Function ula_array_factor 

pub fn ula_array_factor(
    n: u32,
    d: f64,
    freq: f64,
    c: f64,
    theta: f64,
    theta_steer: f64,
) -> f64

Array factor for a uniform linear array (ULA) of n omnidirectional elements spaced d apart at frequency f for steering angle theta_steer [rad].

Returns the normalised power pattern at angle theta [rad]: AF = |sin(N*ψ/2) / (N * sin(ψ/2))|² where ψ = k*d*(cos(θ) - cos(θ_steer)).