Balun for 437MHZ narrowband dipole

Abhiram Deva said:

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P.S my dipole is precisely 50 OHM and so is the coaxial cable so no need for impedance transformation. I only need to eliminate the coax shield currents.

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Abhiram Deva said:

Most of the balun types i have come across are not suitable for my design i.e a UHF dipole antenna for a nanosatellite. Surface mount transformer baluns have insertion loss and reflection which is normally acceptable but due to lack of power on the satellite we cant afford the loss. but these baluns are all wideband which is why they show bad performance. is there a way to design a balun for just one specific frequency where it gives excellent performance.
The closest thing i have come across is microstrip matching but turns out its not suitable for RF. Is there a solution for this situation.


If your special dipole is really 50 OHms, connect the coaxial line directly to it. To reject surface current on the 50-Ohm line, attach a ferrite bead, or add a quarter-wave shorted section to the "ground" end.
On a micro-satellite the radiation pattern is rather defined by satellite metal body (not a perfect ground), so do not worry about the surface current.

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davenn said:

How did you achieve that ? ... dipoles are 75 Ohms by nature ( folded ones 300 Ohms) ... what impedance matching did you do ?


Dave

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jiripolivka said:

Abhiram Deva said:

Most of the balun types i have come across are not suitable for my design i.e a UHF dipole antenna for a nanosatellite. Surface mount transformer baluns have insertion loss and reflection which is normally acceptable but due to lack of power on the satellite we cant afford the loss. but these baluns are all wideband which is why they show bad performance. is there a way to design a balun for just one specific frequency where it gives excellent performance.
The closest thing i have come across is microstrip matching but turns out its not suitable for RF. Is there a solution for this situation.


If your special dipole is really 50 OHms, connect the coaxial line directly to it. To reject surface current on the 50-Ohm line, attach a ferrite bead, or add a quarter-wave shorted section to the "ground" end.
On a micro-satellite the radiation pattern is rather defined by satellite metal body (not a perfect ground), so do not worry about the surface current.

Click to expand...

It is 50 Ohms indeed, but achieving this requires a 96 deg angle between the arms which is pretty steep and causes complications for the mechanism involved in releasing it from a stowed position. And i am not sure if i should compromise and go ahead with a monopole which makes it easier on me but at the cost of performance, i would appreciate any advice. I ask you this cause you sound like you are familiar with antenna design on small sats. Also could you elaborate on adding a quarter wave shorted section to the ground end solution or point me to some source material.

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jiripolivka said:

Abhiram Deva said:

Most of the balun types i have come across are not suitable for my design i.e a UHF dipole antenna for a nanosatellite. Surface mount transformer baluns have insertion loss and reflection which is normally acceptable but due to lack of power on the satellite we cant afford the loss. but these baluns are all wideband which is why they show bad performance. is there a way to design a balun for just one specific frequency where it gives excellent performance.
The closest thing i have come across is microstrip matching but turns out its not suitable for RF. Is there a solution for this situation.


If your special dipole is really 50 OHms, connect the coaxial line directly to it. To reject surface current on the 50-Ohm line, attach a ferrite bead, or add a quarter-wave shorted section to the "ground" end.
On a micro-satellite the radiation pattern is rather defined by satellite metal body (not a perfect ground), so do not worry about the surface current.

Click to expand...

It is 50 Ohms indeed, but achieving this requires a 96 deg angle between the arms which is pretty steep and causes complications for the mechanism involved in releasing it from a stowed position. And i am not sure if i should compromise and go ahead with a monopole which makes it easier on me but at the cost of performance, i would appreciate any advice. I ask you this cause you sound like you are familiar with antenna design on small sats. Also could you elaborate on adding a quarter wave shorted section to the ground end solution or point me to some source material.

Click to expand...

Click to expand...

It is 50 Ohms indeed, but achieving this requires a 96 deg angle between the arms which is pretty steep and causes complications for the mechanism involved in releasing it from a stowed position.

Click to expand...

davenn said:

Have you considered how this is going to adversely affect the radiation pattern of the antenna ?
its not going to have the pattern of a normal dipole any more

Dave

Click to expand...