Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Huge difference between simulation results of the schematic and the layout on ADS

mayjailomo

Newbie level 5
Joined
Jan 18, 2022
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
158
Hi all,

I am recently designing a 5.8GHz wilkinson power divider. FR4 will be used in this design and the thickness of the substrate is 0.8mm. Here is the schematic of the power divider:
Capture.PNG

The resonant frequency is at 5.8GHz for S11 after fine tunning some parameters. However, with the same parameters, the resonant frequency is shifted in the momentum co-simulation. As i believe that momentum co-simulation provides a more reliable simulation result, i tuned the parameters so that the simulation result of the resonant frequency of S11 is at 5.8GHz in momentum co-simulation.
Final simulation result of the schematic:
Capture1.PNG

Final simulation result in momentum co-simulation:

photo1642405085.jpeg

However, after I fabricated the coupler. The measured result is very different from the result in momentum co-simulation. And it has a higher similarity with the simulation result of the schematic.

msg-755675125-293819.jpg



Does anyone know the reason? Thank you for your time.

Here is the link of the workspace: shorturl.at/ntDO1 (Onedrive)
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
49,894
Helped
14,482
Reputation
29,234
Reaction score
13,391
Trophy points
1,393
Location
Bochum, Germany
Activity points
286,515
The ripple seen in the measurement suggests that a large resonant structure is involved. I suspect an unsuitable PCB to cable interface and respective sheet waves.

Regarding systematic deviation between simulation and measurement, huge uncertainty of regular FR4 Er requires an empirical adjustment of PCB parameters according to measurements.
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,264
Helped
1,545
Reputation
3,090
Reaction score
1,409
Trophy points
1,393
Location
Turkey
Activity points
31,663
FR-4 Material may show up pretty much variation by supplier and lot by lot.
It's not suitable for critical 5.8GHz applications.
 

mayjailomo

Newbie level 5
Joined
Jan 18, 2022
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
158
FR-4 Material may show up pretty much variation by supplier and lot by lot.
It's not suitable for critical 5.8GHz applications.
Thanks for your reply. I understand that FR-4 is only suitable for low frequency applications, but there is budget limiation for this device so I have no choice.
 

mayjailomo

Newbie level 5
Joined
Jan 18, 2022
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
158
The ripple seen in the measurement suggests that a large resonant structure is involved. I suspect an unsuitable PCB to cable interface and respective sheet waves.

Regarding systematic deviation between simulation and measurement, huge uncertainty of regular FR4 Er requires an empirical adjustment of PCB parameters according to measurements.
Thanks for your advice. I will resolder the SMA connector to see if I can obtain a better result. So do you think the deviation between simulatio result of layout and schematic is also because of the uncertainty of dielectric constant of FR4? I am worry that that's because I didn't setup the simulation correctly.
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,264
Helped
1,545
Reputation
3,090
Reaction score
1,409
Trophy points
1,393
Location
Turkey
Activity points
31,663
Where is your balancing resistor ?? It's missing.
You have to place a resistor in simulation schematic to simulate your layout.
You placed two pins only..
 

LaTeX Commands Quick-Menu:

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top