Bq. Tian et Wr. Tinga, A MICROWAVE OSCILLATION LOOP FOR DIELECTRIC-CONSTANT MEASUREMENT, IEEE transactions on microwave theory and techniques, 42(2), 1994, pp. 169-176
We designed and analyzed a microwave oscillation loop formed by a diel
ectric loaded cavity, amplifiers and transmission lines for the dielec
tric constant measurement of samples at both room and very high temper
ature. An oscillation condition for an arbitrary loop is derived in S-
parameter notation, by which the commonly used oscillation condition i
n loop phase and gain notation is proved to be valid only in the speci
al case when either S11 = S21 = 0 or S22 = S12 = 0. Based on the S-par
ameter oscillation condition, a theoretical model is established and v
erified with a discrepancy of less than 0.041% between the calculated
and the measured oscillation frequencies. With this model, the loop ch
aracteristics are investigated. From the measured loop oscillation fre
quency, the cavity resonant frequency, and thereby the dielectric cons
tant of the sample in the cavity, can be predicted. Based on this anal
ysis, an active dielectrometer is constructed with resultant errors of
less than 4% for epsilon' < 20 and less than 11% for epsilon' < 80. T
his dielectrometer requires no tuning and no external microwave power
source. Moreover, a high power (> 100W) oscillation loop for the diele
ctric constant measurement of a microwave heated sample (1000-degrees-
C) is developed.