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Now showing items 1 - 16 of 43

  • The Grey Wolf Optimizer and Its Applications in Electromagnetics

    Li, Xun   Luk, Kwai Man  

    The grey wolf optimizer(GWO) is a newly developed swarm intelligence-based optimization technique that mimics the social hierarchy and group hunting behavior of grey wolves in nature. Here, a detailed introduction of the GWO algorithm is given, after which, three sets of examples are investigated: first, numerical experiments on four benchmark functions are conducted; second, the GWO is applied to the synthesis of linear arrays with the aim of reducing the peak sidelobe level under various constraints; and finally, the performance of the GWO is further verified on the optimization design of two representative antennas, namely, a dual-band E-shaped patch antenna and a wideband magneto-electric dipole antenna. The results show that the GWO is capable of outperforming or providing very competitive results compared with some well-known metaheuristics such as the genetic algorithm, particle swarm optimization, and differential evolution. Thus, it may serve as a promising candidate for handling electromagnetic problems.
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  • 3D Printed High Gain Complementary Dipole/Slot Antenna Array

    So, Kwok Kan   Luk, Kwai Man   Chan, Chi Hou   Chan, Ka Fai  

    By employing the complementary dipole antenna concept to the normal waveguide fed slot radiator, an improved antenna element with wide impedance bandwidth and symmetrical radiation patterns is developed. This is achieved by mounting two additional metallic cuboids on the top of the slot radiator, which is equivalent to adding an electric dipole on top of the magnetic dipole due to the slot radiator. Then, a high-gain antenna array was designed based on the improved element and fabricated, using 3D printing technology, with stable frequency characteristics operated at around 28 GHz. This was followed by metallization via electroplating. Analytical results agree well with the experimental results. The measured operating frequency range for the reflection coefficient <=3D -15 dB is from 25.7 GHz to 29.8 GHz; its corresponding fractional impedance bandwidth is 14.8%. The measured gain is approximately 32 dBi, with the 3 dB beamwidth around 4 degrees.
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  • A 5G Wideband Patch Antenna With Antisymmetric L-shaped Probe Feeds

    Mak, Ka Ming   Lai, Hua Wah   Luk, Kwai Man  

    A dual-polarized patch antenna element fed by a pair of antisymmetric L-shaped probes is proposed. The designed twin L-shaped probe feeding structure is able to introduce feed capacitance to the antenna for broadband operation. The lengths of the two L-shaped probe feeds are identical, but the feeds are antisymmetric. This feeding design can minimize the unwanted radiation from the probe effectively. The dual-polarized antenna can be operated in the frequency band 1580-2750 MHz, which covers the current mobile communication systems, 3G and 4G and higher band frequencies. A prototype with dual slanted +/- 45 degrees polarization has been fabricated for validation. Both the simulation and measured results show that the proposed antenna has wide bandwidth of 54% (SWR < 2) with desirable directional radiation patterns in the vertical and horizontal planes, as well as high isolation better than -30 dB between the two input ports.
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  • Polarization Reconfigurable Circular Patch Antenna With a C-Shaped

    Mak, Ka Ming   Lai, Hau Wah   Luk, Kwai Man   Ho, Kin Lun  

    Polarization reconfigurable circular patch antenna with a C-shaped slot is proposed in this communication. It is demonstrated that by introducing a reconfigurable C-shaped slot in a circular patch antenna, the polarization of the radiation of the antenna, operating either in a linearly or circularly polarized mode, can be switched effectively. It is switched between vertical and horizontal polarizations for a linearly polarized mode and switched between left hand circularly polarization and right hand circularly polarization for a circularly polarized mode. The polarization reconfigurable characteristic is realized by controlling the states of the two switching diodes mounted over a concentric circular slot incorporated on the patch, so as to vary the orientation of the C-slot. Prototypes of both linear polarization and circular polarization designs were developed and the performances were validated against measurements. Both antennas exhibit over 20% impedance bandwidth (standing wave ratio (SWR) < 2) and perform broadside radiation over the operating band. The 3-dB axial ratio bandwidth for the circularly polarized case is 4%.
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    Mak, Ka Ming   Lai, Hau Wah   Luk, Kwai Man  

    A simple dual polarized circular slot antenna array for satellite TV is proposed in this letter. The antenna array consists of sixteen elements and each of them is excited by an olive-shaped feeding probe. The proposed antenna array has measured gains of 18 dBi for both polarizations and an input ports isolation excess 30 dB. The antenna can totally cover the bandwidth of the TV satellite application, which is from 11.7 to 12.2 GHz. The antenna is also very low profile, which is much thinner than other conventional stripline-fed planar array antennas. (C) 2017 Wiley Periodicals, Inc.
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  • A Compact and Reconfigurable Circularly Polarized Complementary Antenna

