| Left Handed Metamaterial (LHM) is an artificial metamaterial. It has negative permittivity and negative permeability simultaneously and has attracted great attention these years. When electromagnetic waves transmit through the LHM, electric vector, magnetic vector, and wave vector in it will form a left_handed rule, that's why we call it Left Handed Metamaterial. LHM has a lot of abnormal characteristics different from these conventional natural materials. We can use these characteristics to make high directivity antenna based on LHM. The paper employs the method of Finite Difference Time Domain (FDTD) to investigate characteristics of different LHMs and their applications in patch antennas.The paper firstly introduces the fundamental theory and method concerned with LHM and patch antenna, then novel designs including patch antennas based on novel Photonic Band_Gap (PBG) structures, and patch antennas based on novel LHMs are proposed. The results obtained show that the designed LHM and PBG structures in the paper can improve performances of the antennas, for example, enhance the radiation gain, broaden the frequency band, improve the impedance matching condition, and restrain the high harmonics. The paper mainly includes the following contents:(1) Patch antennas based on drilled and crossed idiosyncratic PBG are designed. Owing to the effect of drilled-PBG's forbidden band, the surface waves in the bottom substrate of the patch antenna would be suppressed, and such substrate will reflect the energy extensively, which would improve the antenna's radiation gain; for the patch antenna based on crossed idiosyncratic PBG, as the forbidden band is broadened, the working frequency band would extend accordingly, and the gain of the antenna would be improved.(2) A patch antenna based on SRRs and notches is designed by employing the traditional construction method, and the metal wires are substituted by periodic notches in the ground, the simulated results indicate that such LHM has the effect of miniaturization to the dimension of the patch antenna. Besides, it also can improve the impedance matching condition, and extend working frequency band; the paper also analyzed the effect of SRR's dimension change to the characteristics of the patch antenna, the obtained data is helpful to the design of the SRR_based LHMs.(3) A patch antenna based on I-shaped LHM is designed, the designed LHM hasthe refraction of n_i≈0, which would make the electromagnetic waves in the bottomsubstrate refract into the free space, and the patch antenna's radiation intensity, together with the radiation gain would be improved.(4) A CSRR-based patch antenna is designed and analyzed. The designed CSRR can suppress the high harmonics effectively. Because the equivalent negative permittivity would occur just around the resonant frequency, the EM waves in this frequency range can not transmit. On the other hand, the transmitted electromagnetic power at the working frequencies wouldn't be influenced, so the patch antenna's radiation efficiency can be improved. Further more, the characteristics of rectangular CSRR are analyzed, the obtained results indicate that the characteristic of forbidden band follows some law, and in accordance with Electromagnetic Duality and complementary theory. |
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