M. Dionigi

A novel technique for complex permittivity measurement based on a planar four-port device

A novel technique for the measurement of the complex permittivity of materials is presented that overcomes many limitations of the conventional measurement methods. The RF signal transmitted through a transmission line loaded with the material under test is combined with a reference signal using a quadrature hybrid in such a way that the complex permittivity can be measured by simply detecting the two output amplitudes. This technique requires a simple calibration procedure, provides good accuracy, and avoids expensive vector measurements, thus combining the advantages of transmission methods, in terms of good accuracy, with those of resonant methods, in terms of scalar measurements. Two microstrip implementations have been realized for measurements at 2.35 and 10 GHz, showing very good accuracy to be achieved in both frequency ranges. The measured permittivities have been compared with those obtained with a resonant and transmission method and with data from literature, resulting in a very good agreement for both epsivr and tandelta

A planar resonant sensor for the complex permittivity characterization of materials

A microwave planar resonant sensor for the measurement of the complex permittivity in compact areas and thin layers of the material under test (MUT) is presented. Compared to transmission or reflection sensors, the adoption of a scalar 2-port measurement procedure reduces the cost of the system and improves its robustness. Compared to coaxial line sensors, a substantial cost reduction is achieved. The low cost of the sensor allows its use even in a disposable manner. Through the fullwave characterization of the probe a simple equivalent semilumped model of the interaction with the MUT has been derived along with a software calibration procedure. An excellent measurement accuracy in a wide range of complex dielectric permittivities is shown to be feasible.

An Accurate and Low Cost Complex Permittivity Measurement System Using a Planar Resonant Sensor

A microwave planar resonant sensor for the measurement of the complex permittivity in compact areas of the material under test (MUT) is presented. Both thin and thick samples can be considered. Compared to transmission or reflection sensors, the adoption of a scalar 2-port measurement procedure reduces the system and improves its robustness. The measuring system requires only the calculation of two parameters, namely the resonant frequency and the 3dB bandwidth, thus achieving a substantial reduction of cost and computation time. The low cost of the sensor is such as to allow its use even in a disposable manner.

A novel technique for complex permittivity measurement based on a planar four port device

A novel four port device for complex permittivity measurement is presented consisting of the cascade of two 3 dB branch line directional couplers connected through two U-shaped transmission line lengths. The material under test (MUT) is brought into contact with one U-shaped section. The complex dielectric permittivity of the MUT is evaluated by simply measuring the amplitudes of the two outputs, thus obtaining a simple and cheap measurement procedure. A prototype has been fabricated and experimentally tested exhibiting very good accuracy.

CAD of folded filters and diplexers by the generalized scattering matrix of the single step discontinuity

We propose a single and rigorous procedure for the full-wave analysis of folded filters and diplexers. By following this procedure, and assuming the availability of a code producing the generalized scattering matrix (GSM) of the step discontinuity, it is shown that, in many cases, it is possible to analyze folded filters and diplexers, avoiding the development of specific routines for bends and T-junctions modelling. The analysis of the entire structure is obtained by simple matrix manipulation of the GSM and by a suitable partitioning of the device. Numerical examples validate the proposed approach.

Dual-Band Permittivity Measurement of Thin Dielectric Layers with a Simple Planar Device

An improvement of a method for permittivity measurement is introduced based on a dual-band four port planar structure, consisting of two cascaded cross-coupled quadrature hybrids connected through two transmission lines. The applicability of the method to permittivity measurement of thin dielectrics is then demonstrated: permittivity are evaluated at two different frequencies f0 and n*f 0 (n=1,2,3..) by simply detecting the two output amplitudes, thus avoiding any phase measurement and allowing a remarkable space reduction. A prototype has been fabricated in microstrip technology and experimentally tested exhibiting very good accuracy for permittivity measurement at two different frequencies spaced by an octave band

3D printing of X band waveguide resonators and filters

We present a novel approach to fabricate microwave passive components using very cheap SLA 3D printing technology associated with copper electroplating of the resulting 3D plastic structures. Some test structures are presented showing the excellent performance of the process.

A novel technique for permittivity and moisture measurements using a planar hybrid junction

A novel technique for permittivity and moisture measurements overcoming the main limitations of conventional methods is introduced. The technique employs a simple measuring device consisting of a planar hybrid junction with the direct and coupled ports terminated by two identical open-ended transmission lines, one being loaded with the Material Under Test (MUT). The complex permittivity of the MUT is evaluated by simply measuring the amplitudes of the reflected and the transmitted signals of the measuring device. The proposed technique can be adopted to estimate the relative moisture content of solid samples, a simple linear fitting being sufficient to model the relation between tandelta and the moisture percentage. A prototype has been fabricated in microstrip technology employing a multi branch line coupler as hybrid junction. Measured permittivities at 3.5 GHz have been compared with data from the literature, resulting in a good agreement for both epsivr and tandelta.