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Author

Ghaffer I. Kiani

Bio: Ghaffer I. Kiani is an academic researcher from King Abdulaziz University. The author has contributed to research in topics: Microwave & Frequency response. The author has an hindex of 14, co-authored 51 publications receiving 856 citations. Previous affiliations of Ghaffer I. Kiani include Commonwealth Scientific and Industrial Research Organisation & Macquarie University.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, a two-layer absorb/transmit frequency selective surface (FSS) is proposed to achieve good frequency stability for both horizontally and vertically polarized waves incident normally or at oblique angles.
Abstract: Oblique incidence performance of a novel two-layer absorb/transmit frequency selective surface (FSS) is investigated. The FSS has good frequency stability for both horizontally and vertically polarized waves incident normally or at oblique angles. Due to its transmission for 900/1800/1900 MHz mobile bands and good absorption for 5 GHz waves, it has the potential as a security wall or isolator for 5 GHz WLAN systems. The absorption in the stop band helps reduce additional WLAN multipath fading caused by conventional reflecting FSS designs. The first layer of the FSS consists of conventional conducting cross dipoles having a circular aperture in the centre, while the second layer uses resistive cross dipoles. Moreover, the conducting cross dipoles have been sandwiched between two dielectric sheets to achieve a stable response for different angles of incidence. The periodicity of both FSS layers is the same while the distance between the two layers is reduced to one eighth of the free-space wavelength. This reduction leads to a more compact design compared to the conventional Salisbury screen, while still achieving acceptable absorption in the stopband. Both theoretical and experimental results are presented to confirm the performance of the absorb/transmit FSS.

129 citations

Journal ArticleDOI
TL;DR: A novel absorb/transmit frequency selective surface (FSS) capable of absorbing, as opposed to reflecting, WLAN signals while passing mobile signals is presented for 5-GHz wireless local area network (WLAN) applications.
Abstract: A novel absorb/transmit frequency selective surface (FSS) is presented for 5-GHz wireless local area network (WLAN) applications. The novelty of the design is that it is capable of absorbing, as opposed to reflecting, WLAN signals while passing mobile signals. The FSS consists of two layers, one with conventional conducting cross dipoles and the other with resistive cross dipoles. The absorption of the WLAN signal is important to reduce additional multipaths and resultant fading otherwise caused by the FSS. The structure has good transmission characteristics for 900/1800/1900-MHz mobile bands and performs well for both horizontal and vertical polarizations. The distance between the two layers is less than a quarter free-space wavelengths. Theoretical and experimental results are presented.

126 citations

Journal ArticleDOI
TL;DR: In this article, a frequency selective surface (FSS) that is electronically switchable between reflective and transparent states is tested, which can be used to provide a spatial filter solution to reconfigure the electromagnetic architecture of buildings.
Abstract: A frequency selective surface (FSS) that is electronically switchable between reflective and transparent states is tested. It can be used to provide a spatial filter solution to reconfigure the electromagnetic architecture of buildings. The FSS measurements show that the frequency response of the filter does not change significantly when the wave polarization changes or the angle of incidence changes up to ±45° from normal. The FSS is based on square loop aperture geometry, with each unit cell having four PIN diodes across the aperture at 90 degree intervals. Experiments demonstrated that almost 10 dB additional transmission loss can be introduced on average at the resonance frequency, for both polarizations, by switching PIN diodes to on from off state.

123 citations

Journal ArticleDOI
TL;DR: In this article, a bandpass aperture type cross-dipole frequency selective surface (FSS) is designed and etched in the coatings of energy-saving glass to improve the transmission of useful signals while preserving IR attenuation as much as possible.
Abstract: Energy-saving glass is becoming very popular in building design due to their effective shielding of building interior against heat entering the building with infrared (IR) waves. This is obtained by depositing a thin layer of metallic-oxide on the glass surface using special sputtering processes. This layer attenuates IR waves and hence keeps buildings cooler in summer and warmer in winter. However, this resistive coating also attenuates useful microwave/RF signals required for mobile phone, GPS and personal communication systems etc. by as much as 30 dB. To overcome this drawback, a bandpass aperture type cross-dipole frequency selective surface (FSS) is designed and etched in the coatings of energy-saving glass to improve the transmission of useful signals while preserving IR attenuation as much as possible. With this FSS, 15-18 dB peak transmission improvement can be achieved, for waves incident with ±45° from normal for both TE and TM polarizations. Theoretical and measured results are presented.

