Compact tunable periodically LC loaded microstrip line for phase shifting applications

The properties of periodically LC loaded lines with tuneable capacitors are investigated for phase shifting applications. Basic equations are derived describing the losses due to the tuning mismatch and the quality of the tuneable material. The performance of microstrip line phase shifting devices with right- and lefthanded wave propagation is compared and evaluated in terms of a defined figure of merit. As a demonstrator, a phase shifter circuit using the principle of periodically LC reactive loading is realized with varactor diodes. The comparison with other circuit topologies confirms the idea to realize compact devices with this circuit concept.