Patch antenna Tutorial.docx

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TUTORIAL On Rectangular Patch Antenna Design using CST MICROWAVE STUDIO Prepared by RAKESH KUMAR TRIPATHI & DINESH SHARMA Under the guidance of Dr. Rajesh Khanna Professor (ECED) ELECTRONICS AND COMMUNICATION ENGINEERING DEPARTMENT THAPAR UNIVERSITY (Established under the section 3 of UGC Act, 1956) PATIALA-147004(PUNJAB)

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CST Tutorial

Transcript of Patch antenna Tutorial.docx

Page 1: Patch antenna Tutorial.docx

TUTORIAL

On

Rectangular Patch Antenna Design using CST MICROWAVE STUDIO

Prepared by

RAKESH KUMAR TRIPATHI

&

DINESH SHARMA

Under the guidance of

Dr. Rajesh Khanna

Professor (ECED)

ELECTRONICS AND COMMUNICATION ENGINEERING DEPARTMENT

THAPAR UNIVERSITY

(Established under the section 3 of UGC Act, 1956)

PATIALA-147004(PUNJAB)

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Before starting the designing part of patch antenna, it is very important to understand the following topics in detail…..

Antenna Parameter S Parameter Smith Chart(very important) Introductory part of patch antenna VSWR Impedance Matching Decibel

Here I am attaching a folder where u can get the description of above topics.

Folder

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CST MICROWAVE STUDIO is a full-featured software package for electromagnetic analysis and design in the high frequency range. It simplifies the process of inputting the structure by providing a powerful solid 3D modeling front end. After the component has been modeled, a fully automatic meshing procedure is applied before a simulation engine is started.

The step by step procedure for modeling of patch antenna is given below:

1. Before modeling the patch antenna on CST, calculate all the required dimensions (like length, width of patch etc.). Also decide that which feeding technique we are going to use.

The dimensions of patch antenna can be calculated by using patch antenna calculator available on the internet.(http://www.emtalk.com/mpacalc.php)

Once we have calculated the length and width of patch the next step is to calculate the dimensions of substrate. The substrate length and width can be calculated by given formula

Ls = Lp +6 hWs = Wp +6 h

Where, h is substrate height that is already chosen by the designer.2. Click on the start button and then select CST Microwave Studio. A window is pop up as

shown below.(figure 1)

Figure 1

3. For patch antenna design select Antenna (Planer) as shown in Figure14. Please ensure that the default units are in mm, GHz and ns. Figure2.

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Figure 25. As we know that patch antenna generally consists of three layers named ground,

substrate, patch as shown in figure 3. So, each layer is modeled on CST one by one.

Figure 3

STEPS FOR SUBSTRATE MODELING OF ANTENNA :

Video 1

i. Select on the object tab and select basic shapes- brick (for rectangular patch antenna).

ii. Then press Esc button from key board a new window will pop up.(figure 4)

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Figure 4

iii. From new window select name of substrate and fill the other calculated dimensions. Be careful while assigning the dimensions.

iv. In materialselect new material: a new window will pop up as shown in figure4. v. Fill the appropriate value of materials. Then press ok.vi. Finally substrate layer is modeled on CST Microwave Studio. (shown in figure 5)

Figure 56. STEPS FOR PATCH MODELING OF ANTENNA

Video 2i. Steps are almost similar as substrate modeling except the selection of material i.e.

select PEC from list of material. ii. Press ok then brick shape of patch is created on the mesh of given shape of some

other color just touching the substrate as shown in figure 6.

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Figure 6

7. STEPS FOR GROUND MODELING OF ANTENNA

There is a different technique for different feeding to model the ground. Here I am assuming the coaxial feeding technique.i. Rotate the structure in such a way so that the back bottom of substrate is on the

front side as shown in figure 7.

Figure 7ii. Select on the object tab- select Pick- Pick face –then double click on bottom side

of structure. (as shown in figure 8.)

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Figure 8

iii. Select object- extrude; a new window will pop up. Take the height of ground 3 times of the height of substrate layer. And do not change the other default values.Finally, a three layer structure is modeled as shown in figure 9.

Figure 9

8. STEPS FOR MODELING FEED LINE (COAXIAL CABLE)

i. For outer cable: Select on the object tab and select basic shapes- cylindrical shape. Then press Esc button from the keyboard. A window is open as shown in figure 9.

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Figure 10

Then fill the required values. Keep in mind that the outer conductor material should be same as substrate material. Press OK tab. Now select option for ADD BOTH SHAPES then press OK and then select option for INSERT HIGHLIGHTED SHAPE then again press OK. You will find updated picture as shown in figure 11.

Figure 11

ii. For inner cable: Select on the object tab and select basic shapes- cylindrical shape. Then press Esc button from the keyboard. A new window will pop up as shown in fig-12. Then fill the values of parameter like radius, Z (height) and materials and do not change other default values. After pressing the OK tab.

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Figure 12iii. Again a new picture will be updated as shown in figure13.

Figure 13

9. STEPS FOR WAVEGUIDE MODELING

i. Rotate the structure in such a way so that the back bottom of ground is on the front side.

ii. Select on the object tab and select Pick- Pick face –then double click on the area between inner and outer cable of structure. Updated figure is shown in figure 14

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Figure 14

iii. Now go to solve tab then waveguide ports then OK. Do not change any other default values. Final updated figure is figure 15.

