Question
Asked 21st Jul, 2021

What all considerations should I take in account while desiging a Micro-strip line at high frequency (70-85 Ghz)?

I want to design a micro-strip line for a mm wave application. I am using formula mentioned in David Pozar`s Micro-wave Engineering book, Is there any other method or analysis I can use to design for the frequency range suitable for my application. Thank-you in Advance

Most recent answer

27th Jul, 2021
Malcolm White
Creo Medical Ltd
Waveguide also works extremely well, and is lower loss than microstrip. E-plane circuits can be easily and cheaply milled from aluminium and interface well with microstrip etc. and antennas.

All Answers (6)

21st Jul, 2021
Martin Obermaier
Technische Universität Dresden
Hello Khalid Shaikh, Pozars book is a good start. There are multiple books written on the topic, that go into more detail and only focus on MS and coplanar designs. At these frequencies you have to take the surface roughness of your materials into account. Due to the skin effect the electromagnetic waves will hardly penetrate the conductor. I would also recommend that you try to simulate your MS line in a suited EM-simulator. The best suited simulator for this case should be SONNET, but I am sure you can also achieve acceptable results with AWR Microwave Office or Ansys HFSS. Please keep in mind, that not everything that can be simulated can also be manufactured. You should check the manufacturing parameters of your PCB supplier and orient your design according to these requirements. You should also think about how to measure your line once it has been produced. You probably need to create probe pads or use special RF connectors ( I think 1mm is required at these frequencies). Best regards
1 Recommendation
22nd Jul, 2021
Malcolm White
Creo Medical Ltd
Microstrip and other lines behave at 85 GHz similar to what they do at lower frequencies, if everything is scaled by the same amount. However, the dielectric may have higher losses and the skin-depth will be thinner, so these things don't quite scale, but impedance and component layout mostly can and should be roughly scaled from lower frequency designs. As Martin Obermaier says, things like surface and edge roughness, and also material variation over a short scale (glass-fibre weave?), have a more significant effect at higher frequencies. You may not want to scale the board thickness, so some things won't be the same, and the track thickness may be larger in proportion to the width, dropping the impedance slightly compared to the same width to height ratio at lower frequencies.
23rd Jul, 2021
Thomas Petsch
RUAG Technology
You could start with online calculators like https://www.microwaves101.com/calculators/1201-microstrip-calculator.
I totally agree with Martin and Malcom, it is a good idea to produce breadboards to test and tweak your design. Make sure to use low loss substrate and keep lines short, Good luck with your project!
26th Jul, 2021
Khalid Shaikh
Universität Bremen
Thank-you for all the recommendations and references Martin Obermaier
Malcolm White Thomas Petsch , It has certainly helped me a lot while designing microstrip line for my application.
27th Jul, 2021
Fritz Caspers
CERN (ESI)
In this frequency range it may be interesting to consider as an alternative also dielectric lines (sort of printed optical fibers) since(metallic) microstrip lines are really getting small then and have considerable losses.
Can you help by adding an answer?

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