"""
.. currentmodule:: skrf.frequency
========================================
frequency (:mod:`skrf.frequency`)
========================================
Provides a frequency object and related functions.
Most of the functionality is provided as methods and properties of the
:class:`Frequency` Class.
Frequency Class
===============
.. autosummary::
:toctree: generated/
Frequency
Functions
=========
.. autosummary::
:toctree: generated/
overlap_freq
Misc
====
.. autosummary::
:toctree: generated/
InvalidFrequencyWarning
"""
# from matplotlib.pyplot import gca,plot, autoscale
from typing import List
import warnings
from numbers import Number
from .constants import NumberLike, ZERO
from typing import Union
from numpy import pi, linspace, geomspace
import numpy as npy
from numpy import gradient # used to center attribute `t` at 0
import re
from .util import slice_domain, find_nearest_index
[docs]class InvalidFrequencyWarning(UserWarning):
"""Thrown if frequency values aren't monotonously increasing
"""
pass
[docs]class Frequency(object):
"""
A frequency band.
The frequency object provides a convenient way to work with and
access a frequency band. It contains a frequency vector as well as
a frequency unit. This allows a frequency vector in a given unit
to be available (:attr:`f_scaled`), as well as an absolute frequency
axis in 'Hz' (:attr:`f`).
A Frequency object can be created from either (start, stop, npoints)
using the default constructor, :func:`__init__`. Or, it can be
created from an arbitrary frequency vector by using the class
method :func:`from_f`.
Internally, the frequency information is stored in the `f` property
combined with the `unit` property. All other properties, `start`
`stop`, etc are generated from these.
"""
unit_dict = {
'hz': 'Hz',
'khz': 'kHz',
'mhz': 'MHz',
'ghz': 'GHz',
'thz': 'THz'
}
"""
Dictionnary to convert unit string with correct capitalization for display.
"""
multiplier_dict={
'hz': 1,
'khz': 1e3,
'mhz': 1e6,
'ghz': 1e9,
'thz': 1e12
}
"""
Frequency unit multipliers.
"""
[docs] def __init__(self, start: float = 0, stop: float = 0, npoints: int = 0,
unit: str = 'ghz', sweep_type: str = 'lin') -> None:
"""
Frequency initializer.
Creates a Frequency object from start/stop/npoints and a unit.
Alternatively, the class method :func:`from_f` can be used to
create a Frequency object from a frequency vector instead.
Parameters
----------
start : number, optional
start frequency in units of `unit`. Default is 0.
stop : number, optional
stop frequency in units of `unit`. Default is 0.
npoints : int, optional
number of points in the band. Default is 0.
unit : string, optional
Frequency unit of the band: 'hz', 'khz', 'mhz', 'ghz', 'thz'.
This is used to create the attribute :attr:`f_scaled`.
It is also used by the :class:`~skrf.network.Network` class
for plots vs. frequency. Default is 'ghz'.
sweep_type : string, optional
Type of the sweep: 'lin' or 'log'.
'lin' for linear and 'log' for logarithmic. Default is 'lin'.
Note
----
The attribute `unit` sets the frequency multiplier, which is used
to scale the frequency when `f_scaled` is referenced.
Note
----
The attribute `unit` is not case sensitive.
Hence, for example, 'GHz' or 'ghz' is the same.
See Also
--------
from_f : constructs a Frequency object from a frequency
vector instead of start/stop/npoints.
:attr:`unit` : frequency unit of the band
Examples
--------
>>> wr1p5band = Frequency(500, 750, 401, 'ghz')
"""
self._unit = unit.lower()
start = self.multiplier * start
stop = self.multiplier * stop
if sweep_type.lower() == 'lin':
self._f = linspace(start, stop, npoints)
elif sweep_type.lower() == 'log' and start > 0:
self._f = geomspace(start, stop, npoints)
else:
raise ValueError('Sweep Type not recognized')
def __str__(self) -> str:
"""
"""
try:
output = \
'%s-%s %s, %i pts' % \
(self.f_scaled[0], self.f_scaled[-1], self.unit, self.npoints)
except (IndexError):
output = "[no freqs]"
return output
def __repr__(self) -> str:
"""
"""
return self.__str__()
def __getitem__(self, key: Union[str, int, slice]) -> 'Frequency':
"""
Slices a Frequency object based on an index, or human readable string.
