Analysis and Optimization of Thin Film Ferroelectric Phase Shifters
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Microwave phase shifters have been fabricated from (YBa 2 Cu3 07 48 or Au)/SrTiO 3 and Au/Ba.Srl.-TiO 3 films on LaAIO 3 and MgO substrates. These coupled microstrip devices rival the performance of their semiconductor counterparts at Ku- and K-band frequencies. Typical
insertion loss for room temperature ferroelectric phase shifters at K-band is ;5 dB. An experimental and theoretical investigation of these novel devices explains the role of the ferroelectric film in overall device performance. A roadmap to the development of a 3 dB insertion loss phase shifter that would enable a new type of phased array antenna is discussed. INTRODUCTION Evolving high data rate communications systems demand greater attention to subtle aspects of information theory and electromagnetic engineering. As the ratio of signaling bandwidth to carrier frequency decreases, less familiar phenomenon enter into system performance. And, new coding techniques are pushing channel capacity ever closer to the Shannon limit [1]. Some of these effects are expected to become quite pronounced if the trend toward wide-band scanning phased array antennas and efficient high-speed modulators continues [2]. For example, in a phased array antenna inter-element spacing, the physical size of the array, and the steering vector can conspire to introduce pulse distortion from group delay, inter-symbol interference, and beam squinting [3,4]. And the operating point of the amplifiers can affect the bit error rate depending on the modulation type and the number of carriers. Naturally one wants the phased array to operate as efficiently as possible given power limitations and thermal management problems. This desire necessitates that the power amplifiers operate in a nonlinear region near saturation. Nonlinear effects cause amplitude-to-amplitude modulation (AM/AM) and amplitudeto-phase modulation (AM/PM) distortion. The net effect of AMIAM distortion is to alternately compress and expand the signal constellation. The net effect of AM/PM conversion is a rotation of the signal constellation [3]. In a receive array, the third order intercept of the low noise amplifiers largely determines inter-modulation distortion and heat dissipation [5]. Phase shifters typically follow low noise amplifiers in a receive array and precede power amplifiers in a transmit array. Since the phase shifter's insertion loss depends on its phase setting and since its switching action represents some finite time domain response, its potential contribution to bit error rate degradation cannot generally be ignored. There will always be some effects in any phase shift keyed (PSK) modulation system, to what degree depends on the steering vector update rate and data rate. In 1963 Berry introduced a new class of antennas that utilized an array of elementary antennas as a reflecting surface [6]. The "reflectarray" has the potential to combine the best attributes of a gimbaled parabolic reflector, low cost and high efficiency, and a direct radiating 3 Mat. Res. Soc. Symp. Proc. Vol. 603 © 2000 Materi
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