NEW APPROACH OF MEASURING THE Q FACTOR OF A MICROWAVE CAVITY
ABSTRACT
A new approach of measuring the quality factor of the reflection type microwave cavity resonator for calculating the complex dielectric permittivity of solid and liquid samples in the cavity perturbation technique is proposed. This approach, based on the measurement of reflected power from the cavity at resonance, effectively reduces the measurement procedure and increases the accuracy. As the quality factor can be measured very fast using this approach, this approach can be extended to monitor the conductivity decay of the semiconductor samples.
Review of Scientific Instruments, Volume 65 No. 2, February 1994, pages. 453-455.
THEORY
For a reflection type cavity, the power transfer function can be written as
Where f is the frequency, k0 is the normalized reflected power at resonance, Q0 is the quality factor of the cavity, f0 is the resonance frequency. The equation takes into consideration of non-zero value of the reflected power at resonance due to coupling factor and walls of the cavity. The area enclosing this power transfer function is always constant for a particular cavity-coupling hole combination in a fixed range of frequency.
The area under the resonance curve (A0) can be obtained by numerical integration of the above equation for a fixed span of frequency.
Once a sample is introduced, the resonant frequency and the quality factor change to fs and Qs. The normalized reflected power also changes to ks. Since the area under the resonance curve is equal,
Therefore, knowing f0, Q0, k0, fs and ks, Qs can be calculated.
ERROR ANALYSIS
Error in the calculation of the quality factor is around + 3%.
Error in the calculation of the quality factor while measuring the photo conductivity of semiconductor using this approach is around + 1%.
ACKNOWLEDGEMENT
This research work has the financial backup from Council of Scientific and Industrial Research, India.