Y. Tawk

Reconfigurable Antennas for Wireless and Space Applications

Reconfigurable antennas, with the ability to radiate more than one pattern at different frequencies and polarizations, are necessary in modern telecommunication systems. The requirements for increased functionality (e.g., direction finding, beam steering, radar, control, and command) within a confined volume place a greater burden on todays transmitting and receiving systems. Reconfigurable antennas are a solution to this problem. This paper discusses the different reconfigurable components that can be used in an antenna to modify its structure and function. These reconfiguration techniques are either based on the integration of radio-frequency microelectromechanical systems (RF-MEMS), PIN diodes, varactors, photoconductive elements, or on the physical alteration of the antenna radiating structure, or on the use of smart materials such as ferrites and liquid crystals. Various activation mechanisms that can be used in each different reconfigurable implementation to achieve optimum performance are presented and discussed. Several examples of reconfigurable antennas for both terrestrial and space applications are highlighted, such as cognitive radio, multiple-input-multiple-output (MIMO) systems, and satellite communication.

A New Reconfigurable Antenna Design for Cognitive Radio

This letter presents a new antenna design suitable for cognitive radio communication. It consists of two structures incorporated together into the same substrate. The first structure is an ultrawideband (UWB) antenna covering the spectrum from 3.1-11 GHz for channel sensing. The second structure is a frequency reconfigurable triangular-shaped patch for establishing communication with another RF device. The antenna reconfigurability is achieved via a rotational motion. A prototype antenna was fabricated and tested in order to validate the suggested method.

Implementation of a Cognitive Radio Front-End Using Rotatable Controlled Reconfigurable Antennas

This communication presents a new antenna system designed for cognitive radio applications. The antenna structure consists of a UWB antenna and a frequency reconfigurable antenna system. The UWB antenna scans the channel to discover “white space” frequency bands while tuning the reconfigurable section to communicate within these bands. The frequency agility is achieved via a rotational motion of the antenna patch. The rotation is controlled by a stepper motor mounted on the back of the antenna structure. The motors rotational motion is controlled by LABVIEW on a computer connected to the motor through its parallel port. The computers parallel port is connected to a NPN Darlington array that is used to drive the stepper motor. The antenna has been simulated with the driving motor being taken into consideration. A good agreement is found between the simulated and the measured antenna radiation properties.

Optically Pumped Frequency Reconfigurable Antenna Design

This letter presents a novel frequency reconfigurable antenna design using photoconductive silicon elements as optical switches. By illuminating these silicon elements with light of suitable wavelength, their physical properties can be altered from that of a semiconductor to almost metal-like, which in turn alters the radiation properties of the antenna structure. Our work builds on similar work conducted in the past, but goes further by demonstrating a new geometry for coupling the light energy onto the silicon switches, thereby facilitating conformal integration of such reconfigurable antennas into next-generation wireless devices. In this letter, we first present a theoretical model characterizing the behavior of silicon substrate under light illumination. We then present experimental results on a stripline circuit employing a single silicon switch under light illumination and compare the theoretical model to experimental measurements. Finally, a novel frequency reconfigurable antenna design utilizing our new coupling geometry is designed, and its experimentally measured RF performance is compared to numerical simulations.

Reconfigurable Antennas: Design and Applications

The advancement in wireless communications requires the integration of multiple radios into a single platform to maximize connectivity. In this paper, the design process of reconfigurable antennas is discussed. Reconfigurable antennas are proposed to cover different wireless services that operate over a wide frequency range. They show significant promise in addressing new system requirements. They exhibit the ability to modify their geometries and behavior to adapt to changes in surrounding conditions. Reconfigurable antennas can deliver the same throughput as a multiantenna system. They use dynamically variable and adaptable single-antenna geometry without increasing the real estate required to accommodate multiple antennas. The optimization of reconfigurable antenna design and operation by removing unnecessary redundant switches to alleviate biasing issues and improve the systems performance is discussed. Controlling the antenna reconfiguration by software, using Field Programmable Gate Arrays (FPGAs) or microcontrollers is introduced herein. The use of Neural Networks and its integration with graph models on programmable platforms and its effect on the operation of reconfigurable antennas is presented. Finally, the applications of reconfigurable antennas for cognitive radio, Multiple Input Multiple Output (MIMO) channels, and space applications are highlighted.

