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Coplaner waveguide PCB design for input matching

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Simo.Da

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Hello guys

I am really seeking some and some guidance regarding the coplaner waveguide.

I am trying to make a PCB design for class A RF PA.
I have done almost the design but I'm struggling in coplaner waveguide input matching (Zin=6.4-j65 at the base). I did the match using ADS, but I don't know how to make the PCB design using circuit maker.
Please find attached what I have done so far, and correct me if anything looks wrong please.
Thanks 003.JPG004.JPG005.JPG002.JPG001.JPG
 

Coplanar or microstrip, why don't you try to reproduce the simulated circuit topology in the PCB design? Instead you have unwanted transmission lines at the transistor terminals.
 

Hi FvM,
Thank you for your reply.
I have designed the input matching using lumped components as you can see attached, but the problem is as I'm working right now at class A (1GHz) and then I need to drive it harder to move it to class C (10 GHz), I couldn't find a 8.8nH inductor resonating at 10 GHz, so for that reason, my supervisor advised me to replace it with a coplaner waveguide and I don't have any previous experience with transmission line design.
Please if anyone can help as the time consuming.

Thanks
 

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Why did you stick to "Coplanar Waveguide" ??Lumped elements are not preferable for beyond of few GHz due to their non-ideal characteristics.
You just have to design a simple matching circuit using with Microstrip Lines for 10GHz.That's it..
 
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Selection between CPW and uStrip line is also dependent on the technology(cost) available to you. For a school project, uStripline would be a better choice than CPW.

Study concept of "stub inductance" for your project. That would be helpful.
 

but the problem is as I'm working right now at class A (1GHz) and then I need to drive it harder to move it to class C (10 GHz)
Click to expand...
I confess, I don't fully understand what you want to achieve. According to the simulation schematics, you are designing for 1 GHz. When moving to class C, harmonic behavior becomes relevant, you may even design explicit matching for certain harmonics. But there's no reference to harmonics in the simulation setup, apparently you are matching for 1 GHz only. Please clarify.

Apart from this point, I agree with the previous comments. Design transmission line matching. If you end up with low characteristic impedances that can't be well implemented as microstrip with the given PCB technology, surface coplanar strip can be considered as a supplement.
 

W.Dabbas said:
I couldn't find a 8.8nH inductor resonating at 10 GHz
Click to expand...

When you wrote "resonating at 10 GHz", do you mean the self resonance frequency?
You can try Murata LQW18AN series, that is what I use for 1GHz matching circuit design. According to my simulation below with data from the Murata model library, SRF is > 10GHz for 8.7nH

If you want to build an inductor from a piece of transmission line, use a narrow line (thinner than 50 Ohm line). However that will implement your 8.8nH only at the target frequency, and might have undesirable response at harmonics. I would go for the SMD component.


lqw18_an.PNG
 

According to post #1, the matching has been designed for small band only, it's still unclear how 10 GHz comes into play.
 

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