    Wu, Fan   Luk, Kwai Man  

    A circular-polarization-reconfigurable complementary antenna with compact size is presented. The proposed antenna has a low-profile planar structure that exhibits an omnidirectional circularly polarized (CP) radiation pattern achieved by combining a printed electric dipole and a quarter-wave shorted microstrip patch. By manipulating the dc biasing voltages, the operation of the antenna can be switched between left-hand circular polarization and right-hand circular polarization. Moreover, by using the meandering line methodology, the lateral dimension of the printed electric dipole is reduced by 25% compared to the conventional design. A prototype of the proposed structure is designed and fabricated for potential use in multifunction application. Measured results are in good agreement with simulation. The CP radiation feature and polarization reconfigurability are also sustained by measurement.
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  • Wideband Tri-Polarization Reconfigurable Magneto-Electric Dipole Antenna

    Wu, Fan   Luk, Kwai Man  

    A wideband polarization reconfigurable magnetoelectric (ME) dipole antenna is presented. The proposed ME dipole is able to work in three different polarization states including one linear polarization and two orthogonal circular polarizations. The linearly polarized operation mode is based on a Gamma-probe-fed ME dipole of four-sectional structure. And perturbation is introduced by connecting the + 45 degrees (or -45 degrees) diagonal parts of the four sections with a diode embedded line to realize circularly polarized (CP) radiation. A simple biasing network driven by one 1.5 V dc source is designed to manipulate the state of four p-i-n diodes and hence switch the polarization. The presented reconfigurable ME dipole demonstrates distinctive features such as stable gain, high front-to-back ratio, and symmetric radiation pattern. Furthermore, a wide effective bandwidth (BW) in terms of the overlapped frequency region within which the impedance BW (S-11 < -10 dB) for all polarization states and the axial ratio (AR) BW (AR < 3) for both CP states are sustained simultaneously is obtained. An antenna prototype based on the proposed design is fabricated and tested for verification. Measured results show an effective BWof 7.9%(with an overlapped impedance BW of 31% and overlapped AR BW of 7.9%), comparatively high gain of 9 +/- 0.8 dBi, and high efficiency of 80%-90% for all polarizations across the operating band.
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  • Magnetoelectric Dipole Antennas With Dual Open-Ended Slot Excitation

    Lai, Hau Wah   So, Kwok Kan   Wong, Hang   Chan, Chi Hou   Luk, Kwai Man  

    Designs of novel magnetoelectric dipole antennas excited by dual open-ended slots for both single and dual linear polarizations are presented in this paper. The antenna can be interpreted as a dual complementary source that exhibits lower profile and higher gain while maintaining excellent radiation characteristics of the original ME dipole, including wideband, low back radiation, and high polarization purity. In addition, high isolation is obtained in the dual polarization design. All the above characteristics show that the proposed antennas can be regarded as potential candidates for various wireless applications. Prototypes are fabricated and measured to confirm the simulation results.
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  • Shorted Bowtie Patch Antenna With Less Susceptibility to Surface Condition

    Lai, Hau Wah   Mak, Ka Ming   Luk, Kwai Man  

    An antenna with less susceptible to surface condition is proposed in this communication. By adding a pair of parasitic shorted patches at the side of a shorted bowtie patch antenna, very low back radiation can be achieved within entire operating bandwidth. Front-to-back ratio, impedance bandwidth and peak gain are over 30 dB, 12.23% and 6.5 dB, respectively, and confirmed by measurement. The proposed antenna has thickness and projection area of only 0.08.0 and 0.77.0 x 0.77 lambda(0). A prototype for 5.8-GHz ISM band application (5.725-5.875 GHz) is also designed. Experimental results confirmed that the reflection coefficient, gain, and radiation pattern have been less affected by mounting on different types of surfaces like human wrist, phantom hand, phantom head, or large metal sheet. Its potential applications include 5.8GWi-Fi, on-body communication, biometric applications, wearable healthcare, and biomedical devices.
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  • Single-Layer Single-Patch Dual-Band and Triple-Band Patch Antennas.

