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This chapter provides an overview over common categories of microwave holography systems. Terms like resolution or speckle are defined and design rules are presented. Performance and cost of the various microwave holography systems are discussed as well as their applications. A special focus is devoted to indirect holographic systems at millimeter wave frequencies. A setup using arrays of planar antenna coupled zero bias Schottky diodes as detectors is presented in detail.

Radar sensors are used widely in modern driver assistance systems. Available sensors nowadays often operate in the 77 GHz band and can accurately provide distance, velocity, and angle information about remote objects. Increasing the operation frequency allows improving the angular resolution and accuracy. In this paper, the technical feasibility to move the operation frequency beyond 100 GHz is discussed, by investigating dielectric properties of radome materials, the attenuation of rain and atmosphere, radar cross-section behavior, active circuits technology, and frequency regulation issues. Moreover, a miniaturized antenna at 150 GHz is presented to demonstrate the possibilities of high-resolution radar for cars.

In a preceding paper a multi-channel test signal generator for UHF radar applications was presented. The present contribution shows the application of this generator to test the performance of multi-channel receivers in selected scenarios. Exemplary measurement results are presented showing the usable dynamic range and the maximum packet reception rate for a secondary surveillance radar receiver and a smart meter data collector. Furthermore the direction-of-arrival estimation precision and the source separation capabilities of the receivers are tested under various conditions.

In this paper, an autofocusing radar technique is presented for tip clearance measurements in combustion turbines capable of resolving the edges of a typical blade tip. The clearance is determined by measuring the reflection at the blade tip while passing by the antenna, subsequently focusing the data by means of a matched filter operation and interpreting the phase of the blade edge reflection according to the continuous wave radar principle. For this, an autofocus approach was developed, which minimizes defocusing effects and provides an estimate of the clearance as the first result, which is utilized to overcome the phase ambiguity and, thus, to increase the measurement range. The autofocus algorithm applies a weighted phase gradient of the pointlike blade edge reflection as cost function and sensitive indicator for the focal quality.

In this paper, principal considerations for a high accuracy millimeter wave (mmw) radar distance measurement system applicable to be used in harsh industrial environments are presented. The system is based on continuous wave (CW) measurement of the reflection coefficient and interpretation of the signal phase. The ambiguity of the phase is overcome by means of a multiple frequency technique. For absolute distance determination, an online calibration procedure is applied. The applicability of the system is underlined by a laboratory demonstrator measurement.

In this contribution, fundamental design considerations for a novel metallization technique to realize millimeter-wave microstrip structures are presented. This hot embossing technology is a fast and economic process originating from the production of three-dimensional molded interconnect devices. Conductive structures are coated onto plastic parts or plastic foils using a heated stamp. This approach shows high potential and therefore will be investigated for the fabrication of low-cost printed antennas at millimeter-wave frequencies. The focus of this contribution is on design guidelines considering process parameters and interactions with substrate and copper foil characteristics derived from the fabrication and measurement of single microstrip patch antenna prototypes for radar applications in the industrial, scientific and medical (ISM) band at 24 GHz. Far-reaching potential lies in the utilization of the three-dimensional manufacturing technology for the construction of conformal integrated antenna systems based on the thermoforming capabilities of polymer substrates.

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.

We examine the possibilities to use a C02-pumped FIR-ring laser system, which was optimized for operation at 2.5THz, for the generation of other FIR-lines using methanol as laser-active medium. Five laser lines between 1.7 and 4.8THz were detected and characterized with respect to the maximum achievable output power, beam quality and optimum methanol pressure. Mode patterns for most of the lines were recorded in order to allow easy adjustment of the system and line-identification.

For focusing reflectors usually paraboloidal and ellipsoidal shapes are used, which are a first degree approximation to an optimal beam transformer. In this paper, the design of such an optimally shaped reflector is described, using basic numerical procedures and common CAD software. The complexity of the described procedure is not much higher than the design of paraboloidal or ellipsoidal reflectors. Measurement data is presented to confirm the functionality of the designed reflector at frequencies beyoned 200 GHz.

