Ghaffer I. Kiani

A novel absorb/transmit FSS for secure indoor wireless networks with reduced multipath fading

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.

Oblique Incidence Performance of a Novel Frequency Selective Surface Absorber

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.

Switchable Frequency Selective Surface for Reconfigurable Electromagnetic Architecture of Buildings

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.

Cross-Dipole Bandpass Frequency Selective Surface for Energy-Saving Glass Used in Buildings

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.

Active frequency selective surface using PIN diodes

A novel active frequency selective surface (FSS) is presented for 2.45 GHz applications. It consists of circular aperture elements with four PIN diodes placed orthogonal to each other on FR4 substrate. The negative dc biasing is provided with cross shaped supply lines from the reverse side of the substrate, while positive biasing is provided from the front side of printed circular structure. This active FSS design enables transmission to be switched on or off at 2.45 GHz, providing high transmission when the diodes are in OFF state, and high isolation when the diodes are ON. The design also provides very good stability to oblique TE incidence, i.e perpendicular polarisation.

Transmission improvement of UMTS and Wi-Fi signals through energy saving glass using FSS

This paper presents a dual-bandpass (DBP) frequency selective surface (FSS) based on hard-coating energy saving glass (ESG). The objective of this study is to generate a novel design of FSS on ESG, which is to be used for future energy smart buildings at Edith Cowan University (ECU). The ESG is made of a transparent coating of conducting layer on glass substrate, which attenuates infrared (IR) radiations for energy saving purpose. However the coating also attenuates useful UMTS and Wi-Fi signals which are necessary for the communication systems within the University. FSS technique is used to improve transmission of RF/MW signals through ESG by generating an array of patterns in the hard coating layer. The design of the DBP-FSS presented here has achieved transmission requirements for two specific frequency bands, with stable frequency response for both transverse electric (TE) and transverse magnetic (TM) polarization at normal and oblique incidence angles up to 60°. The double square loop (DSL)-FSS sustains 92.7% efficiency of ESG by attenuating IR radiations. This design methodology can be adapted as a general reference, which is suitable for applications under similar circumstances. Optimized design and theoretical results are presented.

Design of a bandpass FSS on dual layer energy saving glass for improved RF communication in modern buildings

A bandpass FSS design is presented for dual-layer energy saving glass panels, with the aim to improve RF communication in modern buildings. The proposed FSS design provides satisfactory transmission from 0.5 to 2 GHz. This design has several advantages over recently proposed dual-band FSSs: (a) its transmission bandwidth is significantly wider; (b) it does not block important communication signals such as GSM around 1800 MHz; and (c) it secures 2.45 GHz WLAN signals by confining them to the interior of the building.

Design of RF/Microwave efficient buildings using frequency selective surface

A band-pass frequency selective surface (FSS) which is designed on energy saving glass (ESG) with a layer of hard coating to improve the transmission of RF/Microwave signals through modern buildings is presented. A square loop and top loaded cross dipoles FSSs are combined to produce a dual band-pass filter, to improve the transmission of the most common UMTS and Wi-Fi signals, while maintaining the IR insulation properties of the ESG. An optimized design is presented, which attenuates less than 10 dB within the required microwave bands, while only reducing both the total coating area and IR attenuation by 12.35%. A stable response is achieved between 0° – 60° incident angles, for both TE and TM polarizations. Parametric studies on geometrical dimensions, substrate permittivity and thickness also help clarify the effects of these parameters upon the overall performance of FSS on hard coating ESG and the process of FSS design optimization.

Enhancing RF/microwave efficient transmission through energy saving glass windows using Frequency Selective surface

Recently the use of energy-saving glass windows in building design has become very popular. These are used to prevent transmission of infrared radiation into the buildings. Such windows have a thin metal-oxide coating deposited on one side of float glass which attenuates the infrared waves. Although these windows have been quite successful in attenuating IR due to coating, attenuation also occurs for the useful microwave GSM, GPS and other desired signals resulting in poor communication. This paper presents an FSS to improve the transmission of RF/microwave signals through ESG while keeping IR attenuation to an acceptable level. Preliminary theoretical results are presented.

Transmission analysis of energy saving glass windows for the purpose of providing FSS solutions at microwave frequencies

An inherent transmission problem associated with modern energy-saving glass windows is analyzed. These windows are used in building design to provide thermal insulation which keeps the interior warmer in the winter and cooler in the summer. This thermal insulation is achieved by employing a very thin layer of metallic oxide on one side of the ordinary (float) glass. This layer attenuates infrared waves while remaining transparent to ultraviolet frequencies. But this metallic oxide coating also attenuates the transmission of useful RF/microwave signals (GSM, GPS etc) through the glass window. We have investigated the transmission of microwave frequencies through OptithermtradeSN glass window manufactured by Pilkington. At average, about 30 dB attenuation is observed from 800 MHz to 6 GHz for both TE and TM polarizations at normal incidence. Theoretical and measured results are presented.