# Copyright (c) 2008-2026 Tim Molteno (tim@elec.ac.nz)

#

# Automatically tune antenna

#

import monopole

import scipy.optimize

import numpy as np

from antenna_util import reflection_coefficient

# A function that will be minimized when the impedance is 50 Ohms

# We convert the height and antenna length to positive

# numbers using exp. because otherwise the antenna will lie

# below ground and cause an error in simulation.

def target(x):

global freq

base_height = np.exp(x[0]) # Make it positive

length = np.exp(x[1]) # Make it positive

z = monopole.impedance(freq, base_height, length)

return reflection_coefficient(z, z0=50.0)

# Starting value

freq = 134.5

x0 = [-2.0, 0.0]

# Carry out the minimization

log_base, log_length = scipy.optimize.fmin(target, x0)

base_height = np.exp(log_base)

length = np.exp(log_length)

print("Optimium base_height={}m, h={}m, impedance={} Ohms".format(base_height, length, monopole.impedance(freq, base_height, length)))