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Modeling a distributed LPF in Microwave Office

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vistadude

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I'm trying to implement the low-pass filter from Pozar's Microwave Engineering (2nd ed, p. 466-468) in Microwave Office using the Taconic TLY-5 substrate

(Model TLY_5_200 from the AWR Web site libraries).

Doing that I have encountered a number of questions, which I cannot figure out from the Getting Started and User Guides. (Are there NO books on MWO? I'm

located outside of any areas where MWO courses are offered)

1) Er=2.2 is a reasonably low value for microstrip (correct?). (higher impedance or higher Er equals lower line width to implement) The T/W and W/H ratio's

of the 217.5Ω lines using my chosen substrate is still outside of recommended values, as well as outside of the required values to use MSTEP$.

Is my computed values incorrect, or can the filter not be realized on my chosen substrate?

2) Is schematic 1 an acceptable first approximation of the stub filter? (apart from the ripple, the simulated graph closely matches Pozar's response in

figure 8.37, p. 468)

3) Is schematic 2 (using MTEE$ and MSTEP$) the correct way to model the filter more accurately? (assuming the T/W and W/H issues have been addressed)

PS: The line length was computed as λ/8=(2.9979*0.675)/(40*8) where 2.9979*0.675 accounts for the wave speed in the substrate, 40 for the frequency and 8 for

one eighth wavelength.
 

Manjunatha_hv

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Hello,

I want to mention couple of things...
1. Schematic 1 is wrong & it is not the way Microstripline elements are connected
2. In schematic 2, it is not correct way of using MSTEP$

You need to connect Microstripline elements at Node 1 or infront of $ elements..,
You see the layout then you will understand may be better...

upload your MWO file (*.em), I will try to modify & send you some instructions on
How to impliment Microstripline Filters using MWO...


---manju---
 

Manjunatha_hv

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Hello,

Attached is the modified MWO schematic which provides better results in Simulation & Layout...
If you see I used MTEEX$ which is a em based model & it is accurate compared to MTEE, MTEE$...

Also since your width ratio is very rastic from high value to low value...I recommend you to simulate using electromagnetics simulations of the strcture...

I have attached modified MWO project files for your reference...

---manju---
 

    vistadude

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vistadude

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Thank you very much for the corrections.
Can you explain how MTEEX$ correctly models the physical change in width?
I understand that higher order modes are present at the discontinuities. I assume that directly connecting MLINs with different widths ignores these modal changes. (To get to a layout, I used View->View Layout, and then Edit->Snap Together.)
What I do not understand is that the layout generated has nonzero length for the MTEEX$ model. It is stated (http://edocs.soco.agilent.com/display/ads2009/MTEE+(Microstrip+T-Junction) , note 1) that "A reference plan [sic] shift is added to each of the ports to make the reference planes consistent with the layout".
Is the generated layout of any use for manufacturing?
I would have thought that the MTEEX$ model would not be included in the physical realization - am I correct?

(Also, MWO won't let me add ports to the generated layout, but does allow it if I create a new EM structure and draw the schematic by hand, which is really confusing me.)
 

Manjunatha_hv

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Hello,


Go through the following AWR Help menu & details on em based models at following KB links...
Which will address all your queries...

MWO/AO/VSS User Guide > Schematics > Element Catalog Supplementary Information > EM-Based Discontinuity Models

https://awrcorp.com/download/faq/english/appnotes/xmodels.aspx


---manju--
 

khalifas

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I am new to Microwave office ,, and also i was trying to implement that filter from pozar and i have managed to get it done but it is the layout and extracting the gerber file that i need help in ??
So could anyone please help me with that :
How can I make the layout from my schematic then extrac the gerber file?

Thanks in advance.
 

Manjunatha_hv

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khalifas,

upload ur pozar book filter simulation MWO file, I will try to help you to build layout...

did u used the TXLine calculator to build microstripline schematic?


---manju---
 
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