B.-Z. Wang

A Tunable Bandstop Resonator Based on a Compact Slotted Ground Structure

A new slotted ground structure featuring compact size and spurious-free passband in the context of microstrip lines is proposed. The compactness of the new structure originates from the lengthened coupling gap in the ground. The spurious-free response in a wide passband is a result of combining both narrow and wide slots in the new structure, which effectively forms a stepped-impedance slot resonator. Compared to the previously proposed dumbbell- and H-shaped defected ground structure, over 40% size reduction can be realized in the new structure. The new structure also provides flexibilities in introducing additional functionalities to the bandstop resonators. By embedding varac- tors in the slotted ground structure, tunable bandstop resonators can be implemented and 13% tuning range centered at 2.36 or 2.67 GHz have been obtained.

Compact Broadband Dual-Band Bandpass Filters Using Slotted Ground Structures

Dual-band bandpass filters featuring compact size and flexible frequency choice are demonstrated using resonators based on slotted ground structures. Two resonators based on slotted ground structures form the basis of the filter design. The resonators allow the back-to-back and face-to-face embedding configuration, hence, greatly reduces the physical size of the filters. By changing the sizes of the two resonators independently, the lower and upper resonance frequencies can be adjusted to the desired values. A dual-band broadband bandpass filter was implemented with good compactness and low insertion loss. A good agreement is obtained between the simulation and measurement results.

A Novel Ultra-Wideband Differential Filter Based on Microstrip Line Structures

A novel differential filter with ultra-wideband (UWB) response is proposed in this letter based on microstrip line structures. 180° UWB phase shifters and 360° transmission lines are employed in the design to get the 180° phase shift over broad bandwidth. In this way, the broadband conversion between in- and out-of-phase signals can be realized. Utilizing this characteristic, the undesired common-mode noises will be cancelled out at the center of the filter, while the input differential-mode signals can still propagate well. The proposed new differential filter was calculated by transmission line model, simulated by full-wave electromagnetic simulator, and validated by the measurement. The simulation and measurement results verify its good performance. It is validated that, in the proposed filter, the differential-mode signals can propagate well with UWB frequency response, while the common-mode noises are well suppressed with more than 10 dB suppression in the concerned frequency band.

A Novel Multi-Folded UBW Antenna Fed by CPW

A coplanar waveguide-fed uniplanar multi-folded slot antenna that has impedance bandwidth enough to cover UWB systems is presented. The −10 dB return loss bandwidth of the antenna spans from about 3 GHz to about 11 GHz. Parametric study is presented. Details of the proposed ultra-wideband design are described and simulation results are presented and discussed in this paper.

Novel Broadband Reflectarray Antenna with Compound-Cross-Loop Elements for Millimeter-wave Application

A novel broadband millimeter-wave reflectarray antenna composed of compound-cross-loop elements of variable lengths is proposed. Compared to the conventional single-layer reflectarray elements, the compound-cross-loop elements can realize much larger phase variation range from 0° to 465°, leading to broader bandwidth. Using this technique, a 15°-beam-steering reflectarray operating at 30 GHz is designed. The computed results demonstrate the agreement of the main beam steering with the design requirement, and a 1-dB gain bandwidth close to 25.17% is obtained. The validity of the obtained results is verified by comparing the ones generated by Ansoft High Frequency Structure Simulator (HFSS) with those produced by Ansoft Designer. The antenna is useful for millimeter-wave applications.

Dual-Band Microstrip Stepped-Impedance Bandpass Filter with Defected Ground Structure

A compact dual-band stepped impedance bandpass filter with a defected ground structure (DGS) is proposed. The half-wavelength stepped impedance resonator is adopted to result in two tunable passbands. A DGS is constructed under the two coupling stepped impedance resonators to achieve good passband performance. Compact size and high selectivity is realized with the tap input/output coupling structure. For demonstration, one RF filter operating at 2.45 and 5.2 GHz is designed. Simulated and measured results are provided.

Element-Free Galerkin Method in Electromagnetic Scattering Field Computation

In this paper, one of meshless methods named element-free Galerkin method is firstly employed to analyze electromagnetic scattering problems. Moving least-squares interpolations are used to construct the trial and test functions for the weak form. Numerical studies show that it is working and has good performance in electromagnetic scattering problems computation.

Scattering Analysis of Large-Scale Periodic Structures Using the Sub-Entire Domain Basis Function Method and Characteristic Function Method

In this paper, the sub-entire domain basis function method and characteristic function (CF) method are used to analyze scattering of large-scale periodic structures. The former can dramatically reduce the number of unknows. To reduce the time for impedance matrix generation, the CF method can be used when the distance between the source function and the testing function positions is big enough. Finally, some simulation examples are given to validate the method.

Artificial Ground Planes for Performance Enhancement of Microstrip Antennas

In this work we investigate three different artificial ground planes for microstrip antenna design, which are useful for different applications. The three different ground plane configurations studied include: (i) conventional dielectric substrate backed by a perfect conductor; (ii) a loop type of artificial magnetic conductor (AMC); and a spiral-type of AMC. Both the loop and spiral types of AMCs tend to lower the resonant frequency of the microstrip patch antenna (MPA), as compared to that of the dielectric substrate, for the linearly polarized case. However, the spiral AMC can be used to realize circular polarization as well, at a different frequency band, hence, is useful for designing dual-band dual-polarization microstrip antennas.

A Compact UWB Bandpass Filter with Wide Stopband

A compact ultra-wideband (UWB) bandpass filter is presented by using a modified stepped impedance resonator (SIR) and defected ground structures (DGSs). The modified SIR is to generate multiple-resonant peaks within the UWB passband and tighten the coupling with the feed-lines. Then, the DGSs are to enhance the coupling degree of coupled lines and realize wide stopband. From simulated and measured results, the filter shows good UWB performance, including low insertion loss within the passband, a small group delay variation, and a wide stopband with −20 dB attenuation up to 19.6 GHz.