A Ka-band two-dimensional synthetic aperture interferometric radiometer called BHU-2D has been developed by Electromagnetic Engineering Laboratory of Beihang University. The radiometer obtains images in real-time benefiting from the adoption of a 1bit/2level FPGA-based correlator unit. The design and implementation of the correlator unit in BHU-2D are presented in this paper. The calibration procedures of the correlation coefficients are also presented. For the purpose of simplifying the calibration procedure, a closed form approximation is introduced and applied to BHU-2D, which is used to correct the errors caused by threshold offset of the quantizer. Error analysis of this approximation shows that the method is applicable in SAIRs. In order to verify the design and calibration method, a series of validation experiments have been conducted. Measurement results have proved that the performance of the correlation unit could meet the requirements of BHU-2D.
2. Goodman, J. W., Statistical Optics (Wiley Classics Library), 207-221, Wiley, New York, 2000.
3. Miao, J., "Microwave aperture synthetic radiometer and the passive millimeter wave imager of Beihang University," Proc. ICMTCE, 7, Beijing, China, May 22-25, 2001.
4. Van Vleck, J. H. and D. Middleton, "The spectrum of clipped noise," Proc. IEEE, Vol. 54, No. 1, 2-19, Jan. 1966.
5. Martin-Neira, M., I. Cabeza, C. Perez, M. A. Palacios, M. A. Guijarro, S. Ribo, I. Corbella, S. Blanch, F. Torres, N. Duffo, V. Gonzalez, S. Beraza, A. Camps, M. Vall-llossera, S. Tauriainen, J. Pihlflyckt, J. P. Gonzalez, and F. Martin-Porqueras, "AMIRAS --- An airborne MIRAS demonstrator," IEEE Trans. Geosci. Remote Sens., Vol. 46, No. 3, 705-716, Mar. 2008.
6. Rautiainen, K., H. Valmu, P. Jukkala, G. Moren, and M. Hallikainen, "Four-element prototype of the HUT interferometric radiometer," Proc. IGARSS, Vol. 1, 234-236, Hamburg, 1999.
7. Salmon, N. A., R. Macpherson, A. Harvey, P. Hall, S. Hayward, P. Wilkinson, and C. Taylor, "First video rate imagery from a 32-channel 22-GHz aperture synthesis passive millimetre wave imager," Proc. SPIE, Vol. 8188, 818805, Oct. 6, 2011.
8. Tanner, A. B. , W. J. Wilson, P. P. Kangaslahti, B. H. Lambrigsten, S. J. Dinardo, J. R. Piepmeier, C. S. Ruf, S. Rogacki, S. M. Gross, and S. Musko, "Prototype development of a geosta-tionary synthetic thinned aperture radiometer, GeoSTAR," Proc. IGARSS, Vol. 2, 1256-1259, Anchorage, AK, Sep. 20-24, 2004.
9. Ruf, C. S., "Digital correlators for synthetic aperture interfero-metric radiometry," IEEE Trans. Geosci. Remote Sens., Vol. 33, No. 5, 1222-1229, Sep. 1995.
10. Camps, A., F. Torres, I. Corbella, J. Bara, and J. A. Lluch, "Threshold and timing errors of 1 bit/2 level digital correlators in Earth observation synthetic aperture radiometry," Electron. Lett., Vol. 33, No. 9, 812-814, Apr. 1997.
11. Corbella, I., F. Torres, A. Camps, A. Colliander, M. Martin-Neira, S. Ribo, K. Rautiainen, N. Duffo, and M. Vall-llossera, "MIRAS end-to-end calibration: Application to SMOS L1 processor," IEEE Trans. Geosci. Remote Sens., Vol. 43, No. 5, 1126-1134, May 2005.
12. Colliander, A., S. Tauriainen, T. I. Auer, J. Kainulainen, J. Uusitalo, M. Toikka, and M. T. Hallikainen, "MIRAS reference radiometer: a fully polarimetric noise injection radiometer," IEEE Trans. Geosci. Remote Sens., Vol. 43, No. 5, 1135-1143, May 2005.
13. Camps, A., "Application of interferometric radiometry to earth observation,", Ph.D. Dissertation, Ch. 4, Polytechnic University of Catalonia, Spain, 1996.
14. Camps, A., I. Corbella, J. Bara, and F. Torres, "Radiometric sensitivity computation in aperture synthesis interferometric radiometry," IEEE Trans. Geosci. Remote Sens., Vol. 36, No. 2, 680-685, Mar. 1998.
15. Thompson, R., J. Moran, and G. Swenson, Interferometry and Synthesis in Radio Astronomy, 2nd Ed., 263, Wiley, New York, 2001.