Auxiliary Antenna Research Articles

Theoretical Substantiation of Methods for Reducing the Near-Side Radiation of Antennas for an Earth Satellite Communication Station

Within the framework of this article, various methods of reducing the lateral radiation of the antenna are considered, which mainly relate to the angular directions directly adjacent to the direction of the main radiation of the antenna for an earth satellite communication station. The relevance of this issue is beyond doubt, since it is the behavior of the antenna's diagrammatic orientation in this area that most significantly determines the electromagnetic compatibility of various satellite communication systems. The presence of axial shading leads to a significant increase in the near side lobes. The specified deformation of directional properties in a certain plane can be eliminated by using an additional radiator, the phase center of which in this plane coincides with the phase center of the antenna. Shadow radiation compensation is carried out only in a beam of regions close to the plane perpendicular to the straight line connecting the centers of the main and auxiliary antennas. The angular compensation area can be significantly expanded if the phase centers of the main and auxiliary antennas are combined. This rather trivial conclusion is still waiting for its non-trivial technical implementation. Wide-angle compensation of lateral radiation is proposed to be carried out by two auxiliary antennas located parallel to the suppression plane. The best results can be obtained by optimizing the opening shape of the auxiliary radiators. Studies show that the optimal variant of the directional pattern occurs when the mentioned irradiators are made in the form of rectangles with a length of 0,295 and a height of 0,117 from the opening radius of the main antenna, and the distribution in the openings of the auxiliary antennas is cosine-shaped. In this case, it is possible to suppress the radiation level to -40 dB.

Rejection of Surface Clutter in Far Sidelobes for Airborne Radars

In airborne radar, false alarms caused by surface clutter returns through antenna sidelobes need to be suppressed to detect the target of interest. Sidelobe blanking is widely used to reject false alarms. Ideally, an auxiliary antenna radiation pattern should cover entire sidelobes of the main antenna radiation pattern. However, this may not always be satisfied, especially in the case of far sidelobes (FSL) of the main antenna, for various reasons. In this work, rejection techniques for false alarms caused by surface clutter returns through FSL are proposed. The distortion of the measured angle and velocity of the surface clutter are explained, and a measurement process for estimating the true location and velocity of the clutter is derived. Subsequently, two techniques for false alarm rejection are presented. The first technique is based on the look-up table (LUT) of FSL, which is robust but not practical due to the time and cost required to build a LUT with sufficient resolution. In the second technique, false alarms are rejected when they satisfy predefined criteria derived from their common characteristics, and flight test results confirm that false alarms can be effectively rejected by applying the second technique.

Efficient minimum blind area model for system and interference uncertainty

AbstractIn the anti‐interference of broadband communication radio, interference cancellation performance is seriously affected by the uncertainty of the working frequency selection of the communication system and the direction of hostile interference. The closed‐form solution of the interference cancellation weight value and the signal‐to‐interference noise ratio after the cancellation are derived and simplified to clarify the factors affecting interference cancellation quality. Then, the efficient blind area criterion is established for the low computational complexity in view of cancellation quality, which combines the radio communication index and anti‐interference demand index. Based on this criterion, the minimum blind area model is proposed for robust performance. The experimental results in the auxiliary antenna spacing optimisation are consistent with the theoretical analysis, verifying the effectiveness of the proposed model in dealing with uncertain communication frequency and interference direction. It is very promising in communication interference cancellation.

Inhomogeneous energy transfer dynamics from iron-stress-induced protein A to photosystem I.

Cyanobacteria respond to iron limitation by producing the pigment-protein complex IsiA, forming rings associated with photosystem I (PSI). Initially considered a chlorophyll-storage protein, IsiA is known to act as an auxiliary light-harvesting antenna of PSI, increasing its absorption cross-section and reducing the need for iron-rich PSI core complexes. Spectroscopic studies have demonstrated efficient energy transfer from IsiA to PSI. Here we investigate the room-temperature excitation dynamics in isolated PSI-IsiA, PSI, IsiA monomer complexes and IsiA aggregates using two-dimensional electronic spectroscopy. Cross analyses of the data from these three samples allow us to resolve components of energy transfer between IsiA and PSI with lifetimes of 2-3 ps and around 20 ps. Structure-based Förster theory calculations predict a single major timescale of IsiA-PSI equilibration, that depends on multiple energy transfer routes between different IsiA subunits in the ring. Despite the experimentally observed lifetime heterogeneity, which is attributed to structural heterogeneity of the supercomplexes, IsiA is found to be a unique, highly efficient, membrane antenna complex in cyanobacteria.

