For some experiments, multi-band performance is highly desirable. For example, transient phenomena on the Sun and stars would benefit greatly from simultaneous measurements in two or more bands. One possibility is to support dual-frequency measurements in the 2.4 and 8.4 GHz bands and/or dual-frequency measurements in the 4.9 and 15 GHz bands. An additional benefit of dual-frequency observing is that one of the two bands in a given pair could be corrected for the long-standing problem of beam squint, caused by the VLA asymmetric geometry, through the use of a tertiary mirror.
A practical benefit of dual-frequency observing is that the lower frequency of a given pair can be used to track the phase variation of the atmosphere, from which corrections can be derived and transferred to the high frequency. Implementation of such a scheme will be considered for enhanced high-frequency performance at the VLA.
In the case of solar observing, an alternative to multi-band performance is ``frequency-agile'' performance using a low-performance (helical or log-periodic) feed at the prime focus.