Xiaoguo Huang

Bandpass Filter With Tunable Bandwidth Using Quadruple-Mode Stub-Loaded Resonator

In this letter, a novel quadruple-mode resonator bandpass filter (BPF) with tunable bandwidth is proposed. By using two types of microwave varactors to tune the resonant frequencies and transmission zeros (TZs), the high-side edge of the passband and low-side edge of the passband can be separately varied. Therefore, the bandwidth could be tunable with reasonable adjust of the values of varactors. Theoretical expressions have been derived for the resonant frequencies and the TZs. The measured results of the BPF show that the fractional bandwidth can be tuned from 22% to 34% at a fixed centre frequency 2.0 GHz with a return loss better than dB. The tested results show good agreement with simulated results.

Tunable Bandpass Filter With Independently Controllable Dual Passbands

This paper presents a two-pole dual-band tunable bandpass filter (BPF) with independently controllable dual passbands based on a novel tunable dual-mode resonator. This resonator principally comprises a λ/2 resonator and two varactor diodes. One varactor is placed at the center of the resonator to determine the dominant even-mode resonant frequency; the other is installed between two ends of the resonator to control the dominant odd-mode resonant frequency. These two distinct odd- and even-mode resonances can be independently generated, and they are used to realize the two separated passbands as desired. Detailed discussion is carried on to provide a set of closed-form design equations for determination of all of the elements involved in this tunable filter, inclusive of capacitively loaded quarter-wavelength or λ/2 resonators, external quality factor, and coupling coefficient. Finally, a prototype tunable dual-band filter is fabricated and measured. Measured and simulated results are found in good agreement with each other. The results show that the first passband can be tuned in a frequency range from 0.77 to 1.00 GHz with the 3-dB fractional-bandwidth of 20.3%-24.7%, whereas the second passband varies from 1.57 to 2.00 GHz with the 3-dB absolute-bandwidth of 120 ± 8 MHz.

Electrical Tunable Microstrip LC Bandpass Filters With Constant Bandwidth

In this paper, two- and three-pole microstrip LC constant fractional bandwidth (CFBW) and constant absolute bandwidth (CABW) tunable bandpass filters are proposed. The equivalent-circuit models are presented to study the tunable mechanism. The filter can be reconfigured by changing the capacitance of the LC resonators. Based on electric coupling coefficient compensation, second- and third-order tunable equivalent-circuit models with CFBW/CABW are presented. For demonstration, a semiconductor varactor diode loaded microstrip LC resonator is adopted in our work to design the second- and third-order tunable filters. The S-parameters, group delays, and third-order intercept points for different center frequencies of the filters are presented. Each resonator requires only one varactor diode for both central frequency and resonator coupling coefficient control.

Half-Mode Substrate Integrated Waveguide (HMSIW) Filters and its Application to Tunable Filters

—In this paper, novel bandpass filter and tunable bandpass filter are designed based on half-mode substrate integrated waveguide (HMSIW) embedded with complementary resonators. Various passband characteristics are observed, and lumped equivalent circuit analysis models are developed. The configuration of the proposed bandpass filter is an open structure, and it is easy to load the active devices and build the bias/control networks on the signal plane. The tunable bandpass filter is presented based on the proposed novel bandpass filter loaded with semiconductor varactor diodes, and it has good spurious suppression characteristics and excellent out of band rejection. The prototype with overall size of 15.9 mm × 30.2 mm × 0.5 mm was designed and fabricated so as to validate the new structure. The measured central frequency is 1.538 GHz and 1.718 GHz, and the insertion loss is 5.1 dB and 3.3 dB, at 0 V and 30 V, respectively.

Bandstop Filter based on Complementary Split Ring Resonators Defected Microstrip Structure

Novel bandstop filters based on the defected microstrip structure with complementary split-ring resonators (CSRRs)/half-CSRRs etched on the microstrip surface are presented in this paper. By changing the configurations of the CSRRs, varied stop-band and pass-band characteristics are observed, and half-CSRRs is proposed to build a novel bandstop filter. A detailed explanation for the generation and variations of the stop-band and pass-band has been given. Lumped equivalent circuit analysis model is developed as well. The proposed filters exhibit compact size due to the employment of sub-wavelength resonators, and the overall size of the prototype is 12.2 mm × 28.95 mm × 0.8 mm. The measured −20 dB bandwidth of S 21 is from 2.51 GHz to 3 GHz, and the S 21 exhibits a wide spurious free response up to 10 GHz.

