Rhombic antenna

It is typically fed at one of the two acute (sharper angle) vertices through a balanced transmission line, or alternatively a coaxial cable with a balun transformer.

It is possible to improve the low efficiency and gain of unidirectional rhombics by replacing the termination resistor by a low-loss balanced resonant stub transmission line.

This reflects the power that would have been wasted in the termination resistor back into the antenna with the correct phase to reinforce the excitation from the transmitter.

After World War II the rhombic largely fell out of favor for shortwave broadcast and point-to-point communications work, being replaced by log periodic antennas and curtain arrays.

For example, BBC Monitoring's Crowsley Park receiving station has three rhombic antennas aligned for reception at azimuths of 37, 57 and 77 degrees.

The rhombics' low cost, simplicity, reliability, and ease of construction sometimes outweighs performance advantages offered by other more complex arrays.

Small rhombic UHF television antenna from 1952. Its broad bandwidth allowed it to cover the 470 to 890 MHz UHF television band.
Diagram of radiation patterns (grey) of each segment of the antenna illustrates how it works. By using the correct vertex angle, one of the main lobes of each of the four sides point in the same direction, reinforcing each other, increasing the gain .
A horizontal three-wire rhombic antenna. This example is terminated with a resonant stub transmission line power reflector instead of a resistor to increase efficiency.
AT&T 2 wire rhombic in Dixon, California, in 1937, used for telephone service to Shanghai, China
As of 2023, one last remnant pole still stands from the AT&T pole farm which was located in Mercer County, New Jersey