Wideband Double-Dipole Yagi-Uda Antenna FED by a Microstrip-Slot Coplanar Stripline Transition

This paper describes a wideband double-dipole Yagi-Uda antenna fed by a microstrip-slot coplanar stripline transition. The conventional dipole driver of a Yagi-Uda antenna is replaced by two parallel dipoles with different lengths to achieve multi-resonances, and a small, tapered ground plane is used to allow flexibility in the placement of a pair of reflectors for effective reflection of back-radiated electromagnetic waves. The measured bandwidth of the antenna was 3.48-8.16 GHz for a -10 dB reflection coefficient, with a flat gain of 7.4 ± 0.4 dBi. A two-element array of these antennas was also constructed, with a center-to-center spacing of 36 mm (0.72 λo at 6 GHz) and a common reflector between the elements. The two-element array had a measured bandwidth of 3.56-7.92 GHz, a gain of 8.40-10.43 dBi, a cross-polarization level of <-15 dB, and a mutual coupling of <-16 dB within the impedance-matching bandwidth.