Jochen Weinzierl

Efficient analysis of quasi-optical filters by a hybrid MoM/BI-RME method

This paper presents a novel algorithm for the analysis of quasi-optical filters, consisting of thick metal screens perforated periodically with arbitrarily shaped apertures. The algorithm is based on the widely used method of moments (MoM) in conjunction with entire domain basis functions. Its flexibility, accuracy, and rapidity depend on the use of the boundary integral-resonant mode expansion (BI-RME) method in the numerical determination of the basis functions. A computer code has been developed based on this algorithm. The analysis of two different quasi-optical filters operating at 8 GHz and 280 GHz is reported and compared with experimental data as well as with other simulations. In both cases, the whole analysis requires few seconds on a standard workstation and the theoretical results show a very good agreement with the measured data in a wide frequency band. The capability of the MoM/BI-RME approach to handle completely arbitrary shapes is highlighted in the second example. In this case, in fact, the fabrication process causes small deformations of the nominal shape of the apertures, which must be accounted for, since they play an important role in the frequency response of the filter.

Transmission features of frequency-selective components in the far infrared determined by terahertz time-domain spectroscopy

Transmission and phase-shift characteristics of dichroic high-pass filters with cutoff frequencies as high as 1.11 THz and of a cross-shaped grid bandpass filter with a resonance frequency of 280 GHz were measured with an electro-optic sampling terahertz time-domain spectrometer operating between 0.1 and 2 THz. Good agreement with transmission theories is found. We also compare the transmission performance of cascaded dichroic filters with that of cross-shaped grid bandpass filters. Both types of bandpass filter permit frequency-selective ultrafast experiments in the far-infrared spectral region. In the millimeter and the submillimeter wavelength regions, which are difficult to access by conventional means, knowledge of the frequency response of frequency-selective components is important for applications in frequency mixing, multiplying, and multiplexing in quasi-optical systems.

Design, fabrication, and measurement of frequency-selective surfaces

This paper describes theoretical analysis, fabrication tech- niques, and measurement results for frequency-selective surfaces oper- ating in the millimeter and submillimeter wave region. The analysis is based on the method of moments with entire domain basis functions, obtained by the boundary-integral-resonant-mode-expansion method. This method is particularly efficient and applies to the analysis of thick metal screens perforated periodically with arbitrarily shaped apertures. Three fabrication techniques are discussed and applied: photolitho- graphic etching, galvanizing growth, and milling. Prototypes obtained with the different fabrication techniques are presented. Finally, measure- ments of the frequency response of the prototypes are presented, based on a new spectroscopic tool called terahertz time-domain spectroscopy. In all cases, the measurement data fit very well with the simulations.

Simulation and Measurement of Dielectric Antennas at 150 GHz

Based on the development of a flexible, dielectric waveguide system for frequencies in the region of 150 GHz [1], the antenna characteristics of various tapered ends of dielectric waveguides have been studied. The flexible waveguide consists of a rectangular, dielectric fibre made of polyethylene. The paper describes the simulation and optimization of different tapers using 3D electromagnetic field computation, the precise fabrication of the antennas and the verification of the simulated data by field measurements at 150 GHz.

A Fast Scanning W-Band System for Advanced Millimetre-Wave Short Range Imaging Applications

The paper presents the development of a fast scanning W-Band (75-100 GHz) system and a suitable antenna concept for advanced imaging applications. The goal is to obtain a broadband frequency response from a large target area within a short time period. Two typical approaches for the design of a free space millimetre-wave imaging setup will be discussed. The first approach consists of a focused bistatic measurement setup that includes a combination of a conical horn and a dielectric lens in order to focus the beam. The basic idea of the second approach is to use an unfocused measurement setup employing synthetic aperture radar (SAR) algorithms in order to focus the image numerically. Both measurement setups will be discussed with respect to the capability for fast scanning mm-wave imaging systems. Experimental results on planar test objects demonstrate the performance of the developed W-Band system compared to a commercial vector network analyzer (VNA)

Flexible low-loss dielectric waveguides for THz frequencies with transitions to metal waveguides

A flexible low-loss dielectric waveguide system for sub-millimetre wave frequencies up to 600 GHz is presented, with measured attenuation values shown at 300 GHz. Mode transformers for an accurate and reproducible transition to metal waveguides have been investigated and improved.

