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oscillation of HMC447

Category: Hardware
Product Number: HMC447

Hi all,

    The hmc447 is not working properly on my board when 26G input and 5V power are well supplied,there is a large signal output at 5Ghz around when i checked the output.And the signal is hung and moved which is like self-oscillation.What's worse, the part will no longer work normally when this happen.That menas i have to replace it with a new part if i want to get to work properly.

I have some questions about  hmc447:

1.Does it need a DC-blocked capacitor when there is  a hmc519 before hmc447? i see the output of hmc519 is DC blocked internally from the datasheet,so i didn't add a dc capacitor at the input in my design.

2.when the hmc447 worked abnormally,i checked the input impedance of hmc447 which is 1.5 ohm instead of 50 ohm.Which may cause this happen?