| With the development of Global Navigation Satellite systems(GNSS), four systems(GPS, GLONASS, Galileo, Compass) have wide applications in high-quality global positioning, navigation, geographic survey, timing, mapping services and so on. The broadened GNSSs spectra spread across 1164~1616 MHz. In order to improve the positioning accuracy and reliability, future satellite navigation receivers require multimode operation for efficient utilization of all these satellite navigation systems. Therefore, a multimode circularly polarized antenna which is a key component of the satellite navigation system has attracted considerable research interests.There are two approaches to designing multi-mode GNSS antennas, which is designing multiband circularly polarized(CP) antennas and wideband CP antennas. Based on wideband design approach, three wideband GNSS antennas, a two-feed wideband CP antenna for GNSS, a compact wideband monopole antenna for GNSS and a wideband unidirectional CP monopole antenna for GNSS, were accomplished during my graduate period and they are presented in this thesis.The Wilkinson Power Divider and improved Shicffman Wideband 90°phase shifter were combined to constitute the feed network of the two-feed wideband CP antenna for GNSS. Also, the coupling feed approach of L probe and air gap were utilized to broaden the CP bandwidth. Therefore, the proposed antenna has a 62.40% simulated-10 dB impedance bandwidth from 0.86 GHz to 1.64 GHz and a 51.30% simulated 3 dB axial ratio(AR) bandwidth from 1.00 GHz to 1.69 GHz. During the entire band of GNSSs, its simulated gain is above 1.9 dB. These meet the requirements of multimode GNSS antennas. Furthermore, miniaturization technologies like utilizing higher relative permittivity substrate, cutting slots and putting a superstrate on the radiation patch were also investigated to miniaturize the antenna size.The proposed compact wideband monopole antenna for GNSS exhibits 1.122~2.344 GHz(70.44%) measured-10 dB impedance bandwidth, as well as 1.270~ 1.600 GHz(23.00%) and 1.750~2.450 GHz(33.33%) measured 3 dB AR bandwidths. This agrees well with the CP bandwidth of 1.214~2.410 GHz(66.00%) in simulation with cable model, which verifies the design successful. Besides, the proposed antenna has 0.41 dB, 0.53 dB and 1.66 dB measured gain at 1.275 GHz, 1.575 GHz and 1.80 GHz. If the feed cable was excluded, much high gains were observed in simulation, indicating that the cable causes the reduced gains in small antennas, and the simulated CP bandwidth becomes 1.096~2.243 GHz(68.70%). Therefore, the wideband CP characteristic of this antenna is potential to apply in wideband CP antennas demanded fields like GNSSs. And this antenna was investigated deeply by extensive analysis on the mechanism of wideband CP bandwidth, it not only explains its wideband CP characteristic from the view of “bandwidth overlap”, but also reveals the “frequency independence” of phase difference between two orthogonal E fields that is also crucial to a wideband CP bandwidth. Finally, parametric study conducted is presented as well. All of this comprehensive analysis is anticipated to be extended to the development of other wideband CP antennas.Unidirectional radiation property of antenna can effectively reduce the multipath interference, which can provide higher performance for GNSSs, so the aforementioned compact monopole antenna for GNSS was backed with a composite cavity to gain the unidirectional radiation. Consequently, the propose antenna exhibits a 75.02% measured-10 dB impedance bandwidth from 1.062 to 2.337 GHz and a 67.40% measured 3 dB AR bandwidth from 1.21 to 2.44 GHz. And the measured gain is over 2.5 d B, peaking at 9.90 dB in the entire GNSS band. Overall, it performs excellent. Moreover, it is worthy to mention that it also showed a comparable performance with a high performance commercial multimode GNSS antenna in the field test. This verifies the availability and feasibility of this antenna applying in GNSSs. |
PDF Full Text Request