A.A. Monakov – Dr.Sc. (Eng.), Professor, 

Department «Radio Engineering System»,

Saint-Petersburg State University of Aerospace Instruments

E-mail: a_monakov@mail.ru

N.V. Povarenkin – Ph.D. (Eng.), Associate Professor, 

Department «Radio Engineering System»,

Saint-Petersburg State University of Aerospace Instruments

E-mail: povarenkin.nv@guap.ru

Much attention has been devoted to accident-free landing of aircraft. However, this phase of the flight is still one of the most dangerous. One of the main problems that arise in this case is the difficulty in estimating the angular coordinates of a landing aircraft. Due to the fact that the height of the aircraft flying along the glide path above the underlying surface is small, direction finding of approaching aircraft is a well-known problem of estimation of the angular coordinates of low altitude targets because since the direct signal coming from the aircraft is received on the back-ground of powerful reflections from the underlying surface. In the works by D. Barton, S. Sherman, R.V. Ostrovityanov, F.A. Basalov and other well-known experts in the field of radar theory it is showed that it is impossible to distinguish a direct signal from a low altitude target against the background of reflections using traditional resolution methods, and the only way to get the solution of the problem is the resolution by angular coordinates. Thus, to solve the problem, it is necessary to use a multichannel radar system with an antenna array, which elements have different heights above the underlying surface. One of the possible implementations of such an antenna array is a system consisting of sum-difference monopulse sensors, the phase centers of which are spaced apart in height. The article synthesizes an algorithm for estimating the elevation angle of a low altitude target using the aforementioned antenna system when observing a target over a flat mirror surface. The article shows that the signal processing algorithm reduces to solving a quadratic algebraic equation, which roots are estimates of the angular coordinates of a low altitude target and its antipode. Effectiveness of the obtained algorithm was evaluated by computer simulation. The simulation was carried out under conditions when, in addition to the direct signal and the coherent component of the reflected signal, the received signal contains an incoherent component, which appearance of is caused by the roughness of the surface. Analysis of the simulation results showed that the synthesized algorithm has high efficiency. The proposed algorithm can be used in aircraft landing systems as one of the tools that increase the accuracy of elevation angle estimates when aircraft fly along the glide path.

1. Barton D.K. Radiolokatsionnoy soprovozhdenie tseli pri malykh uglakh mesta: Per. s angl. TIIER. 1974. T. 62. № 6. S. 37–61.  [in Russian]
2. Barton D.K. Modeli meshayushchikh otrazheniy ot zemnoy poverkhnosti dlya analiza i proektirovaniya RLS: Per. s angl. TIIER. 1985.
3. T. 73. № 2. S. 27–34. [in Russian]
4. Ostrovityanov R.V., Basalov F.A. Statisticheskaya teoriya radiolokatsii protyazhennykh tseley. M.: Radio i svyaz'. 1982. [in Russian]
5. White W.D. Low-angle radar tracking in the presence of multipath. IEEE Trans. on Aerospace and Electronic Systems. 1974. V. AES 10. P. 835–853.
6. Sherman S.M. Somplex indicated angles applied to unresolved radar targets and multipath. Trans. on Aerospace and Electronic Systems. 1971. V. AES 7. P. 160–170. 
7. Sherman S.M., Barton D.K. Monopulse Principles and Techniques. Dedham, MA. Artech House. 2011.
8. Monakov A.A., Varfolomeev G.A. K voprosu o fizicheskom smysle kompleksnogo monoimpul'snogo otnosheniya. Uspekhi sovremennoy radioelektroniki. 2011. № 5. S. 52–55. [in Russian]
9. Monakov A.A., Povarenkin N.V. Otsenka ugla mesta nizkoletyashchey tseli: matematicheskaya model' signala, rasseyannogo sherokhovatoy poverkhnost'yu pri skol'zyashchikh uglakh rasprostraneniya. Uspekhi sovremennoy radioelektroniki. 2019. № 11. S. 12–19.