High-Efficiency Angled-Dipole Antennas for Millimeter-Wave Phased Array Applications

A high-efficiency microstrip-fed endfire angled-dipole antenna has been developed for millimeter-wave phased array applications. The antenna is built on both sides of a Teflon substrate $(\varepsilon_{r} = 2.2)$ and this allows a wideband feed from the single-ended microstrip line to the differential dipole. The design results in wide radiation patterns for scanning purposes with a gain of around 2.5 dB at 20–26 GHz and a cross-polarization level of $≪ {- 15}~{\rm dB}$ at 24 GHz. A mutual coupling of $≪ {- 23}~{\rm dB}$ is measured between adjacent elements with 6.8 mm center-to center spacing ($0.50\mathchar"707B 0.54\lambda_{0}$ at 22–24 GHz). A variant of the angled-dipole antenna with a magnetic ground plane edge was also developed, and shows a measured gain of ${> 6}~{\rm dB}$ at 23.2–24.6 GHz and very low mutual coupling between elements ($≪ {- 23}~{\rm dB}$ for a 6.8 mm spacing). Both antennas result in a radiation efficiency of ${> 93}\%$ when referenced to the microstrip line feed (including mismatch loss). The usefulness of these antennas as phased array radiators is demonstrated by several eight-element linear arrays at 22–24 GHz with scan angle up to 50 degrees. The application areas are in automotive radars and high data-rate communication systems.