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This paper proposes a 2D notch generator algorithm based on frequency-invariant (FI)-shaped beampattern synthesis for the Global Navigation Satellite System (GNSS) space–time anti-jamming blind null-steering mode. Unlike conventional blind null-steering anti-jamming algorithms based on the power inversion (PI) algorithm, the developed method treats the blind null-steering spatial filter as a 2D spatial notch filter. The beampattern synthesis method is used to solve the value of the space–time filter. With the jamming direction as prior information, constraints are applied to the flat-top (FT) and nulling (NL) regions, and FI-shaped constraints are added to the FT region to establish the objective function. NL and FI enhancement coefficients are introduced to ensure the convergence speed of the objective function and the depth of nulling. The optimization method based on the alternating direction multiplier method is employed to solve the objective function. This synthesis method is applicable to arbitrary antenna arrays. The simulation shows that compared with the PI-based algorithms, the proposed algorithm ensures undistorted reception of GNSS signals, considerably improves the receiver's signal-to-jamming-noise ratio in different jamming scenes, enhances anti-jamming ability, and achieves an improvement of better than 20 dB in multiple three-jamming scenes. [ABSTRACT FROM AUTHOR]

The analysis of radio emission of three new pulsars discovered at the Pushchino Radio Astronomy Observatory is presented. The detailed observations were carried out at a frequency of 111 MHz using the large phase array and the standard digital receiver with a total bandwidth of 2.245 MHz and a time resolution of 2.46 or 5.12 ms. All pulsars exhibit features of their radiation, the subpulse drift is observed in J0220+3622, the flare activity is exhibited in J0303+2248, and the nulling phenomenon has been detected in J0810+3725.

The occurrence of passive intermodulation (PIM) is inevitable in high-power microwave devices. It interferes with wireless communication and radar systems, resulting in severe deterioration of receiving performance. So far, narrowband PIM analyzers have been realized for different business bands. However, they are incapable of testing wideband systems. To solve this problem, rack-mounted analyzers piled with multiple narrowband analyzers were implemented. While such solutions significantly increase the volume, cost, and power consumption, they cannot provide a wide, continuous bandwidth for PIM localizations. Aiming to solve this problem, we propose a novel solution for realizing ultrawideband PIM analyzers. Based on the principle of cooperative radio frequency and baseband (RF-BB) nulling, we demonstrate an experimental prototype working within a continuous frequency band covering three octaves, exhibiting promising potential in PIM testing applications. [ABSTRACT FROM AUTHOR]

Optically-pumped magnetometers (OPMs) are highly sensitive, compact magnetic field sensors, which offer a viable alternative to cryogenic sensors (superconducting quantum interference devices – SQUIDs) for magnetoencephalography (MEG). With the promise of a wearable system that offers lifespan compliance, enables movement during scanning, and provides higher quality data, OPMs could drive a step change in MEG instrumentation. However, this potential can only be realised if background magnetic fields are appropriately controlled, via a combination of optimised passive magnetic screening (i.e. enclosing the system in layers of high-permeability materials), and electromagnetic coils to further null the remnant magnetic field. In this work, we show that even in an OPM-optimised passive shield with extremely low (

In this article, we consider the problem of beampattern synthesis with sidelobe control using constant modulus weights. We specifically focus on two applications, i.e., notching and sidelobe-level (SLL) control (SLC). The considered problem is a challenging NP-hard due to the employed constant-modulus weights. Here, we convert the problem into an intermediate form by incorporating auxiliary variables and changing the form of the constant modulus. Then, we decompose the intermediate form into subproblems of single constraint each. Finally, we propose an iterative solution following the alternate direction method of multipliers (ADMM) and Proximal frameworks. The proposed solution solves the original problem by iteratively solving the subproblems in coordinated logical order. Importantly, it combines the convergence speed of ADMM and convergence property of Proximal methods. In addition, it always satisfies the constant modulus constraint. The solution has a significant contribution to mitigate interference using notching and to realize RadCom. Simulation results show that the proposed solution has a better performance in terms of computational speed, notching, and constant SLL than the previous works. [ABSTRACT FROM AUTHOR]