114 citations

Journal ArticleDOI
TL;DR: In this paper, a single-layer, bandpass, active FSS with four PIN diodes is presented, which shows good angle of incidence stability for TE incidence, at the operating frequency of 2.45 GHz.
Abstract: A single-layer, bandpass, active FSS is presented. It shows good angle of incidence stability for TE incidence, at the operating frequency of 2.45 GHz. It is based on circular loop aperture with each unit cell having four PIN diodes. A novel method for dc biasing is used. About 12 dB average variation in transmission loss, between ON and OFF states, has been experimentally achieved at 2.45 GHz.

48 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: In this article, the authors discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year.
Abstract: Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year. Moreover, we place emphasis on windows that maintain transparency in the visible region so that additional energy is not required to retain natural illumination. We discuss a number of ways to fabricate windows which remain as permanent infrared control elements throughout the year as well as windows which can alter transmission properties in presence of external stimuli like electric fields, temperature and incident light intensity. We also show the potential impact of these windows on energy saving in different climate conditions.

877 citations

Journal ArticleDOI
TL;DR: In this article, a frequency selective radome is presented, acting as a pass band filter at a given frequency band, while behaving as an absorber above the transmission band, which is obtained by a metallic FSS realized through a compact interdigitated Jerusalem cross element characterized by a very large rejection band.
Abstract: A frequency selective radome is presented, acting as a pass band filter at a given frequency band, while behaving as an absorber above the transmission band. The pass band behavior is obtained by a metallic FSS realized through a compact interdigitated Jerusalem cross element characterized by a very large rejection band. The metallic FSS is used as the ground plane of a thin wideband absorber based on resistive high-impedance surfaces within the total reflection band. The outer absorber reduces the signature of the antenna system when the radome is illuminated by out of band signals. The resistive FSS which comprises the absorber is designed so to minimize losses within the transmitting band of the radome. The composite structure is thoroughly analyzed by an efficient equivalent circuit approach and by full-wave numerical simulations.

584 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

Journal ArticleDOI
TL;DR: Using simulations, it has been shown that the smart environment based on intelligent walls can react to the immediate demands of an indoor wireless system, control radio coverage and, consequently, influence the overall system performance.
Abstract: This study introduces the concept of an intelligent wall as an autonomous part of a smart indoor environment for cognitive wireless networks. Here, an intelligent wall is a wall inside a building equipped with an active frequency-selective surface, simple low-cost sensors and a cognitive engine with machine-learning ability. Using simulations, it has been shown that the smart environment based on intelligent walls can react to the immediate demands of an indoor wireless system, control radio coverage and, consequently, influence the overall system performance. The concept of the intelligent walls is described and evaluated based on a simple implementation of an arrangement of two intelligent walls in a conference centre scenario. Artificial neural networks were employed in the cognitive engine. Elementary orthogonal frequency division multiple access static system simulations are used to analyse the influence of the smart environment on the system performance. Results are discussed in detail and typical characteristics of the aforementioned system are derived and summarised.

209 citations

Journal ArticleDOI
TL;DR: In this article, an efficient approach to achieve the shielding effectiveness (SE) by using a frequency-selective surface (FSS) is presented, which consists of cross dipoles and rings printed on the opposite sides of a single-layer FR-4 substrate, exhibits a wide, 7.5GHz stopband to provide simultaneous shielding in both X and Ka-bands.
Abstract: An efficient approach to achieve the shielding effectiveness (SE) by using a frequency-selective surface (FSS) is presented. This FSS, which consists of cross dipoles and rings printed on the opposite sides of a single-layer FR-4 substrate, exhibits a wide, 7.5-GHz stopband to provide simultaneous shielding in both X- and Ka-bands. Experimental results confirm SE of the prototype over an ultra-wide band with more than 20-dB measured attenuation. The design is compact and suitable to provide shielding against the radiation interference caused by license-free and other radio systems.

190 citations