Coaxial-line reflectometry

An example for a broadband dielectric measurement is given in Fig. 12.10, where the dielectric loss versus frequency is given for poly(propylene glycol) (M = 200 g moP ). The data were obtained by a combination of Fourier correlation analysis and coaxial line reflectometry. 

Dielectric Analysis Based on Distributed-Circuit Methods Coaxial-Line Reflectometry and Network Analysis... 

Coaxial line reflectometry has to be employed at frequencies from 1 MHz to -1 GHz. In contrast to the low-frequency techniques already described, here the sample capacitor is used as the termination of a low-loss precision coaxial line. The complex reflection factor is measured with a microwave reflectometer at the analyzer end of the fine, depending on the sample impedance. For this purpose, the incoming and reflected waves are separated with two directional couplers and their amplitudes are measured. The BDS concept 70 is a commercially available system (Novocontrol Instruments) that uses the coaxial line reflectometry method. This system covers the frequency range between IMHz and 3 GHz with loss factor tan 5 resolution of less than 3 x 10 . The... 

Figure 6.10. (a) The comb electrode geometry (b) RF sample cell suitable for dielectric coaxial line reflectometry measurements in the frequency range from IMHz to 10 GHz. 

Coaxial line reflectometry (6.3.3) 1 MHz-1 GHz The sample capacitor is placed at the end of a low-loss precision coaxial impedance is determined from complex reflection factor, measured with a microwave reflectometer at analyzer end of coaxial line Special sample cells are available for sample thicknesses ranging from 1 pm (thin films) to 20 mm (liquids or solid samples) The turnkey BDS concept 70 system, available from Novocontrol, combines the Agilent HP E4991A RF impedance analyzer with the BDS 2200 RF sample cell the complex permeability of polymers can also be measured by using a magnetic sample cell... 

Usually, the depolarization current is measured to avoid the dc conductivity contribution. The dielectric relaxation spectrum is then obtained by Fourier transform or approximate formulas, e.g., the Hamon approximation [14]. By carefully controlling the sample temperature and accurately measuring the depolarization current, precision measurements of the dielectric permittivity down to 10" Hz are possible [18]. In fast time domain spectroscopy or reflectometry, a step-like pulse propagates through a coaxial line and is reflected from the sample section placed at the end of the line. The difference between... 

---