Design of compact microstrip lowpass elliptic filter with wide stop band using invasive weed optimization
In this paper, the invasive weed optimization technique is used to design a compact microstrip elliptic low pass filter with very high order suppression response. This method enhances the filter stop band bandwidth more than 8.5 f3dB and achieves 47% compactness compared with the traditional elliptic filter. The measurement results of the final optimized fabricated filter are in good agreement with the simulation ones.
Novel Compact Microstrip Lowpass Filters with Wide Stopband Using Defected Ground Structure
In this paper, a novel defected ground structure (DGS) is proposed for lowpass filter (LPF) applications. The proposed structure exhibits wideband attenuation without increasing the circuit size, as compared with the conventional DGS. An equivalent circuit for the proposed DGS is described, and its equivalent-circuit parameters are analyzed and extracted. Benefitting from the quasi-elliptic function of the DGS, a demonstration LPF using one DGS unit and a compensated microstrip line is designed, and an attenuation pole near to the passband edge is realized to enhance roll-off of the stopband. To improve rejection level of the stopband, three cascaded DGS units are utilized for the LPF design. The fabricated LPF shows more than 20 dB attenuation from 2.1 GHz to over 8.0 GHz, as well as sharp rolloff. The simulated and measured results are presented, showing good agreement.
Improved Microstrip Folded Tri-Section Stepped Impedance Resonator Bandpass Filter using Defected Ground Structure
─ In this paper, a study of a microwave microstrip bandpass filter (BPF), based on folded tri-section stepped impedance resonator (FTSIR) and defected ground structure (DGS) is presented. Based on the resonance characteristics of a stepped impedance resonator (SIR), the first spurious resonant frequency can be tuned over a wide range by adjusting its structure parameters. The SIR bandpass filter is designed to have a quasi-elliptic function response and a wide upper stopband. Furthermore, five ground slots (DGS) are used in order to omit the first spurious resonant frequency. Compared to similar microstrip filter without defected ground, the simulated performances of this novel structure indicate some functional advantages. To validate the design and analysis, a prototype of the bandpass filter with DGS was fabricated and measured. It is shown that the measured and simulated performances are in a good agreement. Index Terms ─ Defected ground structure (DGS), folded tri-section stepped impedance resonator (FTSIR), microstrip bandpass filter.