A novel optimization method for attenuating multi‐interferences in satellite communication earth station

SummaryThe study of multi‐interferences plays a pivotal role in advancing the development of next‐generation, high‐performance communication devices. In this paper, we propose a design approach for auxiliary antennas aimed at mitigating multi‐interference challenges within satellite communication earth stations. We introduce an eight‐element auxiliary antenna with an elliptical beam comprising dual radiation patches and a T‐shaped power divider, to attenuate interferences originating from three distinct directions. To enhance the azimuthal beamwidth, we adjust the dimensions of the ground plane and extend the substrate. At a frequency of 12.5 GHz, the antenna exhibits a 3‐dB beam spacing of 38° and an azimuthal width of 162°, with a maximum gain of 7.9 dBi. We employ a sidelobe canceller to optimize the antenna's performance, and both simulations and measurements affirm that the auxiliary antenna achieves an extinction interference cancelation ratio exceeding 27 dB under all circumstances.

A novel adaptive noise canceling system for urea NQR spectrum analysis

Due to its practical ease of use and sufficiently high reliability, Nuclear Quadrupole Resonance (NQR) has largely been used in remote sensing-based detection of quadrupole nuclei, especially Nitrogen-containing materials. Since the received signal of free induction decay (FID) is inherently weak in this technique, the noise and the interference of the environment would dramatically impair the performance of the detecting systems. To handle such challenges, an adaptive noise canceling method was employed to improve the signal to noise and interference ratio (SNIR) in FID signals. FID signals, noise, and interference were received by the main antenna, while similar noise and interference would be received by the auxiliary antenna. The proposed system significantly reduced noise and interference through the digital noise and interference cancellation algorithm, pulse integration, averaging, and singular spectrum analysis (SSA). Urea powder was empirically analyzed outdoors, suggesting that the proposed adaptive noise and interference cancellation (ANIC) system, effectively suppressed noise and interference by 41.13 dB and amplified the FID signal by 53.36 dB. The strongest signal was detected at 2870.4 kHz.

Elements Selection for Auxiliary Array in the Adaptive Sidelobe Canceller Radar System

In a recent paper, the conventional sidelobe canceller radar system was developed by replacing the separate auxiliary antennas by few elements at the center of the main antenna array. The modified system with reused elements was associated with some attenuation in the desired signal due to the emerging correlation between the signals that exists in the main and the reused array elements. This problem was solved by imposing some constraints on the array pattern of the reused elements. In this paper, few of the side elements of the main array are employed as the auxiliary antennas. This new proposed configuration is called sided-elements. Unlike the previous centered-elements configuration, the proposed sided-elements configuration offers more desired features since the pattern of the side elements has sidelobes of similar widths of those of the main array. Moreover, a better diversity is obtained due to the wider separation between the two groups of elements at both sides of the main array. Simulation results fully confirm the effectiveness of the new proposed sided-elements configuration for suppressing the undesired interfering signals and retaining the desired signal undistorted.

Auxiliary antenna design for anti‐interference of satellite communication earth station

AbstractIn this study, a novel elliptical widebeam auxiliary antenna is proposed for anti‐interference of satellite communication earth station. The wide beam width of about 180° in horizontal plane (H‐plane) is achieved by increasing the width of the substrate, reducing the size of the ground plane and adding a V‐shaped aluminum frame. And the narrow beam width of about 30° in elevational plane (E‐plane) is achieved by designing a binary element array. Only two auxiliary antennas are needed for sampling to cover interference from any azimuth direction in H‐plane. The antenna is fabricated and measured, and the results are in good agreement with simulation. The corresponding −10 dB impedance bandwidth is about 17% with maximum gain of 6.5 dBi. The 3 dB beam widths are respectively 33° and 178° in E‐plane and H‐plane. Furthermore, simulation and experiment of the proposed auxiliary antenna in interference cancelation system verify its anti‐interference performance. According to sidelobe canceler, an average interference cancelation ratio of about 27 dB is achieved.

Taper-tip double-layer grating antenna based on SiN-on-SOI with large scale-scanning range for LiDAR

In this article, with the objective of reducing the emission loss, enhancing the emission directionality and scale-scanning range, without increasing the complexity of the LIDAR system, a CMOS-compatible silicon nitride taper-tip double-layer auxiliary grating antenna is proposed and investigated systematically. Compared to conventional double layer grating, the directionality exceeds 72% for wavelengths from 1450 nm to 1600 nm, with a maximum directionality of 97.5% at 1550 nm. Therefore, the far-field divergence angle of 0.0081° × 0.03° and a large field of view of 108.45° × 23.43° can be achieved when the antenna aperture is 1.6 cm × 2.5 cm. These improvements come mainly from the increasing unidirectional emission performance of the phased array by adjusting the key structural parameters of the inverted taper-tip double-layer structure.

