Development of voltage tunable ferroelectric coplanar phase shifters for low cost high performance phased array antennas with beam steering capabilities

In this paper we developed a ferroelectric CPW phase shifters which will be integrated with wideband CTS antenna array. For fabrication of the ferroelectric CPW, the vacuum sputter has been used with a optimized sputtering parameters. The experimental RF performances of the developed phase shifters were compared with those from simulations using WIPL-D software. The results showed that while the approach of using thin Ferroelectric films may be successful in designing low cost tunable coplanar waveguide phase shifters, the amount of achievable phase shifts are small (less that 10°) unless Ferroelectric compatable substrates such as STO are used (phase shifts are 27°). Good agreement was also observed between simulations and measured results and this provides high confidence in the developed fabrication process‥ While our group has been successful in fabricating thin film ferroelectric phase shifter, work is still underway to help develop multilayer ferroelectric phase shifters as well as on the development of an integrated CTS and ferroelectric phased antenna array. As a next step, our group is now pursuing fabrication of a ferroelectric multilayer CPW integrated with the CTS antenna array.

Introduction

Low cost and high performance steerable antennas have been a critically important and challenging topic in satellite communication, radar, navigation, remote sensing, and space exploration. Our group has been working on developing a high performance low cost antenna array using integrated Continuous Transverse Stub (CTS) and Ferroelectric material technologies. Tasks included the design of a CTS antenna array in the Ka-Band with bandwidth of over 1GHz, simulation of the beam steering capability of an integrated CTS array with ferroelectric phase shifters placed between the antenna array elements, the fabrication and characterization of multi-dielectric layers ferroelectric phase shifters, and the possible evaluation of the complete integrated antenna array design. Accomplished tasks include a successful design of the Ka-band CTS antenna array with over 1 GHz bandwidth [1], [2], conducting a comparative study between the multi- and single- layer coplanar waveguide ferroelectric phase shifters design [3], [4], the simulation of the integrated CTS antenna array performance with multi-dielectric layer ferroelectric phase shifters [5], and the more recent successful fabrication and characterization of ferroelectric phase shifters. The numerical studies showed that while the integrated CTS and ferroelectric materials approach is feasible, inclusion of thicker layer of ferroelectric material will be required to achieve beam steering more than . To avoid the use of thicker ferroelectric layers and the corresponding need for a larger DC bias voltage, an approach in which analog phase shifting would be accomplished using this technology while larger phase shifts would be achieved using available digital technologies. It is believed that this combined analog (small beam steering angles) and digital (large steering angles) would lead to optimum phased antenna array designs with performance, cost, and required DC bias voltage all taken into consideration. As the results of the antenna array design and the simulated performance of the integrated CTS and ferroelectric antenna array are available in articles published by our group [5], focus in this paper is placed on the fabrication and characterization aspect of the ferroelectric phase shifters. In this paper, we describe the results of our effort in fabricating the ferroelectric coplanar phase shifters on three different substrates using a vacuum sputter system. We further characterize the resulting phase shift performances as a function of frequency and with different values of bias voltages. This paper also describes the fabrication procedures of ferroelectric phase shifters and discusses the characterization methods of the fabricated devices. Measurement data are presented and compared with simulated results for verification.