#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Plot difference in SWR bandwidth with attenuation

Created on Sun Sep 19 10:30:04 2021

@author: jimlux
"""
import numpy as np
import matplotlib.pyplot as plt

def findvswrbw(freqs,vswr,points=[1.5,2]):
    output = []
    for p in points:
        vswrpts = np.where(vswr<=p)
        vswrbw = freqs[vswrpts[0][-1]] - freqs[vswrpts[0][0]]

        output.append(vswrbw)
    return (output)

""" assume antenna resonance is a classic Lorenzian RLC resonance
    Z = 50 + 1/jwC + jwL, where imaginary part disappears at resonance
    Set for resonance at 10 MHz (omega = 62.8 rad/sec)
    Rres is set to 50 representing something like a inverted V
    
"""
omega0 = 10 * 2 * np.pi
R = 52
C = 4       #pF
L = 63.2    #uH
LC = 1E6/((10*2*np.pi)**2)
C = LC/L

titlestr = "R:%5.2f C:%5.2f pF L:%5.2f uH"%(R,C,L)
freqs  = np.linspace(9.9,10.1,301)

Xc = 1/(freqs * 2*np.pi * C*1e-6)   #pF, MHz
Xl = freqs * 2 * np.pi * L          #uH, MHz

plt.figure()
plt.plot(freqs,Xc)
plt.plot(freqs,Xl)
plt.legend(["Xc","Xl"])
plt.xlabel("MHz")
plt.xlim([min(freqs), max(freqs)])
plt.title(titlestr)
plt.grid()

Zant = R + 1j * (Xl-Xc)

Z0 = 50
gamma = (Zant-Z0)/(Zant+Z0)
mags11 = 20*np.log10(np.abs(gamma))
mags11pad = mags11-2
gammapad = 10**(mags11pad/20)
vswr = (1+np.abs(gamma))/(1-np.abs(gamma))
vswrpad = (1+gammapad)/(1-gammapad)

bws = findvswrbw(freqs,vswr)
bwspad = findvswrbw(freqs,vswrpad)

plt.figure()
plt.plot(freqs,mags11)
plt.plot(freqs,mags11pad)
plt.legend(["no loss","1dB loss"])
plt.ylabel("|S11|")
plt.xlabel("MHz")
plt.xlim([min(freqs), max(freqs)])
plt.title(titlestr)
plt.grid()

plt.figure()
plt.plot(freqs,vswr)
plt.plot(freqs,vswrpad)
plt.legend(["no loss","1dB loss"])
plt.ylim([1,5])
plt.ylabel('VSWR')
plt.xlabel("MHz")
plt.xlim([min(freqs), max(freqs)])
plt.title(titlestr)
textboxstr =    "1.5:1  %5.2f  %5.2f kHz"%(bws[0]*1000,bwspad[0]*1000)
textboxstr += "\n    2:1  %5.2f  %5.2f kHz"%(bws[1]*1000,bwspad[1]*1000)
plt.text(10,4,textboxstr,ha='center',bbox=dict(ec=(0,0,0),fc=(1,1,1)))
plt.grid()