Keysight EEsof EDA

Microstrip and CPW Power Divider Design

Demo Guide
02 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Theory
A power divider is a three-port microwave device that is used for power division or power
combining. In an ideal power divider the power given in port 1 is equally split between the two
output ports for power division and vice versa for power combining as shown below. Power
divider finds applications in coherent power splitting of local oscillator power, antenna feedback
network of phased array radars, external leveling and radio measurements, power combining of
multiple input signals and power combining of high power amplifiers.

Power P1
P3
Divider P2

P1 Power
P3 = P1 + P2
P2 Combiner

Figure 164.

T–Junction Power Divider

The different types of power dividers are a T-Junction power divider, a Resistive divider and a
Wilkinson power and hybrid coupler. The T-Junction power divider is a simple 3-port network
and can be implemented in any kind of transmission medium like microstrip, stripline, coplanar
wave guide etc. Since, any 3-port network cannot be lossless, reciprocal and matched at all
the ports, the T-Junction power divider being lossless and reciprocal cannot be perfectly
matched at all the ports. The T-Junction power divider can be modeled as a junction of three
transmission lines as shown in the figure below.

Figure 165.
03 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Objective
To design various types of Power Dividers at 3 GHz and simulate the performance using ADS.

Design of Distributed T-Junction Power Divider

1. Select an appropriate substrate of thickness (h) and dielectric constant (εr) for the design
of the power divider.
2. Calculate the wavelength λ g from the given frequency specifications as follows:

c
λg =
√ε r ƒ

Where, c is the velocity of light in air.

f is the frequency of operation of the coupler.

εr is the dielectric constant of the substrate.

3. Synthesize the physical parameters (length & width) for the λ/4 lines with impedances of
Z0 and √2 Z0 (Z0 is the characteristic impedance of microstrip line which is = 50 Ω)

Layout Simulation Using ADS

1. Calculate the physical parameters of the T-Junction power divider from the electrical
parameters like Z0 and electrical length using the above given design procedure. The
physical parameters can be synthesized using Linecalc. The Physical parameters of the
microstrip line for the 50 Ω (Z0) and 70.7 Ω ( √2 Z0) are as follows.
2. Dielectric properties: Er = 4.6, Height = 1.6 mm, Loss Tangent = 0.0023, Metal Height =
0.035 mm, Metal Conductivity = 5.8E7.

50 Ω Line:
Width – 2.9 mm
Length – 13.3 mm

70.7 Ω Line:
Width – 1.5 mm
Length – 13.6 mm

3. Create a model of the T-Junction power divider in the layout window of ADS. The Model
can be created by using the available Microstrip library components or by drawing
rectangles.
04 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

4. To create the model using library components, select the TLines – Microstrip library.
Select the appropriate Microstrip line from the library and place it on the layout window
as shown in the next figure.

Figure 166.

–– Connect the Pins and input and output terminals and set the EM simulation as described in
the EM simulation chapter earlier. Once done, it should be as in the figure below.

Figure 167.

–– Define the simulation frequency from 2 to 3 GHz and turn on Edge Mesh from the
Options > Mesh tab in the EM set up window.

Figure 168.
05 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

–– Click the Simulate icon and plot the results to observe the T-Junction power divider
response as shown below.

Figure 169.

Results and Observations

It is observed from the layout simulation that the T-Junction power divider has an insertion loss
(S12 and S13) of 3.0 dB and return loss (S11) of about 29 dB but as expected isolation between 2
output branches is only 6 dB representing real characteristics of T-Junction power divider.
06 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Wilkinson Power Divider

The Wilkinson power divider is a robust power divider with all the output ports matched and
only the reflected power is dissipated. The Wilkinson power divider provides better isolation
between the output ports when compared to the T-Junction power divider The Wilkinson power
divider can also be used to provide arbitrary power division. The geometry of a Wilkinson power
divider and its transmission line equivalent is shown in the figure below.

Figure 170.

Design of a Lumped Model Wilkinson Power Divider

Calculate the values of the capacitances (C1 & C2), inductances (L1, L 2 & L 3) and resistance (R1)
required for the Lumped model of the coupler shown in the illustration below using the given
formulae.

Figure 171.

Where, for any arbitrary impedance Z0 = Ra = Rb = Rc = 50 ohms

ω is the angular frequency
07 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Typical Design
Design frequency = 3 GHz
Angular frequency in radians = 1.88 x 1010
C1 = C2 = 0.75 pF
L 2 = L 3 = 3.75 nH
L1 = 1.87 nH
R = 100 Ω

Schematic Simulation Steps

1. Open the Schematic window.
2. From the lumped components library, select the appropriate components necessary for
the lumped model. Click the necessary components and place them on the schematic
window as shown in the figure below.

