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This paper presents the integration and channel characterization of a highly integrated dual-band digital beamforming space-borne synthetic aperture radar (SAR) receiver. The proposed SAR sensor is a low-cost, lightweight, low-power consumption, and dual-band (X/Ka) dual-polarized module ready for the next-generation space-borne SAR missions. In previous works, by the authors, the design and experimental characterization of each sub-system was already presented and discussed. This work expands upon the previous characterization by providing an exhaustive experimental assessment of the fully integrated system. As it will be shown, the proposed tests were used to validate all the instrument channels in a set-up where the SAR sensor was illuminated by an external source minim the ground reflected waves. Test results demonstrate how the system channels are properly operating allowing the reception of the input signals and their processing in the digital domain. The possibility to easily implement a calibration procedure has also been validated to equalize, in the digital domain, the unavoidable amplitude differences between the different channels.

The well-known German aversion to inflation has attracted a lot of interest and is often attributed to a specific historical memory: Weimar. Yet we do not know much about why hyperinflation seems to overshadow the Great Depression in German collective economic memory. To answer this question, we study what exactly it is that Germans believe to remember about their past. Using original survey data, we show that many Germans do not distinguish between hyperinflation and the Great Depression, but see them as two dimensions of the same crisis. They conflate Weimar economic history into one big crisis, encompassing both rapidly rising prices and mass unemployment. Additionally, more educated and politically interested Germans are more likely to commit this fallacy. Our finding thus nuances ideational explanations for Germany's economic policy stance in the European Union.

This paper presents the first experimental assessment of a highly integrated dual-band dual-polarized antenna tile designed for synthetic aperture radar (SAR) digital beamforming (DBF) satellite applications. The demonstrator described in this paper is the first comprehensive experimental validation of an RF module providing the X-band and Ka-band (9.6- and 35.75-GHz) operation with custom downconversion stages. All the antennas, transitions, and downconversion chips are integrated in the same antenna tile fabricated using a customized 15-layer high density interconnect process. The designed tile goes to the limits of the proposed technology and for the high trace density and for the size of the vertical transitions. The proposed results represent the state of the art in terms of compactness for a DBF SAR RF module even though the demonstrator was manufactured with a standard low-cost technology. The experimental assessment proves the validity of the proposed manufacturing and integration approaches showing a substantial agreement between the performance of the individual blocks and of the integrated system.

How does economic globalization influence domestic political stability? Building on innovations in trade theory, we argue that international trade amplifies political discontent and protest in contexts in which trade losers concentrate, but has a pacifying effect in contexts dominated by beneficiaries of free trade. We examine this argument focusing on variation in Russian regions. Using negative binomial regression models on data from 2007 to 2012, we show that regional education levels condition the effect of trade intensity on protest frequency. High exposure to trade leads to more protests in regions with low average education levels, but fewer protests in regions in which residents are well-educated. Probing the underlying mechanism, we find that the effect of trade on regional economic welfare is conditioned by education levels, that poorly educated Russians face more economic difficulties when they live in regions exposed to trade, and that economically aggrieved individuals participate more in protests.

Synthetic aperture radar (SAR) has always been a promising sensor for Earth observation and remote sensing. In order to cope with the increasing demand on high performance, the system has to be upgraded with innovative multifunctional features. Different challenging techniques are receiving increasing interest, namely digital beamforming and cognitive radar. This paper outlines a concept of a cognitive SAR sensor with advanced tracking and imaging capabilities based on the interaction with the observed scene. The combination of beamforming on transmit and cognitive parameters control yields a new SAR system with improved performance.

In the context of radar spaceborne imaging, the novel multichannel staggered synthetic aperture radar (SAR) mode represents a promising solution for the mapping of ultrawide swaths with very high azimuth resolution. This paper extends the analysis of multichannel staggered SAR to planar antenna architectures and provides system design examples both for planar and reflector antenna architectures. Furthermore, a first proof of concept using measured data acquired by an experimental ground-based system is provided to demonstrate the approach's feasibility.

This paper investigates a new mechanism to explain politically induced changes in bilateral aid. We argue that shifts in the foreign policy alignment between a donor and a recipient country following leadership changes induce reallocation of aid. Utilizing data from the G7 and 130 developing countries between 1975 and 2012 and employing high dimensional fixed effects models, we show that incoming leaders in recipient countries, which politically converge towards their current donors, receive more aid commitments, compared to those that diverge. Accounting for donor leader change, we additionally find that incumbent recipient leaders have an opportunity to get even more aid when political change in donor countries moves them closer to the donor's foreign policy position. Thus, leadership turnover in recipient and donor countries makes otherwise inconsequential deviations in foreign policy alignment highly consequential for aid provision.

