Design and Development of Stacked Microstrip Antenna Array for Mimo Applications

Abstract

There has been a wide and rapid growth in the field of wireless communication systems in the las two decades. Nowadays every modern wireless equipment is implemented with Wi-Fi (Wireless WLAN). As the wireless field is growing day by day it aims at providing better image, speed, and data communications. For the same we need broadband and multi-band antennas to cover the various applications in a same terminal device. In order to have better transmitting and receiving rate broadband antennas are required. In addition, for miniaturising the wireless communication system, the antennas must be small enough to be placed inside the system. The microstrip antennas have various advantages that make them a good candidate for the use in wireless communication systems. In this thesis work firstly a stacked microstrip antenna is theoretically studied using transmission line model. Stacking is a technique used for improving the bandwidth. In stacking a layer of dielectric etched with a metallic patch (known as driven patch) is electromagnetically coupled to the fed patch. The antenna is fed using aperture coupling. The designed antenna resonates at 6 GHz with 656 MHz bandwidth. The antenna characteristics like return loss, bandwidth, directivity, and gain are simulated using CST MWSv’14. Then a dual band aperture coupled microstrip antenna with stacking technique is simulated. The antenna resonates at two frequencies of 3.2 GHz and 4.5 GHz. Hence it finds application in C-band and WiMAX communication systems. Wireless radio links are most affected by the fading. The fading can be combat by using multiple antennas at the communication link ends. When multiple antennas are employed at both or either sides of the communication system, the signals travelling through multiple paths can be used in an advantageous ways by employing various diversity schemes. The system having multiple antennas at both the transmitting and receiving ends is known as MIMO system. To employ the antenna in MIMO system, array of stacked microstrip patch antennas is simulated and fabricated in this thesis. In this context firstly a triple band stacked antenna array is designed and simulated. The antenna is energised using aperture feed. The antenna array has three resonances at 4 GHz, 5.8 GHz, and 6.2 GHz with -25 dB, -22 dB, and -19 dB return losses respectively. iv The antenna array structure simulated can be installed in C-band, WiMAX and STM1 systems. Thereafter a dual-band antenna array is simulated. The structure consists of a reduced ground plane to reduce the back radiations. Slits are cut in the lower patches to improve the bandwidth. To further enhance the performance of the structure, slot is cut in the upper patches as well. Various parameters like return loss, directivity, gain, envelope correlation coefficient, and diversity gain are also discussed. The antenna offers a return loss of -20dB, and -30dB at resonances of 3.6GHz, and 5.2GHz respectively. The bandwidth offered by the structure is 228.3MHz, and 232MHz. System can be fabricated for WLAN applications. Lastly the triple-band and dual-band antenna arrays simulated are then fabricated and tested using VNA. The tested results and the comparison of tested and simulated results are also shown.