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Steering vector and covariance matrix estimation mismatch along with moving jammer/platform, can affect the performance of null-steering beamformer. In this paper, by utilizing null-widening, null-deepening and diagonal loading shrinkage in space–time adaptive processing (STAP) structure, two methods for nullifying GNSS (global navigation satellite system) jamming/interference in cruise moving platforms are introduced. The enhanced performance of the proposed methods is investigated through numerical simulations. The results indicate improvement in the number of acquired GNSS satellites, in heavy jamming (GNSS denied) scenario, by reconstructing and acquiring at least 87% of satellites.

This letter proposes a machine learning inversion scheme for P-band polarimetric interferometric synthetic aperture radar (Pol-InSAR), which can achieve the single-baseline random volume over ground (RVoG) model inversion without the assumption of the null ground-to-volume ratio. First, the potential variables--including the incidence angle and the PDHigh coherence acquired with phase diversity optimization--that are related to the forest vertical structure are analyzed for their correlations with the extinction coefficient in the RVoG model. Then, the machine learning approach is applied to forecast the extinction coefficient characterized by those potential variables. Ultimately, in the case of fixing the extinction coefficient, the forest height is estimated by a geometric process on the complex plane. The actual Pol-InSAR data verification illustrates that the inversion performance of the proposed scheme overmatches that of the traditional schemes.

A high selectivity and high efficiency filtering antenna is presented in this paper. A double-layer filtering patch antenna is first proposed, which can generate a radiation null due to the mixed electric and magnetic coupling between the two patches. By changing the length of the slot line on the patch, the position of the radiation null can be flexibly set at the lower band edge or upper band edge. Based on this mechanism, a three-layer patch antenna with two radiation nulls is designed. Two radiation nulls are introduced on both sides of the passband, consequently, a quasi-elliptic bandpass response can be obtained. Moreover, the proposed antenna features high efficiency since no extra filtering circuit is utilized. A prototype antenna operating at 1 GHz is designed, fabricated, and measured for validity verification. The measured results agree well with the simulated one, showing that the prototype antenna has a fractional impedance bandwidth of 16% (0.91-1.07 GHz), a flat passband gain response with peak value of 8.83 dBi, a high efficiency about -0.41 dB in the passband. The band-edge selectivity is highly improved by the radiation nulls near the passband edge.

A dual-band multi-mode high gain stacked-patch antenna based on substrate integrated suspended line (SISL) is proposed for 5G applications. The proposed antenna comprises five low-cost FR4 dielectric substrate layers and ten metal layers with embedded air cavities. The driven patch generates TM10 mode and TM02 mode, and the other two modes are generated by etching the U-slot and horizontal slot on the driven patch to achieve dual-band. The stacked patch with the U-slot can suppress the radiation pattern split of TM02 mode, improve the antenna gain in the high-frequency band and generate radiation null to increase the out-of-band gain-suppression level. To verify this principle, the antenna is fabricated and measured. The measured results show good agreement with the simulated ones and the proposed antenna operates at 3.21-3.66 GHz and 4.75-5.40 GHz, which can cover the 5G communication band. The antenna has high efficiency. The maximum gains in the two bands are 9.12 dBi and 8.65 dBi, respectively.

A novel design concept to reshape radiated fields of a slot antenna for improved bandwidth and stable radiation pattern is proposed. Initially, the radiated fields of the traditional slot antenna are theoretically studied using characteristic modes (CMs). The results demonstrate that its CM1, CM2, and CM3 are resonated of around 2.39, 4.78, and 7.17 GHz, respectively. For CM1 and CM3, both of them maintain the bidirectional radiation patterns. Whereas, the CM2 generates a radiation null in the broadside direction. Then, in order to utilize the nearby CM1 and CM2 for wide-bandwidth, the linear slot is properly folded so as to transform the non-bidirectional pattern of CM2 into the bidirectional one. After that, the narrow slot is reformed as the stepped scheme, thus reallocating these dual modes in proximity to each other. With these arrangements, the impedance bandwidth of the antenna is dramatically widened with two attenuation poles, while keeping a compact size and stable radiation pattern. Finally, the proposed antenna is fabricated and tested. Measured results show that the antenna without any extra feeding network has gained a wide-bandwidth (|S11

A grating lobe suppression approach based on the null scanning antenna (NSA) for a sparse phased array is proposed. The NSA provides continuous null scanning and beam steering on two orthogonal planes, by connecting four varactor loaded impedance reconfigurable circuits to the four edges of a square patch antenna, respectively. The NSA is introduced into a sparse phased array and the grating lobe is suppressed by keeping the radiation pattern null of NSA pointing at the angle of grating lobe during beam scanning. Meanwhile, the beam direction of NSA is steered to wider angle with the variation of null angle. The main lobes during beam scanning are located within the 3-dB beamwidth of NSA. Thus, the side lobe level (SLL) and scan loss over wide scanning region are improved considerably. A 2×4 sparse phased array with NSA is designed and measured for verification. Both simulated and measured results indicate that the SLL of the sparse phased array with NSA can be suppressed below -9.3 dB within the scan range from -76° to 75°. The maximum realized gain during beam scanning is 17 dBi, with an aperture efficiency of 69.86% and a maximum gain fluctuation of 4.4 dB.

