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The demand on advanced personnel screening systems led to the development of several active and passive imagers. Among them, active multistatic imaging ensures high image quality and allows fully electronic screening. An active E-band imager is presented in this paper, which measures in real-time and delivers images of 30-dB dynamic range. Imaging of humans is achieved by optimizing the acquisition time using a dedicated digital signal processing solution. This paper introduces the system hardware, the calibration procedure, and several measurement results demonstrating high quality imaging capabilities.

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.

Wireless transmission systems in smart metering networks share the advantage of lower installation costs due to the expandability of separate infrastructure but suffer from transmission problems. In this paper the issue of interference of wireless transmitted smart meter data with third party systems and data from other meters is investigated and an approach for solving the problem is presented. A multi-channel wireless m-bus receiver was developed to separate the desired data from unwanted interferers by spatial filtering. The according algorithms are presented and the influence of different antenna types on the spatial filtering is investigated. The performance of the spatial filtering is evaluated by extensive measurements in a realistic surrounding with several hundreds of active wireless m-bus transponders. These measurements correspond to the future environment for data-collectors as they took place in rural and urban areas with smart gas meters equipped with wireless m-bus transponders installed in almost all surrounding buildings.

Due to the enormous advances made in semiconductor technology over the last few years, high integration densities with moderate costs are achievable even in the millimeter-wave (mm-wave) range and beyond, which encourage the development of imaging systems with a high number of channels. The mm-wave range lies between 30 and 300 GHz, with corresponding wavelengths between 10 and 1 mm. While imaging objects with signals of a few millimeters in wavelength, many optically opaque objects appear transparent, making mm-wave imaging attractive for a wide variety of commercial and scientific applications like nondestructive testing (NDT), material characterization, security scanning, and medical screening. The spatial resolution in lateral and range directions as well as the image dynamic range offered by an imaging system are considered the main measures of performance. With the availability of more channels combined with the powerful digital signal processing (DSP) capabilities of modern computers, the performance of mm-wave imaging systems is advancing rapidly.

The interest in active millimeter-wave and microwave imaging systems is increasing due to their utilization in security, medical, and industrial applications. Imaging systems using monostatic arrays suffer from the high number of antenna positions, making a fully electronic solution very costly and impractical. Multistatic arrays, however, offer the chance for high reduction factors in the number of antennas, and then allow for fully electronic solutions. Here, a new array architecture is presented, which is suitable for real-time operation and is capable of delivering high image quality in means of resolution and dynamic range. Various technological solutions were developed for the imaging purpose, which are introduced in detail. An example array for operation from 72 to 80 GHz is demonstrated. The imaging system hardware is introduced, along with several imaging results of humans with concealed objects.

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.

Due to the capabilities of modern vector network analyzers (VNAs), the usage of “True-Mode”-signals for characterizing and testing active differential devices is quite convenient. Nevertheless in cases, in which the device under test (DUT) and/or the measurement setup introduces a coupling between the required stimulus signals, current methods require some iteration time to achieve the desired phase and amplitude settings. In this paper a new approach will be introduced, which leads to an optimized testing time which can be crucial especially in industrial production test.

At airport security checkpoints, authorities are demanding improved personnel screening devices for increased security. Active mm-wave imaging systems deliver the high quality images needed for reliable automatic detection of hidden threats. As mm-wave imaging systems assume static scenarios, motion effects caused by movement of persons during the screening procedure can degrade image quality, so very short measurement time is required. Multistatic imaging array designs and fully electronic scanning in combination with digital beamforming offer short measurement time together with high resolution and high image dynamic range, which are critical parameters for imaging systems used for passenger screening. In this paper, operational principles of such systems are explained, and the performance of the imaging systems with respect to motion within the scenarios is demonstrated using mm-wave images of different test objects and standing as well as moving persons. Electronic microwave imaging systems using multistatic sparse arrays are suitable for next generation screening systems, which will support on the move screening of passengers.

