A Compact Reflector Antenna Fed by a Composite <i>S/Ka</i>-Band Feed for 5G Wireless Communications

A novel dual-band coaperture reflector antenna which sustains the 3.5 GHz band and the 28 GHz band simultaneously is proposed in this article. It allows a switch working mode or dual-band working modes to accommodate different application scenarios. To achieve high efficiencies simultaneously at dual bands, a shared aperture strategy is proposed for the reflector antenna with a large frequency ratio and small aperture. A very compact composite feed consisting of a pair of dipoles and a conical horn is designed to illuminate a shaped axially displaced ellipse (ADE) reflector antenna. At the higher frequency band, the antenna is a classical ADE design. But at the lower frequency band, it is actually a single reflector. The main reflector acts as a back cavity for the lower band dipole pair which is fed by a coaxial cavity with a length of only 5/8 wavelength and the subreflector works like a director of the low-band feed. The measured antenna with aperture diameters of $2.4\lambda $ at 3.6 GHz and $18.7\lambda $ at 28 GHz achieves total efficiencies of 42% and 47%, respectively.