Source code for skrf.media.cpw



'''
.. module:: skrf.media.cpw
========================================
cpw (:mod:`skrf.media.cpw`)
========================================

Coplanar waveguide class


This class was made from the technical documentation [#]_ provided
by the qucs project [#]_ .
The variables  and properties of this class are coincident with
their derivations.

.. [#] http://qucs.sourceforge.net/docs/technical.pdf
.. [#] http://www.qucs.sourceforge.net/
'''
from scipy.constants import  epsilon_0, mu_0
from scipy.special import ellipk
from numpy import real, imag,pi,sqrt,log,zeros, ones
from .media import Media
from ..tlineFunctions import skin_depth, surface_resistivity

[docs]class CPW(Media): ''' Coplanar Waveguide initializer Parameters ------------- frequency : :class:`~skrf.frequency.Frequency` object frequency band of the media z0 : number, array-like, or None the port impedance for media. Only needed if its different from the characterisitc impedance of the transmission w : number, or array-like width of center conductor, in m. s : number, or array-like width of gap, in m. ep_r : number, or array-like relative permativity of substrate t : number, or array-like, optional conductor thickness, in m. rho: number, or array-like, optional resistivity of conductor (None) '''
[docs] def __init__(self, frequency=None, z0=None, w=70, s=4, ep_r=3, t=None, rho=None, *args, **kwargs): Media.__init__(self, frequency=frequency,z0=z0) self.w, self.s, self.ep_r, self.t, self.rho =\ w, s, ep_r, t, rho
def __str__(self): f=self.frequency output = \ 'Coplanar Waveguide Media. %i-%i %s. %i points'%\ (f.f_scaled[0],f.f_scaled[-1],f.unit, f.npoints) + \ '\n W= %.2em, S= %.2em'% \ (self.w,self.s) return output def __repr__(self): return self.__str__() @property def ep_re(self): ''' intermediary parameter. see qucs docs on cpw lines. ''' return (self.ep_r+1)/2. @property def k1(self): ''' intermediary parameter. see qucs docs on cpw lines. ''' return self.w/(self.w +2*self.s) @property def K_ratio(self): ''' intermediary parameter. see qucs docs on cpw lines. ''' k1 = self.k1 if (0 <= k1 <= 1/sqrt(2)): return pi/log(2*(1+sqrt(sqrt(1-k1**2)))/(1-sqrt(sqrt(1-k1**2)))) elif (1/sqrt(2) < k1 <= 1): return (log(2*(1+sqrt(k1))/(1-sqrt(k1)) ))/pi @property def alpha_conductor(self): ''' Losses due to conductor resistivity Returns -------- alpha_conductor : array-like lossyness due to conductor losses See Also ---------- surface_resistivity : calculates surface resistivity ''' if self.rho is None or self.t is None: raise(AttributeError('must provide values conductivity and conductor thickness to calculate this. see initializer help')) t, k1, ep_re = self.t, self.k1,self.ep_re r_s = surface_resistivity(f=self.frequency.f, rho=self.rho, \ mu_r=1) a = self.w/2. b = self.s+self.w/2. K = ellipk # complete elliptical integral of first kind K_p = lambda x: ellipk(sqrt(1-x**2)) # ellipk's compliment return ((r_s * sqrt(ep_re)/(480*pi*K(k1)*K_p(k1)*(1-k1**2) ))*\ (1./a * (pi+log((8*pi*a*(1-k1))/(t*(1+k1)))) +\ 1./b * (pi+log((8*pi*b*(1-k1))/(t*(1+k1)))))) @property def Z0(self): ''' Characterisitc impedance ''' return (30.*pi / sqrt(self.ep_re) * self.K_ratio)*ones(len(self.frequency.f), dtype='complex') @property def gamma(self): ''' Propagation constant See Also -------- alpha_conductor : calculates losses to conductors ''' beta = 1j*2*pi*self.frequency.f*sqrt(self.ep_re*epsilon_0*mu_0) alpha = zeros(len(beta)) if self.rho is not None and self.t is not None: alpha = self.alpha_conductor return beta+alpha