Pulsar J0810+37 with a period of 1.2483 s is detected at a frequency of 111 MHz during the pulsar search at the Big Scanning Antenna (BSA) radio telescope of the Lebedev Physical Institute [1]. In this paper, we present the results of the detailed study of radio emission from J0810+37 which exhibits a rare nulling effect of different durations in a very wide time interval with an average nulling fraction in "switch-on" days 〈NF〉 = 38%; considering "switch-off" days, 〈NF〉 = 74%, since radio emission from this source is interrupted on average by 2–3 days, and then it again revives on average for 1–2 days. The "switch-off" periods reach 7 days. [ABSTRACT FROM AUTHOR]

Nowadays, software-defined radio (SDR) has become a common approach to evaluate new algorithms. However, in the field of Global Navigation Satellite System (GNSS) adaptive array anti-jamming, previous work has been limited due to the high computational power demanded by adaptive algorithms, and often lack flexibility and configurability. In this paper, the design and implementation of an SDR-based real-time testbed for GNSS adaptive array anti-jamming accelerated by a Graphics Processing Unit (GPU) are documented. This testbed highlights itself as a feature-rich and extendible platform with great flexibility and configurability, as well as high computational performance. Both Space-Time Adaptive Processing (STAP) and Space-Frequency Adaptive Processing (SFAP) are implemented with a wide range of parameters. Raw data from as many as eight antenna elements can be processed in real-time in either an adaptive nulling or beamforming mode. To fully take advantage of the parallelism resource provided by the GPU, a batched method in programming is proposed. Tests and experiments are conducted to evaluate both the computational and anti-jamming performance. This platform can be used for research and prototyping, as well as a real product in certain applications. [ABSTRACT FROM AUTHOR]

In high-contrast imaging optical systems for direct observation of planets outside our solar system, adaptive optics with an accuracy of λ/10,000 root mean square is required to reduce the speckle noise down to 1 × 10 level in addition to the nulling coronagraph which eliminate the diffracted light. We developed the speckle area nulling (SAN) method as a new dark-hole control algorithm which is capable of controlling speckle electric field in a wide area quickly, despite an extension of speckle nulling, and is robust not relying upon an optical model. We conducted a validation experiment for the SAN method with a monochromatic light and succeeded in reducing the intensity of areal speckles by 4.4 × 10. [ABSTRACT FROM AUTHOR]

We present an optimization process to improve the rejection ratio in integrated beam combiners by locking the dark fringe and then monitoring its intensity. The method proposed here uses the electro-optic effect of lithium niobate in order to lock the dark fringe and to real-time balance the photometric flux by means of a twostage Mach--Zehnder interferometer waveguide. By applying a control voltage on the output Y-junction, we are able to lock the phase and stay in the dark fringe, while an independent second voltage is applied on the firststage intensity modulator, to finely balance the photometries. We have obtained a rejection ratio of 4600 (36.6 dB) at 3.39 µm in transverse electric polarization, corresponding to 99.98% fringe contrast, and shown that the system can compensate external phase perturbations (a piston variation of 100 nm) up to around 1 kHz. We also show the preliminary results of this process on wide-band modulation, where a contrast of 38% in 3.25- to 3.65-µm spectral range is obtained. These preliminary results on wide-band need to be optimized, in particular, for reducing scattered light of the device at the Y-junction. We expect this active method to be useful in high-contrast interferometry, in particular, for astronomical spatial projects actually under study. [ABSTRACT FROM AUTHOR]