Parameters
----------
key : str, int, or slice
if int, then it is interpreted as the index of the frequency
if str, then should be like '50.1-75.5ghz', or just '50'.
If the frequency unit is omitted then :attr:`unit` is
used.
Examples
--------
>>> b = rf.Frequency(50, 100, 101, 'ghz')
>>> a = b['80-90ghz']
>>> a.plot_s_db()
"""
output = self.copy()
if isinstance(key, str):
# they passed a string try and do some interpretation
re_numbers = re.compile(r'.*\d')
re_hyphen = re.compile(r'\s*-\s*')
re_letters = re.compile('[a-zA-Z]+')
freq_unit = re.findall(re_letters,key)
if len(freq_unit) == 0:
freq_unit = self.unit
else:
freq_unit = freq_unit[0]
key_nounit = re.sub(re_letters,'',key)
edges = re.split(re_hyphen,key_nounit)
edges_freq = Frequency.from_f([float(k) for k in edges],
unit = freq_unit)
if len(edges_freq) ==2:
slicer=slice_domain(output.f, edges_freq.f)
elif len(edges_freq)==1:
key = find_nearest_index(output.f, edges_freq.f[0])
slicer = slice(key,key+1,1)
else:
raise ValueError()
try:
output._f = npy.array(output.f[slicer]).reshape(-1)
return output
except(IndexError):
raise IndexError('slicing frequency is incorrect')
if output.f.shape[0] > 0:
output._f = npy.array(output.f[key]).reshape(-1)
else:
output._f = npy.empty(shape=(0))
return output
[docs] @classmethod
def from_f(cls, f: NumberLike, *args,**kwargs) -> 'Frequency':
"""
Construct Frequency object from a frequency vector.
The unit is set by kwarg 'unit'
Parameters
----------
f : scalar or array-like
frequency vector
*args, **kwargs : arguments, keyword arguments
passed on to :func:`__init__`.
Returns
-------
myfrequency : :class:`Frequency` object
the Frequency object
Raises
------
InvalidFrequencyWarning:
If frequency points are not monotonously increasing
Examples
--------
>>> f = npy.linspace(75,100,101)
>>> rf.Frequency.from_f(f, unit='ghz')
"""
if npy.isscalar(f):
f = [f]
temp_freq = cls(0,0,0,*args, **kwargs)
temp_freq._f = npy.array(f) * temp_freq.multiplier
temp_freq.check_monotonic_increasing()
return temp_freq
def __eq__(self, other: object) -> bool:
#return (list(self.f) == list(other.f))
# had to do this out of practicality
if not isinstance(other, self.__class__):
return False
if len(self.f) != len(other.f):
return False
elif len(self.f) == len(other.f) == 0:
return True
else:
return (max(abs(self.f-other.f)) < ZERO)
def __ne__(self,other: object) -> bool:
return (not self.__eq__(other))
def __len__(self) -> int:
"""
The number of frequency points
"""
return self.npoints
def __mul__(self,other: 'Frequency') -> 'Frequency':
out = self.copy()
out.f = self.f*other
return out
def __rmul__(self,other: 'Frequency') -> 'Frequency':
out = self.copy()
out.f = self.f*other
return out
def __div__(self,other: 'Frequency') -> 'Frequency':
out = self.copy()
out.f = self.f/other
return out
[docs] def check_monotonic_increasing(self) -> None:
"""Validate the frequency values
Raises
------
InvalidFrequencyWarning:
If frequency points are not monotonously increasing
"""
increase = npy.diff(self.f) > 0
if not increase.all():
warnings.warn("Frequency values are not monotonously increasing!\n"
"To get rid of the invalid values call `drop_non_monotonic_increasing`",
InvalidFrequencyWarning)
[docs] def drop_non_monotonic_increasing(self) -> List[int]:
"""Drop duplicate and invalid frequency values and return the dropped indices
Returns:
list[int]: The dropped indices
"""
invalid = npy.zeros(len(self.f), dtype=bool)
for i, val in enumerate(self.f):
if not i:
last_valid = val
else:
if val > last_valid:
last_valid = val
else:
invalid[i] = True
self._f = self._f[~invalid]
return list(npy.flatnonzero(invalid))
@property
def start(self) -> float:
"""
Starting frequency in Hz.
