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Topic: Aperture (antenna)

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	The Antenna Factory: Your source for high performance antennas
		The aperture is often taken as that portion of a plane surface near the antenna, perpendicular to the direction of maximum radiation, through which the major part of the radiation passes.
		Cross polarization discrimination is the measure of the antenna’s ability to differentiate between the vertical and the horizontal polarization of an antenna.
		The polarization of an antenna is defined as the polarization of the electromagnetic wave as described by the shape and orientation of an ellipse, which is the locus of the extremity of the field vector, and the sense in which the ellipse is traversed with time.
	www.antennafactory.com /definitions.html (1366 words)

	[No title] (Site not responding. Last check: 2007-11-07)
		Antenna aperture is a concept that may need some explanation.
		The aperture of the antenna as it faces the signal, is very much larger than the antenna aperture for signals coming in off-axis.
		Its (forward-looking) aperture is not big enough to absorb enough energy coming from the front to be able to overpower the energy picked up from the stronger off-axis signal (coming from the side).
	members.aol.com /bmgenginc/AntPath4.html (601 words)

	Antennas
		Antennas are also used in "receive mode" to collect radiation from "free space" and deliver the energy contained in the propagating wave to the feeder and receiver.
		The biconical antenna, and its derivatives, the broad-banded Yagi, the bow-tie antenna and the phantom conical antenna (which doesn't have a complete conical surface, but just conically disposed rod elements), is a good method of broad-banding a dipole type of antenna.
		In a reflector-aperture antenna fed from the front by a sub-reflector and/or a feed, the far field radiation pattern can be calculated from the Fourier Transform of the field distribution across the aperture, accounting as well for phase variations across the illuminated area.
	www.ee.surrey.ac.uk /Personal/D.Jefferies/antennas.html (9070 words)

	Aperture antenna principles
		We of course assume the amplitude is zero everywhere outside the aperture, on the plane of the aperture.
		For the case of uniformly illuminated apertures of arbitrary shape, a very good idea of the far field patterns can be obtained by photographing the diffraction of a laser beam by a similarly shaped aperture, suitably scaled in wavelength.
		The nulls of an array of isotropes centred on the individual elements of the aperture array are called "grating nulls", whereas the nulls due to the diffraction pattern of an individual aperture are called "aperture nulls".
	www.ee.surrey.ac.uk /Personal/D.Jefferies/aperture.html (2271 words)

	What is Synthetic Aperture Radar? -- Sandia National Laboratories
		Synthetic aperture radar complements photographic and other optical imaging capabilities because of the minimum constraints on time-of-day and atmospheric conditions and because of the unique responses of terrain and cultural targets to radar frequencies.
		Range measurement and resolution are achieved in synthetic aperture radar in the same manner as most other radars: Range is determined by precisely measuring the time from transmission of a pulse to receiving the echo from a target and, in the simplest SAR, range resolution is determined by the transmitted pulse width, i.e.
		The distance the aircraft flies in synthesizing the antenna is known as the synthetic aperture.
	www.sandia.gov /radar/whatis.html (798 words)

	Interpreting Antenna Performance Parameters for EMC Applications - Part 3
		However, unlike antenna gain or directivity, the antenna factor is not dimensionless; it has units of 1/m in the case of electric field antenna factor and units of S/m in the case of magnetic field antenna factor.
		The increasing frequency slope of the antenna factor of the 1.37 meter biconical antenna is not due to mismatch.
		Antenna factor has been shown to be essentially the reciprocal of the effective length of an antenna, which reflects the ability of an antenna to integrate an incident field to provide a potential difference at its output terminals.
	www.djmelectronics.com /articles/emc-antenna-parameters-p3.html (2911 words)

	ANTENNA INTRODUCTION / BASICS
		The gain or directivity of an antenna is the ratio of the radiation intensity in a given direction to the radiation intensity averaged over all directions.
		Therefore, beamwidth is a function of the antenna dimension "L" and the wavelength of the signal.
		The aperture illumination or illumination taper is the variation in amplitude across the aperture.
	www.kyes.com /antenna/navy/basics/antennas.htm (1961 words)

