IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. IM-28, NO. 4, DECEMBER 1979 faster trigonometric functions. The trigonometric algor- ithms could be optimized or replaced with a look-up table with interpolation between points. Another alternative would be to use a recently announced monolithic mathema- tical unit which includes some ofthe trigonometric functions. Better accuracy, reliability, and shorter measurement time could be achieved by an appropriate distribution of the various tasks among two or even three microprocessors. A partition of duties would be to use the first processor for human interface and data acquisition, and the second processor for data processing and output. In this manner, the stimulus data could be processed while the other proces- sor is acquiring one or more response characteristics. This overlapping of the time consuming tasks should shorten the measurement time considerably. The reduction in time between stimulus and response acquisitions should mini- mize the effects of certain instabilities in the TDR hardware, thus improving the accuracy of the measurement. The improved reliability stems from the possibility of having firmware shared between the two processors, so that in the event of a processor failure, the remaining processor could perform both taks. This would give a softly degrading system thus improving the reliability. The measurement results obtained to date indicate some degradation of the data above 1 GHz. This could be due in part to triggering instabilities in the TDR. A computer- controlled time base would facilitate automatic calibration as well as simplify signal averaging during data acquisition. Other useful features could be incorporated into the software, such as the ability to measure transfer function and temperature recording. REFERENCES [1] L. Gans and R. Andrews, "Time domain automatic network analyser for measurement of RF and microwave components," National Bureau of Standards, Boulder, CO, Tech. Note 672, Sept. 1975. [2] A. M. Nicolson, P. G. Mitchell, R. M. Mara, and A. M. Auckenthaler, "Time domain measurement of microwave absorbers," Sperry Rand Research Center, Sudbury, MA, Final Tech. Rep. AFAL-TR-71-353, Nov. 1971. [3] Froysa, Hammerstad, and Kuhnle (ELAB, Univ. Trondheim, Nor- wegian Inst. Technol., Trondheim, Norway), "A microprocessor con- trolled automatic network analyzer in a microwave computer aided design system," presented at 1978 MTT-S Symp., Ottawa, Canada, June 1978. [4] M. J. C. van Gemert, "Time domain reflectometry as a method for the examination of dielectric relaxation phenomena in polar liquids," Univ. Leiden, Leiden, The Netherlands, dissertation, 1972. [5] S. S. Stuchly, M. A. Rzepecka, and M. F. Iskander, "Permittivity meas- urements at microwave frequencies using lumped elements," IEEE Trans. Instrum. Meas., vol. IM-23, pp. 56-62, Mar. 1974. Wide-Range Dynamic Complex Dielectric Constant Measurements Using Microprocessor Control Techniques CEVDET AKYEL, STUDENT MEMBER, IEEE, AND RENATO G. BOSISIO Abstract This paper describes a measurement system operated by a microprocessor for the dynamic measurement of the complex dielectric constant of sample materials over a wide range of dielectric constants. A Q multiplier technique is used for measuring materials which undergo large dynamic increases in dielectric losses. Such increased losses are often encountered when the temperature, pres- sure, illumination, etc., of a sample dielectric or semiconductor material are altered; or whenever important changes occur in the Manuscript received May 15, 1979; revised August 3, 1979. The authors are with the Laboratoire d'Hyperfrequences, Department de Genie Electrique, Ecole Polytechnique de Montreal, C.P. 6079, Succ. "A", Montreal, P.Q. H3C 3A7, Canada. molecular structure related to changes in the physical state (e.g., liquid-solid) of the test sample. A complete functional diagram of the microprocessor program is presented. For the purpose of these measurements an AIM 65 microprocessor system is expanded to operate with up to 16 I/O ports and 20K bytes of RAM memory. I. INTRODUCTION T HE COMPLEX dielectric constant of a sample mat- erial is often measured by using the cavity perturbation technique [1]-[3]. In most cases a cavity with the test sample is used as a passive transmission element in the path of a swept microwave signal. The information in the resonant 0018-9456/79/1200-0272$00.75 © 1979 IEEE 272