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I need to shift the phase of a signal in the 2 GHz range. However, the problem is that this phase shift needs to be trimmable. It must be adjusted only once. Unfortunately it is very difficult to properly simulate the necessary phase shift in advance, and there may also be some manufacturing tolerances.

I wonder whether there is a way of making an adjustable phase shifter, for instance with a trimmer cap? The phase shift should be adjustable in a range of, say, 90°. Further, of course the phase shifter must be matched to 50 ohms.

I thought a RC network may do the job, but unfortunately it is not matched at its ports and further has a lowpass or highpass characteristic, which I would like to avoid.

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  • \$\begingroup\$ What resolution of trimming do you expect? \$\endgroup\$ – Gregory Kornblum Nov 8 '16 at 18:42
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    \$\begingroup\$ You say you can't accept a filter with high or low pass characteristic, but you don't say how wide a band do you need to work with. \$\endgroup\$ – The Photon Nov 8 '16 at 18:48
  • \$\begingroup\$ That's true, your right. I need a bandwidth of 200 MHz at least. \$\endgroup\$ – T. Pluess Nov 8 '16 at 18:53
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I doubt you could use a trimmer cap in that frequency range. At those frequencies everything becomes extremely sensitive to parasitics and probably you would need specialized microwave circuitry.

Anyway you could do with a module like this. Excerpt from the app note:

enter image description here

I just googled for digitally controlled microwave phase shifters. If the digital control through USB seems overkill, maybe you could find some pre-built module with a more "low-level" interface (e.g. SPI, I2C).

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  • \$\begingroup\$ I am pretty sure a trimmer will work because I have, for instance, some 0.6..2.5 pF trimmers here which are specified up to 3 GHz. A digitally controlled phase shifter is definitely overkill, and space is very limited. \$\endgroup\$ – T. Pluess Nov 8 '16 at 18:54
  • \$\begingroup\$ You give very little information on the specific application you are thinking about. In particular specs like precision, accuracy, reliability of the design you are aiming at. A trimmer cap may work, but it may also be very unreliable, depending on the application. \$\endgroup\$ – Lorenzo Donati Nov 8 '16 at 18:58
  • \$\begingroup\$ Keep in mind that the fact that the trimmer cap is specified up to 3GHz it doesn't mean a complete phase shifter design could be based on it. For example, what's the required bandwitdth of the phase shifter? Would it be employed to shift a simple sinusoidal signal? \$\endgroup\$ – Lorenzo Donati Nov 8 '16 at 19:00
  • \$\begingroup\$ Moreover: what level of power must be handled by the phase shifter? In which environment will it be placed (e.g. range of temperature)? \$\endgroup\$ – Lorenzo Donati Nov 8 '16 at 19:01
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You can make a fairly accurate phase splitter that has two outputs and one input. The two outputs will be phase shifted 90 degrees to each other so providing you don't care about the original phase of the input, you get what you want on the output for the price of an inductor, a capacitor and two resistors.

At the frequency centre point , both outputs are 3 dB down. Choose L and C as if designing a parallel resonant circuit at 2.5 GHz. Both L and C have same value series resistors and the value is sqrt(L/C). Output 1 at junction of L and R. Output 2 at junction of C and R.

I believe that this circuit is used in some I and Q modulators

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  • \$\begingroup\$ The phase shifter must be capable of handling up to 20 dBm. I would like to use it to tune an oscillator's output power, which depends on some phase shift. I thought of simply manufacturing different PCBs with different microstrip lengths, but this would be the last option. \$\endgroup\$ – T. Pluess Nov 8 '16 at 21:48
  • \$\begingroup\$ Well I can't say I understand how you would achieve what you want to achieve with any particular circuit. \$\endgroup\$ – Andy aka Nov 8 '16 at 22:08
  • \$\begingroup\$ Well. I have a resonator. At its resonant frequency, its insertion loss is near 0 dB and its insertion phase is 0°. The resonator is then connected to an MMIC to build a oscillator. The problem is, the MMIC has an S21 phase of about 50° or so. Therefore, if I just connect the resonator to the MMIC an form a feedback loop, it will not oscillate because the phase criterion is not met. This phase is what I would like to trim. \$\endgroup\$ – T. Pluess Nov 9 '16 at 6:33
  • \$\begingroup\$ You are describing an XY problem, why not try to fix the root cause instead of using a band-aid. \$\endgroup\$ – Andy aka Nov 9 '16 at 7:50

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