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152 results on '"Sim, Chow-Yen-Desmond"'

2. An Aperture-Shared Vehicular Antenna With Large Frequency Ratio and Pattern Diversity for Future 5G Millimeter-Wave and DSRC Applications

Author

Feng, Botao, Li, Haoming, Rao, Liwei, Ding, Xiao, Sim, Chow-Yen-Desmond, and Chung, Kwok L.

Abstract

A vehicular antenna with diverse radiation patterns is proposed for both the dedicated short range communications (DSRC) and the fifth-generation (5G) millimeter-wave (MMW) communications. The proposed antenna mainly comprised a 2 × 2 MMW subarray, an 8-element DSRC subarray and a corresponding 5-port feeding network. The radiating patches of the MMW subarray are excited by two pairs of coaxial-to-substrate integrated waveguide (SIW) transition (CST) feeding networks that are comprised of two 3-dB couplers, two 90$^{\circ }$-phase shifters, and four power dividers (PDs), which provide in-phase and differential-phase output signals to achieve single-beam and conical-beam radiation patterns. On the other hand, the 8 monopoles of the DSRC subarray arranged around the aforementioned MMW radiator are excited by a coaxial-to-SIW-to-coaxial transition (CSCT) feeding network that includes a 1-to-4 SIW PD and four 1-to-2 microstrip PDs to form an omni-directional radiation and achieve a large frequency ratio (LFR). Measured results indicate that wide bandwidths of 15.44% (24.14-28.18 GHz), 16.09% (24.29-28.54 GHz), 15.01% (23.85-27.72 GHz), and 14.29% (24.05-27.75 GHz) with corresponding high peak gains of 10.97$\pm$1.03 dBi, 11.71$\pm$1.32 dBi, 10.84$\pm$1.00 dBi, and 11.29$\pm$1.28 dBi are obtained by the four MMW subarray ports, while a bandwidth of 11.40% (5.46-6.12 GHz) with an azimuth-plane gain of 0.64 dBi and a peak gain of 4.29$\pm$0.19 dBi for the DSRC subarray port are also obtained. Besides, low cross-polarization (X-pol) levels of −24 dB and −27 dB are achieved for the two subarrays, respectively.

Published
2024
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3. Wideband Low-Profile Endfire Antenna With Polarization Reconfigurability

Author

Jaiswal, Rahul Kumar, Aakash, Ojha, Anuj Kumar, Sim, Chow-Yen-Desmond, and Srivastava, Kumar Vaibhav

Abstract

A wideband, low-profile endfire antenna with polarization reconfiguration is proposed. The endfire antenna can be electronically switched among the left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP) using six PIN diodes in conjunction with biasing lines. The proposed antenna consists of a wideband half-mode substrate integrated waveguide (HMSIW) cavity (vertically polarized magnetic dipole) and tapered switchable electric dipole (horizontally polarized) with a feed line. The impedance bandwidth of the HMSIW cavity is increased by combining the resonance frequencies of quasi-TE1,0.5,0 mode with quasi-TE3,0.5,0 mode by placing the two slotted pairs at the null of quasi-TE3,0.5,0 mode. At LHCP/RHCP states, the proposed endfire antenna exhibited a stacked 10-dB impedance bandwidth (IBW) of 11.66% (6.54-7.35 GHz) and a 3-dB axial ratio bandwidth (ARBW) of 11.23% (6.515-7.29 GHz) with a peak gain of approximately 4.20 dBic. When switched to the LP state, it shows a 10-dB impedance bandwidth of 11.58% (6.87-7.715 GHz) with a peak gain of 5.35 dBi. Therefore, it can exhibit good effective bandwidths (stacked 10-dB IBW and 3-dB ARBW) of 5.93% (6.87-7.29 GHz) and 10.84% (6.54-7.29 GHz) across the three polarization states (LP/RHCP/LHCP) and two CP states (RHCP/LHCP), respectively.

Published
2024
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4. The propagation of VHF and UHF radio waves over sea paths

Author

Sim, Chow Yen Desmond, Warrington, E. M., and Stocker, A.

