V.S. Chernyak - Dr.Sc. (Eng.), Professor, Moscow Aviation Institute (National Research University) E-mail: chernyak@kmail.ru

It is known that if distances between antenna elements in conventional radars with linear Phased Antenna Arrays (PAAs) exceed λ/2, where λ is the wavelength, grating lobes appear in Antenna Directivity Pattern (ADP) for a broad surveillance sector. Therefore, sparse PAAs (with a reduced number of array elements and hence with a reduced cost) are not used for radars with broad surveillance sectors. This drawback may be overcome in MIMO radars. Reasonable number and arrangement of transmitting and receiving elements in the linear sparse (thinned) antenna array of a MIMO radar are considered for detection and Direction Of Arrival (DOA) measurements (without grating lobes in ADP). However, using a sparse receiving antenna array for signal detection in a background of noise-like jamming leads to grating lobes in ADP and deep grating minima in the curve of signal to jamming plus noise ratio versus the signal and jamming direction of arrival (DOA) differences. Therefore, a signal is subtracted together with jamming and is not detected not only when target and jammer directions coincide (or are close one to another) but when a target is in any grating lobe. These difficulties may be overcome, for instance, by the shift of grating lobes as a result of a slight change of working frequency. The possibilities of clutter (from a cloud of interfering reflectors) cancellation with the help of spatial processing (by mutual subtraction) in receiving antenna array elements are considered. It was shown that such clutter cancellation is impossible because of weak clutter mutual correlation at the inputs of different array elements even for the same signals. However, the signal to clutter plus noise ratio may be enhanced significantly in the absence of spatial clutter correlation like in the case of signal detection in a background of internal noise. Sparse antenna arrays are useful in this case. Known clutter protection methods based on temporal selection (MTI) or spatial-temporal adaptive protection (STAP) are applicable (with certain limitations).

 

1. CHeston T., Frank Dzh. Fazirovannye antennye reshetki, gl. 4 v kn. «Spravochnik po radiolokacii» / Per. s angl. T. 2. M.: Sov. radio. 1977.
2. Robey F.C., Coutts S., Weikle D., McHarg J.C., Cuomo K. MIMO Radar Theory and Experimental Results // Record 38th Asilomar Conf. On Signals, Systems and Computers, Pacific Groove. CA. USA. 2004. Nov. V. 1. P. 54-59.
3. Donner B.J., Longstaff I.D. MIMO Radar, Techniques and Opportunities // Proc. 3rd European Radar Conf. EuRAD 2006. UK. P. 112-115.
4. Clare J., Saalmann O. MIRA-CLE X: A new Imaging MIMO Radar for Multi-Purpose Applications // Proc. 7th European Radar Conf. Paris. France. 2010. P. 129-132.
5. Chernyak V.S. About the «New» Concept of Statistical MIMO Radar // Proc. Int. Radar Symp. IRS 2007. Cologne. Germany. Sept. 2007.
6. Chernyak V.S. On the Concept of MIMO Radars // Proc. IEEE Int. Radar Conf. Radar 2010. WashingtonDC. USA. May 2010.
7. CHernjak V.S. O novykh i starykh idejakh v radiolokacii // Uspekhi sovremennojj radioehlektroniki. 2011. № 2. S. 5-19.
8. CHernjak V.S. Mnogopozicionnaja radiolokacija. M.: Radio i svjaz. 1993 / Per. na angl.: Chernyak V.S. Fundamentals of Multisite Radar Systems. Multistatic Radars and Multiradar Systems. Gordon and Breach Science Publishers. 1998.
9. Chernyak V.S. On some important features of MIMO radars with sparse antenna arrays // Proc. 13th European Radar Conference. London. UK. 5-7 Oct. 2016. P. 25-28.
10. CHernjak V.S. Obnaruzhenie signalov v MIMO RLS // Uspekhi sovremennojj radioehlektroniki. 2014. № 7. S. 35-48.
11. CHernjak V.S. Obnaruzhenie signalov na fone prostranstvenno-korrelirovannykh pomekh, dejjstvujushhikh po glavnym lepestkam DN antenn v MPRLS i MIMO RLS // Uspekhi sovremennojj radioehlektroniki. 2015. № 8. S. 3-18.
12. SHirman JA.D., Manzhos V.N. Teorija i tekhnika obrabotki radiolokacionnojj informacii na fone pomekh. M.: Radio i svjaz. 1981.
13. Dwyer P.S., Waugh F.V. On errors in matrix inversion // Journal Amer. Statistical Association. 1953. V. 48. № 262. C. 289-319.
14. Abramovich Yu. I, Frazer G.J. Bounds on the Volume and Height Distributions for the MIMO Radar Ambiguity Function // IEEE Signal Processing Letters. 2008. V. 15. P. 505-508.