Design and Development of a Novel Compact Soft-Surface Structure for the Front-to-Back Ratio Improvement and Size Reduction of a Microstrip Yagi Array Antenna

In this letter, a novel antenna structure based on a microstrip Yagi array antenna and a soft surface (SS) ring is proposed, that enables a highly directional gain in addition to an improved front-to-back (F/B) ratio of more than 20 dB. The SS ring is shown to be capable of greatly improving the performance while miniaturizing the design's size by half. The implementation of the SS ring to a microstrip Yagi array antenna is demonstrated to verify its functionality in suppressing surface waves, showing that an improvement of at least 3 dB in the F/B ratio can be obtained. The design is investigated at the center frequency of 5.8 GHz; however, the structure can be easily scaled to other frequency ranges. A design analysis is performed to give insight into the operational mechanism of the SS ring and the critical dimensions that affect the SS structure surrounding the antenna array. In addition, measurements are presented to validate the results obtained via simulation. The principles established in this letter can be applied to other planar antenna designs.