Jung-Hwan Choi

Quad-Band MIMO Antenna Array for Portable Wireless Communications Terminals

A low-profile quad-band antenna array for multiple-input-multiple-output (MIMO)-enabled wireless communication terminals has been presented in this letter. The proposed dual-element antenna array operates at the following frequency bands: 2.4-2.5 GHz, 3.4-3.6 GHz, 5.15-5.35 GHz, and 5.75-5.875 GHz. A combination of a C-shaped slot and a T-shaped slit is used to excite three current modes in a conventional single-band planar inverted-F antenna (PIFA). A lambda/4 resonator is integrated into the triband antenna structure in order to get an additional resonance for quad-band operation. The proposed array has been designed over a small ground plane measuring 50times100 mm2, whereas each element in the array occupies a volume of 0.63 cm3. Mean effective gain (MEG) and envelop correlation analysis have been used for the array analysis in addition to the capacity and diversity gain measurements in a reverberation chamber. The prototype array exhibits quite low mutual coupling with good input return losses at the desired four frequency bands.

Measurement of the modulated scattering microwave fields using dual-phase lock-in amplifier

A new automatic measurement architecture is proposed for the simultaneous measurement of the amplitude and phase of microwave fields with optically modulated scatterer. The modulated scattering techniques have been popularly used for rapid electric field measurement without scarifying the acceptable level of accuracy. However, the conventional system for measurement of the modulated scattering fields has an unstable measurement ability and a measurement limitation in terms of a wide band frequency range due to the imperfection of in-phase and quadrature phase operation of the coupler. In this letter, we propose an improved measurement system using two signal generators. The measurement results of the proposed system are compared with those of the conventional system to demonstrate the superior performance with the phase prediction result in the near and far-field range and to validate the performance of the proposed system.

Optoelectronic and microwave transmission characteristics of indium solder bumps for low-temperature flip-chip applications

This paper describes low-temperature flip-chip bonding for both optical interconnect and microwave applications. Vertical-cavity surface-emitting laser (VCSEL) arrays were flip-chip bonded onto a fused silica substrate to investigate the optoelectronic characteristics. To achieve low-temperature flip-chip bonding, indium solder bumps were used, which had a low melting temperature of 156.7degC. The current-voltage (I-V) and light-current (L-I) characteristics of the flip-chip bonded VCSEL arrays were improved by Ag coating on the indium bump. The I-V and L-I curves indicate that optical and electrical performances of Ag-coated indium bumps are superior to those of uncoated indium solder bumps. The microwave characteristics of the solder bumps were investigated by using a flip-chip-bonded coplanar waveguide (CPW) structure and by measuring the scattering parameter with an on-wafer probe station for the frequency range up to 40 GHz. The indium solder bumps, either with or without the Ag coating, provided good microwave characteristics and retained the original characteristic of the CPW signal lines without degradation of the insertion and return losses by the solder bumps

Generation of Rayleigh/Rician Fading Channels With Variable RMS Delay by Changing Boundary Conditions of the Reverberation Chamber

This letter presents the properties of the generated Rayleigh/Rician fading channels in the reverberation chamber (RC) experimentally. Radio propagation channels that undergo multipath fading phenomena can be characterized by power delay profiles (PDPs), delay spreads, and statistical distributions of the received power. The RC under the conventional configuration for electromagnetic compatibility/electromagnetic interference (EMC/EMI) evaluations has Rayleigh distribution because there are no direct paths between the TX and RX antennas. Most of the transmitted signals arrive at the RX part through multiple reflection paths. By changing the boundary conditions and the position of the TX antenna, Rayleigh/Rician fading channels with variable root-mean-square (RMS) delay spread can be generated in the RC considering K-factor simultaneously.

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.

Exact Evaluation of Channel Capacity Difference of MIMO Handset Antenna Arrays

This letter presents the exact evaluation of the channel capacity difference of different 2 × 2 multiple-input-multiple-output (MIMO) handset antenna configurations. In order to investigate the performance enhancement of a MIMO antenna system, the channel capacity is estimated in a reverberation chamber with the normalized channel matrix measured using a network analyzer under the conventional configuration for electromagnetic compatibility/electromagnetic interference (EMC/EMI) evaluations. However, performance comparison of different antenna configurations at the same signal-to-noise ratio (SNR) is not an exact evaluation in the same propagation environment because the received power is obviously different. We propose the evaluation method for exact performance comparisons and drive the exact representation of the channel capacity difference of MIMO handset antenna arrays in a reverberation chamber. The estimated results using the proposed method are compared to the channel capacity evaluated at the same SNR for validation.

3D Spherical Antenna Measurement System for CTIA OTA Testing and Characterizing of Mobile MIMO Terminals

This paper describes the 3D spherical antenna measurement system for a passive antenna measurement, CTIA (Cellular Telecommunications & Internet Association) OTA (Over The Air) testing and characterizing of mobile MIMO (Multiple-Input Multiple-Output) terminals. The measurements of the monopole box are performed for the calibration of the proposed measurement system. Finally, the proposed system is able to measure the experimental model of MIMO terminal with adapting the diversity antenna system.

A non-uniform one-arm spiral antenna for WBAN communication

This paper presents a non-uniform one-arm spiral antenna. The proposed antenna can be easily placed in the implant device for WBAN communication because of the compact size (Diameter: 10mm, Height: 1.035mm). The electrical length of the proposed antenna is obtained by adjusting the rate of expansion in a limited space. The characteristics of the proposed antenna have been investigated in the fluid considering the electrical property of human body. The bandwidth is 112MHz (206∼318MHz) and the measured maximum gain is −12.404dBi at 310MHz.

Source location estimation using phaseless measurements with the modulated scattering technique for indoor wireless environments

This paper proposes the source location estimation technique with the modulated scattering technique (MST) for indoor wireless environments. The uniform circular scatterer array (UCSA) that consist of flve optically modulated scatterers as array elements and a dipole antenna at the center of the UCSA is employed for estimating a source location from the impinging signal. In contrast with a conventional uniform circular array (UCA), the proposed method using the MST needs only one RF path. Also, the plane-wave assumption of the impinging signal is not necessary for an array signal processing because the proposed method is based on a phaseless measurement. Therefore, the proposed method can be applied in short-range LOS and NLOS environments that the plane-wave signal cannot be formed. A source location is estimated by using a simple estimation algorithm based on the power difierence of the scattering signals modulated by two scatterers on the UCSA. The power difierence is caused by difierent propagation loss between a source and each scatterer. The performance of the proposed method is demonstrated by measuring the angles of the incoming signals in the anechoic chamber and by comparing the estimated angles with the simulated results.

Doppler Spread Spectrum of a Circularly Moving Receiver in an Anechoic and a Reverberation Chamber

The Doppler phenomena caused by a moving receiver or environmental scatters around a receiver were emulated in an AC (Anechoic Chamber) and a RC (Reverberation Chamber) using platform and mode stirring. In order to verify the emulated Doppler spread spectrum, the measured results in the AC and the RC were investigated by incorporating Jakess and 802.11 TGn Doppler models, respectively.