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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Coescant result was an evener display pattern. You can specify the following parameters: A possibility consists in lower bending of the top of the reflector. The lobe of the radiator is weaker to the margin to, therefore the margins of the reflector are hit weaker as the centre. From Wikipedia, the free encyclopedia. The angle 1 in the above equation and illustration.
CRC Presspp. 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. The following illustration depicts a typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar.
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 cowecant to the aircraft, thereby increasing the energy available at long range. By the fact that the rays turned up don’t have a large power density, the maximum range in the higher squaared is limited with that. Efficiency The efficiency of the antenna a value qntenna 0 and percent. Side-lobe Gain dB The side lobe gain of the antenna pattern.
A radiator is in the focal point of a parabolic reflector and produces a relatively sharply bundled radiation lobe since sauared rays leave the reflector parallelly in the ideal case. Cosecant-squared pattern achieved by displacing the reflector surface from the original parabolic shape.
To get the cosecant squared pattern, a part of the radiated energy must be turned up.
It also illustrates that:. In reality, the diagram is superposed with a number of side lobes mainly on the back at higher elevation angles. 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. Main-lobe Gain dB The main lobe gain squred the antenna pattern.
Cosecant Squared Pattern Antennas
The terrain at further distances returns much less signal due to the radar equation. At an antenna array with Yagi- antennae the pattern is achieved by interference of the direct wave with this at the earth’s surface sauared quotas. The concept originated as part of the development cosrcant the H2S radarwhich scanned the area under an aircraft to provide a radar map of the ground below. The cosecant squared pattern isn’t restricted to parabolic reflectors.
A possible method analogously for this one is, to bend the lower part of the reflector more intense. 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. Retrieved from ” https: The ground directly below the aircraft is at a distance equal to the aircraft’s altitude, which produces the strongest signal. The targets can be assigned to beams with defined elevation there.
Every feed horn already emits directionally. Alpha 2 Angle The angle 2 in the above equation and illustration. According to definition mentioned above the height also shall be squuared. Parameter Description Alpha 1 Angle The angle 1 in the above equation and illustration. See Raemer, Harold R. For ground-based radars, the same modification could be used to provide antwnna at high angles above the station while still sending most of the energy towards low angles to detect aircraft at long range as they rose above the radar horizon.
These permit an adapted distribution of the radiation in the beam and causing a more ideal space scanning.
Cosecant squared antenna – Wikipedia
Antenna with Cosecant Squared Pattern Cosecant squared pattern. Design Frequency The frequency of the antenna.
Cosecant squared antenna
Absolute; not relative to the Main-lobe gain. If one distributes the transmit power unevenly on the single radiating elements, then the antenna pattern approaches a cosecant squared pattern.
The ideal pattern as shown in Figure 1 sqaured a nearly rectangular shape with rounded corners. 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. For an antenna linked to a receiver, transmitter, or radar, the Antenna Design Frequency value gets overridden by the Frequency value set on the Model Specs tab for the transmitter or receiver, and the on the Transmitter Specs aantenna for the Radar.