High-Efficiency Broadband Planar Array Antenna with Suspended Microstrip Slab for X-Band SAR Onboard Small Satellites

In this paper, a high efficiency broadband planar array antenna is developed at X-band for synthetic aperture radar (SAR) on small satellites. The antenna is based on a multi-layer element structure consisting of two dielectric substrates made of Taconic TLY-5 and three copper layers (i.e., the parasitic patch (top layer), the active patch (middle layer), and the ground plane (bottom layer)). The parasitic patch resides on the bottom surface of the upper TLY-5 substrate while the active patch is printed on the top surface of the lower substrate. A Rohacell foam material is sandwiched between the top layer and the middle layer to separate the two dielectric substrates in order to achieve high directivity, wideband, and to keep the antenna weight to a minimum as required by the SAR satellite application. To satisfy the required size of the antenna panel for the small SAR satellite, an asymmetric corporate feeding network (CFN) is designed to feed a 12 × 16 planar array antenna. However, it was determined that the first corporate feed junction at the center of the CFN, where higher amplitudes of the input signal are located, contributes significantly to the leaky wave emission, which degrades the radiation efficiency and increases the sidelobe level. Thus, a suspended microstrip slab, which is simply a wide and long microstrip line, is designed and positioned on the top layer directly above that feed junction to prevent the leaky waves from radiating. The experimental results of the antenna show good agreement with the simulated ones, achieving an impedance bandwidth of 12.4% from 9.01 to 10.20 GHz and a high gain above 28 dBi. The antenna efficiency estimated from the gain and directivity eclipses 51.34%.

Enhanced Pre-STAP Beamforming for Range Ambiguous Clutter Separation with Vertical FDA Radar

Medium pulse repetition frequency (MPRF) is an important mode in airborne radar system. Since MPRF mode brings both Doppler and range ambiguities, it causes difficulty for the airborne radar to suppress ground or sea clutter. In recent years, it has been pointed out that the frequency diverse array (FDA) radar is capable of separating the range ambiguous clutter, which is helpful for the airborne radar in detecting weak moving targets originally buried in ambiguous clutter. To further improve the ambiguous clutter separation performance, an enhanced pre-STAP beamforming for range ambiguous clutter suppression is proposed for the vertical FDA planar array in this paper. With consideration of range dependence of the vertical spatial frequency, a series of pre-STAP beamformers are designed using a priori knowledge of platform and radar parameters. The notches of the beamformers are aligned with the ambiguous clutter to extract echoes from desired range region while suppressing clutter from ambiguous range regions. The notches can be widened by using covariance matrix tapering technique and the proposed method can improve the performance of range ambiguous clutter separation with limited degrees-of-freedom (DOFs). Simulation examples show the effectiveness of the proposed method.

Low Cost High Gain 8×8 Planar Array Antenna for 5G Applications at 28GHz

In next-generation mobile networks, hundreds of diverse devices aim to be interconnected, posing huge challenges in capacity, coverage, efficiency, reliability, and connectivity. These and other challenges are addressed at Radio Frequency (RF) parts such as several radiating unit antennas, with very fine beamforming capabilities along with the requirements of high gains and minimized size. This work presents an 8×8 Aperture Coupled Microstrip Patch Antenna (AC-MPA) in the form of a planar array modeled for the 28GHz frequency band with high gain and compact size, making it suitable for 5G networks. The antenna is designed using a substrate with overall dimensions of 74.6×85.648×0.107mm3 and relative permittivity of ε0 = 4.3.

Very-small-aperture 3D infrasonic array for volcanic jet observation at Stromboli Volcano

Summary This study tested a very-small-aperture three-dimensional (VSA-3D) infrasonic array. A 3D array is ideal for resolving the back elevation angle (BEL), which has become important in the analysis of volcanic jet noise or geologic flows on steep mountain slopes. Although a VSA infrasonic array, with an aperture as small as a few tens of meters, has recently been shown to have a sufficient resolution of the back azimuth (BAZ) of incident signals, its BEL resolution is considered to be poor. We performed a four-element 3D array experiment with a 20-m aperture and 2-m height at the summit of Stromboli Volcano. We analyzed the direction of arrival (DOA) with the MUSIC algorithm as a function of frequency and conducted a cluster analysis for the estimated DOA–frequency functions of eruption signals. As a result, individual infrasonic signals were successfully related to eruptive vents. We also calculated the standard deviation (STD) of the DOAs in each cluster. Of the observed BAZ-STDs and BEL-STDs, 80 per cent were <2.0° and <4.6°, respectively. A comparison among the array geometries showed that the installation of a sensor above the ground, even at only 2 m, improved the BEL resolution, indicating that the VSA-3D array provides more detailed information about the wavefield than a planar array. The observed signals had higher BELs (−20° to 0°) than the vent direction (−30° to −25°) at 3–6 Hz, although signals above 20 Hz arrived from the vent direction. Our array verified that such DOA deviations were significant by the STD analysis and some tests with synthetic data. We infer that the DOA deviations do not indicate the source location and are caused by topographical diffraction.

An ultrasensitive planar array p24 Gag ELISA to detect HIV-1 in diverse biological matrixes

Human immunodeficiency virus-1 (HIV-1) persistence in the presence of antiretroviral therapy (ART) has halted the development of curative strategies. Measuring HIV persistence is complex due to the low frequency of cells containing virus in vivo. Most of the commercially available assays to date measure nucleic acid. These assays have the advantage of being highly sensitive and allow for the analysis of sequence diversity, intactness of the HIV genome or evaluation of diverse RNA species. However, these assays are limited in evaluating translational competent viral reservoirs. In here, we developed an ultrasensitive p24 ELISA that uses the Simoa planar array technology that can detect HIV-1 virions and HIV-1 infected cell with limit of detection similar to nucleic acid assays. Furthermore, the assay is optimized to measure very low levels of p24 in different biological fluids without a major loss of sensitivity or reproducibility. Our results demonstrate that the ‘homebrew’ planar p24 ELISA immunoassay is a broadly applicable new tool to evaluate HIV persistence in diverse biological fluids and cells.