Printed Quasi Yagi Antenna with Closely Spaced and Thick Directors for Triple ISM-Band/Wideband Applications at UHF

Abstract

In this study a printed quasi Yagi antenna realized for almost whole UHF band is given. Within overall UHF band the performances of three well-known ISM frequencies of 433 866 and 915 MHz which are used in many wireless applications such as LoRa IoT M2M M-bus and RFID are desired to be kept relatively better. The proposed antenna includes a printed feed dipole with reflector and two director elements. The directors are quite thick and closely spaced to feed dipole which provides significant enhancement in the bandwidth. According to gathered results the antenna has more than 80% bandwidth for S11 < -6.5 dB between 407 and 955 MHz where return loss values are higher than 10 dB in the bands 417-493 MHz and 700-920 MHz covering three mentioned UHF ISM bands. Additionally it has more than 10 dB front-to-back ratio and 4 dBi realized gain for the frequencies lower than 500 MHz and higher than 850 MHz which again includes 433/866/915 MHz bands, while the gain values in the remaining band are relatively low as being 3.5 dBi on the average.