Adaptive Antenna Arrays for Ad-Hoc Millimetre-Wave Wireless Communications

New technologies that employ millimetre-wave frequency bands to achieve high speed wireless links are gaining more attention (Dyadyuk et. al., 2007, 2009b, 2010a; Hirata et. al., 2006; Lockie & Peck, 2009; Kasugi et. al., 2009; Wells, 2009) due to increasing demand for wideband wireless communications. Very wide uncongested spectrum is available in the E—bands (71-76 GHz and 81-86 GHz) recently allocated for wireless communications in USA, Europe, Korea, Russia and Australia. The E-band provides an opportunity for line-of – sight (LOS) links with higher data rates, well suited for fibre replacement and backhaul applications. Future mobile and ad-hoc communications networks will require higher bandwidth and longer range. An ad-hoc or mobile (e.g. inter-aircraft) network that relies on high gain antennas also requires beam scanning. Adaptive antenna arrays have found a wide rage of applications and are becoming essential parts of wireless communications systems (Abbaspour-Tamijani & Sarabandi, 2003; Do-Hong & Russer, 2004; Gross, 2005; Guo, 2004; Krim & Viberg, 1996; Mailloux, 2005, 2007; Rogstad et al., 2003; Singh et al., 2008). While the spectrum available in the millimetre-wave frequency bands enables multi-gigabit-per second data rates, the practically achievable communication range is limited by several factors. These include the higher atmospheric attenuation at these frequencies and limited output power of monolithic microwave integrated circuits (MMIC) (Doan et al., 2004; Dyadyuk et al., 2008a; Kasper et al., 2009; Floyd et al., 2007; Reynolds et. al., 2006; Vamsi et. al., 2005, Zirath et al., 2004) due to physical constraints. Therefore, the performance of the ad-hoc or mobile millimetre-wave networks requires enhancement by using spatial power combining antenna arrays

Single-Layer Bandpass Active Frequency Selective Surface

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

Antennas for future very-high throughput wireless LANs

We describe a possible very-high throughput system for future indoor wireless local area networks (WLAN) with data rates up to 40 Gbps. We show that to implement such networks, using components available in the foreseeable future, moderate gain multiple beam antennas will be required. Several antennas that can potentially meet the gain requirements and multiple beam functionality are proposed.4 page(s

Multilayer frequency-selective-surface reflector for constant gain over ultra wideband

In this paper the gain enhancement of an ultra-wideband (UWB) antenna, achieved using an appropriately designed multi-layer frequency selective surface (FSS) reflector is demonstrated. The proposed novel FSS reflects effectively in-phase over a bandwidth of about 145%. Consequently, significant enhancement in antenna gain has been achieved with a low-profile configuration without compromising the impedance bandwidth of the UWB antenna. The composite structure is compact, with a total height of λ/4 where λ is the free-space wavelength at the lowest operating frequency of 3 GHz. Experimental results show an impedance bandwidth of 145% BW with FSS and 149% without FSS. The antenna gain is maintained around 9.3 dBi from 3 to 15 GHz with a variation of ±0.5 dB. The predicted wideband antenna performance and gain enhancement due to the presence of the FSS reflector are discussed.3 page(s

A Reconfigurable high-gain partially reflecting surface antenna

A high-gain partially reflective surface (PRS) antenna with a reconfigurable operating frequency is presented. The operating frequency is electronically tuned by incorporating an array of phase agile reflection cells on a thin substrate above the ground plane of the resonator antenna, where the reflection phase of each cell is controlled by the bias voltage applied to a pair of varactor diodes. The new configuration enables continuous tuning of the antenna from 5.2 GHz to 5.95 GHz using commercially available varactor diodes, thus covering frequencies typically used for WLAN applications. Both the PRS and phase agile cell are analyzed, and theoretical and measured results for gain, tuning range, and radiation patterns of the reconfigurable antenna are described. The effect of the varactor diode series resistance on the performance of the antenna is also reported.9 page(s

Frequency selective surface absorber using resistive cross-dipoles

A novel frequency selective surface (FSS) absorber is presented for 5 GHz WLAN applications. It consists of a conventional conducting cross-dipole FSS and a matching resistive FSS. This thin configuration has shown good stopband and absorption characteristics for 5 GHz WLAN signals while allowing 900/1800/1900 MHz mobile signals to pass through almost unattenuated. Preliminary theoretical results on absorption and transmission are described.4 page(s

A novel absorb/transmit FSS for secure indoor wireless networks with reduced mulltipath 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.3 page(s

Active Frequency Selective Surface Design for WLAN

1 page(s

A simple thin antenna with an enhanced gain for MB-OFDM UWB systems

4 page(s