Ji-Whan Ko

Resonant transmission enhancement with a subwavelength aperture

We have considered the degree of enhancement in the transmitted power through the subwavelength aperture, which can be achieved by introducing some perturbation in small aperture shape. The maximum transmission condition has been described from the viewpoint of equivalent circuit representation. This study may find applications such as optical data storage and nanolithography as well as small aperture-type antenna design.

A robust approach for the derivation of closed-form Green's functions for microstrip structures

A robust approach for the derivation of closed-form Greens functions is considered based upon a three level approximation procedure, which can give more accurate evaluation of the spatial Greens functions even without the advance investigation of the spectral functions in comparison with the previous method.

Resonant transmission of a class of sub-wavelength apertures in thin conducting screen

In this paper, we have examined the resonant transmission of a class of sub- wavelength apertures such as a ridged circular aperture and a narrow rectangular slot in thin infinite conducting screen. The transmitted power for varying the ridge gap and the slot length for these apertures, respectively, has been compared with the transmission cross section of the apertures to check out the relationship between them, and the admittance of the apertures have been computed to validate the resonant behavior of them. It turns out that the transmitted power of an electrically small aperture at a resonance converges to the transmission cross section of 3/4pi square wavelengths independent of its shape and size as long as the aperture size is sufficiently small compared to the wavelength.

Equivalent circuit interpretation of transmission resonance through small apertures

Transmission resonances through small apertures in two representative structures are analyzed by using equivalent circuit approach. It has been found that the total admittance of the aperture becomes purely real when the transmission resonance occurs and it is related to the transmission cross section of the aperture.

Design of the Dual Linear Polarized Radiation Element Using a Open-Ended Ridge Waveguide

A design approach for a radiation element of dual polarization, which can be implemented in the waveguide structure, is proposed. For minimization of the radiating element, the ridged waveguide type is used and for dual polarization, the microstrip type of printed dipole structure is additionally installed inside the waveguide. In order to validate the design approach, array antenna is fabricated and its performances such as return loss, co-polarization coupling between adjacent channels, and radiation patterns are investigated. Theory and experiment are observed to be in good agreement. The radiating structure is thought to be a useful one in an application to the phased array antenna system, in particular, requiring dual polarization characteristics.

Analysis of Electromagnetic Resonant Transmission through a Narrow Slit in Thick Conducting Screen

The transmission resonance phenomenon through a narrow slit in the thick conducting screen is analyzed by use of the method of moments. In order to check the validity of this approach, some numerical results for the transmission coefficient is compared with previous ones. In particular, an approximate expression for the transmission width is derived in the analytical form.

Design of Waffle-Iron Waveguide Filter

Simple practical design method is proposed for the waffle-iron waveguide filter. The design procedure comprises two steps. The first step is to calculate the K-inverter based on the transformed ABCD parameter from the S parameter for the single window of waffle-iron structure by use of EM S/W tool. The second step is to optimize the size of the windows such that the calculated K inverters may be in accord with the distributed constant prototype filter. In order to validate the design method, a waffle-iron filter for satellite communications over the Ka band is designed and fabricated. The measured results are in good agreement with the calculated ones.