Wideband Antenna Gain Measurement

[asdfaaa]

horn gain measurement

Hi, Folks in antenna domain,

I have some basic doubts for wideband antenna gain (NOT Directivity) measurement.

would you please elaborate your measurement setup first here? I will post my question to you accordingly.

Regards,

 

[sergio mariotti]

I don't understand if you have a question or not.

In any case a "true" Antenna Gain Measurement is certainly one of the most difficult measurement.
Moreover, as per every measurement, the difficult increase as required accuracy rise.
After this apparently obviously preface, the way i've used is the following:

1) Answer this question: what is the accuracy of commercial (high cost) standard horns? A: +/-0.1dB (that is +/-2.3%) . Of course i cannot do better!

2) Perform a path setup with a reference antenna, a standard gain antenna, then record level on boresight. Then calculate Pathloss+RefAntenna Gain. All in dB !

3) Replace the standard antenna with the AUT, then record a directivity pattern on many cuts (at least 0°, 90°, 45°). Then perform the integration around the sphere, Then, from the itegrated, solid beam, calculate the Directivity Gain.

4) Now, knowing PathLoss+RefAntenna Gain + AUT Directivity Gain , and knowing the signal level, you may calculate the AUT efficiency.

Notes:
:arrow: The efficiency, also indicate with the greek letter ε, is the ratio Gain/DirectivityGain. 0<ε<1
:arrow: AUT=Antenna Under Test
:arrow: Of course , enviroment is reflection free, same wave polarizzation, signal is stable on both freq. and level etc. etc.
Don't hope to be very accurate... it's quite impossible.

 

[plasma]

First you need broadband horn for transmitting than calibrate another one as Standard
Gain horn yourself or sent it for calibration to a lab like "Ticra" or "NSI" then you will able to measure UWB antenna quick. You can add a Ref. antenna depends on your setup.
I attached the Standard Gain Horn Calibration Using the Three-Antenna Method to do it yourself.

PL

 

[asdfaaa]

I don't understand if you have a question or not.

In any case a "true" Antenna Gain Measurement is certainly one of the most difficult measurement.
Moreover, as per every measurement, the difficult increase as required accuracy rise.
After this apparently obviously preface, the way i've used is the following:

1) Answer this question: what is the accuracy of commercial (high cost) standard horns? A: +/-0.1dB (that is +/-2.3%) . Of course i cannot do better!

2) Perform a path setup with a reference antenna, a standard gain antenna, then record level on boresight. Then calculate Pathloss+RefAntenna Gain. All in dB !

3) Replace the standard antenna with the AUT, then record a directivity pattern on many cuts (at least 0°, 90°, 45°). Then perform the integration around the sphere, Then, from the itegrated, solid beam, calculate the Directivity Gain.

4) Now, knowing PathLoss+RefAntenna Gain + AUT Directivity Gain , and knowing the signal level, you may calculate the AUT efficiency.

Notes:
:arrow: The efficiency, also indicate with the greek letter ε, is the ratio Gain/DirectivityGain. 0<ε<1
:arrow: AUT=Antenna Under Test
:arrow: Of course , enviroment is reflection free, same wave polarizzation, signal is stable on both freq. and level etc. etc.
Don't hope to be very accurate... it's quite impossible.

Thank you for puzzle solving. Through this whole measurement setup, you made one assumption that there is no mismatch changing between your excitation source and the RefAntenna. For example, doule ridged horn antenna (18GHz) is widely used in wideband antenna characterization. For normal narrow bandband antenna characrization, the variation of imput impedance of the RefAntenna is quite small, we can treat them the measurement error. But for wideband antenna, this problem is quite serious, because the variation is quite big. This is the reason behind my question.

Regards,

 

[plasma]

don't forget to add attenuator 6÷10dB because there is a difference match between the standard and the AUT for better accuracy.

 

[sergio mariotti]

Thank you for puzzle solving. Through this whole measurement setup, you made one assumption that there is no mismatch changing between your excitation source and the RefAntenna. For example, doule ridged horn antenna (18GHz) is widely used in wideband antenna characterization. For normal narrow bandband antenna characrization, the variation of imput impedance of the RefAntenna is quite small, we can treat them the measurement error. But for wideband antenna, this problem is quite serious, because the variation is quite big. This is the reason behind my question.

Regards,[/quote]
Oh yes of course i've assumed no mismatch errors.

In your case, do you think is possible measure the reflection coefficient of the antennas you use and take it in account?
I.e. if you have enough dinamic range, you may put two, 10 dB well matched pads, on TX and RX line. In this case, the computation of the error introduced by non perfect match of the antennas, step down the difficulty from complex to real calculation.... better than nothing :|

 

[asdfaaa]

Oh yes of course i've assumed no mismatch errors.

In your case, do you think is possible measure the reflection coefficient of the antennas you use and take it in account?
I.e. if you have enough dinamic range, you may put two, 10 dB well matched pads, on TX and RX line. In this case, the computation of the error introduced by non perfect match of the antennas, step down the difficulty from complex to real calculation.... better than nothing :|

I considered to measure the reflection coefficient using 3-dB directional coupler, but the problem is the wideband performance of this coupler, and the resulting calibration complexity. The dynamic range of VNA is not good either. :-( Do you have any comments on antenna radiation efficiency measurement (ex. Wheelcap method)? Thank you!

Regards,

 

[sergio mariotti]

I considered to measure the reflection coefficient using 3-dB directional coupler, but the problem is the wideband performance of this coupler, and the resulting calibration complexity. The dynamic range of VNA is not good either. :-( Do you have any comments on antenna radiation efficiency measurement (ex. Wheelcap method)? Thank you!

Regards,

I don't kwow what Wheelcap is.
Focusing on reflection measurement, if you have a double or quad ridge horn, it's BW may be around 9:1 . Very large but not impossible to measure it's reflection coefficient.
For your purpose, and assuming the generator (and receiver) be reflection less , you need to know only the module of the antenna reflection coeff. that means you need a simple scalar measurement only.

If you have not an SNA, you may use a directional coupler power meter and generator and of course a good absorber in front of antenna.

But why you said the VNA is not good? may be not good enough dinamic for the path range but for the antenna alone... it should be good.

 

[asdfaaa]

I don't kwow what Wheelcap is.
Focusing on reflection measurement, if you have a double or quad ridge horn, it's BW may be around 9:1 . Very large but not impossible to measure it's reflection coefficient.
For your purpose, and assuming the generator (and receiver) be reflection less , you need to know only the module of the antenna reflection coeff. that means you need a simple scalar measurement only.

If you have not an SNA, you may use a directional coupler power meter and generator and of course a good absorber in front of antenna.

But why you said the VNA is not good? may be not good enough dinamic for the path range but for the antenna alone... it should be good.

I used VNA to excite and to measure radiated power (two ports measurement). The maximum output power of VNA is +4dBm, connecting coaxial cable is a little bit lossy. For some prototypes' measurement, I got nothing except noise (noise floor is aroung -80dBm). The scattering of anechoic chamber I am not sure how good it is, but I assume it is good.

For the wideband horn antenna you mentioned, in the covered frequency range, the return loss variation may be higher than 1 dB. And the DUT may have much worse performance in terms of return loss. :-(

Using amplifier to boost the transmitted power has been considered, but the problem is the nolinearity of the amp in wideband range which will make the calibration process very complex. BTW, if the phase information is needed for measurement, then using amplifier is out of my choice again. :-(

Regards,