ENLARGING SAR PATCH-MAPPING AREA BY ANTENNA BEAM SCAN

The approach for enlargement of SAR patch mapping area by antenna beam scan is investigated, which serves for moderate fine-resolution mapping of medium-sized terrain patches. The scanning angular velocity and the scanning angular scope are determined respectively. The angular velocity of the scanning antenna is controlled to scan over just one azimuth 3 dB beam width in the time interval during which the radar platform moves over one synthetic aperture length determined from the desired cross-range resolution, radar wavelength, nominal slant range, and squint angle. The scanning angular scope is mainly determined by the azimuth width of the terrain patch, nominal slant range, squint angle, platform velocity, and azimuth beam width. Finally, the related experimental results of an airborne SAR are presented. The linear range-Doppler algorithm is employed in image formation after motion compensation is conducted to remove the effect of transnational motion of the radar platform relative to the map center.

Two-step Structural Design of Mesh Antennas for High Beam Pointing Accuracy

A well-designed reflector surface with high beam pointing accuracy in electromagnetic performance is of practical significance to the space application of cable mesh reflector antennas. As for space requirements, cir- cular polarizations are widely used in spaceborne antennas, which usually lead to a beam shift for offset reflectors and influence the beam pointing accuracy. A two-step structural design procedure is proposed to overcome the beam squint phenomenon for high beam pointing accuracy design of circularly polarized offset cable mesh reflectors. A simple structural optimal design and an integrated structural electromagnetic optimization are combined to alleviate the beam squint effect of circular polarizations. It is imple- mented by cable pretension design and adjustment to shape the offset cable mesh surface. Besides, in order to increase the efficiency of integrated optimization, an update Broy- den-Fletcher-Goldfarb-Shanno （BFGS） Hessian matrix is employed in the optimization iteration with sequential quadratic programming. A circularly polarized offset cable mesh reflector is utilized to show the feasibility and effectiveness of the proposed procedure. A high beam pointing accuracy in order of 0.0001~ of electromagnetic performance is achieved.

A Novel Beam Design Method for mm Wave Multi-Antenna Arrays with Mutual Coupling Reduction

To overcome the mutual coupling (MC) of multiple antennas in millimeter wave (mmWave) communication systems, a novel beam design method with low complexity is proposed in this paper. Firstly, an equivalent channel model incorporating the effect of MC is analyzed and established, and then an optimal precoding / combiner vector for beamforming is derived. On this basis, by using greedy geometric (GG) algorithm, a novel hybrid beam design method is proposed. Finally, the performance of proposed method is analyzed and compared with other traditional ones. The simulation results show that the proposed method has better suppression of the MC effect as well as lower complexity.

Handover initiation performance of a new multi-cell cellular configuration with a developed base-station multi-beam antenna

A new multi-cell cellular configuration networks is provided for analysis of handover initiation probability, which is based on multi-beam base-station antenna splitting in the elevation-radiating plane. The sum of the received signal power in the mobile station, including both desired and interference signal power, has been introduced into the handover initiation algorithm. Along with the idea, we present three models of handover initiation algorithm with the shadowing process of Gaussian distribution. The formulation of handover initiation probability of those algorithms is also analyzed. The validity of the presented models has been checked through the comparison with simulation results. The results present the performance characteristics of handover initiation vary with cluster number and base-station antenna elevation angle.

Compact wideband microstrip array antenna with beam squint

A compact wideband microstrip array antenna with a squint beam is introduced without the matched load. Its measured beam is at 10° offset to the broadside with a measured gain of 12 dB at 10 GHz. The measured impedance bandwidth （voltage standing wave ratio （VSWR）≤2） is over 16%, which agrees well with the simulated one. It is a low-cost wideband design with compact simple structure, suited for military and commercial application.

Practical realization of dual S arm antenna for beam steering applications

A dual S shaped micro strip antenna with a realistic feed is proposed for generation of tilted beam radiation pattern pertaining for beam steering applications. To achieve this, four feeding points are located at a distance of 5.6 mm from the antenna centre. These feeding points when excited one by one generate four tilted beams in four different space quadrants, thus yielding a beam steerable antenna, Importantly, since the proposed antenna is symmetrical in the structure, all the four tilted beams have the same radiation pattern characteristics. A further enhancement of the antenna bandwidth is also achieved using 100-μn capacitive coupling between the feed and the antenna strip.

