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The R. W. P. King Award is presented to an author under 36 years of age for the best paper published in the IEEE Transactions on Antennas and Propagation during the previous year. [ABSTRACT FROM AUTHOR]

A passive compressive device (PCD), which works at millimeter waves, is proposed in this paper. In a passive manner, the device allows to compress the signals from multiple separate channels into a single or a reduced number of channels. This permits a simplification of the transmitter or receiver chains for radar imaging applications. The PCD is a 3-D cavity that ensures each channel to be decorrelated with each other. If the transfer functions are known, the compressed signals are decompressed in postprocessing. This paper proposes a suitable method to estimate simultaneously the transfer functions of the PCD. This is validated by measurements in a multiple-input-multiple-output (MIMO) configuration to produce a complex synthetic aperture radar image. Measurements revealed that the point spread function generated by the MIMO configuration with the use of the PCD leads to almost similar results, in terms of spatial resolution and sidelobe level ratio, as those of a single-input-multiple-output configuration (uniform amplitude), with a fewer receiving elements. [ABSTRACT FROM AUTHOR]

This paper studies the concept of a new waveguide feeding technique for wideband application of an $X$ -band deployable rectangular parallel-plate slot-array antenna panel network with the vertical polarization for a synthetic aperture radar onboard a 100 kg class microsatellite. The antenna design procedure in high-frequency structure simulator followed by its fabrication and measurement results are explained. Simulations and antenna array measurement results confirmed that the corporate feeding technique achieved wide-beam antenna gain within permissible reflection limit in the desired bandwidth, thereby ensuring wideband operation. The fabricated center antenna panel achieved 35.3 dBi peak gain and 75% peak aperture efficiency, and the four-panel antenna array network achieved 40.8 dBi peak gain and 68% peak aperture efficiency in designed 300 MHz bandwidth. Although there was some mismatch in the measured reflection profile of each panel compared to the simulation results, this discrepancy was subsequently analyzed to be due to the imperfect modeling of the adhesive layer thickness and further analysis revealed that increasing the slot length of all coupling slots in the waveguide feeders by 0.2 mm can nullify this undesired effect. [ABSTRACT FROM AUTHOR]

The uniform diffraction tomographic (UDT) algorithm corrects discontinuities associated with conventional DT algorithms when applied to imaging of objects buried in layered media. The cause of the discontinuities in DT is in the implementation of the stationary phase solution for evaluating the spectral integral. The usual approach is to make a far-field approximation assuming that the depth is large. However, this is not appropriate for near-field imaging. UDT overcomes this issue by choosing the correct large asymptotic parameter in the exponent of the spectral integrand. In this paper, the original 2-D scalar UDT algorithm is extended to a fully vector 3-D solution involving the dyadic Green’s function for the layered media, the polarization of the gain pattern of the probe antenna, and the stationary phase evaluation of a 2-D spectral integral. The 3-D UDT is demonstrated to provide smoothly continuous images, and like the conventional DT, the fast Fourier transform is implemented to generate images in real time. 3-D numerical simulations and experimental results are presented to verify the accuracy and efficacy of the 3-D UDT algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a compact dual-band dual-polarized microstrip antenna array with wide bandwidth and low profile for multiple-input multiple-output (MIMO) synthetic aperture radar- imagery applications where both high resolution and portability are required. This array has a stacked structure, consisting of two shared-aperture dual-band orthogonal-polarized sub-arrays with high isolation. Each pair of driven patches for the two-band shares two parasitic patches to achieve compactness. Slits are etched on the shared parasitic patches to adjust the coupling frequency between two elements of the two bands. The defected ground structure integrated in the array effectively suppresses H-plane cross-polarization. A $4\times6$ array as an MIMO element sized of 77 mm $\times79$ mm $\times2.2$ mm has been fabricated and tested. Both wide beamwidth and stable gain are achieved, where the impedance bandwidth of 27.7%, 30.6%, 15.6%, and 23.8% in X-band vertical, X-band horizontal, Ku-band vertical, and Ku-band horizontal polarizations, respectively. [ABSTRACT FROM PUBLISHER]

This paper investigated the possibility of using an $X$ -band traveling-wave antenna for application in synthetic aperture radar (SAR) on a small-satellite platform. A rectangular slotted parallel-plate antenna panel capable of radiating dual polarization over the same physical aperture was selected for this purpose. The design procedure, which provides for an optimal antenna pattern in a SAR application, is described. A meta-heuristic multiobjective optimization algorithm was applied to synthesize an appropriate far-field pattern, which enhances the quality of the SAR image. Subsequently, the optimization results were used to build a more realistic model of the antenna panel in electromagnetic simulation software. An antenna panel was fabricated, and its electrical characteristics were measured. The fabricated prototype weighed 1310 g and measurements showed nearly 50% aperture efficiency for both circular polarizations [34.6-dBic right-hand circular polarized (RHCP), 34.5-dBic left-hand circular polarized (LHCP), and peak gain at 9.65 GHz], with low side-lobes. A beam shift of 2.1° was observed between the RHCP and LHCP beams at the design center frequency and was later analyzed to be the result of an error in the modeling of the adhesive layer. [ABSTRACT FROM PUBLISHER]

