FAQ - Radio Frequency Engineering

  Research

Q: Is optical ray tracing used to estimate the performance of an anechoic chamber?
A: Yes, optical ray tracing is a simple simulation method. Good results can be obtained if the near field coupling of the antennas can be neglected - so it is well suited for "higher frequencies" where the wavelength is much smaller than the dimensions of the chamber.

Q: What is a discone antenna?
A: It was developed in 1946 for the use in the VHF and UHF range. The advantages are the simple design (a balun is not required) and the large bandwidth. Due to the symmetrical construction the H-plane pattern is circular. Today antennas for a frequency range 1 to 18 GHz are sold. They are called "omnidirectional" but they have many peaks and nulls in the E-plane pattern.

  Antenna Calibration

Q: We have 2 biconical antennas, which are used for emission measurements in our semi anechoic chamber. The antennas are calibrated at a height of 2m and horizontal polarization. Can we use them for NSA measurements of our chamber?
A: For accurate NSA measurements you need to have also a proper calibration for the different positions and polarizations. That means your antennas should be calibrated at horizontal polarization at 1 and 2 m height and vertical polarization at 1 and 1.5m. We determinate the dual antenna factor DAF for the pair of antenna, and the results have to be used as reference for your NSA measurements.
 
Q: Are you able to calibrate a horn antenna up to 40 GHz?
A: We are accredited for antenna calibration up to 20 GHz. In the higher frequency range we are able to determinate the antennafactor. Therefore we will issue a test report, where no uncertainty is stated. For a price-information please request an official offer.
 
Q: What is your correct delivery address?
A: Our delivery address and also a road map can be found at our homepage at the pull down menu: Contact/address 

Q: We would like to know if you are able to calibrate a Reference Radiation Source (comb generator)?
A: We are able to calibrate as follows: Measurement of the radiated RF - Fieldstrength of a comb generator in the frequency range 30 - 1000MHz. The system is set up typical at 1 m height above groundplane. The measurement distance is 3 or 10m. The frequency spacing is 10 MHz. If an other one is needed, please let us know. We recommend to measure at both polarisations. In the moment we are not accredited for this service, we are going to issue an ISO-calibration certificate, with a statement of the measurement uncertainty.

Q: Our pair of biconical antennas have been calibrated on an OATS with a distance of 10 m. The We validate our anechoic chamber with a 10 m measurement range. Can we also use the results for 3 m NSA measurements?
A: For accurate NSA measurements for a distance of 3 m we don´t recommend to use the results, which have been calibrated at 10 m distance: When you change the distance, also the coupling between groundplane and the two antennas yields differently. We made an investigation and found out that the results can be up to +/- 2 dB. So the total uncertainty increases and the value is too big to validate measurements sites in an accurate way (and fulfill the 4 dB criteria). So we recommend to calibrate the pair of antennas also at the matching distance, in your case at 3 m.

Q: In your certificates you state that the uncertainties for generating the reference field is 15% (k=2) for fieldprobe calibration up to 150 MHz. Is a better uncertainty possible, for calibration only at 50 Hz (both E and H field)?
A: Our standard uncertainty in the frequency range 1 Hz – 150 MHz is 15%. The calibration is done in a TEM-cell. If a lower uncertainty is needed, we can do this in this way: At 50Hz we can perform a single frequency calibration. We use a very accurate plate capacitor and a special coil for generating E- and H-fields. Then we achieve an uncertainty lower than 10% for generating the field. This kind of generating works only narrow banded and can´t be used at higher frequencies (>10kHz).

  Field Probe Calibration

  

  Site Validation

Q: Which documents of CISPR 16 deal with the validation of fully anechoic chambers?
A: A project dealing with this topic was started in the year 2000. The output was published 2004 in CISPR 16-1-4 Amd. 1 Ed. 1.0. Additional information can be found at the IEC homepage (you have to be a member of a national standardization committee to download working documents): Link to IEC

  

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