The HA.21.A is an ISM 868MHz quarter-wave monopole helical antenna. Small and compact, yet stable, this helical coil antenna is ideal for typical 868MHz applications such as: - Smart Metering - Smart security systems - Remote asset monitoring and other wireless communication devices. The helical coil antenna offers industry leading 70% efficiency at 868MHz on a 126.8 x 80.1mm ground plane, with matching components (orthogonally mounted to ground plane, see HAD.B.21 performance). Made of copper alloy, the helical coil is mechanically sturdy. It can be easily mounted on the surface by soldering. Since it is a monopole design, it must be connected to the main-board device ground-plane to radiate efficiently.