Antenna with cosecant squared pattern are special designed for air- surveillance radar sets. These permit an adapted distribution of the radiation in the beam. a fan beam. Figure Vertical projection of the radiation pattern of an antenna with cosecant squared characteristic, the blue graph shows the theoretically form, . This paper deals with the analysis and proper design of parabolic reflector antennas to obtain pencil beam, cosecant-squared and inverse cosecant- squared.
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To get the cosecant squared pattern, a part of the radiated energy must be turned up.
Radar Basics – Antennae with Cosecant Squared Pattern
Retrieved cosecatn ” https: In reality, the diagram is superposed with a number of side lobes mainly on the back at higher elevation angles. At use of several receiving channels a height allocation also can be carried out.
According xntenna definition mentioned above the height also shall be constant. Alpha 2 Angle The angle 2 in the above equation and illustration. In the practice a cosecant squared pattern can be achieved by a deformation of a parabolic reflector. Without correction, this produced a display where the ground under the aircraft was very bright on the cathode ray tube display, while the terrain at longer distances was almost invisible.
At an antenna array with Yagi- antennae the pattern is achieved by interference of the direct wave with this at the earth’s surface reflected quotas. This can be realized also with other kind of antennae. The lobe of the radiator is weaker to the margin to, therefore the margins of the reflector are hit weaker as the centre.
To counteract this, the scanning antenna was re-aimed so that it was pointed almost directly forward, thereby sending most of the radar energy at low angles relative to the aircraft, thereby increasing the energy available at long range. The opposite modification could also be used, bending the upper lip csecant, with the same basic outcome.
The cosecant squared pattern isn’t restricted to parabolic reflectors. Azimuth Beamwidth The full width of the beam in the x-y plane of the beam coordinate system.
Cosecant squared antenna – Wikipedia
The concept originated as part of the development of the H2S radarwhich scanned the area under an aircraft to provide a radar map of the ground below. This antenna uses a polar coordinate system. The terrain at further distances returns much less signal due to the radar equation. Sqkared slant range distance between the radar and the terrain is the cosecant of the angle between the fuselage and the target, and the energy falls off with the fourth root of that number.
The result was an evener display pattern. These permit an adapted distribution of the radiation in the beam and causing a more ideal space scanning. Open topic with navigation. That means, we can shorten the height too without changing the dependence. The part of the rays which falls to the less bent area in the top is reflected up now. A cosecant squared antennasometimes known as a constant height patternis a modified form of parabolic reflector used in some radar systems.
This antenna pattern can get the required elevation coverage where the received power is independent squard the radar range for a constant height target It is a means of achieving a more uniform signal strength at the input of the antenn as a target moves with a constant height within the beam.
For an embedded antenna on a receiver, transmitter or squarer, this value corresponds to the Frequency entered cosexant the Model Specs tab for the transmitter or receiver and the Transmitter Specs tab for the Radar. Alpha M Angle The angle m squareed the above equation and illustration. Views Read Edit View history.
The angle m in the above equation and illustration. Vertical projection of the radiation pattern of an antenna with cosecant squared characteristic. The wquared illustration depicts a typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar.
This page was last edited on 30 Decemberat Stacked beam cosecant squared pattern. The angle 1 in the above equation and illustration.
This gives in near range an ssquared gain required for constant echo strength after sensitivity time control. The angle m is the upward tilt angle of the beam relative to the horizontal, generally about half a beamwidth.
A possible method analogously for this one is, to bend the lower part of the reflector more intense. Main-lobe Gain dB The main lobe gain of the antenna pattern.
Cosecant squared antenna
A possibility consists in lower bending of the top of the reflector. Efficiency The efficiency of the antenna a value between 0 and percent. The shape of all these back side lobes is combined into a nearly parabolic slope. This left the area directly under anttenna aircraft receiving no energy at all, so the upper lip of the reflector was bent to reflect a small amount of energy in that direction. Antennae with constant height pattern or cosecant squared pattern are special designed for air-surveillance radar sets.