Optimal geometry of different antennas.

This paper presents a miniaturization technique for microstrip patch antennas operating at the fundamental TM01 mode based on a loading capacitor approach. Several gaps are inserted into the patch, and with the aid of shorting vias, coupled gaps are produced. These function as a slow-wave transmission line, and then, the operating frequency is significantly moved to a lower frequency range. The final radiating element with dimensions of approximately quarter-effective wavelength at 4.5 GHz exhibits good matching performance in the frequency range from 4.48 to 4.52 GHz and broadside gain around 5.0 dBi. It is noted that the proposed design exhibits extremely low cross-polarization radiation of less than –40 dB, which is much lower than that of the conventional quarter-wavelength patch antenna. In comparison with the reported compact patch antennas in literature, the proposed miniaturized patch is one of the smallest design with the smallest cross-polarization level, while having comparable gain. Such operation characteristics demonstrate the suitability of the proposed antenna for compact Internet of Things (IoTs) applications working at 5G New Radio n79 band.