High-impedance electromagnetic surface (HIS) is a new kind of artificial metallic electromagnetic structure. By not supporting propagating surface currents in the manner of conventional metallic conductors, HIS technology offers advantages to many microwave circuit and antenna applications. Chao Wang, Dun-bao Yan, and Nai-chang Yuan of China's National University of Defense Technology use an HIS structure as the antenna groundplane to suppress the propagation of surface waves. In doing so, they improve the performance of an Archimedean planner spiral antenna.
Normally, this wideband, widebeam, circularly polarized antenna uses a flat metal sheet as the groundplane or reflector. When strong surface waves propagate on the finite metal groundplane until they reach the edge and radiate into free space, however, they cause a kind of multipath interference. When HIS is used as the groundplane, though, it can suppress surface waves. In addition, an antenna with an HIS groundplane can produce a more tightly controlled radiation pattern than a similar antenna with a finite metal groundplane. The mutual coupling between multiple antennas also is reduced.
When antennas using HIS technology were compared with those based on a conventional metal groundplane, the radiation pattern was smoother, the gain of the main lobe increased by 0.5 to 1 dB, and the back radiation decreased by 10 to 15 dB. The mutual coupling between the two antennas decreased by roughly 5 to 15 dB. See "Application of High Impedance Electromagnetic Surface to Archimedean Planner Spiral Antenna," Microwave and Optical Technology Letters, January 2007, p. 129.