    Mok, Wing Chi   Wong, Sai Hoi   Luk, Kwai Man   Lee, Kai Fong  

    Recently, it was shown that a dual- or triple-band patch antenna can be designed by cutting U-slots in the patch of a broadband antenna, and the method was applied to the L-probe fed patch, the M-probe fed patch, coax-fed stacked patches, and aperture coupled stacked patches. All these cases involve either a rather complicated feed, or more than one patch, or more than one layer. In this communication, this method is applied to a broadband U-slot patch antenna. When one additional U-slot patch is cut in the patch, a dual-band antenna results. When two additional U-slot patches are cut in the patch, a triple-band antenna results. The advantages of the resultant configurations are (1) the feed is simple and (2) the structures remain single-layer and single-patch. Both simulation and measurement results are presented to demonstrate the feasibility of this design.
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  • A Low-Profile Magneto-Electric Dipole Antenna

    Ge, Lei   Luk, Kwai Man  

    A new low-profile magneto-electric dipole antenna composed of a horizontal planar dipole and a vertically oriented folded shorted patch antenna is presented. The antenna is simply excited by a coaxial feed without the need of an additional balun. A rectangular cavity-shaped reflector is introduced for enhancing the stability in radiation pattern over the operating frequencies. A parametric study is performed for providing practical design guidelines. A prototype with a thickness of 0.173 lambda was designed, fabricated and measured. Results show that an impedance bandwidth of 54.8% for SWR <= 1.5 from 1.88 to 3.3 GHz was achieved. Stable radiation pattern with low cross polarization, low back radiation and an antenna gain of 8.6 +/- 0.8 dBi was found over the operating frequencies. In addition, the antenna is d.c. grounded, which satisfies the requirement of many outdoor antennas.
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  • Phase-Shifted Fiber Bragg Gratings for Terahertz Range

    Zhou, Shu Fan   Reekie, Laurence   Chow, Yuk Tak   Chan, Hau Ping   Luk, Kwai Man  

    We demonstrate notch filters in polymer fiber Bragg gratings for use at THz frequencies. The filters were created by introducing a pi/2-phase shift into narrowband Bragg gratings manufactured in Topas polymer subwavelength fiber. Experimental results are presented and compared with a model of the filter. Excess resonator loss of the notch filter is discussed.
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  • 60 GHz Plated Through Hole Printed Magneto-Electric Dipole Antenna

    Ng, Kung Bo   Wong, Hang   So, Kwok Kan   Chan, Chi Hou   Luk, Kwai Man  

    A wideband unidirectional antenna, which is composed of a planar electric dipole and a magnetic dipole formed by a vertically-oriented shorted patch antenna, is presented for millimeter wave applications. The antenna is realized by a plated through hole printed technique with the use of a microwave substrate and is excited by a T-shaped coupled strip feed. An impedance bandwidth of 33% (S-11 <= -15 dB from 50 to 70 GHz is achieved. Stable radiation patterns with low cross polarizations and a stable antenna gain of similar to 7.5 are achieved across the entire operating bandwidth. This single antenna element yields advantages of wideband, good directional radiation pattern and low fabrication cost.
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  • Multiobjective Optimal Antenna Synthesis for Microwave Wireless Power Transmission

    Li, Xun   Luk, Kwai Man   Duan, Baoyan  

    In microwave wireless power transmission, the end-to-end transmission efficiency is of major concern and should be improved to reduce costs. Toward this end, high beam collection efficiency (BCE) as well as a flat beam pattern is desired. Previous studies have mainly focused on methods aimed at maximizing the BCE alone or only to obtain a flat beam. However, single-objective optimization fails to provide decision makers with enough choices in the tradeoff between BCEs and flat beam patterns. To overcome such a problem, the aperture amplitude distribution is approximated with the Taylor series expansion, and then a multiobjective optimization model is established. Here, the objectives are twofold. The first is to maximize the attainable BCE; and the second is to achieve a flat beam. Afterward, a novel algorithm named multiobjective multiverse optimizer is employed. To investigate the validity of the proposed method, numerical experiments on continuous apertures and array antennas are carried out.
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  • Design of Low-Profile Multi-Band Half-Mode Substrate-Integrated Waveguide Antennas

    Yang, Xujun   Ge, Lei   Ji, Yuan   Zeng, Xierong   Luk, Kwai Man  

    An effective method of designing low-profile cavity-backed multi-band antennas is introduced based on half-mode substrate-integrated waveguide (HMSIW) technique. By loading U-shaped strips outside the radiating aperture of an HMSIW cavity, additional resonances can be produced, thus leading to the realization of multi-band capability. An inset microstrip feedline is employed to energize the HMSIW cavity, whereas the loaded strips are excited through proximity coupling from the radiating aperture of the HMSIW. The proposed antenna is constructed on a single-layered substrate with a low profile of 0.024 free-space wavelength. To validate the multi-band responses, prototypes of the single-band HMSIW antenna as well as dual-band and triple-band antennas are fabricated and measured, respectively. The experimental results show that the proposed antennas possess advantages of stable radiation patterns with a gain of 5-5.9 dBi as well as acceptable front-to-back (FTB) ratio of larger than 10 dB over different frequency bands.
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  • Multiobjective Optimal Antenna Synthesis for Microwave Wireless Power Transmission

    Li, Xun   Luk, Kwai Man   Duan, Baoyan  

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