Cross-coupled Bandpass Filter Research Articles

Design of Cross-Coupled Bandpass Filters with Flexible Coupling via Half-Mode Substrate-Integrated Waveguide

In this article, a simple approach for achievement of flexible coupling is presented based on the half-mode substrate-integrated waveguide (HMSIW). Since both electric and magnetic fields vary along the magnetic wall of the HMSIW, there exists mixed coupling between two adjacent HMSIWs. In this context, only by adjusting the width of the coupling slot at specific regions, both coupling property and strength can be conveniently controlled. Besides, as the coupling slot possesses the merits of simple structure and high flexibility, it is also expected to achieve desired couplings between multimode resonators. For demonstration, three cross-coupled bandpass filters (BPFs) with different kinds of frequency responses are constructed based on the typical cascaded trisection coupling topology by mixing one SIW and two HMSIWs, including two single-band and one dual-band designs. All measured results are highly consistent with the simulated ones, validating that the HMSIW not only has the inherent advantage of smaller size than the conventional SIW counterparts but also possesses unique feature in providing flexible coupling without extra circuit.

A Simple and General Method for Cross-Coupled Bandpass Filters Based on Circular Patch Resonator

In this article, a simple and general method for the design of cross-coupled bandpass filters with compact size is proposed by virtue of the circular patch resonator. Owing to the unique symmetry of the circle, such a circular patch resonator can be freely divided into several circular sector patch resonators along the radii. With this transformation, any two of the divided resonators have a possible coupling region. Specifically, the neighboring resonators have adjacent sides, while the vertices of all resonators are gathered in the center. Given this, the cross couplings can be easily constructed. Moreover, as the circular sector patch resonators with different boundary conditions along two sides have associated resonant properties, both positive and negative couplings can be provided. Consequently, the circular patch resonator should be a good candidate for the design of cross-coupled filters, and the concrete layout of the resultant filter can be determined by the design parameters as extracted from the design specifications. For demonstration, four design examples, including two single-band, one dual-band, and one tri-band bandpass filters, are constructed, fabricated, and measured. All measured results are in good accordance with the synthesized and simulated counterparts, thereby satisfactorily validating the feasibility and universality of the proposed design method.

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.

Compact High-Selectivity Wide Stopband Microstrip Cross-Coupled Bandpass Filter With Spurline

The article presents the design of a compact narrowband microstrip cross-coupled bandpass filter with improved selectivity and a wide stopband. The proposed fourth-order quasi-elliptic filter is designed at 2.5 GHz with a fractional bandwidth of 4% suitable for WLAN applications. At first, doubly-folded half-wavelength hairpin lines have been arranged symmetrically in a cross-coupled configuration combining the electric, magnetic, and mixed coupling. Accordingly, a size reduction of 17% over the folded inline hairpin-line filter with the same specifications has been achieved. Moreover, the selectivity has been improved greatly by the introduction of two deep transmission zeros with an attenuation level of 48 dB at the edges of the passband. However, the presence of the spurious harmonics with an attenuation level of 10 dB limits the performance of the filter related to the stopband rejection. As a remedy, conventional and meander spurlines have been incorporated in each hybrid coupled section of adjacent cross-coupled cells for achieving the modal phase velocity compensation. Accordingly, an extended stopband with a rejection level of 38 dB up to 4<i>f</i>₀ has been recorded by using a meander spurline and an overall size reduction of 33% has been achieved.

Pedestal substrate integrated waveguide filter with both electric and magnetic cross-couplings

In this paper, the recently proposed Pedestal Substrate Integrated Waveguide (SIW) structure, consisting of evanescent-mode SIW cavities, loaded with pedestal-shaped metal inserts, is utilized to design a coupled resonator filter with both positive and negative cross-coupling. It is shown that both types of coupling, for a large range of coupling values for both, can very simply be implemented in this structure, with electric coupling obtained by means of an I-shaped strippine between pedestal tops, and magnetic coupling obtained using inductive irises. The proposed structure can also introduce mixed coupling. Graphs are presented to show the range of coupling values attainable. A proof-of-concept sixth order cross-coupled bandpass filter, with a 5 % bandwidth at 5 GHz, and both real and imaginary axis transmission zeros, are designed and measured.

A Novel Quasi-elliptic Bandpass Filter Using Half-mode Substrate Integrated Waveguide Cavities

A fourth-order cross-coupled bandpass filter (BPF) using three half-mode substrate integrated waveguide (HMSIW) cavities and a spurious resonance is proposed. The HMSIW cavity is derived from diamond-shaped SIW; a new spurious resonance mode is built by adding post-wall irises between the two coupled HMSIW cavities and the resonance of spurious mode is analyzed. From the demonstration, an X-band cross-coupled quasi-elliptic filter is designed, simulated, and fabricated. The measured results are in good agreement with simulated results.

