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PDFAn antenna is a device that transmit and/or receives radio waves for the purpose of point-to-point communication or broadcasting. To be more accurate, an antenna is a transducer that converts electromagnetic (radio) waves to electrical signals and vice versa. The conversion of electromagnetic waves to an electrical signal by an antenna is considered receiving, and the opposite process is considered transmission. Antennas can be designed to either transmit, receive, or both. Antennas that transmit and receive signals are often called transceivers.
There are many different types of antennas with different strengths, weaknesses, and applications. The parameters most commonly used to describe an antenna's characteristics and performance are resonant frequency, bandwidth, directivity, gain, and efficiency.
Resonant frequency is a particular frequency that the antenna was tuned to operate at, and its bandwidth is centered around this frequency. The antenna's bandwidth is the range of frequencies that it is able to transmit and/or receive. Not all antennas have only one resonant frequency, and many times antennas will resonate at multiples of the lowest resonant frequency causing noise or interference.
Gain and directivity are closely related parameters and both have to do with the radiation pattern of the antenna. However, gain takes the antenna's efficiency into consideration. Antenna gain is a dimensionless measurement that compares the intensity of an antenna in a certain direction to an ideal isotropic antenna that radiates in all directions equally. Directivity is essentially a measurement of which direction an antenna radiates most of its energy. A perfect antenna would have the same number for gain and directivity.
The efficiency of an antenna is a measurement of the amount of an antenna's input power that is dissipated through resistance and other losses.
Additional Information:
Automated Antenna Testing Using NI LabVIEW Software and PXI Hardware
Refer to the RF & Communications Resources page for additional information about RF terminology, fundamentals, and National Instruments RF products.
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