All-Metal Endfire Antenna With High Gain and Stable Radiation Pattern for the Platform-Embedded Application

This paper presents a novel high-gain endfire slot antenna array fed by air-substrate microstrip line. It has a simple and compact structure consisting of a copper strip and two copper sheets. Designed based on the slot antenna array, the antenna could be embedded into a large metallic platform. The surface wave above the antenna radiates the energy to free space. Fed by the air-substrate microstrip line, the antenna works on the TEM mode. Therefore, the antenna obtains a suitable phase constant to realize stable endfire radiation pattern and could be designed by a long structure to realize high endfire gain. Because all of the antennas are designed by metal, it has the characteristics of high strength, easy fabrication, and low cost. With the radiating aperture of 3.5 wavelength, the antenna achieves a measured endfire gain of 11.81 dBi. The measured 1 and 3 dB gain bandwidths reach 4.5% and 8.4%, respectively. Good matching and stable endfire radiation pattern are obtained over the entire operating band from 3.75 to 4.15 GHz.