Youngju Lee

Study and prototyping of practically large-scale mmWave antenna systems for 5G cellular devices

This article discusses the challenges, benefits and approaches associated with realizing largescale antenna arrays at mmWave frequency bands for future 5G cellular devices. Key design considerations are investigated to deduce a novel and practical phased array antenna solution operating at 28 GHz with near spherical coverage. The approach is further evolved into a first-of- a-kind cellular phone prototype equipped with mmWave 5G antenna arrays consisting of a total of 32 low-profile antenna elements. Indoor measurements are carried out using the presented prototype to characterize the proposed mmWave antenna system using 16-QAM modulated signals with 27.925 GHz carrier frequency. The biological implications due to the absorbed electromagnetic waves when using mmWave cellular devices are studied and compared in detail with those of 3/4G cellular devices.

Design and analysis of a low-profile 28 GHz beam steering antenna solution for Future 5G cellular applications

A first-of-the-kind 28 GHz antenna solution for the upcoming 5G cellular communication is presented in detail. Extensive measurements and simulations ascertain the proposed 28 GHz antenna solution to be highly effective for cellular handsets operating in realistic propagating environments.

A novel dual-slope mm-Wave channel model based on 3D ray-tracing in urban environments

To solve mobile traffic crunch, the usage of enormous bandwidth in millimeter wave (mm-Wave) is under discussion. In this paper, we investigate radio channel characteristics of mm-Wave frequency in the downtown area of Ottawa using 3D ray-tracing technique. In the results, important parameters of the radio channel model, such as path loss exponent, shadow fading, delay spread and angle spread, are provided. Especially, in case of path loss model in non-line of sight, a novel dual-slope approach is proposed for two conventional deployment scenarios. Comparing to traditional single-slope path loss model, the proposed method has smaller RMS errors in terms of local mean of path loss observations. We believe that the proposed method is appropriate to evaluate performance of the mm-Wave system in dense urban environments.

First Commissioning Results of the KSTAR Cryogenic System

The cryogenic system for the KSTAR superconducting (SC) magnets has been commissioned. It consists of a cold box, distribution boxes (DB) and cryogenic transfer lines. The cold box and DB #1 provide 600 g/s of supercritical helium to cool the SC magnets, their SC bus-lines, and the magnet support structures. It also provides 17.5 g/s of liquid helium to the current leads and supplies cold helium flow to the thermal shields. The main duties of the DB #2 are the relative distribution of the cryogenic helium among the cooling channels of each KSTAR cold component and the emergency release of over-pressurized helium during abnormal events such as quenches of the SC magnets. After individual commissioning, the system was integrated and cooled down with the KSTAR device. In this paper, the construction and commissioning results of the KSTAR cryogenic system will be introduced. In addition, we will present the cool-down results of the KSTAR device.

Construction and Commissioning of the KSTAR Current Feeder System

The function of the current feeder system (CFS) is for conducting large currents from the power supplies to the KSTAR superconducting (SC) magnets. The CFS consists of SC bus-lines, joints, and current leads. The bus-line conductor is a circular cable-in-conduit conductor (CICC), which consists of a 4.5 mm thick stainless steel 316L seamless pipe containing 324 strands of chrome coated NbTi superconductor and 243 strands of OFHC. The ends of the CICC are assembled with specially designed lap joints. The joining resistance is controlled to less than 2.5 nano-ohm to minimize Joule heating. The outer surfaces of the CICC were electrically insulated up to 15 kV with jackets made of Kapton film and prepreged E-glass tape. Helically wrapped conducting fiber was used to measure the voltages of bus-line quenches. Two pairs of prototype brass leads for poloidal field (PF) and toroidal field (TF) coils have been fabricated and tested up to the currents of 26 kA for the PF leads and 35 kA for the TF leads. The test results satisfied all the requirements so that all 18 leads were manufactured and assembled on site. This paper will describe the detailed manufacturing progress and commissioning results of the KSTAR CFS.

Construction and Commissioning of the KSTAR Helium Distribution System

The KSTAR components requiring cryogenic helium coolant for superconducting magnet operations are connected to the helium refrigeration system (HRS) through the helium distribution system (HDS), the final helium distribution station. Twenty eight cryogenic valves including 4 quench protecting valves, many sensors such as temperature sensors, pressure transmitters, and flowmeters are mounted on the system. The HDS has to control the 4.5 K supercritical helium (600 g/s) for 30 superconducting coils and their superconducting bus-lines, 55 K helium (270 g/s) pressurized to 18 bars for the thermal shields and the gravity supports, and a maximum 17.5 g/s of liquid helium for 18 current leads, provided from the HRS which has a 4.5 K equivalent cooling power of 9 kW. The helium distribution system consists of a helium distribution box (DB), 5 helium transfer lines, a PLC based helium control system (HCS), etc. The helium control system is connected to the KSTAR supervisory control & interlock system. The detailed status regarding the construction, commissioning during first cool-down, and the instrumentation & control (I&C) system are included in this paper.