A 2.4 GHz Switched Beam Antenna for Indoor Applications Using Angle of Arrival Estimation

This study introduces a new design of planar antenna array for ISM band applications at 2.4 GHz. This prototype is switched beam antenna, namely planar antenna with four meandered slotted triangular elements (PAFMSTE), which is proposed for wireless indoor applications. The Base Station (BS) equipped with this planar antenna is preferred to be at the center position on the room ceiling to cover all sectors of the room. It is designed to use four directional triangular elements arranged to form a square planar antenna array. The PAFMSTE is used to obtain optimal directivity in four directions in azimuth plane with 3 dB beamwidth of 90°at a specific orientation of 30°in elevation plane. Switched parasitic technique is used to enable PAFMSTE to steer a directional beam through four locations by using four PIN diodes switches. The High Frequency Structure Simulator (HFSS) is used as an efficient simulation tool to optimize the performance of the PAFMSTE antenna. The fabrication and measurements of the PAFMSTE antenna are introduced. The proposed antenna enable radio positioning via Angle of Arrival (AOA) information collected from nearby devices. Then, the Cramér-Rao Bound (CRB) is presented for AOA estimation using identically and equally spaced antenna elements. The CRB depends on the directivity, where the maximum values of CRB are 1.35 × 10-3 and 8 × 10-3 at HPBW of 60° and 90°, respectively.

Rectangular Microstrip Antenna for Symmetrical 3-D Beam Widths for an Efficient Feed of Reflector Antenna and its Quantitative Analysis

A simple rectangular microstrip antenna on low dielectric constant substrate such as air for improved radiation beam performance is theoretically investigated. The conventional patch antenna fabricated on common substrates always produces quite broader E plane pattern compared to its H plane. In the present investigation, the same microstrip antenna is designed on air substrate with a view to develop an efficient feed for parabolic reflector antenna, which shows an excellent radiation pattern with symmetrical 3 dB beam widths at its both E and H plane. The present antenna compared to conventional structure to show its excellence in the beam performance is presented. The complete quantitative analysis to explore such radiation beam characteristics for both the structures (conventional and the present one) is also presented in this paper. An easy and handful relationship between the length of patch antenna and its fringing length for different types of substrate is established in the background of 3 dB beam widths. The proposed idea has been verified through a commercial software package for a patch operating in X band and a concrete physical insight into the phenomenon is developed.

Pencil Beam Grid Antenna Array for Hyperthermia Breast Cancer Treatment System

In this paper, efficient, high gain and pencil beam grid antenna array is proposed for hyperthermia breast cancer therapy system. The proposed antenna bandwidth extends from 4.8 GHz to 4.9 GHz at resonant frequency of 4.86 GHz. This frequency band has been reported for the breast cancer hyperthermia therapy. The grid long and short sides are responsible for the undesired cross-polarized radiation and desired copolarized radiation, respectively. The unsuitability of the conventional grid antenna array is ensured by investigating its radiation properties. The proposed grid antenna array short side width is varied and its long side width is kept wide as possible to enhance the radiation properties and to reduce the losses. Also, a reflector has been used for gain enhancement purpose. The proposed grid antenna array achieves side lobe level and 3 dB beam width of —27.9 dB and 25.9° for the E-plane and —27.9 dB and 26.3° for the H-plane, respectively. The breast phantom is irradiated by both proposed and conventional grid antenna arrays for 10 minutes. The proposed grid antenna array achieves 8°C temperature increase within the breast phantom area compared to 2°C temperature increase for conventional one. The proposed grid antenna array is highly efficient, high gain and light weight, and it has a very suitable radiation property for hyperthermia breast cancer therapy.

Beam-Switching Antenna Based on Plane Dipole Structure

A novel method for designing a beam-switching antenna with the plane dipole is presented. The antenna is composed of double dipoles placed at the center of an active square structure that is divided in four equal sectors by metallic sheets. Metallic patches at the outside of the structure are used to enhance the radiation performance of the antenna. In each step, the diodes in one sector are on, whereas other diodes are off. The sector with off-state diodes defines the direction of the radiation pattern. An antenna model is designed on the substrate of FR4. The proposed antenna operates from 4.8 GHz to 5.5 GHz with gain of 6.3 dBi and F/B （front to back ratio） of 13.2 dBi when the operating frequency is 5.2 GHz. The antenna radiation pattern can be swept in the entire azimuth plane in four steps with a 3 dB beamwidth of 90%. The results reveal that the antenna could be used in the base station of the wireless communication systems.

