Design of Singly Fed Dual-Band Antenna With a Large Frequency Ratio by Introducing a Monopole Mode to Yagi–Uda Antenna

This communication presents a novel design for a singly fed dual-band antenna with a large frequency ratio, which is achieved by introducing a microwave (MW) monopole mode to a millimeter wave (MMW) planar Yagi–Uda antenna. The design involves extending the top metal strip of the feeding stripline of the Yagi–Uda antenna to cross the Yagi–Uda directors, which forms the monopole antenna. The extended top metal strip, together with the crossed directors, achieves a low antenna height of 0.17 wavelength due to the captive loading effect of the directors. The driven dipole of the Yagi–Uda antenna not only excites the MMW Yagi–Uda antenna but also prevents the MMW signal from flowing into the monopole antenna. This design eliminates the need for an additional filtering element, which makes it an efficient and cost-effective solution for 5G applications. The proposed antenna design offers high flexibility, as the antennas in both bands can be designed independently. It is fabricated on a single-layer substrate, which makes it lightweight and easily integrated into the circuitry. A prototype was fabricated to verify the design, and the results showed an impedance bandwidth of 14.4% and 16.3% in the 2.6 and 28 GHz bands, respectively.