How does offshoring affect individual party preferences in multiparty systems? We argue that exposure to offshoring influences individual preferences for those political parties with clear policy positions on issues relevant for individuals with offshorable jobs (left, liberal, and center-right parties) but does not affect voting decisions for parties concentrating on other issues (green or populist right parties). Examining individual-level data from five waves of the European Social Survey for 18 advanced democracies, we find that these effects vary by skill level and exposure. Offshoring increases preferences for liberal and center-right parties that advocate economic openness among the highly skilled. In contrast, low-skilled individuals exposed to offshoring are more likely to prefer leftist political parties that champion social protection and redistribution. Offshoring does not affect the propensity to vote for green and populist right parties.

One of the benefits of synthetic aperture radar (SAR) systems utilizing digital beamforming is the ability to increase the receive power. The relevant SAR technique is known as SCan-On-REceive (SCORE), which steers the receive antenna beam such that it follows the radar pulse echo traversing the ground. This allows the use of a narrow receive beam in elevation, and therefore, the height of the receive antenna can be increased, resulting in a higher gain, which explains the higher receive power. Although advantageous, this technique has some pitfalls, which impose an upper limit on the antenna size and constrain the selection of SAR operation parameters. These limitations (which are often neglected in the system conception) are caused by the pulse extent on the ground and the way it is modulated by the receive antenna pattern. This letter addresses and quantifies the effects caused by the transmit pulse length (here denoted as pulse extension loss) through a rigorous analysis, with the purpose of introducing an important SAR performance figure. Closed expressions are derived for the simplified case of a uniform linear antenna array.

A calibration scheme for future SAR systems utilizing digital beamforming, is suggested. These systems pose new challenges for the calibration, as the increased complexity of multi-channel SAR does not allow for the extrapolation of current calibration techniques. Further, depending on the operation mode, real-time error measurement and correction is unavoidable, which requires a reconsideration to current calibration approaches. On the other hand, the digital hardware already present in multi-channel SAR systems offer new possibilities for novel calibration such as on-board error correction and digital calibration. This paper presents a calibration scheme suitable for multi-channel digital beamforming SAR.

A 60-Channels ADC (Analog to Digital Converter) board for space borne Digital Beam Forming (DBF) Synthetic Aperture Radar (SAR) applications is described. The purpose of the board is to digitize analog signals detected by a dual band SAR receiving array operating at X and Ka band. It contains 48 high speed ADCs, which sample synchronously the incoming data of the antenna front end at Ka band. Other 12 ADCs are used to sample the coming data from the X band antennas. The board is composed by an analog section, a digital section and a clock distribution network used to synchronize the ADCs. Output digital signals from the board are routed to digital boards were are processed in the Digital Beamforming Network (DBFN).

In this paper, a novel low profile aperture-shared X/Ka-band dual-polarized antenna array is proposed for spaceborne digital beamforming (DBF) synthetic aperture radar (SAR) applications. To begin with, the DBF concept and its operation mechanism for SAR system are discussed. In this work, every 2 × 2 Ka-band elements are combined as a subarray and connected to a channel while each one X-band element is connected to a channel. Then, a novel slot-antenna based on substrate-integrated-cavity (SIC) is proposed. The resonant frequency can be controlled by adjusting the length of the U-shaped slot. To share a same aperture, the X-band antenna is interlaced with the Ka-band subarray on the same plane. To verify the concept, an antenna operating at 9.6/35.75 GHz is designed, prototyped and tested. The results demonstrate good performance in terms of impedance matching, channel isolation, and cross polarization level. Such highly integrated low profile antenna can significantly reduce the potential cost of the DBF-SAR system.

Due to a high demand for global Synthetic Aperture Radar (SAR) data sets, recent spaceborne sensors reach their limits in terms of resolution, swath width and repeat cycle. In addition, fully polarimetric operation reduces the maximum swath width approximately by the factor of two. To solve SAR inherent limitations, a new generation of sensors with multiple transmit and multiple receive channels (MIMO) and digital beam-forming (DBF) capabilities is suggested. Using a quad-polarized MIMO-SAR, transmitting simultaneously orthogonal waveforms in horizontal and vertical polarizations, enables data acquisitions without any reduction of the swath width or resolution. In this paper a concept is described, which uses an advanced filtering and processing method to separate the transmitted signals in the receiver and to measure all four parameters of the scattering matrix simultaneously. Ground-based MIMO-SAR measurement results are presented, which serve as a first verification of the suggested technique with an extended, non point-like target.

The first radar was patented 110 years ago. Fast forward to today, radar applications have become ubiquitous in typical applications i.e. speed control, air traffic control, airborne and space-borne missions, military applications and remote sensing. Research for medical radar applications is also progressing well for breast cancer detection and tumor localization. Automotive radar for safety and autonomous driving are meanwhile being produced in millions per year. Despite the significant technological advancements the radar system technology unfortunately did not evolve like the communications and other related technologies for the last 20 years. With the development of high-speed electronic devices and higher demand for radar systems, the current state-of-the-art radar system concepts will undergo a revolution. They will be conceptualized and integrated in the current radar technologies leading to revolutionary radar systems. This will ultimately lead to new radar features and radar signal processing.