Substrate integrated waveguide filters and mechanical/electrical reconfigurable half-mode substrate integrated waveguide filters

In this paper, novel evanescent mode substrate integrated waveguide (SIW) and half-mode substrate integrated waveguide (HMSIW) filters are proposed, and their applications to mechanical and electrical reconfigurable bandpass filters (BPFs) are studied. SIW and HMSIW loaded with coupled complementary split-ring resonators achieve forward electromagnetic wave transmission below the waveguide cutoff frequency due to evanescent wave amplification. The half-mode configuration of the proposed SIW BPF is an opening structure, and the proposed HMSIW BPF is suitable to load with control elements. The electric/magnetic coupling effects and frequency responses reconfigurable mechanics of the proposed HMSIW structure are studied based on lumped equivalent circuit model. By using floating capacitors with mechanical switches and PIN diodes loaded on the HMSIW resonators, two one-bit HMSIW 500 MHz mechanical and 300 MHz electrical reconfigurable BPFs are demonstrated.

A Novel Microstrip Bandstop Filter and its Application to Reconfigurable Filter

Abstract In this paper, a novel bandstop filter based on microstrip LC resonators and 1-bit frequency reconfigurable bandstop filter are presented. The configuration of the proposed LC resonators has open structure and is suitable to load with reconfigurable capacitors. Lumped elements models have been developed, and the frequency tuning capability of the bandstop filter is studied, and it is shown that the filter stopband can be reconfigured by the loading capacitance. A 1-bit reconfigurable bandstop filter is designed based on the proposed novel bandstop filter loaded with two switchable 3.5mm × 6.5mm × 0.508mm Rogers 5880 single metal plane PCB capacitors. The prototype with compact overall size of 22mm × 39mm was designed and fabricated to validate the new structure. The measured stop-band central frequency is 3.04GHz and 2.513 GHz in cutoff state and connected state, respectively. 500 MHz central frequency reconfigurable capability is obtained.

High Selectivity Broadband Bandpass Filter Using Stub-Loaded Quadruple-Mode Resonator

—In this paper, a compact and high selectivity broadband microstrip bandpass filter (BPF) using stub-loaded resonator is proposed. The basic block of the proposed filter is a quadruple-mode resonator consisting of a stepped-impedance resonator and three shunt open stubs. The proposed resonator can provide two even-mode, two odd-mode frequencies and two transmission zeros. The even-mode resonant frequencies can be flexibly controlled by the centre stub, while the odd-mode frequencies are fixed. The two other symmetrical stubs can both affect even- and odd- mode frequencies. The proposed filter exhibits high selectivity profiting from the two transmission zeros (TZs) near the passband created by two types of stubs. The measured –3 dB bandwidth is 1.0 GHz at the centre frequency of 2.5 GHz, and the S 21 exhibits a wide spurious free response up to 6 GHz. Measured results show good agreements with EM simulation results.

A Dual-Band Bandpass Filter with a Tunable Passband

In this paper, a novel dual-band bandpass fllter with a tunable passband is proposed. Based on two quarter-wavelength resonators and one half-wavelength resonator, dual-band character is designed by introducing two independent coupling paths. The fllter structure is designed and can be divided into two parts. The Transmission Zeros (TZs) are derived through simulation. By varying the reverse bias voltage applied to the varactor diodes which are connected to the resonators, the flrst passband can be independently tuned. The second passband can be easily controlled by the width of the half-resonator. Finally, simulation results show a flrst tunable passband with a constant fractional-bandwidth of 3:9 § 0:3%, a center frequency of 1.472{1.886GHz, and the second passband almost remains constant with a fractional-bandwidth 2.4% at frequency range 2.24GHz. The measurement of the fabricated example shows good agreement with the simulation.

A constant absolute bandwidth filter with dual independent tunable passbands

This paper presents a novel procedure to the design of independent tunable dual-band bandpass filters with constant absolute 3-dB bandwidths. Only two bias voltages are required to control the locations of the passbands, respectively. Two kinds of dual-mode resonators are proposed to be selected while designing the passbands. Based on different parameters of even- and odd-modes, there are four types of dual-band selectivity to choose. Three transmission zeros are introduced at the adjacent of passbands, resulting sharp skirt. To demonstrate the design method, a dual-band tunable filter with constant absolute bandwidths was fabricated and measured. From the experimentally results, it was found that the proposed filter exhibited the first passband center frequency tunable range from 1.70 to 2.27 GHz with a constant 3-dB absolute bandwidth 130 ± 10 MHz and the second passband center frequency tunable range from 2.25 to 2.77 GHz with a constant 3-dB absolute bandwidth 80 ± 10 MHz.