Images from a Single Dish Radio Telescope

Since single-dish radio telescopes are small in size (measured in wavelengths), they produce images of resolution given by $\sim \lambda/D$ (See section 1.2.1).

In order to 'resolve' images (i.e make sharp images), the diameter of the telescope or the dish must be many times greater than the operating wavelength. Light waves have wavelengths of $\sim$400$-$700 nanometers and if the collecting mirrors are larger than even ten cms, they can resolve the details of the objects with a resolution of one arc-second. However, radio waves have wavelengths of 0.1m $-$ 10m and hence, even the largest radio telescopes produces with a resolution of tens of arc-minutes. Therefore, a single radio dish would have to be hundreds of kilometers across, in order to achieve a high resolution image at radio wavelengths which is comparable even to a small optical telescope. Building such a telescope is not a practical matter.