Tamer Aboufoul

Reconfiguring UWB Monopole Antenna for Cognitive Radio Applications Using GaAs FET Switches

A novel ultrawideband (UWB) microstrip monopole antenna with reconfigurable multiband function is presented. Reconfigurability is achieved by using GaAs field effect transistor (FET) switches to connect multiple stubs of different lengths to the main feed line of the monopole. The antenna is compact and flexible in terms of the availability of different reconfiguration bands and, most importantly, the simple biasing of the GaAs FET switches will not have a severe effect on the antenna performance. Using GaAs FET switches did not degrade the antenna radiation patterns due to the simple biasing technique and the few external biasing components needed, besides these switches did not degrade the antenna gain and efficiency due to their low insertion loss and low on resistance. When the antenna was reconfigured from UWB to work into multiple frequency bands, the total peak gain improved by 20% compared to the UWB case. In addition, the total efficiency of the antenna has not been significantly reduced in any reconfigured band, whereas the out-of-band total efficiency is hugely reduced, which highlights the filtering role of the reconfiguration process. The total dc power consumption of the antenna switches is still very low (<; 33 μW), and this will lead to simple integration of the antenna in some portable communication systems or future cognitive radio front ends.

Pattern-Reconfigurable Planar Circular Ultra-Wideband Monopole Antenna

A novel pattern-reconfigurable compact planar ultra-wideband monopole antenna is presented. By the incorporation of four p-i-n diode switches and two parasitic elements, the antennas radiation patterns can be shaped to concentrate energy in specific directions while minimising the gain in other unwanted directions without significantly affecting the impedance bandwidth of the antenna. A fully functional prototype has been developed and tested. The measured results of the return loss, radiation patterns, and realised gain verify the effectiveness of the proposed antenna configuration. The antenna switches its radiation patterns between an omni-directional mode and two directional modes with opposite directions in the operating range from 3 to 6 GHz. The proposed antenna could be a suitable candidate for advanced and smart radio applications such as cognitive radio (CR) as it can enhance the radio front-end flexibility and performance by adding the benefits of pattern diversity, specifically in multipath environments.

Pattern-Reconfigurable Microstrip Patch Antenna With Multidirectional Beam for WiMAX Application

A parasitic planar patch antenna capable of multi directional pattern reconfiguration is presented. The antenna structure consists of a driven element surrounded by four parasitic elements that act either as reflector(s) or director(s) depending on the switching arrangement. Beam reconfiguration is achieved by using four p-i-n diode switches where the effect of switching technique on the overall element performance is investigated numerically and experimentally. The proposed antenna achieves nine distinguished main beam angular positions. Moreover, the proposed antenna has achieved excellent realized gain levels at all configuration scenarios with a minimum value of 7 dBi. Simulation and measurement results show good agreement and promising applications of such antenna structure in enhanced WiMAX systems.

Reconfigurable printed UWB circular disc monopole antenna

UWB printed disk monopole antenna with embedded reconfigurable multi band function is proposed. Frequency reconfiguration is achieved by using different stubs. Reconfigurability is introduced in a way we can independently switch ON/OFF stubs of different lengths. These microstrip stubs can be connected to the partial ground or the monopole microstrip feed line. Simulation results of return loss for different switch states and radiation patterns at different frequencies are also presented. Simulation results are verified with measurements.

Single-element reconfigurable planar ultra wideband antenna for cognitive radio front end

A simple UWB microstrip monopole antenna with reconfigurable multi band function is presented. Reconfigurability is achieved by using multiple switches to control the length of different printed stubs. Reflection coefficient, radiation patterns and gain measurements are presented to verify the simulations. Finally the total efficiency of the antenna is characterized and it is compared to the total efficiency of the original UWB antenna.

