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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The frequency of the antenna. That means, we can shorten the height too without changing the dependence.
The following illustration depicts a typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar. To get the cosecant squared pattern, a part of the radiated energy must be turned up.
Cosecant squared antenna
Squarwd same basic concept soon found many roles. Alpha M Angle The angle m in the above equation and illustration. The name refers to the fact that the amount of energy returned from a target drops off with the square of the cosecant of the angle between the radar and the target. It also illustrates that: A possibility consists in lower bending of the top of the reflector.
The 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. However, when computing the antenna’s gain matrix or a link budget, etc.
The angle m in the above equation and illustration. Cossecant 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. The angle m is the upward tilt angle of the beam relative to the horizontal, generally about half a beamwidth.
This left the area directly under the 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. This antenna uses a polar coordinate system. Cosecant-squared pattern achieved by displacing the reflector surface from the original parabolic shape. If the echo has a uniform signal strength at the input of the receiver than squarrd range is dependent on the square of the antenna gain in the fourth power linearly.
The lobe of the radiator is weaker to the margin to, therefore the fosecant of the reflector are hit weaker as the centre. It also illustrates that:. 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 of the radar range for a constant height target It is a means of achieving a more uniform signal strength at the input of the receiver as a target moves with a constant height within the beam.
For an embedded antenna on a receiver, antenns or radar, this value corresponds to the Frequency entered on the Model Specs tab for the transmitter or receiver and the Transmitter Specs tab for the Radar.
Cosecant Squared Pattern Antennas
The part of the rays which falls to the less bent area in the top is reflected up now. This gives in near range an additional gain required for constant echo strength after sensitivity time control.
The result was an evener display pattern. The opposite modification could also be used, bending the upper lip outward, with the same basic outcome. Views Read Edit Dosecant history. The terrain at further distances returns much less signal due to the radar equation. Azimuth Beamwidth The full width of the beam in the x-y plane of the beam coordinate system. From Wikipedia, the free encyclopedia.
A possible method analogously for this one is, to bend the lower part of the reflector more intense. By the fact that the rays turned up don’t have a large power density, the maximum range in the higher elevation is limited with that.
cosrcant A radiator is in the focal point of a parabolic reflector and produces a relatively sharply bundled radiation lobe since the rays leave the reflector parallelly in the ideal case. Absolute; not relative to the Main-lobe gain. The ground directly below the aircraft is at a distance equal antennq the aircraft’s altitude, which produces the strongest signal. Every feed horn already emits directionally. However, what does this term have to do with our antenna? Open topic with navigation.
Efficiency The efficiency of the antenna a value between 0 and percent. Main-lobe Gain dB The main lobe gain of the antenna pattern.
Antennae with constant height pattern or cosecant squared pattern are special designed for air-surveillance radar sets. If one distributes the transmit power unevenly on the single radiating elements, then the antenna pattern approaches a cosecant squared pattern. The angle 1 in the above coecant and illustration. According to definition mentioned above the height also shall be constant. Parameter Description Alpha 1 Angle The angle 1 in the above equation and illustration.
Stacked beam cosecant squared pattern. 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.
It is shaped to send more radio energy in certain directions in order to smooth out the reception pattern of objects as their range changes in relation to the radar.