Achieving Directionality and Transmit Diversity via Integrating Beam Pattern Scanning (BPS) Antenna Arrays and OFDM

In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna array elements mounted at the base station with beam patterns directed toward the desired user. This creates a small beam pattern movement called Beam Pattern Scanning (BPS). In rich scattering environments BPS creates a time varying environment leading to time diversity exploitable at the receiver enhances its probability-of-error performance. Here, we apply OFDM signals to BPS antenna arrays, and we achieve: (1) directionality, which supports Space Division Multiple Access (SDMA);and (2) a time diversity gain, which leads to high performance. We discuss the structure of the base station antenna array and the OFDM receiver that exploits time diversity. We also introduce the merger of BPS and multi-carrier OFDM (MC-OFDM) systems. In MC-OFDM each bit is transmitted over all sub-carriers after serial to parallel conversion. BPS/ MC-OFDM receiver exploits both time diversity inherent in BPS, and frequency diversity inherent in MC-OFDM transmission technique. Simulation results show high Probability-of-error performance is achie- vable via BPS/OFDM and BPS/MC-OFDM schemes comparing to the traditional OFDM and MC-OFDM, respectively. Simulations also reveal that MC-OFDM system as well as its merger with BPS is capable of mitigating large Peak-to-Average Ratio (PAPR) problem in traditional OFDM system. In addition, performance simulations with coded OFDM (COFDM) and coded MC-OFDM (MC-COFDM) and their merger with BPS are studied.

Gradient-based optimization method for producing a contoured beam with single-fed reflector antenna

A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States(CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.

Beam Selection and Antenna Selection: a Hybrid Transmission Scheme over MIMO Systems Operating with Vary Antenna Arrays

In this paper, we have proposed a hybrid transmission scheme which involves beam selection and antenna selection techniques over a MIMO system operating with vary antenna array. Optimal subset of transmit antennas are selected via fast successive selection scheme designed to optimize the target eigenbeam. Optimal eigenbeams corresponding to the largest singular values of the new MIMO channel formed by the selected antennas are exploited for data transmission. To evaluate the performance of the proposed scheme, different array structures, including uniform linear array (ULA) and including uniform circular array (UCA) are employed in the simulations. The transmitter is assumed to be surrounded by scattering objects while the receiver is postulated to be free from scattering objects. The Laplacian distribution of angle of arrival (AoA) of a signal reaching the receiver is postulated. The results presented by this paper indicate that the proposed scheme can significantly improve the performance of data transmission in term of symbol error rate (SER).

BEAM BROADENING SYNTHESIS FOR SAR ANTENNA ARRAY BASED ON PROJECTION MATRIX ALGORITHM

A new beam broadening synthesis technique for Synthetic Aperture Radar(SAR) antenna array, namely Projection Matrix Algorithm(PMA) is presented. The theory of PMA is introduced firstly, and then the iterative renewed manner is improved to resolve the unbalance problem under amplitude and phase control. In order to validate the algorithm correct and effective, an actual engineering application example is investigated. The beam synthesis results of 1.0~4.5 times broadening under the phase only control and the amplitude and phase control using improved PMA are given. The results show that the beam directivity, the beam broadening, and the side-lobe level requirements were met. It is demonstrated that the improved PMA was effective and feasible for SAR application.

Compact and broadband circularly polarized ring antenna with wide beam-width for multiple global navigation satellite systems

A compact and broadband circularly polarized （CP） annular ring antenna with wide beam-width is proposed for multiple global navigation satellite systems （GNSS） in the L1 band. The annular ring is excited by two modified L-probes with quadrature phase difference. It has a 36.3% 10-dB return loss bandwidth and a 13% 3-dB axial ratio bandwidth, because of the orthogonal L-probes with 90° phase difference. The measured peak gain of the antenna is 3.9 dBic. It can detect the satellites at lower elevation as its half power beam-width （HPBW） is 113° in both the x-z and y-z planes, achieving a cross-polarization level of larger than 25 dB. Noticeably, the antenna achieves 89% size reduction compared with the conventional half wavelength patch antennas. It can be used in hand-held navigation devices of multiple GNSS such as COMPASS, Galileo, GPS and GLONASS.

