antenna-theory.com

[oliver]

Dear Sir,

Would you please advise why shorting pin of PIFA if acts inductive reactance will reduce resonant frequency and if acts capacitive reactance will increase resonant frequency?

Thanks and best regards,
Oliver

[admin]

The shorting pin acts as an inductive reactance: it can be viewed as a short circuited transmission line that is a small portion of a wavelength long. It resonates with the open circuited end (capacitive).

The shorting pin is required so that the PIFA can be a quarter wavelength long. Without it, the antenna would be a patch antenna and would have to be approximately a half-wavelength long.

[oliver]

Hi Sir,
Thanks a lot for your prompt response!
May I conclude the effect of shorting pin to resonant frequency as below,
1. pure inductive has lower resonant frequency since longer shorted end transmission line
2. indcutive and capacitive is the original resonant frequency since mid shorted end transmission line
3. pure capacitive has higher resonant frequency since there is no shorted end transmission line (open end)

Thanks and best regards,
Oliver

[admin]

Not sure what you are talking about.

[oliver]

Sorry for confusion!

Since I'm don't quite understand why shorting pin viewed as open circuited end (capacitive) will increase resonant frequency, could you please explain more detailed?

Thanks for your patience!

[admin]

Don't think about capacitive or inductive loading - just think of the PIFA as a quarter-wavelength structure that radiates. The shorting pin enables the antenna to radiate with only a quarter-wavelength size.

If you wanted to further reduce the resonate frequency, then you could think about capacitive loading the open circuited end.