Null Depth Research Articles

Varactor Loaded Pattern Reconfigurable Patch Antenna With Shorting Pins

A varactor loaded pattern reconfigurable patch antenna with shorting pins is presented. Continuous beam reconfigurability and null scanning are realized by introducing two sets of shorting pins and only four varactors into a square patch antenna. For this antenna, the edge-shorting pins are placed along with the parallel edges of the square patch for different $E$ -fields. Another set of shorting pins are fixed symmetrically along the diagonal of the square patch for directivity and null depth enhancement. To achieve continuous pattern reconfiguration, varactors are connected with the edge-shorting pins to provide continuously tunable phase difference. The mechanism of the pattern reconfiguration and effects of the shorting pins are discussed based on a transmission-line model. The proposed antenna has a compact size of $0.4\,\,\lambda _{0} \times 0.4\,\,\lambda _{0} \times 0.06\,\,\lambda _{0}$ . Both the simulated and measured results confirm that the proposed antenna has the capabilities of beam steering and null scanning. The measured main beam scans from −55°to −15.5°and 19° to 54°, with a gain reduction of 3.22 dB relative to maximum (7.55 dBi). Meanwhile, the coverage of radiation pattern null is from −74° to 62°.

Design of an Efficient Wideband Beamformer using OPSO

Wideband beamforming is a technique which is used to produce frequency invariant beampatterns over a wide signal bandwidth. In this paper, orthogonal particle swarm optimization (OPSO) based wideband beamformer is designed to achieve wideband beamforming. Simulations are carried out for two different scenarios to illustrate the capability of the algorithm for wideband beamforming. The beampatterns obtained from three different methods that are standard Frost algorithm, particle swarm optimization (PSO) and OPSO are compared by various parameters such as level of interference, deviation in interference angle and peak side lobe level. It is shown that by using OPSO, SLL (Sidelobe Level), null depth as well as angle deviation in nulls direction can be reduced as compared to PSO and Frost algorithms.

Range-Angle-Dependent Beampattern Synthesis With Null Depth Control for Joint Radar Communication

In this letter, we present an analytical method to design a range-angle-dependent beampattern using frequency diverse array (FDA) with null depth control (NDC) for joint radar and communication applications. A slow time-dependent nonuniform frequency offset is used to lock the phase of transmitted signal at a specific time instant to achieve the objective. Moreover, we introduce range-angle-dependent NDC for the joint radar and communication functionalities. That is, we design two transmit beamspace matrices for the subaperturing FDA to generate a similar main lobe toward the target for radar functionality but distinct null depth levels for communication purpose, so that the transmitted information can be efficiently detected by the intended communication receiver. The performance of the proposed design is evaluated using the bit error rate for communication and using the signal-to-interference-plus-noise ratio for radar.

Atom search optimization algorithm based hybrid antenna array receive beamforming to control sidelobe level and steering the null

Modern and upcoming 5G cellular communication networks require large-scale antenna systems to improve gain in order to face the weaknesses in the suggested millimeter-wave (mmWave) signals and to meet the higher capacity demand. These systems implement digital beamforming which requires radio frequency (RF) chain connected to each antenna. Hybrid analog-digital (HAD) beamforming has been proposed as a solution to many of the challenges facing the implementation of fully-digital beamforming, namely, energy consumption, hardware cost, and complexity. The main goals of this paper are to reduce the peak sidelobe level (SLL) of the beam pattern and steering the nulls in the desired directions along with reducing the power consumption, hardware cost, and complexity. To achieve these goals, a novel partial-connected hybrid analog-digital receive beamformer based on an atom search optimization (ASO) algorithm is proposed. ASO is a recently invented metaheuristic optimization algorithm imitating the physical movements of atoms as described in molecular dynamics simulation with the advantage of having few parameters to tune. The desired optimization weights are accomplished by controlling the amplitudes-only of the digital beamformer’s vector along with the phase shifts of the analog beamformer’s vectors. Finally, to demonstrate the effectiveness of the proposed beamformer, a comparison with other state-of-the-art metaheuristic algorithms through several scenarios is conducted, in terms of peak SLL reduction, null depth, and convergence rates. Simulation results show that the proposed algorithm has always been outperforming other types of beamformers.