Figure 15

10. Now the next step is to assign the frequency range for which patch antenna is simulated. For that

Selects solvefrequency-value-rangeA new window is open as shown in figure 16

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Figure 16

11. BOUNDARY CONDITION:

Select solve-boundary condition; then a window is open as shown in figure 17

Figure 17

For the coaxial cable the boundary condition is shown in figure 17. While for other feeding techniques, the boundary condition should be open (add space) in all the fields.

The final updated model is figure 18.

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Figure 18

Then selectsolve- transient solver; a new window is open as shown in figure19. Select Start. Finally the simulation process will start.

Figure 19

Simulation Results

After the completion of simulation process, results can be viewed by clicking 1D results as shown in figure 20.

1. Return Loss Parameter

Return loss of any antenna can be measured by scattering Parameter (S11). This result can be viewed by selecting….

1D Result- ISI dB(mod of S)

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Figure 20

The most important parameter for any antenna design is the S parameter that basically describes the input-output relationship between ports (or terminals) in an electrical system. For instance, if we have 2 ports (intelligently called Port 1 and Port 2), then S12 represents the power transferred from Port 1 to Port 2. S21 represents the power transferred from Port 2 to Port 1. In general, SNM represents the power transferred from Port N to Port M in a multi-port network.For the faithful operation of patch antenna the value of S11 should be less than -10dB. This value i.e. returns loss parameter improves as the matching between feed line and patch antenna improves.

Method to improve the matching

The first step is to make the impedance of co-axial cable 50 Ohm. This can be done by changing the inner and outer radius of coaxial cable.

Coaxial cable impedance =k outer radiusinner radius

Where, k is any constant.

Thus, to increase the cable impedance, either increase the outer radius or decrease the inner radius.The feed impedance can be seen on the right top corner of the smith chart. For 50 ohm feed line it should be 50 ohm.

The next is to select the proper feed point so that the maximum power can be transferred from source to the load ( According to the maximum power transfer theorem). Since we have selected the 50 ohm for the cable so it is important to select a feed point corresponding to 50 ohm for the maximum power transfer. Fig.21

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Method to select the 50 ohm feed point

The best method is to select the proper feed point is the parameter sweep method.

Parameter sweep method:

In this method feed point is automatically moved across the x line (at y=0).

View parameter list- then assign the values to the variable parameter.

Select solve transient solver.

Click on the parameter sweep; a new window, as shown in figure 21 is opened.

Figure 21

Click on new sequence then click on new parameter; a new window is opened as shown in fig 22.

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Figure 22

Select the parameter and assign the range of values between which you want to move the feed line.fig 23

Figure 23

Then go to add watch and select S parameter as shown in fig (24).

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Figure 24

Finally fig 25 type window appears. Check the Mag (dB) radio button.

Figure 25

Click on the start button as shown in figure 26.

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Figure 26

Now update the X- parameter with L in the outer and inner cable.

Now go to solve –transient- click on parameter sweep new window will pop up and click on start tab.

Now the processing will start and after click on table – S 11 in dB a group curves will shown in fig 27Now, select the maximum negative value dB for best result.Now suppose if you want to vary the length and width of patch then fallow the figure 27.

Figure 27

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The effect of varying length and width can be seen from this graph shown in figure 28. This will help you to decide the length and width of patch antenna for better response.

Figure 28

Smith chart:-

For smith chart of simulated antenna follow the figure 29. Video 3

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Figure 29

Impedance Plot:-

This plot is very important from the antenna performance point of view. For better response of patch antenna the real impedance and imaginary impedance should be approximately 50 Ohm and 0 Ohm respectively at the resonating frequency. ( According to Max. Power Transfer Theory)

To view the impedance plot select

ResultS Parameter Calculation Calculate Z and Y Matrix

Figure 30

On doing so 2 new child is added in 1D Results. Now click on Z matrixReal Part as shown in figure 31.

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Figure 31

As stated earlier the real impedance at the resonating frequency should be approx 50 ohm.( Figure 32)

Figure 32

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VSWR:-

For the VSWR plot select

ResultS Parameter Calculation Calculate VSWR

Figure 33

Figure 34

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Radiation Patterns:-

Video 4

To view the radiation pattern follow the following steps…

Step 1:

Solvefield Monitor

Figure 35

Step 2: Do as shown in figure below.

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Figure 36

When you click on OK button, a 3-D plot as shown in figure will display.

Figure 36

This is the directivity plot of patch antenna at resonating frequency.

Now right click on the plot and select plot properties.

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Figure 37

A new window will open as shown in figure below. From this you can select your plot type.

Figure 38

Now go in Plot Mode tab….. and select the required radiation pattern plot.

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Figure 39

The above discussed radiation pattern plot is plotted only for single frequency. Suppose if we require a plot directivity Vs frequency then we have to follow a different procedure.

The step by step procedure is discussed here.

Macros farfieldBroadband farfield Monitor

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Figure 40

Put the frequency range and frequency steps.

Figure 41

Select ResultTemplatebased Postprocessing

Figure 42

1D Result farfield(broadband)

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Figure 43

Figure 44

To view the simulated result ie radiation patern Vs frequency plot

Tables1D Resultsbroadband gain 3D

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Figure 45

Slot cut:-For slot cut fallow the link video……….

Video 5

Still you have any query regarding this design, please feel free to contact me. My contact details are given below-

Name: Rakesh TripathiEmail- [email protected]

[email protected] +91-7838597621

ORName: Dinesh SharmaEmail- [email protected] +91-9560625333

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