Dong-Hyuk Choi

A Tunable Antenna for DVB-H Applications

A novel wideband built-in antenna with resonance frequency variability for digital video broadcasting-handheld (DVB-H) is proposed. The tunable antenna consists of two channel matching networks and a spiral-shaped monopole type radiator. Based on the matching networks combined with the switches, wide bandwidth and good radiation gains are obtained. As a demonstration, a wideband tunable antenna is designed and measured. The proposed antenna has an approximately omnidirectional radiation pattern and its peak gain is 3 dB greater than the required antenna gain covering DVB-H band. These features are suitable for DVB-H applications.

A varactor-tuned active-integrated antenna using slot antenna

A varactor-tuned active antenna which consists of a series feedback voltage-controlled oscillator (VCO) and a well matched slot antenna is proposed. The fabricated antenna shows stable oscillation at 5.8 GHz band, and the frequency varied from 5.73 to 5.97 GHz, with less than 1.28 dB of amplitude deviation over the frequency range. Since the fabricated active antenna is a simple structure where the operating frequency can be easily tuned through the varactor diode, it may be used as an element in phase-shifterless beam scanning systems. In addition, a capacitor for dc blocking is not necessary due to isolation between the active and radiating element.

Dual-band and dual-polarization patch antenna with high isolation characteristic

A patch antenna with dual-band and dual-polarization operation is proposed and discussed. For feeding the antenna, it is used the electromagnetically coupled microstrip-T junction and coplanar waveguide (CPW)-line. Since both ports of the antenna are electromagnetically coupled, the proposed antenna eliminates the need for capacitors in the RF path for active antenna applications. By using CPW resonant cell, the demonstrated approach results in a significant improvement in port isolation.

A broadband T-shaped microstrip-line-fed slot antenna with harmonic suppression

In this paper, a slot antenna is proposed to achieve both harmonic suppression and wide bandwidth. To obtain these results, a T-shaped microstrip-line-fed slot antenna and U-shaped conductor line connected with the ground plane are applied. At the fundamental and harmonic frequencies, return loss and radiation characteristics are measured and compared with those of the conventional slot antenna. For the proposed antenna, the 10-dB return loss bandwidth could reach 1220 MHz (1730-2950 MHz), which is about 52% with respect to the center frequency of 2340 MHz, and it is observed that the second and third harmonics of the proposed antenna is effectively suppressed.

FDTD analysis of bow-tie antenna by incorporating approximated static field solutions

In this letter, finite-difference time-domain analysis of the bow-tie antenna, including a feeding point, was studied by incorporating an approximated static field solution without additional computation time. By reformulating the static field solution in the rotated coordinate system, we can easily calculate the correction factors and obtain the result that shows a remarkable agreement with the method of moments result in spite of relatively coarse meshes.

A new beam-steering technique using nonreciprocal periphery manipulation

This paper describes new phase-shifterless beam steering techniques which exploit the synchronization properties of coupled nonlinear oscillator arrays. In each, the control parameters are the coupling phases of the local interactions between elements. The one-dimensional oscillator arrays under consideration are described by Phase Model- type equations, implying the assumption that the amplitude dynamics have achieved a steady state. Linear stability analyzes for each technique are provided which reveal significant differences in attainable scan angles.

Varactor-tuned active integrated antenna using slot antenna

A varactor-tuned active integrated antenna which is consisted of a series feedback voltage-controlled oscillator (VCO) and a matched slot antenna is proposed. The fabricated antenna has a stable oscillation at 5.8 GHz band, and the frequency varies form 5.73 GHz to 5.97 GHz, with less than 1.28 dB of amplitude deviation over the frequency range.

Wireless vital signal detection systems and its applications at 1.9GHz and 10GHz [biomedical applications]

A wireless vital signal detection system, which is analogous to Doppler radar, can measure respiration and heart rates with periodic movement of skin and muscle near the heart. The detection system consists of antenna, RF transceiver (transmitter and receiver), and baseband section. In this paper, the link budget of the detecting system is analyzed and the signal detected from the system is compared with the electrocardiogram (ECG) signal of a monitor which is used for patient monitoring in a hospital. Then, the detection of vital signs is also performed according to various environments, such as different distances and behind a wall.