Demonstration of a Cognitive Radio Front End Using an Optically Pumped Reconfigurable Antenna System (OPRAS)

A cognitive radio front end using an optically pumped reconfigurable antenna system (OPRAS) is investigated. The scheme consists of a ultrawideband antenna and a reconfigurable narrowband antenna in close proximity to one another. The narrowband reconfigurability is achieved by a integrating laser diodes within the antenna structure to control the switching state of photoconductive silicon switches. This scheme has the advantage of eliminating the use of optical fiber cables to guide light to the switches, and enables easier integration of the reconfigurable antenna in a complete communication system. The performance of the proposed technique is presented, and comparisons are made to other commonly used switching techniques for reconfigurable antennas, such as techniques based on PIN diodes and RF microlectromechanical systems integration. The application of this antenna design scheme serving as the receive channel in a cognitive radio communication link is also demonstrated.

A Varactor-Based Reconfigurable Filtenna

This letter details a new reconfiguration technique for implementing frequency-tunable bandpass filters. This is achieved by changing the filter total capacitance via an integrated varactor within its structure. The reconfigurable bandpass filter is then incorporated within the feeding line of a printed antenna to form one structure. This combination allows the tuning of the antenna operating frequency without incorporating active components and biasing lines on the antenna radiating surface. The integrated antenna-filter combination, with filtering ability while preserving the radiation performance, is referred to as a “filtering antenna” or a filtenna. A prototype for the reconfigurable filter and the reconfigurable filtenna are fabricated and tested. A good agreement is found between the simulated and the measured data.

Cognitive-radio and antenna functionalities: A tutorial [Wireless Corner]

This paper discusses the fundamental principles of a cognitive-radio RF system. The key points required to achieve a true cognitive-radio device are outlined. The operation of a cognitive-radio system is mainly divided into two tasks. In the first task, a cognitive-radio device searches and identifies any part of the spectrum that is not occupied. The second task consists of achieving an optimal mode of communication by allocating the appropriate channels to be used. In this paper, the RF requirements required to operate a cognitive-radio device are detailed. Such a device can adopt one of two scenarios of a cognitive-radio system: the ?interweave? or ?underlay? mode of operation. For both scenarios, a cognitive cycle is followed. This cycle consists of the following four steps: (1) observe, (2) decide, (3) act, and (4) learn. A cognitive-radio engine is responsible for managing and integrating these four functions together into a single cognitive-radio device. In this tutorial, the realization of the four functions of a cognitive-radio cycle are detailed for both types of cognitive radio, and various RF front-end examples are presented and discussed.

Reconfigurable Filtennas and MIMO in Cognitive Radio Applications

In this paper cognitive radio is described, discussed and compared with software defined radio (SDR). The two types of cognitive radio are presented and examples on both spectrum interweave and spectrum underlay cognitive radio antenna systems are detailed. Reconfigurable filtennas are proposed as communicating antennas in a MIMO setting for both cases of cognitive radio. The benefits of resorting to filtennas as well as to MIMO configuration is shown and discussed herein. The various antenna examples are designed, tested and compared with each other. Conclusions are drawn based on the presented results.

CubeSat Deployable Antenna Using Bistable Composite Tape-Springs

In this letter, a new conductive composite tape-spring is proposed for CubeSat deployable antennas that is constructed using a glass fiber reinforced epoxy with an embedded copper alloy conductor. The tape-spring is bistable enabling the antenna to be elastically stable in both the deployed and stowed states. A dipole antenna is designed, simulated, and tested to prove the viability of the electrical properties of this material.