Study On The Composite Right/Left Handed Transmission Line-Based Microstrip Antenna

Left-handed material is a kind of the "double negative" electromagnetic material, which electric field vector, magnetic field vector and wave vector follow the left-hand screw rule. The transmission form of left-handed material is composite right/left-handed transmission line(CRLH-TL). Compared with the traditional metallic wire array and split-ring resonators structure, the CRLH-TL overcome the defects of the high insertion loss, low broadband, matching difficultly and so on, and it has some incomparable advantages in the antenna design within the specific frequency band due to its distinctive characteristics. In this paper, using the CRLH-TL units to design leaky-wave antenna and small resonant antenna, we try to realize the goals of the main beam scanning consecutively in the half space and the miniaturization of the physical size.The main items of this work are list below:1. According to the transmission line theory, the equivalent circuit model of the CRLH-TL unit is given. The feasibility of using CRLH-TL units to design the microstrip antenna is analyzed. The telegraph equation of the CRLH-TL, voltage and current expression, equivalent constitutive relation are deduced.2. The CRLH-TL units based on the interdigital capacitance and the MIM(Metal-Insulator-Metal) capacitance are proposed, respectively. Modulated the CRLH-TL unit to the equilibrium state in the light of dispersion diagram, the electromagnetic waves radiate from the left-hand area to the right-hand area seamlessly, and then we apply the two types of the CRLH-TL units in design of the multi-unit leaky-wave antenna. The simulations using Ansoft HFSS demonstrate that the 12-units leaky-wave antenna based on the interdigital capacitance radiate from 3.8GHz to 5.7GHz and the 20-units leaky-wave antenna based on the MIM capacitance radiate from 3.7GHz to 5.9GHz. Moreover, the broadside radiation can be found in these two types of the CRLH-TL leaky-wave antenna.3. Loaded the shunt inductance to the transmission line unit, the negative permittivity of the CRLH-TL unit is constructed. According to the electromagnetic wave dispersion relation, the resonant frequency is not related with antenna size. The small dual-frequency CRLH-TL resonant antenna is presented. By optimizing the position of feed network, the lowest operating frequency at 1.66 GHz is gained. Physical size is only twenty-six percent of the right-handed microstrip antenna at same frequency. The advantages of small physical size and low cost are obtained. Ansoft HFSS is employed to simulate the performance of the small CRLH-TL resonant antenna, the results show that it is just like the microstrip antenna radiate directionally on low-frequency modes and is similar to the half space radiate omnidirectionally on high-frequency modes.