Romulo J. Broas

High-impedance electromagnetic surfaces with a forbidden frequency band

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

A high-impedance ground plane applied to a cellphone handset geometry

A high-impedance electromagnetic surface is a new type of metallic structure exhibiting high surface impedance and the suppression of propagating surface currents at a particular frequency band. We experimentally characterize such a high-impedance surface designed near 2.4 GHz. We describe an antenna built on such a surface, integrated into a printed circuit board that was designed for the form factor of a portable handset. Measurement shows high radiation efficiency near 2.4 GHz.

Reconfigurable aperture antennas using RF MEMS switches for multi-octave tunability and beam steering

The requirements for increased functionality within a confined volume will place greater burdens on electromagnetic platforms for air, space, and sea over the next few decades. An important piece of the any solution to these new requirements are transmitting and receiving apertures that can handle multi-octave bandwidths with beam steering capability. The ability of an aperture to be reconfigured for a particular mission will become essential. New types of devices are being developed which will enable the realization of these reconfigurable apertures. This paper presents a discussion of how one of these new devices, the RF MEMS switch, can be utilized to change the phase and frequency characteristics of conventional antenna elements to perform beam steering over a wide range of microwave frequencies.

Antennas on high-impedance ground planes

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Unlike normal conductors, this new surface does not support propagating surface currents, and it reflects electromagnetic waves with no phase reversal. This unique material can serve as the ground plane for new kinds of low-profile antennas.

An application of high-impedance ground planes to phased array antennas

The high-impedance surface was used as the antenna ground plane between two radiator elements to reduce the inter-element coupling between them. Measurement reveals the optimum performance occurred at the bandgap due to the suppression of surface currents in the ground plane.

Comments on "High-impedance electromagnetic surfaces with a forbidden frequency band" [with reply]

For the original paper see ibid., vol. 47, no. 11, p. 2059-2074 (1999). In the aforementioned paper the authors used a jar of water as a substitute for a humans head and then made a statement that the dielectric constant of water is similar to most human tissues. The commenter disagrees with this statement. In reply the authors also disagree with the comments, pointing out that while a jug of water and a human head may differ significantly in function, they differ little in form from the perspective of an electromagnetic field, and the substitution of one for the other offers simple insight into antenna performance near a high-dielectric lossy mass. They concede that the dielectric constant of water is roughly 1.5 times that of average human tissue. However, they believe that this neither invalidates their observation that antenna performance is significantly affected by the presence of a watery mass, nor their statement that one may expect similar degradation of performance near a human head.

High-impedance electromagnetic surfaces with forbidden bands at radio and microwave frequencies

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped circuit elements, and distributed in a 2D lattice. Although it is made of continuous metal, and conducts DC currents, it does not conduct AC currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves. Furthermore, image currents induced in the surface are not phase reversed as they are on a flat metal surface.