Xin Lai

Design of Tri-Band Filter Based on Stub Loaded Resonator and DGS Resonator

A tri-band bandpass filter using stub loaded resonator (SLR) and defected ground structure (DGS) resonator is proposed in this letter. The DGS resonator on the lower plane constructs the first pass-band, and the SLR on the upper plane forms the second and third pass-bands, in which a DGS loop is properly used to provide the coupling between the SLRs. The three pass-bands are combined together with a common T-shaped feed line, and a reasonable tuning method is adopted to tune the three pass-bands with smooth responses. A compact tri-band filter with three pass-bands centered at 2.45, 3.5, and 5.25 GHz is designed and fabricated. The measurement results agree well with the full-wave electromagnetic designed responses.

Design of Dual-Band Filter Based on OLRR and DSIR

A novel dual-band filter using open loop ring resonator (OLRR) and defected stepped impedance resonator (DSIR) is presented in this paper. The OLRR forms one pass on the upper plane, and the DSIR forms the other pass on the lower plane. A proper designed feed structure is analyzed and used, which can provide desired external couplings to the two passes independently. At last, a dual-band filter with cascaded quadruplet (CQ) topology is designed and fabricated, which operates at WLAN bands 2.45/5.25 GHz. The simulated and measured results show good agreements and validate the proposed design method.

Synthesis of Cross-Coupled Triple-Passband Filters Based on Frequency Transformation

A synthesis method is presented for triple-passband filters. The proposed method is based on a frequency transformation from the normalized frequency domain to the actual frequency domain. A novel triple-passband filter topology with cross coupling is obtained, which consists of admittance inverters and parallel resonators. The coupling coefficients and the external quality factors can be calculated analytically. To validate the theory, a triple-passband filter is designed and fabricated using microstrip structure. The theoretical response meets the specifications very well, and the measured result shows a good agreement with the simulated one.

A Novel Wideband Bandpass Filter Based on Complementary Split-Ring Resonator

This paper presents a novel wideband bandpass filter making use of complementary split-ring resonator (CSRR) as the basic resonant unit. The resonant characteristic of CSRR is carefully studied through full wave analysis. The coupling of CSRR structure is very strong that can be used to realize wideband filter with small insertion loss. A filter with center frequency at 3.5 GHz, passband from 3.1 GHz to 3.8 GHz is designed and fabricated. The measured results are in good consistent with simulated results.

Wideband Cross Coupled Filter Using Split-Ring Resonator Defected Ground Structure

A wideband cross coupled bandpass filter making use of square split-ring resonator (SRR) defected ground structure (DGS) and parallel microstrip feed line is presented in this paper. The coupling between a pair of SRR DGS is much larger than that of the conventional SRR, which is fully investigated and applied to the design of wideband cross coupled filter. By extracting the coupling coefficient of various coupling structures and external quality factors of various feed structures, a SRR DGS four-pole filter with center frequency of 2.2 GHz and bandwidth of 20% is designed and fabricated.

Dual-mode filter with asymmetric response using square loop resonator DGS

This paper presents a novel dual-mode filter with asymmetric frequency response making use of square loop resonator DGS. Unlike the conventional dual-mode structure, the square ring resonator with a square patch attached at the corner is placed on the bottom plane, which is coplanar with the defected ground. Two T-shaped orthogonal feed lines are arranged on the top plane, which have an overlapped area with the resonator to excite and couple two degenerate modes. The proposed filter is found to have two transmission zeros on the high side of passband and takes on an asymmetric filtering property. Finally, a compact dual-mode square loop resonator DGS filter is designed and fabricated to operate at 2.68 GHz and its predicted results are verified in experiment.

Wideband Coaxial Filters with Impedance Matching for VHF/UHF Diplexer Design

This paper presents a novel synthesis process for wideband coaxial filter terminated with capacitors. At very high frequency and ultra-high frequency, we make use of helix as series inductor, dielectric disk as series capacitor, gap between inner metal disk and outer metal tube as shunt capacitor. By using the proposed synthesis technology and the extracted element formulas, two wideband quasilumped coaxial filters within different frequency ranges are designed and fabricated. Then they are directly connected to form a diplexer by using coaxial lines as impedance transformers. The diplexer can be used in a transceiver system combining two signals at 235 ∼ 280 MHz (VHF) and 315 ∼ 360 MHz (UHF) into one signal before the transmitted antenna.

Synthesis and realization of novel triple-passband filter based on frequency transformation

An analytical synthesis method for triple-passband microwave filters is presented in this paper. This method is based on a frequency transformation from the normalized frequency domain to the actual frequency domain. The coupling coefficients and the external quality factors can be calculated analytically with no need of optimization. A triple-band resonator is utilized to replace each capacitance in the low-pass prototype circuit as the building block of the triple-passband filter. To validate the synthesis theory, an example triple-passband filter is designed and fabricated with three passbands at 3.0–3.1 GHz, 3.2–3.3 GHz and 3.4–3.46 GHz, respectively, which has a maximum return loss of 20 dB in each passband.