Large Aperture Antenna Research Articles

Si photonic crystal optical antenna serial array and frequency-modulated continuous-wave light detection and ranging action

Photonic crystal waveguide slow-light grating emits a free-space optical beam and steers it widely by changing the optical wavelength or waveguide refractive index. In the reverse process, returned light is coupled into the device again. We have proposed to use this optical transmission and reception antenna as a beam scanner for light detection and ranging (LiDAR). Ideally, a large-aperture antenna can narrow the transmission beam and enhance the reception efficiency. Actually, however, the transmission and reception performance is not scalable owing to waveguide loss even though the waveguide is simply lengthened. A serial array configuration in which the waveguide is divided into multiple antennas is effective for mitigating this problem. In this study, we fabricated such a device using Si photonics technology and obtained a small beam divergence of 0.02° at a telecom wavelength. Then, we observed the ranging operation by adding an optical setup of frequency-modulated continuous-wave (FMCW) LiDAR and confirmed that the divided antenna device improved the reception intensity by 12 dB. Moreover, we fabricated a FMCW LiDAR chip in which the serial array antennas were integrated in parallel with switch trees and Ge photodiodes and obtained point cloud images by two-dimensional beam scanning.

A dual-beam lens-free slot-array antenna coupled high-T c superconducting fundamental mixer at the W-band

This paper presents a W-band high-T c superconducting (HTS) Josephson-junction fundamental mixer which is coupled using a dual-beam lens-free slot-array antenna. The antenna features a uniplanar six-element slot array fed by an ungrounded coplanar waveguide line, of which each element is a long slot loaded by four rectangular loops. Highly directional radiation is therefore realized by utilizing the long slots and array synthesis to form a relatively large antenna aperture. The antenna also enables asymmetric dual-beam radiation in opposite directions, which not only reduces the RF coupling losses but greatly facilitates the quasi-optics design for the integration of the HTS mixer into a cryocooler. The electromagnetic simulations show that a coupling efficiency as high as −2.2 dB, a realized gain of 13 dB and a front-to-back ratio of 10 dB are achieved at the frequency of 84 GHz. Using this on-chip antenna, a W-band HTS fundamental mixer module is experimentally developed and characterized for different operating temperatures. The measured conversion gain is −10 dB at 20 K and −14.6 dB at 40 K, respectively. The mixer noise temperature is predicted to be around 780 K at 20 K and 1600 K at 40 K, respectively. It is also analyzed that the mixer performance can be further improved if the Josephson junction parameters were optimized.

Method of Pointing Temperature Compensation for Deep Space Large Aperture Antenna

In order to achieve long-distance measurement and control of deep space detectors, increasing the aperture is the most direct means to improve antenna performance. However, the increase in antenna size brings structural instability and is easily affected by external environments such as temperature, gravity, and wind gusts. Aiming at the problem that temperature changes affect the antenna pointing accuracy, this paper designs and implements an antenna pointing temperature compensation model, and conducts data collection and test verification. The results show that the antenna pointing accuracy can be compensated effectively under a large temperature environment by the method proposed in this paper, and the received signal strength is improved.

Influence Analysis of Strong Wind on the Performance of Deep Space Large Aperture Antenna

With the continuous increase of the deep space detection range, the establishment of the space-to-earth link and the stable transmission of the signal are the main problems facing. Increasing the antenna aperture of the ground-based measurement and control equipment can effectively improve the signal receiving sensitivity. However, the increase in antenna size brings about an increase in wind resistance. Strong wind will cause resistance to the driving of large-aperture antennas in deep space and cause certain deformations in the structure. This article takes a 35-meter-aperture antenna as an example, aiming at the antenna being orthogonal and parallel to the wind direction, the simulation analysis was performed under the influence of strong wind in the two cases, and the deformation cloud image of the antenna mouth surface was obtained. The antenna gain loss caused by the deformation error of the main surface and the translation of the secondary reflection surface was calculated, and the maximum gain loss reached 3.70dB.

Optimal Design of Antenna for Spaceborne SAR Based on Differential Evolution Algorithm

An important feature of future spaceborne synthetic aperture radar (SAR) is the adoption of large mesh reflectors fed by arrays. The main advantage of this SAR sensor is the provision of large antenna apertures and reconfigurable feed excitation. A large deployable mesh-reflector antennas combinaed with feed arrays is designed for the application of spaceborne SAR on geosynchronous orbit. To decrease the transmit power of feed element and increase the flexibility, a large scale of two-dimensional feedarray is adopted. An approach based on defocused reflector is used to broaden the beams from feed element, so almost all the feed elements can participate in the pattern synthesis in the complete angular domain. This paper presents a new optimization method of the defocused reflector system. The method aims at getting high gain and low sidebobes by optimizing the reflector parameters together with the feed array. The differential evolution algorithm(DE) is used to get globally optimal solution. The performance of the reflector after optimization is computed to demonstrate the effective of the method presented.

