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. However, what does this term have to do with our antenna? Every feed horn already emits directionally. These permit an adapted distribution of the radiation in the beam and causing a more ideal space scanning. Antennae with constant height pattern or cosecant squared pattern are special designed for cosceant radar sets.
Design Frequency The frequency of the antenna. 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.
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. 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.
Cosecant-squared pattern achieved by displacing the reflector surface from the original parabolic shape. The targets can be assigned to beams with defined elevation there.
Sqyared angle 1 in the above equation and illustration. Efficiency The efficiency of the antenna a value between 0 and percent. Azimuth Beamwidth The full width of the beam in the x-y plane of the beam coordinate system.
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. 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.
It is equal to the reciprocal value of the sine function. A cosecant squared antennasometimes known as a constant height patternis a modified form of parabolic reflector used in some radar systems. 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. To get the cosecant squared pattern, a part of the radiated energy must be turned up.
Cosecant squared antenna
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. The result was an evener display pattern. Side-lobe Gain dB The side lobe gain of the antenna pattern. 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.
The cosecant squared pattern isn’t restricted to parabolic reflectors. Antenna with Cosecant Squared Pattern Cosecant squared pattern. The same basic concept soon found many roles. Retrieved from ” https: The angle m is the upward tilt angle of the beam relative to the horizontal, generally about half a beamwidth.
Radar Basics – Antennae with Cosecant Squared Pattern
In the practice a cosecant squared pattern can be achieved by a deformation of a parabolic reflector. 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.
A cosecaant 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.
Alpha 2 Angle The angle 2 in the above equation and illustration. The following illustration depicts a typical use case of a cosecant squared antenna pattern applied to a ground-based air search radar.