Dichroic dual-band microstrip array

It is demonstrated that two microstrip arrays can be superimposed in a common planar aperture to create a dual-band array. The concept relies critically on the invisibility of the uppermost array, which is constructed from a frequency-selective conducting surface (FSCS). Analysis and measurements establish the degree of invisibility obtainable in an FSCS of finite extent and indicate the likely behaviour in a composite system. Measurements for a dual-band array illustrate the findings and good future prospects for the concept, but also show that feeder line radiation, if not reduced, can constrain sidelobe levels.