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Lumped elements to distributed elements

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rf997

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Hello, I want to design a notch filter at 3.7 ghz frequency. When I design the circuit with lumped elements, some capacitor and inductor values are too small. So I want to replace these elements with microstrip lines. How can I do that?
 
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Microstrip is a good option for low capacitance with a low-loss tangent dielectric on 1 side and air on the other side.

For a rule of thumb with Zo=sqrt(L^2/C^2) strips have an incremental Lo and Co per mm that determine Zo.
e.g. if Er=4 @ 3.7 GHz and if the track width, W to height, H above gnd W/H=2:1 then Zo ~ 50 Ohms. But the tolerance Er can be higher than your error tolerance requirements, so electrical testing is an added cost, or there are trimming methods. Here, Co is ~1.14 pF/cm and Lo is ~2.93 nH/cm. So choice of dielectric is key to the design. Getek FR4 is one brand that is popular for low loss at a reasonable cost.

Spiral inductors save space and vias also have L, C properties based on geometric ratios.

There are many good references online.

This may help you get started.
https://www.mdpi.com/2079-9292/8/9/964/htm
 
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Use Microstrip Lines.A sample for you..
1697738156574.png

1697738167561.png
 
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rf997 said:
How did you calculate the lengths of the resonators?
Click to expand...
Do you know the impedance of an open ended lambda/4 stub?
Can you imagine what that does if connect it to a thru line?

The layout shown by BigBoss looks like a refined version with couplers instead of direct connection to the thru line.
 
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Thanks for your help. However, my teacher asked me to first build the circuit with lumped elements and then replace the low values with stubs using the equations in the link. However, when I use these equations, I can not get results. Now I built the circuit with microstrip but it repeats in the frequency spectrum. Can I solve this problem by adding lumped element?

link: https://www.rfcafe.com/references/electrical/lumped-distributed-components.htm
1697993443664.png
1697993471570.png
 
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rf997 said:
Thanks for your help. However, my teacher asked me to first build the circuit with lumped elements and then replace the low values with stubs using the equations in the link. However, when I use these equations, I can not get results. Now I built the circuit with microstrip but it repeats in the frequency spectrum. Can I solve this problem by adding lumped element?

link: https://www.rfcafe.com/references/electrical/lumped-distributed-components.htm
Click to expand...
You're using FR-4 substrate and this materiel is very lossy at 5.8GHz.
Also, transforming lumped components onto distributed elements won't work in all cases. Therefore special filter structures have been developed by engineers and scientists.
Try to use less lossy substrate and optimize the distributed elements' dimensions. You'll get a reasonable result but this will be worse in practical measurements.
 
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rf997 said:
Now I built the circuit with microstrip but it repeats in the frequency spectrum. Can I solve this problem by adding lumped element?
Click to expand...
A transmission line band stop will typically have additional notches at odd multiples of the center frequency. Notches below threefold frequency suggest unsuitable topology, however what's your specification? You didn't talk about frequency range before.
 
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FvM said:
A transmission line band stop will typically have additional notches at odd multiples of the center frequency. Notches below threefold frequency suggest unsuitable topology, however what's your specification? You didn't talk about frequency range before.
Click to expand...

I'm trying to make a notch filter with a bandwidth of 200 Mhz at a center frequency of 3.7 GHz operating between 1.5-6.5 GHz. That's why it shouldn't repeat itself between 1.5-6.5 GHz.
 
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BigBoss said:
You're using FR-4 substrate and this materiel is very lossy at 5.8GHz.
Also, transforming lumped components onto distributed elements won't work in all cases. Therefore special filter structures have been developed by engineers and scientists.
Try to use less lossy substrate and optimize the distributed elements' dimensions. You'll get a reasonable result but this will be worse in practical measurements.
Click to expand...
Hello, is there a way to increase the bandwidth of the l resonator circuit, of which you sent the dxf file above, to 200 Mhz?
 
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Perhaps, if you can realize something like these with exceptionally low L & C in rigid geometry stripline surface waves.

1698156130089.png

0.1 pF was rounded up from 0.05 pF

Some properties seem impossible at first glance to realize with L/C and L*C effects in Transverse or Longitudinal (surface) wave effects over such a wide range fmax/min (>2:1) in such small values.
--- Updated ---

Over a smaller frequency range might look like this.
1698158076093.png
 
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