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Relative directivity factor (RDF) is a figure of merit for radio receiving antennas. [1] It is the antenna gain in the forward direction divided by the gain in all other directions. It is also called the signal to noise improvement factor (SNIF) .
This Z antenna tested at the National Institute of Standards and Technology is smaller than a standard antenna with comparable properties. Its high efficiency is derived from the "Z element" inside the square that acts as a metamaterial, greatly boosting the radiated signal. The square is 30 millimeters on a side. Metamaterial antennas are a ...
Since the directive antenna radiates the same total power within a small angle along the z axis, it can have a higher signal strength in that direction than the isotropic antenna, and so a gain greater than one. In electromagnetics, an antenna's gain is a key performance parameter which combines the antenna's directivity and radiation efficiency.
A high-gain antenna (HGA) is a directional antenna with a focused, narrow beam width, permitting more precise targeting of the radio signals. [1] Most commonly referred to during space missions, [2] these antennas are also in use all over Earth, most successfully in flat, open areas where there are no mountains to disrupt radiowaves. [citation ...
The AN/FLR-9 is a type of very large circularly disposed antenna array, built at eight locations during the Cold War for HF/DF direction finding of high priority targets. The worldwide network, known collectively as "Iron Horse", could locate HF communications almost anywhere on Earth.
The latter factor is quantified by the antenna gain, which is the ratio of the signal strength radiated by an antenna in its direction of maximum radiation to that radiated by a standard antenna. For example, a 1,000 watt transmitter feeding an antenna with a gain of 4× (equiv. 6 dBi) will have the same signal strength in the direction of its ...
Although no real antenna can be exactly isotropic, a few antennas are built to be as near to isotropic as possible; they are used for emergency backup antennas and for test equipment for other antennas: Because the received and transmitted signal strength is the same in (almost) every direction, they work without any need for them to be any ...
Often random wire antennas are also (inaccurately) referred to as long-wire antennas.There is no accepted minimum size, but actual long-wire antennas must be greater than at least a quarter-wavelength ( 1 / 4 λ) or perhaps greater than a half ( 1 / 2 λ) at the frequency the long wire antenna is used for, and even a half-wave may only be considered "long-ish" rather than "truly ...