A mean variance mapping optimization algorithm for three types of antenna array synthesis examples is presented. Mean variance mapping optimization is based on the strategic transformation used for mutating the offspring built on mean variance of a certain dynamic population. The first set of examples is based on side-lobe suppression and null control by controlling element positions with mean variance mapping optimization under constraints to beam width. In the second group of examples, mean variance mapping optimization becomes an optimization tool to calculate the amplitude and phase values of antenna array elements to synthesize shaped beams. In the last set of examples, mean variance mapping optimization is used to mitigate the effect of failure elements on the pattern by recalculating the amplitude values of remaining elements. Additionally, a modification that provides a good balance between exploitation and exploration is applied to the mean variance mapping optimization algorithm to improve its stability and accuracy. The simulation results showed that the proposed mean variance mapping optimization is an effective and easy implementable technique for different antenna array synthesis problems. [ABSTRACT FROM AUTHOR]

A nulling interferometer was proposed to achieve direct detection of extra-solar planets (exoplanets) by suppressing light from the central star using a pair of telescopes. Recently, the stellar coronagraph method has shown rapid progress, which uses an extended concept of the nulling interferometer within single telescope optics. A dynamic range larger than 1 × 10 9 for the detection of Earth-like exoplanets can be attained by reducing diffraction patterns using the nulling coronagraph, and by suppressing speckle noise using an adaptive optics with an accuracy of λ/10000 rms. An unbalanced nulling interferometer (UNI), which is used as fore-optics, improves the wavefront sensing sensitivity and compensation level of the adaptive optics by a factor of 10. Consequently, the dynamic range of the coronagraph can also be improved by two orders of magnitude. The UNI is composed of a modified coronagraph or a traditional interferometer and magnifies the aberrations of incoming wavefronts. [ABSTRACT FROM AUTHOR]

The design and nulling capability of a compact 2 \times 2 dual-band coupled double loop (CDL) GPS antenna array loaded with broadside coupled split ring resonators (BC-SRR) are presented. The high level of L2 band mutual coupling is reduced by utilizing \mu-negative (MNG) BC-SRR metamaterial within the array volume. This metamaterial loading is possible due to the small L2 band electrical size (\lambda0/8.5\times\lambda0/8.5) of the CDL antenna elements. Different than the existing work on coupling reduction of linearly polarized antenna arrays, mutual coupling mechanism within the circularly polarized GPS array is considered and MNG metamaterials are shown to reduce the mutual coupling if they are placed between the antennas in a particular alignment. Specifically, a 2 \times 2 array with \lambda0/3.7 inter-element spacing is designed to be loaded with BC-SRRs and experimentally verified to exhibit a 10 dB L2 band mutual coupling reduction. Through simulations and experiments, it is also demonstrated that the reduction in L2 band mutual coupling improves the L2 band array nulling capability in terms of accuracy and null depth without affecting the already well-behaved L1 band performance. The presented array has an overall footprint size of 4.3^\prime\prime\times 4.3^\prime\prime and can be potentially miniaturized further for different inter-element spacing. [ABSTRACT FROM PUBLISHER]

Abstract: Kirschmann’s Fourth Law states that the magnitude of simultaneous color contrast increases with the saturation of the inducing surround, but that the rate of increase reduces as saturation increases. Others since Kirschmann have agreed and disagreed. Here we show that the form of the relationship between simultaneous color contrast and inducer saturation depends on the method of measurement. Functions were measured by four methods: (i) asymmetric matching with a black surround, (ii) asymmetric matching with a surround metameric to equal energy white, (iii) dichoptic matching, and (iv) nulling an induced sinusoidal modulation. Results from the asymmetric matching conditions agreed with Kirschmann, whereas results from nulling and from dichoptic matching showed a more linear increase in simultaneous contrast with the saturation of the inducer. We conclude that the method certainly affects the conclusions reached, and that there may not be any “fair” way of measuring simultaneous contrast. [Copyright &y& Elsevier]

