tailieunhanh - Design and applications automotive antenna: Part 2

Part 2 of the document Design and applications automotive antenna present the content: TV antennas for cars, satellite TV antennas, ridged waveguide antenna array, electronic beam-controlled phase array, antennas for digital terrestrial TV; satellite radio antennas, basic passive antenna requirements, system with two antenna elements, system with single patch antenna element, GPS antennas, typical GPS antenna parameters, circular annular ring microstrip antenna; antennas for short range communication, compact planar passive antenna, alternative antenna systems for short range communication. | 6_________________________________ TV Antennas for Cars Satellite TV Antennas Satellite TV System Requirements Generally a satellite TV antenna is mounted on the roof of a vehicle. The satellite receiving system tracks the signal received by an antenna from the satellite transmitter when a car is in motion. Therefore the system requires a special sensor to find the satellite with minimal searching. The tracking process must maintain the maximum radiation antenna pattern at a position corresponding to the satellite angle. Direct broadcast satellite DBS TV antenna systems 1 2 must meet certain requirements. They must operate over to GHz with estimated antenna gains of 28 to 34 dBic. Beamwidth varies from to degrees in both elevation and azimuth directions with the antenna gain to system noise temperature G T of 10 to 12 dB K antenna gain is expressed in dBic temperature in K . The antenna must provide 360 degree azimuth scanning and the elevation scanning angle range depends on the TV satellite location. For example complete coverage over the continental . requires an elevation angle range of 20 to 65 degrees for Direct TV and 15 to 60 degrees for EchoStar 1 . The tracking accuracy must about and degrees in elevation and azimuth respectively. The system must be switchable between right-hand circular polarization RHCP and left-hand circular polarization LHCP . Cross polarization isolation must be greater than 25 dB. One commercially available mechanical scanning antenna array system was described in Chapter 1. Here we present in detail an antenna array that combines mechanical scanning in the azimuth plane and electronic scanning in the elevation plane. A very important design concept is to facilitate in-motion pointing of the antenna beam toward a satellite. The simplest method uses only one beam for the tracking algorithm. This beam rotates around the main angle direction and a signal error pointing error assessment algorithm 2