Tri-band cross-coupling bandpass filter with rectangular defected ground structure array

A tri-band cross-coupling bandpass filter (BPF) with rectangular defected ground structure (DGS) array is proposed in this paper. Cross-coupling paths comprised of five resonators are employed to achieve general Chebyshev filtering frequency responses. Besides changing gaps among resonators, a novel rectangular DGS array is proposed to exactly meet coupling coefficients for specific demands for different passband in multi-band BPF. The centre frequency of the tri-band filter that is selected at 2.4, 3.4, 5.5 GHz are for LTE, Bluetooth, WiMAX and WLAN. The 3 dB bandwidth of the three passbands are 5, 3.23 and 3.45%, respectively, meanwhile, more transmission zeros are generated, leading to enhanced selectivity and high out of band isolation. The proposed tri-band filter is completed with a few simple calculations and several brief processes. Measured results of the fabricated filter demonstrate the theory prediction and proposed method well.

Q-band cross-coupled dielectric resonator filter using TM mode for satellite application

AbstractA new structure of Q-band filter comprising rectangular high-permittivity dielectric resonators (DR) operating at TM11δ mode is introduced. The resonator shows high-quality factor (Q) and wide spurious free window compared with other technologies available at Q-band for realizing filters. Low permittivity ceramic material (quartz) is used as a support for holding DR at the center of the cavity. An eight-pole cross-coupled band-pass filter having a bandwidth of 225 MHz at 38.5 GHz was realized. Resonant coupling structure is introduced to realize cross-coupling in filter. The resonator assemblies were optimized precisely to achieve effective linear frequency drift over temperature of the order of 2 ppm/°C. The filter also survived severe sine and random vibration test for satellite application.

Cross-coupled bandpass filter based on circular substrate integrated waveguide resonator

Cross-coupled bandpass filter based on circular substrate integrated waveguide resonator

LTCC Multilayered Substrate-Integrated Waveguide Filter With Enhanced Frequency Selectivity for System-in-Package Applications

This paper presents a cross-coupled bandpass filter with stacked substrate-integrated waveguide cavities on low-temperature cofired ceramic substrates. The proposed filter has a local multipoint distribution service band with a novel same-side-feed input/output structure. Conventionally, a cross-coupled structure generates only a single pair of transmission zeros. The proposed filter can generate two pairs of transmission zeros beside the passband, thereby providing an excellent cutoff rate in the stopband and improved frequency selectivity. The additional pair of transmission zeros is created by the same-side-feed structure, which constructs an additional source-load coupling path without increasing the circuit size. A multipath coupling diagram is used to illustrate the conformation of the second pair of transmission zeros and predict its behavior. The experimental filter exhibits responses centered at 27.95 GHz with an insertion loss of -2.8 dB, and a bandwidth of 9%. Two pairs of transmission zeros (at 26.3 and 29.6 GHz, and at 23.2 and 37 GHz) around the passband were obtained, achieving excellent selectivity and a wide stopband.

Design of Microstrip Cross-Coupled Bandpass Filter With Multiple Independent Designable Transmission Zeros Using Branch-Line Resonators

This letter proposes a novel branch-line resonator to design a fourth-order cross-coupled bandpass filter (BPF). Theoretically, the proposed branch-line resonator plays two crucial roles. First, the arbitrary number transmission zeros can be designed in the stopband of a fourth-order cross-coupled BPF. Second, the required external quality factor can also be designed without an impedance transformer. This study examines a novel fourth-order cross-coupled BPF with a single pair of transmission zeros produced by a cross-coupled mechanism near the passband and five independent designable transmission zeros created by the proposed resonator in the stopband.

V-band cross-coupled SIW band-pass filter with an antisymmetric U-slot negative coupling structure

This study presents an low-temperature cofired ceramic (LTCC) V-band cross-coupled band-pass filter using substrate-integrated waveguide cavities. Two antisymmetric U-shaped slots connected by via is proposed to construct the negative coupling structure, which is simple and especially useful for 60 GHz applications. Moreover, the U-slot structure possesses a wide range of realizable coupling coefficients from −0.008 to −0.075. An experimental LTCC fourth-order filter was fabricated for demonstration, achieving a bandwidth of 12% (7.2 GHz) at 59.6 GHz with superior frequency selectivity.

A Novel Planar Extended Doublet Filter with Substrate Integrated Waveguide Cavity Resonators

A novel planar extended doublet filter based on substrate Integrated waveguide cavity resonators was proposed for the first time. This filter consists of a main doublet with an additional resonator grown in one of the branches. The source and load are coupled to both branches of the doublet in order to generate two transmission zeros. By employing the combinational structure of the TE101-mode and TE102-mode of the SIW cavity resonators, the negative coupling coefficient required for the design of a single-layer cross-coupled SIW bandpass filter is implemented. The measurement results show the return loss of the implemented filter is above 13dB, the insertion loss is below 4.238dB with only 0.56% of the bandwidth.

