Jaehoon Choi

FDTD Dispersive Modeling of Human Tissues Based on Quadratic Complex Rational Function

We propose a dispersive finite-difference time domain (FDTD) suitable for the electromagnetic analysis of human tissues. The dispersion relation of biological tissues is characterized by a quadratic complex rational function (QCRF) that leads to an accurate FDTD algorithm in 400 MHz-3 GHz. QCRF coefficients are extracted by applying the complex-curve fitting technique, without initial guess. Numerical examples are used to illustrate the computational accuracy and stability of QCRF-based FDTD.

Dual-Band On-Body Repeater Antenna for In-on-On WBAN Applications

A dual-band on-body repeater antenna for in-on-on wireless body area network applications is proposed. The proposed antenna has a maximum radiation normal to the human-body surface for communication with implanted devices in the 5.8u2009GHz industrial, scientific, and medical (ISM) band. In addition, to transmit the biological information received from the implanted devices to other on-body devices, the proposed antenna was designed to have a monopole-like radiation pattern along the surface of the human body for communication in the 2.45u2009GHz ISM band. The antenna was fabricated, and its performance was measured by attaching it to a human-equivalent semisolid phantom. In addition, the human-body effect was studied to ensure antenna performance under an actual situation.

Design of a Multiband Antenna for LTE/GSM/UMTS Band Operation

This paper proposes a multiband antenna for LTE/GSM/UMTS band operation. The proposed antenna consists of a meandered planar inverted-F antenna with an additional branch line for wide bandwidth and a folded-loop antenna. The antenna provides a wide bandwidth to cover the hepta-band LTE/GSM/UMTS operation. The measured 6u2009dB return loss bandwidth is 169u2009MHz (793–962u2009MHz) at the low-frequency band and 1030 MHz (1700–2730u2009MHz) at the high-frequency band. The overall dimension of the proposed antenna is 55u2009mm × 110u2009mm × 5u2009mm.

Design of a compact low pass filter for high power RF generators

The low-pass filter (LPF) is a key component for high power RF generators generating 40.68MHz sine wave, since the LPF should reject harmonic noises and handle high input power simultaneously. We propose a novel LPF, operating at 30 kW with good skirt performance. The proposed filter is a 7th order Butterworth type and consists of four capacitors and three inductors. The capacitors and inductors are implemented by copper plates, teflon insulators and copper plates with screws, respectively. The measured values of S11, S21 and phase of the proposed LPF are 26.4 dB, 0.57 dB, and 163.5 degrees at 40.68MHz, respectively. The S21 values at 2nd (81.36MHz) and 3rd (122.04MHz) harmonics are 19.5 dB and 29.3 dB, respectively. The measured spectrum data on the surface of RF cable that is connected to the LPF output were 41.0 dBm at 40.68MHz and 78.8 dBm at 81.36MHz. The difference value of 37.8 dB is sufficient for harmonic suppression. In addition, arcing and thermal problems do not occur.

A MIMO antenna with improved isolation using RFC for LTE mobile application

Multi-input Multi-output (MIMO) antenna with improved isolation using radio frequency choke (RFC) is proposed. By using RFC, the RF signal was suppressed at the desired frequency band, to improve the isolation between the two radiating elements. The isolation between the two radiating elements is improved by approximately 20 dB at the center frequency. The fabricated antenna has a VSWR below 3 and an envelope correlation coefficient below 0.4 in the long term evolution (LTE) band 13 from 746 MHz to 787 MHz.