The hybrid configurations, H75, H168 and H214 combine antennas on both the east-west track and north track with maximum (north-south) baselines of 75m, 168m and 214m respectively. These configurations provide compact arrays with high brightness sensitivity imaging and maximum uv coverage in about six hours observing time, as well as north-south resolution for equatorial sources. The shorter time required for a full synthesis is especially useful for millimetre observations as sources can be observed whilst they are at higher elevations giving significantly lower system temperatures at 3 and 12mm as well as less atmospheric phase fluctuations
See here for a list of standard array configurations and information on effective combinations.
The Virtual Radio Interferometer is very useful to simulate the final images from observations using one or multiple array configurations.
Proposals requiring two or more configurations will usually be given observing time at widely separated times. In this case, you should expect to make either one long visit or two or more visits. There are two observing terms per year, and not all configurations are offered each term. If you are not allocated all the configurations requested, you should re-apply next term, as the proposal will not automatically be reconsidered. Your proposal should specify the maximum extent of your sources, the maximum and minimum baselines required and the number of configurations required. Note that any standard or non-standard configuration can be requested in any term. A request for a non-standard configuration needs to be accompanied by a convincing scientific justification explaining why the standard configurations are unsuitable. The antenna station locations are listed. If you observe your source at two frequencies, you may want the resulting beams to be the same angular size. To achieve this, you need to use a scaled or zoom array. The ATCA stations are not positioned in such a way that exact scaled arrays are possible, but you can combine observations made with configurations of different lengths to achieve a pseudo-zoom array.
The miriad task mfplan is useful for planning observations where this is important. However, do not forget that there may be other factors (like interference) driving decisions about best frequencies for your observations.