Impacts of Phase Noise on the Anti-Jamming Performance of Power Inversion Algorithm.

Power inversion (PI) is a known adaptive beamforming algorithm that is widely used in wireless communication systems for anti-jamming purposes. The PI algorithm is typically implemented in a digital domain, which requires the radio-frequency signals to be down-converted into base-band signals, and then sampled by ADCs. In practice, the down-conversion circuit will introduce phase noises into the base-band signals, which may degrade the performance of the algorithm. At present, the impacts of phase noise on the PI algorithm have not been studied, according to the open literature, which is, however, important for practical design. Therefore, in this paper, we present a theoretical analysis on the impacts, provide a new mathematical model of the PI algorithm, and offer a closed-form formula of the interference cancellation ratio (ICR) to quantify the relations between the algorithm performance and the phase noise level, as well as the number of auxiliary antennas. We find that the ICR in decibel decreases logarithmically linearly with the phase noise variance. In addition, the ICR improves with an increasing number of auxiliary antennas, but the increment is upper-bounded. The above findings are verified with both simulated and measured phase noise data.

Controllable Phycobilin Modification: An Alternative Photoacclimation Response in Cryptophyte Algae

Cryptophyte algae are well-known for their ability to survive under low light conditions using their auxiliary light harvesting antennas, phycobiliproteins. Mainly acting to absorb light where chlorophyll cannot (500–650 nm), phycobiliproteins also play an instrumental role in helping cryptophyte algae respond to changes in light intensity through the process of photoacclimation. Until recently, photoacclimation in cryptophyte algae was only observed as a change in the cellular concentration of phycobiliproteins; however, an additional photoacclimation response was recently discovered that causes shifts in the phycobiliprotein absorbance peaks following growth under red, blue, or green light. Here, we reproduce this newly identified photoacclimation response in two species of cryptophyte algae and elucidate the origin of the response on the protein level. We compare isolated native and photoacclimated phycobiliproteins for these two species using spectroscopy and mass spectrometry, and we report the X-ray structures of each phycobiliprotein and the corresponding photoacclimated complex. We find that neither the protein sequences nor the protein structures are modified by photoacclimation. We conclude that cryptophyte algae change one chromophore in the phycobiliprotein β subunits in response to changes in the spectral quality of light. Ultrafast pump–probe spectroscopy shows that the energy transfer is weakly affected by photoacclimation.

Ionospheric Clutter Suppression with an Auxiliary Crossed-Loop Antenna in a High-Frequency Radar for Sea Surface Remote Sensing

Ionospheric clutter is one of the main problems for high-frequency surface wave radars (HFSWRs), as it severely interferes with sea surface state monitoring and target detection. Although a number of methods exist for ionospheric clutter suppression, most are suitable for radars with a large-sized array and are inefficient for small-aperture radars. In this study, we added an auxiliary crossed-loop antenna to the original compact radar antenna, and used an adaptive filter to suppress the ionospheric clutter. The experimental results of the HFSWRs data indicated that the suppression factor of the ionospheric clutter was up to 20 dB. Therefore, the Bragg peaks that were originally submerged by the ionospheric clutters could be recovered, and the gaps in the current maps can, to a large extent, be filled. For an oceanographic radar, the purpose of suppressing ionospheric clutter is to extract an accurate current speed; the radial current fields that were generated by our method showed an acceptable agreement with those generated by GlobCurrent data. This result supports the notion that the ionospheric suppression technique does not compromise the estimation of radial currents. The proposed method is particularly efficient for a compact HFSWRs, and can also be easily used in other types of antennas.

