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.
|Published (Last):||21 March 2007|
|PDF File Size:||16.23 Mb|
|ePub File Size:||3.1 Mb|
|Price:||Free* [*Free Regsitration Required]|
Absolute; not relative to the Main-lobe gain. Every feed horn already emits directionally.
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. From Wikipedia, the free encyclopedia.
Cosecant squared antenna
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. A possible method analogously for this one is, to bend the lower part of the reflector more intense.
Antennae with constant height pattern or cosecant squared pattern are special designed for air-surveillance radar sets. These permit an adapted distribution of the radiation in the beam and causing suqared more ideal space scanning.
The following illustration depicts coseecant typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar. You can specify the following parameters: CRC Presspp.
It is equal to the reciprocal value of the sine function. In reality, the diagram is superposed with a number of side lobes mainly on the back at higher elevation angles.
Cosecant-squared pattern achieved by displacing the reflector surface from the original parabolic shape.
Main-lobe Gain dB The main lobe gain of the antenna pattern. The angle m is the upward tilt angle of the beam relative to the horizontal, generally about half a beamwidth. 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 squqred means of achieving a more uniform signal cosecan at the input of the receiver as a target moves with a constant height within the beam.
This page was last edited on 30 Decemberat 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 zquared radar and the target. The part of the rays which falls to the less bent area cosrcant the top is reflected up now. Without correction, this produced a display where the ground under square aircraft was very bright on the cathode ray tube display, while the terrain at longer distances was almost invisible.
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.
Views Read Edit View history. However, when computing the antenna’s gain matrix or a link budget, etc.
Radar Basics – Antennae with Cosecant Squared Pattern
It also illustrates that: For an embedded antenna on a receiver, transmitter or radar, this value corresponds to the Frequency antenna on the Model Specs tab for the transmitter or receiver and the Transmitter Specs tab for the Radar. 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. To counteract this, the scanning suared was re-aimed so that it was pointed almost directly forward, thereby sending most of the radar energy at squaref angles relative to the aircraft, thereby increasing the energy available at long range.
At use of several receiving channels a height allocation also can be carried out. Design Frequency The frequency of the antenna. It also illustrates that:. The same basic concept soon found many roles.
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 tab for the Radar.
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. 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. In the practice a cosecant squared pattern can be achieved by a deformation of a parabolic reflector.
Parameter Description Alpha 1 Angle The angle 1 in the above equation and illustration. Azimuth Beamwidth The full width of the beam in the x-y plane of the beam coordinate system. Alpha 2 Angle The angle 2 in the above equation and illustration. The opposite modification could also be used, bending the upper lip outward, with the same basic outcome.
Open topic with navigation. This antenna uses a polar coordinate cosecanf. The angle 2 in the above equation and illustration. The terrain at further distances returns much less signal due to the radar equation. Side-lobe Gain dB The side lobe gain of the antenna pattern. The angle m in the above equation and illustration. The lobe of the radiator is weaker to the margin to, therefore the margins of the reflector are hit weaker as the centre.
However, what does this term have to do with our antenna? According coxecant definition mentioned above the height also shall be constant. If one distributes the transmit power unevenly on the single radiating elements, then the antenna pattern approaches a cosecant squared pattern. The shape of all these back side lobes is combined into a nearly parabolic slope.