5G air interfaces are split into two distinct spectrum blocks: sub-6 GHz (410 MHz–7.125 GHz) and millimetre-wave (24.25–52.6 GHz). At sub-6 GHz the wave-length is still long enough for traditional dipoles or patch elements, but the sheer element count forces designers to miniaturise. Techniques such as meandered arms, high-permittivity substrates and stacked patches shrink the antenna footprint while maintaining impedance bandwidth. Passive beam-forming is usually sufficient because moderate directionality restores link budget without aggressive gain. Millimetre-wave bands, however, behave like quasi-optical links: oxygen absorption, rain fade and brick-wall penetration can exceed 30 dB. Here the antenna must provide high directivity just to close the link, so phased arrays become mandatory. Element spacing drops to 2–3 mm, requiring low-loss packaging, air-cavity-backed patches or dielectric resonators. Thermal design is equally critical; with effective isotropic radiated power (EIRP) approaching 65 dBm, every 0.1 dB of insertion loss turns into watts of heat inside the handset or indoor access point.
