Antena

Simulation of a GPS antenna located at the roof of an automobile


M. Tecpoyotl-Torres, J. G. Vera-Dimas, and J. A. Damián-Morales

Center for Research of Engineering and Applied Sciences, (CIICAp) University of Morelos State (UAEM), 62209,Av. Universidad No. 1001, Col. Chamilpa, Cuernavaca, Mor., Mexico.
tecpoyotl@uaem.mx , gvera@uaem.mx , jdamian@uaem.mx


Abstract:.The highcompetitive environment of the automotive industry has made it one of the productive sectors more preoccupied in the realization of research and implementation of technological developments. Among them, there are navigation systems for vehicles, installed at least in one version of their models. These systems are formed by a global position system (GPS), with a pre-charged base of maps and highways in orderto locate de vehicle. For the reception of the GPS signals, circularly polarized patch antennas are used, which must be designed to operate at 1.57 GHz.
This work is focused on the analysis of a circular antenna performance, designed for GPS, by means of simulation, considering the following cases: antenna without radome, antenna with acrylic radome, and finally antenna on the roof of theautomobile, considering the effect of the complete chassis. The simulation is carried out with the software CADFEKO.

Keywords: Patch antennas, CADFEKO, Rogers RT/Duroid 5880 and circular polarization.


1. Introduction

Various types of microstrip antennas have been developed for use in mobile communication systems due to: their characteristics of small sizes, lightweight, low profileand low cost [1]. One of the most important mobile communication systems is the satellite-based global position system (GPS), which began as a military project and now is used commercially on a large scale.
In the case of the automotive sector, its high competitive environment forces it to develop and to implement a large number of technological advances, among them, the navigation systems, whichare composed by a GPS and a pre-charged base of maps and highways in order to locate de vehicles. The main advantages are: reduction in time of journey, in consume of combustible, and in emission of contaminant gases [2]. Other application of the GPS technology is automatic location of vehicles (AVL), [3-4], as the medium to determine the geographic position of the vehicle and to transmit thisinformation to a point where it can be used and exploited. This tool is extremely useful to the management of fleets of service vehicles, emergencies, construction, public transportation, robberies of vehicles, and public security [5].
Special attention has received the GPS antenna design. Toyota Central R&D Laboratories of Japan has developed an antenna for installation on the roof of anautomobile [1]. They have used a dual-feed, stub loaded single patch to achieve circular polarization at the two frequencies of the satellite. The antenna radomes have received also special attention, not only on the material used, but also in the shape. In [6], it is shown an Automotive Combination Antenna AM/FM + GPS, inside the same aerodynamic package.
Additionally, several companies arededicated to commercialize navigation systems for vehicles that do not account with the original device [7]. The antennas contribute greatly to the total operation of the navigation systems, and they can be designed in accordance to the aesthetics and the requirements of the vehicle, in order to obtain prototypes totally personalized.
Antennas commonly used for circular polarization are based oncorner-truncated square microstrips [8], and on square or circular patches with one or two feed points [1]. A circular polarization can also be obtained from a single-point square or circular patch.
In this research, the design of a circular patch antenna is realized. The interest is focused on the simulation of the antenna, due to the benefits to know the performance of the complete system. The...