Photonics-based dual-functional system for simultaneous high-resolution radar imaging and fast frequency measurement.

A photonics-based dual-functional system is proposed that can simultaneously implement high-resolution radar imaging and fast frequency measurement. In this system, the radar is realized based on photonic frequency doubling and de-chirp receiving, and the frequency measurement is achieved by a novel frequency-to-time mapping method. In the experimental demonstration, the radar works in Ku band with a bandwidth of 6 GHz (12-18 GHz), through which inverse synthetic aperture radar imaging with a resolution as high as ∼2.6 cm×∼2.8 cm is achieved. The frequency measurement module operates in Ka band, which can achieve a measurement frequency range from 28 GHz to 37 GHz, with a measurement resolution of 40 MHz and a refresh rate of 100 kHz.

Compact optical true time delay beamformer for a 2D phased array antenna using tunable dispersive elements.

A hardware-compressive optical true time delay architecture for 2D beam steering in a planar phased array antenna is proposed using fiber-Bragg-grating-based tunable dispersive elements (TDEs). For an M×N array, the proposed system utilizes N TDEs and M wavelength-fixed optical carriers to control the time delays. Both azimuth and elevation beam steering are realized by programming the settings of the TDEs. An experiment is carried out to demonstrate the delay controlling in a 2×2 array, which is fed by a wideband pulsed signal. Radiation patterns calculated from the experimentally measured waveforms at the four antennas match well with the theoretical results.

Optical true time delay unit for multi-beamforming.

An optical true time delay (TTD) unit capable of adding independent time delays to multiple RF signals is proposed, which can be used for multi-beamforming in both transmit and receive modes. In the proposed unit, N RF signals with different center frequencies are modulated on an optical frequency comb (OFC). After transmission through a dispersive element, the RF-modulated OFC is split into N paths. In each path, a comb line is selected by a tunable optical filter. Thanks to the chromatic dispersion of the dispersive element, independently-controllable TTDs can be obtained in all paths. Then, a microwave photonic filter (MPF) is incorporated in each path, allowing a designated RF signal to undergo the TTD in that path. A proof-of-concept experiment is carried out. A two-path unit with a low-pass MPF in one path and a high-pass MPF in the other path is built. Controllable TTDs up to ~1.4 ns with a step of ~69 ps are demonstrated based on a 25-GHz-spacing OFC. In addition, a wideband multi-beam phased-array antenna system that can work in both transmit and receive modes is designed using the proposed TTD unit.

[Construction and identification of SPARC shRNA lentiviral vector and its expression in human SKM-1 cells].

AIM: To construct a lentiviral vector expressing small-hairpin RNA(shRNA) targeting SPARC gene and investigate its silenced effect on SPARC in human myelodysplastic syndromes(MDS) cell line SKM-1. METHODS: The targeting sequence of SPARC gene which can be effectively silenced in RNA interference was confirmed in our previous study. The designed and synthesized single-stranded primers were annealed to double-stranded oligo sequences and subcloned into linear pGCSIL-GFP lentiviral plasmid digested by enzyme Age I and EcoR I to produce GC-shSPARC lentiviraL vector. After being identified by PCR and sequencing, plasmids GC-shSPARC with pHelper 1.0 and pHelper 2.0 were cotransfected into 293T cells to package lentiviral particles. The recombinant lentiviral vector was transfected into human SKM-1 cells, transfection efficiency was evaluated with expression of green fluorescent protein(GFP) determined by fluorescent microscope. Expression of SPARC in SKM-1 cells was detected using RT-PCR and Western blotting. RESULTS: A recombinant lentiviral vector, GC-shSPARC, expressing shRNAs targeting SPARC gene was constructed and confirmed by DNA sequencing. The recombinant lentivirus was harvested from 293T cells with a viral titer of 1×10(9); TU/mL. GFP was observed in the 70% of SKM-1 cells after transfection. Expression of SPARC mRNA and protein was significantly reduced in the GC-shSPARC transfected group than that in the control group (P<0.05). CONCLUSION: The lentivirus RNAi vector targeting SPARC has been successfully constructed, and can effectively inhibit the expression of SPARC in SKM-1 cell line, which shed light on the foundation for researching the inhibition of SPARC siRNA target against human MDS cells proliferation, induction apoptosis and gene therapy.