Coding metasurfaces make it possible to manipulate electromagnetic(EM)waves digitally by means of several discrete particles.Hence,there have been rapid advances in this field recently.Here we propose a novel design o...Coding metasurfaces make it possible to manipulate electromagnetic(EM)waves digitally by means of several discrete particles.Hence,there have been rapid advances in this field recently.Here we propose a novel design of a broadband transmission-type coding metasurface,which is valid to both x-and y-polarized EM incidences from 8.1-12.5 GHz while satisfies the requirements of 1-bit coding without changing the polarization.Two types of multi-layer coding particles with different geometrical parameters are adopted to represent the digital states"0"and"1",which are easily promoted to terahertz and optics through modifying the size scale.To verify the ability to manipulate the EM waves,we first adopt the coding metasurface to achieve broadband beam forming by converting spherical waves to plane waves and realize high-directivity pencil beam in far field with low side lobes.We further arrange the particles according to the coding sequence 010101…to steer two symmetrical beams in different directions controlled by frequencies with the maximum range of the scanning angle of 30°-50.5°.The good agreements between the simulated and measured results validate the proposed broadband coding metasurface,indicating its huge potential in communication and radar imaging systems.展开更多
A convolutional weighting （CW） scheme applied to a half-wavelength spacing array was proposed for multi-user system to joint STBC （space time block ceding） and beam forming （BF）. The transmitting beam is equival...A convolutional weighting （CW） scheme applied to a half-wavelength spacing array was proposed for multi-user system to joint STBC （space time block ceding） and beam forming （BF）. The transmitting beam is equivalent to the product of two sub-beams. One is used to realize interference suppression, while the other is employed to form a couple of uncorrelated channels from base station （BS） to the desited user （to meet the requirement of STBC） and to maximize SINR （signal-to-interference-plus noise ratio） at the desired receiver. As an optimum combination of STBC and beam forming, the proposed scheme can achieve both full diversity order of STBC and array gain of BF. Meanwhile, it can also effec- tively restrain multi-user interference by nulling. Simulation results show that the proposed scheme can significantly improve the BER （Bit Error Rate） performance and enhance system capacity as compared with the conventional eigen-beamforming （EBF） technique applied to a half-wavelength spacing array.展开更多
A multi-beam adaptive antenna is investigated by considering the adaptive beam forming performance for time-variant channels on the focus of mobile to base station or reverse link. This antenna is constructed by Fresn...A multi-beam adaptive antenna is investigated by considering the adaptive beam forming performance for time-variant channels on the focus of mobile to base station or reverse link. This antenna is constructed by Fresnel zone phase-correcting plane （FZP） focusing element and uniformly spaced feeds array. An estimator for the beamforming weight vector in the presence of angle spreads is derived using a code filtering approach. Owing to the time-varying nature of the channels, a recursive method for computing and tracking the above optimal weight vector solution that is easy to implement is applied. The effects of angle spread, maximum Doppler frequency, and forgetting factor are studied. Simulation results showed that this type of adaptive antenna is capable of performing adaptive beam forming for time-variant channels effectively.展开更多
Improvement of frame-rate is very important for high quality ultrasound imaging of fast-moving structures.It is also one of the key technologies of Three-Dimension(3-D) real-time medical imaging.In this paper,we have ...Improvement of frame-rate is very important for high quality ultrasound imaging of fast-moving structures.It is also one of the key technologies of Three-Dimension(3-D) real-time medical imaging.In this paper,we have demonstrated a beamforming method which gives imaging frame-rate increment without sacrificing the quality of medical images.By using wider and fewer transmit beams in combination with four narrower parallel receive beams,potentially increasing the imaging frame-rate by a factor four.Through employing full transmit aperture,controlling the mainlobe width,and suppressing sidelobes of angular responses,the inherent gain loss of normal parallel beamfomer can be compensated in the maximal degree.The noise and interference signals also can be suppressed effectively.Finally,we show comparable lateral resolution and contrast of ultrasound images to normal single widow weighting beamformer on simulated phantoms of point targets,cyst and fetus of 12th week.As the computational cost is linear with the number of array elements and the same with Delay And Sum(DAS) beamformers,this method has great ad-vantages of possibility for high frame-rate real-time applications.展开更多
