LO sythesizer is not giving me a high enough frequency

I was wondering if any body could suggest a remedy to this scenario...

I need to up-convert over a wide bandwidth (~3.5GHz wide) to max upper C-band frequency. the problem is my LO sythesizer is not giving me a high enough frequency to minimize spurs after mixing. I would like to do a high LO mixing (LO>RF)

I know one option would be to use a sub-harmonic mixer (although i'm can't same to find a SMT one at my freq) ....are there any other suggestion?

any suggestion/comment would be deeply appreciated. Thanks in advance.

http://www.hittite.com/products/view.html/view/HMC156C8

Thanks for your suggestion biff44.

I initially had this in mind, but was little reluctant because adding a x2 would require a driving amplifier and BPF which would take up more board space.

again, thank you very much for your help - please let me know if you have any other suggestion...

You could make your own subharmnic mixer. That would take some board space at these low frequencies too to accomodate the quarterwave lines.

why a quarterwave line, if i was to buy one of synergy's subharmonics for example?

My max frequency is around 7GHz..

I thought you said you could not find one.

OK, now i see what you mean. If was to get a subharmonic mixer, i would more than likely have a custom part made through synergy, miteq or any other vendor that design this sort of thing for a living...

Lets go back to fundamentals. You can convert signals to 7 GHz by either using a higher LO frequency (frequency multiply the synthesizer you have), use a subharmonic mixer and the existing synthesizer. Or split your synthesizer and use a dual downconversion.

If you Frequency multiply your synthesizer, you have the option of multiplying and filtering in such a way as you will not have any weird spurs floating around.

If you use the subharmonic mixer, you will have a bunch of spurious frequencies due to the fact that the mixer LO is really at half the frequency you should be at. That gives rise to more spurious product. You also lose because the conversion loss of the subharmonic mixer is typically higher than a fundamental mixer. About the only thing you do pick up is some interference suppression from in-band signals.

If you use two mixers, and split the synthesizer to drive both mixers, you end up with an additional IF stage.

In either case, you WILL incur a 6 dB hit in your phase noise.

biff44,

I understand that option of multiplying my LO for higher LO and will probably use this technique; however, i'm not familiar with the other option: "split your synthesizer and use a dual downconversion" - how would this work in a transmitter

Also, my application has a very lack spec, so the 6dB noise floor degradation should not be an issue...

I really appreciate all your comments/suggestion.