Research On Multi-band And Multi-polarization Microstrip Patch Antennas

Antenna as a key component of a wireless communication system has always been a hot research topic. Specifically, the microstrip patch antenna with advantages of conformal geometry, low profile, ease of fabrication and convenience of integration with active devices, has been widely applied in the aircraft and wireless communication devices in recent years. With the rapid development of wireless communication technology and multimedia technology, the antenna which can operate at different bands simultaneously has drawn more attention. Usually, different operating bands have specific requirements of polarization. For instance, the circular polarization is applied at GPS band, while the linear polarization is adopted at Wi-Fi and GSM bands. Therefore, it is a challenge to design an antenna that can meet different requirements of polarization at multi bands simultaneously. In this dissertation, the performance of the monopole antenna and microstrip patch antenna installed on the Unmanned Aerial Vehicle (UAV) is studied. After that, the method to implement a multi-band microstrip patch antenna with linear polarization is investigated. Based on above analysis, various technologies to realize multi-band microstrip patch antenna with multi-polarization and a miniaturized configuration are studied.The main studies and innovations of this dissertation are listed as follows:1. By considering the background of the UAV communications, the performance of the monopole antenna and microstrip patch antenna mounted on a UAV is analyzed. First, the traditional monopole antenna operating at Wi-Fi band is studied by using the model of the monopole antenna integrated with the UAV. A comparison between the performance of the monopole in free space and that under the UAV environment is given. Second, the model of the microstrip patch antenna operating at Wi-Fi band integrated with the UAV is built. The performance of the patch antenna in free space is compared with the counterpart under the UAV environment. Furthermore, the performance of the monopole antenna and microstrip the patch antenna installed on the UAV is compared and the possible problems are analyzed.2. A slot loaded method is proposed to design multi-band microstrip patch antenna. In this method, the lower operating band is generated by the fundamental mode of the patch antenna, while the higher band is attributed to the loaded slot. The capacitive feeding disc and multi-layer supporting substrate are used in order to widen the bandwidth of the design. By using the proposed method, a dual-band patch antenna with linear polarization and a tri-band patch antenna with linear polarization are designed.3. A dual-feed slot loaded microstrip patch antenna which operates at multi-band with multi-polarization is proposed. The dual-feed excites two orthogonal modes of the radiating patch with a phase difference of around 90°, which results in the right-handed circularly polarized radiation at the GPS L1 band. The loaded slot introduces the radiation at the 2.4-GHz Wi-Fi band with linear polarization. The antenna can meet the bandwidth requirements at the GPS L1 and 2.4-GHz Wi-Fi bands and maintain consistency of the radiation pattern at both operating bands.4. A single-feed L-shaped slot loaded patch antenna with dual-band and multi-polarization is proposed. The antenna operates at the 1.575-GHz band with left hand circularly polarized (LHCP) radiation and at the 2.4-GHz band with linear polarized radiation simultaneously. Additionally, in order to meet the right hand polarization (RHCP) requirement at the GPS L1 band, the top radiating patch of the LHCP antenna is mirrored vertically. These antennas have advantages of simple feed structure, easy fabrication, low cost and conformal geometry.5. A method to miniaturize the single-fed multi-band multi-polarization patch antenna is proposed. By utilizing the substrate with a high dielectric constant, the size of the antenna can be reduced by 40%(referring to the antenna mentioned previously) while the height of the antenna is not changed significantly. The antenna is constructed with three substrate layers. The radiating patch working at the lower band is printed on the upper side of the middle substrates. The patch is fed by a coupling aperture. The radiating patch working at the higher band is printed on the upper side of the top substrate. It is fed by the capacitive feeding disc. The resonant frequencies of the antenna are easy to adjust since the upper and lower patch patches contribute to the two operating bands independently.