Yun-Taek Im

3D Polarized Channel Modeling and Performance Comparison of MIMO Antenna Configurations With Different Polarizations

We propose a three-dimensional (3D) polarized MIMO channel model, which takes into account 3D power angular spectrum and comprehensive propagation characteristics of electromagnetic waves excited by polarized antennas. Based on the model, we derive a close form expression of the spatial correlation as a function of the physical parameters representing both characteristics of arbitrary antennas and propagation environment in 3D space. The spatial correlation expression allows to use the Von Mises Fisher (VMF) distribution, resulting in a more accurate and general channel model. Through simulation, we evaluate and compare performance, in terms of the spatial correlation and capacity, of 2 × 2 MIMO configurations with different polarizations, i.e., V/V, V/H, and slanted ±45° polarizations, as a function of critical input parameters including elevation angle, antenna orientation, antenna spacing, cross-polarization discrimination (XPD), and signal-to-noise ratio (SNR). The effect of the parameters on the performance is analyzed, and verified in certain cases through the literature.

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 T-Shaped Wide-Slot Harmonic Suppression Antenna

This paper proposes a T-shaped wide-slot harmonic suppression antenna at 4 GHz. Harmonic suppression is achieved by using a narrow microstrip-line-fed and a grounded T-shaped conductor line. The return losses and radiation patterns of the antenna at the fundamental and harmonic frequencies are measured and compared to those of the conventional T-shaped slot antenna. Equivalent circuit models are also presented to give physical insight into harmonic suppression mechanism.

A Two Sweeping VCO Source for Heterodyne FMCW Radar

We propose and develop a heterodyne frequency modulated continuous wave (FMCW) radar system. The system operates at 14 GHz with a 500-MHz bandwidth in a 100-μs sweeping period, based on two wideband linear RF voltage-controlled oscillator (VCO) sweeping sources, which are controlled by a direct digital synthesizer (DDS) through a phase-locked scheme, leading to a high linearity of the frequency chirping signal. To achieve low phase noise, the RF signals are synthesized from low-noise baseband signals which are generated through a generation scheme of using phase-locked oscillators operating in the 800-MHz frequency range. Additionally, the proposed architecture can eliminate the phase noise contributions and/or frequency deviation due to the uncorrelation of different VCOs. The results are verified through measurements and derivation.

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.

Slow Modulation Behavior of the FMCW Radar for Wireless Channel Sounding Technology

A frequency-modulated continuous wave (FMCW) radar is used to sounding wireless channel. An intermediate frequency signal of the FMCW radar can be treated simultaneously as a frequency-domain signal as well as a time-domain signal when the modulation time is sufficiently long. This distinctive compatibility enables the FMCW radar system to measure the normalized impulse response for the power delay profile and Rician K-factor by using an oscilloscope. This theory is fully demonstrated and experiments are performed in the reverberation chamber for the small-scale fading environments of Rayleigh and Rician conditions, and all measurements are verified by using the oscilloscope.

Design of a Planar Slotted Waveguide Array Antenna for X-band Radar Applications

A planar slotted waveguide array antenna has been designed at 9.37 GHz for X-band radar applications. The antenna consists of multiple branchline waveguides with broadwall radiating shunt slots and a main waveguide to feed the branch waveguides through a series of inclined coupling slots. The antenna feed point is located at the center of the main waveguide. Element weights in the array have been calculated bysampling a continuous circular Taylor aperture distribution at the 25 dB sidelobe level in both the E and Hplanes. A commercially available electromagnetic (EM) simulation tool has been used to characterize the individual isolated slot and that data hassubsequently been used to design the planar array. The array is finally analyzed in a CST Microwave studio and the measured and simulated results have been found to be in good agreement.

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.