Passive parasitic UWB antenna capable of switched beam‐forming in the WLAN frequency band using an optimal reactance load algorithm

We propose a switched beam‐forming antenna that satisfies not only ultra‐wideband characteristics but also beam‐forming in the WLAN frequency band using an ultra‐wideband antenna and passive parasitic elements applying a broadband optimal reactance load algorithm. We design a power and phase estimation function and an error correction function by re‐analyzing and normalizing all the components of the parasitic array using control system engineering. The proposed antenna is compared with an antenna with a pin diode and reactance load value, respectively. The pin diode is located between the passive parasitic elements and ground plane. An antenna beam can be formed in eight directions according to the pin diode ON (reflector)/OFF (director) state. The antenna with a reactance load value achieves a better VSWR and gain than the antenna with a pin diode. We confirm that a beam is formed in eight directions owing to the RF switch operation, and the measured peak gain is 7 dBi at 2.45 GHz and 10 dBi at 5.8 GHz.     

λ/64‐spaced compact ESPAR antenna via analog RF switches for a single RF chain MIMO system

In this study, an electronically steerable parasitic array radiator (ESPAR) antenna via analog radio frequency (RF) switches for a single RF chain MIMO system is presented. The proposed antenna elements are spaced at λ/64, and the antenna size is miniaturized via a dielectric radome. The optimum reactance load value is calculated via the beamforming load search algorithm. A switch simplifies the design and implementation of the reactance loads and does not require additional complex antenna matching circuits. The measured impedance bandwidth of the proposed ESPAR antenna is 1,500 MHz (1.75 GHz–3.25 GHz). The proposed antenna exhibits a beam pattern that is reconfigurable at 2.48 GHz due to changes in the reactance value, and the measured peak antenna gain is 4.8 dBi. The reception performance is measured by using a 4  4 BPSK signal. The measured average SNR is 17 dB when using the proposed ESPAR antenna as a transmitter, and the average SNR is 16.7 dB when using a four‐conventional monopole antenna.     

Reactance domain MUSIC algorithm for electronically steerable parasitic array radiator

Conventional adaptive array antenna processing must observe signals on all of the array antenna elements. However, because the low-cost electronically steerable parasitic array radiator (ESPAR) antenna has only a single-port output, none of the signals on the antenna's parasitic elements can be observed. A direct application of most of the algorithms for the conventional adaptive array antenna is impractical. In this paper, A technique of estimation of direction-of-arrivals (DoAs) is proposed for the ESPAR antenna. This technique is based on the modified MUltiple SIgnal Classification (MUSIC) algorithm. The correlation matrix used in the MUSIC algorithm is estimated from the signal received through the single-port output of the ESPAR antenna as it switches over a set of antenna patterns. Simulation results show that DoAs can be estimated by the reactance domain MUSIC algorithm for ESPAR antennas. Furthermore, the statistical performance on estimation error variance of the reactance domain MUSIC estimator is analyzed and compared with the Crame/spl acute/r-Rao lower bound. Analytic and empirical results show that high-resolution DoAs estimation can be achieved by using the reactance domain MUSIC algorithm for ESPAR antennas.     

Direction-of-arrival estimation using radiation power pattern with an ESPAR antenna

An approach for estimating direction-of-arrival (DoA) based on power output cross-correlation and antenna pattern diversity is proposed for a reactively steerable antenna. An "estimator condition" is proposed, from which the most appropriate pattern shape is derived. Computer simulations with directive beam patterns obtained from an electronically steerable parasitic array radiator antenna model are conducted to illustrate the theory and to inspect the method performance with respect to the "estimator condition". The simulation results confirm that a good estimation can be expected when suitable directive patterns are chosen. In addition, to verify performance, experiments on estimating DoA are conducted in an anechoic chamber for several angles of arrival and different scenarios of antenna adjustable reactance values. The results show that the proposed method can provide high-precision DoA estimation.     

Blind concurrent beamformer

The electronically steerable parasitic array radiator (ESPAR) is a smart antenna based on the adjustment of reactances at parasitic elements. A new blind beamformer is presented, for use with reactance domain arrays, such as the ESPAR. Two stochastic gradient algorithms work concurrently so that two distinct cost functions are simultaneously minimised. Results show that the new blind beamformer presents a faster convergence and a lower steady-state mean squared error     

Electronic beam steering using switched parasitic patch elements

A new technique is presented demonstrating the use of switched parasitic elements in electronic beam steering applications. Experimental and theoretical results are presented for a linearly polarised five element steerable patch antenna array operating at 1.55 GHz. Shorted parasitic elements have been used to steer the beam in two directions for tracking polar orbiting satellites. The minimum gain of the system for elevation angles >20° above the horizon is -1.5 dBi in the forward direction     