Metamaterial beam scanning leaky-wave antenna based on quarter mode substrate integrated waveguide structure

In this paper, we first propose a metamaterial structure by etching the same two interdigital fingers on the upper ground of quarter mode substrate integrated waveguide（QMSIW）. The simulated results show that the proposed QMSIWbased metamaterial has a continuous phase constant changing from negative to positive values within its passband. A periodic leaky-wave antenna（LWA）, which consists of 11 QMSIW-based metamaterial unit cells, is designed, fabricated,and measured. The measured results show that the fabricated antenna achieves a continuous beam scanning property from backward-43° to forward ＋32° over an operating frequencyrange of 8.9 GHz–11.8 GHz with return loss better than 10 d B.The measured antenna gain keeps consistent with the variation of less than 2 d B over the operating frequency range with a maximum gain of 12 d B. Besides, the measured and simulated results are in good agreement with each other, indicating the significance and effectiveness of this method.

Bi-Function Multi-Beam Graphene Lens Antenna for Terahertz Applications

Bi-function Compact graphene lens antenna in terahertz (THz) band has been investigated. The array function is switched between two status, reflectarray and/or transmitarray. The tunability of graphene conductivity introduces the bi-function characteristics of a single array structure in the THz band. The design depends on changing the graphene DC biasing voltage to transform the transmitting antenna to reflecting antenna. The compact structure of the antenna array saves the cost and the allocation area for the terahertz communication applications. A 13 × 13 reflectarray/ transmitarray antenna covering an area of 364 × 364 μm2 is proposed. A dual-beams reflectarray/transmitarray antenna is achieved by rearranging the cell elements of the array successively. Finally, a single structure is used to work as reflectarray and transmitarray antenna at the same time by rearranging the applied voltages between the different pieces of the graphene sheet using chess board arrangement. The phases of the successive unit-cells are kept the same of their locations in the original full array. The radiation characteristics of the array are investigated using the CST Microwave Studio for the bi-function operation.

基于波束形成的海上智能天线算法

远距离海上雷达探测由于海上环境的复杂性容易受到杂波干扰,常用的最小均方算法通过在干扰噪声中形成主波束并引导至目标信号,有效解决了杂波干扰问题。通过对自适应智能天线波束形成技术的海上应用进行研究,给出了常用的天线阵列结构模型和信号模型,研究了智能天线中的自适应波束成型算法,目前在这一领域的解决方案中最小均方算法最为常见,但其存在收敛速度差、通用性低等问题。本文将优化遗传算法引入,对传统遗传算法中初始种群规划和交叉操作进行了优化和改进。仿真实验表明,与最小均方算法、传统遗传算法相比,优化遗传算法对杂波的抑制效果提高了28%,收敛速度提升了3倍,具有良好发展前景。

L波段全向天线研究与设计

在实际应用中,有时需要全向天线在水平面以上覆盖较广的空域,针对这一需求,文章提出了两种工作在L频段的波束上翘的全向天线。其中一种为使用同轴转平行双线结构进行馈电的串联印刷偶极子天线,且加入反射板保证波束上翘,实测结果表明该天线在工作频段内,电压驻波比(voltage stanting wave ratio,VSWR)小于1.5,水平面增益大于2dBi,俯仰角0°~70°(定义水平方向为0°)增益大于-7dBi,不圆度小于2dB。另一种为双锥天线,使用上下锥体不对称结构保证波束上翘,同时引入固定套环保证天线的稳定性。实测结果表明该天线在工作频段内,VSWR小于2,俯仰角0°~20°增益大于1dBi,俯仰角0°~70°增益大于-7dBi,不圆度小于2.5dB。该天线结构稳定,性能优良,可应用于车载通信或其他通信场景中。

机载分布式智能蒙皮波束综合算法研究

针对机载智能蒙皮天线孔径共形和分布化的特点,开展了基于Broyden族算法的波束综合优化研究。算法以最小化副瓣电平为优化目标,通过K-S函数连续化处理,实现低副瓣波束赋形。通过不同的加权方式对算法的有效性进行了验证,相与遗传算法(genetic algorithm,GA)等随机优化算法,本文算法收敛速度快,能够避免陷入局部最优,适用于大规模非均匀共形天线阵列,具有较高的工程应用价值。