Page 265 - Radar Technology Encyclopedia
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255   loss, limiter [limiting]                                                             loss, radome



           lens(-effect) loss (see atmospheric lens loss).      traction  by external factors, nonoptimum displays and
                                                                lighting, and similar effects. No precise data on operator loss
           Limiter  [limiting] loss results from  passing the signal
                                                                exists, but estimates from 3 to 10 dB are often applied. DKB
           through a hard limiter at intermediate frequency before fur-
           ther  processing.  This loss is applicable to certain types of  pattern-propagation [loss]  factor  (see  PROPAGATION,
           CFAR processor, such as the Dicke fix. The loss is equal to 4/  pattern-propagation factor).
           p or 1.05 dB. DKB
                                                                Polarization loss refers to the reduction in signal power, rela-
           Ref.: Barton (1988), p. 89.
                                                                tive to the use of the same linear polarization for transmit and
           The loss tangent is the ratio of the imaginary part of the com-  receive antennas,  resulting from  use  of other polarizations.
           plex dielectric constant to the real part. The loss in passing  For spheres and typical aircraft targets observed with differ-
           through a  material is proportional to this loss tangent and  ent polarizations, Table L13 shows  the loss. This loss is
           depends in a complex way on the thickness of the material  sometimes included in the range equation as a polarization
                                                                       4
           and the wavelength. DKB                              factor F  in the numerator. DKB
                                                                      p
           Ref.: IEEE (1993), p. 745.                           Ref.: Johnson (1984), p. 23.8.
           Miscellaneous signal-processing loss is the  product of
           receiver-processor losses (type 4 in Table L5), excluding                 Table L13
                                                                              Polarization Loss Estimates
           beamshape loss, filter matching loss, fluctuation loss, and
           integration loss. Since it depends on detection probability, it
                                                                                                   Loss in dB
           should be included in the equation for effective detectability
           factor, rather than as a constant parameter in the radar equa-  Polarizations (transmit/receive)
                                                                                              Typical
           tion. DKB                                                                                     Sphere
                                                                                              aircraft
           Ref.: Blake (1980), p. 378; Barton (1988), pp. 31, 250, 268.
                                                                   H/H or V/V                     0        0
           MTI processing loss is  the  loss resulting from passing the
           signal through an MTI processor, compared with the normal  H/V or V/H                  6        ¥
           video channel. It is defined as the increase in required input
           signal energy for the actual process relative to that required  H/R, H/L, V/R, or V/L  3        3
           for processing without the MTI. It can be divided into three
                                                                   R/H, R/V, L/H, or L/V          3        3
           components:
                                         L
                          L mti  = L mti(a) mti(b) mti(c)          R/R or L/L                     3        ¥
                                    L
           where L mti(a)  results from correlation of noise at the MTI fil-  R/L or L/R          0        0
           ter output,  L mti(b)  is the  blind-phase loss, and  L mti(c)  is the
           velocity response loss. It is dependent on detection probabil-  H = horizontal, V = vertical, R = right-hand circular,
                                                                   L = left-hand circular
           ity. The effect of noise correlation can be expressed in terms
           of a reduction in number of pulses integrated from n to an,
           where                                                processing loss (see miscellaneous signal-processing loss).
               a = 2/3 for a single canceler using I and Q processing.  propagation loss (see atmospheric loss).
               a = 18/35 for a dual canceler using I and Q processing.
                                                                pulse width loss (see array bandwidth loss).
               a = 20/47 for a triple canceler using I and Q processing.
               a = 1/m for a batch-process MTI using I and Q process-  Quantization [quantizing] loss refers to the loss in signal
                  ing on m pulses per batch.                    detection performance resulting from quantizing the receiver
               a = 1/2 times the above values for systems using I-only  output in an  A/D converter before digital processing. An
                  cancelers.                                    extreme case is the binary integration loss, L  » 1.6 dB, when
                                                                                                    b
               The resulting loss can be expressed as the ratio of basic  one-bit quantization is used. When quantizing is carried out to
           detectability factors:                               m bits, the loss is approximately
                                     D an )                                               1.6
                                       (
                                                                                          -------   (dB)
                                      0
                                                                                      q
                             L mti a () =  ------------------                    10log L =  2
                                     D n ()
                                       0                                                  m
           DKB                                                  DKB
                                                                Ref.: Nathanson (1991), p. 662.
           Ref.: Barton (1988), p. 250.
           Operator loss refers to the inability of the operator to detect  Radome loss refers to the reduction in power received from a
           targets according to statistical detection theory. While an alert  target as a result of attenuation through the radome material,
           operator, observing an  optimized  CRT display, can closely  scattering from radome structure, effects of precipitation on
           approach the theoretical performance described by the detect-  the radome surface, and possible distortion of the beam due to
           ability factor, this performance is degraded by fatigue, dis-  refraction in the radome. Typical two-way losses for  dry
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