Runner-Root Algorithm to Control Sidelobe Level and Null Depths in Linear Antenna Arrays

Nature-inspired metaheuristic algorithms have significantly influenced the optimization problems, and there has been a great success in finding optimum solutions. The main aim of this paper is to introduce one such technique, runner-root algorithm (RRA), to the antenna community. RRA is based on the concept of plant intelligence to solve an optimization problem resembling a scenario where a plant finds the best location for its survival. The main advantage of RRA over other algorithms is the execution of exploration (global search) and exploitation (local search) phases independently with a built-in mechanism of reinitialization to overcome trapping in local minima. Hence, attempt has been made for the first time to apply this algorithm to optimize excitation current amplitudes and positions of antenna elements for linear array configurations with the objective of suppressing the sidelobe levels and/or placing nulls at prescribed locations referring to the radiation patterns. Different case studies have illustrated that RRA is capable of performing linear antenna array optimization with promising results in comparison with other well-established metaheuristic algorithms. And hence such demonstration has identified RRA as a potential candidate in the optimization domain.

A New High-Performance Monopulse Feed with a Simple Comparator Network

This paper presents a new high-performance five-element monopulse feed with a simple comparator network for Cassegrain reflector applications. The radiating element is a tapered dielectric rod fed by a circular waveguide which is in turn excited by a printed dipole. The center element is used for the sum pattern, while top and bottom elements are used for the elevation difference pattern, and left and right elements for the azimuth difference pattern. Out-of-phase excitation for the difference pattern is obtained by antisymmetrically placing two dipoles and combining their outputs with a power combiner. The optimally designed feed has been fabricated and measured. Measurement shows that the feed has the maximum sum pattern gain of 16.8 dBi, the difference pattern null depth of –21 dBi, and the reflection coefficient of less than –10 dB over 13.9–16.7 GHz.

Reconfigurable CTS Antenna Fully Integrated in PCB Technology for 5G Backhaul Applications

We present the design and fabrication of a fully integrated continuous transverse stub (CTS)/pillbox antenna for 5G backhaul applications in the E-band. The antenna contains 16 radiating slots excited by a corporate feed network in the parallel-plate waveguide (PPW) technology. These slots are divided into two subarrays of eight slots, each one generating either a sum or a difference pattern along the E-plane. Two pillbox systems are used to feed the two subarrays, and therefore, the radiation patterns can be steered in the H-plane. Such a reconfigurability, both in the E- and H-planes, has not been reported with CTS antennas. Moreover, the recently introduced the substrate-integrated PPW (SI-PPW) technology is used in the printed circuit board technology for complete integration of the antenna module. The structure is thinner than 3 mm, and only low-cost standard fabrication processes are employed for the prototype. The measurement results are in good agreement with simulations. In the E-plane, the sum and difference patterns can cover an angular window of ±10°, and they can be steered in H-plane until ±14° in the complete E-band (71–86 GHz). Over this frequency band, the measured difference pattern exhibits a null depth below −23 dB. The gain remains stable over the band with a maximum of 17.5 dBi and a variation lower than 2.6 dB.

Modified CORPS beamforming network with null‐steering capability

This article proposes CORPS beamforming network (BFNs) with both beam and null steering capability. All simulation results are presented for scannable mono-beam configuration but it can be extended to the multi-beam system. Complex inputs are optimised by means of the PSO algorithm to get the array factor with the desired characteristics that are side lobe level (SLL), directivity (D), and null depth. All sub-blocks of the BFN are designed in the centre frequency of 2.4 GHz.

An Anti-Jamming Null-Steering Control Technique Based on Double Projection in Dynamic Scenes for GNSS Receivers.

