Whitepaper
Complex Fit Normalized Site Attenuation for Antennas with Complex Radiation Patterns
This paper investigates improvements to Normalized Site Attenuation (NSA) calculations, specifically proposing a Complex Fit NSA (CFNSA) method that accounts for complex antenna patterns like those found in Log-Periodic Dipole Arrays (LPDAs). The authors address limitations of the ANSI C63.5 standard’s cosine pattern approximation, finding it inadequate above 500 MHz. They explored higher-order polynomial functions to model LPDA patterns – a fourth order fit F(θ) = R₀ + a₁cos(bθ) + a₂cos²(bθ) + a₃cos³(bθ) + a₄cos⁴(bθ) was found capable of realistically fitting measured H-plane patterns up to 2 GHz. The CFNSA method, using this pattern formulation and a Genetic Algorithm for parameter optimization on test data from two LPDAs (200MHz - 2GHz and 200MHz - 1GHz), demonstrated reduced antenna factor variations – below 1dB from 1-2 GHz versus ~1.5 dB with simpler models.