False targets caused by reflection position determining solution and system for secondary surveillance radar

A method of determining false target positions caused by reflection comprising the following steps:

• step 1:
• generating input data for a multipath position determining system;
• performed within an input data generating component and provides input information of a real target and reflectors, the information of the real target includes an area of range and azimuth where an airplane flies received from a secondary surveillance radar (SSR) system, the input information about the reflector includes the reflector's size, range and azimuth, surface material, and scattering of a reflecting surface provided by surveying a surrounding landscape of the SSR within an observing field of the radar the information also includes information about an antenna beamwidth, a sweeping speed data provided by the SSR;
• a radar cross section, and a target average speed data from references about airplanes' types;
• step 2:
• determining a position of a ghost of the real target in a false target position determining component;
• based on input system parameters, including geometrical similarity, using mirror reflection principles to approach a multipath phenomenon, the real target radiates an answer signal from a range R, azimuth γ giving the false target at range Ri, azimuth γi as follows:
• {
• R
• i
• =
• 2
• ⁢
• R
• r
• ⁢
• cos
• ⁢
• α
• -
• R
• ⁢
• cos
• ⁡
• (
• γ
• r
• +
• α
• -
• γ
• )
• cos
• ⁡
• (
• arctan
• ⁢
• X
• ˜
• )
• γ
• i
• =
• γ
• r
• +
• α
• -
• γ
• -
• arctan
• ⁢
• X
• ˜
• where:
• X
• ˜
• =
• X
• R
• r
• ⁢
• cos
• ⁢
• α
• =
• R
• ·
• sin
• ⁡
• (
• γ
• r
• +
• α
• -
• γ
• )
• 2
• ·
• R
• r
• ⁢
• cos
• ⁢
• α
• -
• R
• ⁢
• cos
• ⁡
• (
• γ
• r
• +
• α
• -
• γ
• )
• with:
• α is the angle between the reflecting surface and a normal line;
• γr is the azimuth of the reflector (from a horizontal center point of the reflecting surface);
• Rr is a range of the reflector (from the horizontal center point of the reflecting surface);
• X is the distance from a reflected point on the reflecting surface to an end of the normal line on the reflecting surface, the normal line drawn from the radar to a plane which includes the reflecting surface;
• with reflection principles and related formulas, calculate a multipath position and a reflected site;
• to determine the reflected site, determine a speed, direction of the airplane, and a sweeping speed of radar, a position where the airplane causes the false target is interpolated between two positions where the airplane is spotted on the radar in two consecutive scanning circles;
• step 3:
• calculate a power correlation between the real target and the false target;
• as for the multipath reflected signal in the SSR, the multipath reflected signal is attenuated as compared to a direct response signal from the target, but still strong enough to cause multipath false targets;
• a power loss of the multipath reflected signal is calculated using formulas of free-space path loss and reflection coefficient of the reflecting surface,
• wherein the free-space path loss formula comprises:
• ΔL=20·log(R)+20·log(f)−147,5
• in which:
• R[m] is a range of the target;
• f[Hz] is a signal frequency,
• the reflection coefficient is formula comprises:
• ρ=ρ0ρsρv
• as:
• ρ0 is a Fresnel reflection coefficient;
• ρs is a rough surface's reflection coefficient;
• ρv is a vegetation's reflection coefficient;
• step 4:
• displaying and transferring false target information including position and power;
• in a displaying and data transferring component, wherein
• the displaying and data transferring component show on an interface input parameters of the reflected real target, the reflector, and calculated parameters of the false target,
• the interface enables to survey several flying targets with several types of landscape along with different reflecting surface features, it also visualizes the multipath phenomenon with airplane position, reflector, and any false target on a monitor,
• plot and export a 3D figure of a received signal amplitude in two dimensions:
• range and azimuth with optional axes limits, allowing saving and interacting with the 3D figure;
• continuously update information about scanning angle, real targets, and any false targets and report whether there are false targets or not;
• using information from the surveay as a basis for a false target suppressing system of the SSR;
• step 5:
• applying a multipath suppressing algorithm on the SSR;
• in a reflected multipath targets suppressing component, using a reflected false target suppressing algorithm, based on multipath position information and power comparison, calculate the parameters for the false target suppressing system,
• the multipath suppressing algorithm compares a power of a main channel at a range R with an adjacent area of a suppressing channel, a range suppressing window is calculated based on information from the airplane and the false target determining system, the range suppressing window's parameters are changeable;
• wherein the range suppressing window's parameters are set as follows:
• + suppressing window:
• Δt≤3 μs
• + suppressing power condition:
• PM≥PS+9 dB, where PM is the power of the main channel and Ps is a power of the suppressing channel
• signal after suppressing is transferred to a next stage, which is a target detecting component, to process, decode and extract information for the radar system.