Bandwidth Tunable Bandpass Filter Research Articles

A 5th-Order Constant Bandwidth Tunable Bandpass Filter With Two Cascaded Trisection Structures

A novel 5th-order cross-coupled tunable bandpass filter based on full-wavelength tunable resonator with four independent coupling regions, including two electric and two magnetic coupling regions is proposed. The slop of the coupling coefficients versus the resonant frequency can be pre-defined to meet the requirement of tunable bandpass filter with constant bandwidth. The 5th-order constant bandwidth cross-coupled bandpass filter is with two cascaded trisection (CT) structures, including one all electric type CT cell and one all magnetic type CT cell, and two CT cells share a common resonator to reduce the size. Therefore, two transmission zeros are generated besides the passband for improving the frequency selectivity. The measurement shows that, the central frequency can be tuned from 1.48 GHz to 1.88 GHz with a −3 dB bandwidth of 92±1.1 MHz, and the −20dB/−3dB rectangle factor is 1.66~1.76.

Frequency and bandwidth tunable reliable MEMS bandpass filter for 24 GHz radar applications

In this work, radio frequency (RF) micro-electromechanical system (MEMS)-based frequency and bandwidth tunable bandpass filter is presented for application in 24 GHz Doppler radar transceivers. The filter is fabricated on 635 μm alumina substrate using surface micromachining process. Total area of the filter is only 2.8 mm2 excluding bias lines and pads. Functional building blocks of the proposed filter are fabricated and tested independently to ensure optimum filter responses. The proposed filter can be tuned to any frequency between 22 and 24 GHz based on electrostatic actuations. It demonstrates insertion loss of 1.67 dB and matching of 18.6 dB at 24 GHz with fractional bandwidth of 6.5%. Filter gives acceptable matching over a 5 GHz bandwidth (21.65-26.65 GHz) with an average insertion loss of 4.7 dB. Filter works satisfactorily up to 10 billion cycles with 0.1 to 1 W of RF power. To the best of our knowledge, this is the first reported tunable MEMS bandpass filter at 24 GHz with 10 billion cycles reliability and with 1 W of RF power for radar applications.

Novel Varactor-Tuned Coupling Mechanism and Its Applications to High-Order Bandwidth-Agile Bandpass Filters

In this paper, a novel tunable coupling mechanism with bandwidth-tunable capability is presented. Metallic via has been utilized to construct the coupling structure, namely via-coupling. Studies show that the via-coupling mechanism provides more flexibility and owns better tolerance to fabrication errors than the traditional gap-coupling. By employing varactor in parallel with the metallic via, the coupling coefficient between each resonator pairs can be effectively tuned. It is worth noting that only one varactor is required for each resonator pair. The lumped-circuit model of the tunable coupling mechanism is investigated and extracted by classical theory derivation and simple programming. For verification, a fourth-order quasi-elliptic bandpass filter (BPF) and a bandwidth-tunable one are designed, fabricated, and measured. For the bandwidth-tunable BPF, the factional bandwidth varies from 2.52% to 5.04%, meaning a double tuning range. The in-band insertion loss varies from 2.8 to 4.8 dB, and the return loss is better than 17 dB. If needed, BPFs with $N$ th-order ( $N > 4$ ) could be designed based on the proposed tunable coupling mechanism and only ( $N + 1$ ) varactors are required.

A constant absolute bandwidth tunable band-pass filter based on magnetic dominated mixed coupling and source–load electric coupling

In this paper, a constant absolute bandwidth (CABW) band-pass filter based on magnetic dominated mixed coupling and source–load electric coupling is proposed. Specially, a novel mixed electric and magnetic coupling structure is presented to control the coupling coefficient variation and thus realize a narrow CABW width. Two transmission zeros are added to the filter response using a source–load coupling technique, leading to a better selectivity. The measurement shows that the –1 dB absolute and fractional bandwidth is 29 ± 3 MHz and 1.8–2.6%, respectively, while the central frequency of the passband varies from 1.11 to 1.51 GHz.

Magnetically Tunable Ferrite-Loaded Half-Mode Substrate Integrated Waveguide

A magnetically tunable ferrite-loaded half-mode substrate integrated waveguide (HMSIW) is presented. To achieve the magnetic tuning, a planar Yttrium Iron Garnet (YIG) slab is loaded along the metalized wall of the HMSIW, where the concentration of the magnetic field is strongest. Static (DC) magnetic bias is applied on the ferrite slab transversely to the direction of propagation. Measured phases of forward and reverse transmission coefficients show the non-reciprocal behavior of this transmission line. Measured results illustrating the comparison between a single ferrite slab-loaded SIW and a HMSIW are presented. As an application example, a two-dimensionally tunable bandpass filter (BPF) operating at X-band is proposed and studied. By controlling the value of loaded lumped capacitors and the applied magnetic bias, a bandwidth tunable BPF is demonstrated.

Bandwidth Tunable and Compact Band-Pass Filter (BPF) Using Complementary Split Ring Resonators (CSRRS) on Substrate Integrated Waveguide (SIW)

In this paper, we present a novel bandwidth tunable bandpass filter (BPF) loaded by complementary split ring resonators (CSRRs). On substrate integrated waveguide (SIW), the CSRRs are modeled and deployed to implement BPFs with tunable bandwidth capability. The microwave tunable circuits are designed in order to observe the various coupling coefficients and external quality factors by changing the orientations of the CSRRs. Four different configurations of filters are proposed and fabricated. These structures provide compact size as well as high frequency selectivity due to the use of the subwavelength resonators preserving sharp rejection and an evanescent wave propagation mode below the waveguide cutoff. Attractive performances of tunable BPFs are validated theoretically and experimentally.