AESs are composed of periodic arrangements of metallic scatterers and permit the enhanced manipulation and control sophisticated manipulation of electromagnetic waves. AESs traditionally encompass frequency selective surfaces (FSSs), reflectarrays, transmitarrays, and impedance surfaces. Traditionally, our lab has exploited AESs for realizing high-gain antenna apertures suitable for applications such as satellite communications, RADAR, and microwave imaging. Our present research seeks to devise ways for improving the capacity of satellite and terrestrial systems using AESs not only in radiating apertuers, but also as building materials in terrestrial environments.
AES such as reflectarrays (reflection mode) and transmitarrays (transmission mode) provide a low-cost, high-performance platform for realizing electronic beam-steering. They allow a fundamental operation, phase shifting, to be encapsulated within elementary scatterers composing the aperture, allow active components such as semiconductors or MEMS to directly manipulate the electrical characteristics of the scatterer. Meanwhile, feed losses traditionally associated with transmission line feeds (as is the case with phased arrays) are mitigated through the use of a spatial feed. The result is an electronically deformable reflector or lens that can operate well into the mm-wave frequency range. Our lab is presently investigating new architectures that will allow lower device technologies to circumvent losses usually associated with using such devices.
Planar space-fed apertures such as reflectarrays have traditionally suffered from poor bandwidth owing to the use of resonant scatterers to achieve the required phase-shift from the constituent elements. Using advanced concepts from transformation optics and impedance surfaces, our research is breaking these limits by realizing printed planar reflectors that realize in excess of 70% fractional bandwidth using very low-profile structures. In particular, "metasurfaces" formed from impedance surfaces mimicking Bessel filters promise to achieve very high bandwidths using very thin reflectors that are suitable for space and RADAR applications.
Reflectarrays and transmitarrays, while planar in nature, still do not represent a low-profile solution for beamforming since they require an external feeding antenna placed a distance in front of / behind the aperture. We are devising techniques to integrate the feed within the aperture itself, making the aperture fully low-profile while maintaining all the performance and cost advantages of space-fed arrays. This is being accomplished to devising leaky-wave feeds for space-fed arrays.
The increasing number of frequency bands and antennas that a handheld device must support necessitates the need for novel antenna design techniques. Furthermore, multi-port antenna architectures that are well-isolated in the same frequency band and across frequency bands, not only allow support of multiple technologies such as MIMO and carrier aggregation (CA) but also ease the design of the RF front-end. Our lab implements an approach using Characteristic Modes to enable the design of multi-port, multiband, reconfigurable antennas for LTE-A that fit within the confines of typical smartphone packages.
Making antennas optically transparent enables novel applications such as printing antennas and AESs on windows, laptops, and glass. One particularly important application is devising optically transparent reflector antennas, such as reflectarrays, which can be overlaid with solar cells aboard a spacecraft. Such as system will allow the large area devoted to solar power collection to be used "double-duty" as a large high-gain antenna aperture. This is especially useful in application where there is limited space for high-gain antennas, such as micro- and nano-satellites, or even deep-space probes operating at opportunistic locations such as the L2 Lagrangian point.
Satellite platforms, particularly micro- and nano-satellites, have very limited space available for antennas. However, high-gain (large effective aperture) antenas are crucial to improving downlink capacity in future generations of satellites. Our research is exploring novel ways of realizing high-gain, "unfoldable" antennas that can be integrated with spacecraft to reduce launch volume and mass while realizing high-gain antenna beam patterns. We work closely with the UTIAS Space Flight Laboratory and have several antenna concepts launching on NEMO-HD and NORSAT-2 in 2017.