Active Microstrip Patch Antenna For Multiband GPS Applications

With the development of using Global Positioning System (GPS) in both military and civilian applications, there has been an increase in demand for the high performance antennas in the GPS antenna market. Compared with the passive antenna, the active antenna can significantly improve the gain and bandwidth of the antenna, and can reduce the size of the antenna. Therefore, the active antennas have been widely used in many applications.This thesis presents the study of active multiband GPS antenna that can be used in the GPS receivers. The proposed active multiband antenna is constructed by combining the passive radiator and the low noise amplifier (LNA).The microstrip patch antenna is used as the radiator of the active multiband antenna because of its numerous advantages, such as compact size, low profile, reliability, low cost, and ease of fabrication. However, the wideband operation is difficult to achieve because the microsrip patch antenna possesses the narrow band characteristic. Therefore, to be able to receive GPS L1, L2and L5signals, the structure of three stacked square patches of different sizes is used as the triband microstrip patch antenna design. The GPS signals are transmitted through the Right Handed Circularly Polarized (RHCP) waves. Therefore, in order to achieve RHCP radiation characteristic, the techniques of truncating corners in all patches and the coaxial probe feeding are used. The triband microstrip patch antenna simulation is performed by the HFSS software and the simulation results met the design requirements. And then, the antenna is fabricated based on the simulated design and measure the results. According to the measured results, the10dB impedance bandwidth is2%,1.5%and2%, the axial ratio is less than0.42dB,4.94dB and2.59dB, and the RHCP gain is0.7dBi,-2dBi and-1.9dBi for L1, L2and L5band respectively.In designing the LNA, Avago’s ATF-54143pHEMT transistor is selected. This transistor has only little changes in S-parameters during the1.1GHz-1.62GHz frequency range and is easy to achieve impedance matching. The two-stage LNA design technique is used and the LNA simulation is carried out by the ADS (RF circuit simulation software). After performing the simulation and optimization processes, the LNA is fabricated and measure the results. According to the measured results, the input return loss during1-1.7GHz is greater than11dB, the output return loss during1.19-1.65GHz is greater than15dB, the gain during1-1.65GHz is greater than28dB, and the noise figure during1.1-1.7GHz is less than0.85dB.After fabricating LNA and antenna successfully, the co-simulation of LNA and passive antenna is performed by the ADS software. And then, LNA and antenna is connected and measure the results. According to the measured results, the10dB return loss frequency range of the active antenna is1.1-1.62GHz and the RHCP antenna gain is28.7dBi,26dBi and26.1dBi for L1, L2and L5band respectively.Finally, the experiment of the active multiband GPS antenna in navigation application is carried out. Experimental results show that the GPS receiver connected with the proposed antenna can track seven satellites and decode the L1and L2signals with the positioning errors of2.12m and1.75m respectively.