In this paper we propose a new hybrid technique to suppress range ambiguities in spaceborne SAR systems with multiple elevation beams. First, conventional scan-on-receive (SCORE) is performed in real-time onboard the satellite by employing a set of dispersive beams that maximize the collected signal energy for each transmitted pulse. The range ambiguities are then removed in a second step by a joint processing of the signals collected by the multiple elevation beams. The suggested two-stage approach has the advantage that a more robust range ambiguity suppression, which may involve advanced nulling techniques to account for local topography as well as satellite attitude and instrument phase errors, can be performed on ground without tremendously increasing the onboard processing demands or the data downlink volume.

Synthetic aperture radar (SAR) with multiple transmit and receive channels (MIMO-SAR) has a higher flexibility and an improved efficiency compared to a conventional SAR system with a single channel. The multiple receive channels can be used, among other things, to increase the swath width at constant azimuth resolution or to suppress spatial interferences. However, multiple transmit channels, which transmit simultaneously in the same frequency band provide currently a challenge. Therefore, in this paper a modified Chirp waveform is introduced which extends in combination with digital beam-forming (DBF) on receive the orthogonality condition to another degree of freedom, thus allowing perfect orthogonality. Furthermore, the hardware design of the MIMO-Radar Demonstrator, a multi-channel measurement system for radar and SAR applications is depicted. The shown measurement result demonstrates the possibility of obtaining all four parameters of the scattering matrix at the same time by transmitting orthogonal waveforms in different polarizations.

Interest on circular and multicircular SAR acquisitions has been increased in the past few years due to the inherent potentials they provide, e.g., full 3-D reconstruction and subwavelength resolution. However, one main limitation is the size of the spotlighted region, which is basically defined by the range ambiguities, the pulse repetition frequency (PRF), and the minimum half-power beamwidth (HPBW) in the range and azimuth directions. This paper introduces multiple-input multiple-output (MIMO) techniques in order to tackle this limitation, thereby being able to extend the applications of CSAR to much wider areas. The basic principle of the proposed solution is based on three methods, namely scan-on-receive (SCORE), multi-channel reconstruction in azimuth (MCRA) and the use of orthogonal waveforms for quad-polarized systems. The impact and dependency of the PRF, HPBW and the range ambiguities is also investigated.

Synthetic Aperture Radar (SAR) based on the Digital Beam-Forming (DBF) concept belongs to the family of Multi-Modal Radar Systems (MMRS) offering higher operational flexibility and improved performance compared to conventional radar systems using analog beam steering. DBF SAR, in particular, overcomes the fundamental limitation of classical SAR systems and can deliver high resolution and simultaneously wide swath images. The purpose of this paper is to present a laboratory prototype of such a MMRS architecture - a reconfigurable radar demonstrator based on the DBF architecture. A hardware configuration of the radar as well as advanced concepts to be experimentally verified using it are considered and discussed.

The success of current spaceborne Synthetic Aperture Radar (SAR) is boosting the performance requirements of next generation systems. In order to cope with the evolution of SAR the design of the new systems will need to meet higher requirements for spacial resolutions and higher coverage. This tendency is recognized nearly independently of the application area and manifests itself through several study programs initiated by space agencies aiming at the design of future SAR systems. A review of several ongoing studies shows that a promising candidate for the next generation SAR systems is a multi-channel radar utilizing digital beam-forming (DBF) techniques, which allows to overcome the fundamental high resolution/wide swath limitations of the conventional SAR systems. In this context the Microwaves and Radar Institute of German Aerospace Center is conducting the research and development of the innovative concepts and advanced operational modes for the future spaceborne SAR systems. The new imaging techniques and technologies have the potential to considerably enhance the imaging performance of future systems compared to the state-of-the-art SAR sensors like TerraSAR-X/TanDEM-X, Radarsat-2 or Sentinel-1. In the framework of these activities a modular reconfigurable multi-channel DBF radar demonstrator operating at multiple frequency bands was developed in the Institute. This paper describes the architecture and calibration of the system. Furthermore, the first measurement results will be presented.

This paper presents a novel tri-band (X/Ku/Ka-band) planar antenna array with dual polarizations and shared aperture. Compared with traditional dual-polarized arrays, the proposed array has advantages of low cost, low profile, and high integration. Three types of antennas resonating at different frequencies, including the perforated patch, stacked patch, and slim crosspatch, are innovatively interleaved in the same aperture. The crosspatch fed by proximity coupling is presented as Ku-band element for its advantages of compact size, high isolation, and pure polarization. The techniques such as series feed and reverse feed are utilized to implement the six feed networks in a compact size with reduced cross polarizations. Measured results agree well with the simulations, showing three operation bands at X-, Ku-, and Ka-bands with the bandwidths of 3.6%, 6.7%, and 5.3%, respectively. The antenna also exhibits excellent radiation performance with the cross-polarization discrimination over 25 dB at the three bands. To the best of the author’s knowledge, this is the first shared-aperture X/Ku/Ka-band dual-polarized antenna array reported, which is useful for potential synthetic aperture radar applications.