Wavelength and antenna length
Radio waves travel at a fixed speed, so faster wiggles mean shorter waves. An antenna is a ruler cut to match the wave.
λ = c / f c = 299 792 458 m/s
Free-space wavelength. A practical wire antenna is about 95% of the ideal quarter wave because of end effects; coax and PCB traces are shorter still (velocity factor). Check local regulations before transmitting.