You can easily use C-band on a Ku dish of the same size. But generally not the other way around. In practice Ku Band does work on C-band dishes, but the mesh dish is not as efficent in reflecting Ku band signals as it is C band.<br />Think of it like the difference between using a mirror or just shiney metal to reflect light.<br />The mirror is just a better reflector.<br /><br />The next consideration is surface accuracy.<br />The wavelength is longer at C band so it is a little more tollerant of imperfections.<br />A dish may have kinks, dints and warps in it, these will effect Ku band gain more than C band.<br />Radiation is being scattered instead of being reflected where you want it to go.<br /><br /> If you think of it in terms of mirrors and light.<br />If a mirror is perfectly flat, the picture reflected is nice and clear. But if the mirror is warped, then your head may look bigger than your body.<br /><br />In simple terms you can use a solid dish for Ku and C band, but a mesh dish for C band (or lower)only.