Figure 172.

3. Setup the S-Parameter simulation from 2.5 to 3.5 GHz with a step size of 0.01 GHz.
Perform the simulation and observe the parameter response as shown below.
08 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Figure 173.

Results and Observations

It is observed from the schematic simulation that the lumped model of the Wilkinson power
divider has an insertion loss (S12 and S13) of 3 dB and return loss (S11) of < 30 dB.

Design of Distributed Wilkinson Power Divider

Layout Simulation Using ADS
1. Calculate the physical parameters of the Wilkinson power divider from the electrical
parameters like Z0 and electrical length similar to T-Junction power divider. The physical
parameters can be synthesized using Linecalc. The physical parameters of the microstrip
line for the 50 Ω (Z0) and 70.7 Ω (√2 Z0) are as follows on the dielectric selected in the in
the T-Junction power divider design.

50 Ω Line:
Width – 2.9 mm
Length – 13.3 mm

70.7 Ω Line:
Width – 1.5 mm
Length – 13.6 mm
09 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

2. The layout of the Wilkinson power divider will be done the same as we did earlier except
for the fact that we will use an isolation resistor of 2*Z0, which in our case will be
100 Ohm since the characteristic impedance is 50 Ohm.
3. Use TLines-Microstrip components or the rectangle/polygon icon to create the power
divider structure. Please note that in the Wilkinson power divider, we will need 2 extra
Pins at the place where we shall later connect a 100 Ohm resistor.

Figure 174.

4. Define a new or reuse the substrate defined earlier in the T-Junction power divider
exercise. Define the frequency sweep from 2.5 to 3.5 GHz and from the Model/Symbol
option in the EM setup window, click the Create Now button under the EM Model and
Symbol fields to generate an EM Model data container and layout look-alike symbol
so that we can use this layout component to perform resistor assembly and EM
cosimulation. Detailed steps for this are provided in the EM simulation section.

Figure 175.

5. Open a new schematic cell, drag & drop this layout on the same and connect
Terminations and Resistor as shown below. Set up a S-Parameter simulation from
2.5 to 3.5 GHz with Step=0.01 GHz.
10 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Figure 176.

6. Click the Simulate icon, then plot the graphs in the data display as shown below.

Figure 177.
11 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Figure 178.

Results and Observations

It is observed from the layout simulation that the Wilkinson power divider has an insertion loss
(S12 and S13) of 3.0dB and return losses (S11, S22, S33) < –25 dB.

Design of CPW T-Junction Power Divider

Objective
To design a CPW T-Junction power divider at 2.4 GHz and simulate the performance using ADS.

Design Procedure
1. Select an appropriate substrate of thickness (h) and dielectric constant (εr) for the design
of the power divider.
2. Calculate the wavelength λ g from the given frequency specifications as follows:

c
λg =
√ε r ƒ

Where, c is the velocity of light in air.

f is the frequency of operation of the coupler.

εr is the dielectric constant of the substrate.

3. Synthesize the physical parameters (length & width) for the λ/4 CPW line with
impedances of Z0 and √2 Z0 (Z0 is the characteristic impedance of CPW line = 50 Ω).
12 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Layout Simulation Using ADS

1. Calculate the physical parameters of the T-Junction power divider from the electrical
parameters, like Z0, and electrical length using the above design procedure. The physical
parameters can be synthesized using Linecalc as shown in the following illustration. The
Physical parameters of the CPW line for 50 Ω (Z0) and 70.7 Ω ( √2 Z0) are as follows:

50 Ω Line:
Width: 3 mm
Length: 20 mm
Gap: 0.37 mm

70.7 Ω Line:
Width : 1.5 mm
Length: 19.6 mm
Gap: 0.69 mm

Figure 179.

2. Create a model of the T-Junction power divider in the layout window of ADS. The Model
can be created by using the available TLines-Waveguide library components or by
drawing rectangles.
13 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

Figure 180.

The ground separation lines will help us as a guiding line for ground creation and we can simply
use the rectangle icon to create the ground for these CPW lines as shown below.

Figure 181.

