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Author

Umair Rafique

Other affiliations: Mohammad Ali Jinnah University
Bio: Umair Rafique is an academic researcher from Capital University. The author has contributed to research in topics: Antenna (radio) & Wideband. The author has an hindex of 9, co-authored 46 publications receiving 231 citations. Previous affiliations of Umair Rafique include Mohammad Ali Jinnah University.

Papers published on a yearly basis

Papers
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Proceedings ArticleDOI
01 Nov 2017
TL;DR: In this paper, an 8-element microstrip patch antenna (MPA) array for dual-band 5G communications is proposed, which is compact with size of 16× 16 mm2 at 28 and 38 GHz, respectively.
Abstract: This paper presents the design of an 8-element microstrip patch antenna (MPA) array for dual-band 5G communications. The proposed antenna array is compact with size of 16× 16 mm2 at 28 and 38 GHz, respectively. The dual-band response is achieved by etching an inverted U-shaped slot from the main radiator. It is observed from the results that the proposed array is able to provide resonance for desired frequency bands. Furthermore, the proposed antenna array exhibits omni-directional radiations and offer an acceptable gain for both frequency bands.

33 citations

Proceedings Article
11 Apr 2011
TL;DR: A frequency selective surface (FSS) with absorber characteristics is presented for 5 GHz wireless local area network (WLAN) security and has great potential to absorb WLAN signals by reducing multipath fading effects while allowing the transmission of other useful RF/microwave signals.
Abstract: A frequency selective surface (FSS) with absorber characteristics is presented for 5 GHz wireless local area network (WLAN) security. The proposed FSS has great potential to absorb WLAN signals by reducing multipath fading effects while allowing the transmission of other useful RF/microwave signals such as mobile phones, VHF/UHF TV etc. It consists of two layers, one with resistive FSS and other with conducting FSS. It has a stable frequency response for both TE and TM polarizations when the angle of incident wave is varied from 0° to 45°. Preliminary simulation results are presented.

27 citations

Proceedings ArticleDOI
20 Oct 2011
TL;DR: Better stability has been achieved for both perpendicular (TE) and parallel (TM) polarizations at 0° incident angle and better transmission and less heat loss has been analyzed and investigated in this paper.
Abstract: Focusing on the radio frequency (RF) transmission through energy saving window, this paper presents the transmission characteristics of a dual-bandpass frequency selective surface (FSS) for GSM 900 MHz and 1800 MHz frequency bands used in GSM system. Through simulation, better transmission and less heat loss has been analyzed and investigated in this paper. Better stability has been achieved for both perpendicular (TE) and parallel (TM) polarizations at 0° incident angle.

19 citations

Journal ArticleDOI
TL;DR: In this article , the design of a 4 × 4 MIMO antenna for UWB communication systems is presented, which is comprised of a fractal circular ring structure backed by a modified partial ground plane having dimensions of 30 × 30 mm2.
Abstract: The design of a 4 × 4 MIMO antenna for UWB communication systems is presented in this study. The single antenna element is comprised of a fractal circular ring structure backed by a modified partial ground plane having dimensions of 30 × 30 mm2. The single antenna element has a wide impedance bandwidth of 9.33 GHz and operates from 2.67 GHz to 12 GHz. Furthermore, the gain of a single antenna element increases as the frequency increases, with a peak realized gain and antenna efficiency of 5 dBi and >75%, respectively. For MIMO applications, a 4 × 4 array is designed and analyzed. The antenna elements are positioned in a plus-shaped configuration to provide pattern as well as polarization diversity. It is worth mentioning that good isolation characteristics are achieved without the utilization of any isolation enhancement network. The proposed MIMO antenna was fabricated and tested, and the results show that it provides UWB response from 2.77 GHz to over 12 GHz. The isolation between the antenna elements is more than 15 dB. Based on performance attributes, it can be said that the proposed design is suitable for UWB MIMO applications.

17 citations

Journal ArticleDOI
TL;DR: The proposed antenna exhibits good radiation characteristics and offers acceptable gain in the entire bandwidth, and has been observed from results that a ratio bandwidth of 66.6:1 has been achieved from 0.3 to 20 GHz.
Abstract: Abstract: In this paper, a design of beveled-shaped planar antenna has been presented for super-wideband applications. The proposed antenna consists of a beveled-shaped radiator, a tapered microstrip feed line, a partial ground plane, and two ground planes on the top side of the substrate. The top ground planes are used to match the impedance at lower frequencies and to minimize spurious radiations caused by the feed line. A tapered feed line has been utilized to enhance the overall bandwidth of an antenna. It has been observed from results that a ratio bandwidth of 66.6:1 has been achieved from 0.3 to 20 GHz. Furthermore, the proposed antenna exhibits good radiation characteristics and offers acceptable gain in the entire bandwidth.

