The Conditions for Certainty of Interception of an Intermittent Signal by a Rotating Directional Antenna
Abstract
The various factors affecting the interception of a rotating beam signal by a rotating directional antenna (such as is often employed for radio direction finding purposes), assuming that the signal is "on" for only a limited number of rotations of the respective beams, are considered. Equations are derived for determining the minimum number of beam rotations and the "Speed Ratios" which produce "Certainty of Interception". The Speed ration is the ration of the angular speed of the directional antenna beam to that of the signal beam. Also an equation is derived for calculating the "Probability of Interception" within a given number of rotations of the signal beam as a function of the "Speed Ratio" for given beam widths of the two beams. It is shown that for many of the more practical and currently employed rotational speeds and beam widths, "Certainty of Interception" exists only within a number of very narrow ranges of "Speed Ratios". It is also seen from Plates 1 - 6 that the "Probability of Interception" shows a general trend of increasing probability in the direction of increasing "Speed Ratios" with points of minimum probability at the "Speed Ratio" corresponding to synchronization of the two beams and at "Speed Ratios" which are simple rational multiples thereof. Hence a slowly rotating direction finder is all but useless in intercepting a rotating beam signal if the signal is to be on for only a few antenna rotations . It is further shown to be the "Probability of Interception" increases with increasing beam widths but that this is of doubtful significance since larger bearing errors will result from increasing the beam width of the direction finder . The derived equations arc generalized in an Appendix to be useful in applications to a wide range of intercept problems such as the "Certainty" and "Probability" of intercepting an intermittent signal by a frequency scanning receiver.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 10, 1946
- Accession Number
- AD1196234
Entities
People
- Henry D. Arnett
Organizations
- United States Naval Research Laboratory