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Author

Qiang Liu

Bio: Qiang Liu is an academic researcher from Hunan University. The author has contributed to research in topics: Antenna (radio) & Wideband. The author has an hindex of 11, co-authored 44 publications receiving 641 citations. Previous affiliations of Qiang Liu include Beijing University of Posts and Telecommunications & Eindhoven University of Technology.

Papers
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Journal ArticleDOI
TL;DR: In this article, a Fabry-Perot (FP) resonator antenna with a wide gain bandwidth in the X band was proposed, which is attributed to the positive reflection phase gradient of an electromagnetic band gap (EBG) structure, constructed by the combination of two complementary frequency selective surfaces (FSSs).
Abstract: This paper presents a novel design of a Fabry-Perot (FP) resonator antenna with a wide gain bandwidth in X band. The bandwidth enhancement of the antenna is attributed to the positive reflection phase gradient of an electromagnetic band gap (EBG) structure, which is constructed by the combination of two complementary frequency selective surfaces (FSSs). To explain well the design procedure and approach, the EBG structure is modeled as an equivalent circuit and analyzed using the Smith Chart. Experimental results show that the antenna possesses a relative 3 dB gain bandwidth of 28%, from 8.6 GHz to 11.4 GHz, with a peak gain of 13.8 dBi. Moreover, the gain bandwidth can be well covered by the impedance bandwidth for the reflection coefficient ( ${\rm S} _{11}$ ) below $-10~{\rm dB}$ from 8.6 GHz to 11.2 GHz.

182 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a dual-band directional circularly polarized (CP) microstrip antenna for handheld radio-frequency identification (RFID) reader applications, which consists of a wideband dual-feed network and two stacked concentric patches assembled by two orthogonally placed vertical probes.
Abstract: This paper presents a compact 0.92/2.45-GHz dual-band directional circularly polarized (CP) microstrip antenna for handheld radio-frequency identification (RFID) reader applications. The proposed antenna comprises a wideband dual-feed network and two stacked concentric patches assembled by two orthogonally placed vertical probes. The dual-feed network feeds quadrature signals across the RFID bands between 0.92 and 2.45 GHz. The two stacked concentric patches provide resonance frequencies in fundamental mode for lower band and higher band, respectively. Additionally, the antenna features only one connection port and same sense CP radiation at two bands, beneficial to cost and complexity reductions of the dual-band front end of RFID readers. The measurement results show the performances of return loss (RL) ${>} {10}\;{\text{dB}}$ , 3-dB gain variation, and axial ratio (AR) ${ are achieved on the bands 0.911–0.933 GHz and 2.40–2.57 GHz. The measured peak gains are 3.8 dBic at 0.926 GHz and 8.9 dBic at 2.48 GHz. In addition, the antenna provides symmetrical patterns with wide-angle half-power beamwidths and wide-angle 3-dB AR beamwidths. The size of the antenna ${\text{110}} \times {\text{110}} \times {\text{6}}.{6}\;{\text{m}}{{\text{m}}^{\text{3}}}$ is much smaller than reported dual-band one port RFID directional CP reader antennas. The antenna appropriates to both ultra-high frequency (UHF) and industrial scientific and medical (ISM) bands in handheld RFID reader applications.

67 citations

Journal ArticleDOI
TL;DR: In this paper, a circularly polarized (CP) patch array antenna is proposed for ultrawideband operation by introducing weak-coupling mechanism into feeding network, feeding unit, and radiation structure, respectively.
Abstract: A circularly polarized (CP) patch array antenna is proposed for ultrawideband operation by introducing weak-coupling mechanism into feeding network, feeding unit, and radiation structure, respectively. As an example, a wideband $2 \times 2$ patch array antenna consists of a weakly coupled-line four-feed network, a coupled feeding unit, and four weakly coupled sequentially rotated symmetric hexagonal patches is designed for verification. Measured results show that the proposed antenna exhibits the 10-dB impedance bandwidth of 98% (2–5.92 GHz), 3-dB axial ratio bandwidth of 96.3% (2.15–6 GHz), and 3-dB gain variation bandwidth of 82.5% (2.65–5.95 GHz) with the peak gain of 9.5 dBic at 5.15 GHz and the maximum efficiency of 88%. By the weak-coupling method, the design achieves not only the largest CP bandwidth and the symmetric radiation patterns without any beam squint over the whole band, but also the smaller volume of ( $1.13 \times 1.13 \times 0.15$ ) $\lambda _{0}^{3}$ ( $\lambda _{0}$ is the wavelength at 4 GHz) compared with the reported patch array antennas. Therefore, the proposed CP patch array antenna is very promising for modern wireless applications such as WiFi, global navigation satellite system, and radio frequency identification systems.

