Calibration methods for microwave free space measurements

In this article calibration methods for the precise, contact-less measurement of the permittivity, permeability or humidity of materials are presented. The free space measurement system principally consists of a pair of focusing horn-lens antennas connected to the ports of a vector network analyzer. Based on the measured scattering parameters, the dielectric material parameters are calculable. Due to systematic errors as e.g. transmission losses of the cables or mismatches of the antennas, a calibration of the measurement setup is necessary. For this purpose calibration methods with calibration standards of equal mechanical lengths are presented. They have the advantage, that the measurement setup can be kept in a fixed position, for example no displacement of the antennas is needed. The presented self-calibration methods have in common that the calibration structures consist of a so-called obstacle network which can be partly unknown. The obstacle can either be realized as a transmissive or a reflective network depending on the chosen method. An increase of the frequency bandwidth is achievable with the reflective realization. The theory of the calibration methods and some experimental results will be presented

Methods for the calibrated measurement of the scattering parameters of planar multi-port devices

In this article, the error-corrected determination of complex scattering parameters of multi-port devices by means of a 2-port vector network analyzer is presented. As only two ports of the device under test can be connected to the analyzer ports at a time, the remaining device ports have to be terminated by external reflections. In order to measure the scattering parameters of the DUT without the influence of systematic errors and of the external terminations, an error correction has to be performed besides the calibration. For this purpose, the application of the multi-port procedure is presented. This method has the advantage, that the external reflective terminations can be chosen arbitrarily. Furthermore, these terminations can be unknown except for one. An automatized measurement system based on a switching network is shown, which is optimized for the measurement of planar microwave circuits. An error model for the description of the measurement setup as well as a calibration procedure for the elimination of the systematic errors are presented

Calibration-measurement unit for the automation of vector network analyzer measurements

With the availability of multi-port vector network analyzers, the need for automated, calibrated measurement facilities increases. In this contribution, a calibrationmeasurement unit is presented which realizes a repeatable automated calibration of the measurement setup as well as a user-friendly measurement of the device under test (DUT). In difference to commercially available calibration units, which are connected to the ports of the vector network analyzer preceding a measurement and which are then removed so that the DUT can be connected, the presented calibrationmeasurement unit is permanently connected to the ports of the VNA for the calibration as well as for the measurement of the DUT. This helps to simplify the calibrated measurement of complex scattering parameters. Moreover, a full integration of the calibration unit into the analyzer setup becomes possible. The calibration-measurement unit is based on a multiport switch setup of e.g. electromechanical relays. Under the assumption of symmetry of a switch, on the one hand the unit realizes the connection of calibration standards like one-port reflection standards and two-port through connections between different ports and on the other hand it enables the connection of the DUT. The calibration-measurement unit is applicable for two-port VNAs as well as for multiport VNAs. For the calibration of the unit, methods with completely known calibration standards like SOLT (short, open, load, through) as well as self-calibration procedures like TMR or TLR can be applied. © Author(s) 2008

Sievenpiper HIS and its influence on antenna correlation

This paper deals with the influence of artificial magnetic conductors (AMC), so-called Sievenpiper High Impedance Surfaces (HIS), on the MIMO and Diversity performance of a planar linear-polarized 2×2 dipole array in the ISM-band at 2.45 GHz. The characteristic performance criteria such as envelope correlation coefficient, spectral efficiency, Mean Effective Gain (MEG) and Diversity gain of a coupled 2×2 dipole array are investigated. By means of full-wave electromagnetic analysis as well as Monte-Carlo simulations applying statistical channel models the characteristic antenna pattern just as the MIMO and Diversity analysis is performed, respectively. The obtained results show that the application of Sievenpiper High Impedance Surfaces to planar antenna arrays enables good MIMO and Diversity performance compared to ideal configurations in free-space while offering the design of low profile antennas with simultaneously enhanced characteristics. © Author(s) 2008

Considerations on the frequency resource of professional wireless microphone systems

