Passive Antennas:

• ANTENNA PATTERN: desired performance of antenna as a function of direction (two dimensions: Azimuth and Elevation)
• AXIAL RATIO: measure of antenna circularity or quadrature balance on its axis of symmetry (often the zenith). Use for circularly polarized antennas only
• BANDWIDTH, 3 dB: immediate frequency range where antenna performs at least half as well as it does at its optimum frequency (usually resonance)
• BANDWIDTH, "x.x" VSWR: immediate frequency range where antenna impedance mismatch equates to a VSWR of "x.x" or lower
• BEAMWIDTH, 3 dB: angular spread where antenna performs at least half as well as it does in its peak direction
• DIRECTIVITY: the idealized gain of the antenna at its peak direction
• DISTANCE TO OTHER OBJECTS AND GROUND: self explanatory
• DUTY CYCLE: the ratio of time the antenna is fed radio power to the total period. Mainly used for antennas subject to high power pulses, or antennas with built-in limiters or EMP protection.
• ELEMENT, ELEMENTS: typically a subset or a more elementary part of a larger antenna system. For example, an ELEMENT of a Yagi-Uda array is normally a Dipole Antenna that, together with other Dipoles, forms the Array. An 8-Element Yagi antenna would then ordinarily have 8 dipoles.
• EMBEDDED ANTENNA: typically an antenna that is enclosed into a product's housing or case, or one that is not readily discernible by a casual observer. The antenna forms an integral, inseparable part of the product.
• FREQUENCY of OPERATION: desired operating center frequency
• GAIN: actual gain of the antenna at its peak direction
• RF IMPEDANCE: the desired complex ratio of voltage to current at the antenna connector, at the design frequency (typically 50 Ohms, real)
• DC IMPEDANCE: the desired ratio of voltage to current at the antenna connector for a Direct Current (can be measured with a simple voltmeter). Typically, this value is either approximately 0 Ohms (short circuit) or very large, depicted as infinite Ohms (open circuit.) A short circuit value is desirable to help protect the transmitter circuitry and the feedline from static energy. If you expect your device to operate in static prone environments, you should request that the DC short circuit impedance have a high ampacity (able to carry a large current), or specify the desired current handling capability in Amperes.
• INVERTED-F ANTENNA: an old antenna gaining popularity each new day. Previously used in Aircraft, Missiles and by many radio experimenters (under the name of DDRR), this antenna is fast becomming an embedded antenna of choice in many applications.
• PATCH ANTENNA: a typically low efficiency short radiating/receiving antenna, popular for its low profile. Patches can have an unlimited number of shapes and sizes, and can be made to conform to most surface profiles. When built using special dielectric materials, smaller than natural antennas can be realized that will fit small packages. Polarization of a Patch Antenna can be Linear or Elliptical (including Circular.) It is a popular choice of antenna these days for almost any application (in many cases overrated.) The bandwidth of a Patch Antenna is usually narrow.
• POLARIZATION: the orientation of the electric field a great distance from the antenna. Appropriate types are: Linear, Vertical; Linear, Horizontal; Linear, Oblique; Circular, Right Hand (RHCP); Circular, Left Hand (LHCP); Elliptical, Right Hand and Elliptical, Left Hand. Typically, your application will require either one of the three Linear polarizations or one of the Circular polarizations.

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