Cross-coupled bandpass filters using QMSIW cavities and S-shaped slot coupling structures

This paper presents a novel cross-coupled bandpass filter using quarter-mode substrate integrated waveguide (QMSIW) cavities. QMSIWs with fictitious magnetic walls on two sides retain similar performances of the conventional SIW, but are almost one fourth the size. The dominant resonant mode of the proposed resonator is the TE101 mode. A special negative coupling scheme with symmetrical S-shaped slots on the top and bottom metal planes connected by metallic vias is developed. The proposed structure provides more design flexibility in arranging the pitch of vias owing to the extended slot length. The experimental filter has a measured fractional bandwidth of 7.44% at 5.57 GHz with a return loss better than −18.1 dB and an insertion loss less than −2 dB.

Design of cross-coupled dual-band bandpass filter using stub-loaded open-loop resonators with different bandwidth ratios

Two cross-coupled dual-band bandpass filters (BPF) using stub-loaded open-loop (SLOL) resonators are presented in this paper. The required coupling coefficients for the two desired frequencies can be achieved by adjusting the relative coupling position and the spacing between SLOL resonators. In addition, the loaded-stub also affects the coupling between the resonators. To validate this concept, two dual-band BPF with different bandwidth ratios are designed and implemented. The measured 3 dB fractional bandwidths are 4.9/4.8 and 8.2/3.8%, respectively. The results are in good agreement with those of the simulation. Furthermore, the proposed filter has two transmission zeros at each band and exhibits high skirt selectivity.

Design of cross-coupled stepped-impedance resonator bandpass filter using low-temperature cofired ceramic technology

A novel compact half-wavelength cross-coupled stepped-impedance resonator filter using low-temperature cofired ceramic (LTCC) technology is presented. The filter not only has good selectivity due to the controllable transmission zeros but also has a small size by the virtue of LTCC structure. Based on the theory of cross-coupled stepped-impedance resonators and 0° feed structure, a bandpass filter with the center frequency of 1.25 GHz has been designed and fabricated. Good agreement between measured and simulated results is observed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2201–2204, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26243

Compact Substrate Integrated Waveguide (SIW) Bandpass Filter With Complementary Split-Ring Resonators (CSRRs)

A novel cross-coupled bandpass filter using new substrate integrated waveguide (SIW) resonators is presented. The resonator is built up by a SIW cavity loaded with a complementary split-ring resonator (CSRR) on its top metal plane. The resonant modes of the proposed resonator are analyzed, with the Q-factor of the dominant mode also extracted. It is shown that our proposed compact filter operates below the cutoff frequency of conventional SIWs. No spurious responses, corresponding to the higher-order resonant modes of the resonator, appear within an octave band of the central frequency. Its attractive performance is validated numerically and experimentally.

Wideband cross‐coupled filter using defected stepped impedance resonator

AbstractA novel wideband cross‐coupled band‐pass filter based on defected stepped impedance resonator (DSIR) is presented in this article. Although the DSIR has opposite impedance characteristic and field distribution to the microstrip SIR, its resonant property is similar to the latter. The internal coupling coefficients of DSIRs are found to be large enough for the wideband filter design. A four‐pole, cross‐coupled band‐pass filter with f0 = 1.6 GHz and FBW = 12% is designed and fabricated using the folded DSIR. Experimental result has good agreement with the simulation. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 558–561, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24972

Design of four-ordered cross-coupled bandpass filters with low-temperature co-fired ceramic technology

A new method to realise the four-ordered quasi-elliptic bandpass filters with low-temperature co-fired ceramic technology has been proposed; in particular, the semi-lumped structure is employed. With the assistance of the non-adjacent cross coupling, a pair of transmission zeros can be generated on both sides of the passband skirt. Moreover, with the coupling between the source and load ports, an extra pair of transmission zeros will be generated so that there will be greater outband suppression on both sides of the passband skirt. The analysis and design procedures are provided. In addition, the match between the electromagnetic simulation and results of measurement validates the proposed structures.

Compact double-mode cross-coupled microstrip bandpass filter with tunable transmission zeros

A compact double-mode cross-coupled microstrip bandpass filter with an asymmetric frequency characteristic and three transmission zeros is presented. The bandpass filter consists of a cross-coupled gap and a double-mode resonator of a half-wavelength line with a shunt-stepped-impedance open stub. In comparison to the conventional square loop dual-mode resonator, the proposed double-mode resonator achieves a 59% size reduction. The parametric studies on the electrical length of the open stub and the capacitance of the cross-coupling are provided in order to gain a better insight into the transmission poles and zeros. Then, a bandpass filter is designed, fabricated and tested to validate the design concept. From 2.3 to 2.5 GHz, the return loss is better than 10 dB and the insertion loss is <1.5 dB. There are three transmission zeros in the upper stopband at 2.8, 3.4 and 4.9 GHz.