Aerospace and Electronic Systems Magazine December 2017 - 44

High-Latitude Application of 3D OTHR Radar

Figure 7.

Figure 8.

First, the increased resolution afforded by the adaptivity overcomes the low crossbeam aperture of the elevation beamformer
to some extent. This allows the target and clutter to be resolved by
using as few as 6 to 8 elements, as opposed to 20 to 25 elements in
the case of conventional beamforming. Second, the 2D array gain
in the case of adaptive processing of Data Set 2 (Figure 8b) does
not achieve a level equal to the product of the 1D broadside and
end-fire array gains, due to azimuth-elevation coupling of the clutter, discussed at length in [14].
Two general comments are in order concerning overall objectives. First, none of the results indicate layouts, beamforming,
or data sets that meet the objective of 50-dB clutter suppression.
Thus, one cannot suppress the clutter on transmit or receive alone,
for array sizes less than 32 × 32. Given the challenges of the adaptive transmit array, one may consider a conventional transmit array
combined with an adaptive receive array. For Data Set 1, 32 × 32
arrays on transmit and receive would be adequate for the task and
would be more than adequate for Data Set 2. The second comment

is that the adaptive results show that the performance rises rapidly
in the first eight elements or so, and after that, slowly rises in proportion to the number of elements (or square of the number, in the
2D case). This provides some confirmation of the form of the gains
being a constant times the number of elements, as was described in
the Mitigations section in the determination of array size requirements for the auroral clutter suppression task.

(a) Conventional beamforming (Data Set 1). (b) Conventional beamforming (Data Set 2).

42

(a) Adaptive beamforming (Data Set 1). (b) Adaptive beamforming
(Data Set 2).

CONCLUSION
This article has briefly examined the applicability of a 3D OTHR
in the high-latitude region of the Earth. The effects of backscatter have mitigations within the scope of 3D OTHR. Experimental
results have shown that planar arrays on both transmit and receive
could achieve the required estimated 50 dB of clutter cancellation,
albeit with a large number of elements. The large element counts
(thousands of elements) required for planar receive arrays are being enabled by reductions in the cost of high-dynamic-range, high-

IEEE A&E SYSTEMS MAGAZINE

DECEMBER 2017



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