jens
a7ec99e218
git-svn-id: http://moon:8086/svn/matlab/trunk@102 801c6759-fa7c-4059-a304-17956f83a07c
99 lines
4.1 KiB
Matlab
99 lines
4.1 KiB
Matlab
## Copyright (C) 2018 Jens Ahrensfeld
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##
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## This program is free software; you can redistribute it and/or modify it
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## under the terms of the GNU General Public License as published by
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## the Free Software Foundation; either version 3 of the License, or
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## (at your option) any later version.
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##
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## This program is distributed in the hope that it will be useful,
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## but WITHOUT ANY WARRANTY; without even the implied warranty of
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## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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## GNU General Public License for more details.
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##
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## You should have received a copy of the GNU General Public License
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## along with this program. If not, see <http://www.gnu.org/licenses/>.
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## -*- texinfo -*-
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## @deftypefn {Function File} {@var{retval} =} tunable_bandpass (@var{input1}, @var{input2})
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##
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## @seealso{}
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## @end deftypefn
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## Author: Jens Ahrensfeld <ahrensfeld@w2ess001vm>
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## Created: 2018-11-26
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## taken from: https://www.mwrf.com/components/bandpass-filters-feature-wide-tuning-ranges
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function tuneable_bandpass(varargin)
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params = struct ('f_low_Hz', 40e6, 'f_high_Hz', 800e6, 'f_step_Hz', 1e6, 'B_geo_Hz', 10e6, 'R_geo', 500, 'R_0', 50, 'k_gamma', 1.0);
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units = struct ('f_low_Hz', 'Hz', 'f_high_Hz', 'Hz', 'f_step_Hz', 'Hz', 'B_geo_Hz', 'Hz', 'R_geo', 'O', 'R_0', 'O', 'k_gamma', '');
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% Parse parameters
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names = fieldnames(params);
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for k=1:nargin-1,
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for n=1:length(names),
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if strcmpi(varargin{k}, names{n})
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params.(names{n}) = varargin{k+1};
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end
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end
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end
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print_parameters(params, units)
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f_low_Hz = params.f_low_Hz; % Minimum tunable filter center frequency (Hz)
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f_high_Hz = params.f_high_Hz; % Maximum tunable filter center frequency (Hz)
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B_geo_Hz = params.B_geo_Hz; % -3 dB RF filter bandwidth (in Hz) at the geometric center frequency
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R_geo = params.R_geo; % Internal filter impedance (in O) at the geometric center frequency of the filter
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R_0 = params.R_0; % Port impedance, usually taken as 50 O
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k_gamma = params.k_gamma; % Constant value. A value of ? = 1.0 results in a constant-Q filter design,
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% while a value of ? = 2.0 results in a constant-bandwidth filter design.
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% A value between one and two will yield a blend of the two filter characteristics.
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% Inductor Q values will be more critical as the value of ? is increased.
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f_step_Hz = params.f_step_Hz;
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f_Hz = f_low_Hz:f_step_Hz:f_high_Hz;
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omega = 2*pi*f_Hz;
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f_geo_Hz = sqrt(f_low_Hz*f_high_Hz) % Hz
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omega_geo = 2*pi*f_geo_Hz % rad/sec
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% Design I.
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R_t = R_geo*(omega/omega_geo).^k_gamma; % Equ. (1)
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L_c = R_geo/omega_geo % Equ. (2)
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C_tgeo = 1./(pi*sqrt(2)*R_geo*B_geo_Hz) % Equ. (3)
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L_eff = 1./(omega_geo^2*C_tgeo) % Equ. (4)
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L_r = L_eff * L_c / (L_c - L_eff) % Equ. (5)
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C_t = (omega_geo./omega).^2 * C_tgeo; % Equ. (6)
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% Tuning capacitances C1 and C2 are given by Eqs. 7 and 8
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C_1 = (omega*R_0).^(-1) .* sqrt((omega_geo./omega).^k_gamma * (R_0/R_geo) + omega.^2.*C_t.^2*R_0*R_geo.*(omega/omega_geo).^k_gamma - 1); % Equ. (7)
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C_2 = ((omega.^2.*C_t)./((omega_geo./omega).^(2*k_gamma) .* (1/R_geo)^2 + (omega.*C_t).^2) - (omega.^2*R_0^2.*C_1)./(1+(omega*R_0.*C_1).^2)).^(-1); % Equ. (8)
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C_1_geo = (omega_geo*R_0).^(-1) .* sqrt((omega_geo./omega_geo).^k_gamma * (R_0/R_geo) + omega_geo.^2.*C_tgeo.^2*R_0*R_geo.*(omega_geo/omega_geo).^k_gamma - 1) % Equ. (7)
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C_2_geo = ((omega_geo.^2.*C_tgeo)./((omega_geo./omega_geo).^(2*k_gamma) .* (1/R_geo)^2 + (omega_geo.*C_tgeo).^2) - (omega_geo.^2*R_0^2.*C_1_geo)./(1+(omega_geo*R_0.*C_1_geo).^2)).^(-1) % Equ. (8)
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subplot (2,1,1)
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plot(f_Hz*1e-6, C_1*1e12); grid; xlabel("f/MHz"), ylabel("C_1 [pF]");
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subplot (2,1,2)
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plot(f_Hz*1e-6, C_2*1e12); grid; xlabel("f/MHz"), ylabel("C_2 [pF]");
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% Design II.
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L_c = R_geo/omega_geo; % Equ. (9)
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L_eff = R_geo./(pi*sqrt(2)*B_geo_Hz); % Equ. (10)
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L_r = L_eff - L_c; % Equ. (11)
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C_tgeo = 1./(L_eff*omega_geo^2); % Equ. (12)
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C_t = (omega_geo./omega).^2 * C_tgeo; % Equ. (13)
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a = -omega.^2*R_0.*R_t; % Equ. (14)
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b = 1./C_t; % ...
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d = R_t/R_0; % Equ. (14)
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alpha = (d-b.^2/a)./(1+b.^2/a - d); % Equ. (15)
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beta = (b./a)./(1 + b.^2/a - d); % Equ. (16)
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C_2 = alpha.*C_1 + beta; % Equ. (17)
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endfunction
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