Performance improvement methodology of isolation in a dual-standby mobile phone by optimizing antenna topology and position

The mutual coupling between two internal antennas using same communication band in simplified dual-standby simulation model has been researched. Furthermore, the excited current distributions on the PCB and the electric field distributions in the near field have been investigated as the cause of coupling. In terms of antenna type, PIFA type antenna was better than monopole type in the isolation viewpoint in dual-standby phone (max. 8~9 dB). Also, in terms of feed position, position 1 and 4 was the best through all positions which can be combined from 6 feed positions of Fig. 1. The coupling difference between min. and max. was 4.5 dB in monopole, 10.8 dB in PIFA. The results will be used to guidelines in the initial stage of phone design for achieving new specifications with respect to isolation of dual-standby phone.

PCB-Embedded Antenna for 80 GHz Chip-to-Chip Communication

We propose a printed circuit board (PCB)-embedded antenna for millimeter-wave chip-to-chip communication. The antenna is 0.18 mm in height which is 1/20 wavelength at 80 GHz. In order to realize such a low profile, a zeroth-order resonator antenna with a periodic array of four unit cells is employed, and its geometry is optimized to cover an 8-GHz bandwidth from 76 to 84 GHz. With this, the antenna is capable of radiating in a direction parallel to the board length despite the short distance between the ground and the radiator. Simulation and measurement results show that the optimized design has low reflection coefficients and consistent radiation patterns throughout the target bandwidth.

Multi-polarized antenna array configuration for mmWave 5G mobile terminals

Novel antenna design technologies are devised at 28 GHz to realize vertical and horizontal polarizations and its combined radiation characteristics using ultra-thin printed circuit board (PCB) substrates. Details of the design methodologies, simulation and measurement results are presented and discussed in relation to the targeted mmWave 5G mobile application.

Design and testing of a millimeter-wave beam-steering mesh-grid array for 5 th generation (5G) mobile communication handset devices

Summary form only given. The steady advancement of silicon and compound semiconductor technologies has triggered the possibility of utilizing millimeter-wave frequencies for next-generation cellular data networks (“5G”). In comparison to 4G networks, the millimeter-wave 5G network offers significant advantage in data throughput due to the much wider RF bandwidth. Recent publications by other authors in (T.S. Rappaport, Y. Qiao, J.I. Tamir, J.N. Murdock, and E. Ben-Dor, Radio and Wireless Symposium, 2012, IEEE, pp. 151-154) have successfully demonstrated the possibility of a millimeter-wave cellular network by characterizing the propagation and angle-of-arrival for an adaptive beam-steering system operating at 38 GHz with full consideration of obstructions by foliage and other structures. However, the advent of an affordable, low-profile beam steering antenna remains one of the most critical issues for future 5G devices. Deployment of a beam-steering antenna array within a cellular handset device is unprecedented in the wireless community. This paper presents a first-of-the-kind phased-array which is specifically conceived for future millimeter-wave 5G cellular networks. The technical challenges associated with the inherent properties of the utilized 28 GHz frequency band and the real-life design constraints in the consumer electronics industry are identified and addressed. The well-understood laser and mechanical via structure within a high-volume printed circuit board technology is used to devise a novel mesh-grid patch antenna element topology. The presented mesh-grid patch features a fan-beam radiation characteristic with a o measured 3dB elevation beamwidth of more than 130 . The required horizontal 2 footprint is less than 3 x 1 mm which is smaller by several factors compared to a conventional Yagi-Uda or a planar dipole topology. Furthermore, the proposed antenna element does not require a ground fill-cut region, greatly alleviating the space constraints when integrating within a cellular handset device. The antenna element is further expanded into a beam-steering phased array configuration and integrated within a cellular handset prototype. The far-field radiation patterns of the mesh-grid array are first measured independently in the anechoic chamber and the procedure is subsequently repeated after integration with the 28 GHz RF transceiver unit. The maximum scanning angles for both measurements are controlled by adjusting the phase configurations of each antenna elements within the array. Measurements confirm the 28 GHz mesh-grid array exhibits a o maximum boresight gain of more than 10.5 dBi and ±170 scanning range in the azimuthal plane despite the degradations incurred due to the cellular handset chassis.