This paper presents the development of a compact sized, low cost wide range tunable bandpass filter based on a novel RF structure. The proposed design offers a narrow passband with a relative bandwidth down to 3.9%, a wide tuning range from 700 MHz to 1150 MHz and the ability to adapt bandwidth and insertion loss during operation. Tuning is achieved by reverse biased varactor diodes with a low supply voltage of 5 V max. Design of the novel bandpass structure, integration and miniaturization to reduce its size down to approx. 6 cm2 is discussed. Measurement results over the whole tuning range are presented and the design of a miniaturized multi channel bias controller for easy frequency setting and temperature compensation is described.

The experimental verification of a novel sensor topology capable of measuring both the position and energy of an electron beam inside a compact electron linear accelerator for radiotherapy is presented. The method applies microwave sensing techniques and allows for the noninterceptive monitoring of the respective beam parameters within compact accelerators for medical or industrial purposes. A state space feedback approach is described with the help of which beam displacements, once detected, can be corrected within a few system macropulses. The proof-of-principle experiments have been conducted with a prototype accelerator and customized hardware. Additionally, closed-loop operation with high accuracy is demonstrated.

Scattering parameter measurements in the presence of crosstalk is a well documented problem. The available calibration methods, suited for the general 16-term error model, capable of taking the crosstalk into account, suffer from the required Thru-Standard, which has to be perfectly known. This information is hard to acquire in some cases. An approach which makes the advantage of the 7-term SOLR (Short-Open-Load-Reciprocal) accessible to the 16-term error model is discussed in this article. The mathematical description, the feasibility for multiport applications, measurement results and a brief sensitivity analysis will be presented.

The demand on advanced personnel screening systems led to the development of several active and passive imagers. Among them, active multistatic imaging ensures high image quality and allows fully electronic screening. An active E-band imager is introduced in this paper, which operates in real-time and delivers images of 30-dB dynamic range. Imaging of humans is achieved by optimizing the acquisition time using a dedicated digital signal processing solution.

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.

The increasing demand on developing advanced imaging methods for the personnel screening applications has motivated many researchers to explore new techniques suitable to the emerging problem. Among the known methods, the active imaging using multistatic arrays in connection to digital-beamforming proofs efficient imaging with high image quality in terms of dynamic range and resolution. As any active imaging method, the illumination of the imaged object becomes an issue due to specular reflections. The human skin causes relatively strong specular reflections in the millimeter-wave range, and hence hinders the visibility of the body to some extend. Therefore, a consolidated understanding of the geometrical problem is essential for the optimization of the illumination issue. In this work, a simulation model is presented to address the problem precisely; and a measurement verification in the frequency range of 75 to 82 GHz is made to demonstrate the exactness of the proposed model. Additionally, an illumination analysis of a typical screening scenario of a human is presented.

A non-destructive microwave measurement setup for broadband complex permittivity determination of solid materials over a frequency band from 0.05 GHz to 6 GHz is presented. The setup design was optimized for measurements of glass materials with planar and convex surfaces, but works with other dielectric materials as well. The measurement method is based on the near field coupling of two open-ended coaxial probes through the material under test (MUT). A theoretical modeling of this measurement configuration was performed, using a 3D full-wave electromagnetic field simulator. Two identical coaxial probes and an equivalent calibration kit, in order to perform a TRL calibration of the proposed setup, were designed. The calibration procedure of the measurement setup is explained and experimental results are presented.

The interest on active millimeter-wave and microwave imaging systems is increasing nowadays due to their utilization in security, medical, and industrial applications. Imaging systems using monostatic arrays suffer from the high number of antenna positions, making a fully electronic solution very costly and impractical. Multistatic arrays, however, offer the chance for high reduction factors in the number of antennas, and then allow for fully electronic solutions. Here, a new array architecture is presented, which is suitable for real-time operation and is capable of delivering high image quality in means of resolution and dynamic range. An example array is demonstrated for operation from 72 to 80 GHz. The imaging system hardware is introduced, along with imaging results of humans.