The possibility to detect and analyze multipath signals of global navigation satellite systems (GNSS) caused by aircrafts is an attractive basis for the development of a passive surveillance sensor. Due to the fact that the received signal strength of global navigation satellite systems on earth surface is very low and the radar cross sections (RCS) of an aircraft strongly varies with the illumination and observation angles, such a passive sensor will offer a high probability of detection with respect to a hemispheric field of view preferably in a multistatic sensor array configuration. In this work measurements with a single sensor and considerations about possibilities to range an aircraft with a multistatic sensor array are presented.

Two approaches for differentially fed, polarimetric antennas with a center frequency of 77.5GHz are introduced. These are an aperture-coupled patch (ACP) antenna and a monopole antenna with two differentially fed monopole pairs. Easy planar integration with differential MMICs is given through the differential stripline feed. Both antennas are designed for high bandwidth from 70 to 85GHz for 10 dB return loss and high polarization purity. A stacked conical horn included in both designs results in a high gain of 8.5 dBi and a radiation pattern with one symmetric main beam without significant side lobes, reducing coupling to other elements in a future antenna array. After an introduction, design goals for the antennas are presented. Then, the design procedures for the two concepts are described together with simulation results. For measurement of the antennas, a feed network has been developed and the monopole antenna has been chosen for realization. The paper will be concluded by measurement results that are in good agreement with the simulations.

In the classical indirect holographic setup, a wave emitted by the measurement object is superimposed with a reference wave at the aperture of the imaging system. The resulting interference pattern can be recorded with a simple intensity detection. However, the complex object field can be obtained from the plane wave spectrum (PWS) of the interference pattern. Dedicated methods can be used to calculate the field distribution at the object position, which is equivalent to the object properties and to an image of the object, respectively. This paper shows that the resolution of the created image is restricted due to the fact that the bandwidth of the extracted field is limited by the extraction process. A relation between the maximum possible bandwidth and the geometrical dimensions of the imager setup is deduced. Furthermore, a formula for the minimum achievable resolution is derived. Experimental results are presented to illustrate the issue.

Our DOA estimation sensor has shown the potential to provide highly precise estimates (0.54° RMSE) of SSR signals. The CRB in this scenario is closely approached by using NC Unitary ESPRIT. Further improvements by calibration can be attained with higher resolution A/D-converters in order to increase the SNR of the used reference signals.

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.

In this paper a novel tunable high isolation bandpass filter is presented. The filter consists of two shielded coplanar transmission lines coupled by a rectangular waveguide. Hexagonal ferrite spheres are used to cover a tuning frequency range from 50 to 80GHz. Measurement results up to 69GHz are shown. The measured insertion loss of the filter lies between 7.1 and 9.3dB. An off-resonance isolation better than 60dB is achieved what is extraordinarily high for a two spheres filter. The typical 3dB-bandwidth is about 250MHz. As planar transmission lines are used, the filter can be integrated into a coplanar or microstrip environment easily what is advantageous for the construction of highly integrated modules. The operating frequency range can be expanded up to 80GHz by replacing the 1.85mm-connectors by 1mm-connectors or using other suitable waveguide transitions, thus covering considerably more bandwidth than rectangular waveguide based coupling structures.

This paper presents simulation results for a 600 GHz micromachined waveguide mixer with integrated horn antenna, a hybrid-integrated planar Schottky diode and IF filter structures on a quartz substrate. In addition to the simulated electrical performance we show approaches for the manufacturing of the split-block mixer by both micro-mechanical milling and silicon etching technology.

In this paper we present measurement results of a micro-machined split-block waveguide mixer for 600 GHz. The mixer implements a planar GaAs Schottky diode on a quartz substrate. Two different diode designs used for this mixer design are compared. The overall performance of the waveguide mixer is demonstrated by measurements of the mixer in a quasi-optical setup at 600 GHz. In this setup we are able to measure single sideband conversion losses of 9-14 dB at 600 GHz and voltage responsivities of 421-1690 mV/mW.

