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In this letter, we explore the concept of group sparse representation (GSR) to exploit the intrinsic structure of synthetic aperture radar (SAR) image. Noting that dictionary design is a crucial factor in GSR performance, we propose an over-complete dictionary to better fit the SAR image despeckling problem. This over-complete dictionary consists of the prespecified dictionaries and learned dictionary. Different kinds of dictionaries emulate the image from different angles. In this way, we can simultaneously obtain better performance on speckle noise suppression and image detail preservation. The experimental results on real SAR images demonstrate that the proposed over-complete dictionary based on GSR can achieve more effective speckle reduction as well as image detail preservation.

In this paper, we present an algorithm for curvilinear Video-SAR (CViSAR) persistent imaging with distortion correction. Firstly, we derived the mapping between the actual and reconstructed location of any target in any frame image formed by curvilinear persistent polar format algorithm, named as curvilinear persistent mapping (CPM). Then, through a combination of the non-uniform input wavenumber spectrum with the non-uniform output imaging grids calculated by CPM, distortion-free frame images can be formed directly via a single non-uniform fast Fourier transform of type 3 (NuFFT-3). Simulation experiments are provided to demonstrate the effectiveness of the proposed algorithm.

A broadband and high-gain slot antenna array operating in the Ku-band is reported in this study. The antenna is with waveguide-fed cavity backed configuration and made entirely via simple milling process. The overall antenna structure consists of four layers. The bottom layer is a waveguide feed network to provide corporate power division. In turn, the waveguide feed network is excited by a conventional coaxial probe from the back. The waveguide network couples energy to an array of cavity via an aperture plate. These constitute the middle two layers. Each cavity then excites a subarray of 2 × 2 radiating slots in the top layer. The radiating slot elements and the feed network are designed to achieve wide bandwidth and high-gain performance. Finally, an 8 × 8 array antenna has been designed and fabricated with about 25 dBi gain over 14.8% bandwidth, and the cross-polarisation was around -30 dB in the boresight.

Bandpass filters with surface acoustic wave (SAW)-filter-like selectivity and much wider bandwidth compared to conventional SAW filters are presented. The proposed topology consists of SAW resonator networks and parallel coupled lines. Each ladder type resonator network has a series resonator and two shunt resonators to define the upper and lower cutoff frequencies and realize the sharp passband selectivity. Analysis of the proposed SAW resonator network and a comparison with a traditional ladder type SAW filter is provided. Two filters are designed, fabricated, and measured using chip SAW resonators and microstrip coupled lines on Rogers RO4003C. As the available SAW resonators are discrete, they are connected together using 1-mil bond wires to form the SAW resonator network. The resonators are also wire bonded to the coupled lines and ground patch. The bandwidth of the two filters is 10.5% and 17%, respectively, which is much wider than conventional SAW filters with a bandwidth of a few percent. An analysis is provided for the bulk wave effects, ripples due to finite transducer, gratings of resonators, and second-order effects from series and parallel resonators, which cause deterioration of the passband performance. The impact of bond wire inductance and parasitic coupling, which cause spurious responses at the stopbands, are also discussed.

Inspired by the idea of multiantenna interferometric processing in interferometric inverse synthetic aperture radar, based on monostatic low-resolution narrowband radar with three antennas, a three-dimensional (3-D) interferometric imaging and micromotion feature extraction method for spinning space debris is proposed. First, the micromotion characteristic of the target in low-resolution radar is explained. Next, by taking advantage of the target’s micro-Doppler characteristic on time-frequency (TF) domain, the time-varying two-dimensional imaging of scatterers in both the normal mode and the squint mode is achieved through interferometric processing. Finally, the height information of scatterers is solved by an ellipse fitting-based method; thus 3-D imaging for the spinning space debris is realized. Meanwhile, some 3-D micromotion features are exactly extracted during imaging, and the relevant issues, including window width determination of TF analysis, scatterer separation, and noise suppression are discussed in detail. Simulation results in diverse occasions validate the effectiveness and the robustness of the method.

The Direct Metal Laser Sintering (DMLS) 3-D printing technique is used to fabricate a relatively large 8×8 wideband waveguide array with an integrated corporate-fed network. This DMLS rapid prototyping technique offers the flexibility to fabricate complicated waveguide-based structures with good reliability and high-precision. Experimental results show antenna efficiency is higher than 80% over a wide operation bandwidth and even exceeding 90% at most frequencies. This work demonstrates the 3-D DMLS technique is a promising manufacturing method for the fabrication of complex waveguide antenna arrays.

The aim of this paper was to investigate a hybrid technology that combined striplines and E-plane metallic waveguides for the application of dual-polarized array in Ku-Band. The array was a sandwich structure consisting of multiple metal and substrate layers. The stripline circuits coupled the input power from the E-plane waveguide to form a hybrid structure, which was used to feed the radiators directly to obtain high gain. Here, the design of an efficient waveguide-to-stripline structure was a key issue to the whole feeding network as it was used as main feed line to construct a 4×4 Ku-Band dual-polarization array with circular radiators. Design details of the array and structural realization are given. Result data shows a good agreement between simulation and measurement, which reveals the hybrid structure is a promising technique for wideband and high-gain dual-polarized array application.

