Accurate and simplified network model for composite right-left handed transmission line

In this paper, a general and simplified design method for composite right-left handed transmission line (CRLH-TL) with arbitrary number of unit cells is proposed and validated. In the cases where tens of cascaded cells are required to achieve high radiation efficiency or narrow beamwidth, the optimum design of CRLH-TL is prohibitively computational expensive. Since the optimum design of multi-cell CRLH-TL can't be obtained through single cell optimization directly, due to the existence of inter-cell coupling effect and the end-cell discontinuity. To overcome this disadvantage, we develop an accurate network model for arbitrary length multi-cell CRLH-TL by accounting for the inter-cell coupling effect and the end-cell effect, where only less than 4 cascaded unit cells are needed to extract the inter-cell and end-cell effect. The accurate network model obtained with low cost is then exploited in the CRLH-TL optimization procedure to reduce the computational burden. To validate the proposed method, a CRLH-TL based leaky wave antenna with 30 unit cells is design and optimized. The multi-cell CRLH-TL network model accuracy is verified by comparing the radiation characteristic predicted by the network model with that from CST simulation. The prediction error of the radiation angle and radiation beamwidth is less than 1^o and 2^o, respectively. Moreover, the time cost of the optimization procedure has been significantly reduced to less than 10%.