# Forum: Analog Circuits frequency doubling with a ring mixer

 Author: oscillator (Guest) Posted on: 2015-01-29 23:18

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Hi!

Actually I am thinking about rf-oscillators. Could it be possible to
double the frequency of an oscillator if I forward the signal through a
wilkinson divider to split the signal into two paths and then feed those
two paths into a ratrace-coupler? The mixing products should be f1 + f2
and f1 - f2.

Thanks!

 Author: Sven (Guest) Posted on: 2015-01-29 23:24

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A ratrace coupler is not a nonlinear element so it can by itself not do
mixing, or can it?

Basically you can do frequency doubling with any non-linear element.
Feeding your signal through a diode is enough already to get a component
with twice the frequency (as well as other harmonics). All you need is a
filter to select the harmonic you want.

 Author: oscillator (Guest) Posted on: 2015-01-29 23:54

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Hm, wiki (http://en.wikipedia.org/wiki/Rat-race_coupler) sais: "Rat-race
couplers are used to sum two in-phase combined signals with essentially
no loss". Is that wrong?

But I will also keep the hint with the diode and the filter network in
mind. Thank you :)

 Author: oscillator (Guest) Posted on: 2015-01-29 23:57

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Aah... the "sum" is not the sum of the frequency, just of the voltage,
right?

 Author: oscillator (Guest) Posted on: 2015-01-30 00:03

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OK, I got my mistake. In some radar applications ratrace couplers are
used as mixers but they always have diodes at their ports. Now I
understand why. The diodes do the mixing! :)

 Author: Sven (Guest) Posted on: 2015-01-30 00:15

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Yes, exactly. Whenever a device generates frequencies at its output
which are not present at its input, there must be a non-linear device
(such as a diode) involved, and a microstrip arrangement is to my
knowledge never non-linear.

 Author: Sven (Guest) Posted on: 2015-01-30 00:23

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And yes, the sum is of the frequencies, not the voltages; you need to
multiply the voltages to get the mixing effect. You can most easily see
that by denoting the signal as sin(w*t) and then looking at sin(w*t) +
sin(w*t) = 2+sin(w*t) (no new frequency components) and sin(w*t) *
sin(w*t) = 1/2 (1-cos(2*w*t)), which contains half the amplitude in the
difference frequency (the "1", which is DC because your two frequencies
are equal) and half in the sum frequency 2*w, which is exactly what an
ideal frequency mixer would give you.

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