Recently, unmanned aerial vehicles （UAVs） acting as relay platforms have attracted considerable attention due to the advantages of extending coverage and improving connectivity for long-range communications. Specifi...Recently, unmanned aerial vehicles （UAVs） acting as relay platforms have attracted considerable attention due to the advantages of extending coverage and improving connectivity for long-range communications. Specifically, in the scenario where the access point （AP） is mobile, a UAV needs to find an efficient path to guarantee the connectivity of the relay link. Motivated by this fact, this paper proposes an optimal design for beamforming （BF） and UAV path planning. First of all, we study a dual-hop amplify-and-forward （AF） wireless relay network, in which a UAV is used as relay between a mobile AP and a fixed base station （BS）. In the network, both of the AP and the BS are equipped with multiple antennas, whereas the UAV has a single antenna. Then, we obtain the output signal^to-noise ratio （SNR） of the dual-hop relay network. Based on the criterion of maximizing the output SNR, we develop an optimal design to obtain the solution of the optimal BF weight vector and the UAV heading angle. Next, we derive the closed-form outage probability （OP） expression to investigate the performance of the dual-hop relay network conveniently. Finally, computer simulations show that the proposed approach can obtain nearly optimal flying path and OP performance, indicating the effectiveness of the proposed algorithm. Furthermore, we find that increasing the antenna number at the BS or the maximal heading angle can significantly improve the performance of the considered relay network.展开更多
In this paper, we analyze the scheme of Space-Time Coded BeamForming (STC-BF)for the downlink of DS-CDMA system over frequency-selective fading channels and give the numericalsimulations on the scheme. The blind multi...In this paper, we analyze the scheme of Space-Time Coded BeamForming (STC-BF)for the downlink of DS-CDMA system over frequency-selective fading channels and give the numericalsimulations on the scheme. The blind multiuser detection is employed at receiver to suppress theMulti-Access Interference (MAI). The Space-Time Coding (STC) and BF are combined to mitigate theperformance degradation due to multipath fading and various interferences. The numerical simulationsshow that the BF can compensate the performance loss of STC due to the channel correlation and thenthe STC-BF can greatly improve the performance of CDMA system.展开更多
The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas invol...The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas involved in these gadgets are to be designed very stringently so as to avoid interferences & coupling and to improve compatibility, susceptibility, etc. Compact smart antenna with improved performance is highly essential to meet this challenging scenario. Mutual coupling between various elements of an array is one of the main factors which can be considered for improvement of performance of the antenna. Influence of mutual coupling on performance of the antenna is considered in this paper and various techniques to minimize this effect are presented. Effect of mutual coupling on radiation characteristics of the antenna can be compensated employing various methods like Conventional Mutual Impedance (CMI), Receiving Mutual Impedance (RMI). Analysis is presented as comparison between the two methods for different number of elements in the array. Analysis is also presented for different geometries of the array like circular and elliptical for improved performance. The results show performance improvement in the proposed array for parameters like SNR and Speed of convergence.展开更多
With the increasing demand for high speed reliable communications, smart antennas, such as the Butler Matrix array, can be used to develop a system that increases the performance of a wireless system. The Butler matri...With the increasing demand for high speed reliable communications, smart antennas, such as the Butler Matrix array, can be used to develop a system that increases the performance of a wireless system. The Butler matrix is a switched beam array system which can produce orthogonal uniform beams. The main objective is to improve the efficiency of the power in a 90-degree bend. Also, the double-mitered bend is particularly interesting since it provides a substantially lower reflection coefficient and a lower value of S12 at a frequency of 2.4 GHz compared to an unmitered one. Therefore, this paper describes an optimum design using a double-mitered method with a 2 × 2 and a 4 × 4 Butler Matrix array, operating at 2.4 GHz which is used in wireless systems with an FR4 substrate.展开更多
Time-modulated array(TMA)antennas,introduce the dimension of time into antenna design to control the radiation patterns and frequency spectral characteristics,thus improve the reconfigurability of array antennas and p...Time-modulated array(TMA)antennas,introduce the dimension of time into antenna design to control the radiation patterns and frequency spectral characteristics,thus improve the reconfigurability of array antennas and provide multiple functional-ities.They have great application potential in military and civilian fields,such as precision guidance and mobile communication,and are currently a hot spot of academic research.This article provides a review on the fundamentals and applications of TMAs.First,the basic theory and mathematical formulations of TMAs are introduced.Second,the most important applications of TMAs,namely time-modulated phased arrays(TMPA),are discussed from the perspectives of harmonic suppression and harmonic utiliza-tion,which are used for single-beam and multibeam radiation.Then,we survey the combination of TMA with various types of novel antenna arrays,such as single-channel digital beamforming(DBF)arrays,frequency diverse arrays(FDAs),and retrodirective arrays,to create new hardware implementation methods and enhance their performance.Next,recent advances in dedicated integrated chips for TMA,which have played a significant role in driving the progress of TMAs from academic research to practical applications,are presented.Finally,the challenges and prospects for TMAs are discussed,including new research directions and emerging applica-tion scenarios.展开更多