Cognitive Antenna Selection for Automotive Radar Using Bobrovsky-Zakai Bound

Automotive imaging radars require high angular resolution which can be achieved by a large antenna aperture. In order to obey Nyquist spatial sampling rate, a large number of array elements and receive channels is required. In practice, this solution results in a prohibitively high cost and complexity. This work proposes a new cognitive receiver configuration, in which a large number of sensor array elements is connected to a small number of receive channels via a switching matrix. The state of the switching matrix is sequentially updated using information from previous observations and prior information. According to the proposed scheme, denoted as cognitive antenna selection (CASE), the state of the switching matrix is obtained by the minimization of conditional Bayesian bounds on the mean-squared-error of the direction-of-arrival estimate. We show that the Bayesian Cramér-Rao bound (BCRB) is an inappropriate optimization criterion since it ignores the effect of ambiguity. This work proposes the Bobrovski-Zakai bound (BZB), which accounts for the effect of ambiguity, as a criterion for cognitive antenna selection. The performance of the proposed CASE-BZB approach is evaluated via simulations in single and multiple target scenarios. It is shown that the CASE-BZB outperforms random and linear switching algorithms both asymptotically and in the threshold region.

Influence of climatic factors on the amplitude-phase field distribution at the digital antenna array aperture

Problem statement. During operation, stationary large-aperture digital antenna arrays (DAA) are affected by climatic factors, including snow and ice cover. This influence inevitably leads to distortion of the amplitude-phase distribution (APD) of the field at the DAA aperture, which makes it necessary to consider and compensate for these factors on the APD of the antenna array field.Objective. Development of a more technically simple and precise method for compensating for APD field distortions at the aperture of a stationary large-aperture DAA caused by the influence of climatic factors of snow and ice cover.Results. The article analyzes the influence of climatic factors of snow and ice on the distortion of the APD field at the DAA aperture. The dependence of the power reduction of the probing signal on the thickness of the snow and ice layer at the aperture is obtained. The correction method of APD field distortions caused by climatic factors’ influence is developed, which is characterized by simplicity of technical implementation and higher accuracy of correction of distortions. A technical realization of the method of correction of distortions of the APD field is proposed.Practical implications. The developed method can be used at the stages of creation and operation of stationary large-aperture DAAs, taking into account the influence of climatic factors of snow and ice cover on the field APD.

Correction Method of Antenna Pointing Error Caused by the Main Reflector Deformation

The pointing accuracy of a radio telescope is usually less than one-tenth of its antenna beam width. For large-aperture antennas at the short-centimeter band or millimeter-wave band, the pointing accuracy must be as high as several arc seconds. Therefore, for large-diameter and high-frequency reflector antennas, the pointing problem has become an important focal point to realize the antenna performance. Among many structural subsystem factors that affect the antenna pointing accuracy, there has been only less study on the factor of main reflector deformation. Based on the structural characteristics of the antenna, a reflector space coordinate system is established in this paper. And based on the space coordinates of the main reflector surface points after deformation, a non-linear least squares fitting method with 3 degrees of freedom is proposed to accurately predict the antenna pointing. Finally, the space geometric relationship is used to strictly derive the precise adjustments on the elevation and azimuth in order for correcting the antenna pointing error, and the indirect relationship between the main reflector deformation and the pointing error is constructed. This has certain guiding significance for improving the pointing accuracy of large radio antennas.

In vivo liver thermoacoustic imaging and demonstration based on localization wire.

Liver disease causes significant morbidity and mortality worldwide. Liver imaging plays an essential role in the noninvasive liver disease evaluation because of the limitation of liver biopsy. This paper aims to image in vivo liver with thermoacoustic imaging (TAI) and demonstrate this liver imaging technique with a cross-validation method. The imaging system composed of a large aperture antenna and a flexible transducer array was used, and we performed the position calibration using the delay and sum algorithm. The localization wire was utilized in the cross-validation of in vivo liver TAI. We successfully validated in vivo liver TAI. In vivo images of different liver lobes without labels were observed. The imaging depth reached about 4cm. TAI has the potential to image the liver and provide useful dielectric properties of the liver tissue. This study realized the first in vivo liver TAI, suggesting its prospect in detecting liver disease noninvasively.

