Research On Broadband Beamforming Of Over-the-horizon Array Signal

When the partial irregularities of dielectric constant in the troposphere irradiated by microwave ultra-short wave radio and other bands, the incident will be re-radiated electromagnetic energy in all directions, also known as "scatter", so the scattered waves can "see" some range that the radio emission points cannot "see", that is Over-The-Horizon propagation through troposcatter, which can be utilized to detect radar carried by ships Over-The-Horizon. In order to solve the contradiction between wide spatial coverage requirement and high gain receiving requirement, the array antenna is used as receiving antenna, and how wide-band emitter signals received by the array beam forming is the key to the detection performance. This paper focuses on the receiving wideband beam forming method, mainly studied three aspects as the tropospheric scatter signal propagation modeling, the wideband received multi-beam forming and the multi-beam detection algorithm based on the signal characteristics.Firstly, to the Radio-communication Sector of International Telecommunication Union (ITU-R) recommendations, a model of the scattered signal were established based on analysis of the troposphere scatter signal propagation loss with transceiver beam angle, target distance and receiving antenna height changes and other factors, and the characteristics of the scattering signal fading under passive detection background. Combined with U.S. military active duty AN/SPS-48E radar parameters, simulation model for the scattering signal is obtained in the form of specific target signal.Secondly, according to the wide signal band differences as well as the wide airspace, this paper proposes an airspace broadband multi-beam forming algorithm based on a non-equidistant array, solving the contradiction among antenna aperture, the array element size and the received signal band expansion through controlling the spacing ranging of array element, to extract the received signal of each element of the spatial information by an improved FFT multi-beam forming algorithm, using spatial interpolation and adding FFT point to deal with the angle ambiguity, focused the target signal power on and output at signal arrival angle beam, this output can also provide the initial value for the subsequent signal detection and accurate angle measurement. Simulation results show that the algorithm is adaptable to wide airspace broadband weak signal.Finally, according to the troposphere scattering signal spectral characteristics this paper presented a multi-beam power spectrum peak accumulation detection algorithm accordance with the known frequency interval, having binary hypothesis testing for each beam output. Simulation results show the validity of the detection algorithm in low SNR scattering signal and less priori information conditions.