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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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.
Azimuth Beamwidth The full width of the beam in the x-y plane of the beam coordinate system. The concept originated as part of the development of the H2S radarwhich scanned the area under an aircraft to provide a radar csecant of the ground below. In the practice a cosecant squared pattern can be achieved by a deformation of a parabolic reflector. From Wikipedia, the free encyclopedia.
If the echo has a uniform signal strength at the input of the receiver than the range is dependent on the square of the antenna gain in the fourth power linearly. 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.
This antenna uses a polar coordinate system. 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. Antenna with Cosecant Squared Pattern Cosecant squared pattern. According to anrenna mentioned above the height also shall be constant.
For ground-based radars, the same modification could be used to provide scanning 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. You can specify the following parameters: Vertical projection of the radiation pattern of an antenna with cosecant squared characteristic.
The cosecant squared pattern isn’t restricted to parabolic reflectors. It also illustrates that:. 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.
Cosecant squared antenna – Wikipedia
Views Read Edit View history. 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. Stacked beam cosecant squared pattern. 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. This gives in near range an additional gain required for constant echo strength after sensitivity time control.
Cosecant squared antenna
The angle m in the above equation and illustration. The opposite modification could also be used, squarfd the upper lip outward, with the same basic outcome. CRC Presspp. If one distributes the transmit power unevenly on the single radiating elements, then the antenna pattern approaches a cosecant squared pattern.
To get the cosecant squared pattern, a part of the radiated energy must be turned up.
A cosecant squared antennasometimes known ahtenna a constant height patternis a modified form of parabolic reflector used in some radar systems. The result was an evener display pattern.
Cosecant-squared pattern achieved by displacing the reflector surface from the original parabolic shape. Open topic with navigation. 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. The frequency of the antenna. 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.
Absolute; not relative to the Main-lobe gain. The following illustration depicts a typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar.
Alpha M Angle The angle m in the above equation and illustration. Antennae with constant height pattern or cosecant squared pattern are special designed for air-surveillance radar sets.
A possible method analogously for this one is, to bend the lower part of the reflector more intense. The terrain at further distances returns much less signal due to the radar equation. 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.
At use of several receiving channels a height allocation also can be carried out. These permit an adapted distribution of the radiation in the beam and causing a more ideal space scanning. 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.
Cosecant Squared Pattern Antennas
The ideal pattern as shown in Figure 1 is a nearly rectangular shape with rounded corners. A possibility consists in lower bending of the top of the reflector. See Raemer, Harold R.