Exercise # 2 (Day-1)

Objective

Learn the Designing Power Divider at 2.4GHz

Learn to generate the layout for fabrication

Learn to perform simulation in ADS-Momentum (EM-tool)

Understand the relationship between the Microstrip line dimension with the impedance

I. Background and Theory Power dividers (also power splitters and, when used in reverse, power combiners) are passive

devices used in the field of radio technology. They couple a defined amount of the electromagnetic

power in a transmission line to a port enabling the signal to be used in another circuit. Power

dividers have many applications, these include; providing a signal sample for measurement or

monitoring, feedback, combining feeds to and from antennae, antenna beam forming, providing taps

for cable distributed systems such as cable TV, and separating transmitted and received signals on

telephone lines.

An ideal half-split power divider would divide incident power at port 1 equally between ports 2 and

3. The S-matrix for the ideal Wilkinson divider is given below:

This ideal Wilkinson power divider would have perfect matching at all ports (S11=0, S22=0)

,S33=0). Also, there would be perfect isolation between ports 2 and 3 (S23 = 0). The insertion loss

between ports 1 and 2 should be , and the insertion loss between ports 1 and 3 should be (|S12| =

|S13| = ). The implementation of the divider uses quarter wavelength lines that cause the phase

shift of /2. Since the device is passive, the S-matrix is reciprocal.

when a signal enters port 1, it splits into equal-amplitude, equal-phase output signals at ports 2 and 3.

Since each end of the isolation resistor between ports 2 and 3 is at the same potential, no current

flows through it and therefore the resistor is decoupled from the input. The two output port

terminations will add in parallel at the input, so they must be transformed to 2xZ0 each at the input

port to combine to Z0. The quarter-wave transformers in each leg accomplish this; without the

quarter-wave transformers, the combined impedance of the two outputs at port 1 would be Z0/2. The

characteristic impedance of the quarter-wave lines must be equal to 1.414xZ0 so that the input is

matched when ports 2 and 3 are terminated in Z0.

Simulation Using Physical Microstrip Transmission Line

Steps

Use of LineCalc (tool of ADS) to find the lines physical dimensions

Each Physical track of Microstip lines has two parameters

Impedance

Electrical Length

Impedance depends on the width of physical track and Electrical Length depends on the

physical length of the track

It means each of our ideal line will be transformed into a different physical microstrip line

Physical Length and Width along with the Impedance and Electrical Length depends on the

parameters of the substrate

Parameters of FR-4 are given in the start

Procedure:

Determine all the important Transmission lines required to design the Power Divider

50 Ohm Line

100 Ohm Line

Quarter wave transformer 70.7 Ohm

1. Open new schematic file

2. Save it on the defaults location with any name (no spaces/dashes, underscore is acceptable)

3. Convert Ideal line to Physical line

Open LinCalc

On the schematic file goto Tools->LineCalc->Start LineCalc

LineCalc will open in new window

50 line

/4, 2*50 line

/4, 2*50 line

100

SMD 1206 package

50 line

50 line

Port-1

Port-2

Port-3

4. LineCalc (see its important blocks)

5. Enter the Parameters of FR_4 in substrate definition block (Leave which are not given, Use

scroll bar to move down)

6. Adding Substrate Parameter to Schematic

In Schematic go to Tools->LineCalc->Place New Synthesized Component (this will add

MSUB block in schematic which is substrate definition, delete any additional block if it

comes till this point)

7. Adding Transmission Line (for the input line)

Enter frequency, Impedance and Electrical Length at the specified locations in LineCalc

In Physical section of LineCalc change units from mil to mm

Press Synthesize button which has upward arrow

Simulator will run and values of L and W will be calculated (Note down the values on

Notebook against the input line of the wilkinson power divider)

Finding Physical Length and Width of different Transmission Lines

Impedance Electrical Length Physical Length Physical Width

50 (Input and Output) 180 33.93 (depends on your

layout requirement)

2.99

70.7 (Quarter Wave

Transformer)

90 17.47 1.55

100 (for the SMD

Resistor of 100 Ohm)

180 35.94 (depends on your

layout requirement)

0.65

Line with this dimension on FR-4 will be equivalent to the one simulated in first part of the lab

In the schematic go to Tline-Microstrip from the component palette drop down menu and add

the MLIN in your design

Change physical dimensions of MLIN (TL1) according to the one found from LineCalc

noted in notebook

8. Adding Transmission Line (for the Transformer)

As was done for the input line

Adjust the parameters so that the dimensions of the two transformer can be found

Place another MLIN from the component Palette and adjust its physical dimensions also

Since the two legs (transformer) are identical in Wilkinson power divider so you can simply

copy paste this last MLIN to get another

9. This is the simulation of power divider which works at a certain frequency therefore

frequency domain solver S-Param needs to be added

Go to Simulation-S_Param from Palette

Add S-Parameter simulator into your schematic Design

10. Set

Start Frequency 1GHz

Stop Frequency 5GHz

Step 1MHz

Hint:

To do this, either double click on S_Param or simply click on the parameter to change value

11. Add termination Ports and ground all the termination

To run schematic design with S_Param we need to add the termination at the three ports

Pick and place Term from the same Palette

12. Run the Simulation and plot the results

Go to Simulate->Simulate or press F7

Plots following

S11

S21

S31

S32

S23

You should be able to observe the following

S11 : Dip at your desired frequency (indicates good matching)

S21: Peak at the desired frequency (indicate power division)

S31: Peak at the desired frequency (indicate power division)

S32: Dip at the desired frequency (indicates isolation of the output ports)

S23: Dip at the desired frequency (indicates isolation of the output ports)

Expected Graphs of S11, S21 and S31 (place marker to read values accurately)

Final Design Schematics

This cannot be used to generate the proper layout

Generating Proper Layout

To generate proper layout we need MTee at all the nodes and Mcorn at all the bends, Bends and

Nodes are identified in figure below

Figure with Mcorn and MTee (both are available in TL-Microstrip palette), two lines of 100 ohm

are also added to generate the proper layout (length of these lines depends on the separation which

you want to achieve between the output ports)

After the above additions Split Quarter wave Transformer into two equal transmission lines so each

will have length of 8.735 mm with the same width of 1.55mm. This is important to generate proper

layout.

Next step is to generate the layout. Go to Layout->Generate/Update Layout

Window will appear asking for the layout setting, you can take the default values and click OK.

Layout will appear in layout window

To improve the results you can Tune the Length of Quarter Wave Transformer and then update

the layout. You can generate the Gerber file and fabricate your design on FR-4 Sheet.