How to build a 40dB or more attenuator up to 3GHz or more

[Tuxgvf33]

Hi all,

I have tried to build an homebrew attenuator let's say a 40dB attenuator using online calculator.
I used a 50ohm line and a pi structure with 2 resistor in parrallel at the input and the output.
The result is poor as the smd component natural isolation is around 30dB (natural isolation of a 50ohm line ).
Does anybody have any trick to improve the isolation to build high attenuator value? (As flat as possible not 0.1 dB but couples of db flatness around 40dB or greater will be a good start). I assume that it is not possible to build a 80 to 90dB attenuator in a single pi structure. I bet i need 2 attenuator of 40db cascadable.

Many thanks,
Regards

[9aplus]

While ago I built something old fashion way, using switches and through hole resistors on perfboard.
My goal was just to assist/test SDR reception on HF.
One day while doing some tests on ADSB 1090 MHz freq. I was missing some more attenuation and used that device...
all within acceptable results.
My setup is 5 + 5 + 10 + 10 + 20 dB so all ON result is 50 dB it is not far from that number
even on 1 GHz. 

[radiolistener]

I assume that it is not possible to build a 80 to 90dB attenuator in a single pi structure. I bet i need 2 attenuator of 40db cascadable.

40 dB for a single cascade is too much. I suggest to use less than 10-20 dB per cascade.
And use proper shielding, for 40-60 dB and higher it is very important.

[ejeffrey]

Is this to use on a PCB?  What power handling?  Mini-circuits, Susumu, and probably others make surface mount attenuators.  For low power applications these will perform much better than trying to make one out of discrete components.  Don't do more than 20 dB/stage, and do use shielding, I try to keep no more than 40 dB of attenuation or gain without shielding.

[RadioNerd]

how about four of these?
https://www.susumu.co.jp/common/pdf/n_catalog_partition30_en.pdf?v=20180406

you'll certainly get better performance than using discrete resistor arrangements

[djidji]

don't waste your time and money. you will never ever DIY any decent 3GHz attenuator especially not the cheap one. better go to the some online e-commerce website and buy real RF attenuator for a fraction of the money what would you spent on DIY.