Optimization of a fast scanning millimetre-wave short range SAR imaging system

This paper presents the development of a W-band short range imaging system for security and non-destructive testing applications, which uses an unfocused measurement setup employing SAR algorithms in order to focus the image numerically. The active imaging system offers the possibility to get a broadband frequency response from each pixel in the measurement plane. For real-time applications a fast scanning, monostatic virtual antenna concept has been developed and optimized. The monostatic setup is demonstrated in two different configurations, on the one hand using a quasioptical, broadband diplexer with high decoupling between transmitter and receiver channel and on the other hand a very compact setup using a commercially available high directivity waveguide coupler. The measurement setups are compared with special respect to their RF-performance. Experimental results on specific test objects are presented to prove the performance of the fast short range SAR imaging system.

Design and measurement of a bandpass filter at 300 GHz based on a highly efficient binary grating

A bandpass filter for 300 GHz with a stopband at 450 GHz based on a highly efficient binary grating as a frequency-selective element was developed and optimized. The geometry of the grating was carefully designed for a maximum difference angle between reflected beams at 300 and 450 GHz and for maximum efficiency at 300 GHz. The grating efficiency was optimized using a rigorous theory of diffraction, yielding a maximum efficiency of over 99.5% neglecting conductor losses. Antennas and elliptical mirrors are used for optimum quasi-optical illumination of the grating and Gaussian beam shaping. After an optimization and a comprehensive examination of the grating in an experimental heterodyne measurement setup at 300 GHz, the filter was implemented fixed tuned into a small housing with waveguide flanges. The fixed tuned setup with corrugated feed horns results in an overall flange-to-flange insertion loss of only 2.8 dB.

Multistatic Short Range Ka-Band Imaging System

This paper presents the concept of a Ka-Band (26.5 - 40 GHz) multistatic active short range imaging system. The motivation for this work was the development of a fast scanning imaging system for non destructive testing (NDT) or security scenarios. The goal was to derive a 3D reconstruction of the device under test (DUT). The imaging system consists of a linear receive array and spatially distributed transmitters with non focussing antenna elements. This transmit/receive array is moved perpendicular to the array dimension. By switching between each transmitter and simultaneous reception of the scattered field by each receiver, a fast sampling of the 2D aperture plane is achieved. Due to unfocussed antenna elements numerical reconstruction algorithms have to be applied for a highT lateral resolution. An aperture synthesis concept is presented to reconstruct the raw data. It is based on the separation of the reconstruction kernel into a horizontal and a vertical part. Range resolution is achieved by a broadband stepped frequency continuous wave (SFCW) radar. In order demonstrate the efficiency of the new reconstruction kernel first results are demonstrated with simulated and measured data.

Investigation of the Hot Embossing Technology for Low-Cost Antennas Printed on Polymer Substrates

In this contribution a novel metallization technique for the realization of millimeter-wave microstrip patch antennas is presented. This technology called hot embossing is a fast and economic process originating from the production of three-dimensional molded interconnect devices (3D-MID). Conductive structures are coated onto plastic parts or plastic foils using a heated stamp. To the best knowledge of the authors, this approach has not yet been employed and therefore will be investigated for the fabrication of low-cost printed antennas at millimeter-wave frequencies. The focus of this contribution is on the evaluation of process parameters and interactions with substrate and copper foil characteristics as well as the fabrication and measurement of single microstrip patch antennas designed for the 24 GHz ISM-band. Far-reaching potentials lie in the utilization of the three-dimensional manufacturing technology for the construction of conformal integrated antennas.