Ji-Hwan Ko

Resonant Transmission of an Electrically Small Aperture with a Ridge

A resonant transmission of an electrically small aperture with a ridge in a conducting plane is analyzed. It is an example of resonant transmission and the ridge inserted at the center line of the electrically small aperture resonates it by increasing an equivalent capacitance of the aperture. At resonance condition, the transmitted power through the aperture can be significantly enhanced compared to that at off-resonance. It is found that the transmitted power at the resonance condition converges to the transmission cross section of the aperture regardless of its size or shape. In addition, the electric and the magnetic fields distributions on the aperture with and without the ridge are compared to facilitate the understanding of the resonant behavior.

Transmission Through a Narrow Slot in a Thick Conducting Screen

In this communication, the electromagnetic transmission problem through a narrow slot in a thick conducting screen is dealt with by using the modal expansion Galerkins method in the space domain. The main concern centers on the condition for maximum power transmission through the slot in the thick conducting screen. Transmission cavity resonance phenomena, which are observed only when the resonance cavity is formed along the longitudinal direction inside the slot region in the thick conducting screen, are investigated. These transmission resonance peaks occur at particular values of the screen thickness, that is, when the thickness of the conducting screen is a little less than an integer number of half guide wavelength of the fundamental guided mode inside the slot region. It is also found that there is another type of transmission resonance phenomenon occurring regardless of the screen thickness. The latter type of transmission resonance is observed only when transverse resonance condition holds and can be taken as a generalization of the slot resonance in a thin conducting screen to that in an arbitrarily thick conducting screen.

A Study on the Resonant Transmission through a Ridge-Loaded Small Circular Aperture

In this paper, the electromagnetic wave transmission through a ridge-loaded small circular aperture is considered. The transmission problem when a plane wave is normally incident on the aperture in an infinite conducting plane is solved by a method of moments(MoM). From the results for the transmitted power and the patterns of radiation from the aperture, the transmission characteristics of a small sub-wavelength circular aperture, a ridge-loaded circular aperture, and a half wavelength slot are compared. In addition, the theoretical study is verified through the experiments for the apertures fabricated on an Flexible Printed Circuit Board(FPCB), which shows fairly good agreements with the simulated results.

Resonant Transmission through C-Shaped and H-Shaped Small Apertures and the Mutual Coupling Effect between Two C-Shaped Apertures

Transmission cross section characteristics as a measure of transmission efficiency has been analyzed numerically for the H-shaped and C-shaped small apertures in the infinite conducting plane when illuminated by a plane wave. It has been found that C-shaped aperture has the larger transmission cross section than that of H-shaped aperture under the condition of the same perforated aperture area. Main attention has been focused on studying the mutual coupling effect between two C-shaped apertures on the transmission cross section characteristic. Parallel configuration which is composed of two C-shaped apertures arranged along the x-axis and collinear configuration which is composed of two C-shaped arrayed along the y-axis have been investigated from the viewpoint of enhanced transmission cross section characteristics.

Analysis of resonant transmission characteristics of two sub-wavelength apertures with a ridge located in parallel

There have been numerous studies for the problem of electromagnetic coupling through electrically small holes or apertures in microwave areas and optics. Bethe was first treated this problem using the aperture polarizability concept and it was found that the transmittance normalized to the area scales as (a/λ)4 where a is the hole radius and λ is the wavelength [1]. This problem was generalized by Harrington introducing radiation terms in the equivalent circuit and he suggested an easy way of improving the poor transmittance by satisfying resonance condition [2]. The resonance condition can be realized by loading the small aperture with a capacitive lumped element or a capacitive structure. Recently, Yeo et. al. have analyzed an electrically small circular aperture with a ridge for resonant transmission and have shown the convergence of the transmitted power of an electrically small aperture to the transmission cross section [3].

Equivalent circuit-based analysis of a small resonant circular aperture

In the problems of electromagnetic coupling, the transmission of the electromagnetic wave through such a hole is typically very weak when the lateral dimensions of an aperture are smaller than half the wavelength. It is usually believed to scale as the fourth power of the aperture diameter for example for small circular aperture [1]. Recently a kind of ridged aperture [2] that provides a significant enhance of the transmission efficiency through the small aperture was proposed for applications of near-field optical areas such as optical data storage, nano-lithography, and nano-microscopy.

Electromagnetic Transmission through Slits in Two Adjacent Conducting Parallel-Plates

In this paper, the problem of electromagnetic transmission through slits in two parallel conducting plates which separate two half spaces is considered. The coupled integral equations for the electric field distributions over the slits are developed for the case that the TM polarized plane wave is incident on the slit and solved by the method of moments. The transmitted power beyond the slit-perforated conducting parallel plates is computed in order to check the variations of the coupled power through slits against some parameters such as the incident angle of the TM polarized wave, slit width, lateral distance between two slits, and distance between the conducting plates. When the lateral distance between two slits approaches near the multiples of half wavelengths, the transmission resonance (maximum power transmission) is observed. If the slit width in the incident side is narrow and the distance between conducting plates is small compared to the wavelength, the maximum of transmitted power is observed to be nearly independent of the incident angle and slit width. In addition, the mechanism of the transmission resonance in the present geometry is explained using a simplified geometry and its equivalent circuit.

Experimental verification of electromagnetic scattering via two-dimensional periodic array of small resonant apertures

The transmission characteristics of a frequency selective surface (FSS) consisting of small resonant circular apertures with a ridge are related to the transmission cross section of a single ridged aperture, and the performance is verified experimentally. The FSS structure with a ridged circular aperture has a lower resonant frequency, enlarged fractional bandwidth, and a larger wavelength-to-periodicity ratio compared to an FSS with a conventional circular aperture. Experiment results show that the resonant frequency of the proposed FSS structure can be lowered from 13.98 GHz to 7.30 GHz (47.8%) by adding the ridge.

Design and experiment of miniaturized small resonant aperture using modified ridge structure

A design method for a miniaturized small resonant aperture by modifying a ridge structure is presented, and its performance is verified experimentally. The proposed miniaturized aperture was designed by deforming the straight ridge structure of an H-shaped aperture with a two-step ridge of different lengths and widths, which resembles the capacitor symbol shape of the electric circuit. Experiment results show that the resonant frequency of the proposed aperture decreases from 5.06GHz to 2.565GHz (49.3%) compared to the conventional H-shaped aperture. Its transmission cross section increased by 3.78 times, and the aperture length-to-wavelength ratio is reduced to 0.09.

A Study of Center Longitudinal Shunt-Series Coupling Slot Fed by Asymmetric Compound Iris for Waveguide Slot Coupler

This paper proposes a new coupling element of microwave slot coupler for designing waveguide slot array which can reduce the effect of undesired higher order mode coupling between coupling and radiating slots in the branch waveguide. The proposed device is composed of a centered longitudinal shunt-series coupling slot at the center of broad wall shared by two crossed rectangular waveguides and an asymmetric compound iris that excites the coupling slot. We first have obtained scattering parameters for the proposed coupler by use of EM S/W tool HFSS and then extracted the parameters of T- network equivalent circuit for the coupling slot. We also have analyzed the resonant properties such as resonant length and normalized admittance by changing the geometrical dimensions. The measured results for the fabricated coupler with short-circuited block away from the coupling slot are well agreed with the simulated ones.