Coupled Microstrip Line Ferroelectric Phase Shifter for Ka-Band Phased Array Antenna

Abstract

This work presents the design, fabrication and microwave performance of coupled microstrip line phase shifter (CMPS) based on (Ba,Sr)TiO₃ (BST) thin films for Ka-band phased array antenna. Ferroelectric BST thin films were deposited on MgO single crystal substrates by pulsed laser deposition. Because this CMPS design can bear the high dielectric constant of ferroelectric thin films at Ka-band, it has many advantages like the high tunability and the low loss. This design is proposed as a component in low-cost beam scanning phased array antennas. Though methods for calculating the characteristics of coupled line are well known, coupled line on the ferroelectric thin film is difficult to analyze because of the high dielectric constant and very thin thickness with respect to that of MgO substrate. So the coupled line on ferroelectric thin films was analyzed here simply using even and odd mode propagation concepts of coupled line by full-wave electromagnetic simulation. The measured results were in good agreement with the simulated results at the frequencies of interest. The measured differential phase shift based on BST thin films was 45° and the insertion loss decreased from −5.7 dB to −3.6 dB with increasing the bias voltage from 0 to 200 V at 30 GHz.

Keywords:

• Ferroelectric thin films
• coupled microstrip line phase shifter
• even impedance
• odd impedance
• phase velocity
• phased array antenna

ACKNOWLEDGEMENTS

The authors would like to thank Dr. W. J. Kim for useful advice. This work was supported by the Minister of Information and Communications Department of Korea.