Shorted triangular patch antenna with circularly polarization

Abstract

Shorted Triangular Patch Antenna with Circularly Polarization Circularly Polarized (CP) Antennas have been used widely in satellite broadcasting and communication systems. In this project, the base station antenna is designed to work in Satellite Communication Systems, receiving dual frequencies (1.268 GHz in China and 1.575 GHz in USA). Through ionosphere, the signal will attenuate. Some shorted bowtie Circular polarisation Antenna can improve the performance on this aspect. However, previous proposed bowtie antenna has too many element .It increase the cost of production and size of antenna. In the project, a novel design for circular polarization (CP) antenna is presented. One group antenna contains three identical shorted triangular patches fed by L probes. The novel design has attractive features. For example, the shorted wall can minuses the size of the patch due to the mirror effect, the design of triangular patch allows the integration of two group of antenna , the L-probes are built inside the patch to avoiding occupation of extra space and the structure is simple . A properly designed feeding network is to provide the 120 phase difference. The probes connecting with the transmission line can be radiated with uniform power and in sequence. In this way, the rotation of field and circular polarisation can be obtained. Firstly, single low frequency antenna and high frequency antenna are designed .they operate in 1.268 GHz and 1.575 GHz separately. Secondly, two group of antenna (low frequency and high frequency antenna) are integrated in order to receive the signal of navigation systems in China and USA. Modification should be imposed in integration. In the project, two products are presented. One is the 1.2 GHz CP antenna. The other is the combined antenna of low and high frequency antenna. For the 1.2 GHz CP antenna, return loss is below -40 dB. The axial ratio at 1.2 GHz is about 1.19. The gain at (0,0) is 6 dib. Beam width is over 89 degree. With reference of the information in chapter 4.4, it can be found that the antenna has the attractive features of low axial ratio, high gain and wide beam width. It performs better than the ordinary antenna. For the combined antenna, the simulation result shows that the bandwidth of both low and high frequency antenna are over 6% , axial ratio of are lower than 2.7 , and beam widths are about 90 degree. The product also has similar attractive features mentioned above. However the tolerance in manufacture makes the experimental perform not close to the simulated result. The Axial ratios are little bit higher than the simulated one. Overall, the most simulated result are confirmed by the experimental result and the information indicates that the shorted triangular patch antenna with circular polarisation has attractive features of base station antenna such as high gain, wide beamwidth, simple structure etc.