about the character of mixer spur

hello,everyone.
i have a question,i want to design a mixer,but the spur need 55dBc,i found that there are many spur in band,they are 2LO+2IF,or 4IF,or nLO+mIF,or nLO-mIF,etc.
can the mixer reject that spur 55dBc?
can anybody offer me some mixer's model?
thanks to all.

littlemmx said:

hello,everyone.
i have a question,i want to design a mixer,but the spur need 55dBc,i found that there are many spur in band,they are 2LO+2IF,or 4IF,or nLO+mIF,or nLO-mIF,etc.
can the mixer reject that spur 55dBc?
can anybody offer me some mixer's model?
thanks to all.

Click to expand...

Dear littlemmx,
As you consider 2LO+2IF,or 4IF,or nLO+mIF,or nLO-mIF in band signals it seems you are desinging an upconverter mixer, i think i can give good help at it, but i need to know are you doing a system level design or circuit level design? if you are designing an RFIC i strongly suggest double balanced architecture as -theoritically- it rejects all LO feedthrough components, but if you are designing a system then you need what is called IMT files for mixer intermodulation data. You can achieve 55dBc rejection for those in-band harmonics by proper choice of architecture without the need of SAW filters, please give me for information to help.

you can use double up-conversion with filters in between converters. this will keep away spurs as % of your useful band.

Dear godz,
thanks for you reply.
well,i just design a system,i need a mixer,which RF/LO up to 18GHz,IF up to 2GHz,the LO level 10~13dBm.and i need the mixer's intermodulation rejection is very well.can you introduce me some mixers apply for me?
thank you very much!

Hi Littlemmx,
Well as you are designing a downconverter system with the frequency plan you mentioned, i guess you shouldn't worry about the RF and LO feedthrough to IF, they are nearlly 1 decade away from the IF, with a simple passive-LC filter at the IF output you can get 40dB attenuation of RF and LO feethough in addition to the mixer inherent RF-IF and LO-IF isolation.
There is a mixer made by Watkins-Johnson, part number M50 that operate until 15GHz, also check mini-circuits, they may have mixers in this range.
please don't hestitate to ask.
regards,

littlemmx said:

hello,everyone.
i have a question,i want to design a mixer,but the spur need 55dBc,i found that there are many spur in band,they are 2LO+2IF,or 4IF,or nLO+mIF,or nLO-mIF,etc.
can the mixer reject that spur 55dBc?
can anybody offer me some mixer's model?
thanks to all.

Click to expand...

It sounds to me as if you are asking for trouble :?

First of all, you should look for a doubly balanced mixer, as this will supress all even products, but I doubt you will reach 55 dB... we are talking microwaves!

One way of acheiving better supression of spurs is to terminate the unwanted energy at 50 ohm i.e. using a diplexer, this might be useful on all ports! If yo have the RF at 18 and the IF at 2 GHz it sounds like you should really be shooting for a dual conversion as suggested in a previous posting,

It sounds to me you might have to revise the design as it might be impossible to have that spur supression in your mixer alone.

I don't think Mini-Circuits will be able to help but take a look at https://www.macom.com for a starter, they might have someting that will get you going.

Good Luck
/WD