A Millimeter-Wave Tri-Modal Patch Antenna

This letter presents a millimeter-wave (mmWave) tri-modal patch antenna with a size of $0.46\,\lambda _{0}\times 0.46\,\lambda _{0}\times 0.11\,\lambda _{0}$, in which $\lambda _{0}$ is the wavelength in air at the center frequency. It is the first example of a tri-modal patch antenna in the mmWave frequency range. Compared to previous sub-6 GHz tri-modal patches, special approaches to handle the three port excitation at mmWave are required. The radiation performance with various feeding structures, fabrication approaches, and the challenges of designing tri-modal patch antennas in mmWave bands are detailed. The advantage of utilizing the tri-modal patch concept is that with proper excitation, a compact three-port antenna can be designed to exhibit broadside radiation and low mutual coupling within a single element. Experimental results demonstrate a three-port antenna operating at 26 GHz with an impedance bandwidth and realized gain of 5.4% and 5.0 dBi, respectively, which is suitable for use as a unit cell in mmWave massive multiple-input--multiple-output (MIMO) antenna applications.