Reconfigurable Broadband Fabry-Perot Cavity Antenna

Fabry-Perot interferometer was invented by C. Fabry and A. Perot in 1899. It can gernerate a thin spectrum with narrow half bandwidth based on multiple-beam interference principle. This type of interferometer has a very high chromatic resolving power. Moreover, it can accurately measure and control the frequency and wavelength of light, which leads to its wide applications in optical communication and optical spectroscopy. Its transmission spectrum as a function of wavelength exhibits peaks of large transmission corresponding to the resonance condition. With the rapid development of laser technology, Fabry-Perot interferometer has a new form- Fabry-Perot cavity, which has become an important part of the laser devices. Fabry-Perot cavity antenna can be a good alternative to traditional high-gain antennas due to its advantages of low profile, high gain, and simple feed network. It has become a research focus in recent years in the field of microwave and millimetre wave antennas.Fabry-Perot cavity antenna is based on Frequency Selective Surface(FSS). It consists of a ground plane, a source antenna which is located above the ground plane, and a partially reflective surface(PRS) which is located a proper height above the source antenna. A cavity structure is formed by the ground plane and the partially reflective surface. Fabry-Perot cavity antenna overcomes the demerits of the traditional microstrip patch antenna, such as low gain and low efficiency. It can be used to enhance the gain with no need to construct array antenna or to employ complex feed network. However, since the Frequency Selective Surface and the cavity structure itself all have narrow band properties, the impedance bandwidth and gain bandwidth of the Fabry-Perot cavity antenna are usually very narrow, which limits its usage in many applications. This type of antenna can have more practical applications when the bandwidth performance is improved.For the other, reconfigurable antenna with functional diversity can be more suitable to satisfy the requirements of contemporary communication systems, such as changeable channel and high speed. Moreover, it can greatly reduce the number of antenna devices on the device platform, which will simplify the electromagnetic environment. In order to meet the needs for high-gain and multifunctional simultaneously, the concept of reconfigurability has been introduced in Fabry-Perot cavity antenna designs. Nevertheless, it is really challenging to reconfigure one characteristic of an antenna, without affecting others, since the frequency response and the radiation characteristic are always highly related.In addition, how to get a simple dc bias network which has little influence on the antenna performance is another issue in the design process of reconfigurable antenna.In this dissertation, the research is focused on the reconfigurable broadband Fabry-Perot cavity antenna. Based on four model analysis methods, the basic concept of Fabry-Perot cavity antenna is introduced at the beginning. Then the approaches are summarized, which can help Fabry-Perot cavity antenna to achieve broadband and reconfigurability. According to the above theory and methods, a variety of newly designed Fabry-Perot cavity antennas have been proposed, fabricated, and tested. To some extent, some key problems has been effectively solved in this field.Specifically, the major contribution of this dissertation is summarized as follows:1. A broadband Fabry-Perot cavity antenna with wedged ground plane is proposed in this dissertation. A new approach is introduced in Fabry-Perot cavity antenna design to improve its radiation performance, as well as enlarging its bandwidth, namely employing wedge structure on the ground plane. By utilizing this method, the quality factor of the cavity can be reduced and the phase difference caused by different reflection path can be compensated. Based on these principles, a novel broadband Fabry-Perot cavity antenna is designed and measured. The results verify the above analysis.2. A broadband Fabry-Perot cavity antenna which employs a double-layer FSS as the PRS structure is presented in this dissertation. Three new PRS units are proposed. Their frequency response all have the characteristic of positive phase gradient, which can be used to broaden the bandwidth. Among the three unit designs, the last one with double-layer double-side-printed square ring shows the best reflection response. Therefore, it has been employed in the final design for Fabry-Perot cavity antenna to realize wide radiation bandwidth.3. A pattern reconfigurable Fabry-Perot cavity antenna is proposed in this dissertation with the capability of discrete beam scanning. A phased array is used as the source antenna in this design. By employing a reconfigurable feed network based on the defected microstrip structure, its beam can be tilted towards-10°, 0°, and 10°. Moreover, by introducing a reconfigurable PRS structure, the antenna can reconfigure its beam within ±15°. Compared to other reported pattern reconfigurable Fabry-Perot cavity antenna, our design is much simpler with no need to employ other impedance matching network, and the beam tilting range is wider.4. A broadband polarization reconfigurable Fabry-Perot cavity antenna is presented in this dissertation which can realize the switch between one linear polarization and two circular polarizations. By employing a new reconfigurable feed network, and embedding it to a shorted annular patch antenna as the source, this design can achieve polarization switch in a relatively wide overlapped bandwidth(13.1%). Compared to other antennas, our design can realize broadband and relatively high gain simultaneously, which will be more adaptive for modern wireless communication.