EX.NO:

DATE:

DESIGN OF A BRANCH LINE COUPLER

Aim:

To design and analyze the characteristics of a directional coupler using ADS

Apparatus required:

1. Personal computer

2. ADS software

Theory:

A branch-line coupler outputs from the coupled port (pin 3) a fraction of

the power presented at the input (pin 1). The remainder of the power is passed through to

the output port (pin 2). At the center frequency the phase difference between the outputs

is 90 degrees, with the coupled port representing the quadrature (Q) output and the output

port representing the in-phase (I) output. The coupling coefficient specifies the ratio of

the input power to the coupled power (P1/P3). Pin 4 represents the isolated port, and it is

typically well isolated from the input port near the center frequency. The coupling

coefficient must be positive and greater than 3 dB. Best results are obtained for tight

couplings of 6 dB or better (C < 6 dB). Choosing the coupling parameter larger than 6 dB

often causes width constraint violations to occur on the MTEE components, resulting in

warning messages during design and simulation.

A coupling coefficient of 3 dB provides an equal power split between the

two outputs. For broadband performance, the coupler can have multiple sections. If the

number of sections N is set to zero, the Design Assistant chooses N such that the

reflection coefficient is less than R max over the bandwidth Delta (centered at the design

center frequency). The resulting bandwidth can be broader than that specified. Otherwise,

r max and Delta are ignored. The Response Type specifies the distribution of the partial

reflection coefficients seen at each section interface - Uniform, Binomial, and Chebyshev

distributions are available. The optimization minimizes the input reflection coefficient

(S11) at the design center frequency by changing the length of the lines forming the four

branches. All branches are changed by the same physical length during the optimization.

PROCEDURE:

Step1: Open the ADS software.

Step2: Create a new project from the file menu

Step3: Open the schematic window of ADS.

Step4: From the components library select the appropriate necessary for the required

model.

Step5: Click on the necessary components and place them on the schematic windows of

ADS.

Step6: Terminate both the ports of the branchline coupler using terminations selected

from the simulation –S_param library.

Step7: Click the S-param icon to open the S-parameter simulation diolog box. In the

dialog box give the start, stop and step frequencies for the simulation.

Step8: Save the schematic window of ADS.

Step9: Simulate the project.

BRANCHLINE COUPLER

freq (1.000GHz to 10.00GHz)

S(1

,1)

Input Reflection Coefficient

freq (1.000GHz to 10.00GHz)

S(2

,2)

Output Reflection Coefficient

2 3 4 5 6 7 8 91 10

-35

-30

-25

-20

-15

-10

-5

-40

0

freq, GHz

dB

(S(1

,2))

Reverse Transmission, dB

S-Parameters vs. Frequency

2 3 4 5 6 7 8 91 10

-35

-30

-25

-20

-15

-10

-5

-40

0

freq, GHz

dB

(S(2

,1))

Forward Transmission, dB

OUTPUT:

Result:

Thus the Branch Line coupler was simulated using ADS and the output was

verified successfully.