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A Low-cost measurement system suited for in situ moisture monitoring of buildings is presented. The system consists of a robust and compact resonant microwave sensor linked to a miniaturized, low-cost vector network analyzer. Several such systems can be controlled by a central monitoring station. The measurement accuracy is enhanced significantly by vectorial self-calibration. To determine the magnitude and the required 360°-phase information, an inexpensive combined gain and 180°-phase detector is used, where the full phase information is obtained by adequately modeling the sensor's and the calibration standards' phase response. Different self-calibration circuits are examined and their suitability is proved by comparative measurements. Finally, the system's performance is tested in a high humidity environment. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 287–293, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23083

This contribution focuses on a scattering description of infinite arrays of small metallic helices. The latter are assumed to scatter like dipoles. A numerical approach is extended to account for the influence of the lattice with more precision. This is done by a simple extrapolation scheme, which accelerates the convergence of the arising series. For regular arrays, a comparison with a commercial software tool reveals a good agreement, at least as long as the distance between the particles is large enough for the dipole assumption to be valid. This also applies at resonance, the most critical case. The effects on random arrays are also investigated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2609–2613, 2007; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.22788

In this paper, a very compact 16-element digital beamforming (DBF) receiver-array module operating in the Ka-band is demonstrated for the first time. The active microwave circuitry is outlined and, following this framework, challenging electronics-integration aspects are discussed in detail. The first measurement results of the module performance are included. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 83–86, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20554

Some common and fast recursive methods for solving the scattering problem of many randomly distributed particles are reviewed. The particles are characterized by means of a T-matrix. The useful range of these algorithms is discussed with respect to the number of scatterers and the packing density. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 523–529, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20023

A parameter study of multilayered sensor structures is presented. These consist of planar microwave resonators coated with a thin, sensitive membrane. The influence of the various layers on the sensor characteristics is studied, and design rules are formulated. Two sensors with a moisture-sensitive coating are realized. The experimental results confirm the simulation. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 21–25, 2002.

In this contribution, the potential of graded-chiral/dielectric absorbers is explored theoretically. To this end, two different design procedures are introduced that allow us to improve single-layer and graded-dielectric Dallenbach absorbers. Both design concepts finally lead to graded-chiral/dielectric Dallenbach absorbers. The first experiments prove the concept, and allow us to identify and discuss the effects and problems associated with the practical realization. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 254–257, 2001.

In comparison to some other chirowaveguides the geometry of the chiral coaxial line offers an additional degree of freedom, namely, the ratio of inner to outer conductor radius. The influence of this parameter on the dispersion characteristics, in particular also of the dominant mode, is investigated in this report. © 1995 John Wiley & Sons, Inc.

Generalized microstrip T-junctions are investigated by means of a method of moments (MoM) wavelet analysis. The focus is on the optimization of the grid for both efficiency and accuracy. Numerical results for different geometrical parameters show that, in contrast to simpler junctions, this grid has to be designed very carefully. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 280–282, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10894

A refined method to compute the radiation characteristics of microstrip antennas on finite substrates is presented. Electric surface and volume polarization currents are approximately calculated using the Green's function of an infinite dielectric slab. A comparison with measured radiation patterns shows that the excitation via coaxial probe needs to be included in the calculations for more accurate results. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 263–265, 1999.