Key interactions with deazariboflavin cofactor for light-driven energy transfer in Xenopus (6\u20134) photolyase

Photolyases are flavoenzymes responsible for light-driven repair of carcinogenic crosslinks formed in DNA by UV exposure. They possess two non-covalently bound chromophores: flavin adenine dinucleotide (FAD) as a catalytic center and an auxiliary antenna chromophore that harvests photons and transfers solar energy to the catalytic center. Although the energy transfer reaction has been characterized by time-resolved spectroscopy, it is strikingly important to understand how well natural biological systems organize the chromophores for the efficient energy transfer. Here, we comprehensively characterized the binding of 8-hydroxy-7,8-didemethyl-5-deazariboflavin (8-HDF) to Xenopus (6–4) photolyase. In silico simulations indicated that a hydrophobic amino acid residue located at the entrance of the binding site dominates translocation of a loop upon binding of 8-HDF, and a mutation of this residue caused dysfunction of the efficient energy transfer in the DNA repair reaction. Mutational analyses of the protein combined with modification of the chromophore suggested that Coulombic interactions between positively charged residues in the protein and the phenoxide moiety in 8-HDF play a key role in accommodation of 8-HDF in the proper direction. This study provides a clear evidence that Xenopus (6–4) photolyase can utilize 8-HDF as the light-harvesting chromophore. The obtained new insights into binding of the natural antenna molecule will be helpful for the development of artificial light-harvesting chromophores and future characterization of the energy transfer in (6–4) photolyase by spectroscopic studies.

Development of a direct penetrating signal compensator in a distributed reception channel of a surveillance radar

General structure of a compensator of a direct penetrating signal in the diversed reception channel was developed. It is advisable to use the antenna and the receiver of the auxiliary diverted reception channel as an auxiliary antenna and an auxiliary channel. To be able to suppress the penetrating signal in the band of the receiving device of the surveillance radar, distance between the antennas should be up to 6 m. In general, the compensator of the penetrating signals should contain an adder in which the signals received by the main channel are added with the signals received by the auxiliary channel and sent through the amplifier with a corresponding complex transmission coefficient. The direct penetration signal compensator features the obligatory condition of adjusting the value of the complex transmission coefficient of the auxiliary channel signal amplifier. The direct penetration signal compensator is digital and uses the direct method of forming weighting coefficients without the use of feedback. To reduce the time of formation of weighting coefficients when using direct methods of calculation of the correlation matrix, the technology of parallel computational processes was used. The quality of operation of the direct penetrating signal suppression system in the diverted reception channel was evaluated. It was established that without the use of suppression of direct penetrating signals, their powerful response at the output of the matched filter mask weak echo signals. When using a direct penetrating signal in the main channel of the compensator, its response at the output of the matched filter is significantly reduced. This makes it possible to observe weak echoes against the background of a strong penetrating signal. The use of the developed direct penetrating signal compensator provides suppression of the direct penetrating signal from 57 dB to 70 dB

능동위상배열안테나의 부엽제거기 적용 시 모노펄스 왜곡 보정

The sidelobe canceler is used to remove the received sidelobe jamming signal on the receive antenna pattern. The sidelobe canceler does not use the main antenna but is constructed using an auxiliary antenna. The sidelobe canceler generates a sidelobe cancel beam of the auxiliary antenna using the received signal of the main and auxiliary antennas. The main beam pattern that cancels the jamming signal is generated by combining the main antenna beam and sidelobe cancel beam pattern. However, in the case of a jamming signal received near the main lobe of the main antenna, distortion occurs in the main antenna pattern by applying a sidelobe canceler. Owing to this distortion, the monopulse slope characteristic for the angle estimation of the target is also distorted. This paper proposes a simple and effective method using antenna measurement data (e.g., near-field chamber measured data) to compensate for the monopulse slope distortion that occurs when the sidelobe canceler is applied. The proposed method was verified using simulations wherein the improvement in the distorted monopulse slope characteristics was confirmed.

Improved Sidelobe Recognition Method Using Boresight Error in a Uniform Circular Array for Wideband Direction Finding System

A strong signal through the antenna sidelobes can be interpreted as a main lobe signal and may cause a major angle error in the direction finding system. An auxiliary antenna channel in the Maisel’s sidelobe blanking system increases the cost, and the method using each boresight error (BSE) of the monopulse and interferometer causes many errors in the real antenna. In this paper, a sidelobe recognition method applicable to a wideband uniform circular array without auxiliary antenna channel is proposed. Four boresight errors are obtained from monopulse and interferometer in the circular array and then the maximum value of differences between boresight errors is taken and is compared to the optimal threshold value. The results have the effect of reducing errors occurring in the sidelobe region while maintaining the performance in the main lobe region. To validate the proposed method, a circular array antenna with eight wideband microstrip antennas is designed and manufactured. As a result, there is a significant improvement in the error rate compared to the existing method. It is confirmed that there is no error when the threshold value is from 0.5 ° to 0.7 ° at 6, 9, and 12 GHz, and the error rate is less than about 1 % when the threshold value is between 0.4 ° and 1.0 °.

