Ali Ramadan

A RECONFIGURABLE U-KOCH MICROSTRIP ANTENNA FOR WIRELESS APPLICATIONS

In this paper, a low-cost multiband printed-circuit-board (PCB) antenna that employs Koch fractal geometry and tunability is demonstrated. The antenna is fabricated on a 1.6mm-thick FR4- epoxy substrate with dimensions 4cm £ 4.5cm, is microstrip-line fed and has a partial ground plane ∞ushed with the feed line. The proposed antenna is simulated using the Finite-Element Method for three difierent switching cases and the return loss is measured for each case. It is shown that the antenna can cover the bands of several applications including 3G, WiFi, WiMAX as well as a portion of the UWB range. The radiation patterns are satisfactorily omnidirectional across the antennas operation bands.

RECONFIGURABLE FILTER ANTENNAS FOR PULSE ADAPTATION IN UWB COGNITIVE RADIO SYSTEMS

The design of fllter antennas with reconflgurable band stops is proposed. They are meant for employment in ultrawideband cognitive radio (UWB-CR) systems, where unlicensed users communi- cate using adaptive pulses that have nulls in the bands used by licensed users. Neural networks or circuits implementing the Parks-McClellan algorithm can generate such pulses. With fllter antennas, reconflg- urable bandstop fllters are flrst designed, to induce adaptive nulls in UWB pulses, and are then integrated in the feed line of a UWB an- tenna. The advantages of this combination are discussed. The fllters are based on split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs). The relationship between the SRR and CSRR parameters and the stop band is also studied.

Design based on complementary split-ring resonators of an antenna with controllable band notches for UWB cognitive radio applications

This paper presents a planar antenna for employment in overlay and underlay ultra-wideband cognitive radio (UWB-CR). The antenna can be operated as ultra-wideband, for underlay CR and for sensing in the overlay CR. When used in the overlay CR mode, the proposed antenna can selectively have one, two or three notches in the WLAN, WiMAX, and U-NII bands, to prevent interference to primary users operating in these bands. The band notches are induced using complementary split-ring resonators (CSRRs), and are controlled using three electronic switches mounted over the CSRRs.

Design and ground plane consideration of a CPW-fed UWB antenna

In this paper, a novel ultrawideband (UWB) antenna with co-planar waveguide (CPW) feed is presented. The antenna is based on an egg-shaped conductor printed on a 30×40 mm2 FR4 substrate of 1.6-mm thickness. Two configurations of the antenna are studied. In the first, the ground plane features a large egg-shaped slot, and in the second, the ground plane is partial and rectangular in shape. The measured and computed return loss responses are given. Other characteristics of the antenna are computed using a finite-element-based EM solver. The radiation patterns, peak gain, and radiation efficiency of both configurations are presented and compared. The results show that the design based on the large slot yields better omnidirectional patterns and higher gains in the principal planes. The second design has slightly larger radiation efficiencies, and larger peak gains at high frequencies.

Tunable Filter-Antennas for Cognitive Radio Applications

In this paper, frequency-tunable microstrip antennas, for cognitive radio applications, are proposed. The approach is based on electrically tuning the antennas operating frequency by integrating reconflgurable band pass fllters into wideband antenna structures. The design of an open loop resonator (OLR)-based bandstop fllter, and its transformation to a bandpass fllter, are investigated flrst. Then, the incorporation of the bandpass fllter, with a wideband antenna, is detailed. The same methodology is employed to design cognitive radio pattern and polarization diversity tunable fllter-antennas. A good agreement between the simulated and measured results for the difierent fabricated prototypes is attained.

A Reconfigurable Cedar-Shaped Microstrip Antenna for Wireless Applications

This paper presents a frequency reconflgurable cedar- shaped fractal antenna. The special shape of the patch makes it simpler to integrate RF switches to connect consecutive branches. The proper activation/deactivation of the switches alters the current ∞ow and changes the resonance frequency. Simulated and measured results show the characteristics of the presented design.

A UWB antenna combined with a reconfigurable bandpass filter for cognitive radio applications

A single-port small-size antenna for cognitive radio (CR) applications is presented. The antenna is based on an ultra-wideband (UWB) design and has a reconfigurable bandpass filter integrated in its feed line. The UWB operation is required for the sensing task in a CR system. Upon activating the filter, the UWB frequency response is transformed into a tunable narrowband one, which is needed for the communication task.

A novel printed diversity antenna for WiMAX applications

In this paper a novel printed diversity antenna for WiMAX applications is proposed. The antenna consists of two identical monopoles, and operates over a wide band spanning the 2.8–4.7 GHz frequency range, over which it has high isolation of over 20 dB. The diversity performance of the antenna, which is attributed to the configuration of the slots placed in its ground plane, is assessed by calculating the envelope correlation coefficient and mean effective gain. The results show that the proposed antenna provides pattern diversity, which enables it to combat multi-path fading in channels used by WiMAX devices.

A simple estimation and verification technique for electrical characterization of textiles

In this paper, a simple method to estimate the relative permittivity εr and the tangential loss tan(δ) of wearable textiles is presented. Quarter-wavelength stub-line band-stop filters, based on jeans and cordura textiles, are designed assuming reasonable initial values of εr and tan(δ), fabricated and experimentally tested. The filter designs are then re-simulated, by tweaking the values ofεr and tan(δ), until the computed results are matched to the already obtained measured ones. The parameters εr and tan(δ) of the jeans textile are studied in the 800MHz band. Results indicate that the difference between their initial values and the obtained actual estimates is large in this band. The study is repeated for both jeans and cordura textiles in the 2.4 GHz band. In this band of interest, the deviation of the initial εr and tan(δ) from their actual values is small. To verify the reliability of the obtained estimates, jeans- and cordura-based wearable antennas are designed for operation in the 2.4 GHz band. Prototypes of these antennas are fabricated. A good agreement between measured and simulated results is revealed, thus verifying the correctness of the proposed electrical characterization method.

Design of a small printed monopole antenna for ultrawideband applications

In this paper, a small-size low-cost printed monopole antenna for ultra-wideband operation is presented. The proposed antenna, which was designed and simulated using the FEM-based HFSS, is based on a 20 mm × 40 mm × 1.6 mm FR4-epoxy dielectric, is microstrip-line fed and has a partial ground plane flushed with the feed line. To verify its frequency response, the antenna is also simulated using CST Microwave Studio, and a prototype is fabricated and the return loss is measured. A credible analogy between computed and measured return loss data is witnessed. Furthermore, the antenna shows acceptable peak gain figures, good radiation efficiency values and omnidirectional radiation patterns over its band of operation.