"""
return self.f[0]
@property
def start_scaled(self) -> float:
"""
Starting frequency in :attr:`unit`'s.
"""
return self.f_scaled[0]
@property
def stop_scaled(self) -> float:
"""
Stop frequency in :attr:`unit`'s.
"""
return self.f_scaled[-1]
@property
def stop(self) -> float:
"""
Stop frequency in Hz.
"""
return self.f[-1]
@property
def npoints(self) -> int:
"""
Number of points in the frequency.
"""
return len(self.f)
@npoints.setter
def npoints(self, n: int) -> None:
"""
Set the number of points in the frequency.
"""
warnings.warn('Possibility to set the npoints parameter will removed in the next release.',
DeprecationWarning, stacklevel=2)
if self.sweep_type == 'lin':
self.f = linspace(self.start, self.stop, n)
elif self.sweep_type == 'log':
self.f = geomspace(self.start, self.stop, n)
else:
raise ValueError(
'Unable to change number of points for sweep type', self.sweep_type)
@property
def center(self) -> float:
"""
Center frequency in Hz.
Returns
-------
center : number
the exact center frequency in units of Hz
"""
return self.start + (self.stop-self.start)/2.
@property
def center_idx(self) -> int:
"""
Closes idx of :attr:`f` to the center frequency.
"""
return self.npoints // 2
@property
def center_scaled(self) -> float:
"""
Center frequency in :attr:`unit`'s.
Returns
-------
center : number
the exact center frequency in units of :attr:`unit`'s
"""
return self.start_scaled + (self.stop_scaled-self.start_scaled)/2.
@property
def step(self) -> float:
"""
The inter-frequency step size (in Hz) for evenly-spaced
frequency sweeps
See Also
--------
df : for general case
"""
return self.span/(self.npoints-1.)
@property
def step_scaled(self) -> float:
"""
The inter-frequency step size (in :attr:`unit`) for evenly-spaced
frequency sweeps.
See Also
--------
df : for general case
"""
return self.span_scaled/(self.npoints-1.)
@property
def span(self) -> float:
"""
The frequency span.
"""
return abs(self.stop-self.start)
@property
def span_scaled(self) -> float:
"""
The frequency span.
"""
return abs(self.stop_scaled-self.start_scaled)
@property
def f(self) -> npy.ndarray:
"""
Frequency vector in Hz.
Returns
----------
f : :class:`numpy.ndarray`
The frequency vector in Hz
See Also
----------
f_scaled : frequency vector in units of :attr:`unit`
w : angular frequency vector in rad/s
"""
return self._f
@f.setter
def f(self,new_f: NumberLike) -> None:
"""
Sets the frequency object by passing a vector in Hz.
Raises
------
InvalidFrequencyWarning:
If frequency points are not monotonously increasing
"""
warnings.warn('Possibility to set the f parameter will removed in the next release.',
DeprecationWarning, stacklevel=2)
self._f = npy.array(new_f)
self.check_monotonic_increasing()
@property
def f_scaled(self) -> npy.ndarray:
"""
Frequency vector in units of :attr:`unit`.
Returns
-------
f_scaled : numpy.ndarray
A frequency vector in units of :attr:`unit`
See Also
--------
f : frequency vector in Hz
w : frequency vector in rad/s
"""
return self.f/self.multiplier
@property
def w(self) -> npy.ndarray:
r"""
Angular frequency in radians/s.
Angular frequency is defined as :math:`\omega=2\pi f` [#]_
Returns
-------
w : :class:`numpy.ndarray`
Angular frequency in rad/s
References
----------
.. [#] https://en.wikipedia.org/wiki/Angular_frequency
See Also
--------
f_scaled : frequency vector in units of :attr:`unit`
f : frequency vector in Hz
"""
return 2*pi*self.f
@property
def df(self) -> npy.ndarray:
"""
The gradient of the frequency vector.
