Design of metamaterial unit cell antennas with defected ground structure for 5G applications

5G technology is the latest iteration of mobile wireless communication. It not only ensures widespread coverage but also supports for all services covered by the previous technology. It works with three frequency ranges such as Sub-1 GHz frequency spectrum, Sub-6 GHz frequency spectrum and Millimetre wave frequency spectrum. Antenna designers will face some key challenges to design antennas for 5G namely, achieving enhanced channel bandwidth, stable radiation characteristics over the entire bandwidth with acceptable gain and compact structure. Metamaterial structures can give resonance at frequencies with dimensions smaller than one tenth of the operating wavelength. Among them single negative structures are easy to design and fabricate than double negative structures. On the other hand, it is possible to design Defected Ground Structures (DGS) carefully to cause multiple resonances within short interval which will enhance the bandwidth without any additional design modification on the patch. An extensive performance analysis is done on three antennas to see the effects of these two methods for the applications of 5G NR bands n77 and n78. In addition, the polarization purity of the antennas is also investigated. Firstly, a conventional patch antenna with DGS is proposed which shows an impedance bandwidth of 12.49% and 4.49% for |S11| < -10 dB where a peak gain of 4.02 dB is realized. Secondly, another patch antenna is developed in which the patch comprises of epsilon negative resonator and the ground plane is a partial ground plane. It shows an impedance bandwidth of about 19.71% for |S11| < -10 dB where a peak gain of 1.15 dB is realized within the bandwidth and it covers the n78 band. In this case, the levels of the cross-polarization in both E-plane and H-plane are less than -12 dB. Finally, another antenna is proposed in which a meander line loaded split ring resonator is used as the patch and the ground plane is defected by a meander line. This design causes a high bandwidth of 26.6% for |S11| < -10 dB where a peak gain of 1.26 dB is realized. In addition, it achieves a good level of miniaturization of about one fourth of the operating wavelength with respect to the centre frequency. Moreover, the measured level of the cross-polarization in the horizontal plane is found to be less than -15 dB. The prototype which combines the single negative radiator with the DGS technique exhibits excellent radiation characteristics while at the same time maintaining a compact as well as wideband property