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Richards, Theory and experiment on microstrip antennas, IEEE Trans Antennas Propagat AP-27 (1979), 137–145. © 2002 Wiley Periodicals, Inc. ANTENNA INTEGRATION WITH A WAVEGUIDE PHOTODETECTOR FOR HIGH CAPACITY WIRELESS COMMUNICATIONS Majid M. Khodier, 1 Christos G. Christodoulou, 1 Tsai S. Liao, 2 and Paul K. L. Yu 2 1 The University of New Mexico, Department of EECE Albuquerque, NM 87131 2 University of California at San Diego Department of Electrical Engineering Received 23 April 2002 ABSTRACT: This paper proposes the integration of an antenna with a photodetector for high capacity wireless communications. A waveguide photodetector (WGPD), illuminated on the side, is used to convert the RF-modulated optical power into a microwave signal. That microwave signal is used to feed an antenna built on the same plane as the photo- detector. The WGPD is a standard p-i-n device grown on a semi-insu- lating InP. The performance of this RF/photonic antenna in the fre- quency range 17–20 GHz is studied theoretically and experimentally. An equivalent circuit model for the WGPD is developed to predict the pho- todetector impedance as a function of frequency. The photodetector is matched to the input impedance of the antenna. The agreement between measurement and the circuit model results for the WGPD impedance is very good. It is envisioned that a large number of such RF/Photonic antenna elements could be networked together into a star configuration, feeding in and out of a radio hub. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 179 –184, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 10550 Key words: waveguide photodetector; slot antenna; circuit model 1. INTRODUCTION The rapid increase in personal wireless communications and Internet access creates the urgent demand for more capacity in wireless systems. This demand is the main driving factor for the great interest in the development of wireless communications systems operating at millimeter wave frequencies and higher. The combination of photonic devices and RF components is a promising approach in increasing the capacity problems in wireless communications. The flexibility of the fiber optic sys- tems and the enormous RF signal processing capability offered by photonics are attracting a great interest in the wireless community. Fiber-optic technologies have reached the point where insertions into various commercial RF systems are a must [1– 8]. The evolution of RF/Photonics systems for wireless communications consists of three steps. The first step has been towards using photonics to replace several conventional RF components. Optical fibers, when compared to the to coaxial cable, provide a more ideal medium for broadband RF commu- nication systems. The light weight property of fibers, and their immunity from outside interference make them very critical in the development of future RF distribution systems. The second, and more difficult step, is in the seamless integration of pho- tonics and RF wireless circuits. The challenge in this step is to blend photonics and RF circuits and use them as complimentary to each other. Finally, the third step is towards the development of optically coupled antennas. In this step the aim is to elimi- nate the need of local oscillators, mixers, amplifiers and a number of other parts by directly feeding an antenna through a fiber at millimeter wave frequencies. MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 35, No. 3, November 5 2002 179