一种平面印刷电控波束扫描天线阵

该文设计了一种平面印刷偶极子波束扫描寄生阵列天线,可用于移动终端设备以提高通信质量和系统容量。通过改变加载在寄生单元中的电抗值可以控制天线的最大辐射方向。天线基本结构用电磁场全波软件设计,所需加载的电抗值通过差分进化算法(DE)优化得出。实测的天线主波束方向在xoy平面内-34~38之间扫描;在各方向上,中心工作频率上的增益在3.6~4.9 dBi之间变化,反射系数小于-10 dB的频带在5.63~5.96 GHz之间,带宽为330 MHz。实测结果表明,天线具有良好的波束扫描性能,采用的设计和优化方法准确高效。     

差分馈电双极化四波束方向图可重构天线

提出了一种平面差分馈电双极化四波束方向图可重构天线.该天线由两个相互正交的偶极子和四个带PIN二极管的寄生单元构成,有两个差分馈电端口,通过短截微带线给两个相互正交的偶极子馈电.两个偶极子正交摆放、异面垂直,与寄生单元蚀刻在同一基板上,整体结构简单.切换PIN二极管的不同状态得到四个波束的方向图可重构和两种方式的极化可...     

一种倾斜波束双极化天线

提出了一种具有倾斜波束辐射特性的新型双极化天线。该双极化天线由两个正交的纺锤形偶极子 组成,根据准八木天线原理,在偶极子两侧加载寄生振子作为反射器和引向器,用以实现倾斜波束辐射。这种纺锤 形偶极子可以增加电流长度从而减小天线的整体尺寸。同时在每个偶极子贴片上蚀刻两个梯形槽,以实现良好的 阻抗匹配。另外,通过连接到同轴线的金属短截线对纺锤形偶极子进行激励,简化了天线馈电结构。测试结果表 明,天线的阻抗带宽为3. 36~3. 69 GHz(S11 <-10 dB),两个极化端口之间的隔离度大于16 dB,波束倾斜度为30°,波 瓣宽度约为85°,可适用于单侧大角度扫描阵列。     

Disc-loaded monopole antenna array for switched beam control

Switched beam control is demonstrated using a disc-loaded monopole antenna on a finite ground plane with four parasitic elements. The beam direction can be switched by open circuiting one of the parasites. The array antenna gives a gain of 5.1 dBi at 2.45 GHz, which is more than three times that of a single element. The input return loss bandwidth is 24% and the radiated beam is elevated above the ground plane by about 500. The measured results show good agreement with simulations.     

An aperture-coupled linear microstrip leaky-wave antenna array withtwo-dimensional dual-beam scanning capability

This paper describes an X-band 4×1 aperture-coupled series-fed electronically steerable microstrip leaky-wave antenna (LWA) array design, which has dual-beam radiation pattern and two-dimensional (2-D) beam-scanning capability. The LWA array is operated in the first higher order mode and excited by center-fed aperture coupled for dual-beam operation. The varactor-tuned phase shifters are placed between the antenna elements. The measured half-power beamwidth of the H-plane and quasi-E-plane radiation patterns are less than 30°. By tuning the reverse dc bias of the varactor diodes, the main beam can be scanned in azimuth plane from -13° to +13° off broadside. In the elevation plane, the beam-scanning angle is close to 20° as the operating frequency tuned from 11.58-12.5 GHz. Taking into account each phase-shifter insertion loss and phase progression, the measured results compared closely with the theoretical prediction. The proposed antenna array is suitable for wireless communication and collision warning radar systems     

Mutual Impedance Extraction and Varactor Calibration Technique for ESPAR Antenna Characterization

An extraction and calibration technique is proposed that allows electronically steerable parasitic array radiator (ESPAR) antennas to achieve high efficiency and precision in performance characterization. The proposed technique is based on a reactive-near-field measurement or direct acquisition of RF current. We present a simple formulation that requires minimal current measurements to successfully extract the mutual impedance. Currents are predicted for an arbitrary combination of bias voltages that are used to control the reactance of varactor diodes integrated with the antenna's parasitic elements. These predicted currents are compared by conducting an experiment with a seven-element ESPAR. For the bias voltage combinations that have reasonably good symmetry, the differences in relative gain, beam direction and half power beam width (HPBW) actually fall within 0.5 dB, 4deg and 9deg, respectively. Directivity patterns obtained by calculating the predicted currents are verified with those obtained by calculating the directly measured currents. Furthermore, the calculated patterns are verified through comparison with far-field measurements in a conventional anechoic chamber. The differences in beam direction and HPBW are also found to be acceptable. Using the proposed technique, the required number of measurements is reduced from 85,766,121 to just 149 for a seven-element array     

Fast beamforming of electronically steerable parasitic array radiator antennas: theory and experiment

A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum cross correlation coefficient criterion is proposed. The simulation and experimental results validate the algorithm. In an environment where the signal-to-interference-ratio is 0 dB, the algorithm converges within 50 iterations and achieves an output signal-to-interference-plus-noise-ratio of 10 dB. With the fast beamforming ability and its low-power consumption attribute, the ESPAR antenna makes the mass deployment of smart antenna technologies practical.     

