Microwave synthesizer with multiple phase adjustable output

In this paper a wideband microwave synthesizer capable of generating multiple synchronized RF signals is presented. These signals are digitally phase adjustable with a sub-degree accuracy. First, the generation of phase adjustable signals using synchronized direct digital synthesizers (DDS) is described. Because this technology limits the output frequency to some hundred megahertz an architecture of phase locked loops (PLL) is developed that transforms the multiple synchronized DDS output into microwave bands. Therefore the heterodyne PLL is introduced to maintain the high phase resolution between the reference and PLL outputs. Furthermore, a hardware example that illustrates the developed architecture is presented. The phase noise of the synthesizer output is discussed and verifying measurements are shown. Finally, the excellent phase adjustment ability of the multiple RF output is demonstrated by measurements.