where [[eta].sub.c] denotes the azimuth center time when the beam center passes through the target; [[theta].sub.Tr,c] and [[theta].sub.Rr,c] denote the squint angles for the transmitter and receiver with respect to [[eta].sub.c]; [R.sub.0t] and [R.sub.0R] denote the nearest distance at the initial time [t.sub.0]; [V.sub.T] and [V.sub.R] denote the velocity of the radar and the target; [R.sub.T]([eta]) and [R.sub.R]([eta]) denote the slant distance between the radar and the target at time [eta].

The center of the imaging area is [P.sub.i], and the nearest slant distance between [P.sub.t] and the radar is [R.sub.0].

where [f.sub.a][member of] (-PRF/2, PRF/2), [R.sub.Bq]= [square root of [([Y.sub.q]- [y.sub.1]).sup.2] +[H.sup.2]] is the vertical distance form scatter point ([x.sub.1], [y.sub.1], [z.sub.1]) to flight track, [R.sub.pq,1] ([f.sub.a]) is the instantaneous distance of scatter point, [[phi].sub.k] is the angle of instantaneous slant distance and flight track, and cos [[phi].sub.k]([f.sub.a]) = [f.sub.a]/[f.sub.am], [f.sub.am] = 2v/[lambda].

According to the forgoing analysis, if the scatter instantaneous slant distance satisfies the preceding equation, (7) can be shown as

For different point target slant distance [R.sub.l], the subpulse time delay should be added.

Point O' is the footprint of O, and the slant distance between them is [R.sub.0].

The instantaneous slant distance of the target B can be obtained by the triangle APB, and it is expressed as

After Taylor expansion, the instantaneous slant distance R(t; [R.sub.0]) can be approximately as [19]

It determines range by

slant distance calculation based on relative signal amplitude, a method limited by the fact that transponder power output isn't a constant, thus it's difficult to distinguish a powerful transponder at great distance from one of lesser power closer to the receiving antenna.

All that matters is the straight horizontal distance, not the

slant distance up or down.

Whole-body average SAR values for the adult male and girl models are plotted as a function of slant distance r, in Figure 4.

In these two Figures, the behaviour of SAR can be characterized by three distinct intervals of slant distance. The first interval is the near-field from the closest distance to r [approximately equal to] H (Antenna Length = 1.34 m).