The Study Of Electromagnetic Band-Gap Structure Used In Antenna Design

The electromagnetic band-gap(EBG) is a kind of material structure which consists of near-surface mounted unit cells arraied periodically. It can prohibit the surface wave propagation and achieve in-phase reflection at certain frequencies, which caused it outstanding in improving the performance of microwave devices and became research hotspots in microwave fields. In this paper, the designing theory and bandgap characteristics of High Impedance Surface Electromagnetic Band-Gap(HIS-EBG) structures are studied firstly. Then the new-type EBG structures are applied to antenna design. Contents of our researches are outlined as follows:(1) On the basis of traditional mushroom-like EBG structure, the first new type “two pinwheels-shaped” HIS-EBG structure with frequency ranging from 3.60 GHz to 5.50 GHz is designed. The frequency is covered 1.9GHz at the transmission coefficient S21≤-40 dB standard. Using the miniaturization technology of EBG, we design the second compact HIS-EBG structure. The size of this EBG structure decreases 32.8%. Applying the means of slotting on metal pad, the third L-shaped slots HIS-EBG structure which has dual bandgap is designed.(2) To overcome the disadvantage of microstrip antenna’s narrow bandwidth and small gain, the “two pinwheels-shaped” HIS-EBG structure is applied to a plane microstrip patch antenna which composed of four spiral slots and has dual band. Microstrip antenna is surrounded by the HIS-EBG unit cells. Making use of the surface wave prohibation characteristics of EBG structure, the gain of patch antenna is sucessfully increased by 1.87 dB and 1.56 dB at frequency ranges of 4.43~4.56 GHz and 4.96~5.10 GHz respectively. Meanwhile, the impedance bandwidths of those two work frequencies are expanded 3.4% and 6.5% respectively.(3) Traditional base station antenna uses the metal aluminum as reflector, which causes a large back radiation. To this problem, the compact HIS-EBG cells are arrayed to form a new reflector of the spatial structure die-casting base station antenna. Compared with the antenna with metal aluminum reflector, back radiation of the antenna with HIS-EBG reflector decreases 0.87 dB, 1.07 dB and 0.85 dB at 1.71 GHz, 1.94 GHz and 2.17 GHz respectively, with the help of this HIS-EBG structure.(4) For the antenna array, the coupling of electromagnetic waves between the elements of antenna array is strong. In this paper, the HIS-EBG structure with dual bandgap characteristics are arranged between the elements of antenna array of WLAN which has a dual band. Since the HIS-EBG structure can restrain the surface wave, the mutual coupling of the array elements is decreased. The isolations are improved 17.42 dB at low band of WLAN(2.40~2.4835GHz)and 13.97 dB at high band of WLAN(5.15~5.35GHz)realizing the high isolation performance of array antenna.