The calibration of test fixtures or the estimation of their performance are well known tasks. In the case of fixtures with variable length, there are some established methods to de-embed the DUT (Device Under Test). The calibration or evaluation of a fixture with a fixed length, like a socket or a probe-card offers less possibilities. This contribution presents a novel calibration procedure, capable of gathering not only the information required for a proper de-embedding but also for an absolute characterization of fixed length fixtures, including crosstalk. In order to achieve this, specific assumptions have to be made. These assumptions, the resulting calibration scheme as well as a first validation through a known device will be addressed together with a first discussion on error propagation.

Methods to estimate Directions of Arrival (DOA) on radio signals are susceptible to hardware and signal deficiencies. In the following, the robustness of four algorithms is evaluated by numerical and experimental tests. The focus lies thereby on Secondary Surveillance Radar (SSR) signals, but the algorithms can generally be used on any kind of radio signal. It will be shown that variants of the ESPRIT algorithm provide highly accurate DOA estimates on SSR signals even without calibration.

A contiguous planar diplexer in suspended stripline technology with ultrawideband channels from DC to 40 GHz and 40 GHz to 80 GHz is presented. The design of the diplexer is based on quasi-complementary LC lowpass and highpass prototypes which are directly transformed into transmission line elements by using a quasi-lumped approach. This very straightforward design procedure requires no susceptance annulling networks and no introduction of unit elements which could limit the diplexer's operation bandwidth. For achieving an optimal compatibility with external circuits, an ultra-broadband SSL-MSL (suspended stripline - microstrip line) transition with a return loss of more than 18 dB from DC to 83 GHz was designed. The realized diplexer is extremely compact (6×4.5mm) and features a return loss of more than 12 dB from DC to 81 GHz with very low channel insertion losses of typically less than 1 dB after proper optimization.

In this paper a novel tunable bandpass filter based on open ended finlines is presented. Hexagonal ferrite spheres are used as resonators to cover a tuning frequency range from 39GHz to 68GHz. The measured insertion loss of the filter varies from 5.3dB to 7dB with a typical 3dB-Bandwidth between 300MHz and 400MHz. An off-resonance isolation of about 60dB is achieved although only two spheres are used.

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.

Novel wideband planar Marchand baluns in the millimeter wave range from 40 to 80 GHz are presented. The circuits can be fabricated in a regular thin-film process due to less stringent specifications by using defected ground structure (DGS) technology. The return loss of the balun is better than 10 dB from 40 -80 GHz and better than 15 dB from 43-73 GHz. The amplitude balance is better than 2 dB from 40-80 GHz and better than 0.5 dB from 43-73 GHz. The phase balance error is smaller than 8deg over the entire frequency range. Simulation and measurement results are fitting very well. Several additional versions of the proposed balun are presented providing IF-paths to build a complete double-balanced mixer circuit. To show the applicability of the baluns, a low cost hybrid ring mixer for an IF of 500 MHz has been fabricated. Measurement results show a flat conversion loss of about 9 dB from 33 -69 GHz. Further measurement results for a second mixer for IF frequencies up to 23 GHz are presented.

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. >

In the millimeter wave region several communication and sensor systems are emerging which presently are served only by III/V based technologies. First sensor systems of relevant volume market are tested at 76 GHz for automotive sensors, with other systems operating at 60 GHz and 94 GHz. For mm-wave communication systems volume applications arise at 38 GHz for the interconnection of PCN cells. This paper describes GaAs based technologies and components which are available to serve the requirements of mm-wave communication sensor systems up to 80 GHz.

This paper describes the problem of characterizing multiport networks at high frequencies, especially such devices which are stimulated by a common-mode or differential-mode source. An overview over the definition of mixed-mode S-parameters and their relation to nodal S-parameters is given. A measurement system is presented, which enables to measure all S-parameters of a 4-port with a 2-port network analyzer in an automated procedure. The functionality of this measurement system is described and possible ways for calibration are shown.

Results of electromagnetic simulations and measurements of simple interconnect structure are discussed in this paper. The presented structure was realised on LTCC multilayer board which are suitable for manufacturing of multichip modules for next generation communication systems with clock rates in the 10-100 GHz range. From the presented results it is possible to obtain an impression about distortion of high speed digital signals after passing this or similar interconnect structures. Precision microwave measurement techniques that are important for verification of such simulations are discussed, too.

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.