1. A method of searching for an incident angle of an incoming wave, for use in a multibeam radar apparatus, comprising: transmitting a transmission wave through a plurality of beam elements defining an antenna; receiving the incoming wave, which has been reflected from a target in response to the transmission wave being transmitted by the plurality of the beam elements; mixing the incoming wave with the transmission wave to generate beam signals; sending the beat signals to a processor; creating a plurality of steering vectors a(n, θ) for a plurality of θ at the processor using an equation (4) where n represents a number of virtual array elements and θ represents a searching incident angle; and searching for the incident angle of the incoming wave using the plurality of steering vectors a(n, θ); wherein M is a total number of the plurality of beam elements, y(m, θ) is m-th beam element data at the searching incident angle, θ, a(n, θ) is a steering vector at the searching incident angle θ, u(m)=2π sin θ m , θ m is a direction of an m-th multibeam, and v(n) is a position of the n-th virtual array element a ⁡ ( n , θ ) = 1 2 ⁢ ⁢ π ⁢ ∑ m = 1 M ⁢ y ⁡ ( m , θ ) ⁢ ⅇ - j ⁢ ⁢ u ⁡ ( m ) ⁢ v ⁡ ( n ). ( 4 )