Two planar quasi-isotropic antennas are presented in this letter, and the filtering response is implemented on the second antenna. Firstly, a printed shorted patch which can be equivalent to a magnetic dipole is utilized with a fan-shaped monopole serving as an electric dipole to achieve quasi-isotropic radiation. A lumped capacitor, a pair of near-field parasitic elements (NFPEs) and a slot are introduced to improve the roundness. Ultimately, the gain deviation is reduced to 3.5 dB. Further, a half mode substrate integrated waveguide (HMSIW) is applied to achieve the magnetic dipole for the second antenna. The filtering response is obtained by introducing a uniform impedance resonator (UIR). A radiation null is obtained above the operating band, while a quasi-isotropic radiation is achieved in band with a gain deviation of 7.3 dB.

A 3.4–3.7 GHz dielectric rod waveguide probe for near-field measurements is proposed for applications on the 5G sub-6 GHz band. By implementing a dielectric filled waveguide, the probe achieved a higher resolution and low scattering characteristics through a miniaturized aperture compared to the open-ended waveguide (OEWG) used for conventional near-field probes. An 8 × 8 pixelated grid structure in the dielectric launcher section of the probe is implemented to further reduce the scattering characteristics of the probe. The proposed probe is fabricated and experimentally verified. A coating of silver is applied to the dielectric during a production process. Measurement shows that the –10 dB reflection coefficient bandwidth meets 3.4–3.7 GHz requirement and that the radiation pattern shows a broadside gain of about 3.8 dBi with no null at the forward hemisphere. The results of a scattering characteristic experiment indicate decreased interferer level of 7.3 dB compared to an OEWG.

This paper presents a wide-band high-gain filtering antenna for 5G applications based on substrate integrated suspended line (SISL) platform. The filtering antenna mainly consists of a driven patch, a stacked patch, and a rectangular loop. By adding a rectangular loop to the conventional patch antenna, an additional resonance can be excited. Meanwhile, the frequency selectivity of the lower band is obtained due to the formation of a radiation null. Then, a patch is stacked on the driven patch, which also generates an extra resonance mode and a radiation null at the upper band-edge. Therefore, a bandpass filtering function is realized and the bandwidth is greatly improved with three resonance frequency points. The fractional bandwidth is from 4.28 to 5.34 GHz (22.04%), covering the specific 5G n79-band (4.45.0 GHz). Besides, the height of the antenna is only 0.080 (0 is the wavelength in free space of the central operating frequency), and the peak gain of the antenna is 10.4 dBi. It is worth mentioning that the whole design is low-cost since it is based on full FR4 substrates.

A stacked-coil technology is demonstrated that realizes size-adjustable coil systems to compensate the notorious problem of lateral misalignment in nonradiative wireless power transfer (WPT) systems. The proposed system has a simple structure that consists of multiple layers of coils with various sizes. Depending on the misalignment, the coil pair that provides the best transfer efficiency is switched on . Thus, not only the transfer null is removed, but also a very high transfer efficiency is maintained even with extreme misalignment. Experimental results at 6.78 MHz show the effectiveness of the stacked coil for both short- and mid-range wireless power transfer systems. The transfer efficiency maintains abovementioned 80% up to 87% and 65% lateral misalignment when the separation between Tx and Rx coils are 10% and 50%, respectively, relative to the largest dimension of the coil. The three-layer short-range system successfully removes the transfer null to maintain a minimum transfer efficiency of 39.7% up to 126% misalignment. The two-layer mid-range system maintains transfer efficiency abovementioned 50% up to 103% misalignment. Furthermore, the performance is virtually the same even in an asymmetric WPT system, i.e., when the technique is applied to only one of the two coils. A detailed design procedure is also provided.

The high-pressure electro-pneumatic servo valve (HESV) is a core element of the high-pressure pneumatic servo system. The annular clearance and the rounded corner of the spool-sleeve can cause the leakage at null position, thereby affecting high-precision control and stability of the servo system. This paper investigates the effects of the clearance structure on leakage behavior at null position of the HESV. A numerical approach was employed to evaluate the effects, and then a mathematical model was established to obtain the variation law of leakage flow rate at null position. The results indicate that the leakage flow rate at null position varies linearly with supply pressure and rounded corner radius, and is nonlinear as a quadratic concave function with annular clearance. The leakage flow rate of the annular clearance and the rounded corner varies with the valve opening in an invariable-nonlinear-linear trend. A test rig system of leakage behavior at null position of the HESV was built to confirm the validity of the numerical model, which agrees well with the conducted experimental study.

DQE and eDQE were evaluated for a slot scan X-ray system using four standard radiation qualities: RQA3, RQA5, RQA7, and RQA9. The results showed that the system under consideration, KARS-BKS2 fluorograph, provided maximal DQE(u,v) and eDQE(u′,v′) in the case of radiation quality RQA5 and a small focal point. At null spatial frequencies DQE(0) was greater than 40% and eDQE(0) was 35%.

A wideband single-layer substrate integrated waveguide (SIW) filtering slot antenna with compact structure is investigated, which is originated from a SIW resonant cavity operating at its TE110 mode. A straight radiating slot is integrated on the top surface of the cavity. The resonator can be splitted into two half-mode resonators, generating a radiation null at higher edge of the passband. At same time, two U-shaped slots are etched on the bottom surface of the cavity. One of the U-shaped slots is used to introduce a radiation null at the left edge of the passband while the other U-shaped slot introduces the modified half-TE110 mode in the right half cavity, broadening the bandwidth of the antenna. Finally, the third-order filtering antenna is obtained with 11.84% impedance bandwidth in only one SIW resonant cavity. To validate design, a prototype is fabricated and measured. Compared with other designs, the proposed antenna owns features of simple structure, wide bandwidth, and compact size, satisfying the increasing requirement for the miniaturization and integration of RF devices.

