A Direct Near-Field-to-Far-Field Transformation Method for Single-Cut Pattern Measurements

This paper proposes a single-cut near-field antenna measurement method. Unlike the existing spectral domain harmonics method and equivalent source method, the proposed near-field-to-far-field transformation method does not rely on any intermediate variables such as Fourier coefficients and equivalent sources. Starting from the representation of the radiation field using cylindrical Hankel harmonics, the method derives the asymptotic series expansion of the Hankel function. Thus, the single-cut radiated field can be rewritten as a series of spherical waves e^-jk ρ /(k ρ)^p, where the far-field pattern as first-order expansion coefficient determines all higher-order expansion coefficients via mathematical derivative functions. Based on the difference form of these derivative functions, the far-field pattern can be directly solved and obtained from near-field data. Especially, this method outperforms the existing spectral domain harmonics method in the presence of spatial truncation. Simulation and measurement validate the proposed method.