Abstract-In this paper a dual band circularly polarized antenna is designed, fabricated, and measured. Based on the concept of composite right and left handed (CRLH) metamaterials, the same phase constants and current distributions on the ring antenna are achieved at two frequency bands. Thus, the antenna has similar radiation patterns at both bands. The circular polarization is implemented by feeding two vertical ports from power dividers that provide equal magnitudes and quadrature phase excitations.

A bandwidth improvement method in reflectarray antennas by using closely space elements, i.e., unit-cell sizes smaller than λ/2, has been investigated both numerically and experimentally in this paper. A new definition of phase error has been introduced to analyze the broadband mechanism of closely spaced phasing elements. Through full wave EM simulations, it is revealed that closely spaced elements achieve a smaller phase error over the band. Based on these theoretical studies two Ka-band reflectarrays were fabricated and their performance was measured across the frequency range of 30 to 34 GHz. It is demonstrated that the reflectarray designed with closely spaced elements achieves a notable improvement in gain bandwidth performance.

Abstract-Compact spiral artificial magnetic conductors (AMC) have been investigated in this paper. First, single and double spirals are examined to achieve an in-phase reflection at a lower frequency compared to a conventional patch element of the same size. However, these two designs generate a large cross polarization. The cross polarization affects the operating frequency and bandwidth. In order to eliminate the cross polarization effect, a four-arm spiral element is introduced. This geometry does not generate a cross polarization, and an operating frequency that is 49.45% lower than the reference patch element has been achieved.