Applied Antennas and Materials
Leo Kempel | kempel@egr.msu.edu | https://www.egr.msu.edu/emrg/
Leaky-wave Antennas
Leaky-wave antennas offer a potentially wide bandwidth (in terms of both VSWR and pattern) near end-fire aperture with high gain. This is in contrast to conventional resonant antennas (such as microstrip patches, wires, and dielectric resonantors) that by their nature are useful over a narrow instantaneous bandwidth and radiate most effectively in the broadside direction. Resonant antennas can be used for near end-fire applications if complex and expensive phase shifters are used; however, even so, phased array antennas suffer from scan blindness under certain circumstances. Near end-fire apertures with nearly 1 GHz bandwidth in C-band have been designed, simulated, and constructed.
Michigan State University in partnership with the Air Force Research Laboratory and the University of Dayton have developed a number of innovations in leaky-wave antenna design built upon the so-called “half-width leaky-wave antenna”. This aperture offers advantages over conventional leaky-wave antennas primarily in construction and feeding networks.
Recent innovations include the use of tunable reactive loads on the open edge of the antenna. This permits tuning of the antenna performance as a function of frequency. The result is unprecedented ability to control the spectral behavior of the antenna to meet design requirements. Traditional leaky-wave antennas steer the beam as a function of frequency. Such antennas have limited applications. As shown in the figure to the left, this antenna maintains a consistent main-beam direction across the operational bandwidth.
Magneto-dielectric Material Design
Traditional non-conductive materials for use in VHF-K-band and beyond are usually non-magnetic. Such dielectric materials have a variety of uses and have been the subject of concerted design effort for over five decades. Design and synthesis of magneto-dielectric materials (e.g. having a non-trivial relative permeability as well as non-trivial relative permittivity) have undergone a renaissance as of late due to the introduction of advanced material synthesis methods and the more prolific talent in nanocomposite material design. The goal of this research is relatively low loss materials for use UHF-L-bands having a permeability that is modest (e.g. 2-10 relative units) with comparable relative permittivity. Such materials open the design space for microwave devices such as antennas, radomes, and transmission lines.
The materials have a polymer matrix with metallic and metal oxide inclusions. These inclusions are usually spheroidal, linear (e.g. rods) or platelets. Such inclusions couple individual inclusion impact to realize the desired macroscopic effect. Partners at sister-institutions synthesize the materials developed under this project. Michigan State University provides recommendations on the design (e.g. target permittivity, permeability, loss factors, etc.), characterizes the synthesized coupons, and provides potential application designs (e.g. antennas). Over the past decade, the upper limit of low-loss materials from this program has advanced from VHF (30-300 MHz) to UHF (300-1000 MHz). New materials that have the potential for use in L- and S-bands have begun to emerge. These materials offer the potential for smaller apertures with wider bandwidth than is typically available. Current research is focused on the most challenging design aspects of resonant structures (e.g. designs that require lower loss factors).
