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A monolithic digital phase shifter with novel means of precise phase adjustment has been developed. A conventional switched low-pass/high-pass filter structure has been modified for precision phase control. For very fine phase adjustments, in the order of a few degrees, the adjustment is obtained by allowing a relatively small variable signal through the "off' channel and adding it vectorially to the main signal. Tests on a sizeable lot confirmed the feasibility of this approach in dealing with process variations.

Various parameters of a phase-locked upconverter for a digital SCPC satellite terminal application have been investigated. Voice tests, BER tests and spectral measurements, using constant envelope QPSK modulation have been carried out. It is shown that constant envelope modulation has ideal characteristics for this type of upconverter. A spurious mode-locking mechanism has also been investigated and a means of preventing it has been devised and tested.

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