Chang-Hong Liang

A wide-angle polarization-insensitive ultra-thin metamaterial absorber with three resonant modes

In this paper, we report the design, fabrication, and measurement of a metamaterial absorber that is constructed of a periodic array of tetra-arrow resonators (TARs) printed on a dielectric material backed by a metal ground. The TAR absorber can operate at three different resonant modes. By adjusting geometry parameters of the structure, we can obtain a dual-band, polarization-insensitive, wide-angle thin absorber or a single band but ultra-miniature absorber that corresponds to three different resonant modes. Waveguide experiments are conducted to verify the proposed designs effectively. The measurement results show that all three absorptivity peaks come near to perfection.

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

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.

Polarization Reconfigurable U-Slot Patch Antenna

A compact U-slot microstrip patch antenna with reconfigurable polarization is proposed for wireless local area network (WLAN) applications. PIN diodes are appropriately positioned to change the length of the U-slot arms, which alters the antennas polarization state. Two antenna prototypes with identical dimensions are designed, fabricated and measured. The first antenna prototype enables switching between linear and circular polarization by using a PIN diode and a capacitor located on the U-slot. The second antenna prototype uses two PIN diodes to switch between the two circular polarization senses. A good impedance match (S11 ≤-10 dB) for both linear and circular polarization is achieved from 5.725 to 5.85 GHz, a band typically used for WLAN applications, and the 3 dB axial ratio bandwidth is greater than 2.8%. Details of the simulated and measured reflection coefficient, axial ratio, gain and radiation patterns are presented.

Frequency Reconfigurable Quasi-Yagi Folded Dipole Antenna

A frequency reconfigurable planar quasi-Yagi antenna with a folded dipole driver element is presented. The center frequency of the antenna is electronically tuned by changing the effective electrical length of the folded dipole driver, which is achieved by employing either varactor diodes or PIN diodes. Two antenna prototypes are designed, fabricated and measured. The first antenna enables continuous tuning from 6 to 6.6 GHz using varactor diodes and the reflection coefficient bandwidth (≤ -10 dB) at each frequency is greater than 15%. The second antenna enables discrete tuning using PIN diodes to operate in either the 5.3-6.6 GHz band or the 6.4-8 GHz band. Similar end-fire radiation patterns with low cross-polarization levels are achieved across the entire tunable frequency range for the two antenna prototypes. Measured results on tuning range, radiation patterns and gain are provided, and these show good agreement with numerical simulations.

A Pattern Reconfigurable U-Slot Antenna and Its Applications in MIMO Systems

A new compact pattern reconfigurable U-slot antenna is presented. The antenna consists of a U-slot patch and eight shorting posts. Each edge of the square patch is connected to two shorting posts via PIN diodes. By switching between the different states of the PIN diodes, the proposed antenna can operate in either monopolar patch or normal patch mode in similar frequency ranges. Therefore, its radiation pattern can be switched between conical and boresight patterns electrically. In addition, the plane with the maximum power level of the conical pattern can be changed between two orthogonal planes. Owing to a novel design of the switch geometry, the antenna does not need dc bias lines. The measured overlapping impedance bandwidth (|S11| <; -10 dB) of the two modes is 6.6% with a center frequency of 5.32 GHz. The measured radiation patterns agree well with simulated results. The antennas are incorporated in a 2 × 2 multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system to demonstrate the improvement in system capacity. In the real-time MIMO-OFDM channel measurement, it is shown that compared to omnidirectional antennas, the pattern reconfigurable antennas can enhance the system capacity, with 17% improvement in a line-of-sight (LOS) scenario and 12% in a non-LOS (NLOS) scenario at a signal-to-noise ratio (SNR) of 10 dB.

Study on High Gain Circular Waveguide Array Antenna with Metamaterial Structure

Abstract—A new method to improve the gain of circular waveguide array antenna with metamaterial structure is presented. The electromagnetic characteristics of metamaterial and circular waveguide antenna with metamaterial structure are studied by using numerical simulation method, which are also compared with those of the conventional circular waveguide antenna. The simulation and experimental results show that this method is effective and metamaterial structure can realize congregating the radiation energy, so the gain of the antenna increases while the side lobe level decreases.

Novel Design of Dual -Mode Dual-Band Bandpass Filter with Triangular Resonators

A novel dual-mode dual-band bandpass filter based on conventional triangular dual-mode filter is designed in this paper. The filter has the characteristics of compact structure, low insertion loss and so on. Based on the current design schemes, the design of dualmode and dual-band filter can be integrated in a novel filter structure. Several attenuation poles in the stopband are realized to improve the selectivity of the proposed bandpass filter. The experimented results were in good agreement with simulated results.

Locally resonant cavity cell model for electromagnetic band gap structures

Mushroom-like electromagnetic band gap (EBG) structures exhibit unique electromagnetic properties that have found a wide range of electromagnetic device applications. This paper focuses on the local resonance behaviors of EBG structures, and a simply locally resonant cavity cell (LRCC) model for mushroom-like EBG structures is presented to gain insight to the physical mechanism of the EBG structures and the interaction of electromagnetic waves with EBG structures. The LRCC model proposes two kinds of main resonance modes: One is the mono-polarized mode that accurately predicts the position of the surface wave suppression bandgap, which is equivalent to the LC parallel resonance based on quasistatic assumption in principle, and the other is the cross-coupling polarized mode that exhibits some interesting resonant phenomena, which has not been observed previously. Parametric studies including the radius effect of the metal plated vias are effectively performed by using the LRCC model. Some numerical simulations and experiments of EBG structures, such as square, triangle, and hexagon lattices, are given to illustrate the applications and validation of LRCC model proposed by this paper.

Compact UWB Band-Notched Antenna Design Using Interdigital Capacitance Loading Loop Resonator

In this letter, a new compact ultrawideband (UWB) antenna with band-notched characteristic is proposed for UWB communication applications. By using a C-shaped ground, the overall dimension of the proposed antenna is dramatically decreased to 24 × 28 × 1 mm3. To avoid potential interferences, interdigital capacitance loading loop resonator (IDCLLR) is utilized to reject certain bands within the passband of the antenna. Due to its high capacitance, the resonator has a smaller size and forms a narrower notched band than many other structures, thus the present design effectively saves many more useful frequencies. Good agreement is achieved between the simulation and measurement, which shows that the proposed antenna has an operation frequency band from 3 to 13 GHz with good rejection to the wireless local area network bands (WLANs) (5.2- and 5.8-GHz bands).

Novel Second-Order Dual-Mode Dual-Band Filters Using Capacitance Loaded Square Loop Resonator

This paper presents a novel approach for designing dual-mode dual-band bandpass filters using capacitance loaded square loop resonators (CLSLR). The CLSLR features compactness and spurious response suppression because of the loaded capacitance. A dual-band response is obtained via an extremely large perturbation in a single resonator and second-order dual-mode dual-band filters are realized by a new cascading principle. Coupling coefficients between two resonators in both bands can be controlled independently and external quality factors are also controlled by a particularly-designed coplanar waveguide (CPW) feed line. Three types of filters are designed to validate the analysis. They are direct coupling dual-mode dual-band filter, source-load coupling dual-mode dual-band filter with a better band-to-band isolation and CPW-feed dual-mode dual-band filter with a wider bandwidth. Measured results show good agreement with the design specifications.