A tapered continuous-element leaky-wave antenna is presented, which has the merits of suppressed higher order harmonics and reduced sidelobe level (SLL). Two important design strategies are utilized for assuring good radiation pattern purity. First, the phase difference between the main radiating edge in each unit cell is disturbed to avoid higher order mode superpositioning in-phase. Second, an extra element with a relatively large phase constant is introduced for canceling the field of the first sidelobe location. The measurement results show a continuous scanning beam with an equalized gain is achieved at the frequency band of 5.6–8.8 GHz, the corresponding normalized SLL is decreased to about –20 dB and the radiation of HOH in the high frequencies is null at the backward direction.

This paper presents a novel technique based on Hybrid Spatial Distance Reduction Algorithm (HSDRA), to compensate the effects of deformity and mutual coupling occurred due to surface change in conformal arrays. This antenna surface deformation shifts the position of null points and loss of the main beam resulting in reduced antenna gain along with substantial undesirable effects on the antenna performance. The proposed algorithm, which cumulatively incorporates the Linearly Constraint Least Square Optimization (LCLSO) and Quadratically Constraint Least Square Optimization (QCLSO) techniques, is formulated to minimize/reduce the absolute distance between the actual (simulated/measured) radiation pattern and the desired radiation pattern while keeping the direction of main beam and nulls position under control. In particular, a 4x4 conformal microstrip phased array from planar surface is deformed to prescribe spherical-shape surface with various radii of curvature, is validated. For the enhancement of Gain of the conformal array antenna, Gain Maximization Algorithm is also proposed, the simulated results of which is compared to the traditional Phase compensation technique and unconstraint least squares optimization. The analytical results for both planar and spherical deformed configurations are first evaluated in MATLAB and then validated through Computer Simulation Technology (CST).

This article presents the design and fabrication of a monopulse radial line slot array (RLSA) antenna excited with a circular cavity connected to a modified Butler matrix at 94 GHz. The antenna consists of two pieces: the RLSA antenna implemented over a low loss dielectric substrate and a 3-D-printed Butler matrix based on gap waveguide. The interface between both parts is a circular cavity that couples two different modes into the RLSA through a coupling slot in the dielectric substrate. The coupled mode depends on the input excitation of the Butler matrix for the generation of simultaneous sum and difference radiation patterns. This interface is deeply detailed in this article, together with the design of the RLSA antenna and the integration of the full monopulse antenna. The measured S-parameters fit very well with simulations. The operation is inherently narrowband with a realized gain of 27.8 dBi at 94 GHz, a radiation efficiency of 70%, 0.3 dB axial ratio, and a maximum null relation between sum and difference patterns higher than 50 dB.

A scheme for deception jamming detection based on beam scanning is proposed in this letter. This scheme detects the authenticity of the corresponding signal by forming a null in the direction of each visible satellite in turn. At the same time, the null direction is adjusted based on the attitude angle measured by the inertial unit to support the applicability of the scheme in scenarios where the attitude of the array changes continuously. Then, from an engineering point of view, an equalization scheme for arrays and radio frequency (RF) channels is proposed to improve the accuracy of the null direction. Finally, the effectiveness of the proposed scheme is verified by simulation.

International audience; Purpose: We present in vivo testing of a parallel transmit system intended for interventional MR-guided cardiac procedures.Methods: The parallel transmit system was connected in-line with a conventional 1.5 Tesla MRI system to transmit and receive on an 8-coil array. The system used a current sensor for real-time feedback to achieve real-time current control by determining coupling and null modes. Experiments were conducted on 4 Charmoise sheep weighing 33.9-45.0 kg with nitinol guidewires placed under X-ray fluoroscopy in the atrium or ventricle of the heart via the femoral vein. Heating tests were done in vivo and post-mortem with a high RF power imaging sequence using the coupling mode. Anatomical imaging was done using a combination of null modes optimized to produce a useable B1 field in the heart.Results: Anatomical imaging produced cine images of the heart comparable in quality to imaging with the quad mode (all channels with the same amplitude and phase). Maximum observed temperature increases occurred when insulation was stripped from the wire tip. These were 4.1℃ and 0.4℃ for the coupling mode and null modes, respectively for the in vivo case; increasing to 6.0℃ and 1.3℃, respectively for the ex vivo case, because cooling from blood flow is removed. Heating < 0.1℃ was observed when insulation was not stripped from guidewire tips. In all tests, the parallel transmit system managed to reduce the temperature at the guidewire tip.Conclusion: We have demonstrated the first in vivo usage of an auxiliary parallel transmit system employing active feedback-based current control for interventional MRI with a conventional MRI scanner.

In this letter, a high selectivity filtering magnetoelectric (ME) dipole antenna with harmonic suppression is investigated. By etching a complementary split resonant ring (CSRR) on shorted wall of ME dipole, a radiation null at upper passband edge can be obtained. The intrinsic radiation null at lower passband edge of ME dipole is utilized, together with the radiation null generated by CSRR, to obtain high selectivity. In addition, to suppress the third harmonic of the antenna, a stepped impedance resonator is loaded on the Г-shaped feeding structure. For verifying, a prototype operating from 1.44–2.79 GHz is designed, fabricated, and measured. Compared with the traditional ME dipole antenna, the proposed filtering antenna shows upper and lower stopband rejection levels as high as 16.61 and 17.84 dB, respectively. Furthermore, a third harmonic suppression level of 12.78 dB is obtained. Good agreement can be observed between the simulation and measurement.

