64
4 Measuring Principles and Techniques …
Fig. 4.7 Maximum method
illustration
of k, a boresight characteristic (directional pattern) becomes higher, creating better
conditions for measuring of angular coordinate. Usually k = π
d a
λ
.
Within passing time of radiofrequency beam through a target (greatly slower than
radio waves movement to a target and back) at the receiver output of pulse radar not
one, but a train of reflected pulses are generated (as a rule, several dozens of), the
amplitude of which regenerates a directional pattern of antenna (Fig. 4.7). Pulses
train reflected from a target per one radiofrequency beam passing is called burst or
pulses packet. On two-dimensional display with plan position indicator (PPI) sweep
(radial-circular scanning) when electronic radius rotates synchronously with antenna
directional pattern rotation, reflected pulse burst form a lighten arch, in the middle
of which (central pulse of burst) an operator reads off direction to a target. In radar
with automatic coordinates detection, the middle is determined via corresponding
processing of received burst. For example, after the coordinates of the first and the
last burst pulses were defined, exceeding the threshold (Fig. 4.7) via discrete count
method, an angular coordinate of a target is counted out.
In real conditions of measurements, i.e., in conditions of interfering random influence, one should somehow consider all pulses exceeding the threshold in favor
of measurements accuracy. In other words, all reflected by a target energy should
be considered in measurements. The maximum method as for application in radar
location is frequently called an analysis method of envelope.
Maximum method differs by simplicity of implementation, single-valuedness of
reading (count) and often is used in surveillance modes of large space sectors (up
to all-round surveillance). As it was mentioned before, a vital importance is for
direction-finding (boresight) characteristic curvature (steepness) in clutter conditions. At long-range measuring, an essential value has a direction-finding characteristic curvature near the point where high-energy pulses are received (peak point
of direction-finding characteristic). However, at maximum method, a curvature of
direction-finding characteristic near a high-energy pulse of the central point is small.
So, the maximum method is almost used only in the case when requirements to
measuring accuracy of angular coordinates are low.
Calculate a directional pattern width of radar antenna. We are interested in width at
0.7 level from a maximum voltage value or, that is the same, at 0.5 level from a square
4 Measuring Principles and Techniques …
Fig. 4.7 Maximum method
illustration
of k, a boresight characteristic (directional pattern) becomes higher, creating better
conditions for measuring of angular coordinate. Usually k = π
d a
λ
.
Within passing time of radiofrequency beam through a target (greatly slower than
radio waves movement to a target and back) at the receiver output of pulse radar not
one, but a train of reflected pulses are generated (as a rule, several dozens of), the
amplitude of which regenerates a directional pattern of antenna (Fig. 4.7). Pulses
train reflected from a target per one radiofrequency beam passing is called burst or
pulses packet. On two-dimensional display with plan position indicator (PPI) sweep
(radial-circular scanning) when electronic radius rotates synchronously with antenna
directional pattern rotation, reflected pulse burst form a lighten arch, in the middle
of which (central pulse of burst) an operator reads off direction to a target. In radar
with automatic coordinates detection, the middle is determined via corresponding
processing of received burst. For example, after the coordinates of the first and the
last burst pulses were defined, exceeding the threshold (Fig. 4.7) via discrete count
method, an angular coordinate of a target is counted out.
In real conditions of measurements, i.e., in conditions of interfering random influence, one should somehow consider all pulses exceeding the threshold in favor
of measurements accuracy. In other words, all reflected by a target energy should
be considered in measurements. The maximum method as for application in radar
location is frequently called an analysis method of envelope.
Maximum method differs by simplicity of implementation, single-valuedness of
reading (count) and often is used in surveillance modes of large space sectors (up
to all-round surveillance). As it was mentioned before, a vital importance is for
direction-finding (boresight) characteristic curvature (steepness) in clutter conditions. At long-range measuring, an essential value has a direction-finding characteristic curvature near the point where high-energy pulses are received (peak point
of direction-finding characteristic). However, at maximum method, a curvature of
direction-finding characteristic near a high-energy pulse of the central point is small.
So, the maximum method is almost used only in the case when requirements to
measuring accuracy of angular coordinates are low.
Calculate a directional pattern width of radar antenna. We are interested in width at
0.7 level from a maximum voltage value or, that is the same, at 0.5 level from a square