We propose and simulate a method for generating a three-dimensional （3D） optical cage in the vicinity of focus by focusing a double-ring shaped radially and azimuthally polarized beam. Our study shows that the combi...We propose and simulate a method for generating a three-dimensional （3D） optical cage in the vicinity of focus by focusing a double-ring shaped radially and azimuthally polarized beam. Our study shows that the combination of an inner ring with an azimuthally polarized field and an outer ring with a radially polarized field and a phase factor can produce an optical cage with a dark region enclosed by higher intensity. The shape of the cage can be tailored by appropriately adjusting the parameters of double-mode beams. Furthermore, multiple 3D optical cages can be realized by applying the shift theorem of the Fourier transform and macro-pixel sampling algorithm to a double-ring shaped radially and azimuthally polarized beam.展开更多
The performance of ground moving target detection for distributed satellites will be affected signifi-cantly when there is an image registration error,clutter decorrelation and array error.In this paper,a new approach...The performance of ground moving target detection for distributed satellites will be affected signifi-cantly when there is an image registration error,clutter decorrelation and array error.In this paper,a new approach to moving target detection and relocation is proposed based on multi-channel and multi-pixel adap-tive signal processing in an image domain.First,multi-channel and multi-pixel joint data are equated to a simple array model.Given that there is an image registration error,the real steering vector of the moving target can be estimated through a space projection approach.The optimal beam forming approach is used to cancel clutter,and at the same time the cross-track velocity of the mov-ing target can be determined by searching for the peak value of the cost function.The moving target can then be relocated on the SAR image.The simulation results indicate that this method has a good robustness to image registration error,clutter decorrelation and array error.The detection performance and the estimation accuracy are significantly improved.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0700201,2017YFA0700202,and 2017YFA0700203)the National Natural Science Foundation of China(Grant Nos.61631007,61731010,61735010,61722106,61701107,and 61701108)+4 种基金the Fund for International Cooperation and Exchange of the National Natural Science Foundation of China(Grant No.61761136007)the Overseas Expertise Introduction Project for Discipline Innovation(Grant No.111-2-05)the Fundamental Research Funds for the Central UniversitiesPostgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX17_0092)the Scientific Research Foundation of Graduate School of Southeast University(Grant No.YBJJ1815)。
文摘Coding metasurfaces make it possible to manipulate electromagnetic(EM)waves digitally by means of several discrete particles.Hence,there have been rapid advances in this field recently.Here we propose a novel design of a broadband transmission-type coding metasurface,which is valid to both x-and y-polarized EM incidences from 8.1-12.5 GHz while satisfies the requirements of 1-bit coding without changing the polarization.Two types of multi-layer coding particles with different geometrical parameters are adopted to represent the digital states"0"and"1",which are easily promoted to terahertz and optics through modifying the size scale.To verify the ability to manipulate the EM waves,we first adopt the coding metasurface to achieve broadband beam forming by converting spherical waves to plane waves and realize high-directivity pencil beam in far field with low side lobes.We further arrange the particles according to the coding sequence 010101…to steer two symmetrical beams in different directions controlled by frequencies with the maximum range of the scanning angle of 30°-50.5°.The good agreements between the simulated and measured results validate the proposed broadband coding metasurface,indicating its huge potential in communication and radar imaging systems.
基金Supported by the National Natural Science Foundation of Chin（No. 60302020）.
文摘A convolutional weighting （CW） scheme applied to a half-wavelength spacing array was proposed for multi-user system to joint STBC （space time block ceding） and beam forming （BF）. The transmitting beam is equivalent to the product of two sub-beams. One is used to realize interference suppression, while the other is employed to form a couple of uncorrelated channels from base station （BS） to the desited user （to meet the requirement of STBC） and to maximize SINR （signal-to-interference-plus noise ratio） at the desired receiver. As an optimum combination of STBC and beam forming, the proposed scheme can achieve both full diversity order of STBC and array gain of BF. Meanwhile, it can also effec- tively restrain multi-user interference by nulling. Simulation results show that the proposed scheme can significantly improve the BER （Bit Error Rate） performance and enhance system capacity as compared with the conventional eigen-beamforming （EBF） technique applied to a half-wavelength spacing array.