The field of view of wide angle dielectric lens antennas for focal plane arrays is mainly limited due to astigmatic aberrations which are often not taken into consideration even in more complex coma-corrected lens designs with two aspheric surfaces. The paper describes an efficient compact range setup for the measurement of high-gain lens antennas in small antenna chambers and presents a thorough experimental study of the effects of astigmatism and feed displacement/misalignment on the pattern degradation for large scanning angles. An experimentally derived method to minimize these aberrations is explained, resulting in a fairly constant beam quality with a maximized gain over a large field of view of 40/spl deg/.

In this paper, simulated Brillouin scattering in Raman fiber amplifier was numerically calculated. The theoretical results show that much more power could be transferred from the pump to the signal in Raman fiber amplifier with no SBS and Brillouin frequency shift in a given fiber depends on temperature and on mechanical strain. And spatially variable longitudinal strain distribution in standard fibers for SBS suppression in active devices was proposed.

A lineselective CO2-laser with an unstable resonator is presented. The CO2-laser is realised with an rf-excited slab geometry to get a compact design with high output power. As lineselective element a grating in Littrow mount is used. The gratings are manufactured by anisotropic etching of silicon. The grating has a variable duty cycle to obtain a variable reflectivity. Furthermore, gratings are presented that have focusing propteries by a variation of the grating periodicity.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A broadband low cost millimeterwave slotline detector circuit is proposed that can efficiently be realized on a low permittivity substrate (/spl epsiv//sub r/= 2.2) which is required for the integration of an antenna. The experimentally approved design achieved a voltage sensitivity of 1660 mV/mW at 77 GHz, with more than 1000 mV/mW between 62 and 85 GHz, a tangential signal sensitivity below -45 dBm and a 1-dB-compression point at -14.8 dBm. The sensitivity is about the same as for commercially available waveguide detectors despite the unfavourably low substrate permittivity. The compact design and the low cost allow the integration of a larger number of such slotline detectors with antennas on a single substrate for a receiver array in a millimeterwave focal plane imaging system.

Dielectric rod antennas of rectangular cross section are of increasing interest at mm-wave frequencies. For many applications, like e.g. densely packaged feed arrays for reflector/lens systems or electromagnetic field probes, an exact knowledge of the phase center location is required. This work describes a simple experimental method to determine the phase center of antennas by means of a phase pattern measurement and a numerical least square fit procedure. For feed antennas, the method can be adopted to the numerical aperture of reflector or lens systems. Phase center locations of various dielectric rod antennas with rectangular cross section are presented and the influence of geometrical parameters and frequency on the phase center an analysed and interpreted in detail.

With the increasing interest in new artificial materials ranging from meta-materials to photonic bandgap materials there is a growing need for accurate models of artificial materials. We examine the design of a three-layer structure with an artificial dielectric as an anti-reflection-coating on both sides of a dielectric slab. We present a field-equivalent circuit theory to calculate the effective dielectric constant of the structured dielectric. The materials discussed in this paper have a lateral periodicity smaller than /spl lambda//10 and can easily be manufactured from high density polyethylene (HDPE) for frequencies up to 20 GHz. The field-analog circuit theory can also be used to calculate the polarization dependence of the artificial dielectric. Theoretical results of three geometrically different structures were compared with waveguide measurements at X-band and showed excellent agreement. Applications such as the design of new components at millimeter and submillimeter wave frequencies are discussed, considering the X-Band measurements as a scaled model.

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.

The LHFT is currently working on a broadband heterodyne receiver for stratospheric measurements at 2.5 THz. Many molecules and radicals such as OH, H/sub 2/O and O/sub 3/ which are involved in the stratospheric ozone chemistry exhibit characteristic emissions in this spectral range. In order to measure these spectra and extract concentration data of the single components, a platform operating at high altitudes is necessary to overcome atmospheric absorption due to water vapor. Research at the LHFT includes the construction of a stable and compact local oscillator (LO) as well as the development of the receiver front end. In the LO subsystem an RF excited grating tunable sealed off CO/sub 2/ laser with an apodized out-coupling element will be used as a pump source. The compact and rugged design is realized by a slab discharge geometry and a metal tube housing. Long term stable gas composition for sealed off operation is optimized during the design phase of the laser by making use of tunable diode laser absorption spectroscopy (TDLAS). A methanol ring-laser with an output power of up to 49 mW at 2522.8 GHz (pump power 20 W) has been developed and is available as a very powerful FIR source. The optimization of the front end concentrates upon broadband and low noise performance. A mixer with newly developed substrate-less Schottky diodes followed by a broadband, noise matched IF-amplifier allow for low noise operation over a frequency range from 6 to about 13 GHz, thus covering emission lines of at least the three species mentioned above.

