genfreqaxis.m

雷达信号处理、或阵列信号处理中能够用上的重要的matlab工具箱——阵列信号处理工具箱

function [freqAxis, freqLow, freqHigh] = genfreqaxis(carrierFreq, bandwidth, noFreq)

%GENFREQAXIS Generates values for a frequency axis.
%
%--------
%Synopsis:
%  freqAxis = genfreqaxis(carrierFreq, bandwidth, noFreq)
%  freqAxis = genfreqaxis(carrierFreq, {freqLowOffset, freqHighOffset},noFreq)
%
%  [freqAxis, freqLow, freqHigh] = genfreqaxis(carrierFreq, bandwidth, noFreq)
%  [freqAxis, freqLow, freqHigh] = genfreqaxis(carrierFreq,
%    {freqLowOffset, freqHighOffset},  noFreq)
%
%Description:
%  Generates a vector with values for a frequency axis which can be used
%  for example to when plotting a frequency spectrum created by "fft".
%
%Output and Input:
%  freqAxis (RealVectorT): The generated vector with frequency values [Hz].
%  freqLow (RealScalarT): The lowest frequency in the bandwidth [Hz].
%  freqHigh (RealScalarT): The highest frequency in the bandwidth [Hz]. 
%    Note that this is not equal to the highest value in the vector
%    "freqAxis".
%  carrierFreq (RealScalarT): Carrier frequency [Hz]. This can be specified to
%    zero for baseband signals.
%  bandwidth (RealScalarT): Bandwidth [Hz].
%  freqLowOffset (RealScalarT): Relative low frequency limit [Hz].
%  freqHighOffset (RealScalarT): Relative high frequency limit [Hz].
%  noFreq (IntScalarT): Number of frequency values to generate.
%
%--------
%Notations:
%  Data type names are shown in parentheses and they start with a capital
%  letter and end with a capital T. Data type definitions can be found in [1]
%  or by "help dbtdata".
%  [D] = This parameter can be omitted and then a default value is used.
%  When the [D]-input parameter is not the last used in the call, it must be
%  given the value [], i.e. an empty matrix.
%  ... = There can be more parameters. They are explained under respective
%  metod or choice.
%
%Examples:
%  noSamples = 64;
%  endTime = 10;
%  sampleTime = endTime /(noSamples-1)
%  samplefreq = 1/sampleTime
%  bandwith = samplefreq/2;		% A real valued time signal.
%  t = linspace(0,endTime,noSamples);
%  s = sin(2*pi*t);
%  plot(s), figure
%  plot(genfreqaxis(0,samplefreq,noSamples).',abs(fftshift(fft(s))))
%  plotxline([-samplefreq/2, samplefreq/2],'m','--')
%
%Software Quality:
%  (About what is done to ascertain software quality. What tests are done.)
%
%Known Bugs:
%
%References:
%  [1]: Bj鰎klund S.: "DBT, A MATLAB Toolbox for Radar Signal Processing.
%    Reference Guide", FOA-D--9x-00xxx-408--SE, To be published.
%
%See Also:


%   *  DBT, A Matlab Toolbox for Radar Signal Processing  *
% (c) FOA 1994-2000. See the file dbtright.m for copyright notice.
%
%  Start        : 990208 Svante Bj鰎klund (svabj).
%  Latest change: $Date: 2000/10/16 15:40:15 $ $Author: svabj $.
%  $Revision: 1.6 $
% *****************************************************************************

chkdtype(carrierFreq, 'RealScalarT')
chkdtype(bandwidth, 'RealScalarT', 'CellArrayT')
chkdtype(noFreq, 'IntScalarT')

if (iscell(bandwidth))
  freqLow = carrierFreq + bandwidth{1};
  freqHigh = carrierFreq + bandwidth{2};
else
  freqLow = carrierFreq - bandwidth/2;
  freqHigh = carrierFreq + bandwidth/2;
end%if

freqAxis = linspace(freqLow, freqHigh, noFreq+1);
freqAxis = freqAxis(1:noFreq).';

%freqAxis.', freqLow, freqHigh		% For debugging.