Kate borrowed this statement bracelet (worn on her right wrist) from Queen Elizabeth II for the October 2015 state banquet.
This was originally a choker necklace worn by Queen Mary (Queen Elizabeth II’s grandmother).
Here is the closeup of the bracelet:
You can see that the design of the choker remains in the bracelet. It appears that the bars of diamonds have been placed closer together, but the linear pattern is mostly unchanged.