K-band Waveguide BPF

Design using Agilent

EMPro 2013

Anurag Bhargava

Application Consultant

Agilent EEsof EDA

Filter Specifications

Center Frequency (Fc): 25 GHz

3dB Bandwidth: 150 MHz

Rejection: 40 dB @800 MHz offset from Fc

Insertion Loss: Better than 1 dB

Return Loss: Better than 10 dB

Filter Geometry Design

• Open EMPro 2013.07 and create a new project

• Go to Edit->Project Properties->Display Units and change the

Length unit to “mm” if it is not already set as mm

• Click on Parameters icon on the right hand side icon

panel and define parameters as shown below

Filter Geometry Design

• Click on Extrude icon or select Create->Geometry->Extrude

• To create a waveguide we shall create the base rectangle and then

extrude it in Z-direction. Click on rectangle icon and press Tab and

enter coordinate as U’=0 mm and V’=0 mm as shown below and press OK

• Press Tab again and enter U’ = 36.576 mm and V’ = 10.668 mm and press

OK. Now we should be able to see a rectangle outline with desired

dimension.

• Go to Extrude Tab and enter Extrude Distance as 4.318 mm (height of

waveguide) and click Done

Waveguide Design: (Waveguide Selected: WR42)

Filter Geometry Design

• Use left mouse button to see isometric view of the WR42 waveguide as shown

below

• Now we have to perform Shelling operation on this waveguide so that we can

have opening on either side of the waveguide and we can also provide some wall

thickness to our WR42 waveguide.

Waveguide Design:

Filter Geometry Design

• Click on waveguide in GUI, right click and select Modify->Shell

• 1st step is to select both faces of the waveguide which we have to remove, select

faces along waveguide as shown below by selecting 1st face then rotating the

waveguide and press CTRL key and select other face as well

• Go to Specify Thickness tab and enter Shell Thickness = 0.5 mm and click Done

• Now we should be able to see waveguide with both end open and with wall

thickness of 0.5 mm

Waveguide Design:

• Save the project with name:

Kband_BPF_Design

Filter Geometry Design

• We shall use 3 cylindrical resonators in our filter design, for

better visibility of these resonator creation we can set the

transparency by clicking % of Change Global Parts

Opacity. Set the slider to @ 33%

• Click on Extrude icon or select Create->Geometry->Extrude.

Select Circle and press Tab, enter U’ = dis, V = 5.334 mm

(center point of 1st resonator). Press tab again to enter Radius

as sr1 (defined as 1.2 mm in parameters)

• Go to Extrude tab and enter extrude distance as 4.318 mm and

click Done to see a cylindrical post inside the waveguide

• From the Parts list in Project Workspace Tree, rename Model

(default name) to be WG42 and Post1 as shown below

Creating Resonators in Waveguide

Filter Geometry Design

• Click on Extrude icon to insert 2nd cylindrical resonator with

parameters as shown here

– Center: U’ = dis*2, V’ = 5.334 mm

– Radius: sr2

– Click Done and rename it as Post2

• Click on Extrude icon to insert 3rd cylindrical resonator with

parameters as shown here

– Center: U’ = dis*3, V’= 5.334 mm

– Radius: sr1

– Click Done and rename it as Post3

Resonators in Waveguide

Material Assignment

• EMPro provides Default Material Library with plenty of material definition included.

Users can also define their own material if needed.

• In the Project Tree, right click on Materials and click on Select from Default

Material Library.

• From the available list, select Copper or Cu and click on Add. Notice that Copper

or Cu is now under Material list.

• Select this material, drag & drop it on each object i.e. WR42, Post 1, 2, 3 & 4 so

that this is assigned to all the object and we can see the colour change in our filter

geometry.

Port Assignment

• Now as that we have created and assigned the material to our geometry we can

create the simulation ports.