This Paper presents the results of spectral observations in the UHF TV Bands IV and V from 470 MHz up to 862 MHz with focus on the TV-Channels 61 to 63 and 67 to 69. Concerning the discussions on citet{WRC} this frequency range is in great demand of several applications and is usually treated as a "white space" in the TV-Bands. According to typical scenarios, two different spectral loads will be presented considering the requirements of professional wireless microphone receivers with respect to in-band intermodulation

Novel algorithms for the characterization of n-port networks by using a two-port network analyzer

The measurement of the scattering matrices of n-port networks is an important task. For this purpose two ports of the n-port network are connected with the network analyzer and the remaining ports are connected to reflecting terminations. In order to specify the scattering matrix of a n-port network with the multi-port method (Rolfes et al., 2005), n reflecting terminations are required from which at least one reflection factor needs to be known. There are some cases, in which the multi-port method shows weak convergence properties. For example, a T-junction cannot be identified if the reflecting terminations used are short circuits and if the line length is equivalent to a multiple of a half wavelength. This is due to the fact that the two ports connected to the network analyzer become isolated. Two new algorithms, named the sub-determinant method and the wave-identification method, respectively, which employ a second set of reflection terminations that have to differ from the first set, allow to identify every n-port network without the necessity to distinguish different cases. Both methods are based on least square algorithms and allow to determine all scattering parameters of a n-port-network directly and uniquely

Comparison of methods for broadband electromagnetic characterization of Molded Interconnect Device materials

Combining the Molded Interconnect Device technology with the Laser Direct Structuring technology exhibits the potential of designing electrical and mechanical components on three-dimensional surfaces to increase functionality, level of integration and to reduce costs. When taking advantage of this technology especially in the design of RF devices, a precise knowledge of the electromagnetic parameters of the MID material is required, as the complex permeability and permittivity strongly influence the device performance. At present time, these materials are not electromagnetically characterized in the RF frequency range. In this paper different methods are therefore presented and compared with respect to their potentials for broadband electromagnetic characterization of Molded Interconnect Device materials

Considerations on radar localization in multi-target environments

In a multitude of applications like e.g. in automotive radar systems a localization of multiple passive targets in the observed area is necessary. This contribution presents a robust approach based on trilateration to detect point scatterers in a two-dimensional plane using the reflection and transmission information of only two antennas. The proposed algorithm can identify and remove ambiguities in target detection which unavoidably occur in certain target constellations in such a two-antenna configuration

Compact mode-matched excitation structures for radar distance measurements in overmoded circular waveguides

This contribution deals with guided radar level measurements of liquid materials in large metal tubes, socalled stilling wells, bypass or still pipes. In the RF domain these tubes function as overmoded circular waveguides and mode-matched excitation structures like waveguide tapers are needed to avoid higher order waveguide modes. Especially for high-precision radar measurements the multimode propagation effects need to be minimized to achieve submillimeter accuracy. Therefore, a still pipe simulator is introduced with the purpose to fundamentally analyze the modal effects. Furthermore, a generalized design criterion is derived for the spurious mode suppression of compact circular waveguide transitions under the constraint of specified accuracy levels. According to the obtained results, a promising waveguide taper concept will finally be presented. © Author(s) 2008

Manipulating ionization path in a Stark map: Stringent schemes for the selective field ionization in highly excited Rb Rydberg atoms

We have developed a quite stringent method in selectivity to ionize the low angular- momentum ($\ell$) states which lie below and above the adjacent manifold in highly excited Rb Rydberg atoms. The method fully exploits the pulsed field-ionization characteristics of the manifold states in high slew-rate regime: Specifically the low $\ell$ state below (above) the adjacent manifold is firstly transferred to the lowest (highest) state in the manifold via the adiabatic transition at the first avoided crossing in low slew-rate regime, and then the atoms are driven to a high electric field for ionization in high slew-rate regime. These extreme states of the manifold are ionized at quite different fields due to the tunneling process, resulting in thus the stringent selectivity. Two manipulation schemes to realize this method actually are demonstrated here experimentally.Comment: 10 pages, 4 figure