Tatsuo Itoh Member of National Academy of Engineering
UCLA
Title: Recent Advances and Promise of Metasurface for Microwave Applications
Abstract
Periodic structures formed in one- to three dimensions have been studied as photonic and microwave components for over 50 years. Corrugations on a guided wave structure has been considered as circuit elements and are used as a slow wave structure (delay line), or a stopband filter based on Bragg phenomena depending on the operating frequency. If the frequency is further increased, the structure supports guided wave which causes leaky structure. Multi (2 or 3) dimensional periodic structures are often called Photonic Crystals or Electromagnetic Bandgap (EBG) structures because of the similarity of the dispersion diagram to that of naturally found crystalline configuration. In late 1970s till 90s, significant scientific and engineering applications of the EBG have been witnessed with the majority in two-dimensional configurations which are fabricated by then standard planar circuit configuration. At the same time, dielectric waveguide structures were also used with a view to application to futuristic millimeter and submillimeter circuits. Examples include Bragg Gunn oscillators similar in structure to Distributed Bragg Reflector (DBR) laser diode. The DBR structures have also been incorporated to planar integrated circuits to control the signal flow. Periodic perturbation is incorporated in the ground plane of the output port of the high-power amplifier from which the second harmonic is suppressed. The signal control by means of ground plane holes were widely used as the defected ground structure (DGS)....
In early 2000, significant interest on the interest of the EBG in two dimensions came out in antenna community for improving the radiating characteristics of planar antenna. Various two-dimensional periodic structures were also studied such as impedance plane, perfect magnetic surface, etc. Around this time, a composite EBG (UC-PBG) was introduced which has unit cells made of reverse Jerusalem cross printed on the top surface of a grounded substrate. Since two layers can be used, surface impedance can be controlled more effectively.
Circa 2020 was the time of surprise birth of the artificial (manmade) structures named Metamaterial. Experimental demonstration of negative phase velocity was carried out by periodic structure with the unit cells made of split ring resonator(s) generating negative inductance and wire medium generating negative capacitance. Soon after this demonstration, it was reported that the negative velocity can be realized by using series capacitance and shunt inductance in a unit cell of periodic structure. Since generation of the negative velocity is accomplished by conventional (not resonant) broadband planer circuit elements, this new structure called Composite Right/Left-Handed (CRLH) was widely used for various microwave components including the dual-band couplers, 0th order resonators and entire domain scanning leaky-wave antennas.
Although these Metamaterials can be 1-d, 2-d and 3-d periodic configuration and resemble to EBG structure in appearance, their nature is fundamentally different. Strictly speaking EBG should not be called Metamaterial. It is interesting, however, that their two-dimensional versions are called Metasurface, perhaps because the interest and usage of the metasurface are along the study of scattering properties.
The terminology metasurface appeared to have origin in optical science and photonic engineering. In optical regime, it is easy to obtain physical size of the components much larger than wavelength. Often, in beam optics configuration, the optical beam is well within the diameter of lens and mirrors. Situation is quite different in microwave electronics. Even for a large phased array, it is rare that the size rarely exceeds 100wavelength. However, the situation in THz electronics is not so bad and the use of “optical” technique might be convincing.
For instance, THz amplifying metasurface reflectors were developed for quantum-cascade lasers (QCL) to achieve high output power and high-quality beam pattern. Some traditional optical devices can find their equivalent metasurface design with much smaller size. Blazed gratings were imitated by a metasurface with periodic simple planar elements, such as metal strips and patches, to reflect the beam back to the path of incidence (retroreflection). Later, metasurface gratings with resonant unit cells at blazing points were designed for wide bandwidth and wide angle of operation. To enhance the retroreflection efficiency, non-periodic metasurfaces were developed assisted by optimization technique. They can overcome the physical constraints faced by the periodic metasurface gratings and can be used to retroreflect circularly polarized wave with either preserved handedness or reversed handedness. If translated to appropriate frequencies, all these metasurfaces may find their applications in Littrow external cavity lasers, radars, RFID, etc.