A mirror-symmetric hybrid feeding network is proposed in this paper for the design of a dual-polarization high-gain array antenna in Ku-band. The hybrid structure consists of E-plane waveguides and series-feed stripline circuits. Input power is coupled from a simple E-plane waveguide to all stripline branches, which are used to excite the circular waveguide radiators individually. However, for the sake of avoiding long line effect from the series-feed circuits in large array, key issue of equal-phase distribution among radiators should be solved efficiently. Two 8×4 stripline sub-networks are placed in a mirror-symmetric position. Such arrangement could introduce another 180 degree phase difference to compensate the antiphase caused by E-plane T-junction waveguide power divider in the design. In turn, all the radiators could be fed in equal-phase. The hybrid feeding network has been realized on an 8×8 array. Design details of the feeding network and array structure are given. The mirror-symmetric hybrid structure can be considered as a good candidate for dual-polarized large array application.

We theoretically and experimentally demonstrate the focusing of macroscopic 3D darkness surrounded by all light in free space. The object staying in the darkness is similar to staying in an empty light capsule because light just bypasses it by resorting to destructive interference. Its functionality of controlling the direction of energy flux of light macroscopically is fascinating, similar in some sense to the transformation-based cloaking effect. Binary-optical system exhibiting anti-resolution (AR) is designed and fabricated, by which electromagnetic energy flux avoids and bends smoothly around a nearly perfect darkness region. AR remains an unexplored topic hitherto, in contrast to the super-resolution for realizing high spatial resolution. This novel scheme replies on smearing out the PSF and thus poses less stringent limitations upon the object's size and position since the created dark (zero-field) area reach 8 orders of magnitude larger than the square of wavelength in size. It functions very well at arbitrarily polarized beams in three dimensions, which is also frequency-scalable in the whole electromagnetic spectrum., 11 pages, 5 figures

A wideband bandpass filter (BPF) using two cascaded sections, each consisting of a SAW-like resonator and one or two transmission lines, is proposed. The lower and higher transitions of the passband are separately defined by the SAW-like resonators. The roll-off at the band edges can be controlled by properly designing the SAW-like resonators to achieve a highly selective passband. As an example, a prototype BPF centered at 0.42 GHz is implemented on PCB, in which the SAW-like resonators are realized by lumped elements. The measured filter has a 3-dB bandwidth of 47% and high passband selectivity is observed. To obtain a wideband rejection, one transmission line in the filter is loaded with an open stub and a low pass filter is added. Experimental results show good high out-of-band rejection up to more than 20 GHz.

A Ka-band lumped element Dual-Behavior Resonator (DBR) filter in 0.13-μm CMOS is presented. The DBR filter consists of Dual-Behavior Resonators (DBRs) and inverters connecting the DBRs. The inverters and the DBRs, which define the stopband transmission zeros, are realized by CMOS spriral inductors and metal-insulator-metal (MIM) capacitors. A second order DBR filter with two transmission zeros is designed and fabricated in standard 0.13-μm CMOS technology. The measured filter has a 3-dB bandwidth of 15% at the center frequency of 27.8 GHz. High rejections larger than 48 dB are realized at the two transmission zero frequencies of 20.2 GHz and 37 GHz.

The chirp scaling algorithm (CSA) is considered as an efficient SAR imaging algorithm. The existence of the range-uncompressed chirp is the necessary condition for CSA to be used. However, if the range chirp is large in the high squint angle case, there will be a strong coupling between the range chirp and azimuth frequency. This coupling will render the relationship between range curvature and Doppler frequency non-linear and hence make the CSA lose its precision in such a case. An analysis about this coupling effect and a compensating method are given in this paper. Computer simulation has confirmed the coupling effect. A possible solution to this problem is also mentioned.

Synthetic aperture radar (SAR) systems are increasingly demanding for real real-time performance. As part of an effort to develop a real-time range-Doppler digital SAR processor to produce image maps of the scanned area immediately as raw data are collected, this paper describes the conceptual architecture design for a high-speed front-end video pre-filtering. The evolved architecture consists of richly interconnected planes of novelly-adapted Modified Transverse FIR parallel tapped delay elements. Both the range and azimuth prefilterings are performed simultaneously in a continuous input-output flow without the need to worry about corner turning caused by azimuth preprocessing on data samples that are collected in the range direction.

A multifractal spectrum, which gives a complete statistical description of images, can be used to characterize radar images. In this paper, a new method based on multifractal analysis is proposed to segment the SAR image into regions and to highlight their boundaries. A computation experiment shows that the segmentation result is encouraging.

This paper proposes a modification to the eigen-image classifier approach to Automatic Target Recognition (ATR), which improves classification performance in the case where intra-class variation is large.

形態: カラー図版あり, 形態: DVD-ROM1枚, Physical characteristics: Original contains color illustrations, Note: One DVD-ROM, 資料番号: AA0065135120, レポート番号: JAXA-SP-11-007E

The phase-gradient autofocus (PGA) technique is robust over a wide range of imagery and phase error functions but the convergence usually requires 4-6 iterations. The authors propose to speed up the estimation convergence by selectively increasing the pool of quality synchronisation sources and not to be limited by the range pixels of the SAR map. This is highly probable since each range bin contains more than 1 prominent scatterers across the integration aperture. It is also highly probable that the least brightest selected scatterer in a range gate may turn out to be of higher energy as compared to the maximum brightest scatterer of another gate. With appropriate target filtering to finally select the quality scatterers out of the large pool and higher-order phase error measurement tool, the new algorithm achieves near convergence quality without iteration. The authors named this solution the Quality PGA algorithm (QPGA).