Radar terms, and definitions

Previous set of "P" definitions and terms.

PENCIL BEAM: A narrow circular radar beam from a highly directional antenna (such as a parabolic reflector).

PENTAGRID TUBE: An Electron tube having 5 grids, with one anode and one cathode.

PERIODIC ANTENNA: An antenna whose impedance varies as the frequency changes.

PERSISTANCE: The length of time a phosphor dot glows on a crt before disappearing.

PHASED ARRAY RADAR: Radar using many antenna elements which are combined in a controlled phase relationship. The direction of the beam can be changed as rapidly as the phase relationships (usually less than 20 microseconds). Thus, the antenna typically remains stationary while the beam is electronically scanned. The use of many antenna elements allows for very rapid and high directivity of the beam(s) with a large peak and/or average power. There is also a potential for greater reliability over a conventional radar since the array will fail gracefully, one element at a time.

PIN DIODE: A diode with a large intrinsic (I) region sandwiched between the P- and N- doped semiconducting regions. The most important property of the PIN diode is the fact that it appears as an almost pure resistance at RF. The value of this resistance can be varied over a range of approximately one-10,000 ohms by direct or low frequency current control. When the control current is varied continuously, the PIN diode is useful for attenuating, leveling and amplitude modulation of an RF signal. When the control current is switched on and off or in discrete steps, the device is useful in switching, pulse modulating, and phase shifting an RF signal.

PLANAR ARRAY: An antenna in which all of the elements, both active and parasitic, are in one plane. A planar array provides a large aperture and may be used for directional beam control by varying the relative phase of each element.

PLANE WAVEFRONTS: Waves of energy that are flat, parallel planes and perpendicular to the direction of propagation.

PLANNED-POSITION INDICATOR: A radar display in which range is indicated by the distance of a bright spot or pip from the center of the screen and the bearing is indicated by the radial angle of the spot.

POINT CONTACT DIODE: This was one of the earliest semiconductor device to be used at microwave frequencies. Consisting of a spring-loaded metal contact on a semiconducting surface, this diode can be considered an early version of the Schottky barrier diode. Generally used as a detector or mixer, the device is somewhat fragile and limited to low powers.

POLARIZATION: The direction of the electric field (E-field) vector of an electromagnetic (EM) wave. The most general case is elliptical polarization with all others being special cases. The E-field of an EM wave radiating from a vertically mounted dipole antenna will be vertical and the wave is said to be vertically polarized. In like manner, a horizontally mounted dipole will produce a horizontal electric field and is horizontally polarized. Equal vertical and horizontal E-field components produce circular polarization.

Next set of "P" definition and terms.