This paper presents a microwave camera design operating in the 20–30 GHz frequency range and capable of producing 3-D images at video frame rate (i.e., real-time), using synthetic aperture radar (SAR) technique. This microwave camera has the potential to provide real-time inspection and diagnosis capabilities in the nondestructive testing, biomedical and security applications, to name a few. The camera utilizes an array composed of a novel array element with built-in dual receivers at its radiating end. The dual receiver design has two significant features particularly important for SAR imaging, namely, it provides for nonuniform spatial sampling, and allows the use of antennas whose sizes are greater than half of the operating wavelength. The camera operates in the monostatic mode where each antenna in the array is used as the transmitting and receiving antenna. A major advantage of this real-time camera design is the simplicity of the microwave circuitry, which reduces the overall size, power consumption, and, cost and renders it portable. The detail design of this wideband microwave 3-D real-time camera is provided along with several images of diverse and complex targets to demonstrate its capabilities and functionality. [ABSTRACT FROM AUTHOR]

This paper presents a novel shared-aperture dual-band dual-polarized (DBDP) high-gain antenna for potential applications in synthetic aperture radars (SARs). To reduce the complexity of SAR antennae, a DBDP high-gain antenna based on the concept of Fabry–Perot resonant cavity is designed. This antenna operates in both $C$ - and $X$ -bands with a frequency ratio of 1:1.8. To form two separate resonant cavities, two frequency selective surface layers are employed, leading to high flexibility in choosing desired frequencies for each band. The beam-scanning capability of this proposed antenna is also investigated, where a beam-scanning angle range of ±15° is achieved in two orthogonal polarizations. To verify this design concept, three passive antenna prototypes were designed, fabricated, and measured. One prototype has broadside radiation patterns, while the other two prototypes have frozen beam scanned to +15°. The measured results agree well with the simulated ones, showing that the high gain, high port isolation, and low cross-polarization levels are obtained in both the bands. Compared with the conventional high-gain DBDP SAR antennae, the proposed antenna has achieved a significant reduction in the complexity, mass, size, loss, and cost of the feed network. [ABSTRACT FROM AUTHOR]

This paper numerically validates a simple formula to calculate the aperture efficiency reduction due to grating lobes in planar phased arrays. Array antennas with element spacing greater than one wavelength will produce grating lobes. Grating lobes are not a big problem in most new millimeter-wave applications, except for the fact that they reduce the aperture efficiency and thereby normally the directivity. When the element pattern is known, the simple formula can be used to calculate the aperture efficiency in the presence of grating lobes. The formula is verified by the simulations of a large uniformly excited planar slot array. The agreement is good for both broadside radiation and a phased main beam, even if we use the far field of an isolated slot. Using the far field of the embedded slot element gives almost the same results, except when a grating lobe radiates along the ground plane and the isolated element pattern is nonzero in this direction. [ABSTRACT FROM PUBLISHER]

Parallel-plate slot array antenna fed by rectangular waveguides at its lower-edge sides has been proposed. This antenna panel can be applied for dual circularly polarized deployable synthetic aperture radar (SAR) antenna onboard small satellite. As to confirm the feasibility of the antenna implementation, a development of one panel antenna system with single polarization (RHCP) has been conducted. The antenna design with simplified model by high-frequency structure simulator (HFSS) and antenna measurement results are explained in this paper. It is shown that antenna with gain and efficiency of 34.9 dBic and 54%, respectively, are achieved at the targeted center frequency (9.65 GHz). [ABSTRACT FROM PUBLISHER]

The theory of compressed sensing (CS) states that an unknown sparse signal can be accurately recovered from a limited number of measurements by solving a sparsity-constrained optimization problem. In this paper, we present a new framework of high-resolution bistatic inverse synthetic aperture radar (Bi-ISAR) imaging based on CS. A phase-preserved CS approach for high-range resolution imaging is proposed. The phase of a Bi-ISAR signal can be extracted by constructing a phase-preserved Fourier basis, which is crucial to azimuth processing of Bi-ISAR imaging. After performing CS reconstruction in range, we present an improved version of CS-based cross-range imaging by combining modified Fourier basis and weighting with CS optimization. Simulated data are used to test the robustness of the Bi-ISAR imaging framework with two-dimensional (2-D) CS method. The results show that the framework is capable of accurate reconstruction of Bi-ISAR image in both range and cross-range. [ABSTRACT FROM PUBLISHER]

This paper presents a forward approach to establish parametric scattering center models for known complex radar targets. In this approach, an automatic technique based on ray tracing and clustering is first developed to extract scattering centers directly from the computer-aided design (CAD) model of the targets. Following this, a set of forward methods is developed to determine the physically relevant parameters of two-dimension (2-D) attributed scatterers, such as type, amplitude, position and length. Finally, this approach is validated through the parametric model establishment of two complex targets and good agreement has been demonstrated between the reconstructed and actual radar characteristics. Different from the familiar inverse extraction approaches, the proposed approach provides a new forward way of constructing radar targets' feature database based on 2-D parametric scattering center model, which will ultimately facilitate the feature matching in the synthetic aperture radar (SAR) automatic target recognition (ATR) system. [ABSTRACT FROM PUBLISHER]

This paper discusses the degradation of space-borne synthetic aperture radar (SAR) imaging due to anisotropic ionospheric irregularities. In the case of the oblique incidence and anisotropy of ionospheric irregularities, two types of potential ionospheric effects on SAR imaging are derived from an improved transverse correlation function. First, in the range direction, the image shift due to both multiple scattering and dispersion of irregularities is considered. In addition, pulse broadening due to multiple scattering of the irregularities is also studied, which leads to degradation of the range resolution. Second, in the azimuthal direction, the decorrelation distance is obtained by the second moment of the generalized ambiguity function. Using the range Doppler algorithm (RDA), several degraded point target responses due to the ionospheric irregularities are evaluated. The simulation results show that the adverse effects of ionospheric irregularities on SAR imaging are worsened at lower frequencies and stronger ionospheric fluctuations. [ABSTRACT FROM PUBLISHER]