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Indoor Point to Point Wireless Communications System Using Microstrip Antennas
Luis Alonso-Mozqueda, Eduardo Mexía-Grano, and Alejandro García-Juárez Universidad de Sonora Departamento de Investigación en Física. Blvd. Luis Encinas y Rosales S/N, Hermosillo, Sonora, México C. P. 83000 agarcia@cifus.uson.mx

ABSTRACT
An indoor point to point wireless communications system for distributingTV signals by using microstrip antennas is presented in this paper. The experimental setup is based on a coherent demodulation scheme where the local oscillator signal used in the receiver is synchronized, in frequency as well as in phase with that used in the transmitter. Additionally to this paper, an optical heterodyne microwave generation for measuring the reflected power of the microstripantenna is presented. Keywords: Microstrip Antennas, Coherent Demodulation, Optical Heterodyne.

1. INTRODUCTION
Over the past few years, there has been an increasing effort in researching new design of indoor point to point wireless communications systems, due to connectivity that they show in a room or in a building. Currently, several companies of telecommunications use purely omni-directionalantennas in their wireless routers to transmit data to laptops in close vicinity. The properties of microstrip patch antennas and arrays with their planar configuration present an attractive option for indoor communications where the gain is considerably enhanced [1]. In this sense, an indoor point to point wireless communications system using a couple microstrip antennas for transmitting andreceiving information in a coherent demodulation scheme is proposed in this paper. The proposed experimental setup in this paper consists in recovering a baseband signal from a modulated microwave signal, which is located at 1.25GHz. In order to recover integrity of the baseband signal, the local oscillator signal used in the receiver is synchronized exactly, in frequency as well as in phase withthat generated in the transmitter. This method is known as coherent demodulation. The remainder of this paper is structured as follows. A brief theoretical description of the microstrip antennas, modulation, and the optical heterodyne technique is presented in Section 2. The experimental setup for measuring the reflected power of antennas by using optical heterodyne is described in section 3. Thewireless transmission system is described in Section 4. Finally, we show our conclusion to this work in Section 5.

2.

THEORETICAL DESCRIPTION

2.1 Antennas The antenna is a device that provides a transition from a guided wave on a transmission line to a free-space EM wave (or vice versa) [2]. A microstrip device, as shown in figure 1, consists of a sandwich of two parallel conducting layersseparated by a single dielectric substrate [3]. The lower conductor functions as a ground plate, and the upper conductor may be a simple resonant rectangular or a circular patch, a resonant dipole, or a monolithically printed array of patches or dipoles and the associated feed network.

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Figure 1. Rectangular Patch Microstrip Antenna. The properties of microstrip patch antennas andarrays with their planar configuration present an attractive option for indoor communications systems where the gain is considerably enhanced. The advantages of microstrip antennas have made them a perfect candidate for use in the wireless applications, due to their versatility, conformability, low cost and low sensitivity to manufacturing tolerances. Though bound by certain disadvantages, microstrippatch antennas can be tailored in a way so they can be used in the new high-speed broadband WLAN systems [4]. The directivity of the antenna helps to reduce the delay spread of the radio channel and the diversity of the antenna guards against fading. Since any kind of wireless communication system require a modulated signal is necessary to follow the rules and modulated the signal, that is why...