Reactively Steered Ring Antenna Array for Automotive Application

A novel type of smart antenna, called a reactively steered ring antenna array (RSRAA), is proposed. The antenna features a conformal configuration with three overlapping one-wavelength ring elements. Directivity can be controlled by changing the values of variable reactance circuits that are embedded in the antenna. The antenna can be mounted on the windshield of an automobile without interfering with the view of the driver. An equivalent model of six dipole elements is derived from the original antenna configuration to enable simple calculation of directivity when a set of reactance values is given. The validity of the proposed equivalent model is confirmed by comparing simulation results calculated by the equivalent model and by the method of moments. Another simulation shows that the conventional reactance domain multiple signal classification algorithm can be applied to the proposed antenna while keeping the estimated direction-of-arrival number equal to the number of reactance circuits. In addition, the characteristics of an RSRAA, which is optimized at 2.4 GHz and is mounted on an automobile, are measured in an anechoic chamber, and directivity control is found to be implemented effectively.     

One- and two-dimensional antenna arrays for microwave wireless power transfer (MWPT) systems and dual-antenna transceivers

In this work, we demonstrate novel one-dimensional (1D) and two-dimensional (2D) antenna arrays for both microwave wireless power transfer (MWPT) systems and dual-antenna transceivers. The antenna array can be used as the MWPT receiving antenna of an integrated MWPT and Bluetooth (BLE) communication module (MWPT-BLE module) for smart CNC (computer numerical control) spindle incorporated with the cloud computing system SkyMars. The 2D antenna array has n rows of 1 × m 1D array, and each array is composed of multiple (m) differential feeding antenna elements. Each differential feeding antenna element is a differential feeding structure with a microstrip antenna stripe. The stripe length is shorter than one wavelength to minimise the antenna area and to prevent being excited to a high-order mode. That is, the differential feeding antenna element can suppress the even mode. The mutual coupling between the antenna elements can be suppressed, and the isolation between the receiver and the transmitter can be enhanced. An inclination angle of the main beam aligns with the broadside, and the main beam is further concentrated and shrunk at the elevation direction. Moreover, if more differential feeding antenna elements are used, antenna gain and isolation can be further enhanced. The excellent performance of the proposed antenna arrays indicates that they are suitable for both MWPT systems and dual-antenna transceivers.     

Array Pattern Optimization for Steerable Circular Isotropic Antenna Array Using Cat Swarm Optimization Algorithm

In this paper the steerable isotropic circular array antenna is designed for reducing the side lobe level (SLL) using evolutionary optimization technique. The optimization techniques particle swarm optimization and cat swarm optimization algorithm are used to reduce the SLL as well as to steer the main beam in specific direction. In this design of steerable circular arrays the amplitude excitations are optimized. Obtained results show that the maximum peak of SLL of the resultant patterns are as per requirement. This paper present a good performance in the array factor response and suppressed SLL for different number of array elements with different steering angle of the main beam using evolutionary optimization technique.     

End-fire hybrid array antennas

A heuristic approach useful in the design of end-fire array antennas is described. When an array is scanned "beyond end fire," the last elements of the array, in the direction of the end-fire beam, generally receive net power transmitted by other elements of the array. This received power might conceivably be recirculated and reradiated at the price of substantial complexity in the feed network. It is relatively simple to absorb this power in appropriate resistive loads at the price of reduced gain. The resulting end-fire antenna is a hybrid-array consisting of two classes of elements: elements excited directly and elements excited parasitically. A compromise termination of these parasitic elements in reactive loads especially determined to preserve desired pattern characteristics is examined.     

MIMO transmission and reception techniques using three-element ESPAR antennas

A novel scheme for spatially multiplexing two BPSK signals using a 3-element ESPAR (electronically steerable parasitic array radiator) antenna was reported in. In this paper we first optimize the set of loads controlling the parasitic elements within the transmission mode by maximizing the outage capacity. We also propose different reception techniques for spatially demultiplexing real and complex signals (using the same set of loads). The proposed transmission and reception schemes are evaluated in an indoor peer-to-peer mobile ad-hoc channel via simulations, where each ad-hoc node is equipped with a 3-element ESPAR terminal.     

含有寄生单元的倒F天线分析与设计

提出了在普通倒F天线的两侧和底部同时添加寄生单元的改进倒F天线,该天线与普通的倒F天线相比有更宽的带宽.设计了一个工作于中心频率1.2GHz的改进倒F天线.对该天线的电气特性进行了仿真计算,并对天线主要结构参数对谐振频点和阻抗带宽的影响进行了详细分析.该天线相对带宽达到了33%(VSWR<2),约为普通倒F天线阻抗带宽的4倍,有效地展宽了传统倒F天线的工作带宽,在宽带通信系统中有较好的应用前景.     

一种三单元新型宽波束扫描电控无源阵列天线

通过电抗加载来控制方向图主瓣指向的天线称为电控无源阵列天线,简称ESPAR天线.提出了一种三单元H形缝隙耦合馈电贴片ESPAR相控阵天线,该天线通过分别改变加在两侧寄生辐射贴片馈电端的直流控制电压来改变相应的电抗加载值,从而使其实现宽波束扫描.给出了该天线的详细分析,以及电磁仿真结果,结果表明,该天线在H面上能实现-30°～30°的宽波束扫描.