• Right click on Circuit Components/Ports and select New Waveguide Port

• 1st step is to select the face on which we want to apply the Port. Click on the Arrow icon and select the

face of waveguide

• Go to the Boundary Extension and uncheck the option “Auto extend to simulation domain boundaries”

• Go to Properties tab and select Waveguide Port Definition as 1W Modal Power Feed

• Go to Impedance Lines and click on Arrow under Endpoint 2 (+) Parameterized Position

– Select midpoint on upper edge of waveguide face

– Click on Arrow under Endpoint 1 (-) and click on midpoint of lower edge of waveguide face.

– Once done it will similar to the one shown below (provided you are referring to input side (near origin side of filter)

• Click on Done

Rotate the waveguide and assign

Port2 on the other side using the

procedure defined here.

Port Assignment

Once Ports are defined properly filter would look similar to one shown below.

Note Port location in the snapshot below and make sure the Arrow direction on both

ports are same in your design.

FEM Padding • FEM padding sets the boundary of a simulation domain. It specifies the area that is

meshed and solved during a simulation. The FEM padding value should be large

enough to avoid any interactions between the object and boundary. However, it

should not be too large to avoid long time to mesh and solve.

• It should be zero in the direction where we use waveguide ports

• For our case, we don’t need padding in any direction because all of the energy will

be enclosed in the waveguide and it is a non-radiating structure.

• Double click on FEM Padding and select “Custom” and define 0 mm padding in all

directions of the structure.

FEM Simulation Setup

• Change the simulation type to FEM Simulation

• Click on the spanner icon i.e. Edit Simulation Setup

• Define frequency range as 24 GHz – 26 GHz with 51 points

• Under Mesh Refinement, define following

– deltaError = 0.01

– Consecutive Passes of delta error = 2

– Minimum number of adaptive passes = 3

– Maximum number of adaptive passes = 15

• Under Solver tab, select Direct Solver

• Click on Create and Queue Simulation

Filter Simulation Results

• Click on Results button

• Select Domain = Frequency, Result Type = S-Parameters

• Select S21 and S11, right click and select Create Line Graph….

• Click on View

Filter Simulation Results

Filter Simulation Results

• We can notice that Filter passband is slightly offset on higher

side

• We can modify the resonator dimension slightly to center the

response at 25 GHz

• Alternatively we can also employ tuning screws in between

resonator rods to obtain higher level of tuning if required

• In our present case we shall first perform a simple parametric

sweep on center resonator’s radius to observe the frequency

shift

Parametric FEM Sweep

• Click on Tools->Add-Ons->Simple Parameter Sweep

• From the pop up window, select Parameter = sr2 (remember sr2 is the radius of

center resonator rod)

• Enter Start = 2 mm, Stop = 2.1 mm and Step = 0.05 mm

• Click on Create & Queue Simulations

• Click on Simulations icon and see that 3 simulations

have been added to our list and EMPro will perform these

simulations one by one as shown below

FEM Parametric Simulation

• Once all the simulations are performed, click on Results icon, select Simulation Ids 2, 3 and 4 by pressing SHIFT key and left

mouse click so that all results appear in the list

• Select S21 of all simulation run by pressing CTRL key and left mouse button

• Right click and select Create line graph to see Parametric results as shown in next snapshot

FEM Parametric Simulation

FEM Parametric Simulation

Observations:

• Filter response is very sensitive to resonator radius.

• While we try to center the response by varying the resonator

radius dimension but it might be very difficult to control

considering manufacturing tolerance in mind

• It might be necessary to keep tuning screws to adjust the final

assembly performance if necessary

• For this case study we shall adjust the center resonator

radius to 2.09 mm and perform the simulation again

FEM Simulation with sr2=2.095 mm

Click on Parameters icon and modify the sr2 parameter = 2.095 mm and run the simulation again to plot S21

and S11 as shown below

Resources

1. Agilent EEsof: www.eesof.com

2. Agilent EMPro: www.agilent.com/find/empro

3. Agilent Knowledge Center: www.agilent.com/find/eesof-knowledgecenter

4. Agilent EEsof on You Tube: www.youtube.com/AgilentEEsof