基金the Natural Science Foundation of Chongqing Municipal (CSTC2006BB2360)
文摘A multi-beam adaptive antenna is investigated by considering the adaptive beam forming performance for time-variant channels on the focus of mobile to base station or reverse link. This antenna is constructed by Fresnel zone phase-correcting plane （FZP） focusing element and uniformly spaced feeds array. An estimator for the beamforming weight vector in the presence of angle spreads is derived using a code filtering approach. Owing to the time-varying nature of the channels, a recursive method for computing and tracking the above optimal weight vector solution that is easy to implement is applied. The effects of angle spread, maximum Doppler frequency, and forgetting factor are studied. Simulation results showed that this type of adaptive antenna is capable of performing adaptive beam forming for time-variant channels effectively.
文摘Improvement of frame-rate is very important for high quality ultrasound imaging of fast-moving structures.It is also one of the key technologies of Three-Dimension(3-D) real-time medical imaging.In this paper,we have demonstrated a beamforming method which gives imaging frame-rate increment without sacrificing the quality of medical images.By using wider and fewer transmit beams in combination with four narrower parallel receive beams,potentially increasing the imaging frame-rate by a factor four.Through employing full transmit aperture,controlling the mainlobe width,and suppressing sidelobes of angular responses,the inherent gain loss of normal parallel beamfomer can be compensated in the maximal degree.The noise and interference signals also can be suppressed effectively.Finally,we show comparable lateral resolution and contrast of ultrasound images to normal single widow weighting beamformer on simulated phantoms of point targets,cyst and fetus of 12th week.As the computational cost is linear with the number of array elements and the same with Delay And Sum(DAS) beamformers,this method has great ad-vantages of possibility for high frame-rate real-time applications.
基金supported by the National Natural Science Foundation of China (Nos. 61202351, 61271255)the Natural Science Foundation of Jiangsu Province (No. BK20131068)+2 种基金the Open Research Fund of National Mobile Communications Research Laboratory in Southeast University (No. 2012D15)the Funding of Jiangsu Innovation Program for Graduate Education (No. CXLX11_0202)the Fundamental Research Funds for the Central Universities
文摘Recently, unmanned aerial vehicles （UAVs） acting as relay platforms have attracted considerable attention due to the advantages of extending coverage and improving connectivity for long-range communications. Specifically, in the scenario where the access point （AP） is mobile, a UAV needs to find an efficient path to guarantee the connectivity of the relay link. Motivated by this fact, this paper proposes an optimal design for beamforming （BF） and UAV path planning. First of all, we study a dual-hop amplify-and-forward （AF） wireless relay network, in which a UAV is used as relay between a mobile AP and a fixed base station （BS）. In the network, both of the AP and the BS are equipped with multiple antennas, whereas the UAV has a single antenna. Then, we obtain the output signal^to-noise ratio （SNR） of the dual-hop relay network. Based on the criterion of maximizing the output SNR, we develop an optimal design to obtain the solution of the optimal BF weight vector and the UAV heading angle. Next, we derive the closed-form outage probability （OP） expression to investigate the performance of the dual-hop relay network conveniently. Finally, computer simulations show that the proposed approach can obtain nearly optimal flying path and OP performance, indicating the effectiveness of the proposed algorithm. Furthermore, we find that increasing the antenna number at the BS or the maximal heading angle can significantly improve the performance of the considered relay network.
基金This work is supported by Jiangsu Provincial Natural Science Research Fund of China.
文摘In this paper, we analyze the scheme of Space-Time Coded BeamForming (STC-BF)for the downlink of DS-CDMA system over frequency-selective fading channels and give the numericalsimulations on the scheme. The blind multiuser detection is employed at receiver to suppress theMulti-Access Interference (MAI). The Space-Time Coding (STC) and BF are combined to mitigate theperformance degradation due to multipath fading and various interferences. The numerical simulationsshow that the BF can compensate the performance loss of STC due to the channel correlation and thenthe STC-BF can greatly improve the performance of CDMA system.
