20-07-2013, 02:51 PM
Measurement of resonance characteristics of a microstrip ring resonator and determination of dielectric constant of the substrate.
(A) Aim:
Measurement of resonance characteristics of a micro strip ring resonator and
determination of dielectric constant of the substrate.
Components Required:
power supply,VCO,50 ohm transmission line, ring
resonator,50 ohm terminations, cables with Oscilloscope/VSWR meter/power meter.
Theory :
The ring resonator is known as a simple printed resonator that is useful for making
approximate measurement of dielectric constant. It is also used in filters, and in
antennas.
Ring resonators can be analyzed in two ways. Looking at a ring resonator in
isolation, it may appear that the field would be in the form of a wave circulating
around either direction, but in reality, the coupling structure plays an important role.
Procedure:
Part (a)
Set up the system as shown in figure.
Keeping the voltage at minimum, switch on the power supply.
Insert a 50ohm transmission line and check for the output at the end of the
system using a CRO/VSWR meter/RF power meter.
Vary the power supply voltage and check the output for different VCO
frequencies.
Replace the 50 ohm transmission line with ring resonator.
Vary the supply voltage, tabulate VCO frequency Vs output.
Plot a graph frequency and find the resonant frequency.
Tabulation:
Part (b)
Select a VCO frequency(say f1) where there is a measurable ouput.note
down the magnitude/power level of the output.
Place the unknown dielectric material on top of the ring resonator.Ensure
that there is no air gap between the dielectric piece and the resonator surface.
Observe the change in the magnitude/power level at the output.
Now reduce the supply voltage till maximum power level(before inserting
the dielectric) is achieved.This is the new resonance condition due to the
insertion of new dielectric material (eg:trflon).
Note down the VCO frequency (say f2).
Calculate the dielectric constant of the unknown material by using formula.
Experiment may be repeated with different unknown material or with same
material but for different hight of the material.
Conclusion:
Measurement of resonance characteristics of a micro strip ring resonator
and determination of dielectric constant of the substrate is
achieved successfully.