65 citations

Journal ArticleDOI
TL;DR: In this article, a circular polarization (CP) and mode reconfigurable wideband orbital angular momentum (OAM) patch array antenna is presented, which can be reconfigured between the left hand CP with a mode $l = +1$ and right-hand CP (RHCP) with amode $l= -1$, over the wide impedance bandwidth of 21%.
Abstract: A circular polarization (CP) and mode reconfigurable wideband orbital angular momentum (OAM) patch array antenna is presented. The proposed design is based on a reconfigurable feed network (RFN), a direct current (dc) bias circuit, and a $2 \times 2$ patch array. By changing the dc bias voltages of p-i-n didoes, the operating state of the antenna can be reconfigured between the left-hand CP with a mode $l = +1$ and right-hand CP (RHCP) with a mode $l = -1$ , over the wide impedance bandwidth of 21%. For the two states, the measured peak gains are larger than 5.3 and 5.2 dBi, and the axial ratios in half-power main beam directions are lower than 1.29 and 1.05 dB, respectively. Different from existing OAM antennas, the diversities of polarization, frequency, and mode, as well as the CP with inherently high cross-polarization discrimination are simultaneously integrated in the proposed antenna, which serves as a good basis for improving the capacity and spectral efficiency of radio systems. In addition, the antenna features single-external input port, a simple RFN occupying a small number of diodes, and a compact size of $1.28 \times 1.28 \times 0.07 \lambda _{0}^{3}$ ( $\lambda _{0}$ is the free-space wavelength at center frequency), all of which ease implementation and reduce fabrication cost. Therefore, the proposed antenna is very promising for modern high-speed and large capacity wireless communication systems.

61 citations

Journal ArticleDOI
TL;DR: In this paper, a dual-band 0.92/2.45 GHz circularly-polarized (CP) unidirectional antenna using the wideband dual-feed network, two orthogonally positioned asymmetric H-shape slots, and two stacked concentric annular-ring patches is proposed for RF identification (RFID) applications.
Abstract: A dual-band 0.92/2.45 GHz circularly-polarized (CP) unidirectional antenna using the wideband dual-feed network, two orthogonally positioned asymmetric H-shape slots, and two stacked concentric annular-ring patches is proposed for RF identification (RFID) applications. The measurement result shows that the antenna achieves the impedance bandwidths of 15.4% and 41.9%, the 3-dB axial-ratio (AR) bandwidths of 4.3% and 21.5%, and peak gains of 7.2 dBic and 8.2 dBic at 0.92 and 2.45 GHz bands, respectively. Moreover, the antenna provides stable symmetrical radiation patterns and wide-angle 3-dB AR beamwidths in both lower and higher bands for unidirectional wide-coverage RFID reader applications. Above all, the dual-band CP unidirectional patch antenna presented is beneficial to dual-band RFID system on configuration, implementation, as well as cost reduction.

59 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a generalized sheet transition conditions (GSTC) with a bianisotropic surface perceptibility tensor model of the metasurface structure is presented.
Abstract: The paper overviews our recent work on the synthesis of metasurfaces and related concepts and applications. The synthesis is based on generalized sheet transition conditions (GSTCs) with a bianisotropic surface susceptibility tensor model of the metasurface structure. We first place metasurfaces in a proper historical context and describe the GSTC technique with some fundamental susceptibility tensor considerations. On this basis, we next provide an in-depth development of our susceptibilityGSTC synthesis technique. Finally, we present five recent metasurface concepts and applications, which cover the topics of birefringent transformations, bianisotropic refraction, light emission enhancement, remote spatial processing, and nonlinear second-harmonic generation.

