An antenna apparatus for harvesting ambient radio frequency, RF, energy, comprises one or more RF antenna components arranged to receive RF energy. The antenna components comprise a plurality of frequency filtering components, each filtering a respective frequency band of the received RF energy. A rectifying circuit is arranged to convert a variable electrical signal received at an input from an associated antenna, into a direct current electrical signal for supplying to an electrical energy storage unit. A power management module has an input arranged to receive the direct current and control supply of the direct current to the electrical energy storage unit. The rectifying circuit comprises a plurality of transmission lines, and the input of the rectifying circuit and the input of the power management module are connected via the transmission lines. The power management module is arranged at least partially within a boundary defined by the transmission lines.