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High radiating resistance antenna

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jabidof

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radiation resistance of beam antennas

Hello!

There exists many antennas that differs in their radiating resistance. But can we say that a 50 ohms p@tch antenna is less sensitive to e.g. the hand than a 300 ohms folded dipole antenna?

To enlarge the issue, what antenna characteristic (-10dB bandwidth, environment sensitivity, etc.) is affected by a low resp. a high radiating resistance value?

Thanks for your inputs.

BR
 

high radiation resistance antenna

jabidof said:
Hello!

There exists many antennas that differs in their radiating resistance. But can we say that a 50 ohms p@tch antenna is less sensitive to e.g. the hand than a 300 ohms folded dipole antenna?

To enlarge the issue, what antenna characteristic (-10dB bandwidth, environment sensitivity, etc.) is affected by a low resp. a high radiating resistance value?

Thanks for your inputs.

BR
Click to expand...

Generally speaking, the antenna's connector impedence, and radiation rasistance may be different.
Radiation resistance is a model, the power dissipate into the radiating resistance is the power sent into the space.
Of course not all power sent to a TX antenna is radiated, a little will be reflected (VSWR) and little will heat the antenna.
In VHF, UHF and Microwave internal loss are negligible.
After this preface, i'll try to answer.

The term "sensitivity" don't apply to antennas.
Antennas are identified by:
-Directivity (the thickness of the beam)
-Freedom from sidelobes
-Cross-polar performances
-VSWR

Often the Gain may be found instead Directivity.
Higher Gain means thinner beam !

Gain is mainly related to aperture Area and λ.

The importance of the input impedence is only related to power reflection consideration. You should minimize the reflection coefficient!
So 50 Ω antennas connected to 50Ω generators and 300Ω dipole connected to 300Ω generators.

The impedence itself don't influence the Gain
 

    J

    jabidof

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high radiation resistance in short antennas

sergio mariotti said:
jabidof said:
Hello!

There exists many antennas that differs in their radiating resistance. But can we say that a 50 ohms p@tch antenna is less sensitive to e.g. the hand than a 300 ohms folded dipole antenna?

To enlarge the issue, what antenna characteristic (-10dB bandwidth, environment sensitivity, etc.) is affected by a low resp. a high radiating resistance value?

Thanks for your inputs.

BR
Click to expand...

Generally speaking, the antenna's connector impedence, and radiation rasistance may be different.
Radiation resistance is a model, the power dissipate into the radiating resistance is the power sent into the space.
Of course not all power sent to a TX antenna is radiated, a little will be reflected (VSWR) and little will heat the antenna.
In VHF, UHF and Microwave internal loss are negligible.
After this preface, i'll try to answer.

The term "sensitivity" don't apply to antennas.
Antennas are identified by:
-Directivity (the thickness of the beam)
-Freedom from sidelobes
-Cross-polar performances
-VSWR

Often the Gain may be found instead Directivity.
Higher Gain means thinner beam !

Gain is mainly related to aperture Area and λ.

The importance of the input impedence is only related to power reflection consideration. You should minimize the reflection coefficient!
So 50 Ω antennas connected to 50Ω generators and 300Ω dipole connected to 300Ω generators.

The impedence itself don't influence the Gain
Click to expand...

I agree but how does the impedance of let say a folded dipole vary when a human hand approaches? Does the antenna become more capacitive due to the ground path that appears with the approaching hand?

I have another question regarding the antenna radiation resistance. How can i build an antenna whose radiating resistance is high (>300 Ω)?

Thanks for your reading,
jpc
 

High R? Just make it short. I think the radiation resistance of a standard automotive antenna in the AM band is around 5000 ohms.
 

biff44 said:
High R? Just make it short. I think the radiation resistance of a standard automotive antenna in the AM band is around 5000 ohms.
Click to expand...

Thanks for the input. Actually, i am looking for High R antenna at UHF (900 - 3000 MHz).
 

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