Search

A novel method of using the harmonic generation and optoelectronic mixing properties of Mach-Zehnder modulators to generate modulated subcarrier signals at high-order harmonics of the input signals is presented. The method permits the simultaneous transmission over optical fiber of a modulated and an unmodulated signal, both at high-order harmonic frequencies of the input signals, for the purpose of transmitting both a local oscillator tone and the modulated signal required at a base station for microcellular applications. We present the theory of operation and demonstrate the validity of the concept with a narrow band single-tone FM experiment as well as a 20-Mb/s [Pi]/4 DQPSK experiment.

We designed and analyzed a microwave oscillation loop formed by a dielectric loaded cavity, amplifiers and transmission lines for the dielectric constant measurement of samples at both room and very high temperature. An oscillation condition for an arbitrary loop is derived in S-parameter notation, by which the commonly used oscillation condition in loop phase and gain notation is proved to be valid only in the special case when either [S.sub.11] = [S.sub.21] = 0 or [S.sub.22] = S12 = 0. Based on the S-parameter oscillation condition, a theoretical model is established and verified with a discrepancy of less than 0.041% between the calculated and the measured oscillation frequencies. With this model, the loop characteristics are investigated. From the measured loop oscillation frequency, the cavity resonant frequency, and thereby the dielectric constant of the sample in the cavity, can be predicted. Based on this analysis, an active dielectrometer is constructed with resultant errors of less than 4% for [epsilon] [less than] 20 and less than 11% for [epsilon] [less than] 80. This dielectrometer requires no tuning and no external microwave power source. Moreover, a high power ([greater than] 100W) oscillation loop for the dielectric constant measurement of a microwave heated sample (1000 [degrees] C) is developed.

Traditionally, Q measurement requires a nonzero frequency bandwidth or time period. Contrasted to this, the principle of a new single-frequency relative Q measurement method is developed. It is found that Q is directly or inversely proportional to the normalized input resonant resistance if a moderate perturbation condition is satisfied. Theoretical proof and experimental verification of the single-frequency method's validity are presented. Consequently, a relative Q, often used in dielectric measurements, can be measured using a much simpler measurement system. Moreover, error analysis shows that, in making a relative Q measurement, the error in the single-frequency method is smaller than that in the traditional bandpass method when using a reflectometer.

In response to the new developments in high temperature microwave dielectrometers, (1), (2) a field analysis of a composite sample insertion hole in a coaxial re-entrant cavity is performed via a mode-matching formulation. In this paper, the formulation and the numerical method are presented. The numerical results are discussed with attention focused on the hole effects on the dielectric loaded cavity. By virtue of this analysis and the structure which allows for the sample insertion holes, a new dielectrometer is obtained featuring both ease of sample insertion and accuracy in dielectric determinations. This paper demonstrates that solid, liquid or powdered samples can be readily accommodated and measured, and the dielectric data obtained via two theoretically calculated calibration curves are in good agreement with published data.

This paper proves that a linear relationship between a cavity's Q-factor and its input resonant resistance holds rigorously true provided the Q variation is caused only by power loss in the cavity.