	Antenna gain - Wikipedia, the free encyclopedia
		In antenna design, gain is the logarithm of the ratio of the intensity of an antenna's radiation pattern in the direction of strongest radiation to that of a reference antenna.
		For dish-type antennas, gain is proportional to the Aperture (reflective area) and surface accuracy of the dish, as well as the frequency being transmitted/received.
		The antenna's efficiency rating is the percentage of signal captured by the parabolic reflector that actually is received by the feedhorn.
	en.wikipedia.org /wiki/Antenna_gain (609 words)

	Synthetic monopulse radar - Patent 4387373
		The synthetic aperture radar of claim 10 in which said first integrating means integrates the backscattered energy of sampling points in a first half of the synthetic aperture; and said second integrating means integrates the backscattered energy of sampling points in a second half of the synthetic aperture.
		As a consequence of the non-coherent transmission from the elements of the synthetic aperture, the resolution of a synthetic aperture radar is substantially the same as could be achieved with the use of an antenna array which was twice as long as the synthetic array length.
		After the antenna has traversed K number of sampling points, the signals stored in the memory device are somewhat similar to the signals that would have been received by the elements of a conventional linear array antenna arranged along the flight path 14 of the aircraft 12.
	www.freepatentsonline.com /4387373.html (7287 words)

	Antenna aperture - Wikipedia, the free encyclopedia
		As a receiver, antenna aperture can be visualised as the area of a circle constructed broadside to incoming radiation where all radiation passing within the circle is delivered by the antenna to a matched load.
		Generally, antenna gain is increased by directing radiation in a single direction, while necessarily reducing it in all other directions since power cannot be created by the antenna.
		Thus the higher the gain, the larger the aperture and the narrower the beamwidth.
	en.wikipedia.org /wiki/Antenna_aperture (174 words)

	RADAR and SAR Glossary
		For a pair of antennas in a transmit-receive configuration, the polarisation beamwidth is defined as the angle between the two directions from the transmitter at which the polarisation efficiency is one-half of its maximum value.
		Moving antennas can be used to form a synthetic aperture, where the physical antenna is small compared to the synthesised antenna, and has a sufficiently wide radiation pattern to illuminate the observed surface over a significant period of platform motion.
		The sensitivity of the antenna is sensitive to angle and the radiometric compensation adjusts for variation in the received signal due to this effect.
	envisat.esa.int /dataproducts/asar/CNTR5-2.htm (6565 words)

	What is imaging radar ?/jpl
		The radar antenna alternately transmits and receives pulses at particular microwave wavelengths (in the range 1 cm to 1 m, which corresponds to a frequency range of about 300 MHz to 30 GHz) and polarizations (waves polarized in a single vertical or horizontal plane).
		Thisbackscatter returns to the radar as a weaker radar echo and is received by the antenna in a specific polarization (horizontal or vertical, not necessarily the same as the transmitted pulse).
		Aperture means the opening used to collect the reflected energy that is used to form an image.
	southport.jpl.nasa.gov /desc/imagingradarv3.html (1912 words)

	ALA100 Large Aperture Active Loop Antenna reduces local interference
		The active antenna solves the problem of impedance matching to the feeder and yet the performance is comparable with larger antennas.
		The large aperture of the ALA 100 improves the signal pickup to optimise the signal to noise ratio and also reduces fading at HF, this is a very important advantage compared to small active antennas.
		Whip antennas that use the feeder as an RF return path are prone to interference induce on the feeder screen and mains borne noise.
	www.wellbrook.uk.com /ALA100.html (1063 words)

	Radio Direction Finder Antenna Systems
		Furthermore, DF antennas designed for the VHF air band are available in either a 16 element, wide aperture array or an 8 element, medium aperture array.
		Mathematical analysis of the operational concepts of all standard DF antennas (including all those in use today) is reported together with the analysis of the effect of reflections on the bearing error of each type of antenna.
		The RMS error, because of the unusual advantages of the Doppler antenna in minimizing the effects of reflections over most of the circle from which reflections could come, is a much smaller percentage of the peak error than is the case with the Adcock or time-of-arrival type antenna.
	www.servo.com /radio.htm (1612 words)

