Antenna Glossary

Antenna: A metallic device used in the transmission and reception of electromagnetic waves. An antenna is a passive or an active device which permits transmission. Antenna Power Gain: The ratio of the antenna's maximum radiation intensity in a stated direction to the maximum radiation intensity of a reference antenna (dipole, isotropic antenna) with identical power applied to both. Attenuation: The loss in power of electromagnetic signals between transmission and reception points. Azimuth: Horizontal direction expressed as the angular distance between the direction of a fixed point (as the observer's heading) and the direction of the object. Bandwidth: A range of consecutive frequencies comprised of a band (i.e. the US cellular bandwidth is 72 MHz wide between the frequencies of 824 MHz - 894 MHz) over which an antenna shall perform without the need of any adjustment. Base Station: In a cellular communication system, a base station could be considered a central mode of transmission and reception for the network. Currently, this station includes an omnidirectional antenna or several sectoral antennas. Beamwidth: The angle of signal coverage provided by an antenna. Beamwidth typically decreases as antenna gain increases. Cable Loss: A numeric value describing the amount or signal loss from one point on a length of cable to another. This is measured in decibels (dB). Center Fed: Transmission line connection at the electrical center of an antenna radiator. Coaxial Cable: Cable consisting of a single copper conductor in the center surrounded by a plastic layer for insulation and a braided metal outer shield. Coax is used to transfer radio frequency energy from the transmitter to the antenna. Collinear Array: A system of two or more antenna radiators arranged in a line and connected end-to-end to generate a directed field pattern (serial linear topology). Coupler: Referring to on-glass antennas, a coupler is the two-piece interface between the coaxial cable on the inside of the glass and the radiator on the outside of the vehicle. It is designed to efficiently couple RF energy through the glass. The formulation of the glass and glass thickness normally have a substantial effect on coupler performance. dBd: Quantification of the gain for an antenna in comparison with the gain of a dipole. dBi: The dB power relative to an isotropic source. dBm: A measure of power based upon the decibel scale, but referenced to the milliWatt: i.e. 1dBm = .001 Watt. dBm is often used to describe absolute power level where the point of reference is 1 milliWatt. In high power applications the dBW is often used with a reference of 1 Watt. dBW: The ratio of the power to one Watt expressed in decibels. DC Ground: An antenna which is a dead short to a DC current, and has a shunt fed design. To RF it is not seen as a short. Dipole: An antenna — usually a half wavelength long — split at the exact center for connection to a feed line. Directional Antenna: An antenna having the property of radiating or receiving electromagnetic waves more effectively in some directions than others. Directivity: The theoretical characteristic of an antenna to concentrate power in only one direction, whether transmitting or receiving. Driven Element: A radiator element of an antenna system to which the transmission line is connected. Efficiency: The ratio of useful output to input power, determined in antenna systems by losses in the system including losses in nearby objects. Electrically Small Antenna: Some antennas (such as various low profile antennas, some base loaded whips and often rubber duckie portable antennas) are physically considerably smaller than either a 1/2 or 1/4 wavelength antenna. The challenge with electrically small antennas is to maintain radiating efficiency. A greater challenge is to design an antenna with adequate bandwidth. Careful design using high quality materials often overcome these obstacles. Embedded Antennas: Antennas directly integrated into a system such as an access point, a terminal or a handset. In most cases, this antenna is matched to the system and can not be used in other applications without modification. E-Plane and H-Plane: Antenna measurements in general and radiation patterns in particular must be performed with polarization in mind. Since polarization is defined as having the same orientation as an antenna's electric field vector, it is common practice to refer to measurements aligned with either the electric vector ( E-plane) or magnetic vector (H-plane). ERP: Effective Radiated Power. Fiber Optic Cable: A cable, consisting of a center glass core surrounded by layers of plastic that transmits data using light rather than electricity. It has the ability to carry more information over much longer distance. Field Strength: An absolute measure in one direction of the electromagnetic wave field generated by an antenna at some distance away from the antenna. Frequency: The number of cycles per second of a wave. Front-To-Back Ratio: The ratio of radiated power off the front to the back of a directive antenna. A dipole would have a ratio of 1, for example. Full Duplex: Refers to a communication system or equipment capable of transmission and reception simultaneously. Gain: Gain is the practical value of the directivity of an antenna. It takes into account the efficiency of the complete structure. Gigahertz (GHz): One billion cycles per second. GPS: Global Positional Satellite or Global Positioning System. Ground Plane: A man made system of conductors placed below an antenna to serve as an earth ground. Hertz (Hz): A unit of frequency equal to one cycle per second. Impedance: The Ohmic value of an antenna feed point, matching section or transmission line at a radio frequency. An Impedance may contain a reactance as well as a resistance component. Lightning Protector: A device designed to divert large surges of current such as a lightning strike from reaching the RF equipment. There are many types of lightning protectors including Quarter Wave Stub and Gas Discharge Tubes. Load: The electrical entity to which power is delivered. The antenna system is a load for a transmitter. Megahertz (MHz): 1 million cycles per second. Mount: A mount is the device onto which a mobile antenna attaches. It is the mechanical and electrical interface between an antenna and the vehicle. Noise: Any unwanted and un-modulated energy that is always present to some extent within any signal. Omnidirectional: An antenna providing a 360-degree transmission pattern. This type of antenna is used when coverage in all directions is required. Parabolic Antenna: An antenna consisting of a parabolic reflector and a radiating or receiving element at or near its focus. Parabolic antennas are very directive and includes a preliminary source and a parabolic reflector to focus the energy. PCB: Printed Circuit Board. Planar Array: An antenna in which all of the elements, both active and parasitic, are in one plane. Point-to-Point: A communications channel running from one point to another. Point-to-Multipoint: A communications channel running from one point to several other points. Polarization: The sense of the wave radiated by an antenna. This can be horizontal, vertical, elliptical or circular (left or right hand circularity) depending on the design and application. Radiation Pattern: The graphical representation of the relative field strength radiated from an antenna in a given plane, plotted against the angular distance from a given reference. Radiator: A discrete conductor radiating RF energy in an antenna system. Radome: A typically rigid dielectric cover over the radiating portion of an antenna, and nearly always separated from the radiator by an air gap. A radome (the merger of radar and dome) has the purpose of protecting the radiator from natural weather phenomena and contamination by dirt. It usually includes aerodynamic shaping to minimize wind loading. Receiver (Rx): An electronic device which enables a particular signal to be separated from all and converts the signal format into a format for video, voice or data. Relative Antenna Power Gain: The ratio of the average radiation intensity of the test antenna to the average radiation of a reference antenna with all other conditions remaining equal. RFDC: Radio Frequency Data Communications. RFID: Radio Frequency IDentification. RSSi: Received Signal Strength Indicator. Provides a signal for logic circuit processing that is a function of received RF signal strength. RSSI is used both by the switch and the mobile or portable. Standard Impedance: The nominal impedance associated with the transmission line and test equipment. Transmission Line: The connecting link allowing the radio frequency energy generated by the radio to be delivered to the antenna. (Coaxial cable, microstrip or coplanar lines in our industry.) Transmitter : An electronic device consisting of oscillator, modulator and other circuits which produce a radio electromagnetic wave signal for radiation into the atmosphere by an antenna. Voltage Standing Wave Ratio (VSWR): VSWR of the antenna is the ratio of the maximum to minimum values of voltage in the standing wave pattern appearing along a lossless 50 Ohms transmission line with an antenna as the load.