Antenna impedance is a measure of the resistance to an electrical signal in one antenna. Many factors affect the signal transmission capability of the antenna, including the environment that the antenna is in and the composition and design of the antenna. Understanding antenna impedance is very important when designing components that connect an antenna to a transmitter or receiver.
Antenna impedance is equal to the ratio of voltage to current, is expressed in units called ohms. The antenna impedance represents the power that is dispersed by it as it comes into contact with an electromagnetic wave as well as the power that is absorbed by the antenna. Different wavelengths of electromagnetic radiation will give different impedance values of the same antenna. In electronics, ohm is a measure of the resistance within a wire, and a measurement of zero ohms means that there is no resistance, while a measurement of infinite ohms means that there is complete resistance. The antenna impedance would be zero ohms if the current and voltage stayed the same from one point in the antenna to another. But this is never the case in real-world antennas, however, which generally have an impedance of between 15 and 1,000 ohms.
Environmental factors may affect antenna impedance.The objects around antenna, the height of antenna above the ground, and whether antenna is enclosed indoors or exposed to the elements all change its resistance when exposed to an electromagnetic signal. Under the optimal conditions, a simple half-wave dipole would have an 75 ohms impedance . Coaxial cable, which is used in conjunction with half-wave dipole antennas for transmitting television signals, is matched to this impedance and also has an 75 ohms impedance.
Impedance matching is an very important consideration when designing antennas of many different types. As it involves the transmission of power through the antenna. The antenna must transfer this information into a receiver of some sort, allowing people observers to collect the information picked up by the antenna. This information travels through the antenna and various cables, such as the coaxial cable that feeds information into a television. Finding cables that match the same voltage to current ratio helps keep the signal clean and strong as it passes from one device to another.
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