Antennas

Wavelength:

$\lambda = \frac{c}{f}$

A half-wave dipole is about $\lambda/2$ long (at 2.4 GHz: ≈ 6.2 cm; at 433 MHz: ≈ 35 cm). A quarter-wave monopole over a ground plane is $\lambda/4$.

Key specs: gain (dBi), radiation pattern, impedance (usually 50 Ω), bandwidth and VSWR (match quality). For PCB antennas, follow the module maker's keep-out area exactly — copper or metal nearby detunes the antenna.