A SIMPLE MICROSTRIP PHASE-SHIFTER

A novel, inexpensive, series-connected loaded-line (SCOLL) phase shifter has been developed for the Molonglo Observatory Synthesis Telescope. The phase shifter, which operates at 0.843 GHz, consists of a approximately 3-lambda/8 length of microstrip with series connected varactors at each end. Although designed as a binary phase shifter, the insertion phase varies almost linearly with varactor reactance, with very little gain variation for phase ranges up to 90-degrees. Thus, driven by a digital-to-analogue (D/A) converter, a SCOLL becomes a programmable phase shifter of any desired resolution. The same technique would be suitable for narrow-band low power applications in the frequency range 0.1 to 10 GHz. This paper gives the basic theory of SCOLL phase shifters, a design chart, construction details and performance data.