Raheel M. Hashmi

Wideband High-Gain EBG Resonator Antennas With Small Footprints and All-Dielectric Superstructures

A novel method is presented to design single-feed high-gain EBG resonator antennas (ERAs) with significantly wider bandwidths. Dielectric contrast is introduced to 1-D EBG superstructures composed of unprinted dielectric slabs, and the thicknesses of each of these slabs is optimized to achieve a wideband defect mode in a unit-cell model. Next, antennas are designed and their superstructure areas are truncated to increase the antenna bandwidth and aperture efficiency while decreasing antenna footprint. We demonstrate that a small superstructure area increases the 3-dB bandwidth of ERAs significantly. A prototype ERA designed with a single feed and superstructure area as small as 1.5 λ0 ×1.5 λ0 has a measured 3-dB directivity bandwidth of 22% at a peak gain of 18.2 dBi. This prototype antenna was made out of three slabs of different dielectric constants, two of them touching each other. This prototype demonstrates more than 85% reduction in the ERA footprint alongside a drastic improvement in bandwidth over the 3%-4% measured bandwidth of the classical single-feed ERAs with unprinted slabs.

A Class of Extremely Wideband Resonant Cavity Antennas With Large Directivity-Bandwidth Products

Extremely wideband resonant cavity antennas (RCAs) with large directivity-bandwidth products (DBPs) are presented. Their distinct feature is a single-slab superstrate that has a permittivity gradient in the directions transverse to the antenna axis. The application of such a superstrate in a single-feed RCA improves the DBP by a factor of three or more as compared with superstrates composed of uniform dielectric slabs. Their very small area enables an antenna designer to achieve unprecedented figures of DBP per unit area, from a simple planar antenna. Prototype RCAs have been fabricated and measurements have validated the concept. A measured 3-dB directivity bandwidth of 52.9% was demonstrated with a measured directivity of 16.4 dBi for an RCA that has a very small total footprint area of 1.54

Improved Secure Network Authentication Protocol (ISNAP) for IEEE 802.16

\lambda_0^2

Towards secure wirelessMAN: Revisiting and evaluating authentication in WiMAX

at the lowest operating frequency (2.84

Wideband high-gain EBG resonator antenna employing an unprinted composite superstrate

\lambda_{0,c}^2

Directive beaming with lens-like superstates for low profile Fabry-Perot cavity antennas

at the center frequency). This represents an increase of 90% over the previous best measured RCA directivity bandwidth of 28%.

Achieving high directivity-bandwidth through flat GRIN superstrates in Fabry-Perot cavity antennas

Security is amongst one of the major issues in Broadband Wireless Access (BWA) Networks. After the launch of the IEEE 802.16 standard (WiMAX), a number of security issues were reported in several articles. Ever since the beginning, work has been in progress for the neutralization of these identified threats. In this paper, the analysis of the authentication protocols implemented in WiMAX has been presented along with the description of the threats posed to them. The paper also describes security sub-layer and limitations of the existing architecture. An approach has also been presented for the prevention of these threats like the avoidance of replay; suppress replay and man-in-the-middle attacks. The proposed approach enhances the network security and strengthens it by resynchronization of the Subscriber Station with the Base Station.

Effect of truncating the superstructures in broadband Fabry-Pèrot cavity antennas

Wireless communication is highly susceptible to security outbreaks with shear advancement in signal processing technology followed by immense deployment of high-speed mobile communication networks. Pitfalls in current architecture of IEEE 802.16 or Worldwide Interoperability for Microwave Access (WiMAX) have been put forth in recent literature, based on analytical reasoning and design methodologies. With identification of these vulnerabilities, some solutions have also been proposed for their rectification; however, the experimental assessment of these solutions has not been carried out in appropriate manners to justify the satisfaction of constraints. In this paper, we present a generic methodology to simulate and analyze the authentication protocols in WiMAX based on obtained results. We focus on the 1st and 2nd version of Privacy & Key Management (PKM) Protocols, which are implemented in the WiMAX architecture at present and compare their performance characteristics with another proposed solution ISNAP; which claims to eradicate most of the existing threats with introducing minimum overheads. The performance evaluation of these protocols has been carried out by simulating the behavior of BS and SS nodes in real-time wireless network using Linux based hosts. This work intends to establish the formal basis to justify the claims put forth in the specification of ISNAP against PKM v1 & v2.

A planar feeding technique for wideband, low-profile resonant cavity antennas

A single-feed high-gain EBG resonator antenna with extremely wideband performance is presented. The bandwidth is enhanced through a novel composite superstrate made from a combination of unprinted dielectric slabs with uniform thickness. The composite superstrate leads to wide defect-mode bandwidth and offers slowly increasing reflection phase profile over a wide frequency band. A single slot is used to excite the cavity. Peak antenna gain of 17.17 dBi with half-power gain bandwidth of 33.9% centered at 12.6 GHz is predicted. More than 100% increase in 3-dB directivity bandwidth with 55% reduction in aperture size is obtained as compared to conventional designs.

Arrays of high aperture efficiency wideband EBG resonator antennas

Lens-like superstrates designed to exhibit a spatial reflectivity map are studied for use as the partially reflecting surface in Fabry-Perot cavity antennas. Profile reduction is obtained by using only a single dielectric layer of such surfaces which is found to provide improved performance than the multi-layered superstrates. The use of such surfaces results in a varied reflectivity within the cavity and makes the boresight emissions spatially coherent. This provides high boresight directivity with improved bandwidth characteristics. With this surface as super-strate of a resonant cavity antenna, performance is evaluated for a single feed exciting the cavity. Highly directive beams with 17.6dBi peak directivity and fairly suppressed side lobes are obtained over a very wide bandwidth with only a single layer lens-like surface.