Youngjoon Lim

High-Efficiency W-Band Electroforming Slot Array Antenna

A W-band 8 × 8 slot array antenna is proposed and fabricated by electroforming for high-precision manufacturing. The external mutual coupling between radiating shunt slots is compensated for input impedance matching and a uniform held distribution. The overall antenna aperture area is 473.1 mm2 with slot spacings of 2.8 and 2.64 mm in the transverse and longitudinal direction, respectively. The measured maximum gain is 26.8 dBi and the corresponding antenna efficiency is 81.9% at 94 GHz. The measured impedance bandwidth when the VSWR is less than 2.0 (-10 dB) is 8.3%, with a range from 89.9 to 97.6 GHz.

Target-to-Clutter Ratio Enhancement of Images in Through-the-Wall Radar Using a Radiation Pattern-Based Delayed-Sum Algorithm

In this paper, we compare the quality of images reconstructed by a conventional delayed-sum (DS) algorithm and radiation pattern-based DS algorithm. In order to evaluate the quality of images, we apply the target-to-clutter ratio (TCR), which is commonly used in synthetic aperture radar (SAR) image assessment. The radiation pattern-based DS algorithm enhances the TCR of the image by focusing the target signals and preventing contamination of the radar scene. We first consider synthetic data obtained through GprMax2D/3D, a finite-difference time-domain (FDTD) forward solver. Experimental data of a 2-GHz bandwidth stepped-frequency signal are collected using a vector network analyzer (VNA) in an anechoic chamber setup. The radiation pattern-based DS algorithm shows a 6.7-dB higher TCR compare to the conventional DS algorithm.

Mutual coupling analysis of antennas in layered media through equivalent sources for wireless power transfer

Summary form only given. In recent years, wireless power transfer has received much attention and been widely studied. Wireless power transfer has many applications. For example, there are the systems that transfer energy wirelessly to an electric car, sensors buried in a wall, devices beyond a wall, and devices in the ground. The one of the modeling method for such systems is to assume that antennas are in layered media and solve the mutual coupling between antennas. In this work, we propose the method for calculating the Z-parameter between antennas in layered media and the maximum power transfer efficiency of a wireless power transfer system. According to spherical wave theory (R. J. Pirkl, IEEE Trans. Antennas Propag., vol. 60, no. 12, pp. 5654-5662), the S-parameter between two antennas in arbitrary environments can be calculated using the generalized scattering matrix of an antenna. When we calculate the S-parameter using this method, the specified antenna structures are not needed. A canonical minimum scattering (CMS) antenna is an antenna that does not scatter electromagnetic fields when its feeding ports are open-circuited. Many antennas that are small relative to the wavelength can be considered CMS antennas. Therefore, we can assume that antennas are CMS antennas when we analyze wireless power transfer. The generalized scattering matrix of a CMS antenna can be determined solely from the radiation pattern and radiation efficiency. Therefore, the maximum power transfer efficiency of a wireless power transfer system depends on only the radiation pattern and radiation efficiency of CMS antennas. Let the antenna structures in two wireless power transfer systems be different. If the radiation pattern and radiation efficiency of the antennas in the two wireless power transfer system are identical, the maximum power transfer efficiency of the two wireless power transfer system are the same because the S-parameter of the two systems are the same. Therefore, we can change the original antenna structures to the current distributions that have the same modal transmitting pattern as the original antennas to calculate the maximum power transfer efficiency. To analyze wireless power transfer, we change the original antenna structures in layered media to simple equivalent sources. The Z-parameter between antennas can be determined from equivalent sources using the induced EMF method. From the Z-parameter, we can investigate the characteristics of wireless power transfer.

A dual-band FMCW radar for through-wall detection

In this paper, a dual-band, frequency-modulated continuous-wave (FMCW) radar for short-range through-wall detection is proposed and implemented. This radar adopts a shared-aperture antenna technique for reducing antenna area and high-speed chirping to avoid flicker noise. It operates at the S-band (3 GHz) and the X-band (9 GHz), with 486 MHz chirp bandwidth and 860 MHz chirp bandwidth, respectively. The chirp rates are 11,050 GHz/s and 22,000 GHz/s at the S- and X-bands, respectively. The radar has successfully detected a target through a wooden wall.

A simple plane wave source for the 3D-FDTD simulation of dispersive layered media

In this paper, a simple and efficient plane wave excitation method for 3-D finite-difference time-domain simulation of dispersive layered media is proposed. A 1-D auxiliary simulation and total-field/scattered-field method are used with closed boundary to introduce the plane wave. The total-field/scattered-field simulation with closed boundary makes the near-field to far-field transformation possible. Stored 1-D auxiliary simulation data file can be used in iterative simulations of same geometry without repetition of same 1-D simulations.

An FDTD formulation for communication through a plasma with a linear density profile

A finite-difference time-domain (FDTD) formulation employing an nonlinear bulk velocity of electron is studied and applied to analysis of multiple electromagnetic wave propagation in an unmagnetized and cold plasma layer with a linearly increasing electron density profile. The formulation is suitable for studying the performance of communication through plasma sheath in re-entry or hypersonic vehicle. Resonant absorption of electromagnetic wave and its angle dependency in plasma sheath are analyzed using the developed formulation. Gradient pressure of linear bulk velocity of the electron and distortion of the electron density are applied to the nonlinear correction of electromagnetic wave propagation. The nonlinear interaction of two incident waves and scattering process are investigated. Scattering wave captured at the vehicle shows that high frequency pump wave launched at the vehicle is modulated by low frequency signal wave transmitted from ground. The result is analogous to the Raman scattering process and can be applied to show the feasibility of communication through high density plasma sheath.

Matnetic tripolarizaiton antenna for DSRC applications

A magnetic tripolarization antenna is proposed for DSRC (Dedicated Short Range Communication) applications. A conventional patch antenna, which is usually used to generate the horizontal polarization, is modified to generate the perpendicular polarizations by including the ring slots. The opposite currents flowing the upper and under conductors generate loop current. For the horizontal polarization ZOR (Zeroth Order Resonance) loop antenna is included in the proposed structure. The uniform current of the ZOR loop antenna effectively generates the horizontal polarization. The simulated result shows that the proposed antenna has -10 dB impedance bandwidths from 5.85 to 5.94 GHz, which is appropriate for DSRC applications. The isolation between ports is higher than 25 dB over DSRC bandwidth. The proposed antenna has a size of 32 × 32 × 1.57 mm3.

Millimeter-wave slot array antenna using SIW and electroforming techniques

In this paper, two types of slot array antennas are introduced and summarized for millimeter-wave applications. The substrate integrated waveguide (SIW) technology is applied to design 45°-inclined series radiating slots for Ka-band. In addition, the design method has been verified by a linear and a planar slot array application. Lastly, the conventional W-band slot array antenna is fabricated using electroforming technique and the high radiation efficiency is obtained from its high fabrication accuracy.

Reconfigurable shorted patch antenna using via-hole connection control

Patch antennas that have many attractive features like low-profile, planar surface are widely used in Wireless Body Area Network applications. As the patch antenna has a ground structure behind the patch, its radiation efficiency is higher than the antennas without ground structure in on-body environment.