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Rhombic Antenna

Travelling-Wave Antennas

A large diamond of wire, terminated to give high-gain, single-direction radiation.

Band: HF (wideband)
Gain: ~12-20 dBi
Polarization: Horizontal

Photos

Real-world photo of a Rhombic Antenna in use — Real-world example. Source: Wikimedia Commons (CC BY-SA 4.0; Ulrich Eitler).

Radiation / wave patterns

Idealized radiation pattern of the Rhombic Antenna — Idealized azimuth radiation pattern (illustrative, generated). Radial scale in dB.

How & why it works

A rhombic is a big horizontal diamond of wire, several wavelengths on each leg, fed at one apex and resistively terminated at the opposite apex. The termination absorbs the reflected wave so a travelling (not standing) wave runs along the wires; the four legs are angled so their individual radiation lobes line up and reinforce in one direction, yielding very high gain over a broad frequency range. The trade-offs are a large footprint and power lost in the terminating resistor.

Real-world uses

Historic long-haul HF broadcasting and point-to-point circuits; large fixed HF stations.