	Patch Antenna Fed via Unequal-Crossed-Arm Aperture NASA Tech Briefs - Find Articles (Site not responding. Last check: 2007-11-07)
		In designing a rectangular-patch CP antenna, one chooses the dimensions of the patch and of the crossed arms of the aperture to introduce a 90° phase shift between the two orthogonal electromagnetic modes of the patch.
		In the case of a conventional "nearly square" design, the aperture arms are constrained to have equal dimensions, it is assumed that the value of the resonance quality factor (Q) is the same for both modes, and the effects of the electromagnetic modes of the crossed aperture arms are neglected.
		In designing an antenna as proposed, to compensate for an axial ratio that deviates from 1 by an unacceptably large amount, the dimensions of the aperture arms along one direction could be adjusted in tandem with the corresponding orthogonal patch dimension.
	www.findarticles.com /p/articles/mi_qa3957/is_200506/ai_n13642860 (607 words)

	Sample Article from Antenna Systems & Technology
		Exposed antennas at Ka Band suffer from increased fade and dropout during heavy rain because the antenna main beam is significantly defocused by the water on the surface of the antenna.
		Characterization of the RF performance of these small aperture terminal radomes is accomplished by detailed numerical modeling, explicitly including an accurate description of the characteristics of the antenna system enclosed by the radome.
		The latter is particularly important for many types of antenna systems for which the angle of incidence at the radome surface is substantially oblique over much of the projected antenna aperture.
	www.antennasonline.com /articles/jan01-1.htm (2322 words)

	Antenna Theory
		The aperture of an isotropic source is a circle with a diameter of 5/16 wavelength.
		The aperture of a dipole antenna is roughly the shape of a rugby ball (elliptical) when viewed from a point 90 degrees from the line of the conductor.
		Actual construction of these antennas is such that the antenna conductor is continued on down to the ground, where a matching network transforms the high impedance of the 1/8 wavelength long, single conductor, feed line to the low impedance of the line running to the transmitter.
	k9erg.tripod.com /theory.htm (1866 words)

	Parabolic antenna - Wikipedia, the free encyclopedia
		The parabolic antenna is a high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (RADAR), on the UHF and SHF parts of the electromagnetic spectrum.
		This antenna is typically a low-gain type such as a half-wave dipole or a small waveguide horn.
		The feed antenna is connected to the associated radio-frequency (RF) transmitting or receiving equipment by means of a coaxial cable transmission line or hollow waveguide.
	en.wikipedia.org /wiki/Parabolic_antenna (960 words)

	University of Mississippi Dept. of Electrical Engineering
		New configurations of coplanar patch antennas (CPA) and coplanar aperture antennas (CAA) and combinations are proposed for use as an element of a phased array antenna, specifically designed for radar, aircraft, missile, and satellites systems, as well as space stations.
		Antenna performance is tuned, or optimized, by using slots, shorts, and by mitering sharp corners on the antennas and feeding element for enhanced antenna characteristics.
		The primary disadvantage of the patch or aperture antenna is the narrow operational bandwidth.
	www.ee.olemiss.edu /researchbriefs/widebandprintedantenna.asp (516 words)

	Untitled Document
		Arrays of half waves, such as collinears, have smaller apertures extending just beyond the physical structure, while parabolic antennas have apertures that are slightly smaller than the physical size of the dish.
		For horizontally polarized antennas, the vertical stacking distance is referred to as the h-plane or magnetic field plane.
		The reason being that with the larger aperture of the 144 yagi, more metal may be introduced within that space with less effect than with a smaller aperture antenna.
	www.directivesystems.com /STACKING.htm (3174 words)

