about the character of mixer spur

[littlemmx]

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.

 

[godz]

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.

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.

 

[venus]

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

 

[littlemmx]

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!

 

[godz]

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,

 

[webdog]

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.

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