How to design a helical antenna in CST MWS with minimum back lobe radiation pattern?

Hello

I want to design a helical antenna in CST MWS with minimum back lobe radiation pattern. The antenna size should be small and input impedance of 50 Ohms.

Please Help. I am a beginner.

What frequency, what size, what bandwidth, what gain ?

2.45GHz (ISM Band), Gain and Bandwidth are flexible. Size should be such that the antenna can be fixed on a stick.

i am working on mode converter..i have two issues as follows:-

1.how to give a TM01 mode to a circular bent waveguide in CST microwave studio..?

2.how to check on the output different modes coming out of circular waveguide in cst. The dominant mode of circular waveguide is TE11.
i want to plot a graph with fractional power of different modes on y-axis Vs. frequency on x-axis. my frequency range is 1-10 GHz.

the above are two issues, i have already designed the structure, but dont know how to give the TM01 input and check the various fractional power.

This has absolutely nothing to do with the thread. Start another thread.

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You need to design the antenna using your head, and simulate it using CST.

Do yourself a favor. Go and get a copy of Kraus's antennas book, and look up the helical antenna. You will find that for the most common type (axial mode):

• There is a simple formula to work out the circumference - it is simply the wavelength.
• There's a pretty simple formula to work out the spacing between turns - the pitch.
• The input impedance is about 140 Ohms, so you need a matching network.
• The gain is proportional to the number of turns.
• The antenna is quite wide band, so no problem covering the 2400-2500 MHz, which is what I think you want, though I expect the ISM band varies by country.

Since you have not stated the length, diameter, type of material of this stick, I will asssume it is carbon fibre, 50 mm in diameter and 1000 mm long. That will support quite a large antenna, so you can get high gain.

A piece of copper strip, about 6 mm wide, soldered to the bottom quarter of a turn of the antenna and placed near the groundplane can be used to match it to 50 Ohms.

It is normal to have a groundplane with a helix, and for minimum backlobes, you are going to want to increase the size of it. To keep the weight down, if my assumptions about your "stick" are wrong, you might want to consider a mesh.

There is a method of feeding a helix without a groundplane, where there are turns in front and behind the feed point. That might make it easier to cut down the weight, but I've no idea how it performs - look in Kraus.

BTW, you would make your life a lot easier if you actually wrote what your specifications were. Initially you gave no frequency, gain or any other useful information. You have now told us it needs to be mounted on a stick, with no idea of the length or diameter of that stick.

Thank you DeboraHarry for the reply. It was very useful. I referred to the textbook and I have designed a basic helix antenna structure with some calculated parameters (as mentioned in Kraus).
The antenna will be mounted on the stick. The stick can have dimensions: 125x12.1x8.8mm and is insulated.

I think increasing the ground plane will make the antenna heavy. I have seen the ground plane is replaced by two loops. I want to make the antenna directional to minimize the back lobe. Please guide me as to how to move further with the design

Thank You.

But how do you plan to make the helical antenna directional ? I have heard of making the dipole antenna directional as in Sector antennas wherein we have a ground plane on one side of the dipole. By doing so, we can control the beam-width of the antenna and also the gain will be enhanced as compared to dipole antenna though there will be a compromise of beam-width from 360 degrees to say 90 / 120 degrees max.

Do send across your .geo file and shall try to check on your design.

hello,
i have a problem in this design!....
I made a helical 4-elements array design..I got a very good value of gain. But, unfortunately when I made a Hexagonal 6-elements array a null presented in the radiation pattern, beside bad gain and a very wide beam width...
can any one help me in finding a solution for this problem please?
I'm using waveguid ports.
I would really appreciate it if anyone can help me :)

best regards,
Hassan

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