	An Airborne Global Broadcast Service/Military Strategic and Tactical Relay Satellite Wideband Antenna
		The antenna ground plane is mounted on bearings and rotated using low-cost stepper motors.
		By comparison, the vertical dimension of the HLL antenna's aperture is always 2h, which is twice as large as the maximum allowable vertical height of a planar array or reflector antenna.
		The antenna, shown in Figure 4, is mounted on bearings and driven by a large diameter ring gear.
	www.afrlhorizons.com /Briefs/0009/IF9906.html (1838 words)

	Jampro Antennas Jampro Journal 3 (Site not responding. Last check: 2007-11-07)
		stacked aperture antenna system was recently installed utilizing broadband UHF panels and a VHF spiral antenna to serve the Honolulu market and the greater Oahu.
		The UHF broadband antenna panels can be modularly placed around a tower to produce omni or directional patterns.
		This is just one example of stacking two proven and reliable antennas into a common aperture.
	www.jampro.com /new/journal3.htm (263 words)

	Micro-X Vehicles
		The conventional practice of beam forming by means of analog radio-frequency combining networks in circuitry spanning the antenna aperture is adequate for narrower-band signals and smaller-aperture, non-electronicallyronmental steerable antennas, but cannot meet the challenge to ensure phase stability and coherence while providing for steerability in the contemplated wide-band, verylarge- aperture application.
		The approach taken in designing the DBF subsystem to meet this challenge starts with the use of compact, high-performance analog-to-digital converters and digital circuitry to sample and coherently process the received signals at the sub-aperture (antenna-panel) level rather than to initiate digital processing farther along the signal-processing chain as in conventional practice.
		Because of the large antenna size and wide-band operation, phase shifters at each transmit/receive (T/R) module are not, by themselves, sufficient for achieving correlation among the 32 antenna panels.
	www.afrlhorizons.com /ETB/ETBriefs/Mar06/NPO_41047.html (538 words)

	Jampro Antennas: NTSC/DTV (Site not responding. Last check: 2007-11-07)
		There are many combinations of stacking TV antennas to accommodate each broadcaster such as top mounting both antennas or top mounting one antenna and side mounting another.
		With more batwing antennas produced and installed by JAMPRO throughout the world, JAMPRO is the most experienced manufacturer of this antenna.
		The JUHD antenna is based on a modular design and can be configured to provide various azimuth and elevation patterns.
	www.jampro.com /tva/stacked.htm (559 words)

	Coaxial dipole antenna with extended effective aperture (US4504834)
		A coaxial dipole antenna includes a first radiator which is approximately one quarter wavelength long.
		A second radiator exhibits length less than one quarter wave length and is coupled to the feed port by a reactive element which has an electrical reactance which is insufficient to increase the electrical length of the second radiator to one quarter of the wavelength.
		The length of a dipole antenna is substantially shortened while an effective aperture of one half wavelength is maintained by causing a portion of the transceiver housing to radiate in phase with the antenna.
	www.delphion.com /details?pn10=US04504834 (381 words)

	Aperture (disambiguation) - Wikipedia, the free encyclopedia
		Aperture, in optics and photography, the opening that limits the amount of light that can pass through
		Aperture (computer memory), a region of the physical address space associated with a particular device or memory unit
		Aperture (botany), a weaker spot in the wall of a pollen grain
	en.wikipedia.org /wiki/Aperture_(disambiguation) (181 words)

	Aperture Antennas
		The electric far field components radiated by a circular aperture antenna are given by
		where r is the distance from the antenna to the point of observation, a is the radius of the circular aperture, E
		Two applets can be used to explore the properties such as radiation pattern of circular apertures.
	www.analyzemath.com /antenna_tutorials/aperture_antennas.html (225 words)

	An Aperture-Coupled Patch Antenna on Modified-Shape Ground-Plane -- KUGA E88-B (6): 2597 -- IEICE Transactions on ...
		The author is with the Graduate School of Engineering, Yokohama National University, Yokohama-shi, 240-8501 Japan.
		to show an potential as a polarization diversity antenna.
		Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues.
	ietcom.oxfordjournals.org /cgi/content/short/E88-B/6/2597 (194 words)

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