Design of Compact Lowpass Filter With Ultra-Wide Stopband Using Thin Slots

Abstract

Abstract-This paper presents a compact microstrip steppedimpedance lowpass filter with ultra-wide stopband by using back-toback C-shaped and triple C-shaped thin slots. The properties of several thin slots in the ground plane have been investigated in this paper. With the full-wave simulation results and a simplified equivalent model, the total equivalent inductance of the thin slots can be extracted at cutoff frequency for lowpass filter design purpose. On the other hand, the thin slots work as bandstop filter at the stopband of the lowpass filter for a better stopband rejection. The proposed lowpass filter with a cutoff frequency of 2 GHz shows a wide stopband with an over 25-dB attenuation up to 17.5 GHz. From dc to 2 GHz, the insertion loss is less than 0.3 dB and the return loss is greater than 20 dB. In comparison to the conventional stepped-impedance lowpass filter with the same passband performance, the proposed lowpass filter shows not only a 24.3% size reduction but also a better stopband rejection.

Improvement of Compactness of Low Pass Filter Using New Quasi-Yagi-DGS-Resonator and Multilayer-Technique

“…Newly, photonic structures, defected microstrip structures (DMSs) and defected ground structures (DGSs) have gained much interest for their planar topology and easy and inexpensive fabrication with photolithographic technique or printed-circuit board technology [1][2][3][4][5]. Periodic or non-periodic DGSs show a good repressed reject band in some frequency, thus restrain spurious response by repressing harmonic in the microwave circuits [6,7].…”

A Novel Compact CPW LowPass Filter Integrating Periodic Triangle DGS Cells

“…In the research, augmentation of DGS elements number were used as a good solution to design a compact microwave filter, [7,8,9]. The performance of LPF with periodical DGSs was used here to have a much wider stopband compared with one DGS.…”

High-Performance LPF Using Coupled C-Shape DGS and Radial Stub Resonators for Microwave Mixer

“…An arrangement of several stepped impedance, radial stub and folded open stub resonators is proposed in [4] and [5] to realize a LPF with superior specifications such as sharp roll-off, wide stopband, good return loss and compact size, but this improvement has cost complicate structure. Another LPF design technique employing various forms of defected ground structures DGS [6] is presented in [7][8][9][10][11][12][13][14]. In [7], spurious harmonic of an even-order elliptic function LPF is eliminated by using conventional shaped DGS.…”

“…In [7], spurious harmonic of an even-order elliptic function LPF is eliminated by using conventional shaped DGS. In [8] and [9], stepped-impedance low-pass filter employing I-shaped and C-shaped thin slots DGS is presented to achieve ultra-wide stopband with 2 GHz cutoff frequency. In [10], a compact dual-planar electromagnetic bandgap microstrip low-pass filter configuration is investigated for achieving wide stopband.…”

“…Different techniques and structures have been reported in the recent researches to achieve a LPF with improved characteristics [2][3][4][5][6][7][8][9][10][11][12][13][14]. A stub-loaded coupled-line hairpin unit [2] and a folded stepped impedance open stub [3] are exploited to achieve a microstrip lowpass filter with high selectivity and wide stopband.…”