This article proposes a systematic approach for stacking uniform linear arrays (ULAs) of different sizes to reduce sidelobes and form nulls to the radiated beam pattern. In sidelobe reduction, the nulls and sidelobes of the vertically stacked ULAs are aligned to reduce the overall sidelobe level (SLL). In nulling, the nulls of varying length ULAs are aligned to configure the null direction and simultaneously reduce the sidelobes. Both approaches are relaxed to ensure the feasibility of the implementation. The stacking methods are studied by an extensive set of simulations together with azimuth and elevation beamforming. A sidelobe reduction method showed potential for better than 30 dB SLL and more than 20 dB relative null depth with less than 100 antenna elements. Finally, the concepts are validated by beam pattern measurements of a 28 GHz 64-element, 16-chain phased-array transceiver using a 100 MHz wide 5G waveform.

A new method of designing a wideband differentially fed dual-polarized antenna by using three-strip transmission lines (TS-TLs) is presented. A wideband power divider composed of four TS-TLs is firstly proposed and illustrated by using its equivalent circuit. Based on the proposed power divider, a wideband differentially fed dual-polarized antenna with four in-band resonances is developed. To enhance the outof-band selectivity, two radiation nulls with quasi-elliptic response are obtained by utilizing the specifically designed structures in the TS-TL based power divider. The first radiation null at the lower out-of-band is produced by the resonance from the center strip of TS-TL and shorting coaxial cable. The second radiation null at the upper out-of-band is produced by the resonance from the slot formed by the dipole arm and the outer strip of TS-TL. Combining with the high 2nd -order harmonic suppression owing to the differentially fed method, the presented differentially fed antenna is demonstrated that it not only has high inband selectivity covering 1.67-2.91 GHz, but also has high out-of-band suppressions of 33.8 dB and 20.6 dB over the frequency bands of 0.6-1 GHz and 3.3-5 GHz. In addition, stable gain and beamwidth are achieved for base station applications.

A novel beamforming technique that resembles the principle of interference is proposed for sonar arrays to suppress the side lobes while the main lobe is kept intact. It uses two window functions. The first one is a rectangular function that produces a primary beam pattern. A secondary new window function is derived and its beam pattern is steered such that the null or trough of the main lobe of the new window coincides with the peak or crest of the first side lobe of the rectangular window and so on to other major side lobes. Pattern multiplication was used to get a final beam pattern. The approach is simulated and verified through a sonar array with 24 hydrophone sensors.

In this paper, the effects of mutual coupling and antenna surface deformity in a conformal wedge-shaped antenna array are compensated using a linear pattern correction technique. The problem is formulated to reduce the absolute distance between the actual (simulated) and the desired radiation patterns and to allow for null positioning control. The individual field patterns for the antenna elements are deformed due to changes in mutual coupling and the conformal surface. The deformed patterns of the individual antennas for specific bend angles are stored as lookup tables and interpolated to get the desired radiation pattern at any arbitrary bend-angle. The problem is linearly and quadratically constrained at the null points and performance compared with unconstrained optimization. The proposed solution for diminishing the effect of mutual coupling and surface deformity is independent of main lobe direction, type of individual antenna, array geometry, and spacing between antenna elements. The closed-form results are validated through Computer Simulation Technology (CST) for the wedge-shaped deformed dipole antenna array. The results for the proposed scheme are also assessed with the traditional Open Circuit Voltage Method (OCVM) and show superior compensation for deformity and the mutual coupling effects in conformal beam-forming arrays in terms of main beam direction, position and depth of nulls.

A novel method based on alternating linear programming optimization is presented to synthesize sparse linear arrays with sum and difference patterns. This method can find the optimized element positions and excitations shared for both sum and difference patterns with accurate control of multiregion sidelobe distribution and difference pattern null slope. In addition, the constraints on the minimum element spacing and dynamic range ratio of the obtained excitations can be also appropriately incorporated into this alternating optimization process. Two synthesis examples with different pattern shape requirements are conducted to validate the effectiveness and advantages of the proposed method.

The nonstationarity of interferences and array errors may bring fatal degradation to the interference cancellation performance of an adaptive beamformer. Covariance matrix tapering (CMT) can produce wide troughs in receiving pattern and becomes a promising solution. However, not only the full adaption methods but also the robust sidelobe canceller widen all nulls symmetrically to the original directions of arrival (DOAs) with the same width. In fact, in most cases, the adaptive pattern does not need symmetrical and equivalent-width nulls since it is of little possibility that different interference poses the same nonstationarity. To cover the worst nonstationarity, traditional CMT methods need to produce a widest null and will suffer a waste of degrees of freedom (DOFs). In this paper, a flexible method for null widening is proposed which can produce wide null with different desired width and asymmetry. The asymmetry is developed from the spatial asymmetrical interference cluster, and the unequal null width is produced by disturbing different interference space with different tapering matrix. Computer simulation result corroborate the feasibility and merits of the proposed method.

The synthesis and design methods of a novel filtering antenna with flexible passband and radiation null based on parallel scheme are presented in this letter. The filtering antenna is constructed by parallelly connecting two inverted-fed resonant antenna elements to a common feed point. The two resonant antenna elements can be separately designed and adjusted. A specific filtering performance with a radiation null can be synthesized using the proposed sum-of-transfer-functions method based on resonant frequencies and quality factors of the two elements. Finally, a practical filtering antenna centered at 5.78 GHz with the bandwidth of 190 MHz and a radiation null at 5.6 GHz is fabricated. The gain of 5.0 dBi is reached within the total size of 0.864 λ 0 × 0.576 λ 0 × 0.020 λ 0, where λ 0 is the free-space wavelength of the center frequency.