When a global navigation satellite system (GNSS) receiver suppresses interference in a dynamic scene, the direction of the interference signal arriving at the receiver may change rapidly. The null formed by the spatial filtering based on the array antenna will become wider and shallower, and the anti-jamming performance will deteriorate. A null-steering control technique based on a dual projection algorithm is proposed in this paper, which can effectively increase the depth of the null. In this paper, the dynamic model between the interference and the receiver is established first. Based on the model, the rate of change of the arrival direction of the interference is analyzed, and the phenomenon of the spatial filtering null becoming wider and shallower is simulated and verified. Then, the double projection algorithm is introduced to effectively deepen the null. The simulation results show that the proposed method can effectively increase the null depth by 30 to 50 dB, which significantly improves the anti-jamming performance of the spatial filtering in dynamic scenes.

Deep, Broad Null Formation for Canceling Moving RFI in Radio Astronomical Arrays

Radio frequency interference (RFI) is rapidly becoming a major issue for many applications. It is especially problematic for radio astronomy, where signal-to-noise ratios (SNRs) are less than unity. Antenna array systems such as phased array feeds (PAFs) and interferometric imaging arrays are able to cancel RFI through adaptive projection-based spatial notch filtering techniques. Current methods for formulating these projection operators suffer from an unfortunate trade-off. They must sacrifice integration time when calculating the sample spatial correlation matrix in order to track RFI motion, but this consequently increases sample estimation error and reduces null depth. In this work, we propose a new way to process spatial correlation matrices to form a broad null that reliably cancels moving RFI without increasing sample estimation error due to insufficient integration. Additionally, when assisted by an RFI-tracking auxiliary antenna, this approach also reduces the total data rate coming out of a spatial correlator, thus making broad-null-based RFI cancelation more computationally efficient and practical for real-time active array-based RFI mitigation systems.

Wideband Radiation Reconfigurable Microstrip Patch Antenna Loaded With Two Inverted U-Slots

A wideband rectangular microstrip patch antenna with reconfigurable radiation patterns is proposed in this paper, which contains two symmetrically inverted U-slots, and incorporates two coaxial probes along the resonant length of the patch. By controlling the phase shift of applied currents through these probes, the antenna can be set to excite either the SUM or the Difference mode, in accord with the TM01 and TM02 modes, respectively. Unlike previous endeavors on U-slot microstrip antennas, a wide impedance bandwidth of 68% is realized, along with stable polarization and symmetrical radiation patterns. It is worth mentioning that the thickness of the substrate is very small, which is in the order of $0.02 \lambda _{d}$ , where $\lambda _{d}$ is the wavelength in the dielectric medium at the center frequency of 3 GHz. The slot and patch parameters are numerically analyzed to achieve wide bandwidth along with symmetric radiation patterns. The realized null depth in the Difference mode is well below −30 dB, which makes the proposed antenna well suited for monopulse radar applications. The antenna covers a frequency range of 1.98–4 GHz. A prototype is fabricated and tested. Good agreement between the measured and simulated results is observed.

A Dual Circular-Polarized Extremely Thin Monopulse Feeder at <italic>W</italic>-Band for Prime Focus Reflector Antenna

A thin monopulse feeder is very important in a radar system with strict profile limitation. Besides, to implement polarization-agile radar, a monopulse feeder with two orthogonal polarizations is required to synthesize an arbitrary polarization. To achieve these requirements, a dual circular-polarized extremely thin monopulse feeder at W-band is investigated and realized for a prime focus reflector antenna, which can be used in a tri-mode seeker. To begin with, two kinds of the 2 × 2 substrate integrated waveguide (SIW) slot antenna array topologies are discussed based on the standard of circular polarization efficiency. After that, the better one integrated with a compact and single-layer SIW comparator is used to feed the reflector antenna. The total thickness of the developed feeder is only 0.56 mm. For a prime focus 140 mm diameter reflector antenna with the blockage of a diameter of 40 mm, the measured gain of the entire antenna system is 35.6 dBi at 94 GHz. The DIFF-beam null depth is -20.1 dB in xoz plane and -20.5 dB in yoz plane. The gain ratios of the SUM- and DIFF-pattern are 3.5 dB in xoz plane and 4 dB in yoz plane. The results show that this type of antenna has great prospects in a monopulse tracking system with polarization agile function.

