# Down conversion Reference delay

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#### Hawaslsh

##### Full Member level 2
Hello All,

I am trying to make an X-Band phase detection circuit using some commercially available components. I attach a simplified block diagram of the circuit above. The goal is to compare the phase difference between the down converted reference IF to the Test IF from identical double balanced mixers. The title of this post is a bit miss-leading but I didn't know a better way to describe the problem. I can account for the reference delay within the Test IF by knowing the phase added by the directional coupler and 2x (βl1), but I was wondering if the phase difference between the LO pumps, βL3 < βL4, will also lead to a phase difference in the down converted IFs. I am currently re-arranging my board design to try and make those two t-lines equal, but just wanted to see if anyone had run into something similar before and could save me a lot of time in Autocad.

Thanks again!
Sami

#### Attachments

• LO delay between mixers.jpg
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#### ferdem

##### Full Member level 2
I do not understand coupler's function here. Anyway, It is a fact that if the LO phase changes, downconverted signal's phase changes. The amount of the phase changes will be the same. Think about trigonometric identities, sin at*sin bt, sin at*sin(bt-phi)?
See below multiplications:
sin(w1*t)*cos(w2*t) yields a product at w1-w2
sin(w1*t)*cos(w2*t-phi1) yileds a product at the same frequency but with a phase lag of phi1.

Hawaslsh

### Hawaslsh

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#### Hawaslsh

##### Full Member level 2
Thanks! Appreciate the help greatly!

I am using the coupler simply to create a reference and sample the reflected test signal using a single RF synthesizer. I am not married to the idea if a more practical solution exits.

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