In this paper, a class of triple-band bandpass filters with two transmission poles in each passband is proposed using three pairs of degenerate modes in a ring resonator. In order to provide a physical insight into the resonance movements, the equivalent lumped circuits are firstly developed, where two transmission poles in the first and third passbands can be distinctly tracked as a function of port separation angle. Under the choice of 135° and 45° port separations along a ring, four open-circuited stubs are attached symmetrically along the ring and they are treated as perturbation elements to split the two second-order degenerate modes, resulting in a two-pole second passband. To verify the proposed design concept, two filter prototypes on a single microstrip ring resonator are finally designed, fabricated, and measured. The three pairs of transmission poles are achieved in all three passbands, as demonstrated and verified in simulated and measured results.

Compact Dual-Mode Triple-Band Bandpass Filters Using Three Pairs of Degenerate Modes in a Ring Resonator

A tri-band bandpass filter designed based on a stub-loaded step-impedance resonator (SIR) is proposed. The resonant behavior of the stub-loaded SIR is analyzed. By properly controlling the impedance ratio K1, the length ratio (α) and the length ratio (r) of the stub-loaded SIR, the center frequencies are designed at 1.575, 2.4, and 3.5 GHz, respectively, corresponding to the GPS, WLAN and WiMAX applications. Furthermore, a 0° feed structure is used to provide at least one transmission zero near passband edge of each passband, resulting in high selectivity. Experimental results show good agreement with the simulated results.

A New Tri-Band Bandpass Filter Based on Stub-Loaded Step-Impedance Resonator

Because of the inherent structural flexibility in coupling design and topological arrangement, substrate integrated waveguide (SIW) filter topologies enjoy better out-of-band frequency selectivity and/or in-band phase response with the allocation of finite transmission zeros (FTZs). In the first article in this series, basic design rules and fundamental electrical characteristics have been presented that indicate the superior performances of SIW structures and their filter applications. Advanced design techniques and innovative structure features have recently been reported in a large number of publications. They include cross couplings realized by physical and nonphysical paths and SIW filters with dual-mode or multimode techniques. Miniaturization-enabled techniques including low-temperature cofired ceramic (LTCC) technology have been developed and applied to the development of SIW filters to reduce the size for low-gigahertz applications using nontransverse electromagnetic (non-TEM) modes. Wideband SIW filters, multiband SIW filters, and reconfigurable SIW filters have also been reported by various research groups. This article reviews these advanced and innovative SIW filter technologies, and related examples are presented and discussed.

Substrate Integrated Waveguide Filters: Design Techniques and Structure Innovations

Microstrip quad-band bandpass filters with controllable passband center frequencies are presented and intensively investigated in this study. The newly proposed quad-band filter principally comprises two dual-band filters. Specifically, the two distinct types of dual-band filters with different dual-band generating mechanisms are studied and then combined to provide the quad-band responses. By incorporating parallel coupled lines as input sections and interstage impedance inverters built with quasi-lumped inductors, the type-I filter is constructed with thorough network analysis. As for the type-II filter, with novel quad-pole-splitting techniques analyzed by mixed-mode S-parameters, dual passbands of close band proximity could be realized. Eventually, based on the parallel-path transmission theory along with the two dual-band filters, a novel quad-band filter is thus implemented. The measurement and simulation results show good agreement.

Microstrip Dual/Quad-Band Filters With Coupled Lines and Quasi-Lumped Impedance Inverters Based on Parallel-Path Transmission

Net-type resonators with dual- and tri-mode electrical behaviors have been presented and analyzed theoretically in this paper. The proposed net-type resonator is constructed by a short-ended and several open-ended transmission-line sections, which has the advantages of small size and more flexible resonant frequency allocation and is therefore particularly suitable for applications to the design of microwave devices. To verify the usefulness of the proposed resonators, three experimental examples, including a dual-mode bandpass filter, a dual-passband filter, and a triplexer, have been designed and fabricated with microstrip technology. Each of the designed circuits occupies a very small size and has a good upper stop and performance. All measured results are in good agreement with the full-wave simulation results.

Design of Multimode Net-Type Resonators and Their Applications to Filters and Multiplexers

Atri-bandbandpassfilterusingstubloadedresonator (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 pro- videthecouplingbetweentheSLRs.Thethreepass-bandsarecom- bined together with a common T-shaped feed line, and a reason- able 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. Index Terms—Defected ground structure (DGS) resonator, stub- loaded resonator (SLR), tri-band filter, T-shaped feed line.

http://ieeexplore.ieee.org/iel5/7260/5458313/05445051.pdf

Design of Tri-Band Filter Based on Stub

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.

/pdf/design-of-tri-band-filter-based-on-stub-loaded-resonator-and-3aijkhsk63.pdf

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

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.

Synthesis of Cross-Coupled Triple-Passband Filters 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.

Hao Di

Papers

Design of Tri-Band Filter Based on Stub

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

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

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