Subjects
621.38411
Abstract

This thesis is concerned with the statistical studies of VHF/UHF radio wave propagation over the sea path at the limits of line-of-sight range. The objective is to provide a set of data that leads to the understanding of the characteristic of VHF/UHF radio wave over the sea path. A series of experiments were conducted using two paths of around 33 and 48 km across the English Channel. These two paths are between fixed land-based locations that provide an unobstructed condition. This allows a prolonged period of data collection under several sea states and atmospheric conditions without the heavy expenses of ship borne trial. The statistic studies showed that the high signal strength variation observed at both receiving sites are the results due to ducting and super-refraction. It occurred around 43 to 76% and 31 to 48% of the total time (percentage of days) during summer 2001 and 2002 respectively. In comparison, the total time was below 10% during winter period. Across the Jersey-Alderney path (48 km), high fading phenomenon was observed which is a result due to interference fading between the diffracted and troposcattered signal. The statistics showed that it occurred at around 35 to 55% of the total times during summer with an average fading range of around 10 and 7 dB during autumn and summer respectively, with an average fading period of around 7 seconds. The results from simulation showed that when the VHF/UHF signal reaches the radio horizon, the dominant propagating mechanism is smooth earth diffraction. Beyond the radio horizon, the attenuation rate increases dramatically and at a certain distance (depending on the frequency, antenna height and seasonal condition), the diffracted signals will be weaken and the troposcatter effect will become the dominant propagating mechanism.

Published
2002

11. Fringing Aperture Modulation of Transverse Electric Mode Excited Microstrip Antenna for Wireless Underground Sensor Networks

Author

Annavarapu, Sarath Kumar, Ghosh, Abhijyoti, Singh, Lourembam Lolit Kumar, Chattopadhyay, Sudipta, and Sim, Chow-Yen-Desmond

Abstract

In the present era, the key challenge for a low-frequency planar antenna applied to a wireless underground sensor network (WUSN) and other underground wireless communication is to achieve positive gain with good efficiency. Besides that, a relatively wider bandwidth with more than one operating frequency is desirable for operational versatility. In this work, a simple artificial magnetic conductor (AMC)-integrated rectangular microstrip antenna (RMA) of size $0.28\lambda _{0} \times 0.28\lambda _{0} \times 0.07\lambda _{0}$ is employed. By meticulously exploiting a dual-periodic AMC along with dielectric strips (AMC radiating patch and AMC ground plane) and proper utilization of an L-probe feed, two resonances at 572 MHz (low band) and 768 MHz (high band) can be yielded with a wide bandwidth of around 12%. Unlike the classical RMA design, a transverse electric (TE) mode excited RMA is proposed. The proposed antenna can also achieve good positive gains of 4.3 dBi (572 MHz) and 6.1 dBi (768 MHz) across both bands with an efficiency of 71% and 75%, respectively.

Published
2023
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22. A Compact Vehicle-Mounted Garden-Themed Artistic Antenna With Isolation Improvement for 2G/3G/LTE/5G Sub-6-GHz/WiFi/Bluetooth Communications

Author

Feng, Botao, Yang, Baifa, Sim, Chow-Yen-Desmond, Deng, Li, Zhou, Zhengdong, and Ding, Xiao

Abstract

A multi-band vehicle-mounted garden-themed antenna with isolation improvement for 2G/3G/LTE/5G sub-6 GHz/WiFi/Bluetooth is proposed in this paper. This antenna is mainly comprised of three printed circuit board (PCB) substrates. For good isolation level, two pavilion-shaped 4G-band (including the 2G/3G/LTE frequency bands) patches and two tree-shaped 5G-band (including the 5G sub-6 GHz bands) patches are diagonally placed at the four corners of the top-layer substrate, whereas the other two tree-shaped 5G-band patches and a peach-shaped WiFi-band patch, are arranged in a line on the bottom substrate. To further improve the isolation, two fence posts are arranged between the neighboring antenna elements on the bottom substrate. Finally, a flower-shaped patch array printed on the middle substrate is employed to reduce the mutual coupling factor, broaden the frequency bandwidth, improve the peak gain and the radiation efficiency, especially for the 5G-band antenna element printed on the bottom-layer substrate. Characteristic mode analysis (CMA) method is introduced to the antenna radiation pattern and frequency bandwidth. The measured results showed good impedance bandwidths of 20.69$\%$ (0.78-0.96 GHz) and 106.8$\%$ (1.37-4.51 GHz) for 2G/3G/LTE bands, 71.81$\%$ (2.41-5.11 GHz) for 5G bands, and 84.34$\%$ (2.4-5.9 GHz) for WiFi bands are achieved with a compact size of 0.338 $\times\; 0.130\;\times$ 0.094 $\lambda _{0}^{3}$ (free-space wavelength at the starting frequency). Furthermore, across the above bands of interest, an isolation level of better than 16 dB can be achieved.