A number of applications of microwave and, in particular, millimeter-wave MMICs (monolithic microwave integrated circuits) in automotive systems are under development. The authors review these applications and give the current status of some of these developments. The applications considered are sensors (both radar and radiometric), communication systems, and traffic control systems. MMICs for the following specific systems are considered: speed sensors, electronic toll collection, and collision avoidance radar. >

A variety of transitions between rectangular dielectric waveguides and planar waveguides like microstrip or slotline have been designed to combine the advantages of dielectric wave-guides at millimeterwaves with the excellent hybrid integration capabilities of planar circuits. FDTD field simulations have been applied to analyze and optimize the designed transitions with respect to low insertion and return losses as well as minimized mutual coupling between adjacent transitions. Experimental investigations between 60 and 90 GHz proved the promising results of the simulations with insertion losses between 0.5 and 1.5 dB over the full waveguide band (WR-12). The transitions can well be used for the integration of planar circuits into dielectric waveguides or rod antennas and the designed structures are scalable up to frequencies beyond 100 GHz.

Various design procedures for millimeter-wave dielectric lenses have been studied and compared with regard to the wide angle characteristics of the resulting lens contours. The paper describes the simulation and optimisation of the focusing properties of the lenses for large scanning angles using a hybrid method involving ray-tracing techniques and aperture field integration, the realisation of unzoned and zoned lenses and the farfield pattern measurements at 75 and 150 GHz. The theoretical and experimental results show that a scanning range of 40° (±20°) with very low beam degradation can be achieved.

In this study the design and construction of an ultrawideband backward wave directional coupler is presented. The symmetric, non-uniform coupler covers the frequency range from 2 to 50 GHz with an average coupling of 16.6±2.4 dB while establishing directivity values greater than 10 dB from 10 MHz to 33.8 GHz and 8 dB up to 48.4 GHz. The design is based on coupled microstrip lines suitable for integration into planar front end modules of modern measurement systems. To account for the dispersive behaviour of such waveguides, wiggly-line technique is utilised. Accurate extraction of the waveguide frequency-dependent distributed equivalent circuit parameters is done by 2D finite element electromagnetic field (EM) simulation. To balance out the remaining mistuning appropriate scaling parameters are introduced. The influence of common manufacturing and assembly tolerances on the device performance is analysed. Measurement results of the synthesised coupler with planar matched isolated port are presented.

Quasiplanar waveguides are analyzed which consist of a thin, partially metallized dielectric substrate inserted in the E-plane of a rectangular waveguide. Several slots or strips in symmetric or non-symmetric positions are allowed on each substrate surface. The analysis is based on a simplified formulation of the spectral domain immittance matrix followed by a Galerkin's method. The analysis has been extended to include the computation of higher order propagating and evanescent modes as well as the characteristic impedances of the dominant modes. Numerical results are presented for various configurations with strips or slots on one or both air-dielectric interfaces illustrating the flexibility of the applied method.

The letter reports new results on a broadband fin-line PIN-diode attenuator furnished with double-ridge waveguide flanges. The full bandwidth capabilities of fin line can thus be utilised. The attenuation is adjustable between 2 and 35 dB over the entire frequency band from 18 to 40 GHz.

A quasiplanar 3 dB hybrid suitable for integration in millimetre-wave fin-line circuits is presented. The performance of the device is characterised by 0.5 dB insertion loss, less than 0.5 dB imbalance and 20?25 dB isolation over the entire Ka-band (26.5?40 GHz).