Dinghong Jia

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.

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 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.

A 2.285–3.195 GHz electrical tunable bandstop filter with constant absolute bandwidth

In this paper, a tunable bandstop filter with constant absolute bandwidth is proposed based on electric coupling compensation of tunable capacitor network. The equivalent circuit model of the tunable capacitor network is presented to study the tunable mechanism. The electric coupling factor of the tunable capacitor network increases while the tunable capacitor increasing. This mechanism can be used to compensate the bandwidth of the tunable bandstop filter. In our work semiconductor varactor diode loaded microstrip LC resonator is adopted to design the tunable filter. Each resonator requires only one varactor diode for both central frequency and resonator coupling coefficient control. The S-parameters and group delays of the tunable bandstop filter are presented. The measurement shows that the -30 dB absolute bandwidth varies from 371 MHz to 305 MHz while the central frequency of the stopband varying from 3.195 GHz to 2.285 GHz.

Microstrip tunable bandstop filter with constant absolute bandwidth

This paper presents a novel designing approach for tunable bandstop filters (BSPs) with constant absolute bandwidth (CABW). A simple bandstop unit is introduced to design tunable BSPs. Through the analysis, the bandwidth and center frequency of the unit can be fully controlled. Furthermore, when the center frequency is tuned, the bandwidth can be kept constant by choosing proper loaded stub impedances. Then, profiting from this unique property, tunable filter designs with CABW are introduced. A compact cascade structure is adopted to satisfy the tuning requirement on J-inverter while designing tunable filters with CABW. For demonstration, second-order tunable BSP is designed, fabricated, and measured. The filter can be tuned from 1.55 to 2.21 GHz with CABW, a wide fractional tuning range up to 43%. High rejection levels are realized at the mid-stopband. The measurement shows good agreement with the simulation.

A two-pole tunable filter with constant fractional-bandwidth characteristics

In this paper, a tunable filter with constant fractional bandwidth is designed and fabricated on εr = 2.2, h = 0.508 mm duroid substrates. A new mixed electrical and magnetic coupling scheme is introduced by this structure to achieve an overall constant coupling coefficient during the tuning range, which can meet the requirement of constant fractional bandwidth. A detailed analysis on the external quality (Qext) and coupling coefficient is presented. Two-chip capacitors (CM = 1 pF), using radio frequency (RF) and microwave capacitors, were used to enhance Qext. The Qext (22 ± 3) shows a relatively small variation over the entire tuning range. The tunable constant fractional-bandwidth filter shows a tuning range of 1.28–1.86 GHz, a 3-dB bandwidth of 5.3 ± 0.6% and an insertion loss of 5.11–2.69 dB. The measured and simulation results are in a good agreement.

A HIGH SELECTIVITY DUAL-BAND BANDPASS FILTER USING DUAL-MODE AND TRIPLE-MODE RESONATORS

In this paper, a novel high selectivity dual-band microwave bandpass fllter (BPF) using dual-mode and triple-mode resonator is proposed. First, a dual-band fllter comprising two dual-mode single band fllters using common input/out lines is designed. Each single BPF is realized using a stepped-impedance resonator (SIR) with a centrally-loaded shunt open stub. The flrst and second passband can be independently controlled by the two dual-mode resonators, respectively. The proposed fllter also ofiers three transmission zeros (TZs) to improve the selectivity. To further improve the selectivity over high side band of the flrst passband, a novel triple-mode resonator is designed to replace the dual-mode resonator. The basic structure of triple-mode resonator is microstrip-to-coplanar waveguide (CPW) structure. The microstrip structure provides one odd mode and one even mode resonant frequency and the CPW structure can provide another even mode resonant frequency without increasing circuit size. Both simulated and measured results show that the fllters exhibit a good performance, including a small insertion loss, selectivity.

Tunable 3-pole bandpass filter with constant absolute bandwidth and >60 dB rejection at desired location of stopband

This paper presents a novel design approach for tunable 3-pole bandpass filter (BPF) with constant bandwidth (ABW) and deep rejection at the desired stopband. First, by properly designing the coupling coefficient and Qext, the tunable 3-pole BPF is designed with the characteristic of constant ABW. Only two bias voltages are adopted to complete the tuning, among which one of them is used to tune the center frequency and the other one is adopted to control the Qext. Then, bandstop resonators are introduced to provide deep rejection at desired stopband. A deep rejection level >60 dB can be easily controlled by varying the loaded capacitor Cbs among the stopband. Furthermore, the designed deep rejection point can be constant and produces little influence on the passband. For demonstration, a 3-pole tunable BPF is designed, fabricated, and measured. The filter can be tuned from 0.98 to 1.4 GHz with constant ABW, a wide fractional tuning range up to 40% can be attained. High rejection level >60 dB is realized at the pre-designed stopband point 0.65 GHz. The measurement shows good agreement with the simulation.