Reconfigured and Notched Tapered Slot UWB Antenna for Cognitive Radio Applications

A compact reconfigurable and notched ultra-wideband (UWB) tapered slot antenna (TSA) is presented. The antenna reconfiguration operation principle relies on 2 mechanisms: in the first mechanism a resonator parasitic microstrip line electrically coupled to the TSA is used to notch the TSA at a specific frequency and the second mechanism relies on changing the input impedance matching of the antenna by means of changing the length of a stub line extended from an additional tiny partial ground on the back side of the antenna. The reflection coefficient, radiation patterns, and gain simulations and measurements for the proposed antenna are presented to verify the design concepts featuring a very satisfactory performance. Total efficiency simulations and measurements are also presented to highlight the filtering performance of the reconfigured antenna. When the antenna was reconfigured from the UWB to work into multiple frequency bands, the radiation patterns were still the same and the total peak gain has slightly improved compared to the UWB case. In addition, when the antenna operated in the notched mode, the gain has significantly dropped at the notch frequency. The simplicity and flexibility of the proposed multimode antenna make it a good candidate for future cognitive radio front ends.

Pattern reconfigurable planar UWB antenna array for future cognitive radio portable devices

A novel pattern reconfigurable planar ultra wideband 2×2 antenna array is presented. This UWB planar array has a high gain that can be useful in sensing the spectrum for cognitive radio applications. The array can provide basic pattern reconfiguration to enhance the scanning and the communication performance in cognitive radio operation by limiting interference coming from specific directions. The reflection coefficient, radiation patterns, gain and total efficiency simulations of the UWB mode and the reconfiguration modes are presented. The pattern reconfigurablity of the proposed antenna is also investigated by simulating indoor coverage and power received in a realistic environment for different pattern configurations.

A planar dual fed UWB monopole antenna with polarization diversity for cognitive radio sensing

A dual fed compact ultra-wideband microstrip monopole antenna with reconfigurable polarisation capability is presented. By having two feeds to excite the patch from two different locations, the polarisation can be changed from vertical to horizontal. The level of coupling between the input ports can be significantly reduced if the two 50 Ω feed lines are from different transmission line technology (e.g. One is coplanar waveguide -CPW and the other is Microstrip -MS). The RF switches used for simulating the switching mechanism are currently copper bridges, for proof of concept. Simulation results of refelction coefficient for each port, transmission coefficient between the two ports, radiation patterns, and peak gain are all presented featuring very good performance. The proposed antenna can be very helpful in cognitive radio (CR) systems by decreasing the potential for signals to be undetected due to polarisation blindness when sensing the surrounding RF environment.

Polarisation reconfigurable ultra wideband antenna for cognitive radio devices

A novel compact planar ultra wideband monopole antenna with reconfigurable polarisation capability is presented. By adding two rectangular slots near the edges of the patch, the antenna can be switched from linear polarisation (LP) to right hand circular polarisation (RHCP) or left hand circular polarisation (LHCP). The frequency band at which the antenna is radiating circular polarisation (CP) can also be controlled by carefully changing the lengths of the etched slots embedded in the patch using RF switches. The simulated and measured results of the reflection coefficient and axial ratio verified the effectiveness of the proposed antenna configuration. The proposed antenna demonstrates suitable candidate for cognitive radio (CR) systems by adding the benefits of polarisation diversity.

Reconfigurable notched Tapered Slot Ultra Wideband Antenna for Cognitive Radio applications

A compact reconfigurable Tapered-Slot Ultra Wideband Antenna that can be useful in Cognitive Radio applications is presented. The antenna reconfiguration operation principle relies on 2 concepts; the first concept depends on using a resonator parasitic structure electrically coupled to the TSA antenna to notch the TSA at a specific frequency and the second concept relies on changing the input matching of the antenna by means of changing the length of a stub line extended from an additional tiny partial ground on the back side of the antenna. Reflection coefficient, radiation patterns and gain simulations for the proposed antenna are presented to verify the design concepts featuring a very satisfactory performance.