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AntennaMan
Antenna-Theory.com Newbie
Joined: 12 Jul 2012
Posts: 3
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 Posted: Thu Jul 12, 2012 3:13 pm Post subject: How do you calculate the Resonant Frequency of an antenna? |
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Hey Everyone,
How do I calculate the RF of my antennas? I have a VNA, oscilloscope, etc.
Thanks! |
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bigSteve
Antenna Wizard
Joined: 14 Mar 2009
Posts: 265
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| Posted: Thu Jul 12, 2012 5:14 pm Post subject: Antenna Resonance |
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If you have a VNA, just hook your antenna up to it and measure VSWR. The resonance is loosely defined as where the antenna becomes matched well (i.e. say, VSWR < 2, although there's no hard criterion). If you have something like a dipole antenna, there should be distinct resonance(s). If you have a very broadband spiral or horn antenna, the resonance may be an extended range of frequencies.
The oscilloscope won't be very helpful for resonant frequencies. |
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AntennaMan
Antenna-Theory.com Newbie
Joined: 12 Jul 2012
Posts: 3
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| Posted: Thu Jul 12, 2012 6:52 pm Post subject: |
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| What do you mean "matched well"? Does that refer to impedance? |
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bigSteve
Antenna Wizard
Joined: 14 Mar 2009
Posts: 265
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| Posted: Thu Jul 12, 2012 8:33 pm Post subject: Radiation Resistance |
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Yes - matched well refers to impedance. However, if you have a simple antenna (no resistance, loss materials, or matching components), then if the antenna has an impedance close to 50 ohms (well matched), then the impedance comes from the antenna's radiation resistance.
Basically this means the antenna is radiating power. From a circuit perspective, radiated power is lost power and can be modeled as a resistor. |
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