Published
2023
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24. Dual-feed dual-polarized patch antenna with low cross polarization and high isolation

Author

Sim, Chow-Yen-Desmond, Chang, Chun-Chuan, and Row, Jeen-Sheen

Subjects
Antennas (Electronics) -- Design and construction, Mobile communication systems -- Research, Wireless communication systems -- Research, Electromagnetic waves -- Polarization, Electromagnetic waves -- Measurement, Wireless technology, Business, Computers, Electronics, Electronics and electrical industries
Published
2009

35. Ultra-Wideband RCS Reduction of Circular Polarization Slot Antenna Array Based on Polarization Conversion Structures and Frequency-Selective Rasorber.

Author

Yu-Xin Zhang, Yong-Ling Ban, and Sim, Chow-Yen-Desmond

Subjects
SLOT antenna arrays, CIRCULAR polarization, RADAR cross sections, ULTRA-wideband radar, COPLANAR waveguides, BANDPASS filters, QUALITY factor, ANTENNA arrays
Abstract

This paper proposes an absorption-transmission-absorption (A-T-A) type frequency-selective rasorber (FSR) with high selectivity that is loaded above a polarization conversion structure (PCS) and applied to a circular polarization (CP) slot antenna array for ultra-wideband radar cross section (RCS) reduction. Outside the operational frequency band (out-of-band) of the antenna, the energy of the incident electromagnetic (EM) wave is directly absorbed by the FSR, whereas from within the operational frequency band (in-band) of the antenna, the incident EM wave penetrates the FSR and irradiates it on the PCS placed on the lower layer of the FSR structure, which meets the phase cancellation condition and is diffused at the same time, thereby realizing the in-band RCS reduction. Due to the lower insertion loss in the passband, higher quality factor (Q value) in the transmission band, and wider absorption band, the proposed FSR can minimize the gain loss (only 0.2 dB) of the CP slot antenna array and widen the RCS reduction bandwidth to 135.5% (5–26 GHz). In addition, due to the central symmetry of the FSR and PCS structures, the CP slot antenna array has monostatic RCS reduction performance for both horizontally polarized (HP) and vertically polarized (VP) incoming waves. [ABSTRACT FROM AUTHOR]

Published
2021
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46. Wideband CPW-Fed Oval-Shaped Monopole Antenna for Wi-Fi 5 and Wi-Fi 6 Applications.

Author

Kulkarni, Jayshri and Sim, Chow-Yen-Desmond

Subjects
MONOPOLE antennas, ANTENNA design, WIRELESS LANs, RADIATORS, ANTENNAS (Electronics), OMNIDIRECTIONAL antennas, RADIATION
Abstract

A wideband coplanar waveguide (CPW) fed monopole antenna designed for Wi-Fi 5 and Wi-Fi 6 applications is proposed. The proposed antenna (main radiator) has a designed footprint of only 20 × 8.7 × 0.4mm³, which is composed of an oval-shaped ring radiator with three concentric rings and a double-T structure loaded with a J-shaped slot. The main novelty of this work is that the measured wideband operation of 34.5% (5.15-7.29 GHz) is contributed by only a single resonance at 6.2GHz, conforming to the bandwidth requirement of Wi-Fi 5 (5.15-5.85 GHz) and Wi-Fi 6 (5.925-7.125 GHz). Furthermore, the proposed antenna also exhibits good radiation characteristics, including a gain around 2.25 dBi, a radiation efficiency above 80%, a total efficiency above 70%, and omnidirectional radiation patterns with a low magnitude of cross polarization throughout the bands of interest. [ABSTRACT FROM AUTHOR]

Published
2020

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