To deal with the single-phase open-circuited fault, an enhanced fault-tolerant model predictive current control with continued modulation is proposed in this article. This method includes reconstructing the postfault vector distribution and adopting a multistep vector selection method. In the reconstruction procedure, the transition vectors are generating to realize standard pulsewidth modulation waveforms. Then, the unreachable area can be filled by creating new synthetic vectors. Finally, the vectors with oversized amplitudes are optimized by using null vectors. In order to cover the full modulation area, a multistep vector selection method is used to determine the phase angle and amplitude of the optimal vector. The phase angle can be determined by defining two cost functions and adopting duty cycle modulation technology. The amplitude of the optimal vector can be optimized by utilizing the duty cycle modulation technology again. The oscillation, due to the back electromotive force, is compensated in each step. A thorough experimental evaluation has been conducted to confirm the effectiveness and superiority of the proposed fault-tolerant method.

UHF near-field RFID reader antenna based on leaky waveguide is proposed and the performance is evaluated using numerical simulation and experiment. In order to suppress the standing wave along transverse direction, a pair of notches is placed on the transverse edge of the mesh layer of the planar waveguide. Diversity operation by switching impedance of the end terminal of the planar waveguide antenna is also introduced to suppress the standing wave effect along longitudinal direction. Numerical simulation and experiment show that the near-field null lines parallel to the longitudinal direction is almost removed by the presence of the notches and the distribution of the field strength becomes almost uniform because of the utilization of the switching diversity. It is demonstrated that the reading performance of the commercial RFID tags is greatly improved by using the proposed RFID reader antenna with the diversity operation of termination impedance.

Antenna array is one of the methods which can generate Orbital Angular Momentum (OAM) waves. However, OAM waves generated by different antenna arrays have different characteristics of Electric-field (E-field) components’ distribution and radiation patterns. In order to solve this problem, we derive E-field formulas of OAM waves generated by different kinds of dipole antenna array in this paper. The dipole antenna arrays are arranged by three methods: 1) antenna elements are in the same direction of y axis, 2) antenna elements are in the radial direction and 3) antenna elements are in the azimuthal direction. Results show that x components, y components and z components carry different OAM modes under the three conditions. Simulation results show that the same direction antenna array produces the best OAM waves because the y component is dominated by OAM mode l and RHCP/LHCP waves are negligible in energy, while the pure OAM waves carried by the z components generated by the other two antenna arrays have little energy. In addition, only the radiation pattern of l = 0 produced by the same direction antenna array does not have a null zone in the propagation direction. Radiation patterns of l = ± 1 do not have null zones in the propagation direction generated by other two antenna arrays.

The adaptive digital beamforming technique in the space-polarization domain suppresses the interference with forming the coupling nulls of space and polarization domain. When there is the interference in mainlobe, it will cause serious mainlobe distortion, that the target detection suffers from. To overcome this problem and make radar cope with the complex multiple interferences scenarios, we propose a multiple mainlobe and/or sidelobe interferences suppression method for dual polarization array radar. Specifically, the proposed method consists of a signal preprocessing based on the proposed angle estimation with degree of polarization (DoP), and a filtering criterion based on the proposed linear constraint. The signal preprocessing provides the accurate estimated parameters of the interference, which contributes to the criterion for null-decoupling in the space-polarization domain of mainlobe. The proposed method can reduce the main lobe distortion in the space-polarization domain while suppressing the multiple mainlobe and/or sidelobe interferences. The effectiveness of the proposed method is verified by simulations.

Multiple-input multiple-output (MIMO) radar systems are popular for their ability to mitigate the target radar cross section fluctuations and null Doppler. However, MIMO radar fundamentally suffers from a notable signal-to-noise ratio (SNR) loss compared to an ideal phased-array (PA) radar. In order to overcome this drawback, a distributed MIMO radar scheme with joint optimal transmit and receive signal combining method is proposed in this work. In view of the optimality, the proposed scheme outperforms the most popular combining methods of MIMO radar addressed in the literature. Also, the proposed scheme performs same as the ideal PA radar in case of the nonfluctuating target. In case of fluctuating targets, the proposed scheme outperforms PA radar at high SNR.

We report multiwavelength study of a complex M-class solar eruptive flare that consists of three different sets of flare ribbons, viz. circular, parallel, and remote ribbons. Magnetic field modelling of source active region NOAA 12242 exhibits the presence of 3D null-point magnetic topology that encompasses an inner bipolar region. The event initiates with the faint signatures of the circular ribbon along with remote brightening right from the pre-flare phase that points toward the ongoing slow yet persistent null-point reconnection. We first detected flux cancellation and an associated brightening, which are likely signatures of tether-cutting reconnection that builds the flux rope near the polarity inversion line (PIL) of the inner bipolar region. In the next stage, with the onset of M8.7 flare, there is a substantial enhancement in the brightening of circular ribbon, which essentially suggests an increase in the rate of ongoing null-point reconnection. Finally, the eruption of underlying flux rope triggers ‘standard flare reconnection’ beneath it producing an abrupt rise in the intensity of the parallel ribbons as well as enhancing the rate of null-point reconnection by external forcing. We show that within the the fan dome, the region with magnetic decay index n > 1.5 borders the null-point QSL. Our analysis suggests that both the torus instability and the breakout model have played role toward the triggering mechanism for the eruptive flare. This event is a nice example of the dynamical evolution of a flux rope initially confined in a null-point topology that subsequently activates and erupts with the progression of the circular-cum-parallel ribbon flare.