A Single-Layer SIW Slots Array Monopulse Antenna Excited by a Dual-Mode Resonator

The conventional monopulse comparator, which commonly consists of a power divider, a standard 3dB-coupler and a 90-degree phase shifter, occupies a significantly large area of the antenna aperture. This results in a low efficiency. In order to improve the antenna's aperture efficiency and keep a planar single-layer structure simultaneously, a substrate integrated waveguide (SIW) slots array monopulse antenna excited only by a square dual-mode (TE120 and TE210) SIW resonator is proposed, fabricated and measured in this communication. The sum and difference beams are obtained when the feeding cavity operates at two high-order modes, respectively. The needless of complex feeding network reduces the antenna's structure complexity and improves its aperture efficiency. The aperture efficiency of the antenna can reach 42%. Besides, the sum and difference ports have good isolation due to the orthogonality between the two modes. The proposed antenna obtains a 100 MHz impedance bandwidth, determined by the reflection coefficient less than -10 dB. The measured gain of the sum pattern is 11.9 dBi at 10 GHz, while the null depth of the difference pattern is lower than -27 dB.

New multi‐objective optimisation algorithm for uniformly excited aperiodic array synthesis

A new multi-objective optimisation algorithm called non-dominated sorting and local search (NSLS) algorithm is proposed for uniformly excited aperiodic array synthesis here. Two design cases of uniformly excited linear and planar array synthesis are conducted to verify the outperformance of NSLS. Synthesis results indicate that NSLS is able to obtain the lowest maximum sidelobe level (MSLL) and the deepest null depth level in linear array design case, along with the lowest MSLLs in two planes of radiation pattern in planar array design case compared with the other latest algorithms. In addition, the convergence performance and computational costs of NSLS in the design cases are investigated. The synthesis results combined with excellent convergence performance and low computational costs of NSLS make it a reliable and promising optimisation algorithm for uniformly excited aperiodic array synthesis.

A New Tool to Estimate Inundation Depths by Spatial Interpolation (RAPIDE): Design, Application and Impact on Quantitative Assessment of Flood Damages

Rapid tools for the prediction of the spatial distribution of flood depths within inundated areas are necessary when the implementation of complex hydrodynamic models is not possible due to time constraints or lack of data. For example, similar tools may be extremely useful to obtain first estimates of flood losses in the aftermath of an event, or for large-scale river basin planning. This paper presents RAPIDE, a new GIS-based tool for the estimation of the water depth distribution that relies only on the perimeter of the inundation and a digital terrain model. RAPIDE is based on a spatial interpolation of water levels, starting from the hypothesis that the perimeter of the flooded area is the locus of points having null water depth. The interpolation is improved by (i) the use of auxiliary lines, perpendicular to the river reach, along which additional control points are placed and (ii) the possibility to introduce a mask for filtering interpolation points near critical areas. The reliability of RAPIDE is tested for the 2002 flood in Lodi (northern Italy), by comparing the inundation depth maps obtained by the rapid tool to those from 2D hydraulic modelling. The change of the results, related to the use of either method, affects the quantitative estimation of direct damages very limitedly. The results, therefore, show that RAPIDE can provide accurate flood depth predictions, with errors that are fully compatible with its use for river-basin scale flood risk assessments and civil protection purposes.