147 citations

Journal ArticleDOI
TL;DR: In this paper, a chessboard arranged metamaterial superstrate (CAMS) is used to enhance the antenna gain and reduce the radar cross-section (RCS) of a Fabry-Perot (FP) resonator antenna.
Abstract: The simultaneous improvement in radiation and scattering performance of an antenna is normally considered as contradictory. In this paper, wideband gain enhancement and radar cross section (RCS) reduction of Fabry–Perot (FP) resonator antenna are both achieved by using chessboard arranged metamaterial superstrate (CAMS). The CAMS is formed by two kinds of frequency-selective surfaces. The upper surface of CAMS is designed to reduce RCS based on the phase cancellation principle, and the bottom surface is used to enhance antenna gain on the basis of FP resonator cavity theory. Both simulation and measured results indicate that compared with primary antenna, the gain of the proposed FP resonator antenna is enhanced by 4.9 dB at 10.8 GHz and the 3 dB gain bandwidth is from 9.4 to 11.1 GHz (16.58%). Meanwhile, the RCS of the proposed FP resonator antenna is reduced from 8 to 18 GHz, with peak reduction of 39.4 dB. The 10 dB RCS reduction is obtained almost from 9.6 to 16.9 GHz (55.09%) for arbitrary polarizations. Moreover, the in-band RCS is greatly reduced, owing to the combined effect of CAMS and FP resonator cavity.

137 citations

Journal ArticleDOI
TL;DR: A critical review of metasurfaces, which are planar metamaterials, can be found in this paper, where the authors discuss salient features and applications of metamurfaces; wavefront shaping; phase jumps; non-linear metasuranfaces; and their use as frequency selective surfaces (FSS).
Abstract: This paper is a critical review of metasurfaces, which are planar metamaterials. Metamaterials offer bespoke electromagnetic applications and novel properties which are not found in naturally occurring materials. However, owing to their 3D-nature and resonant characteristics, they suffer from manufacturing complexity, losses and are highly dispersive. The 2-dimensional nature of metasurfaces allows ease of fabrication and integration into devices. The phase discontinuity across the metasurface offers anomalous refraction, thereby conserving the good metamaterial properties while still offering the low-loss characteristics. The paper discusses salient features and applications of metasurfaces; wavefront shaping; phase jumps; non-linear metasurfaces; and their use as frequency selective surfaces (FSS).

136 citations

Journal ArticleDOI
TL;DR: In this paper, a flexible dual-band antenna with a metamaterial structure (MS) is presented, which makes the antenna thin and bendable, is used as the substrate for the antenna.
Abstract: A flexible dual-band antenna with a metamaterial structure (MS) is presented. Polyimide substance, which makes the antenna thin and bendable, is used as the substrate for the antenna. When the MS is placed between the antenna and the human’s forearm, the antenna gain is increased by 9.3 and 5.37 dB, and the radiation efficiency is increased by 48.4% and 35.7%, at 2.45 and 5.8 GHz, respectively. In addition, the specific absorption rate is decreased by more than 70%, considering the limitations imposed by Federal Communications Commission and the regulation of International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the frequencies cited above. The fabricated prototype of the antenna with the integrated MS was investigated by placing it on different places of human body, as also on different human bodies. The obtained results show that the proposed antenna is safe and suitable for use, in terms of the ICNIRP standards of World Health Organization.

118 citations

Journal ArticleDOI
TL;DR: In this article, a modified 2 × 2 and 3 × 3 series-fed patch antenna arrays with beam-steering capability are designed and fabricated for 28 GHz millimeter-wave applications.
Abstract: New modified 2 × 2 and 3 × 3 series-fed patch antenna arrays with beam-steering capability are designed and fabricated for 28-GHz millimeter-wave applications. In the designs, the patches are connected to each other continuously and in symmetric 2-D format using the high-impedance microstrip lines. In the first design, 3-D beam-scanning range of ± 25° and good radiation and impedance characteristics were attained by using only one phase shifter. In the second one, a new mechanism is introduced to reduce the number of the feed ports and the related phase shifters (from default number 2 N to the reduced number N + 1 in the serial feed (here N = 3) and then the cost, complexity, and size of the design. Here, good scanning performance of a range of ± 20°, acceptable sidelobe level, and gain of 15.6 dB are obtained. These features allow to use additional integrated circuits to improve the gain and performance. A comparison to the conventional array without modification is done. The measured and simulated results and discussions are presented.

113 citations