文摘The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas involved in these gadgets are to be designed very stringently so as to avoid interferences & coupling and to improve compatibility, susceptibility, etc. Compact smart antenna with improved performance is highly essential to meet this challenging scenario. Mutual coupling between various elements of an array is one of the main factors which can be considered for improvement of performance of the antenna. Influence of mutual coupling on performance of the antenna is considered in this paper and various techniques to minimize this effect are presented. Effect of mutual coupling on radiation characteristics of the antenna can be compensated employing various methods like Conventional Mutual Impedance (CMI), Receiving Mutual Impedance (RMI). Analysis is presented as comparison between the two methods for different number of elements in the array. Analysis is also presented for different geometries of the array like circular and elliptical for improved performance. The results show performance improvement in the proposed array for parameters like SNR and Speed of convergence.
文摘With the increasing demand for high speed reliable communications, smart antennas, such as the Butler Matrix array, can be used to develop a system that increases the performance of a wireless system. The Butler matrix is a switched beam array system which can produce orthogonal uniform beams. The main objective is to improve the efficiency of the power in a 90-degree bend. Also, the double-mitered bend is particularly interesting since it provides a substantially lower reflection coefficient and a lower value of S12 at a frequency of 2.4 GHz compared to an unmitered one. Therefore, this paper describes an optimum design using a double-mitered method with a 2 × 2 and a 4 × 4 Butler Matrix array, operating at 2.4 GHz which is used in wireless systems with an FR4 substrate.
基金supported by the National Natural Science Foundation of China(Grant Nos.62101258,62071235 and 62271260)the Jiangsu Province Science&Technology Department(Grant No.BE2021017).
文摘Time-modulated array(TMA)antennas,introduce the dimension of time into antenna design to control the radiation patterns and frequency spectral characteristics,thus improve the reconfigurability of array antennas and provide multiple functional-ities.They have great application potential in military and civilian fields,such as precision guidance and mobile communication,and are currently a hot spot of academic research.This article provides a review on the fundamentals and applications of TMAs.First,the basic theory and mathematical formulations of TMAs are introduced.Second,the most important applications of TMAs,namely time-modulated phased arrays(TMPA),are discussed from the perspectives of harmonic suppression and harmonic utiliza-tion,which are used for single-beam and multibeam radiation.Then,we survey the combination of TMA with various types of novel antenna arrays,such as single-channel digital beamforming(DBF)arrays,frequency diverse arrays(FDAs),and retrodirective arrays,to create new hardware implementation methods and enhance their performance.Next,recent advances in dedicated integrated chips for TMA,which have played a significant role in driving the progress of TMAs from academic research to practical applications,are presented.Finally,the challenges and prospects for TMAs are discussed,including new research directions and emerging applica-tion scenarios.
基金supported in part by the National Natural Science Foundation of China(Nos.91750202,11530046,and 11474156)the National Key R&D Program of China(No.2017YFA0303700)+1 种基金the Collaborative Innovation Center of Advanced Microstructures of Chinathe Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Electronics of China
文摘We propose and simulate a method for generating a three-dimensional （3D） optical cage in the vicinity of focus by focusing a double-ring shaped radially and azimuthally polarized beam. Our study shows that the combination of an inner ring with an azimuthally polarized field and an outer ring with a radially polarized field and a phase factor can produce an optical cage with a dark region enclosed by higher intensity. The shape of the cage can be tailored by appropriately adjusting the parameters of double-mode beams. Furthermore, multiple 3D optical cages can be realized by applying the shift theorem of the Fourier transform and macro-pixel sampling algorithm to a double-ring shaped radially and azimuthally polarized beam.
基金supported by the National Natural Science Foundation of China(Grant No.60472097).
文摘The performance of ground moving target detection for distributed satellites will be affected signifi-cantly when there is an image registration error,clutter decorrelation and array error.In this paper,a new approach to moving target detection and relocation is proposed based on multi-channel and multi-pixel adap-tive signal processing in an image domain.First,multi-channel and multi-pixel joint data are equated to a simple array model.Given that there is an image registration error,the real steering vector of the moving target can be estimated through a space projection approach.The optimal beam forming approach is used to cancel clutter,and at the same time the cross-track velocity of the mov-ing target can be determined by searching for the peak value of the cost function.The moving target can then be relocated on the SAR image.The simulation results indicate that this method has a good robustness to image registration error,clutter decorrelation and array error.The detection performance and the estimation accuracy are significantly improved.