A Fabry-Perot Cavity Antenna With Non-Uniform Superstrate and EBG Ground for High Gain and High Aperture Efficiency

A design of high-gain Fabry-Perot cavity (FPC) antenna is presented with non-uniform frequency selective surface (FSS) superstrate and electromagnetic band gap (EBG) reflecting ground. The non-uniform FSS superstrate and EBG ground are utilized to flexibly control the attenuation constant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> over a large antenna aperture while ensuring the resonance condition of the FPC. The uniformity of the amplitude of the aperture field is improved significantly while obtaining appropriate radiation efficiency. Therefore, the high gain and high aperture efficiency can be achieved within a desirable bandwidth. The theoretical gain estimation is conducted to prove the superiority of the proposed antenna over a referenced uniform one. A straight-forward design methodology is proposed based on the radial leaky-wave theory and the modified transverse equivalent network (TEN) model. The non-uniform high-gain FPC antenna with a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.6\lambda _{0}$ </tex-math></inline-formula> is designed at the frequency of 15 GHz. Simulated results show that a gain of 24.6 dBi with an aperture efficiency of 67.9% has been achieved. The measured gain is 24.0 dBi with an aperture efficiency of 58.4%. The 10dB return loss bandwidth and 3 dB gain bandwidth are 5.3% and 3.2%, respectively. The proposed antenna overcomes the limit on aperture efficiency and gain of conventional uniform FPC antennas, and the presented methodology can guide the design of two-dimensional non-uniform high-gain FPC antennas.

Generation of SAR Images Using Deep Learning

Synthetic aperture radars (SAR) are a type of high-resolution radars that are used for terrestrial and airborne imaging. They use a moving source to simulate a large antenna aperture, thereby providing a high-quality map of the surroundings. They are popular due to their wide variety of applications in airborne naval and defense systems as well as topography and seismology. In defense applications, they are mainly used for reconnaissance and mapping of enemy targets such as armored vehicles, tanks, and runways. In recent times, there has been a heavy need for machine learning algorithms that are capable of automatically recognizing the targets detected by the SAR without human input. Such algorithms demand large-scale labeled datasets for training, validation and testing. Due to the nature of the SAR, acquisition and collection of these labeled datasets is quite a tedious and expensive task requiring a lot of man hours. Thus, alternate methods to produce new SAR image data are needed. In this paper, generative adversarial networks (GAN) are used to generate new spotlight SAR images from a limited pre-existing dataset. To quantitatively verify the effectiveness of the images produced by the GAN, a novel convolutional neural network (CNN) is devised and trained on the Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset images.

Hardware and Software Implementation for Global Navigation Satellite System Signal Processing by Temporary Accumulation Method to Monitor Radio-navigation Signals

Currently, a scope of satellite radio-navigation applications is more and more extending. Accordingly, there are also increasing requirements for the quality of determining coordinates and time. Therefore, radio-navigation signals monitoring, in particular their waveform control, waveform distortion analysis, is a challenge. However, a power of navigation signals is lower than the noise level, therefore, the special methods and equipment, which provide increasing a signal-to-noise ratio, are necessary to analyze their waveform. Usually, complexes based on the large aperture antennas are used for this purpose. But they have a number of disadvantages, namely high complexity, high price, large size, necessity to guide and track each individual satellite.The paper gives a brief description of the temporary accumulation method (TAM). This method can be applied to signals containing repetitive elements (basic elements). Radio-navigation signals are such signals. TAM allows you to increase the signal-to-noise ratio and evaluate the waveform of signal basic elements by superimposing and averaging the appropriate signal samples. Gain increases with increasing accumulation time.The paper proposes a small-scale breadboard of the software-hardware complex to monitor signals of global navigation satellite systems (GNSS) based on an omnidirectional antenna, a software-defined radio system, and a personal computer. This breadboard allows recording of digital samples of the navigation signals observed, and then their processing by the temporary accumulation method.Presents operation estimates of the proposed breadboard for monitoring GNSS signals. Gives estimates of the GLONASS navigation signal waveforms in the time domain (signal basic elements) and in the frequency domain (energy spectrum). Also based on the use of TAM, estimates the signal power and energy gain. Proves that using the hardware-software complex proposed for radio-navigation signals monitoring is possible.The proposed scheme of the small-scale breadboard for monitoring GNSS signals can be used directly for monitoring and also to test various methods and technologies of navigation signal processing based on the use of information about the waveform of the received signal.

