Issues with HP8753D, while calculating the tuning frequency of an antenna

[saviour2009]

I am using a monopole antenna and trying to verify its resonant frequency using an HP8753D VNA. The process I am using is as explained below:

1. Calibrate the VNA using S11-1 port calibration method.
2. Connect the antenna using a co-axial cable to the VNA and check the S11 parameter graph over the frequency range.
3. For a length of 7.6 cms, I should have resonant frequency around 1 GHz, however I am also getting larger dips at higher frequencies (at around 3.5 GHz). As per the logic I should only have a dip at the resonant frequency.

Please advise what could be the possible reason behind the above mentioned situation.

Thanks...!!

 

[jiripolivka]

I am using a monopole antenna and trying to verify its resonant frequency using an HP8753D VNA. The process I am using is as explained below:

1. Calibrate the VNA using S11-1 port calibration method.
2. Connect the antenna using a co-axial cable to the VNA and check the S11 parameter graph over the frequency range.
3. For a length of 7.6 cms, I should have resonant frequency around 1 GHz, however I am also getting larger dips at higher frequencies (at around 3.5 GHz). As per the logic I should only have a dip at the resonant frequency.

Please advise what could be the possible reason behind the above mentioned situation.

Thanks...!!

Many antennas, filters and other devices "resonate" at various harmonics and elsewhere. Your task is to optimize S11 at a desired frequency. Do not care about other "dips", and if you do not like them, insert a band-pass filter between your source and your antenna.