Nowadays, the design of dividers is based on electromagnetic software that optimizes some geometric parameters to obtain the required performance. The choice of the geometry of the discontinuities contained in the divider and of the optimization initial point is quite critical to satisfy the divider requirements. In the last years, it is quite rare to find in the literature a theoretical approach helping the designers in the choice of the divider geometry. Helpful suggestion can derive by the analysis of the electric field in a trial divider that satisfies power division among the output ports in a thin band. In fact, the electric field null can be filled with metallic septa that ensure the same behavior at any frequency. The optimization of the septa position/form with numerical electromagnetic software permits to obtain divider with large bandwidth. A further analysis of the electric field null in the divider permits to add lateral metallic septa that further enlarge the transmission band. Finally, the design of an input matching network increases the transmitted power to the desired value.

The Fresnel and Arago interference laws relate the polarization of the electromagnetic field to the interference phenomenon. Different methods and interferometers have been reported to verify these laws; most of them rely on visual inspection to determine the positions of maximum and minimum interference. In this report, the observation and verification of the Fresnel and Arago interference laws using adaptive photodetectors are presented. These photodetectors generate an electrical current proportional to the square of the visibility of the interference pattern; thus the gradual change from the appearance of the interference pattern (maximum visibility) to its disappearance (minimum or null visibility) is detected as an electrical current. The extreme values of the interference pattern visibility can be accurately assessed, in real time and without any signal processing using. A difference of 3 orders of magnitude between the signals measured in the positions of maximum and minimum interference is demonstrated. Due to the adaptive properties of the adaptive photodetectors (compensation of the irregularities of the interfering beams and suppression environmental fluctuations), the proposed method can be suitable for teaching purposes in undergraduate laboratories.

A novel design of bandpass frequency selective surface (FSS) with high selectivity is proposed based on the antenna-filter-antenna (AFA) concept. Traditional AFA-based FSSs improve filtering performance by adding the order of resonator or the coupling paths. On account of the reciprocity theorem, transmission zeros are here introduced by the antenna's radiation null. The proposed FSS consists of two patch antennas connected with one pin and a C-type slot on the ground. The aforementioned structure generates two controllable radiation nulls related to the lengths of slots without any extra circuits. Therefore, two transmission zeros at both edges of the passband can be controlled by adjusting the dimension of slots. A prototype is fabricated and measured. Numerical simulation and measured results are in good agreement, which demonstrates that the proposed AFA-based FSS exhibits a quasi-elliptic bandpass response and a low profile.

Differential microphone arrays (DMAs) can achieve high directivity and frequency-invariant spatial response with small apertures; they also have a great potential to be used in a wide spectrum of applications for high-fidelity sound acquisition. Although many efforts have been made to address the design of linear DMAs (LDMAs), most developed methods so far only work for the situation where the source of interest is incident from the endfire direction. This paper studies the steering problem of differential beamformers with linear microphone arrays. We present new insights into beam steering of LDMAs and propose a series of steerable differential beamformers. The major contributions of this paper are as follows. 1) A series of ideal functions are defined to describe the ideal, target beampatterns of LDMAs. 2) We prove that first-order differential beamformers with linear microphone arrays are not steerable and their mainlobes can only be at the endfire directions. 3) We deduce the fundamental conditions for designing steerable differential beamformers with LDMAs. 4) We develop a method to design steerable beamformers with LDMAs using null constraints. Simulations and experiments validate the properties of the developed method.

In this letter, a compact substrate integrated waveguide (SIW) monopulse antenna array based on microstrip feed is proposed. The antenna cell is composed of two layers of dielectric substrates, the model of the dielectric substrate is Rogers 5880. The TE20 mode is excited in the bottom SIW cavity, and the mirrored TE20 mode is used to realize the function of a monopulse comparator, which makes the structure of the antenna simple and superior in performance. Furthermore, an array is formed on the basis of the cell. The performance of the array was verified in simulated software and the prototype was fabricated for testing. The measured results are consistent with simulated results. The antenna works in the X-band, and the measured and beam gain reaches 16.4 dBi, and the null depth is 33.8 dB. The antenna aperture efficiency reaches 43%, which has great advantages compared with similar antennas.

Unwanted signal such as spoofing, jamming, and multipath is one of the major error factors in GNSS positioning. The purpose of this research is to mitigate the unwanted signal especially multipath error using an array antenna with six elements. We verified the effectiveness of the DCMP (Directionally Constrained Minimization of Power) algorithm to mitigate the unwanted signal. DCMP algorithm is one of the signal synthesis methods using the array antenna and can direct the ``Null'' to the unwanted signal direction by setting some constraint conditions. Testing in multipath-rich environment showed that the positioning accuracy was improved by constraining the ``Null'' toward the building which reflected GNSS signal.

It is shown that, in a line-of-sight setting, a receiver equipped with two antennas may approximately null an arbitrary large number of spatial directions to any desired degree, while maintaining the interference-free signal-to-noise ratio, by judiciously adjusting the distance between the antenna elements, provided that the spacing can be made sufficiently large. The main theoretical result builds on ergodic theory. The practicality of the scheme at moderate signal-to-noise values is demonstrated for a scenario where each transmitter is equipped with a single antenna and each receiver has two receive chains and where the desired spacing between antenna elements is achieved by selecting the appropriate antennas from a large enough linear antenna array. We further extend the proposed scheme to show that interference can be nearly eliminated also in specular multipath channels as well as multiple-input multiple-output interference channels where a single additional receive antenna suffices to approximately align all interferers into a one-dimensional subspace. To demonstrate the performance of the scheme, we show significant gains for interference channels with four as well as six users, at low to moderate signal-to-noise ratios ( $0\text{--}20$ dB). The robustness of the proposed technique to small channel estimation errors is also explored.

