% EXAMPLE INTERFEROMETER (exinter)
% In this example 2 x 4m diameter dishes are positioned
% 10m apart to form an interferometer. An arrangement frequently
% used in radio-astronomy applications.
% Notice how the fringing pattern in the phi=0 cut, follows
% the envelope of the phi=90 pattern.
% If the antenna is swept past a celestial radio-source in the phi=0
% plane. There are two main possibilities for the received signal :
% 1) If the radio-source is dimensionally small and subtends an angle
% approximately the same or smaller than the width of a single fringe
% lobe. Then the received signal will appear as a replication of the
% fringing pattern.
% 2) If the radio-source is dimensionally large and subtends an angle
% covering many fringe lobes. Then the received signal will appear
% as an integration of the fringing pattern and more like the phi=90
% By making measurements of the same radio-source with different dish
% spacings, the point at which 'pattern integration' begins can give
% the astronomer a good indication as to the size of the radio source.
% In this way dimensionally small radio-sources can be resolved without
% the need for a huge dish (of diameter equal to the separation of the
% smaller dishes).
% There is of course a downside to this approach, which is that it does
% not provide the same directive gain as a single large dish and is
% therefore less able to detect weak radio-sources.
% Note : When using large apertures the default range_config value of 999m
% may not be large enough to meet the (2*D^2)/Lambda far-field criteria.
% I have found that the maximum value for range_config is around 2e6 (m).
% This corresponds to an aperture of 1000 Lambda and hence the maximum
% antenna aperture that can be analysed.
% Beyond 2e6(m) and the internal trig calculations begin to break down.
init; % Initialise global variables
Dia=4; % Dish diameter (m)
Sep=10; % Dish separation (m) Max is about 200(m) at 1420 MHz
freq_config=1420e6; % Specify frequency (Hz) Hydrogen Line reception
lambda=3e8/freq_config; % Calculate wavelength (m)
dish_config=[Dia,2.5,10]; % Set up dish parameters, (Dia)m dish with 10dB edge taper
range_config=2e6; % Set summing distance commensurate with larger apertures
% The upper limit for range_config is around 2e6 corresponding
% to an aperture of around 1000 lambda, using (2*D^2)/Lambda.