Steerable Antenna Solution for Communication between Cars

Abstract

This thesis describes the work on designing and testing an antenna solution for communications between cars. The antenna that is to be used is a so called ESPAR antenna or Electronically Steerable Passive Array Radiator using monopoles over a circular ground plane. Simulations were made on the following variations of the antenna: The number of passive monopoles and the angle between them The radius and height of the active and passive monopoles The height of the skirt and the radius of the ground plane Matching schemes The antenna that was decided to be the best for this application had these characteristics: - Ground plane radius 75 mm or half a wavelength - Skirt height of 37.5 mm or a quarter wavelengths - Six parasitic monopoles with a height of 39 mm equally spaced around an active monopole of 35 mm - Distance from active monopole to parasitic monopoles of a quarter wavelengths - Half power beam width of about 90 degrees and a front to back ratio of 16 dB - Gain of about 7.5 dB and an elevation angle of 25 degrees From these results a prototype of the antenna was constructed with different heights of the active and parasitic monopoles. The measurements showed less variation between the different configurations of the antenna than the simulations indicated. The largest difference was the elevation angle of the antenna. This was found to be about 0 degrees for all configurations which is an improvement of about 25 degrees from the simulated results. The best results was found to be with an antenna that has the same configurations as the simulated one described above but with a parasitic monopole height of 37 mm. The measurements showed the following specifications: - Gain of about 9.5 dB - HPBW of 80 degrees - FTBR of about 12 dB Because of certain elements in the construction of the antenna the measurements of the matching were inconclusive, and were not weighed heavily in this thesis.