Study on bandwidth enhancement of three-element Yagi-Uda antenna with narrow spacing

It had been shown that the working gain of about 7 dBi can be realized by a three-element Yagi-Uda antenna even if the inter-element spacing is narrowed down to 0.025 wavelength, which is one-tenth of the normal interval [1]. The antenna becomes narrowband as a compensation for compactness. The narrowband is not disadvantageous for use in an inter vehicle communications system to prevent traffic accidents because the allocated frequency band is narrow (10 MHz in the frequency band from 710 MHz to 730 MHz) in Japan. However, a three-element Yagi-Uda antenna can be used in many applications if its frequency band is enhanced. Thus, enhancement of the frequency band is examined in this study. The antenna is designed for the frequency band, 720 MHz, that is the same as that of the inter vehicle communications system because the application for developing this antenna is not specified.