In order to detect directly faint planets around other stars it is important to develop techniques to cancel the central starlight. We report progress in terms of null depth on the visible nulling experiments at JPL, essential for NASAs future space missions as well as for an upcoming sounding rocket based experiment. A level of 1 Million to 1 nulling ratio (1e-6 rejection ratio) has been obtained for the first time for visible laser light, and a level of 100000 to 1 nulling ratio has been obtained for a relatively large (5%) bandpass at 650nm. Using a combination of a fiber array and deformable mirror a null of 1e-6 would correspond to a contrast of 1e-9 at a distance of 2-3$\lambda$ in the airy disk plane, only 10x away from TPFs goal. The configuration used was a fiber fed Mach Zender type interferometer, using 2 or 3 mirrors in each two arm, placed in an enclosed air container. For broadband light we used tilted dispersion glass plates in the nuller arms and an avalanche photon diode module to cover the large dynamic range. We describe a variety of conditions that have to be met and optimized to reach very deep nulls and sub-nanometer optical path difference stability, such as optical alignment, symmetry in the two arms, mechanical stability and vibration isolation. [ABSTRACT FROM PUBLISHER]

The Planet Detection Testbed is designed to simulate the architecture and operation of a space-borne four-telescope nulling interferometer. Constructed in the form of a dual chopped Bracewell interferometer together with star and planet sources, it reproduces the principal features of the flight beam combiner designed at JPL for the proposed TPF-I Formation Flying Interferometer. The aims of the testbed are to demonstrate stable four-beam nulling and planet detection at representative star-planet contrast ratios. In the flight design, starlight between 7 and 17 micron wavelength is to be nulled, and 2 to 3 micron starlight is used for fringe tracking and phasing the interferometer. There are also metrology systems and alignment systems which are required for deep and stable nulling. The testbed reproduces these features; 2 to 3 micron light from a thermal source is used for fringe tracking, and nulling and planet detection is performed at 10 microns. The testbed also incorporates laser metrology and other systems enabling continuous control of beam alignment. The ultimate goal is to simulate planet detection at star-planet contrast ratios of order $10^{-7}$ during full rotations of the telescope array using the phase chopping method. The latest results from the testbed are presented including four-beam nulling experiments at null depths of $10^{-5}$ and planet signal detections at similar contrast ratios. [ABSTRACT FROM PUBLISHER]

The Darwin and TPF-I missions are Infrared free flying interferometer missions based on nulling interferometry. Their main objective is to detect and characterize other Earth-like planets, analyze the composition of their atmospheres and their capability to sustain life, as we know it. Darwin and TPF-I are currently in study phase. A number of mission architectures of 3 and 4 free flying telescopes are evaluated on the basis of the interferometer's response, ability to distinguish multiple planet signatures and starlight rejection capabilities. The characteristics of the new configurations are compared also to the former, more complex Bowtie baseline architectures as well as evaluated on base of their science capability. [ABSTRACT FROM PUBLISHER]

Nulling interferometry is one of the promising techniques for the study of extra terrestrial planets. This technique will be applied in the future space missions Darwin and TPF-I, and from the ground with GENIE. The nulling interferometry techniques require high symmetry of the interfering beams, to obtain the required contrast (typically $10^6$ to detect terrestrial exo-planets in the thermal infrared). In this paper we consider the polarization symmetry issue, such as polarization rotation and polarization phase shifts occurring on slightly misaligned optics. We study the consequences of these symmetry requirements on a nulling interferometer design. We find the relation between the misalignment tolerances and the achievable nulling, and we show that this tolerance is highly dependent on the interferometer configuration (the way beams turn right, left, up or down in the interferometer arms). It is typically of the order of the arcminute (not the arcsecond) for a $10^6$ contrast. We present a analytical and numerical analyses. [ABSTRACT FROM PUBLISHER]

