Dual-band microstrip bandstop filter using dual-mode loop resonator

Abstract

A dual-band bandstop filter (DBBSF) with a dual-mode loop resonator is presented. In order to allow the DBBSF to exhibit high skirt selectivity and to generate a wide rejection bandwidth a capacitive coupled-line section is introduced. By properly controlling the length of the coupled-line section and the cross-coupled capacitor, more than two finite transmission zeros were inserted at the stopband and enhanced the rejection bandwidth.Introduction: A high performance bandstop filter (BSF) is one of the most important components of microwave circuits. To meet the size requirements of modern microwave communications systems, BSFs with low insertion loss, sharp rejection and wide rejection bandwidth are in high demand. A microstrip dual-mode loop resonator BSF has been developed for the aforementioned requirements [1,2]. In recent years, various topologies for microstrip dual-mode loop-resonators (DMLRs) have been reported to elucidate the mechanism of coupling between the two degenerated modes, which is mainly determined by the feed-line structure or different types of perturbation [1][2][3][4][5]. In [3][4][5], dual-mode BSFs have been illustrated to obtain high selectivity, low insertion loss and good stopband attenuation. However, the loopresonator coupled to a thru-line is suitable for the design of narrowband BSFs. In this Letter, in order to achieve size reduction and a wide rejection bandwidth, a dual-mode BSF with a cross-coupled capacitor is proposed and a frequency-selecting coupling structure (FSCS) is implemented [6,7]. The basic FSCS is realised by using a capacitive coupled-line section between microstrip feeding lines. The rejection bandwidth is extended by the FSCS and the design of the DBBSF. Moreover, adjusting the length of the capacitive coupledlines can determine the centre frequency of the first stopband and produce three transmission zeros (TZs) which effectively enhance the rejection bandwidth. The proposed DBBSF achieves the stopband frequency at 2.1 GHz with over 100% fractional bandwidth. More than 20 dB rejection is measured from 1.1 to 3.4 GHz.

Compact Triple-Band Bandstop Filters Using Embedded Capacitors

“…Multi-band bandstop filters play an important role and are tremendously preferred, which can be simultaneously used for stopping different signal frequencies. Some effective methods have been proposed to develop dual-band [1][2][3][4] and triple-band bandstop filters [5][6][7][8][9][10][11][12]. However, the design of triple-band bandstop filters (TB-BSFs) and controlling the stopband frequencies within the specified band are difficult.…”

A Novel Miniaturized Dual-Band Bandstop Filter Using Dual-Plane Defected Structures

“…Recently, there is an increasing interest in the implementation of dual-band bandstop filters (DBBSFs) [5][6][7][8][9][10][11][12] since they can effectively suppress the undesired concurrent interference at two separate frequencies. It is demonstrated that [5] the DBBSF has a more compact size, lower cost, less passband insertion loss and lower group delay compared with a simple cascade of two conventional single-band bandstop filters.…”

“…In [5], the dual stopbands are synthesized by applying frequency-variable transformation to the lowpass prototype. Most recent research has been focused on size reduction of DBBSF, which may be achieved by using two-section [6] or three-section [7] stepped-impedance resonators (SIRs), or a dual-mode loop resonator [8]. The compact DBBSFs may also be realized by using a single end-shorted parallel coupled microstrip line and open-ended SIRs [9], or combining a spur-line structure and a rectangle slot [10].…”

A Compact Tunable Dual-Stop-Band Filter Based on DMS and DGS

“…In [5][6][7][8][9], tunable one stop-band filters are proposed based on varactor loaded split ring resonators, RF-MEMS metamaterials and DGS respectively. In [10][11][12], filters with dual stopband are based on tri-section stepped-impedance resonators, dual-mode loop resonator and microstrip open-loop resonators.…”