Hosung Choo

Simulation of MIMO channel capacity with antenna polarization diversity

A simulation study of the channel capacity of a multiple-input multiple-output (MIMO) antenna system exploiting multiple polarizations is carried out. We focus on a simple yet realistic trimonopole antenna structure, taking into account all the mutual coupling and casing effects using the computational electromagnetics solver-numerical electromagnetics code. Simulation results show that, with a special transmit geometry, using the collocated trimonopole antennas at a size-constrained receiver can offer channel capacity that approaches the capacity of an uncorrelated MIMO Rayleigh channel. In addition, it is shown that the capacity increase is mainly attributed to polarization diversity instead of pattern diversity. Furthermore, we find that the mutual coupling and casing effects in the trimonopole system can actually provide a large capacity increase with less constraint on the antenna configurations than the idealized tridipole system.

Multi-Band, Wide-Beam, Circularly Polarized, Crossed, Asymmetrically Barbed Dipole Antennas for GPS Applications

This communication presents a multi-band, circularly polarized (CP), wide beamwidth, highly efficient antenna for use in global positioning systems (GPS). The primary radiating elements are two crossed printed dipoles, which incorporate a 90° phase delay line realized with a vacant-quarter printed ring to produce the CP radiation and broadband impedance matching. To achieve multiple resonances, each dipole arm is divided into four branches with different lengths, and a printed inductor with a barbed end is inserted in each branch to reduce the radiator size. An inverted, pyramidal, cavity-backed reflector is incorporated with the crossed dipoles to produce a unidirectional radiation pattern with a wide 3-dB axial ratio (AR) beamwidth and a high front-to-back ratio. The multi-band antennas have broad impedance matching and 3-dB AR bandwidths, which cover the GPS L1-L5 bands.

Design of electrically small wire antennas using a pareto genetic algorithm

We report on the use of a genetic algorithm (GA) in the design optimization of electrically small wire antennas, taking into account of bandwidth, efficiency and antenna size. For the antenna configuration, we employ a multisegment wire structure. The Numerical Electromagnetics Code (NEC) is used to predict the performance of each wire structure. To efficiently map out this multiobjective problem, we implement a Pareto GA with the concept of divided range optimization. In our GA implementation, each wire shape is encoded into a binary chromosome. A two-point crossover scheme involving three chromosomes and a geometrical filter are implemented to achieve efficient optimization. An optimal set of designs, trading off bandwidth, efficiency, and antenna size, is generated. Several GA designs are built, measured and compared to the simulation. Physical interpretations of the GA-optimized structures are provided and the results are compared against the well-known fundamental limit for small antennas. Further improvements using other geometrical design freedoms are discussed.

On the Wheeler cap measurement of the efficiency of microstrip antennas

The Wheeler cap method for measuring the efficiency of microstrip antennas is revisited. First, we show that the parallel RLC model is a more appropriate model to use than a series one for the microstrip antennas under consideration. Our results are verified by numerical simulation using ENSEMBLE. Second, the role of the interior cavity modes is investigated and a reduced-height Wheeler cap is proposed. Finally, the Wheeler cap method is applied to measure the efficiency of miniaturized microstrip antennas designed using genetic algorithms.

Design of a Circularly Polarized Tag Antenna for Increased Reading Range

We introduce a novel circularly polarized tag antenna, consisting of a truncated patch, a shorting plate, and a ground plane, to increase the reading range while remaining in compliance with EIRP regulations. The reading range of the proposed tag is twice that of linearly polarized tags, due to the decreased polarization mismatch between the reader and tag antennas. An additional parasitic patch is loaded onto the structure to boost the reading range in the UHF RFID band. As a result, an average reading range of 8 m is achieved between 860 MHz and 960 MHz, compared to a range of about 3 m with conventional dipole tags.

Design of multiband microstrip antennas using a genetic algorithm

A genetic algorithm (GA) is used to design patch shapes of microstrip antennas for multiband operations. For dual-band operation, the optimized patches show that arbitrary frequency spacing ranging from 1:1.1 to 1:2 can be achieved. Tri-band and quad-band microstrip shapes are also generated and the resulting designs show good operations at the designated frequencies. All results were verified by laboratory measurements on an FR-4 substrate.

Design of UHF small passive tag antennas

We explore structures of planar tag antennas that permit high efficiency, a low profile, and reliable performance on a variety of dielectric materials. For the basic structure of the antenna, we used the inductively coupled feed concept to efficiently reduce the size of the tag antenna. We examined two different types of windings for the antenna body to achieve better performance with the given RFID tag chip. To find detailed design parameters that attain multiple design goals, we employ a Pareto genetic algorithm with an IE3D of Zealand EM simulator. The finalized designs were built on a 5 mil thick Duroid substrate with the Alien tag chip. The size of the optimal design was reduced to kr=0.2, with a readable range of 40 cm-280 cm.

Planar Near-Field RFID Reader Antenna for Item-Level Tagging

In this letter, we propose a novel UHF planar near-field antenna for the application of RFID item-level tagging. The proposed antenna was designed to have a strong and uniform Hz-field over a broad antenna aperture to identify the various items with stable reading performance. To obtain a strong near Hz-field, two coupled patches are employed along with a microstrip-line feed, resulting in average Hz of -15 dBA/m on antenna aperture (30 × 30 × 10 cm3). We also measured the reading range, and it confirmed that the proposed antenna is suitable for a commercial RFID smart-shelf application.

Multiband Dual Spiral Stripline-Loaded Monopole Antenna

We propose a multiband antenna that exhibits a dual coupling characteristic and dual frequency operation using a dual spiral stripline-loaded monopole in conjunction with L-shaped slots in a ground plane. The slots allow the upper part of the ground plane to function as an additional monopole that resonates in concordance with the existing resonances of the upper and lower spiral stripline monopoles. As a result, the impedance band- widths are greatly enhanced while maintaining relatively good omnidirectional radiation characteristics. The proposed antenna occupies a volume of 36 times 7 times 102 mm3 including the ground plane, and the measured impedance bandwidths with VSWR < 2 simultaneously cover CDMA, GSM900, DCS1800, PCS1900, UMTS, IMT-2000, and WiMAX2350 bands. We describe the detailed antenna structure and present measurement results.

Design of Novel RFID Tag Antennas for Metallic Objects

In this paper, a novel tag antenna is proposed; it has a very simple structure that does not require a ground plane or shorting pins. The proposed tag antenna has significant advantages over other types of tag antennas for metallic objects, such as low cost, light weight, and ease of fabrication. The body of the antenna is printed as a single planar strip line on a thin PET substrate (polyethylene, epsir =3.9, tandelta=0.003) and it is mounted on foam substrate (epsir=1.0). The detail design parameters of the proposed antenna were optimized using the Pareto genetic algorithm (GA) in conjunction with the IE3D EM simulator and the resulting tag antenna has readable ranges of about 2.8 m when mounted in the air and 1.8 m when mounted on a metallic surface