scipy.signal.windows.chebwin¶

scipy.signal.windows.
chebwin
(M, at, sym=True)[source]¶ Return a DolphChebyshev window.
Parameters:  M : int
Number of points in the output window. If zero or less, an empty array is returned.
 at : float
Attenuation (in dB).
 sym : bool, optional
When True (default), generates a symmetric window, for use in filter design. When False, generates a periodic window, for use in spectral analysis.
Returns:  w : ndarray
The window, with the maximum value always normalized to 1
Notes
This window optimizes for the narrowest main lobe width for a given order M and sidelobe equiripple attenuation at, using Chebyshev polynomials. It was originally developed by Dolph to optimize the directionality of radio antenna arrays.
Unlike most windows, the DolphChebyshev is defined in terms of its frequency response:
\[W(k) = \frac {\cos\{M \cos^{1}[\beta \cos(\frac{\pi k}{M})]\}} {\cosh[M \cosh^{1}(\beta)]}\]where
\[\beta = \cosh \left [\frac{1}{M} \cosh^{1}(10^\frac{A}{20}) \right ]\]and 0 <= abs(k) <= M1. A is the attenuation in decibels (at).
The time domain window is then generated using the IFFT, so poweroftwo M are the fastest to generate, and prime number M are the slowest.
The equiripple condition in the frequency domain creates impulses in the time domain, which appear at the ends of the window.
References
[1] C. Dolph, “A current distribution for broadside arrays which optimizes the relationship between beam width and sidelobe level”, Proceedings of the IEEE, Vol. 34, Issue 6 [2] Peter Lynch, “The DolphChebyshev Window: A Simple Optimal Filter”, American Meteorological Society (April 1997) http://mathsci.ucd.ie/~plynch/Publications/Dolph.pdf [3] F. J. Harris, “On the use of windows for harmonic analysis with the discrete Fourier transforms”, Proceedings of the IEEE, Vol. 66, No. 1, January 1978 Examples
Plot the window and its frequency response:
>>> from scipy import signal >>> from scipy.fftpack import fft, fftshift >>> import matplotlib.pyplot as plt
>>> window = signal.chebwin(51, at=100) >>> plt.plot(window) >>> plt.title("DolphChebyshev window (100 dB)") >>> plt.ylabel("Amplitude") >>> plt.xlabel("Sample")
>>> plt.figure() >>> A = fft(window, 2048) / (len(window)/2.0) >>> freq = np.linspace(0.5, 0.5, len(A)) >>> response = 20 * np.log10(np.abs(fftshift(A / abs(A).max()))) >>> plt.plot(freq, response) >>> plt.axis([0.5, 0.5, 120, 0]) >>> plt.title("Frequency response of the DolphChebyshev window (100 dB)") >>> plt.ylabel("Normalized magnitude [dB]") >>> plt.xlabel("Normalized frequency [cycles per sample]")