The aero-optical effects of an optical seeker with a supersonic jet for hypersonic vehicles in near space were investigated by three suites of cases, in which the altitude, angle of attack, and Mach number were varied in a large range. The direct simulation Monte Carlo based on the Boltzmann equation was used for flow computations and the ray-tracing method was used to simulate beam transmission through the nonuniform flow field over the optical window. Both imaging displacement and phase deviation were proposed as evaluation parameters, and along with Strehl ratio they were used to quantitatively evaluate aero-optical effects. The results show that aero-optical effects are quite weak when the altitude is greater than 30 km, the imaging displacement is related to the incident angle of a beam, and it is minimal when the incident angle is approximately 15°. For reducing the aero-optical effects, the optimal location of an aperture should be in the middle of the optical window.

Aero-optical effects of an optical seeker with a supersonic jet for hypersonic vehicles in near space.

We investigated the influences exerted by the nonuniform aerodynamic flow field surrounding the optical window on the imaging quality degradation of an airborne optical system. The density distribution of flow fields around three typical optical windows, including a spherical window, an ellipsoidal window, and a paraboloidal window, were calculated by adopting the Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras model provided by FLUENT. The fourth-order Runge–Kutta algorithm based ray-tracing program was used to simulate the optical transmission through the aerodynamic flow field. Four kinds of imaging quality evaluation parameters were presented: wave aberration of the entrance pupil, point spread function, encircled energy, and modulation transfer function. The results show that the imaging quality of the airborne optical system was affected by the shape of the optical window and angle of attack of the aircraft.

Comprehensive analysis of imaging quality degradation of an airborne optical system for aerodynamic flow field around the optical window.

A method and system for measuring a device under test (22) are disclosed. In some embodiments, a system includes, at a central location (64) exterior to a test chamber (65), an emulator core (70) configured to introduce an impairment in each of at least one of a received signal and a transmit signal to produce a digital impaired signal, and at a remote location interior to the test chamber (65) for each of a plurality of antennas (12) in communication with a device under test (DUT) (22), at least one of a transmitter (83) configured to convert the digital impaired signal to an analog RF signal and a receiver (93) configured to convert a received analog RF signal to a received signal to be impaired by the emulator core (70) to produce the impaired signal.

Distributed system for radio frequency environment simulation

Design of one-dimensional composite photonic crystal with high infrared reflectivity and low microwave reflectivity

When a high-speed aircraft flies in the atmosphere, the imaging window is subjected to airflow friction, the kinetic energy of the airflow is converted into thermal energy, which makes the surface temperature of the imaging window rise unevenly, the imaging quality is significantly reduced, called aero-optical thermal radiation effects. The continuously increasing nonuniform thermal radiation bias field is not conducive to the precise identification of the target. To remove the bias field in degraded infrared images, this article proposes a progressive nonuniformity correction method. First, we establish a progressive thermal radiation effects correction model to estimate the thermal radiation bias field based on bilateral filtering and Bézier surface fitting. Then, to avoid overfitting the bias field, the degree of Bézier surface is reduced progressively during the iterative process. Finally, according to the properties of the heat transfer of the aero-optical thermal radiation effects, a gradient orientation prior is imposed for both the thermal radiation bias field and the latent clear image. Experiments on simulated degraded images and real degraded IR images show that our method can reduce the thermal radiation effects residual compared with the current aero-optical thermal radiation effects correction methods. 

/pdf/progressive-nonuniformity-correction-for-aero-optical-1m02cy3e.pdf

Progressive Nonuniformity Correction for Aero-Optical Thermal Radiation Images via Bilateral Filtering and Bézier Surface Fitting

We investigated the design, optimization, and evaluation method of an infrared (IR)/microwave (MW) multilayered dielectric plate type of beam combiner. The MW multilayered dielectrics design theory and IR film design theory were unified using transmission line theory. The principles in designing the initial structure of a beam combiner were presented. An objective function was presented in optimizing the beam combiner. Six evaluation indices were constructed to evaluate the performance of the beam combiner. To verify the feasibility of the proposed method an example was given. The results showed that the method could meet the joint design, optimization, and evaluation requirements of a beam combiner’s IR and MW characteristics. Finally, the design, optimization, and evaluation procedure was summarized.

IR/MW multilayered dielectric plate beam combiner design, optimization, and evaluation.

We investigated the design method of an infrared (IR)/microwave (MW) micromirror array type of beam combiner. The size of micromirror is in microscopic levels and comparable to MW wavelengths, so that the MW will not react in these dimensions, whereas the much shorter optical wavelengths will be reflected by them. Hence, the MW multilayered substrate was simplified and designed using transmission line theory. The beam combiner used an IR wavefront-division imaging technique to reflect the IR radiation image to the unit under test (UUT)’s pupil in a parallel light path. In addition, the boresight error detected by phase monopulse radar was analyzed using a moment-of method (MoM) and multilevel fast multipole method (MLFMM) acceleration technique. The boresight error introduced by the finite size of the beam combiner was less than 1°. Finally, in order to verify the wavefront-division imaging technique, a prototype of a micromirror array was fabricated, and IR images were tested. The IR images obtained by the thermal imager verified the correctness of the wavefront-division imaging technique.

Infrared/microwave (IR/MW) micromirror array beam combiner design and analysis

A radio frequency/optical semi-physical simulation composite target simulation system comprises a microwave unreflected chamber, a three-freedom-degree gesture rotating table, a radio frequency antenna array, a clamp of the radio frequency antenna array, an optical target simulator, a follow-up mechanism of the optical target simulator, a radio frequency/optical signal composite device and a simulation control platform which are connected. The system can achieve a semi-physical simulation test of microwave/optical, millimeter wave/optical combined guidance detectors so as to provide economical and reliable simulation test means of development and verification for the composite detector.

Radio frequency/optical semi-physical simulation composite target simulation system

The invention discloses a semi-physical simulation target analog system. The semi-physical simulation target analog system comprises a first point source target module, a second point source target module, a control module, an imaging target module and an optical synthesizing device. The imaging target module and the optical synthesizing device form an infrared imaging analog channel, the first point source target module and the optical synthesizing device form a wide-waveband point source analog channel, the second point source target module and the optical synthesizing device form another wide-waveband point source analog channel, and the channels can be used singly or combined arbitrarily. Therefore, analog of infrared scene images in dynamic change and analog of wide-waveband point sources can be realized, two point sources can move in a field of view in real time, and the semi-physical simulation target analog system is pretty flexible in use and meets various infrared semi-physical simulation target analog demands.

Semi-physical simulation target analog system

The invention discloses a semi-physical simulation infrared point source/imaging compound target calibration device which comprises an infrared focal plane detector, a calibration tool and an infrared imaging lens, the infrared focal plane detector and the infrared imaging lens are fixed on the calibration tool, all parts are positioned on the same axis by machining precision, the calibration device is mounted on a turntable and connected with a control computer through a cable, and a target simulator is calibrated. When a calibration method is used, the infrared focal plane detector and the infrared imaging lens are fixed on the calibration tool to form the calibration device, the calibration device is mounted on the turntable through a fixture, the turntable can rotate by 360 degrees, the calibration device is self-calibrated, a corresponding calibration method is used for calibration according to a calibrated target, the lapse state of the target simulator can be changed by calibration, precision of the target simulator is improved, errors are quantized, and corresponding theoretical basis is provided for evaluation of confidence coefficient of the compound target simulator and a whole simulation system.

Semi-physical simulation infrared point source/imaging compound target calibration device and calibration method

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