Comments on 'Synthesis of offset dual shaped subreflector antennas for control of Cassegrain aperture distributions'

In the paper by V. Galindo-Israel and R. Mittra it is claimed that a dual shaped subreflector (DSS) feed can be used to upgrade the efficiency of classical Cassegrain antennas. In this comment it is shown that upgrading is not possible unless the diameter of the DSS feed is extremely large. In fact, if the Cassegrain antenna at Goldstone, CA, used as an example in the above paper, is fed by the DSS feed, the efficiency in X-band will be about the same as or less than if it is fed directly by an optimized scalar horn. The low efficiency is caused by diffraction. Instead, the efficiency can be upgraded by using a scalar horn with shaped lens.