15 citations


Cited by
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01 Jan 2016

733 citations

Journal ArticleDOI
TL;DR: In this paper, a frequency-selective rasorber (FSR) was proposed to produce a passband with small insertion loss and to reduce the reflection at frequencies below and above the passband in the meanwhile.
Abstract: A novel design of a transmission window within the absorption band of a circuit analog absorber, named as frequency-selective rasorber (FSR), is presented. Based on an equivalent circuit model, the conditions are formulated to produce a passband with small insertion loss and to reduce the reflection at frequencies below and above the passband in the meanwhile. Simple design guidelines of our proposed FSR are then developed. With loaded lumped elements, the arrays of square-loop and cross-dipole are combined to realize its implementation. It is shown through measurements that an insertion loss of 0.68 dB can be obtained at 4.42 GHz and the fractional bandwidth for at least 10 dB reflection reduction within the lower and upper frequency bands is 92.3% under the normal incidence. A good agreement between simulated and measured results validates our design.

299 citations

01 Jan 2008
TL;DR: In this article, a simple, fast and efficient method for designing wideband radar absorbers is proposed by utilizing the asymptotic behavior of such an absorber at low frequency and replacing the bandstop resonating frequency selective surfaces with low-pass capacitive ones, which can be synthesized by square patches.
Abstract: A simple, fast and efficient method for designing wideband radar absorbers is proposed. The idea is to modify the circuit analog absorber method without perturbing the bandwidth. This is done by utilizing the asymptotic behavior of such an absorber at low frequency and replacing the band-stop resonating frequency selective surfaces with low-pass capacitive ones, which can be synthesized by square patches. It is shown that higher frequencies are not influenced by these modifications. A thin wideband capacitive circuit absorber (CCA) is presented with 28% reduction of thickness and 57% increase of bandwidth in comparison to the Salisbury screen. It is also explained why some optimized metamaterial designs fail to compete with the CCA method. For high permittivity layers, it is shown that the CCA is a better solution than the Jaumann absorber and improvements both in thickness and bandwidth are possible. A three layered ultra wideband (4-24 GHz) CCA is presented with total thickness of 15.1 mm. Finally, a design capable of handling oblique angles of incidence for both polarizations and fulfilling different mechanical, thermal and fabrication constraints is given. The absorption band covers the entire C, X and Ku radar bands (4-18 GHz), showing significant improvement compared to the published circuit analog absorbers. (Less)

162 citations

Journal ArticleDOI
TL;DR: In this paper, a switchable low-profile broadband frequency rasorber/ absorber based on slot arrays is presented and investigated, which exhibits small insertion loss at the transmission window and a bandwidth around 100%.
Abstract: Switchable low-profile broadband frequency rasorber/ absorber based on slot arrays is presented and investigated. First, an equivalent circuit model is proposed to synthesize a rasorber with the transmission window within the absorption band. Based on the slot arrays, simple design guidelines for rasorber design are further developed. Low-profile broadband rasorber and high-selectivity rasorber are, respectively, designed and analyzed to verify the design strategies. Moreover, by loading the switching diodes, a switchable rasorber/absorber is proposed and analyzed, which exhibits small insertion loss at the transmission window and a bandwidth around 100% while the thickness is less than 10% of the free-space wavelength at the lowest operating frequency. Moreover, one extension of dual-polarized rasorber is also designed and analyzed to further validate the design strategy. For demonstration, the rasorber prototypes are fabricated and measured, good agreement between the simulation and measured results is observed.

156 citations

Journal ArticleDOI
TL;DR: In this paper, a compact frequency selective surface (FSS) composed of a modified swastika unit cell having the smallest dimension of 7 × 7 mm2 is proposed, aimed at the rejection of 5 GHz WLAN band.
Abstract: In this letter, a compact frequency selective surface (FSS) composed of a modified swastika unit cell having the smallest dimension of 7 × 7 mm2 is proposed. The design is aimed at the rejection of 5-GHz WLAN band. The unit-cell geometry resembles the shape of crossed dipoles to achieve compactness. The proposed FSS provides 400 MHz bandwidth with 20 dB insertion loss. The proposed design holds a stable response for TE and TM modes of polarization as well as oblique incidence angles, thus ensuring polarization and angular independent operation. The simulated results are validated with measured results obtained from the fabricated FSS.

91 citations