. Airborne radar. Airplanes; Guided missiles. 10-5] PATTERN SIMULATION AS LINK the main lobe of a cylindrical beam, it is found convenient to use 2VbP ith e 521 (10-6) where p is the normalized one-way power pattern, Q is angular displacement from the parabola centerline, and 6 is the beamwidth. When a more complete description of a pattern .is needed having side- lobes, one of the Bessel functions is found useful.^ For example, the second- order function has first sidelobes about 25 db below the main lobe. This might be considered a good design practice for a narrow-beam tracking system. &quo
. Airborne radar. Airplanes; Guided missiles. 10-5] PATTERN SIMULATION AS LINK the main lobe of a cylindrical beam, it is found convenient to use 2VbP ith e 521 (10-6) where p is the normalized one-way power pattern, Q is angular displacement from the parabola centerline, and 6 is the beamwidth. When a more complete description of a pattern .is needed having side- lobes, one of the Bessel functions is found useful.^ For example, the second- order function has first sidelobes about 25 db below the main lobe. This might be considered a good design practice for a narrow-beam tracking system. "J2( 64 '' J ith e (10-7) Both of these functions are shown in Fig. 10-5 as compared with measure- ments on a typical pencil beam. The measured pattern is for an offset beam tracking antenna. This ac- counts for its lack of symmetry about the vertical axis, particularly in the side lobes For any calculations within 10 db of the peak of the beam such as error signal sensitivity, the radiation pat- tern may be fitted very nicely by the exponential of Equation 10-6. With this assumption, the modulation sensitivity for zero target error is given by^ 4 los„ 2 6' = -^^^AXl00percent. (10-8). Here, A is the lobing angle between extreme beam positions during the cycle of conical scan (squint angle), e is beamwidth, and 6" is the per cent modulation per unit of angular error. Another useful result derivable from this pattern approximation is the db difference expression that has been Fig. 10-5 The Radiation Pattern of a Typical Offset Feed Conically Scanning Antenna as Compared with Two Pattern Shape Approximations That Are Often Used to Represent the Actual Antenna Pattern. ''Silver, op. cit., p. 194. 8J. B. Damonte and D. J. Stoddard, "An Analysis of Conical Scan Antennas for Track- g," 1956, IRE Convention Record, Part I, Page Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colora
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