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The results of this work could be extended by:

• Considering more complex scenes with additional transmitters. Multistatic ef- fects caused from signals with different parameters or structures have not been considered.

• Set up a scene with more objects of varying reflectivities to more explicitly show the benefits of sidelobe suppression.

• Derive more concise metrics to evaluate image quality and range profile quality. • Further modify the form of the MLSMMF to further improve sidelobe suppres- sion. Changes may include a more rigorous definition of the ideal filter response for oversampled signals to reduce resolution loss.

Bibliography

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5. A. J. Zejak, E. Zentner, and P. B. Rapajic, “Doppler optimised mismatched filters,” Electronics Letters, vol. 27, no. 7, pp. 558–560, March 1991.

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Acronyms

ISLR integrated sidelobe ratio. ix, 19, 20, 21, 22, 30, 31, 33, 35, 47, 49, 51, 54, 57, 60, 61, 75

LSMMF least-squares mismatched filter. vii, 2, 3, 4, 15, 17, 19, 24, 25, 27, 28, 31, 36, 41, 47, 75, 76

LTE Long-Term Evolution. 8

MLSMMF modified LSMMF. vi, vii, ix, 18, 19, 24, 30, 31, 32, 34, 35, 36, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77

OFDM orthogonal frequency-division multiplexing. v, ix, 3, 4, 7, 8, 9, 11, 20, 25, 27, 28, 30, 31, 34, 35, 40, 42, 44, 46, 50, 51, 53, 54, 56, 57, 58, 59, 63, 66, 67, 69, 73

PSF point spread function. v, ix, 21, 22, 23, 37, 39, 41, 43, 45, 47, 73

PSK phase shift keying. 7

QAM quadrature amplitude modulation. 7

SAR synthetic aperture radar. v, 1, 4, 5, 6, 7, 8, 13, 21, 26

SNR signal-to-noise ratio. vi, ix, 1, 15, 27, 28, 30, 31, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 53, 54, 56, 57, 58, 59, 60, 61, 62, 63, 66, 67, 69, 70, 71, 73, 74, 75, 76

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19–03–2020 Master’s Thesis Sept 2018 — Mar 2020

Mismatched Filter Effects On Synthetic Aperture Radar Image Quality Metrics

Kempf, Jerrod M., Captain, USAF

Air Force Institute of Technology

Graduate School of Engineering and Management (AFIT/EN) 2950 Hobson Way

WPAFB OH 45433-7765

AFIT-ENG-MS-20-M-030

Air Force Research Laboratory - Sensors Directorate

Dr. Braham Himed, AFRL/RYMD Division Research Fellow 2241 Avionics Circle, Bldg. 620, WPAFB, OH 45433

(937) 713-8124

Email: [email protected]

AFRL/RYMD

DISTRIBUTION STATEMENT A:

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED.

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

Detection of targets across a wide dynamic range is an enduring challenge in radar. This work formulates a modified least-squares mismatched filter that greatly reduces these sidelobes in order to enable the detection of small radar cross section targets in the presence of considerably larger scatterers, increasing the dynamic range. Unlike previous

mismatched filters, the proposed filter is applicable to noisy, oversampled signals with no requirements on signal structure. Range profiles and images are presented to demonstrate the superior sidelobe suppression of the modified least-squares mismatched filter in comparison to the commonly employed matched filter. Various weighting vectors are introduced to further increase sidelobe suppression for particular scene geometries. The modified mismatched filter created with the addition of a noise compensation term is shown to have superior sidelobe suppression to that of the matched filter across all signal-to-noise ratios, coming at the relatively low expense of a small degree of mainlobe energy loss and widening, as well as increased processing time.

mismatched filters, least-squares, filter design, sidelobe suppression techniques, passive SAR

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