High-Gain Millimeter-Wave Holographic Antenna in Package Using Glass Technology

A novel concept for a holographic antenna in package is presented, enabling the seamless integration of high-gain antennas at millimeter-wave frequencies. The antenna is based on a holographic impedance approach stimulating a leaky wave mode at 150 GHz. Since the antenna structure is placed on top of the glass package, a large antenna aperture with high angular beamwidth and efficiency was achieved. The surface wave launcher of the antenna connected to the integrated active circuitry is designed in a very compact fashion using a vertical through-glass-via and solder balls. The performance of the proposed holographic antenna package has been investigated by an analytic model and full-wave simulations. The measurement results of the antenna prototype on glass using anisotropic unit cells show excellent agreement to the simulated values. A maximum gain of 24.7 dBi, a sidelobe level of 15 dB, and a 3 dB beamwidth of 4.7 $^\circ$ are achieved. The measured 3-D radiation pattern shows a highly directive pattern in all cuts.

On Computing the Mutual Coupling Between Two Antennas

The calculation of mutual coupling usually demands intense computations, especially for large aperture antennas placed in the near-field region of each other. In this article, the validity of an integral coupling formula is evaluated to demonstrate its utilizations where an efficient method for computing mutual coupling is most required. The integral coupling formula is used to compute the mutual coupling between two antennas in the near-field and far-field regions. The formula demonstrates fast and accurate computing properties based on typically available information such as 3-D vector far-field patterns and antenna configurations. Based on the coupling formula, a comprehensive evaluation is performed with respect to diverse antenna configurations, computation time, accuracy, and different polarizations. The expanded applicability of the formula is also examined through an antenna configuration, which includes a circular polarization selective surface (CPSS) structure to reduce the level of mutual coupling.

A novel modular deployable mechanism for the truss antenna: Assembly principle and performance analysis

The truss antenna based on the tetrahedral deployable mechanism has the advantages of good deployment stability, high stiffness, large folding rate and high profile accuracy. A new modular deployable antenna mechanism based on the 3RR-3URU tetrahedral symmetrical combination unit is proposed in the present study. It should be indicated that the construction method of the modular mechanism is proposed initially based on the 3RR-3URU tetrahedral symmetrical combination unit as a basic module. The assembly method of modular mechanism and the arrangement of the joints connecting different modules are introduced in detail. Moreover, the large aperture antenna mechanism composed of more modules is described. The basic module and the modular mechanism composed of multiple modules belong to the spatial multi-closed-loop mechanism, so the degree of freedom (DOF) of the one-circle modular mechanism is analyzed by using the idea of ‘equivalent mechanism’ and screw theory. Moreover, the law of DOF of the multi-circle modular mechanism is further explored. The screw topological graph and screw coefficient matrix are applied for this kind of multi-closed-loop mechanism to obtain the results of the reasonable choice of actuation. Then, kinematics analysis of the modular mechanism is completed by the coordinate transformation and vector method. The folding rate is discussed and compared with other mechanisms for the truss antenna based on the kinematics. Finally, the simulation analysis model is established by using Solidworks and Adams modeling and simulation software. The correctness of the DOF and kinematics theory analysis is verified by the simulation analysis. Furthermore, the proposed mechanism is compared with the existing mechanisms. The proposed modular deployable antenna mechanism has the advantages of large folding rate and high reconfigurability. Therefore, it obtains great application prospects in the fields of the aerospace deployable antennas.

MOM/GA-Based Virtual Array for Radar Systems.

This paper introduces a novel antenna array synthesis for radar systems based on the concept of a virtual antenna array (VAA) and the method of moments/genetic algorithm (MoM/GA) synthesis method. The VAA concept is applied to both scanning and fixed radiation pattern arrays. The proposed VAA is introduced to simultaneously support the medium-range radar (MRR) and the long-range radar (LRR) with beam width ±7° for LRR and ±37° for MRR. The proposed VAA is distinguished by its minimum number of antenna elements, simple feeding network, high efficiency, and gain, but all of these are at the expense of a large aperture antenna size compared to the planar antenna array (PAA). The VAA has the ability to have the feeding network and the radiating elements on the same layer, as compared to the multilayer PAA. The newly proposed concept is analyzed and verified analytically and experimentally. Two orthogonal (16 elements) VAAs are designed to operate in the frequency range from 23.55 to 24.7 GHz and to support a flat-shoulder shape (FSS) radiation pattern for LRR/MRR. The antenna was fabricated and tested experimentally, and good agreements between the simulated and measured results were noticed. The proposed VAA is introduced to solve the problems of large size, low isolations, low efficiency, feeding network, low resolution, and small coverage range for the antenna arrays of automotive radars. The proposed antenna array is introduced for automotive radar applications at 24 GHz.

