Xiao-Kun Wei

Substrate integrated waveguide (SIW) filter with hexagonal resonator

A novel substrate integrated waveguide (SIW) hexagonal resonator structure and its applications to bandpass filters are presented. Based on the SIW techniques, the resonance characteristic of proposed resonator is investigated. The hexagonal SIW resonators, which can combine flexibility of rectangular cavities and performance of circular cavities, are convenient for bandpass filters design. Since any of the six sides of a hexagonal resonator can be utilized for coupling, the filter configurations are flexible and adaptable. By changing the coupling sides of the hexagonal resonators, two types of experimental circuit configuration at the same central frequency of 10 GHz but with different fractional bandwidths of 3 and 6%, including third-order Chebyshev and crossed-coupling trisection, are constructed, fabricated, and measured. Measured results show a good agreement with simulated ones and validate the proposed configurations.

Design of a wide-stopband bandpass filter using stepped impedance resonators

In this paper, a compact bandpass filter (BPF) with improved stopband characteristics using stepped impedance resonators (SIRs) is proposed. The filter consists of two quarter-wavelength SIRs with radial stubs and a PI-network of capacitance, which is used to suppress the upper frequency spurious signals. An odd- and even-mode analysis is adopted considering the structure’s symmetry. A new BPF centered at 1.57 GHz has been designed and fabricated to verify the validity of the proposed method. Measured results are in good agreement with the electromagnetic simulation. The frequency selectivity was enhanced via introducing two finite transmission zeros (TZs) near the passband, located at 1.21 GHz with 43.5 dB rejection and 3.10 GHz with 62.3 dB rejection, respectively. The spurious frequencies of the upper stopband are suppressed better than 20 dB from 2.07 to 16.25 GHz. And the circuit only occupies 0.09 λ g  × 0.09 λ g.

Compact bandpass filter with multiple transmission zeros using modified stepped-impedance resonators

A modified quarter-wavelength stepped-impedance resonator (SIR) is proposed and analyzed in this article. In the modified SIR, the low characteristic impedance stub of a conventional SIR is replaced by a closed rectangular loop. Based on the modified SIRs, a compact third-order bandpass filter (BPF) with multiple transmission zeros is presented. The filter consists of two novel SIRs and one half-wavelength embedded spiral-line resonator locating in the closed rectangular loops. Mixed-cross (M–C) coupling and source–load (S–L) coupling are introduced to the filter. Owing to the M–C coupling and S–L coupling, multiple transmission zeros and the suppression of harmonics can be obtained in the stopband for the enhanced frequency selectivity. A new BPF centered at 2.4 GHz with 25% fractional band width for wireless local area networks application has been designed, fabricated and measured to verify the validity of the above method.

Miniaturized substrate integrated waveguide symmetric filter with high selectivity

A compact substrate integrated waveguide symmetric filter with source–load coupling using low temperature cofired ceramic (LTCC) technology for high-selectivity application is presented. The proposed filter with second-order resonators has two transmission zeros which can be controlled flexibly by adjusting the coupling strength and modifying coupling style. With the assistance of the multilayer LTCC structure and refined coupling manner, the proposed filter has a more compact size while maintaining high selectivity. A demonstration filter is designed, fabricated, and measured to validate the proposed structure. Measured results are provided to show good performance and in agreement with the simulated results. Moreover, thanks to the vertical LTCC multilayer structure, the overall size of the proposed filter is only  mm3.

Miniaturized mixed-cross coupling bandpass filter with source–load coupling

A miniaturized trisection bandpass filter (BPF) with improved stopband characteristics is presented. The proposed BPF consists of three stepped impedance resonators (SIRs), where the nonadjacent SIRs share a common shorted stub, and the other SIR is embedded inside the nonadjacent SIRs. To improve frequency selectivity, mixed-cross (M-C) coupling and source–load (S–L) coupling were introduced in the nonadjacent resonators and source/load ports, respectively. Owing to the M-C and S–L couplings, multiple transmission zeros (TZs) can be employed for high skirt selectivity and upper wide stopband. A new BPF centered at 2.45 GHz with 17.6% fractional bandwidth has been designed and fabricated to verify the validity of the proposed method. The measurement result shows four finite TZs in the stopband, located at 2.09, 2.98, 4.64, and 12.47 GHz, respectively. The circuit only occupies 6.70 × 8.60 mm2

An efficient higher-order PML in WLP-FDTD method for time reversed wave simulation

