Transmission-Line Model of Nonuniform Leaky-Wave Antennas

Nonuniform leaky-wave antennas (LWAs) are analyzed and synthesized using a lossy transmission line model. The analysis is based on a general waveguide circuit theory. Compared to the classical approach, the model yields a higher accuracy in the computation of both aperture field distribution and radiation patterns. The proposed analysis is also able to provide scattering parameters of the whole structure in a fraction of a second, which is valuable for antenna optimization. Based on the analysis, a general method for far-field pattern synthesis utilizing global optimization is presented. As an application demonstration, the half-mode substrate-integrated waveguide (HMSIW), or half-width microstrip line, has been selected as basis structure for the LWA designs. Two antennas have been optimized targeting different specifications, i.e., a low-sidelobe level and a wide null in the radiation pattern. Experimental results are provided for these selected examples of nonuniform LWAs, which ultimately validate the proposed technique as an improvement over the classical approach.

I. Introduction

The general analysis method for leaky-wave antennas (LWAs) was first introduced in [1] and has been covered in many antenna textbooks such as [2] and [3]. This analysis method has been used widely in the literature for design and pattern synthesis due to its simplicity and reasonable prediction on the antenna radiation patterns such as in [4]–[6]. Nevertheless, the analysis relies on simplifying assumptions, which have to be emphasized and recognized, otherwise inaccurate prediction on both near-field and far-field distributions could be obtained (these assumptions will be discussed in the next section). To achieve a more accurate analysis, a different technique to analyze nonuniform LWAs with smooth profile variations is proposed based on a general waveguide circuit theory propounded by Marks and Williams in 1992 [7].