Helical Antenna Design in CST

 Helical Antenna Design in CST MWS

Objective: To understand, design helical antenna and observe the simulated results.

Antenna-Theory: It is a type of antenna in the shape of helix. Its polarization and radiation properties depend on the diameter, pitch, number of turns, wavelength, excitation and spacing between the helical loops. Helical antenna consists of helical loops made of thick conductor which give the appearance of screw thread. 

Fig. 1.1 Helical antenna

Step 1. Parameter Calculation 

The center frequency of the required helical antenna is 3 GHz. However the coil radius, coil height, number of turns of coil and angle increment is shown below in table.

Fig. 1.2 Design values of loop antenna

Step 2. Designing 

As you have list of parameters it's time to design the helical antenna in CST software. For that you need to perform following minor steps. All of these highlighted steps are already explained in half wave dipole antenna design tutorial. 

1. Create new project.

2. Select Antennas.

3. Click on Wire.

4. Select time domain.

5. Enter frequency range.

6. Final Summary. 

After creating a CST MWS project for helical antenna. Now construct a linear coil model as shown in image below. All of the values are mentioned in table.

Click on Macros Tool>>Coils>>3D linear helical spring>>Enter Coil radius 4.77, Coil height 67.32, Number of Turns 9, Angle increment 14.

Fig. 2.1 Constructing a helical model

Click on modeling tool, Select pick edge from picks. This will select the end point of helical spring.

Fig. 2.2 Assigning radius values

Use curves tool for helical radius. a circle is required to be created near edge of helical spring. This shape will help us to create a helical spring.

Fig. 2.3 Assigning radius values

Select Sweep Curve from Curve tools and change the material. This will ask you to select the first shape(circle) and then press ok. After that select the second shape(helical) and then press ok. 

Fig. 2.4 Assigning radius values

Now you need to make a coaxial cable for that you need a cylinder tool with local coordinates. Use the values mentioned in above table.

Fig. 2.5 adding coaxial port

To create a coaxial cable you have to have outer conductor, dielectric and inner conductor. we have to create an inner conductor first that can be seen in figure below.

Fig. 2.6 adding inner conductor of coaxial

To create a dielectric you need to assign the values by clicking on cylinder tool and then put the given values of radius. Yon need to chose the material vacuum or Fr4.

Fig. 2.7 adding dielectric material

Again click on cylinder tool to make the outer conductor around the dielectric material. Use the values mentioned in table.

Fig. 2.8 adding outer coaxial conductor

You also need to create a GND as shown in the image below. Further after creating a ground the antenna should be given a discreate port for that you shall use the pick edge option where you shall chose option"pick point on circle". The first point is on outer conductor and second point is on inner conductor. Next you need to assign the discrete port and simulate the ultimate design. 

Fig. 2.9 Inserting a Ground

Click on field, click on far field and repeat the same process for E&H-field.

Fig. 2.10 Simulating the antenna

Step 3. Results 

Fig. 3.1 S11 of Helical antenna