Rhombic antenna
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A rhombic antenna is a broadband directional antenna, mostly used in HF (high frequency, also called shortwave) ranges.
It is named after its "rhombic" diamond shape, with each side typically being of wavelength size. Each vertex is supported by a pole, several metres tall. It is fed at one of the sharp angles through a balun transformer, and is terminated at the opposite sharp angle with a non-inductive resistor. It is directional towards the resistor end, so it points towards the region of the world it is designed to serve.
The rhombic antenna can radiate close to the horizon or at a higher angle depending on its length, width, and height relative to the operating frequency. Likewise, its beam can be narrow or broad. A proper combination of size, height, and operating frequency make it fit for short- medium- or long-range communication.
Due to its considerable size, it is not very practical as the sole antenna of a radio station if operating conditions are expected to change rapidly. Moreover, it plainly requires a lot of land—especially if several must be combined to serve a variety of geographic targets at different distance ranges and on widely different frequencies.
On the other hand, it is one of the best options for predictable point-to-point circuits. Its size gives it a degree of gain, and allows it to capture energy from a wide area, thus making it a little less susceptible to sharply localized fading than smaller antennas.
