Rhombic

Image of the Rhombic.

The Rhombic antenna is primarily used for long distance communication using ionospheric reflection in the HF band, although recent developments have shown useful topologies for the microwave band. For the HF band, the antenna is usually designed to radiate at a certain elevation angle to optimise ionospheric reflection. Since it is a travelling wave antenna, it is easy to design for wideband impedance characteristics. However, the direction of the main-beam elevation is frequency dependant, and usually limits the practical operational bandwidth.

This antenna can be seen as two back-to-back travelling wave Vee-dipoles. This configuration avoids the difficulty inherent in terminating the widely separated ends of a travelling wave Vee-dipole. It also has higher gain than a Vee-dipole or simple long-wire travelling wave antenna. Directionality in azimuth and increased gain is obtained by combining rhombic antennas in an array. Apart from steerable linear or circular arrays, stacked and stacked-and-interlaced arrays of rhombic antennas are often used.