The direct detection of a planet close to its parent star is challenging because the signal detected from the parent star is between 109 and 106 times brighter than the signal of a planet in the visual and IR, respectively. Future space based missions like DARWIN and TPF concentrate on the wavelength range between 6 and 18 μm, a region that contain the CO2, H2O, O3 spectral features of the atmosphere. The presence or absence of these spectral features would indicate similarities or differences with the atmosphere of terrestrial planets. The concepts for space nulling interferometers and the influence of different schemes of beam combination on the detected signal are investigated. Based on the background contribution to the detected signal, the wavelength range where the detection sensitivity should be maximised is identified. The use of integrated optics to combine the spectral channels is discussed. The resulting transmission maps are evaluated on base of the symmetry, rejection values, null depth and applications for extra-solar planet search. [Copyright &y& Elsevier]

A new method based on the differential evolution (DE) algorithm is proposed for antenna-array pattern synthesis with prescribed nulls. The array excitation amplitudes are the only controlling parameters, and the objectives are to synthesize array patterns with nulls imposed on directions of interferences while keeping the sidelobe levels (SLLs) below prescribed levels. Many factors such as the excitation dynamic range ratio, null depth level, null width, and SLLs are taken into account in the synthesis. Simulation results of several typical problems are compared with published results to illustrate the effectiveness of the proposed method. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 57–63, 2004. [ABSTRACT FROM AUTHOR]

A new and flexible method is presented that is based on the ant colony optimization algorithm for the pattern synthesis of linear antenna arrays with the prescribed nulls. Nulling of the pattern is achieved by controlling only the amplitude of each array element. To show the versatility of the present method, some design specifications such as the side lobe level, null depth, and dynamic range ratio are considered by introducing a set of weighting factors in the cost function constructed for the ant colony optimization algorithm. Several illustrative examples of Chebyshev patterns with the imposed single, multiple, and broad nulls are given. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 375–383, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce10034 [ABSTRACT FROM AUTHOR]

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• OPMs offer a step change for MEG, but rely on controlled magnetic field environments. • Here, optical tracking is combined with magnetometer data to create precision field maps. • Field maps are used to inform optimal currents in magnetic field cancellation coils. • The remnant static magnetic field experienced by the OPMs is reduced to 0.29 nT. • Motion artefact in OPM-MEG data is reduced by a factor of 5 via field nulling. Optically-pumped magnetometers (OPMs) are highly sensitive, compact magnetic field sensors, which offer a viable alternative to cryogenic sensors (superconducting quantum interference devices – SQUIDs) for magnetoencephalography (MEG). With the promise of a wearable system that offers lifespan compliance, enables movement during scanning, and provides higher quality data, OPMs could drive a step change in MEG instrumentation. However, this potential can only be realised if background magnetic fields are appropriately controlled, via a combination of optimised passive magnetic screening (i.e. enclosing the system in layers of high-permeability materials), and electromagnetic coils to further null the remnant magnetic field. In this work, we show that even in an OPM-optimised passive shield with extremely low (<2 nT) remnant magnetic field, head movement generates significant artefacts in MEG data that manifest as low-frequency interference. To counter this effect we introduce a magnetic field mapping technique, in which the participant moves their head to sample the background magnetic field using a wearable sensor array; resulting data are compared to a model to derive coefficients representing three uniform magnetic field components and five magnetic field gradient components inside the passive shield. We show that this technique accurately reconstructs the magnitude of known magnetic fields. Moreover, by feeding the obtained coefficients into a bi-planar electromagnetic coil system, we were able to reduce the uniform magnetic field experienced by the array from a magnitude of 1.3 ± 0.3 nT to 0.29 ± 0.07 nT. Most importantly, we show that this field compensation generates a five-fold reduction in motion artefact at 0‒2 Hz, in a visual steady-state evoked response experiment using 6 Hz stimulation. We suggest that this technique could be used in future OPM-MEG experiments to improve the quality of data, especially in paradigms seeking to measure low-frequency oscillations, or in experiments where head movement is encouraged. [ABSTRACT FROM AUTHOR]