A higher-order PML is proposed for the WLP-FDTD method.The parameter values in the higher-order PML are optimized by MOGA.The higher-order PML is efficient in terms of absorbing performance.The WLP-FDTD method is employed to analyze the TR wave propagation problem. Derived from a stretched coordinate formulation, a higher-order complex frequency shifted (CFS) perfectly matched layer (PML) is proposed for the unconditionally stable finite-difference time-domain (FDTD) method based on weighted Laguerre polynomials (WLPs). The higher-order PML is implemented with an auxiliary differential equation (ADE) approach. In order to further improve absorbing performance, the parameter values of stretching functions in the higher-order PML are optimized by the multi-objective genetic algorithm (MOGA). The optimal solutions can be chosen from the Pareto front for trading-off between two independent objectives. It is shown in a numerical test that the higher-order PML is efficient in terms of attenuating propagating waves and reducing late time reflections. Moreover, the higher-order PML can be placed very close to the wall when analyzing the channel characteristics of time reversal (TR) waves in a multipath indoor environment. Numerical examples of TR wave propagation demonstrate the availability of the proposed method.

An Optimized Higher Order PML in Domain Decomposition WLP-FDTD Method for Time Reversal Analysis

In this paper, an efficient higher order complex frequency shifted (CFS) perfectly matched layer (PML) derived from a stretched coordinate formulation is proposed for the unconditionally stable finite-difference time-domain method based on weighted Laguerre polynomials. The higher order CFS-PML, which is implemented with an auxiliary differential equation (ADE) approach, has apparent advantage in reducing late-time reflections compared with the standard unsplit-field PML and lower order CFS-PML. Furthermore, the parameter values of stretching functions in the higher order ADE-CFS-PML are optimized with the multiobjective genetic algorithm to improve absorbing performance. The optimal solutions can be chosen from the Pareto front for trading-off between two independent objectives. The numerical formulation is derived and its absorbing ability is validated through three numerical tests. Moreover, the proposed higher order PML can be placed very close to the objects and the simulation area can be further reduced accordingly. Numerical examples of time reversal wave propagation in a real indoor environment are included to validate the accuracy and efficiency of the proposed scheme.

Miniaturized Dual-Band Bandpass Filter with Multiple Transmission Zeros Using Modified Stepped-Impedance Resonators

Abstract In this article, a modified stepped-impedance resonator is proposed in which an open stub is loaded between the low-impedance line and high-impedance line of a conventional λ/4 stepped-impedance resonator. Based on the proposed modified stepped-impedance resonators, a compact dual-band bandpass filter with an enhanced stopband is presented. Multiple transmission zeros are employed for high selectivity and a wider upper-stopband by the mixed electric/magnetic coupling and open stub loaded in the input/output port. To verify the proposed method, a new dual-band bandpass filter that operated at 2.4/5.2 GHz for wireless local area networks application is fabricated and measured. The measured result shows six finite transmission zeros in the stopband, located at 1.82, 3.14, 5.83, 7.01, 10.50, and 13.14 GHz, respectively; the circuit only occupies 0.07 λg × 0.11 λg.

Design of a Dual-Mode Tunable Wide-Bandstop Filter with Controllable Bandwidth

Abstract In this article, a compact dual-mode tunable wide bandstop filter with controllable bandwidth is presented. The proposed filter consists of an open-loop stepped-impedance resonator with a T open stub loaded. Varactor diodes Cv1 and Cv2 are loaded at two ends of the stepped-impedance resonator and the loaded T stub, respectively. By properly adjusting the capacitances Cv1 and Cv2 of the varactor diodes, the constant fractional bandwidth and constant absolute bandwidth can be achieved, respectively. A new dual-mode tunable wide bandstop filter with 61.0% constant fractional bandwidth and 2.0-GHz constant absolute bandwidth has been designed and fabricated to verify the validity of the proposed method. The measured results are in good agreement with the electromagnetic simulation.

Compact Dual-Layer Bandpass Filter Using Novel Stepped-Impedance Resonators

ABSTRACT In this article, a compact third-order bandpass filter with high-frequency selectivity using novel dual-band stepped-impedance resonators is presented. In the proposed novel dual-band stepped-impedance resonator, the conventional low-impedance stub of the stepped-impedance resonator is replaced by a closed rectangular loop. The high-impedance stub is embedded in the closed loop for more compact structure. Multiple transmission zeros are introduced near the passband to improve the frequency selectivity and stopband performance. The proposed filter was designed, simulated, and fabricated to verify the validity of the proposed method. The measured results show that the center frequency is 2.83 GHz with a fractional bandwidth of 9.32%, and five transmission zeros were introduced near the passband, which are located at 1.76 GHz with 70.2-dB rejection, 2.53 GHz with 30.7-dB rejection, 3.95 GHz with 67.2-dB rejection, 8.85 GHz with 45.5-dB rejection, and 12.3 GHz with 34.5-dB rejection, respectively. The circuit only occupies 0.11λg × 0.08λg.