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 angle m in the above equation and illustration. If one distributes the transmit power unevenly on amtenna single radiating elements, then the antenna pattern approaches a cosecant squared pattern.
Cosecant squared antenna
To get the cosecant squared pattern, a part of the radiated energy must be turned up. 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. The targets can be assigned to beams antejna defined elevation there.
Views Read Edit View history. The same basic concept soon found many roles. The angle m is the upward tilt angle of the beam relative to the horizontal, generally about half a beamwidth. The terrain at further distances returns much less signal due to the radar equation. At use of several receiving channels a height allocation also can be carried out.
The cosecant squared pattern isn’t restricted to parabolic reflectors. The ideal pattern as shown in Figure 1 is a nearly rectangular shape with rounded corners. Vertical projection of the radiation pattern of an antenna with cosecant squared characteristic.
A possibility consists in lower bending of the top of the reflector. This can be realized also with other kind of antennae. The concept originated as part of the development of the H2S radarwhich scanned the area under squsred aircraft to provide a radar map of the ground below. 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.
Radar Basics – Antennae with Cosecant Squared Pattern
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. This antenna uses a polar coordinate system. Design Frequency The frequency of the antenna.
See Raemer, Harold R. In reality, the diagram is superposed with a number of side lobes mainly on the back at higher elevation angles. Stacked beam cosecant squared pattern.
CRC Presspp. Antenna with Cosecant Squared Pattern Cosecant squared pattern.
The angle 2 in the above equation and illustration. Efficiency The efficiency of the antenna a value between 0 and percent. The opposite modification could also be used, bending the upper lip outward, with the same basic outcome. 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.
Cosecant squared antenna – Wikipedia
Antennae with constant height pattern or cosecant squared pattern are special designed for anfenna radar sets. 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. For an embedded antenna on a receiver, transmitter or radar, this value corresponds to the Cosecwnt entered on the Model Specs tab for the transmitter or receiver and the Transmitter Specs tab for the Radar.
It is equal to the reciprocal value of the sine function. This page was last edited on 30 Decemberat Alpha M Angle The angle m in the above equation and illustration. Side-lobe Gain dB The side lobe gain of the antenna pattern. A radiator is in the focal point of a parabolic squareed and produces a relatively sharply bundled radiation lobe since the rays leave the reflector parallelly in the ideal case. 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.
The following illustration depicts a typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar.
Main-lobe Gain dB The main lobe gain of the antenna pattern. According to definition mentioned above the height also shall be constant. You can specify the following parameters: Alpha 2 Angle The angle 2 in the above equation and illustration.