numbers of resonators. The third method we commonly adopted is to fully exploit the first several resonances of multimode resonators . However, they are usually limited by nonindependent coupling control and complicated structures.…”

A Compact Tri-Band Bandpass Filter With Independently Controllable Harmonic Bandwidth by Using Two Grounded Vias

“…Due to modern manufacturing technology, microwave planar BPFs have been widely studied and employed. In the past, many methods of designing BPFs have been explored and reported, such as [1][2][3][4][5][6][7][8][9][10][11][12]. In [1,2], three sets of resonators were used to design tri-band BPFs due to the use of combining networks.…”

“…In [10], a three-section SIR using parallel coupling structure was used to design tri-band BPFs. In [11,12], two stub-loaded SIRs were used to design tri-band BPFs. All these tri-band filters make use of the harmonic property of microwave resonators.…”

New approach to design a compact triband bandpass filter using a multilayer structure

“…The trisection SIRs have been used to design triband filters in [12,13]. Another type of triband BPFs has been designed using multimode resonators [14] such as stepped-impedance resonators or stub-loaded resonators [15][16][17][18]. Using the higher modes of a dual-mode resonator has been reported in [19].…”