Jee-Hoon Lee

A Spiral-Dipole Antenna for MIMO Systems

A new circular polarization spiral-dipole antenna has been proposed for multilple-input-multiple-output (MIMO) systems. A dipole antenna is loaded with spirals at both of its ends to generate omnidirectional left-hand or right-hand circular polarization. The sense of polarization [left-hand circular polarization (LHCP) or right-hand circular polarization (RHCP)] depends on the orientation of the spirals. The measured bandwidth of the antenna is 8% at the center frequency of 5.2 GHz with 3.6-dBic gain. The isolation ( S 21) between collocated LHCP and RHCP antennas is better than 30 dB that makes them suitable for MIMO.

Characterizing the Impact of Moving Mode-Stirrers on the Doppler Spread Spectrum in a Reverberation Chamber

A moving mode-stirrer in a reverberation chamber (RC) not only changes the field distributions within the reverberation chamber, but also causes a Doppler effect. In this letter, the Doppler spread spectrum of a received signal in a reverberation chamber is characterized according to the radius and rotational velocity of the mode-stirrers and TX antenna positions.

Noninvasive Biosignal Detection Radar System Using Circular Polarization

This paper proposes an integrated hypersensitive Doppler radar system through a circular polarization characteristic. Through the idea of a reverse sense of rotation when the reflecting surface is perfectly conducting, it is shown that the detecting property of the system can be effectively improved by using antennas that have a reverse polarization. This bistatic radar system can be used in noninvasively sensing biosignals such as respiration and heart rates with the periodic movement of skin and muscle near the heart. The operating frequency of the system is in the X-band and the radar size is 95 times 50 times 13 mm3.

A DDS and PLL-based X-band FMCW radar system

A DDS and PLL-based FMCW range meter system is described. The DDS is used as a reference clock of a linearly frequency modulated signal source, and the PLL is controlled by it. The bandwidth and the sweep time of the FMCW radar system are 150 MHz, and 270 us. Zero-padding and spectral centroid processing techniques are used to measure a target range, and the range resolution is less than 0.25 m.

Doppler radar sensing system of respiration and heart rate

In this paper, Doppler radar system is designed, which is composed of oscillator, mixer, LNA, and antennas. The idea of this paper is using reverse circular polarization for bio-detection Doppler radar to selectively receive signals reflected from highly conductive body surfaces. To improve isolation property between transmitter and receiver, we use the bistatic system using LHCP and RHCP antennas. The budget of system is analyzed and the experimental results are discussed.