IEEE - Aerospace and Electronic Systems - November 2019 - 24

Additively Manufactured Luneburg Retroreﬂector

Figure 10.

Figure 11.

Measured (blue) and simulated (orange) RCA for the additively
manufactured retroreflector at 16.7 GHz.

Measured (blue) and simulated (orange) RCA for the additively
manufactured retroreflector at 22.5 GHz.

where a set of background data were collected with no
DUT in the chamber in order to coherently subtract out
the background. Finally, a calibrated corner reflector was
measured in place of the DUT to provide a calibrated RCS
response for the processed results. The processed results
are shown in the following section.

reasons: the FDM voxel size is optimized for Ku -band.
This work revealed additively manufactured Luneburg
lenses are suitable for RCS augmentation and calibration
systems.

RESULTS
The simulated and measured results for X, Ku , and K bands
(10, 16.7, and 22.5 GHz respective center frequencies) are
shown in Figures 9-11. Due to the symmetry of the Luneburg lens, the RCS in the E-field and H-field planes are presumed identical. Therefore, only an azimuth monostatic
RCS sweep was done. The additional lobe structure of the
measured data within the back lobe is due to the tape "slats"
that make up the end-cap. These can likely be eliminated
via application of a smooth, one-piece-construction end
cap. The results for Ku -band in Figure 10 are the most consistent between the measured and simulated RCS plots.
This result is intuitively satisfying since the unit cell size of
the space-filling curves used in the generation of the test
unit is most appropriate for these frequencies.

ACKNOWLEDGMENT
The authors would like to thank M. Guarnieri for offering
his invaluable expertise during the chamber testing of the
device.

REFERENCES
[1] S. Robertson, "Targets for microwave radar navigation,"
Bell Syst. Tech. J., vol. 26, no. 4, pp. 852-869, Oct. 1947.
[2] J. Bohnert and H. Coleman, Applications of the Luneburg
Lens. Naval Research Lab, Washington, D.C., USA,
Report 4888, Mar. 7, 1957.
[3] G. Peeler and H. Coleman, "Microwave stepped-index
Luneburg lenses," IRE Trans. Antennas Propag., vol. 6,
no. 2, pp. 202-207, Apr. 1958.
[4] Z. Larimore et al., "Use of space-filling curves for additive manufacturing of three dimensionally varying graded
dielectric structures using fused deposition modeling,"
Additive Manuf., vol. 15, pp. 48-56, 2017.

CONCLUSION

[5] Z. Larimore, S. Jensen, A. Good, A. Lu, J. Suarez, and

The results found in this work demonstrated that is possible to leverage the Luneburg graded refractive index
(GRIN) lens to create a high RCS system with Æ70 elevation and azimuth acceptance angles. The measured and
simulated results display good agreement. The reasons for
minor discrepancies can be explained by the following
24

M. Mirotznik, "Additive manufacturing of Luneburg lens
antennas using space-filling curves and fused filament
fabrication," IEEE Trans. Antennas Propag., vol. 66,
no. 6, pp. 2818-2827, Jun. 2018.
[6] E. Knott, J. Shaeffer, and M. Tuley, Radar Cross Section.

IEEE A&E SYSTEMS MAGAZINE

2nd ed., Rijeka, Croatia: SciTech, 2004, pp. 480-484.

NOVEMBER 2019

IEEE - Aerospace and Electronic Systems - November 2019

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