Automatic measurement of permittivity and permeability at microwavefrequencies using normal and oblique free-wave incidence with focusedbeam

A free-wave method for determining the dielectric and magnetic properties of materials from reflection measurements made at normal incidence and transmission measurements made at normal and oblique incidence is proposed. The method combines frequency domain measurements and time domain (TD) analysis and uses polarization to avoid typical ambiguities in the results. Varying the incident angle and the polarization, measurements were made in the X-band. The technique was validated by comparing the results obtained with those from well-established waveguide techniques. A focusing assembly makes it possible to measure relatively small samples, thus avoiding diffraction problems. It also improves the ambiguity-solving procedure proposed for the technique. The measurement procedure is fully automated by using the HP8510 network analyzer controlled by an HP362 computer, which also processes the data. Results for low-loss dielectrics such as teflon, nylon, and polymethyl methacrylate (PMMA) and for microwave-absorbing materials are reported     

Automatic technique for measuring the Polder resonance in ferritespheres

An automatic technique for measuring the parameters of Polder resonance in polycrystalline ferrite spheres is proposed. The diagonal elements of the external susceptibility tensor versus DC magnetic field are calculated from the changes in resonance frequency and unloaded Q factor of a microwave cavity by perturbation theory. From these diagonal elements, all the elements of the intrinsic permeability tensor can be obtained. By fitting the theoretical curves to experimental data, the parameters of Polder resonance, ΔH M_s, and the g factor, are simultaneously calculated. The whole measurement procedure is controlled by a desktop computer. An accuracy of 5% is obtained in ΔH and M _s, and of 0.1% in the g factor     

Dielectric property measurement system at cryogenic temperature andmicrowave frequencies

A system based on the resonant cavity method has been developed to measure the permittivity and loss tangent at 12-18 GHz over the temperature range 80-300 K. Changes of permittivity as low as 0.01% in the range 1-30, 3x10^-6 for loss tangent values below 10^-2, can be measured without requiring temperature stability. The thermal expansion coefficient and resistivity factor of copper have been measured between 80 K and 300 K. The permittivity of sapphire and loss tangent of alumina of 99.9% purity in the same temperature range are presented     

Comments, with reply, on `Comparison of Ampere's law (ACL) and thelaw of Biot-Savart (LBS)' by H.A. Kalhor

The commenters agree with the author of the above-named work (ibid., vol.E-31, p.236-8, Aug. 1988) that the application of Ampere's circuital law can cause confusion in the minds of students. However, it is argued that section III of the original paper further confuses the issue and creates problems that are worse than the one being solved. In addition several minor errors in the original paper are corrected. In replying, the original author points out that for presentation to students, the treatment in section IV of the original is clearer and more easily understandable     

A method for measuring the permittivity without ambiguity usingsix-port reflectometer

Automatic network analyzers are used for the broadband measurement of permittivity in different experimental arrangements. In many of them ambiguity appears because permittivity is calculated by solving a transcendental equation. This makes automatic measurements difficult. A method of eliminating this ambiguity is shown, with no additional experimental data required, except for a manipulation of the existing data. Theory and experimental results for low-loss dielectrics are shown for the short-circuited waveguide method using a six-port reflectometer. Errors are analyzed and several samples with permittivities of up to 16 are measured with an accuracy on the order of 1%     

Dual five-port analyzer using fixed probes

A dual 5-port network analyzer using fixed electric probes is presented. To measure S₁₁ and |S₂₁|, the RF signal is applied to port 1 of the DUT through one 5-port junction. The same RF signal reflected by a short circuit at the end of the line is used for measuring S₂₂. In this way, dividers, switches, and phase shifters as used in the standard dual technique are avoided. But S₂₂ can only be measured for devices with |S₂₁|>0.3. The 5-port junctions are inexpensive and very simple to design and operate. The mathematics involved uses simple linear algorithms, and iterative methods are not needed. Measurements for several loads have been performed in X-band, and the results agree with those obtained using an HP 8510B network analyzer     

Comparison between the Kittel and Polder resonances inpolycrystalline ferrites

Kittel and Polder resonance parameters in polycrystalline ferrite spheres have been determined simultaneously using the perturbation theory. Measurements were made with the same sample in order to establish a proper comparison between the Kittel and Polder parameters. The meaning of the shift of the ferromagnetic resonance field and the different parameters used to characterize the resonance losses in polycrystalline ferrites are discussed. Discrepancies between the Kittel and Polder parameters are explained by studying the dependence of the linewidth and the ferromagnetic resonance field on the applied field. There is good agreement between the experimental results and the theoretical predictions     

Eliminating the ambiguity in nonperturbation microwave measurementsof permittivity

The authors propose a method for eliminating the ambiguity in the dielectric constant which appears in many measurement techniques at microwave frequencies. They describe the procedure in a general way and apply it to the TE cavity technique to measure the permittivity of liquids and to the short-circuited line technique. The viability of the procedure and its simplicity compared with commonly used methods are shown. Complicated calculations involved in the comparison of two sets of solutions of two transcendental equations are avoided, and the correct value of the dielectric constant is obtained from the root of a simple algebraic equation