Precise Internal Calibration Scheme for Very-High Resolution SAR System and Its Airborne Campaign Results

For future ultra-high resolution spaceborne SAR missions, large beam-steering capability and large antenna aperture are demanded to increase the azimuth resolution and to maintain the sensor sensitivity simultaneously. Thus, large-deployable antenna is a desirable option as compared with planar array antenna for these missions, since it is advantageous in terms of mass, size, and cost. Moreover, its antenna pattern will not have any distortion with mechanical beam-scanning approach. In this paper, a novel reflector SAR system, including its platform configuration, attitude maneuvering strategy as well as SAR payload electronics are presented in detail. Furthermore, the key technique of very-high resolution SAR-internal instrument calibration scheme is also provided so as to remove the imbalance among channels to guarantee coherency and then to extract the range replica consequently. In the end, a carried-out airborne flight campaign is described and its imaging results are presented to validate the effectiveness of our system as well as calibration approach.

Reduction of the Reconstruction Error With Lower and Upper Bounds in Synthetic Aperture Imaging Radiometers

Synthetic aperture imaging radiometers (SAIRs) are powerful instruments for high-resolution Earth observation by use of small-aperture antennas sparsely arranged to achieve a large-aperture antenna. High-precision reconstruction algorithm is one of the key contents of SAIRs. Owing to the ill-posed problem and band-limited physical characteristic, there is a still large residual error for traditional regularization methods. It should be noted that the prior information like the lower and upper bounds of the brightness temperature distributions has not been utilized in the reconstruction procedure, especially for the open ocean with relatively small brightness temperature difference. In order to reduce the reconstruction error in SAIRs, a reconstruction method based on active set algorithm is presented by solving the least squares problems with lower and upper bounds. The simulation experiment results show that the proposed method can more effectively reduce the reconstruction error and better improve the accuracy of retrieved brightness temperature distributions in SAIRs than the band-limited regularization method, demonstrating the effectiveness of the proposed method.

Distributed Radar Sounder: A Novel Concept for Subsurface Investigations Using Sensors in Formation Flight

Spaceborne radar sounders are nadir-looking sensors operating in the high frequency (HF) or very high frequency (VHF) bands with subsurface sensing capabilities. Due to technological limitations, this type of sensors often deploys omnidirectional antennas. This results in undesired artifacts such as off-nadir clutter which could hinder data interpretation. Very recent technological advancements open up the possibility of synthesizing very large antenna apertures in HF/VHF band by using small satellites array deployed in suitable orbital formation flying. Accordingly, in this study, we propose a novel concept of distributed radar sounder system. The proposed concept is complemented with a mathematical model for performance prediction which takes into account the uncertainty on the position of the sensors. Moreover, we discuss possible orbital solutions for the problem of the deployment of the distributed radar sounder system. The results show that a distributed radar sounder operating in small satellites formation flying is particularly appealing as it can: 1) substantially reduce the impact of surface clutter; 2) increase the across-track resolution; 3) increase the signal-to-noise ratio (SNR) (or, alternatively, decrease the overall required transmitted power with respect to a traditional single configuration radar sounder design); and 4) provide large flexibility in the data processing of the signals acquired by the different sensors.

Derivation of surface shape for inflatable large aperture antennas

Large deployable aperture inflatable antennas are an emerging technology that is being investigated for potential use in science and exploration missions. In particular, for missions to Mars and beyond, large deployable aperture antennas can provide the antenna gain required for high data rate communications, where the necessary antenna diameter exceeds the available volume of typical launch vehicle platforms. Previous efforts have found that inflatable large aperture antennas do not follow a parabolic shape, and so the nominal Ruze equation is not applicable due to the macroscopic shape errors that exist in this type of technology. Therefore, geometric evaluations of the surface profile cannot simply correlate root‐mean‐square shape error with a parabolic surface to antenna gain degradation. Consequently, the focus of this work is to derive an accurate mathematical model of an inflatable large aperture antenna so that its performance can be characterized. That derivation activity is described in this paper through the calculus of variations methodology, augmented with experimental test data obtained with a laser radar system to validate the surface profile model predicted.