Wayne Kim

Implementation and Experimental Verification of Hybrid Smart-Antenna Beamforming Algorithm

In the literature (Zhang et al., and Rezk et al.), a hybrid beamforming algorithm utilizing a subset of array elements according to receive signal strength is proposed. The algorithm utilizes a smart switch which selects a subset of antennas that receive the signals with higher strength and a beamforming algorithm is performed to calculate the weights for the selected antennas. Since earlier results were based on simulations by Zhang et al., and Rezk et al., in this letter we present experimental results of testing a smart-antenna prototype with an eight-element array. This array is designed and implemented by the authors to verify the accuracy and performance of the proposed hybrid-beamforming algorithm. In general, the experimental results confirmed the simulation data. Specifically, it is shown that the proposed hybrid algorithm using a subset of the array has nearly the same performance as the adaptive system with the full array. Tradeoffs regarding beamwidth and the sidelobe levels are confirmed and additional experimental results illustrating the angle resolution of the developed system are presented

A new coplanar waveguide continuous transverse stub (CPW-CTS) antenna for wireless communications

To address the continuing demand for low-cost, light-weight and high-performance antennas, and multiband antenna arrays for wireless communications, we developed a new design of the continuous transverse stub (CTS) antenna technology. The design is based on a coplanar waveguide (CPW) feed which combines the advantages of the planar designs originally developed by Hughes Aircraft and the newer 50 /spl Omega/ coaxial version recently developed by our group . To examine the feasibility of the approach, a one-element CPW-CTS antenna is designed and a prototype is built in the frequency range of 5.2-5.6 GHz. S-Parameters and radiation pattern results shows good agreement between the simulation results and the experimental data.

Performance comparison of a novel hybrid smart antenna system versus the fully adaptive and switched beam antenna arrays

In this letter, we investigate and compare the performance of a newly proposed hybrid smart antenna system with the fully adaptive and switched beam smart antenna arrays. Simulation results show that the adaptive and the proposed hybrid systems have nearly the same performance accuracy, with the hybrid system offering faster tracking time, improved computational efficiency, and a possible reduction in the implementation cost. The comparative study also included measured radiation pattern from a recently developed coplanar waveguide continuous transverse stub (CPW-CTS) antenna.

Narrow beam adaptive array for advanced wireless applications

To help develop high performance adaptive phased array antennas, we examined the tradeoffs in implementing a hybrid approach that was described in an earlier publications [Z. Zhang et al., 2003]. Simulation results using both the LMS and CMA beamforming algorithms show that the hybrid approach described in Z. Zhang et al. (2003) actually successfully predicts DOA, but on the expense of the beam width. Narrower beam widths would require increasing number of elements and this may be possible to achieve and hence suitable for implementation in larger arrays. The performance of the hybrid beamforming approach was further simulated using measured radiation patterns from the new CPW-CTS antenna. Future extension of the proposed approach to the case of narrower beam width subarrays (single feed) in a larger CTS antenna array system is also described.

Antenna Arrays and Propagation Models for Advanced Wireless Systems

The development of advanced phased array antennas and new propagation models that address wireless applications in challenging propagation environments have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and Satellite technologies. In spite of the significant advances in these technologies, challenges continue to preclude their low cost, reliable, and high speed application in tough propagation environments including urban areas, UAVs, and other DoD applications. In this paper we describe some of the ongoing research activities at the University of Hawaii in the area of advanced wireless systems. In the antenna array design technology, two complementary antenna arrays designs will be described and the development of an ultra-wideband ground plane for foliage penetrating radars will be discussed. For the propagation modeling area, new models for characterizing indoor/outdoor transmission and for evaluating wireless coverage in urban areas taking into account the radiation patterns of the transmitting and receiving antennas will be presented. In all cases simulation results will be presented and validation with experimental observations will be included whenever available.

High performance low cost ferroelectric phase shifters designed for simple biasing

A novel approach in ferroelectric phase shifters design using Ba/sub x/Sr/sub 1-x/TiO/sub 3/ (BSTO) films in a multilayer dielectric coplanar waveguide structure is described. By including a low loss dielectric layer (SiO/sub 2/) between the coplanar waveguide conductors and the ferroelectric material in conjunction with a via to allow the signal conductors to contact the ferroelectric layer to employ biasing, significant reduction in insertion loss can be achieved in conjunction with a three fold increase in figure of merit (/dB) compared to the case with direct metallization on the ferroelectric layer.

On the feasibility of using GPR technology for the UXO detection and discrimination in the volcanic soil of Hawaii

In this paper we describe the recent results from an ongoing project at the University of Hawaii to use advanced GPR technology for the detection and discrimination of UXO in the high iron content volcanic soil of Hawaii. To help determine a suitable frequency range for detecting targets at two feet depth from the surface, a soil characterization effort has been implemented. Both the dielectric and magnetic properties of the earth soil are being measured using a unique shunt capacitance terminating a transmission line method and a recently fabricated TEM cell. Both the reflection and transmission S-parameters are being measured to determine both the complex permittivity and permeability of the soil. Furthermore, a TLS-Prony method together with FDTD 3D simulations of typical detection environments are being used to extract the complex natural resonance frequencies (CNR) of targets from the late arrival signals associated with the scattering mechanisms from these targets. A UXO testbed has been development to help experimentally validate simulation results and provide data to check and improve the accuracy of the detection/discrimination algorithm. Results from this study including dielectric and magnetic characterization of the volcanic soils, and CNR of typical UXO targets encountered in Hawaii will be presented.

Integrated Phased Antenna Array Design using Ferroelectric Materials and the Coplanar Waveguide Continuous Transverse Stub Technologies

A phased array antenna with electronic beam scanning capabilities was designed based on the integration of the multilayer ferroelectric phase shifter and the coplanar waveguide continuous transverse stub technology. A new biasing approach for the multi-dielectric layer phase shifter is proposed and simulation results demonstrated its effectiveness in biasing the tunable ferroelectric layer. A three element phased array was designed at 10 GHz and the obtained simulation results of the integrated phase shifter and CTS designs demonstrated nearly 31deg of beam scanning in conjunction with good impedance match. Efforts to develop designs that increase the beam steering capabilities are underway. Experimental verification of these simulation results for both the phase shifters and the integrated phase shifter/CTS phased array antenna design are currently being pursued

Low cost phase shifters and integrated phased antenna arrays designs based on the ferroelectric materials technology

A novel, high performance, and low cost phase shifter design is proposed and its performance has been simulated and numerically evaluated. The proposed design is based on a multi-dielectric material CPW design and the utilization of ferroelectric material for achieving the phase shifting. It is shown that, by including a low loss thin dielectric layer between the coplanar conductors and the ferroelectric materials, significant improvement in the insertion loss can be achieved (/spl sim/5 dB) and as high as three fold increase in the figure of merit (/spl deg//dB) is possible. A similar multilayer approach was implemented on a phased antenna array using continuous transverse stubs (CTS) technology to achieve low cost and high performance, including beam steering. Initial results are encouraging, particularly regarding the reduction in insertion loss, increasing the input impedance to values of practical interest, and also achieving beam steering.