Sparse aperture imaging systems are capable of producing high resolution images while maintaining an overall light
collection area that is small with respect to a fully filled aperture yielding the same resolution. However, conventional
sparse aperture systems pay the penalty of reduced contrast at
mid-band spatial frequencies.
The modulation transfer function (MTF), or normalized autocorrelation, provides a quantative measure of both the
resolution and contrast of an optical imaging system. Numerical MTF calculations were thus used to examine mid-band
contrast recovery through the systematic increase of autocorrelation redundancy in a Golay-9 sparse array.
In a Golay-9 sparse aperture arrangement, three sets of three
sub-apertures can be shown to lie at unique radii from the
center of the array. In order to increase the mid-frequency contrast we then have two options. The first, and most
influential, is to increase the size of the sub-apertures located at the intermediate radius from the array origin. This
directly increases autocorrelation redundancy at mid-band frequencies. The second option, though less effective, is to
increase the relative mid-band frequency response by attenuating the outer most sub-apertures.
We will demonstrate that by increasing the diameters of the mid-radii sub-apertures, mid-band contrast can be increased
by over 45%, compared to uniform sub-aperture diameter arrays. We will also demonstrate that attenuating the outer
most sub-apertures can further increase mid-band contrast recovery, but only by less than 1%. The effects on array fill
factor will also be discussed.