PAT1220-C-10DB-T5 is a 10dB attenuator. (This chip is just an example, it could be any other component as well).

1. Can I simply connect 3 of them in series in a PCB design to make my cheap 30dB attenuator?

2. I have a few attenuator modules with an SMA connector. One of them is 20dB while others are 6dB and 10dB. Can I again connect them in series to get higher attenuation?

• Be aware that as you get to >> 40 dB attention, leakage around the components will start to exceed the attenuated signal. You start to need to put each stage in a separate shielded can or cavity. – tomnexus Apr 9 '19 at 17:39
• Thank you. How can i shield in such case. – nandflash1 Apr 9 '19 at 18:37
• @nandflash1 Please ask about the shielding in a new question on electronicsSE, including an image of the PCB. Not only is printed circuit board design off-topic for this site, but you are likely to get a better answer there. :-) – Mike Waters Apr 9 '19 at 20:31

Yes, you can cascade attenuators to realize more attenuation. Attenuation (in dB) will increase algebraically, as long as all individual attenuators are designed to operate at the same impedance and they are operating at that impedance. For example, mixing 75$$\Omega$$ and 50$$\Omega$$ attenuators may produce unexpected results. Same for using terminators in a system that doesn't terminate in the appropriate characteristic impedance.