3. Assign Pins in layout for the CPW transmission line by clicking the Pin icon and placing
them in the circuit i.e. 1 Port on the main line and placing 2 ports attached to the ground
fill on either side of the main signal pin. For the present case, we shall have a total of 9
Pins, i.e. 3 Signal Pins and 6 ground pins. For easy remembrance, place 3 signal pins so
that they are named as P1, P2 & P3 and then start placing P4 & P5 around P1, P6 & P7
around P2 and P8 & P9 around P3. It is strongly advised to place ground ports slightly
inside the ground pattern.
14 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

4. Defining the CPW substrate without the ground at the bottom will require the substrate
to be defined differently than what we have done so far. Open the EM setup window,
define the required dielectric as described in earlier labs and do the following additional
actions:
a. Right-click the FR4 and select Insert Substrate Layer Below. Right-click the Cover
and select Delete Cover.
b. Change the bottom side dielectric to be AIR (which is by default provided in the
substrate definition window). Once done, it should look as shown below.

Figure 182.

5. Go to the Ports option in the EM setup window and select Ports 4 to 9, right-click and
delete so that they are removed from the list and appear at the bottom side.

Figure 183.

6. From the Unconnected Layout Pins, drag and drop P4 and P5, which are placed on either
side of P1 in the layout on -GND so that it looks as below. Do this also for P2 and P3
using the respective unconnected Layout Pins.

Figure 184.
15 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

7. Once done, Port assignment will be as shown below.

Figure 185.

8. Setup simulation frequency as 2 to 2.8 GHz and turn on Edge Mesh from the
Options > Mesh option of the EM Setup window. Perform simulation and plot the
desired response to observe the Simulation Results as shown below m1 freq=2.400 GHz
dB(S(1,1))=-20.244 dB(S{2,1))=-3.784 dB(S{3,1))=-3.446

Figure 186.

Congratulations! You have completed Microstrip and CPW Power Divider Design. Check out
more examples at www.keysight.com/find/eesof-ads-rfmw-examples
16 | Keysight | Microstrip and CPW Power Divider Design - Demo Guide

For more information on Keysight

Download your next insight Technologies’ products, applications or

services, please contact your local Keysight
office. The complete list is available at:
Keysight software is downloadable www.keysight.com/find/contactus
expertise. From first simulation through
first customer shipment, we deliver the Americas
tools your team needs to accelerate from Canada (877) 894 4414
data to information to actionable insight. Brazil 55 11 3351 7010
Mexico 001 800 254 2440
United States (800) 829 4444
–– Electronic design automation (EDA)
Learn more at
software
www.keysight.com/find/software Asia Pacific
–– Application software Australia 1 800 629 485
–– Programming environments China 800 810 0189
Start with a 30-day free trial. Hong Kong 800 938 693
–– Productivity software
www.keysight.com/find/free_trials India 1 800 11 2626
Japan 0120 (421) 345
Korea 080 769 0800
Evolving Since 1939 Malaysia 1 800 888 848
Singapore 1 800 375 8100
Our unique combination of hardware, software, services, and people can help you Taiwan 0800 047 866
reach your next breakthrough. We are unlocking the future of technology. Other AP Countries (65) 6375 8100
From Hewlett-Packard to Agilent to Keysight.
Europe & Middle East
Austria 0800 001122
Belgium 0800 58580
Finland 0800 523252
France 0805 980333
Germany 0800 6270999
Ireland 1800 832700
Israel 1 809 343051
Italy 800 599100
Luxembourg +32 800 58580
Netherlands 0800 0233200
myKeysight Russia 8800 5009286
www.keysight.com/find/mykeysight Spain 800 000154
Sweden 0200 882255
A personalized view into the information most relevant to you.
Switzerland 0800 805353
Opt. 1 (DE)
www.keysight.com/find/emt_product_registration Opt. 2 (FR)
Register your products to get up-to-date product information and Opt. 3 (IT)
find warranty information. United Kingdom 0800 0260637
Keysight Services
www.keysight.com/find/service For other unlisted countries:
Keysight Services can help from acquisition to renewal across your www.keysight.com/find/contactus
instrument’s lifecycle. Our comprehensive service offerings—one- (BP-9-7-17)
stop calibration, repair, asset management, technology refresh,
consulting, training and more—helps you improve product quality
and lower costs.
DEKRA Certified
ISO9001 Quality Management System

Keysight Assurance Plans www.keysight.com/go/quality

www.keysight.com/find/AssurancePlans Keysight Technologies, Inc.
Up to ten years of protection and no budgetary surprises to ensure DEKRA Certified ISO 9001:2015
your instruments are operating to specification, so you can rely on Quality Management System
accurate measurements.

Keysight Channel Partners

www.keysight.com/find/channelpartners
Get the best of both worlds: Keysight’s measurement expertise and
product breadth, combined with channel partner convenience.

This information is subject to change without notice.

© Keysight Technologies, 2017
Published in USA, December 1, 2017
5992-1632EN
www.keysight.com