Pattern synthesis is a significant research focus in smart antennas due to its extensive use in several radar and communication systems. To improve the optimization performance of pattern synthesis of uniform and sparse linear antenna array, this paper presents an optimization method for solving the antenna array synthesis problem using the Mayfly Algorithm (MA). MA is a new heuristic algorithm inspired by the flight behavior as well as the mating process of mayflies, it has a unique velocity update system with great convergence. In this work, the MA was applied to linear antenna arrays (LAA) for optimal pattern synthesis in the following ways: by optimizing the antenna current amplitudes while maintaining uniform spacing and by optimizing the antenna positions while assuming a uniform excitation. Constraints of inter-element spacing and aperture length are imposed in the synthesis of sparse LAA. Sidelobe level (SLL) suppression with the placement of nulls in the specified directions is also implemented. The results gotten from this novel algorithm are validated by benchmarking with results obtained using other intelligent algorithms. In the synthesis of uniform 20-element LAA with nulls, MA achieved an SLL of −31.27 dB and the deepest null of −101.60 dB. Also, for sparse 20-element LAA, an SLL of −18.85 dB was attained alongside the deepest null of −87.37 dB. MA obtained an SLL of −35.73 dB and −23.68 dB for the synthesis of uniform and sparse 32-element LAA respectively. Finally, electromagnetism simulations are conducted using ANSYS Electromagnetics (HFSS) software, to evaluate the performance of MA for the beam pattern optimizations, taking into consideration the mutual coupling effects. The results prove that optimization of LAA using MA provides considerable enhancements in peak SLL suppression, null control, and convergence rate with respect to the uniform array and the synthesis obtained from other existing optimization techniques.

A wideband filtering dielectric patch (DP) antenna with reconfigurable bandwidth is investigated in this paper. Adjusting the aspect ratio of the DP resonator can make the high-order TE121 mode close to the dominate TM101 mode to facilitate the design of wideband filtering DP antenna. Meanwhile, the high-order TM111 mode is adjacent to the TE121 mode and then used as a non-excitation and non-radiation mode for producing an upper band-edge radiation null. On this basis, two slots with different sizes in parallel are introduced into the ground plane to excite the DP resonator, resulting in a lower band-edge radiation null, which sharpens the lower band-edge roll off. A pair of slits between the two coupling slots are incorporated and the varactor diodes are loaded on the slits to tune the electrical distance of the coupling slots, thereby electrically controlling the frequency of the lower band-edge radiation null. In this way, the fractional bandwidth (FBW) of the resultant filtering antenna can be flexibly tuned from 21% to 15.3%. A prototype has been designed, fabricated, and measured. Reasonable agreement was obtained between the simulated and measured results.

This paper presents a differentially fed dual-band hybrid antenna with broadside radiation, enhanced bandwidth, and high selectivity. The proposed antenna is constructed using a single- layer substrate based on rectangular patch resonator and substrate integrated waveguide (SIW) cavity. Herein, TM10 and TM12 modes of the rectangular patch resonator, together with TE21 and TE23 modes of the rectangular SIW cavity, are selected for resonances in the concerned dual-band radiation. Among them, TM10 and TE21 are employed for the lower passband, while TM12 and TE23 for the higher passband. Besides, for achieving broadside radiation performances in both bands, two arrays of shorting pins are loaded in the rectangular patch resonator and the constituted electric wall surround the rectangular SIW cavity is properly truncated to reshape the radiation patterns of TM12 and TE23, respectively. Notably, the resonant and radiation properties of all the involved modes are obtained with theoretical deduction. Furthermore, the cascaded trisection composed of the SIW cavity, the patch resonator, and the radiation impedance creates two radiation nulls in each upper stopband of both passbands and the mixed coupling between two resonators generates another radiation null to be located in the lower stopband of the higher passband. For demonstration, a prototype antenna with the dual bands at 3.5 and 5.8 GHz is fabricated and tested. The measured results show that the antenna has achieved an improved bandwidth ( $|\textrm {S}_{\mathrm{ dd11}}| < -10$ dB) from 3.26 to 3.58 GHz and 5.60 to 5.90 GHz, respectively, with stable broadside gains of around 8.5 dBi. In addition, in the stopband, three radiation nulls are created at 3.71, 5.32, and 6.12 GHz for effective enhancement of dual-band frequency selectivity.

In production testing, it is of importance to measure the key radiation parameters of an antenna under test (AUT), e.g., main beam peak and direction, sidelobes, and null depth and direction in a cost-effective setup with a short measurement time. As a result, practical measurement setups are often compact and equipped with only a few probes (or probe locations). However, these system limitations would introduce errors for AUT antenna testing. This problem has become even more pronounced for 5G radios due to utilization of large-scale antenna configuration and high frequency bands. Spherical near-field measurements are nowadays an accurate and mature technique for characterizing AUTs, which however, necessitates a full spherical acquisition, leading to a long measurement time. Single-cut near-to-far-field transformation is a promising strategy since most of the key AUT parameters are available in the single-cut pattern and it requires much reduced measurement time. In this work, a simple and flexible scheme is proposed to evaluate errors introduced by limitations in practical setups for single-cut far-field (FF) antenna radiation pattern reconstruction, where the near-field data can be easily generated and modified according to the limitations introduced in practical multi-probe anechoic chamber setups, e.g., measurement distance, truncation range, and sampling interval. The reconstructed FF pattern is obtained using a commercial near-field to far-field transformation tool, SNIFT. The proposed scheme is numerically validated via comparing the reference FF pattern of a 4×8 uniform planar array composed of ideal Hertzian dipoles and reconstructed FF pattern. With the proposed scheme, the impact of practical system limitations on single-cut reconstruction accuracy can be easily analyzed.