Correction of array failure using grey wolf optimizer hybridized with an interior point algorithm

We design a grey wolf optimizer hybridized with an interior point algorithm to correct a faulty antenna array. If a single sensor fails, the radiation power pattern of the entire array is disturbed in terms of sidelobe level (SLL) and null depth level (NDL), and nulls are damaged and shifted from their original locations. All these issues can be solved by designing a new fitness function to reduce the error between the preferred and expected radiation power patterns and the null limitations. The hybrid algorithm has been designed to control the array’s faulty radiation power pattern. Antenna arrays composed of 21 sensors are used in an example simulation scenario. The MATLAB simulation results confirm the good performance of the proposed method, compared with the existing methods in terms of SLL and NDL.

Broadband monopulse microstrip antenna array for X‐band monopulse tracking

In this study, a broadband planar multilayer monopulse antenna at the X-band for monopulse tracking applications is presented. A monopulse comparator has been designed using four hybrid ratrace for feeding the radiating elements of the antenna. Each radiating part of the monopulse antenna consists of 4 × 4 electromagnetically coupled microstrip antenna array. To achieve circular geometry as well as better side-lobe level (SLL), a hybrid feeding technique is used in radiating antenna array by adding a few elements in series at the end elements of the parasitic layer of a 4 × 4 corporate fed array. The prototype has been fabricated, tested and measured results are compared with simulated results. The simulated impedance bandwidth for | S 11 | ≤ -10 dB is 21% (8.6-10.6 GHz). A measured peak sum beam gain of 24.4 dBi has been obtained. Measured SLL of <;-15 dB has been achieved in both elevation and azimuth planes along with a null depth of <;-35 dB for difference patterns in both the planes. The radiation pattern is symmetrical in both the planes with half-power beamwidth nearly equal to 9.0°.

A miniaturized broadband monopulse comparator with all DELTA channels nulling in Ku band

AbstractA compact monopulse comparator with complete nulling in all DELTA channels is designed and fabricated. The proposed comparator has small dimension and consists of interconnections of four broadband branch-line couplers and several 90° phase shifters with multistage Schiffman coupled-lines. This comparator has been characterized by its eight-portS-parameters to generate the SUM and DELTA channel frequency responses. Over 30-dB null depth was achieved in DELTA channels across the SUM channels in pass band from 14.8 to 18.2 GHz frequency range.

A High-Density L-Shaped Backscattering Chipless Tag for RFID Bistatic Systems

Chipless radiofrequency identification (RFID) technology is very promising for sensing, identification, and tracking for future Internet of Things (IoT) systems and applications. In this paper, we propose and demonstrate a compact 18-bit, dual polarized chipless RFID tag. The proposed tag is based on L-shaped resonators designed so as to maximize the spectral and spatial encoding capacities. The proposed RFID tag operates an over 4 GHz frequency band (i.e., 6.5 GHz to 10.5 GHz). The tag is simulated, fabricated, and tested in a nonanechoic milieu. The measured data have shown good agreement with the simulation results, with respect to resonators’ frequency positions, null depth, and null bandwidth over the operating spectrum. The proposed design achieves spectral and spatial encoding capacities of 4.5 bits/GHz and 18.8 bits/cm2, respectively. This, in turn, gives an encoding density of 4.7 bits/GHz/cm2. For code identification, we exploit the frequency content of the backscattered signals and identify similarity/correlation features with reference codes.

Cosine Least Mean Square Algorithm for Adaptive Beamforming

Beamforming and multiple-input multiple-output (MIMO) antenna configurations have received worldwide interest during the recent time. Various beamforming algorithm has been proposed and employed in different applications. The Least Mean Square (LMS) algorithm has become one of the most widespread adaptive beamforming techniques because of its simplicity and robustness. This paper presents a new variant of LMS algorithm named as Cosine Least Mean Square (Cos-LMS) which uses the efficient computation of array factor for linear antenna array.This algorithm gives improved performance in beam width reduction, side lobe level reduction, null depth, and stability as compared to standard LMS and other variants of LMS algorithm. The performance improvement by Cos-LMS algorithm is accomplished without increasing the computationalcomplexity of standard LMS algorithm.