Electromagnetic Band Gap Structures And Their Application Study In Antenna Design

As a special artificial electromagnetic material, since the late1980s,electromagnetic band-gap (EBG) structures have attracted much interest fromresearchers, which has been widely used in the microwave and antenna field. However,the study of novel EBG structures is still weak, such as multi-band EBG,ultra-wideband EBG, and miniature EBG. Some applications in antenna field also needto be further explored. Therefore, the study of novel EBG structures and the applicationexplore for antennas have theoretical significance, academic value, and applicationprospect. In this dissertation, by using the method of combining theoretical analysis andexperiments, several novel EBG structures are designed and the application of EBGstructures for the harmonic suppression, notch bands, low profile, and high gain ofantennas are provided. The main works and contributions in this dissertation areoutlined as follows:1. A multi-band EBG with slots on patch, a miniature EBG with spiral groundplane, and a miniature EBG with inductance loaded spiral ground plane are introduced.The multi-band EBG is achieved by making slots on the EBG patch surface, which canadd extra capacitances and generate multiple resonant circuits. Measured results showthe EBG structure can form three frequency band-gap and the designed EBG may beused in multi-band antennas. The miniature EBG is realized by changing the EBGsquare ground plane into four-arm spiral structure, which can increase the equivalentinductance of the EBG structure and reduce the resonant frequency. On this basis, thesize of the EBG structure is further reduced by loading inductance on the spiral groundplane. Compared with traditional mushroom-like EBG structures, the EBG with spiralground plane achieves77%size diminution and the EBG with inductance loaded spiralground plane achieves81%size diminution. The proposed EBG structures may be usedin phased array antennas.2. A rectangle microstrip antenna with harmonic suppression and anultra-wideband monopole antenna with notch bands are designed. The second and thirdharmonics of the rectangle microstrip antenna are suppressed by using the resonators ofmushroom-like EBG units, which can reduce the harmonic radiation disturbance to themicrowave devices around. The radiation of the UWB antenna around5.2and5.8GHzis suppressed via using the resonators which consist of a narrow microstrip line and asector surface, which prohibit the disturbance to WLAN IEEE802.11a. 3. A low-profile Yagi antenna with reconfigurable patterns and a low-profileplanar equiangular spiral antenna are designed. In the design process, RF diodes areused to control the interchange of the director and the reflector and the EBG groundplane is used to reduce the antenna height, which achieves the low-profilepattern-reconfigurable Yagi antenna. The height of the equiangular spiral antenna isremarkably reduced by using EBG ground plane instead of traditional1/4wavelengthbacked cavity. The height of the designed equiangular spiral antenna is1/10of the workwavelength.4. A high directive dipole antenna and an omnidirectional horizontally polarizedantenna with gain enhancement are designed. By adding the metal cylinder EBGmaterial with the effective permittivity eff=0.46, the omnidirectional dipole antenna ischanged to radiate along the four EBG surfaces and the antenna gain is evidentlyimproved. Then, reducing the period of three EBG surfaces and the antenna finallyradiate along one EBG surface. An omnidirectional horizontally polarized antenna isadded with EBG cavity which is similar with metal cylinder EBG structures to improvethe antenna gain. At the work frequency of5.7GHz, the gain of the antenna withoutEBG cavity is2.23dBi, while the gain of the antenna using the EBG cavity is4.95dBi.