Modal Analysis of an Endfire Traveling Wave Antenna With High Gain and High Efficiency

In this communication, we propose and analyze an endfire traveling wave antenna with high gain and high efficiency. The antenna is composed of an offset double-sided parallel-strip line, that is, loaded by a set of closely spaced T-shaped patches. The structure supports an improper leaky wave mode, that is, evolved from the TEM mode in the parallel transmission line, and a common and differential proper surface wave modes that are evolved from the corrupted-conductor-like surface wave mode in a single conductor line with T-shaped patches loaded. When fed at one end, the leaky wave mode and the differential surface wave mode can be excited. With their phase constants close to the wavenumber in free space, the two modes contribute to endfire radiation wherein the surface wave mode plays the dominant role. A prototype of the antenna is fabricated and measured. The antenna with a size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.65\lambda _{0}\times 0.43\lambda _{0}\times 0.03\lambda _{0}$ </tex-math></inline-formula> achieves a high gain of 15.1 dBi and a peak efficiency of 95.8%, with a 3-dB gain-bandwidth of 18.5%.