Note
----
The gradient is calculated using::
`gradient(self.f)`
"""
return gradient(self.f)
@property
def df_scaled(self) -> npy.ndarray:
"""
The gradient of the frequency vector (in unit of :attr:`unit`).
Note
----
The gradient is calculated using::
`gradient(self.f_scaled)`
"""
return gradient(self.f_scaled)
@property
def dw(self) -> npy.ndarray:
"""
The gradient of the frequency vector (in radians).
Note
----
The gradient is calculated using::
`gradient(self.w)`
"""
return gradient(self.w)
@property
def unit(self) -> str:
"""
Unit of this frequency band.
Possible strings for this attribute are:
'hz', 'khz', 'mhz', 'ghz', 'thz'
Setting this attribute is not case sensitive.
Returns
-------
unit : string
lower-case string representing the frequency units
"""
return self.unit_dict[self._unit]
@unit.setter
def unit(self, unit: str) -> None:
self._unit = unit.lower()
@property
def multiplier(self) -> float:
"""
Multiplier for formatting axis.
This accesses the internal dictionary `multiplier_dict` using
the value of :attr:`unit`
Returns
-------
multiplier : number
multiplier for this Frequencies unit
"""
return self.multiplier_dict[self._unit]
[docs] def copy(self) -> 'Frequency':
"""
Returns a new copy of this frequency.
"""
freq = Frequency.from_f(self.f, unit='hz')
freq.unit = self.unit
return freq
@property
def t(self) -> npy.ndarray:
"""
Time vector in s.
t_period = 1/f_step
"""
return linspace(-.5/self.step , .5/self.step, self.npoints)
@property
def t_ns(self) -> npy.ndarray:
"""
Time vector in ns.
t_period = 1/f_step
"""
return self.t*1e9
[docs] def round_to(self, val: Union[str, Number] = 'hz') -> None:
"""
Round off frequency values to a specified precision.
This is useful for dealing with finite precision limitations of
VNA's and/or other software
Parameters
----------
val : string or number
if val is a string it should be a frequency :attr:`unit`
(ie 'hz', 'mhz',etc). if its a number, then this returns
f = f-f%val
Examples
--------
>>> f = skrf.Frequency.from_f([.1,1.2,3.5],unit='hz')
>>> f.round_to('hz')
"""
if isinstance(val, str):
val = self.multiplier_dict[val.lower()]
self.f = npy.round_(self.f/val)*val
[docs] def overlap(self,f2: 'Frequency') -> 'Frequency':
"""
Calculates overlapping frequency between self and f2.
See Also
--------
overlap_freq
"""
return overlap_freq(self, f2)
@property
def sweep_type(self) -> str:
"""
Frequency sweep type.
Returns
-------
sweep_type: str
'lin' if linearly increasing, 'log' or 'unknown'.
"""
if npy.allclose(self.f, linspace(self.f[0], self.f[-1], self.npoints)):
sweep_type = 'lin'
elif self.f[0] and npy.allclose(self.f, geomspace(self.f[0], self.f[-1], self.npoints)):
sweep_type = 'log'
else:
sweep_type = 'unknown'
return sweep_type
[docs]def overlap_freq(f1: 'Frequency',f2: 'Frequency') -> Frequency:
"""
Calculates overlapping frequency between f1 and f2.
Or, put more accurately, this returns a Frequency that is the part
of f1 that is overlapped by f2. The resultant start frequency is
the smallest f1.f that is greater than f2.f.start, and the stop
frequency is the largest f1.f that is smaller than f2.f.stop.
This way the new frequency overlays onto f1.
Parameters
----------
f1 : :class:`Frequency`
a frequency object
f2 : :class:`Frequency`
a frequency object
Returns
-------
f3 : :class:`Frequency`
part of f1 that is overlapped by f2
"""
if f1.start > f2.stop:
raise ValueError('Out of bounds. f1.start > f2.stop')
elif f2.start > f1.stop:
raise ValueError('Out of bounds. f2.start > f1.stop')
start = max(f1.start, f2.start)
stop = min(f1.stop, f2.stop)
f = f1.f[(f1.f>=start) & (f1.f<=stop)]
freq = Frequency.from_f(f, unit = 'hz')
freq.unit = f1.unit
return freq