Now, the metasurface has become an efficient tool to manipulate the magnitude, phase, and polarization of electromagnetic waves in microwave. Different types of metasurfaces, such as Reactive impedance surface (RIS), high impedance surface (HIS) and frequency select surface (FSS), are evolving to impact many microwave applications. They were widely used in antenna miniaturization and performance enhancement, EM field absorbers, and polarization converters to name a few.
Plenary Talk - Speaker 2
Baoyan Duan Academician of Chinese Academy of Engineering
Xidian University
Title: On Electromechanical Coupling Problems in Large Phased Array Microwave Antennas
Abstract
Large phased array antenna (PAA) is a kind of complex integrated system involving electromagnetic, mechanical and thermal technologies. Advanced mechanical technology is needed to maintain the electronic performance of the PAA, otherwise, it may restrict the realization of the PAA with high performance. With the three new developing trends of high frequency and high gain, high density and miniaturization, and fast response and high pointing accuracy, the tightly coupling between these technologies can be imagined. This talk will focus on the coupling problems of the PAA....
Firstly, the multifield coupling (MFC) model among electromagnetic, structural displacement and temperature field for phased arrays of microwave antennas is introduced.
Secondly, the influence mechanism (IM) of nonlinear mechanical errors on the electronic performance of antennas is described.
Thirdly, the MFC and IM based multidisciplinary design optimization methodology is proposed.
Finally, several engineering applications are given to demonstrate the MFC model, IM and optimization methodology.
Plenary Talk - Speaker 3
Ke Wu Fellow of the Royal Society of Canada
University of Montreal
Title: Emerging Deep Integration and Topological Cohabitation of Front-End Circuit and Antenna for Future Wireless Systems
Abstract
Large-scale integration of front-end circuit (FEC) and antenna for wireless systems has undergone a remarkable progress with the evolution of operating frequency ranges over time. Spurred by performance-limited conventional approach in which FEC and antenna are developed independently, the co-design scheme of FEC with antenna, widely known as active integrated antenna (AIA), has gained prominence and significance. Nevertheless, there are still significantly detrimental issues in the AIA platform, which become much more pronounced at the rapidly emerging millimeter wave and terahertz range frequencies. Therefore, there is an immediate and tremendous need in search for disruptive solutions....
To this end, we have proposed and demonstrated a transformative concept of unified and integrated circuit antenna (UNICA) with focus on topologically cohabitating active devices and antennas. This emerging technology is to realize joint circuit and antenna functions through a unified space without resorting to additional connecting lines and impedance matching networks. In this talk, we will discuss the architectural evolution of FEC integration schemes with antenna, covering the state of art deep integration techniques for realizing various active circuit-antenna functions such as oscillation, amplification, mixing, and frequency multiplication, which are implemented in either PCB or on-chip platforms.
Plenary Talk - Speaker 4
Nader Engheta H. Nedwill Ramsey Professor
University of Pennsylvania
Title: Extreme Metastructures
Abstract
Metamaterials and Metasurfaces have provided versatile platforms for wave-matter interactions with various applications in microwave, THz, and optical domains. Since material parameters can be tailored to achieve exciting functionalities in such platforms, various extreme scenarios for these parameters can be considered. In my group, we have been exploring the salient wave-based features of extreme-parameter metamaterials and metasurfaces. One of our research programs in this area is the concept of metastructures that can perform mathematical computing with waves, e.g., properly designed platforms that can solve equations with near speed of light, as the waves traverse through them. In such structures, one can envision metamaterials that function as analog computing machines....Another category of extreme metastructures is the near-zero-index (NZI) media in which the effective relative permittivity and/or relative permeability can attain near-zero values around the operating frequencies of interest. In such NZI structures, effective wavelength “stretches”, and consequently numerous unprecedented wave phenomena emerge. In this talk, I will give an overview of some of our ongoing research programs in the areas of extreme metastructures. I will also present physical insights into the results, and will forecast future research directions in these areas.
