In-Sang Yoo

We propose a spatial multiplexing system using reconfigurable cavity-backed metasurface antennas. The metasurface antennas consist of a printed cavity with dynamically tunable metamaterial radiators patterned on one side and fed by multiple radio frequency ports on the other side (each port representing one communication node), forming a shared aperture. By individual tuning of the radiators, the antennas can generate steerable, concurrent beams that can be adapted to the properties of multiple-

The combination of orthogonal frequency modulation (OFDM) and multiple-input multiple-output (MIMO) techniques plays an important role in modern communication systems. In order to meet the growing throughput demands, future MIMO-OFDM receivers are expected to utilize a massive number of antennas, operate in dynamic environments, and explore high frequency bands, while satisfying strict constraints in terms of cost, power, and size. An emerging technology to realize massive MIMO receivers of redu

We present a metamaterial element designed as an efficient radiator for waveguide-fed metasurface antennas. The metamaterial element is an electrically-small, complimentary electric-LC (cELC) resonator designed to exhibit large radiated power while maintaining low ohmic losses. The shape of the element is tapered to simultaneously achieve broadband operation and suppression of cross polarization radiation. Full-wave numerical studies at the K-band are conducted to examine its performance when et

We present an analytic model of a coax-fed planar cavity-backed metasurface antenna for radiation pattern synthesis. The metasurface antenna consists of a printed cavity loaded with metamaterial elements which is excited by a coaxial connector. Each metamaterial element radiates a portion of the reverberating fields in the cavity, contributing to an overall beam pattern. To synthesize a desired pattern, the elements need to be arranged in an aperture and radiate with proper weights at their loca

We present a systematic design method for a cylindrical conformal array of rectangular waveguide-fed metasurfaces. The conformal metasurface consists of multiple curved rectangular waveguides loaded with metamaterial elements—electrically small apertures—inserted into the upper conducting walls of the waveguides. Each element radiates energy into free space to contribute to an overall radiation pattern. Thus, the geometry or electrical configuration of each of the elements needs to be tailored t

We present a model for waveguide-backed metasurface antennas fed by one or more coaxial ports and compute key antenna parameters using the model. The metasurface antenna consists of a coax-fed planar waveguide/cavity embedded with subwavelength-sized metamaterial radiators that convert energy from the guided mode into a radiated wave. Designing a metasurface requires tailoring the geometry of the individual metamaterial elements and arranging them over the aperture to achieve a desired radiation

We propose a MIMO system using a dynamic cavity-backed metasurface antenna (DMA) as a transmit antenna to improve the channel capacity of indoor MIMO channels. The DMA is a printed cavity loaded with tunable metamaterial radiators and fed by radio frequency ports. The DMA can generate radiation patterns that are adaptive to MIMO channels by individual tuning of the metamaterial radiators. In this letter, we study a 4 × 4 MIMO system operating at 5.9 GHz, consisting of a simulated DMA as transmit

We confirm experimentally that the essential electromagnetic properties of a single, waveguide-fed, tunable metamaterial radiator can be described within a coupled dipole framework, providing a foundation for metasurface array antenna design. The metamaterial element considered here is an electrically small aperture consisting of a complementary electric-LC resonator with its resonance frequency controlled by a pair of varactor diodes. Using the dipole framework, we reduce the detailed propertie

We propose an uplink massive MIMO system using an array of holographic metasurfaces as a sector antenna operating at 3.5 GHz. The antenna consists of a set of rectangular waveguide-fed metasurfaces combined along the elevation direction into a planar aperture, each with subwavelength-sized metamaterial elements as radiators. The metamaterial radiators are designed such that the waveguide-fed metasurface implements a holographic solution for the guided (or reference) mode, generating a directiona

The realization of phase discontinuities across metasurfaces has led to a new class of reflection and refraction. Here we present theory and experiment on the discontinuous propagation of wavepackets across subwavelength-thickness meta-atoms. Using acoustic waves, we observe the process of wavepackets traversing a meta-atom with abrupt displacements, which appear as path discontinuities on a space-time diagram. We construct a tunable meta-atom from two coupled resonators at ~500 Hz, map the spat

We propose an uplink massive MIMO system using an array of holographic metasurfaces as a sector antenna. The antenna consists of a set of rectangular waveguide-fed metasurfaces combined along the elevation direction into a planar aperture, each with subwavelength-sized metamaterial elements as radiators. The metamaterial radiators are designed such that the waveguide-fed metasurface implements a holographic solution for the guided (or reference) mode, generating a fan beam towards a prescribed d

Physiological changes in thoroughbred racehorses during the race were investigated by measuring concentrations of metabolites and exercise-related hormones before and after a race. The conversion point from anaerobic to aerobic exercise during the race was estimated subsequently. Blood samples were taken from the jugular vein of 53 thoroughbreds at different times -three h before and 45 min after-for measuring the concentrations of glucose, non-esterified fatty acids (NEFA), lactate, uric acid,

We present a method for computing the input impedance of a rectangular waveguide-backed metasurface array excited by a common feed network. The metasurface array consists of rectangular waveguides loaded with subwavelength metamaterial radiators fed by the guided modes, excited with the feed. Thus, computation of the impedance at the input feed requires considering the electromagnetic interaction of the metasurfaces with its feed. Recently, semi-analytical models of metasurfaces using a coupled

We study the modeling of metamaterial elements etched into planar, dielectric-filled waveguides for metasurface antennas. Metamaterial elements in these devices are subwavelength-sized, resonant openings embedded in waveguide walls-that can be modeled as the electric and magnetic dipoles-and couple to waveguide modes and radiate into free space. Due to a dielectric filling the waveguide, the dipole moments representing the element can contribute unequally to the scattered fields into the wavegui