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ADF4118 - simultaneous use of multiple synthesizers

Question asked by gdmt on Nov 28, 2017

dear community,

i'm designing a multiple synthesizers solution based on ADF4118.


i'm currently using two EVAL-411xEBZ1 working at 2453MHz and i connected their output either to a couple of patch antenna spaced at lambda/2 or to a 2-way passive combiner.


the problem is that the two synthesizers are not locked for any phase relationship among the two outputs (see attachments. one is perfectly locked combined outputs, the other two are not working phase condition with two different frequency spans). maybe it could be a problem of injection locking/pulling?


if i add some attenuators to the PLL outputs (e.g. -30dB) they always work, and this seems to confirm that it is something related to the insulation among the outputs.


what is the right design choice to implement simultaneous use of multiple synthesizers? improving the insulation through a buffer at each output or changing the design to add a buffer solution inside the loop instead of the 2-way passive splitter between VCO, PLL IC and output?


i found a buffer device from another vendor that seems to be the right choice for this (they offer a one input - one buffered output solution OR a one input - two buffered output solution to implement the two above topologies) ... maybe ADI has its own solution too?


thank you