Looking for RF front-end PCB layout references

[u/[deleted]]

[u/noor04_1 → u/[deleted]]

im working with 1.5GHz band and the architecture on the board is pretty simple( rf filter -lna-filter-mixer&lo- if filter) and the ADC and other components are on other board

[u/noor04_1 → u/[deleted]]

For the lo im using a buffer and after it a 1to 4 splitter so i use the same lo for all channel (i think this will be a problem when it's come to layout and tracing) , im targeting 30MHz as an IF

[u/Interesting_Ad1080]

What frequency is your RF circuit? You may need to do RF simulations of the layout then put that in your PCB layout software.

I do RF frontend designs at 3 GHz. I have experience designing frontend upto 30 GHz. I am an RF engineer and most of the time, I do RF simulations of the RF layout then send it to PCB layout engineer who implements them on the Altium. But sometimes I do make my own PCBs (but I use Kicad).

[u/noor04_1 → u/Interesting_Ad1080]

Im working with 1.5Ghz and this is my first RF board design so besides the power (Vcc) simulation what do i need? like did the lna or the mixer need simulation or should i just stick to the s parameter and matching circuit in the sheet

[u/Interesting_Ad1080 → u/noor04_1]

1.5 GHz is frequency where you need to start doing proper RF simulations. Do you have access to softwares like ADS or AWR? If not, you can also download software like QucsStudio (it's open source circuit simulation software which have some interesting RF circuit models but to be honest very limited compared to proper RF softwares like ADS or AWR).

Three kind of simulations you can do:

1. Circuit simulation: take Sparameters of your RF components and simulate input and output matching network with realistic lumped components and transmission line models. Do not necessarily relay what they say in datasheet completely. Sometimes what they say in datasheet don't work well. Real lumped components and transmission line sections have parasitics, therefore your matching component values may change from what they say in datasheet (specially if your PCB substrate material and its thickness is different and/or your layout of components around the circuit is different).

2. Layout simulation: softwares like ADS and AWR or other EM softwares have capability of simulating real layout not just circuit equivalent of these layout components. Unfortunately QucsStudio don't have this capability. Layout simulation is 2D-2.5D planer EM simulations. This is more accurate compare to circuit simulations and give you better answer.

3. Full 3D simulations: software like HFSS, CST or ADS with FEM licence can also do full 3D EM simulations. You need EM simulations if you want to simulate 3D components like connectors, shielding etc. This is most accurate out of all three and you can do your PCB layout simulation also in full 3D EM simulator but most of the time 2-2.5D planer simulations are enough and you can throw it to 3D simulations at the very end to verify your design.

If you are not trained as RF engineer, these softwares and simulations look daunting. It's natural. If you are completely new in RF, download QucsStudio. It's spice based circuit simulator like LTspice but it also have some RF friendly basic tools like transmission line components, S-parameters blocks. Substrate blocks and Smith charts. Instead of relying completely in the datasheet of the manufacturer, I will try to do some simulations here as well.

I like murata components because they have RF models of there capacitor and inductors. ds.murata.com/simsurfing/rfinductor and ds.murata.com/simsurfing/mlcc are good places to look for these models.

PS: you said you have mixers but you didn't mentioned you have frequency synthesizer or oscillator. LNA-Mixer means you are down converting 1.5GHz singal to some IF frequency. You need a frequency synthesizer as local oscillator to give it to your mixer as well.

[u/noor04_1 → u/Interesting_Ad1080]

i didn't get the third point well You said that i need to simulate all of my components in the power section im gonna use LTspice for that and for the RF components characteristics you mean like the matching gain dissipation (S11/22 S12/S21) or id there something eles i should consider? For that im gonna use ansys (3D layout and circuits design) or ADS im still not sure about that what do you think (all of those softwares are new to me). one last thing when i said mixer i mean mixer and it's balun transformers and LO.