S. Hemmady

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.

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.

Implementation of a cognitive radio front-end using optically reconfigurable antennas

This paper presents a reconfigurable radio front-end antenna scheme suitable for cognitive radio communications. Our scheme comprises of an UWB antenna structure (antenna-1) and a reconfigurable antenna structure (antenna-2) incorporated together on the same substrate. The UWB antenna-1 is used for channel sensing while the reconfigurable antenna-2 is designed to frequency-hop between pre-determined communication channels. The reconfiguration of antenna-2 is achieved by using photoconductive switches which are selectively illuminated by laser light from a series of integrated laser diodes. A prototype was fabricated and tested to prove the applicability of our proposed radio front-end scheme.

Optically pumped reconfigurable antenna systems (OPRAS)

This paper presents a new reconfigurable antenna design using optical switching which overcomes any biasing associated with standard MEMs and PIN switches. In our approach, the switching elements comprises of doped silicon, and the change in the elements RF conductivity from that of a semiconductor material to that of a metal-like material is achieved upon exposure to a laser light coupled through an optical fiber cable. Two prototype antennas are fabricated and tested to demonstrate the proposed approach. Good qualitative agreement is observed between the simulated and measured data.

Measuring the transition switching speed of a semiconductor-based photoconductive switch using RF techniques

This paper presents a new technique for measuring the switching speed of reconfigurable antenna systems driven by semiconductor-based photoconductive switches. Laser diodes are integrated within a stripline transmission line in order to efficiently illuminate the incorporated photoconductive switches. An experimental setup and measurement technique for estimating the ON←→OFF transition speed of the photoconductive switches, driven by a pulsed laser source, are presented.

A cognitive radio antenna design based on optically pumped reconfigurable antenna system (OPRAS)

This paper presents a new antenna scheme for cognitive radio communication. The antenna structure consists of two ports. The first antenna port is a UWB structure for channel sensing while the second one is a reconfigurable structure for communication. The reconfigurability is based on integrating laser diodes within the antenna substrate in order to activate the photoconductive switches. A prototype was fabricated and tested. A good agreement between the simulation and the measurement data is noticed. A coupling of less than −20 dB is achieved between the 2 antenna ports.

Recent advances in high power microwave sources and the science of electronics in extreme electromagnetic environments at the university of new mexico

The University of New Mexico (UNM) has two research thrusts in high power electromagnetics: (i) the development of novel sources of high power microwave (HPM) radiation with ever-increasing beam-to-microwave conversion efficiency in the frequency range from 1 GHz to over 100 GHz, and (ii) the development of physics-based predictive models on how electronics (and software execution) are affected when they are exposed to fluctuating voltages (in the microwave frequencies) that stress their operation slightly beyond specification. This paper summarizes recent advances in these two areas.

The effect of feeding techniques on the bandwidth of millimeter-wave patch antenna arrays

Antenna design at E-band frequencies is recently gaining more interest with the development of automotive radar applications and with research focusing on the possibility of using this frequency band for cell phone and data communication. At E-band frequencies, typical coaxial connectors cannot be used to feed printed antennas because their operation is limited to frequencies below 26.5 GHz. The use of other feeding techniques is needed. This paper discusses the effect of two different feeding techniques on the bandwidth of an array of rectangular patches used for automotive radar applications. The first feeding technique uses an RF-Probe which will be mounted on a transition from a grounded CPW (GCPW) to a microstrip line. The second feeding technique uses a rectangular waveguide to microstrip line transition. Both feeding techniques designs are easy to fabricate and do not incorporate any via holes connecting the upper ground plane to the lower ground plane. The array designed to test the differences caused by the feeding techniques consists of 64 elements of rectangular patches, with inset feeds, radiating at a center frequency of 73 GHz. A corporate feed is used to feed the elements of the array in phase. Both feeding techniques are used for comparison. It is shown that the bandwidth of the antenna array fed using GCPW is 3.75 GHz while it is 800 MHz for an antenna array fed using a rectangular waveguide (WR-12). Thus, feeding with an RF probe allows the array to exhibit a bandwidth that is 4.6875 times greater than the bandwidth of the antenna array fed using a rectangular waveguide (WR-12). The difference in the gain between the two arrays is negligible. The radiation pattern exhibits two main lobes in the 45o direction in the E-plane in both designs. The implementation and testing of the waveguide feeding technique is carried out at 34 GHz and show good agreement with simulated results.

An experimental setup for measuring the tuning time of an optically pumped frequency reconfigurable antenna system

This paper presents an experimental setup for measuring the tuning time of an optically pumped reconfigurable antenna system. The reconfigurability in the antenna operating frequency is obtained by integrating silicon switches within its structure. The activation of this type of switching elements is obtained by integrating laser diodes with the antenna structure. A prototype antenna is fabricated and used to determine the time needed to tune its operating frequency.