# Combining 2 power amplifiers in different frequencies to widen bandwidth

1. ## Combining 2 power amplifiers in different frequencies to widen bandwidth

Hi,

I have two RF power amplifiers.
The first one works in frequency range 60-75 GHz and the second works in 75-90 GHz.
Is it possible to combine the two PAs to realise a PA working in the frequency range 60-90 GHz?
If it is possible, how?

I considered,
1, Parallel connecting the two PAs. The phase information of the PA output is unavailable.
2, Serial connecting the two PAs. The first output power would exceed the input power of the second PA. An attenuator to limit the input power to the second PA?

Any suggestions are welcome.
Thanks

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2. ## Re: Combining 2 power amplifiers in different frequencies to widen bandwidth

Just because the range is 60-75GHz doesn't mean there's no output at 76GHz. Paralleling the outputs just sounds like a bad idea to me. Distortion at the very least; damaged components more likely.

I totally don't understand the series concept. If each amp has, say, zero gain outside it's band, then putting them in series guarantees no output at any frequency.

Can you switch the outputs, or are you just trying to make a wideband amp?

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3. ## Re: Combining 2 power amplifiers in different frequencies to widen bandwidth

PAs are NOT connected in series to improve the bandwidth.They are simply combined with a standard Wilkinson ( or similar ) to get a wider bandwidth.
When the signal frequency is lower than 75 GHz first amplifier works, beyond second one starts to work.
But the case may not be easy as said in practice.If an amplifier shifts the phase while second one is working, you loose the power.( phases are important in combining for single frequency)
Because neither one is ideal amplifier and there will absolutely be an overlapped working bandwidth.
Either you have to place a sharp filter at the output of each amplifier (bad idea ) or you will automatically align the phases regarding to band of interest..
It's not so easy..

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4. ## Re: Combining 2 power amplifiers in different frequencies to widen bandwidth

Thanks for the replies.

BigBoss, how can I automatically align the phases of two PAs?

Are these ways normally implemented in distributed amplifiers to achieve a very wide frequency band?

Barry, I just try to make a wideband amp.

5. ## Re: Combining 2 power amplifiers in different frequencies to widen bandwidth

Phase can be adjusted by observing the output so max. signal level can be achieved by aligning phase at the input of the "other" amplifier.The other amplifier can contribute to the level of the signal but if the phase is shifted a bit, this contribution will be negative consequently wanted power level cannot be obtained.
This is a very hard to implement way..
Distributed amplifier is obviously a better choice.However designing an Power Amplifier that will supply a Power Level from 60GHz-90GHz is as you recognize a difficult task.

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