Hyok J. Song

Two-dimensional beam steering using an electrically tunable impedance surface

By covering a metal ground plane with a periodic surface texture, we can alter its electromagnetic properties. The impedance of this metasurface can be modeled as a parallel resonant circuit, with sheet inductance L, and sheet capacitance C. The reflection phase varies with frequency from +/spl pi/ to -/spl pi/, and crosses through 0 at the LC resonance frequency, where the surface behaves as an artificial magnetic conductor. By incorporating varactor diodes into the texture, we have built a tunable impedance surface, in which an applied bias voltage controls the resonance frequency, and the reflection phase. We can program the surface to create a tunable phase gradient, which can electronically steer a reflected beam over +/- 40/spl deg/ in two dimensions, for both polarizations. We have also found that this type of resonant surface texture can provide greater bandwidth than conventional reflectarray structures. This new electronically steerable reflector offers a low-cost alternative to a conventional phased array.

A Method for Improving the Efficiency of Transparent Film Antennas

This letter presents an optically transparent antenna, which is made of conductive AgHT coated film, with an improved efficiency by applying a highly conductive coating or metallization in the form of a very narrow strip to selective antenna areas of high current density. A measurement showed that the proposed method improved the maximum gain of a fabricated transparent antenna using the AgHT film from -5 dBi to 0 dBi at 2.2 GHz while preserving much of the optical transparency. A 3D electromagnetic model using a full-wave method of moments was developed to investigate the effect of width of the highly conductive narrow strip on the efficiency of the transparent antenna.

Single-Feed Dual-Band Stacked Patch Antenna for Orthogonal Circularly Polarized GPS and SDARS Applications

We describe a single-feed stacked patch antenna design that is capable of simultaneously receiving both right hand circularly polarized (RHCP) satellite signals within the GPS LI frequency band and left hand circularly polarized (LHCP) satellite signals within the SDARS frequency band. In addition, the design provides improved SDARS vertical linear polarization (VLP) gain for terrestrial repeater signal reception at low elevation angles as compared to a current state of the art SDARS patch antenna.

Development of Reduced Order Model for Modeling Performance of Tire Pressure Monitoring System

An electromagnetic (EM) math model of TPMS calculates the data links RF pathless profile of each four wheels that was later translated into an estimate of packet errors registered by the TPM system using a higher level system simulation tool. A reduced order model (ROM) of a vehicle structure for modeling TPMS performance was developed after investigating four vehicle models having different degree of complexity and identifying effects of various vehicle structures on the pathless profile. Pathless profile of the ROM of a CTS vehicle compared very well with that of the measurement data if variances are minimal in the RF channels between the transmitter and the receiver. The higher-level system model showed the system performance of the ROM converged to that of the measurement data.

The Impact of Vehicle Structural Components on Radiation Patterns of a Window Glass Embedded FM Antenna

The relative long wavelength of FM radio signals compared to a typical vehicle length means that a window glass-embedded FM band antenna couples strongly to vehicle structural components. Numerical simulations have been conducted to identify which key structural components in a full-size SUV have an effect on the average antenna gain patterns. In particular, it was found that the rear hatch and the seats of the SUV had a large effect on FM antenna gain patterns and thus required more careful modeling for the electromagnetic simulation. Also, it was found that the sunroof status, opened or closed, had a moderate effect on FM antenna gain patterns. Comparison with experimentally obtained FM antenna gain patterns demonstrated the importance of using the most detailed model possible when simulating patterns in the FM band.

Effects of Mutual Coupling on LTE MIMO Capacity for Monopole Array: Comparing Reverberation Chamber Tests and Drive Tests

The roof of an automobile would appear to be an ideal platform to place multiple-input-multiple-output (MIMO) antennas, having a large ground plane with plenty of space to separate antennas for optimum embedded element radiation efficiency. However, styling concerns often require that the antennas are to be placed close together. Thus, mutual coupling plays an important role in the performance of an MIMO antenna system as it affects the embedded element efficiency and the channel correlation. In this letter, we present a comparison between the measured mutual coupling effect on the ergodic channel capacity of a 2 ×2 MIMO system in a reverberation chamber (i.e., Rayleigh channel) and in a suburban outdoor environment (i.e., Rician channel) at Long Term Evolution (LTE) radio band 13. The outdoor MIMO capacity was obtained during a vehicle drive test using commercial over-the-air (OTA) LTE test equipment. All measurements were conducted with two-element monopole antennas on a 24-in-diameter circular ground plane. The impact that mutual coupling has in the degradation of the embedded element radiation efficiency and increased correlation between the antennas, and ultimately the decrease in ergodic MIMO channel capacity, is highlighted by these measurements. In addition, the results provide insight into the differences of channel capacity obtained in the rich isotropic multipath environment of a reverberation chamber and the channel capacity obtained in a real-world suburban environment.

RF Link Budget Analysis of a 315MHz Wireless Link for Automotive Tire Pressure Monitoring System

Inclusion of a Tire Pressure Monitoring System (TPMS) in a vehicle presents a new design challenge in terms of automotive electrical system integration. This paper examines the dynamic RF signal path characteristics of a TPMS data link operating at 315MHz as a short-range device Electromagnetic modeling results and anechoic chamber measurements provide signal path loss estimates for various system configurations. A qualitative link budget formulation is proposed that accounts for observed dynamic and quasi-static variation of the TPMS signal.

MEMS-based switched diversity antenna at 2.3 GHz for automotive applications

Our previous work is presented on diversity antenna experiments in the 2.3 GHz band, specifically for applications in the automotive environment. We describe the case of two-element position diversity, and we study the effects of the antenna positions on the amount of diversity gain. The presentation consists primarily of measurement data on a moving vehicle, with software post-processing to determine the effects of diversity combining. We present several diversity combining schemes, and describe a switched diversity circuit that we have built to address one of these schemes. An in-house developed SPDT MEMS switch, which has desirable insertion loss and isolation characteristics for the diversity switch, is shown. Also, a discussion on using a switch for the switched diversity antenna is included.

Modeling effect of lightning induced EMP on wire harness in automobiles

A MoM-based EM code was applied to model the electromagnetic fields coupled to a vehicle by nearby lightning return strokes. The return stroke model was applied to investigate the effect of the lightning induced electromagnetic fields on an automobile wiring harness; the effect generates high peak current electromagnetic pulse (EMP) and potential EMI/EMC concerns regarding electrical and electronics (E/E) components. The frequency content of the lightning induced current pulse on the wire cable harness was also analyzed by fast Fourier transform (FFT).

Evaluation of vehicle-level MIMO antennas: Capacity, total embedded efficiency, and envelope correlation

The paper describes an approach to estimate 2×2 MIMO channel capacity of a shark-fin radome antenna designed for multiple LTE bands by using channel matrices measured from drive tests in a real driving environment with a commercially available LTE radio network analyzer. The nonproduction shark-fin radome antenna that is mounted on the roof of a sedan is treated as a black box, and the estimated channel capacity is compared with that of a reference MIMO antenna consisting of identical monopoles tuned at 750 MHz. The two element λ/4 monopole array was also measured in a rich isotropic multipath environment at a reverberation chamber so that it can be used as a reference with known channel capacity. Total embedded efficiency and envelope correlation derived from measured s-parameters for the black box and the reference antennas are presented and discussed. The results show that the channel capacity depends on both the embedded efficiency and the correlation, and the approach estimating the MIMO throughput based on the channel matrices measured from the drive tests is shown to be useful to evaluate multiple MIMO antennas in a real driving environment.