BendixKing IN-182A System RDR-2000 - Manual (Page 22)

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Effective Date: 5/98 RDR 2000 Pilot's Guide: Rev 3
Theory of Operation
ALTITUDE RING (RANGE RING)
Not all radar transmitted energy is contained in the main beam radiation
pattern. Some of the energy is radiated in the side lobe pattern. The
characteristics of some radomes and/or nose caps can cause detrimental
side lobe radiation. Should this occur, the side lobe can be radiated down
toward the earth and the reflected energy received by the radar may be
displayed on the indicator as a narrow ring of video. When the indicator is
on the 10 or 20 nm range, this can be seen at a distance corresponding to
the altitude, typically one mile per 6000 feet. During “Wx” operation, when
this phenomenon occurs, no appreciable degradation of the radar to
depict weather exists. This phenomenon is largely dependent upon the
shape and physical condition of the radome or nose cap on the aircraft.
RADOMES
A radome is a covering that shields the radar antenna from hostile envi-
ronments, such as fast moving air, rain, bugs, and ice. It allows the
microwave energy to pass through relatively undisturbed. This means
that very little of the microwave energy passing through it will be
absorbed, reflected, or redirected as a result of it’s presence. Some
radomes closely approximate this definition, while others do not.
Here are some faults which can occur in radomes:
1. A pitted honeycomb radome can result from being struck by high
velocity projectiles, such as rain, ice, sand, bugs, etc. Once the
surface integrity has been broken, water intrusion can occur and
cause significant radar signal loss.
2. A poorly sealed plastic radome nose boot which has allowed
moisture to be trapped behind it.
3. Paint containing metallic particles mistakenly applied to all or part
of the radome.
4. An improperly fabricated fiberglass radome.
5. A poorly repaired “ding” on the radome.
6. An object, usually metallic, located inside the radome and in the
path of part of the transmitted microwave energy.
As a result of items 5 and 6 above, a “phantom ring” may appear on the
radar display. Normally the cause is an obstruction in the bottom of the
radome. This obstruction can cause some of the radiated energy to be
directed down to the ground instead of in the forward direction.
Reflective material in the top of the radome can result in the same situa-
tion. In either case, energy returns from the same direction that it was
transmitted causing an “altitude ring” to be presented on the radar dis-