Efficient DOA Estimation Method Using Bias-Compensated Adaptive Filtering

We consider the DOA estimation problem by using adaptive nulling antenna technology and bias-compensated adaptive filtering framework. The adaptive nulling antenna array consists of one reference antenna element and multiple auxiliary antenna elements, which forms nulls in certain directions. By defining the reciprocal of array pattern as the spatial spectrum, the DOA estimation problem is considered as the peak searching for it. In this paper, we present an efficient bias-compensated adaptive filtering algorithm for DOA estimation based on the adaptive nulling array. First of all, a new noise-free mean square error (NF-MSE) cost function associated with the adaptive nulling array is provided. Secondly, the proposed algorithm, called variable step-size bias-compensated least mean square (VSS-BC-LMS) algorithm, can be derived by minimizing the NF-MSE. Due to the bias compensation, the bias of the estimated weight vector caused by noises is canceled. More importantly, in order to resist the unsatisfactory DOA estimation performance when using the fixed step-size, a variable step size scheme is introduced. And then, its mean stability, steady state mean square performance and computational complexity are discussed. Additionally, we also explore a noise variance estimation method for calculating the bias term. Simulation results indicate that the proposed algorithm achieves an improved DOA estimation performance compared with other adaptive methods.

A blind source separation jamming suppression method based on channel ratio function

ABSTRACT In order to counteract the main lobe multi-false target jamming of radar, a blind source separation jamming suppression method based on channel ratio function is proposed. The cross-polarised auxiliary antenna is used to expand the receiving channel, and the blind signal processing method is used to separate the jamming from the target echo. This method utilises the statistical characteristics of channel ratio function and chooses the time unit with only jamming to process. And it realises jamming suppression and echo extraction. The simulation results show that the proposed method has good jamming suppression performance and is not affected by channel noise and polarisation purity of auxiliary antenna.

Dual antenna system for metal frame mobile phone applications

A dual antenna system with 77 mm × 10 mm × 7.5 mm for metal frame (MF) LTE/GPS mobile phones is proposed and studied. The antenna proposed in this study comprises two antenna elements (Ant 1 and Ant 2) and a decoupling line. Ant 1 as the main antenna that covers the lower band (698-960 MHz), the GPS band, and the higher band (1710-2690 MHz) consisting of a ground branch, a coupled line, and a tuning line. Ant 2 as the auxiliary antenna that covers the higher band consisting of a monopole branch and a match circuit. Ant 1 and Ant 2 form a two-element MIMO antenna covering the higher band. The advantages of the proposed antenna are that the main antenna (Ant 1) covers the GPS band and all of the 2G/3G/4G bands, and the two-element MIMO antenna covering the higher band, which consists of Ant 1 and Ant 2 located at the same side of a mobile phone with an MF, is obtained. A prototype is manufactured and tested. For Ant 1, the measured working bands (under −6 dB condition) are 685 to 965 MHz and 1480 to 2800 MHz, and the LTE700, GSM850, GSM900, GPS, GSM1800, GSM1900, UMTS, LTE2300, and LTE2500 bands are covered. For Ant 2, the measured working band (under −6 dB condition) is 1640 to 2720 MHz, and the GSM1800, GSM1900, UMTS, LTE2300, and LTE2500 bands are covered. The measured isolations between Ant 1 and Ant 2 are larger than 12 dB at the working bands. The measured efficiencies, envelope correlation coefficients, and mean effective gains are also presented.

Integrated 4G/5G Multiservice MIMO Antenna for Hand-Held Devices

A novel compact monopole antenna with integrated services for 4G/5G application has been proposed in this manuscript. The 4G services such as Long Term Evolution (LTE) and GSM 850/900 is provided by the primary antenna of size 45 × 15 mm. The 5G communication services are supported by the auxiliary antenna of size 19 × 15 mm. The monopole radiator with the combination of multi-branch stubs and meandered structures in the primary radiator introduces the resonance at the desired operating frequency. The impedance bandwidth of the primary antenna is 170 MHz (0.8–0.97 GHz) and 900 MHz (1.8–2.7 GHz) for LTE and GSM applications. The impedance bandwidth of the auxiliary antenna is 7 GHz (13–20 GHz) for 5G application bands. To achieve the desired operating bands, the length and width of the stubs are used as the tuning parameters. The large ground plane of size 200 × 150 mm is used as the mock-up system for the proposed antenna structure. To enhance the coverage of the handheld devices, the primary and auxiliary antenna is integrated in the mock-up system. The efficiency and gain of the antenna are in the range of 3–5 dBi and 70–96%. The simulated and measured results are correlated with each other.