Jeong-Hae Lee

Epsilon Negative Zeroth-Order Resonator Antenna

It is confirmed that zeroth-order resonance appears in the epsilon negative (ENG) meta-structured transmission line (MTL) as well as in the conventional double negative (DNG) MTL. The zeroth-order resonant characteristics are described using dispersion relation of ENG MTL based on Bloch and Floquet theory. Appling the novel concept of the ENG zeroth-order resonator (ZOR), an ENG ZOR antenna is proposed. The radiation characteristics of the ZOR antennas using the DNG and ENG MTL are simulated and measured, and are proven to be the same.

Zeroth Order Resonance Loop Antenna

A new type of low-profile omnidirectional antenna is proposed in this paper. The proposed antenna has the conceptual configuration of the horizontal magnetic loop current on perfect electric conductor plane, which has been realized by the zeroth-order resonator (ZOR) antenna using mushroom structure. The mushroom structure as a transmission line has negative, zero, and positive propagation constant depending on its operation frequency since mushroom structure is artificial composite right-left handed transmission line. Zeroth-order resonance, of which frequency is independent of physical length, is naturally presented. In particular, mushroom ZOR antenna generates a uniform vertical electric field against ground plane, so that it omnidirectionally radiates in a horizontal plane. Operation frequency, absolute gain, and gain variations for omnidirectional radiation of the designed prototype are 7.9 GHz, 2.6dBi, less than 1.5 dBi, respectively

Omnidirectional Circularly Polarized Antenna Utilizing Zeroth-Order Resonance of Epsilon Negative Transmission Line

The omnidirectional circularly polarized (CP) antenna using a circular mushroom structure with curved branches is proposed. The antenna is based on the zeroth-order resonance (ZOR) mode of epsilon negative (ENG) transmission line (TL) to obtain a vertical polarization and an omnidirectional radiation pattern. Also, the horizontal polarization is obtained by the curved branches. The 90° phase difference between two orthogonal polarizations is inherently provided by the zeroth-order resonator. Therefore, the antenna has an omnidirectional CP radiation pattern in the azimuthal plane. In addition, this antenna is planar type and simply designed without a dual feeding structure and 90° phase shifter. The measured average axial ratio and left-hand (LH) CP gain are 2.03 dB and - 0.40 dBic, respectively, in the azimuthal plane.

Mu-Zero Resonance Antenna

We present mu-zero resonance (MZR) antennas that use an artificial mu-negative (MNG) transmission line (TL). The equivalent circuit for verifying the peculiarity of the MNG TL is derived and analyzed. To operate the MZR antenna properly, the antenna is fed by magnetic coupling. The analysis and design of the MZR antenna are performed according to theory and simulation based on a dispersion diagram and field distribution. The surface current distribution shows that the radiation mechanism of the MZR antenna is essentially identical to that of a small-loop antenna. Applying the novel concept of the MZR antenna, a dual-band MZR antenna using two MZR antennas with different MZR frequencies is proposed. The radiation characteristics of the antenna are simulated and measured at two frequencies. The measured characteristics show agreement with the simulated results. It is confirmed that the characteristics of the MZR antenna, including the efficiency, gain, and fractional bandwidth, are suitable for a multiband antenna.

Dual-Band Omnidirectional Circularly Polarized Antenna Using Zeroth- and First-Order Modes

This letter discusses the development of a dual-band omnidirectional circularly polarized (CP) antenna using the zeroth- and the first-order resonance modes of epsilon-negative (ENG) transmission lines (TLs). The antenna is based on a circular mushroom structure with curved branches and designed without additional feeding parts for a 90 ° phase difference between two orthogonal modes as well as additional radiators for dual-band operations. A left-hand CP (LHCP) and a right-hand CP (RHCP) are obtained at the zeroth- and the first-order resonance modes, respectively, because the current direction of the curved branch, which is related to a horizontal polarization, at the zeroth-order resonance (ZOR) mode is opposite to that at the first-order resonance (FOR) mode. The measured average axial ratios at the resonance modes in the azimuthal plane are 1.57 and 0.86 dB, respectively. The measured average LHCP and RHCP gains are - 0.24 dBic at the ZOR mode and -0.51 dBic at the FOR mode, respectively. These results are congruent with simulated data.

Light transmission along dispersive plasmonic gap and its subwavelength guidance characteristics

Light transmission along dispersive plasmonic gap with varied gap widths and its subwavelength guidance characteristics are numerically investigated over a wide frequency range. Mode numbers for each guided modes of the dispersive plasmonic gaps are properly assigned in order to be in consistency with the parallel plate waveguide composed of the perfect electric conductor. Overall and salient features of the role of the gap widths on the guided propagation characteristics are clearly understood by investigating several dispersion curves of varied gap widths. Cutoff frequency downshifts of the dispersive plasmonic gap compared with the perfect electric conductor based parallel plate waveguides are also observed. Finally, surface plasmon polariton modes having subwavelength guidance capability are described in more detail, which are directly governed by the plasmonic property of the metals. The results are expected to be utilized in designing various potential subwavelength nanophotonic devices.

Electromagnetic wave propagation through doubly dispersive subwavelength metamaterial hole

The characteristics of the guided electromagnetic wave propagation through a subwavelength hole surrounded by a doubly dispersive metamaterial are investigated. Characteristic equations are derived for the surface polariton modes related to the subwavelength hole and mode classifications established. The surface polariton modes for two different hole-radii are numerically obtained and their electromagnetic dispersion curves and power flux characteristics analyzed and compared with each other. In particular, it was found that the border of the counter-propagation between the forward and backward Poynting vectors was located within the metamaterial, rather than at the interface between the metamaterial and the free space.

Linear lumped loads in the FDTD method using piecewise linear recursive convolution method

This letter gives a new algorithm to include linear lumped elements into finite difference time domain algorithm. The proposed method can efficiently account for two-terminal networks made of several lumped elements. The piecewise linear recursive convolution (PLRC) technique is used to implement lumped loads into Yee cells. Using this method, it is possible to simulate equivalent circuits of terminations for microstrip structures, integrated circuits, or digital devices. The advantage of the PLRC technique is addressed and simulation results validating this method are presented.

Effective medium approach of left-handed material using a dispersive FDTD method

Left-handed material (LHM) exhibiting negative permittivity and negative permeability in certain band has dispersive medium property varying with frequency. The effective permittivity and permeability function of this material have a similar form of Lorentz material model. Piecewise linear recursive convolution (PLRC) technique for finite difference time domain (FDTD) method is applied to simulate the propagation characteristic of LHM effectively. Modified anisotropic perfectly matched layer (APML) is proposed for absorbing boundary condition of LHM. The simulation results show narrow pass band in the stop band where LHMs have double negative properties.

Comparative analysis of four types of high-impedance surfaces for low profile antenna applications

We have analyzed and compared four types of high-impedance surfaces for low profile antennas. The considered high-impedance surface (HIS) structures are: mushroom-like electromagnetic band gap (EBG); uniplanar compact EBG (UC-EBG); Peano curve; Hilbert curve. These structures are designed to behave effectively as a magnetic conductor surface at 2.45 GHz. The various properties, namely, the return loss, radiation pattern, and gain, of a horizontal wire antenna placed in close proximity to the four types of high-impedance surfaces are simulated and compared using a full wave simulation tool.