In this article attempt has been made for the first time to apply the reported strawberry optimization technique to antenna array synthesis problem. The algorithm is further modified by reinforcing it with adaptive values for the two key parameters known as runner length and root length embedded in the mathematical expression governing the movement of the mother plant from one position to another in the search space to locate the optimum solution. The case studies cited here refer to linear and circular array configurations. The design constraints are limited to minimizing the side lobe level and restricting the first null beam width, which play significant roles in antenna array performances. The important features which greatly influence in achieving the said objectives are either placement of antenna elements or amplitudes of excitations of these elements or both. And the recently reported nature inspired metaheuristic optimization algorithms have addressed to these antenna problems quite effectively and the application of the strawberry algorithm for the first time and the unraveling of a new algorithm known as reduced step size strawberry algorithm (rss-SBA) a variant of the existing SBA have shown quite exciting results thus opening avenues for these techniques to be the potential contenders in the race of authenticating their positions in the domain of nonlinear function optimization.

This paper introduces a novel transparent proximity-coupled-fed patch antenna with enhanced impedance bandwidth and good filtering response. The proposed antenna consists of a ground plane, a specific feeding structure and a slotted patch. All the conducting surfaces are realized with metal meshes printed on glass substrates. Optical transparency of the antenna depends on the mesh density. The feed line of a traditional proximity-coupled-fed patch antenna is terminated with a driven stub etched with a half-wavelength U-shaped slot. This modification introduces an additional resonant mode but also a radiating null. By further etching a pair of quarter-wavelength open slots on the radiating patch, another resonant mode accompanied with an extra radiation null is generated. Finally, three resonant modes within the operating band along with two radiation nulls near the two edges of the passband are achieved. The proposed antenna is implemented to demonstrate an impedance bandwidth of 7.6% from 3.41 to 3.68 GHz and a maximum gain of 4.6 dBi.

An optimization method of pattern synthesis is proposed for peak sidelobe level (PSLL) suppression and null controlling via element rotation and phase optimization. The purpose of this method is to...

In this paper, a new SVPWM switching technique, named ZSVM_1TI, has been proposed for a three-level (3L) T-type Z-source inverter (ZSI). ZSVM_1TI is based on three main modifications of the existing PWM techniques for 3L inverters. First, the existing SVPWM of a 3L ZSI has been modified to double the frequency of the null interval. After that, an improved version of the maximum boost control (MBC) has been proposed based on modified SVPWM to eliminate the problem of the sixth frequency ripple components of inductor current with the existing MBC technique of ZSIs. Finally, a new switching pattern of a reduced common-mode voltage (CMV) PWM technique has been proposed to increase the switching frequency of the impedance network so that the size of the passive elements can be reduced. The proposed ZSVM_1TI has been compared with the existing PWM technique in terms of the size of the impedance network, the dc-link utilization, and the inductor current ripple profile. The above-mentioned findings have been successfully validated using theoretical analysis, simulations, and experimental results.

A completely passive method of enabling 1-D beam-scanning for a monopulse antenna array with controllable sidelobe levels (SLLs) is presented in this letter. To achieve this unique function, a compact frequency-dependent phase-shifter composed of stripline resonators is proposed. This proposed phase-shifter provides similar sensitivity as conventional meander striplines, while its size is much smaller, enabling a successful implementation into a highly integrated feeding network with monopulse functions. The validation is provided by a 4 × 16 monopulse antenna array operated at X -band. A good correspondence is achieved between simulation and measurement for both S -parameter and far-field results. Measurement results of the prototype indicate a scanning range from −54° (10.5 GHz) to 48° (11.5 GHz) can be covered. Within the entire operational frequency range, the sidelobe levels are smaller than −15 dB for the sum channel, while a null depth better than −20 dB is observed in the difference channel. The proposed method is characterized by control simplification and very suitable to be deployed in cost-effective tracking systems.

In this article, a novel design approach to triple-resonant, circular sector patch antenna with wideband null frequency scanning functionality is advanced. At first, the operation principle of null frequency scanning functionality is revealed by the simplest, straight electric dipole under multiple resonances. Then, a triple-resonant circular sector patch antenna is designed based on a double-wavelength prototype magnetic dipole by synthesizing it usable resonant modes. As synthesized, the resonant TM12/17,1, TM36/17,1, and TM60/17,1 modes within a 255° circular sector patch radiator can be simultaneously excited, properly perturbed, and then used to realize a wideband null frequency scanning functionality. Next, different prototype antennas are designed and fabricated and experimentally verified the design approach on a single layered air substrate. As finally demonstrated, the antenna can exhibit a null frequency scanning range from $\theta =+ 35^{\circ }$ to −60° within an available radiation bandwidth (ARB) of 24% (i.e., 2.20–2.80 GHz) for null depth smaller than −10 dB.

The article describes and analyzes the existing problems when using linear measuring devices for measuring temperature. When measuring temperature with resistive temperature sensors, a modified null method is proposed to use, which ensures the invariance of the meter to changes in the measuring path gain. The null balance in the measuring path is maintained automatically by synchronous pulse-amplitude and pulse-width modulations and using of a tracking circuit for adjustment of the width signal. Once the null balance is achieved, the width modulation control pulse duration will be linearly related to the resistance of the temperature sensor. Modification of the null method simplifies the design of a thermometer with a resistive sensing element. In this proposed mechanism, two precision resistors which are passive units replace the active precision units to increase the accuracy and improve the linearity of its conversion characteristics. The work reports the errors of temperature measurements by the modified null method and describes the calibration of a manufactured digital thermometer with a miniature platinum resistance temperature sensor. The proposed modification of the null measurement method can be used to construct devices comprising a sensor with a sensing element, namely electrical resistance that is altered under the influence of a non-electrical parameter.