Miniaturized Planar Yagi Antenna Utilizing Capacitively Coupled Folded Reflector

Abstract

The analysis and design of a unidirectional and wideband printed Yagi antenna with miniaturized size using a capacitively coupled reflector is presented. Reflectors have been widely used for canceling back radiation of Yagi antennas. However, their application to reduce the size of printed Yagi antennas while maintaining their radiation characteristics has not been previously investigated. This is important for applications operating at low microwave frequencies requiring compact antennas, such as telemetry and microwave imaging. To that end, the driven element, which is a bowtie dipole, is loaded with a pair of capacitive gaps. Moreover, the reflector is folded toward the bowtie driver, capacitively coupling them together. This modification excites a patch mode that is considerably lower than the main resonance of the bowtie. To enhance the directivity of the antenna, a half-bowtie director is added near the driven bowtie. Thus, the structure is miniaturized by more than 60% compared to the existing wideband printed Yagi antennas. Moreover, the antenna attains a wide fractional bandwidth of 48% at 0.69-1.12 GHz with peak front-to-back ratio and gain values of 10 dB and 5.5 dBi, respectively. © 2002-2011 IEEE.