Radar Field Analyser - RFA641 Edition Date: 28-Feb-18
11. ANNEXES
11.1. Annex 1: Critical Parameters of SSR Antennas
Critical Parameters of SSR Antennas that should be included in the Out-of-Tolerance Detection (OTD):
Facility of the Polar Diagram Plotter developed by Intersoft Electronics NV (copied from document 3E/T/322
Eurocontrol Directorate, 6/11/91).
Critical parameters that should be monitored by the OTD are :
• the presence of sidelobe punch-through (position and level) ;
• the level of the highest ∑ sidelobe (other than the backlobe) (typically <-22 dB)
• the ∑ / Ω cross-over levels (dB) and positions (degrees) (typical level ,-18 dB ± 3 dB)
• the ∑ mainlobe -3 dB beam width (degrees) (typically -2.35° ± 0.25°)
• mean ∑ sidelobe level (typically <-24 dB)
• Ω pattern notch depth , or the highest point within the notch (typically <-24 dB) ;
• the ∑ backlobe level (typically <-24 dB) ;
• the ∑ / ∆ cross-over levels (dB) and positions (degrees), (typically -3 dB ± 0.5 dB, ±1.25° from
mainlobe axis ) ;
Since there are many different types of SSR antennas (LVAs, hog-through, integrated with PSR, conformal
phased array) and different sizes (9 m, 4.5 m, even 2 m) and also variation in parameters between
manufacturers, it is expected that a “footprint” is made for each secondary radar site and a given
measurement point and that when later measurements show a significant deviation (to be defined for each
parameter), than an “alarm” indication is given for the out-of -tolerance parameter(s).
This will also allow the effect on OTD of radar siting and eventual changes in propagation conditions
(weather, ground conductivity, local obstructions) to be minimized .
It should be noted that the typical figures given above for levels, beamwidths, positions, etc. are only
provisional and might be updated according to experience.
IE-UM-00165-005 RFA641 User Manual.odt 98/110
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