#!/usr/bin/python3

import numpy as np
import scipy.optimize as opt
import microstrip as ms

def Butterworth(n):
    '''
    Return koefficents of Butterworth n-th order filter
    g0 and gn+1 are assumed to be 1

    [g0, g1, ... gn, gn+1] = Buttherworth(n)
    '''
    gi = 2*np.sin((2*np.arange(1,n+1)-1)*np.pi/2/n)
    return np.hstack([1,gi,1])

def Tchebysheff(n, ripple):
    '''
    Return coefficents of Tchebysheff n-th order filter
    with specified ripple in passband.
    
    [g0, g1, ... gn, gn+1] = Tchebysheff(n, ripple)
    n <- order of filter
    ripple <- ripple in passband (dB)
    '''
    b = np.log(1/np.tanh(ripple/17.37))
    k = np.sinh(b/2/n)

    g = np.ones(n+2)
    g[1] = 2/k*np.sin(np.pi/2/n)
    for i in range(2,n+1):
        g[i] = 1/g[i-1]*4*np.sin((2*i-1)*np.pi/2/n)*np.sin((2*i-3)*np.pi/2/n)/\
                (k**2+np.sin((i-1)*np.pi/n)**2)

    if n % 2 == 0:
        g[-1] = 1/np.tanh(b/4)**2

    return g

def mclBPF(h, e_r, fbw, gk, f0):
    '''
    Calculate dimensions of microstrip coupled lines bandpass
    filter.

    h <- height of substrate (mm)
    e_r <- dielectric constant of substrate
    fbw <- fractional bandwidth of bpf
    gk <- filter coefficents
    f0 <- central frequency (GHz)
    '''

    n = len(gk)-2
    J = np.ones(n+1)
    J[0] = np.sqrt(np.pi*fbw/2/gk[0]/gk[1])
    J[-1] = np.sqrt(np.pi*fbw/2/gk[-2]/gk[-1])
    for j in range(1,n):
        J[j] = np.pi*fbw/2/np.sqrt(gk[j]*gk[j+1])

    Zo = np.zeros(n+1)
    Ze = np.zeros(n+1)

    for j in range(n+1):
        Ze[j] = 50*(1+J[j]+J[j]**2)
        Zo[j] = 50*(1-J[j]+J[j]**2)

    lambda4 = 3e8/f0/1e9/4 *1e3
    W = np.zeros(n+1)
    s = np.zeros(n+1)
    l = np.zeros(n+1)
    for j in range(n+1):
        x = ms.get_mcl(Ze[j],Zo[j],h,e_r,f0)
        W[j] = x[0]
        s[j] = x[1]
        dl = ms.open_end(W[j],h,e_r,f0)
        eps = ms.mcl_eps(W[j],h,s[j],e_r,f0)
        # popravek z upostevanjem disperzije
        l[j] = lambda4/np.sqrt(np.sqrt(eps[0]*eps[1]))-dl
        #print(l[j])
        # popravek s staticnim eps
        l[j] = lambda4/np.sqrt(np.sqrt(eps[2]*eps[3]))-dl
        #print(l[j])

    return {'W':W, 's':s, 'l':l, 'f':f0, 'fbw':fbw}

def prtmclBFP(bfp):
    '''
    Print filter in readable format
    '''
    n = len(bfp['W'])
    print("Microstrip coupled line bandpass filter:\nAll dimensions in mm.")
    print("\tW\ts\tl")
    for i in range(n):
        print("{}:\t{:.2f}\t{:.2f}\t{:.2f}".format(i+1,bfp['W'][i],\
                bfp['s'][i],bfp['l'][i]))

    print("Length of filter: {} mm".format(sum(bfp['l'])))
    print("Width of filter: {} mm".format(sum(bfp['W'])+sum(bfp['s'])))


if __name__ == '__main__':
    gk = Tchebysheff(7,0.05)
    #bfp = mclBPF(1.54, 3.66, 0.1, gk, 10.2)
    bfp = mclBPF(0.76, 3.66, 0.1, gk, 10.2)
    #prtmclBFP(bfp)
    
    print(ms.getWf(50, 0.76, 3.66, 10.2))

    print("=== interstage filter za bfp840 ===")
    gk = Butterworth(7)
    bfp = mclBPF(0.8, 3.66, 0.3, gk, 10.5)
    prtmclBFP(bfp)
    print("=== interstage filter za bfp840 ===")
    gk = Butterworth(5)
    bfp = mclBPF(0.8, 3.66, 0.3, gk, 10.5)
    prtmclBFP(bfp)
    print("=== interstage filter za bfp840 ===")
    gk = Butterworth(5)
    bfp = mclBPF(0.8, 3.66, 0.05, gk, 10.5)
    prtmclBFP(bfp)
    print("=== interstage filter za bfp840 ===")
    gk = Butterworth(3)
    bfp = mclBPF(0.8, 3.66, 0.05, gk, 10.5)
    prtmclBFP(bfp)