Reduction Of Errors Caused By Cross-Polarization In A Microstrip Antenna

ABSTRACT

Microstrip antennas are used for transmitting and receiving electromagnetic signals. The transmitted signals can be reflected back within the building. This affects the strength of signal transmission. Polarization of the electric field determines the signal strength of the electromagnetic wave. If cross polarization occurs then it results in multiple signals which interfere with each other causing some signal loss during transmission. The main focus of the study was to reduce cross polarization in a microstrip antenna. The study involved designing a circular patch antenna (CPA) and Concentric microstrip patch antenna (CMPA) with an annular patch enclosing the circular patch. Simulation and optimization was also done using Ansoft high frequency structure simulator (HFSS). The antenna was then fabricated using photolithography method using the optimized radii. The results obtained during simulation and fabrication process were then analysed and evaluated. During optimization, the initial radius of the circular patch and the width of the annular patch were varied to match the required frequency of 2.4GHz. The antennas were fed using a single coaxial probe towards the centre of the circular patch. The antenna characteristics like the radiation efficiency, directivity, gain, return loss (RL) and the radiation patterns were studied using HFSS software and the patch size optimized to obtain the best results. The analysis and testing of the fabricated antenna was done using a Scalar Network Analyzer (SNA). The RL in decibels (dB) was studied to show the effect of cross polarization on a CPA and the Concentric Microstrip Patch Antenna (CMPA). In Ansoft HFSS, the circular patch had a gain of 1.8147 and directivity of 4.1753 while the circular patch with annular had a gain of 2.3354 and directivity of 5.3212. The simulated data showed a performance improvement of 29% for the gain, 27% for the directivity and 11% for RL. A study of the radiation patterns of the two designs showed reduced cross-polarization in the performance of the antenna with an annular patch around it. The RL of the fabricated antenna; CPA and CMPA were studied using the SNA. The experimental circular patch had a Return loss of -9.697dB and the CMPA had a Return Loss of -13.170 dB. The experimental CMPA reduced cross polarization by 35.8% as compared to the fabricated CPA. The research has therefore proved that an annual ring can be used as a polarization filter to reduce cross polarization errors of signals transmitted by a circular patch antenna. The experimental CMPA gave the best performance in error reduction as compared to the CPA. The results obtained show that cross polarisation can be reduced by removing some metal on the surface of a circular patch antenna and the size of the antenna should be reduced as much as possible to enable it fit in handheld devices.