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hologram, mosaic                                                   hologram, three-dimensional (3D)  212



               This type of hologram is used for increasing the contrast  aperture, the field is measured at discrete point, and the radio
           and improving the quality of restored images and also to  hologram is recorded through commutation or parallel pro-
           increase the angle of view when inspecting optical holograms  cessing of signals at the output of the receiver elements. The
           transformed from radio holograms. IAM                properties of quasioptical radio holograms are similar to the
           Ref.: Safronov (1973), p. 204.                       properties of optical holograms, which possess similar ratios
                                                                of apertures to lengths of the illuminating waves.
           A multiplicative hologram is registered using detection of
                                                                    High-quality images  of objects  with a  number of
           the product of the object signal U  and reference signal U ref
                                      ob
           waves at a high or intermediate frequency:           resolved elements on the order of a hundred using an antenna
                                                                array may  be obtained at  ranges which in the  best case
                       h (x,y) = Re[ U (x,y) U  (x,y) ]
                                   ob
                                          ref
           where x, y are the spatial coordinates, and Re(x) is the real  amount to tens of linear dimensions of the object. For this rea-
                                                                son  such radio holograms are  used effectively in close-in
           part of the quantity x.
                                                                radars.
               The multiplicative radio hologram, like the quadratic
                                                                    Coherent radio holograms using a  system of antennas
           hologram, can be registered in complex form. The multiplica-
                                                                separated by a distance on the order of tens or hundreds of
           tive radio hologram does not have an optical analog. IAM
                                                                kilometers makes it possible to produce quality images of air-
           Ref.: Tuchkov (1985), p. 131.
                                                                craft at ranges of 100 to 1,000 km, respectively. However the
           A one-dimensional (1D) hologram is one in which the val-  realization of such systems is associated with great technical
           ues of the scattering function of an object are re-created from  difficulties in supporting the coherent  functioning of  many
           one coordinate, and from the other its integral transform. An  receiver elements in large areas. IAM
           image received by a radar with a linear antenna and transmit-  Ref.: Safronov (1973), p. 218.
           ted pulses that are short compared with the length of the tar-
                                                                A synthesized [synthetic] hologram is one formed by regis-
           get can serve as an example of a one-dimensional radio
                                                                tration of a field reflected from an object at various points of
           hologram. The values of the scattering function are restored
                                                                space successively in time using one receiving antenna. The
           along the line of sight in the form of amplitudes of the inter-
                                                                synthesis can take place in one or several coordinates, in two
           ference relief of the radio hologram.
                                                                in the picture plane (perpendicular line of sight) and a third
               During restoration of images from one-dimensional radio
                                                                along the line of sight. In synthesis in the picture plane, any
           holograms, special  circuits are used in which an integral
                                                                relative motion of the object, the source of radiation, and the
           transform is taken in accordance with one coordinate, and the
                                                                receiver in accordance with a known law may be used. The
           scattering function of the object is reproduced in accordance
                                                                resolution of radio holograms in this case is determined by
           with the other. IAM
                                                                the size of the synthesized aperture (length of synthesis) (see
           Ref.: Safronov (1973), pp. 174, 189.
                                                                hologram). In synthesis along the line of sight, wideband fre-
           A planar hologram is one in which the registered interfer-  quency-modulated waveforms are used, and the resolution dl,
           ence relief is an integral transform (Fourier or Fresnel) in two  is determined by the width of the spectrum DF according to dl
           coordinates.                                         = pc/DF, where c is the speed of light.
               Planar radio holograms are constructed on the basis of a  Synthesized radio holograms are  widely used in radars
           real aperture in two coordinates (quasioptical hologram), on  mounted on moving objects and having antennas of limited
           the basis of a synthesized aperture in two coordinates (using  size, on ground radars for raising the accuracy of coordinate
           small antennas and a “point” aperture, or antennas with a lin-  determination and receipt of target images, and also for mea-
           ear aperture and  range  synthesis through linear  frequency  surement of local characteristics of scattering of radar targets
           modulation of the signal), and also through a combination of  in anechoic chambers. IAM
           a real and synthesized aperture in different coordinates. IAM  Ref.: Safronov (1973), p. 172; Tuchkov (1985), p. 130.
           Ref.: Safronov (1973), p. 173.
                                                                A  three-dimensional (3D) hologram is  one that makes  it
           A quadratic hologram is registered using quadratic  detec-  possible to form a 3D image of an object. The three-dimen-
           tion of the subject of the object U  and reference waves U op  sional radio hologram can be realized by three methods: (1)
                                      ob
           at a RF or intermediate frequency:                   through successive arrangement at specific distances from
                       h (x,y) = | U  (x,y) + U  (x,y) | 2      one another of planar hologram; (2) through formation of a
                                ob
                                          op
           where x, y are the coordinates of the antenna aperture.  radio hologram in 3D structures which permit fixation of the
               Recording of the quadratic hologram is done in quadra-  changes in parameters of the electromagnetic  field in the
           ture form or in the form of amplitude and phase components.  three dimensions; and (3) by synthesis from linear and point
           Quadratic  radio  holograms are  the  analog to optical  holo-  elements or their combinations.
           grams. IAM                                               As  a rule, radio holograms are  formed  in digital form
           Ref.: Tuchkov (1985), p. 131.                        using algorithms of fast Fourier transforms. IAM
           A  quasioptical radio  hologram is formed using antenna  Ref.: Safronov (1973), p. 204.
           arrays or a system of separated antennas. In contrast to syn-  two-dimensional (2D) hologram (see planar hologram).
           thesized holograms, a quasioptical radio hologram uses a real
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