Log-periodic antenna for pulsed radiation

An antenna capable of radiating a bandlimited pulse with minimal distortion, negligible loss and significant directivity is reported. The design is a modified log-periodic dipole array with independent feeds to each dipole. This was modelled with a time-domain integral equation program and then realised in hardware; measurements showed good agreement with the predicted performance     

采用新型背腔的对数周期缝隙天线

针对超宽带雷达探测系统,提出了一款具有定向辐射性能的背腔式对数周期缝隙天线.该天线由一种具有超宽带匹配特性的渐变共面波导馈电.通过在缝隙天线背面设置谐振腔,使缝隙天线具有定向的辐射方向图.根据矩形谐振腔的特点,设计了一种新型结构的谐振腔,使得天线的驻波比（Voltage Standing Wave Ratio, VSWR）小于2.5.仿真与实测结果表明：天线在整个频带(0.9~5 GHz)内具有稳定的定向辐射方向图,新型谐振腔和吸波材料的使用使天线最低工作频率可到0.9 GHz,可使天线在整个频带内得到较高的天线增益.设计的天线适于应用在导航、探测以及超宽带(Ultra-wide Band,UWB)雷达等领域.     

A wideband stepped-impedance open-slot antenna with end-fire directional radiation characteristics

In this paper, new techniques are proposed to increase the front-to-back ratio of the stepped-impedance (SI) open-slot antenna for operation from 1.67 GHz to 4.25 GHz, covering the required frequency bands of the wireless communications systems, such as DCS, PCS, IM-2000, and WLAN. By designing a stub-protruded feedline and adding two symmetrical stubs at the edge of a quarter-wavelength slot, additional capacitance is introduced to the resonator. Hence, the impedance-matching condition of the SI open-slot antenna is not only effectively improved, but also the resonance frequency of the slot antenna is significantly shifted down and then an improvement in impedance bandwidth is achieved. In order to decrease the back radiation, two pairs of symmetrical open slots with uniform width are etched at the back of the blocking open slot such that the currents along the longitudinal edges of the ground plane cannot flow to the back direction. In addition, by embedding an array of seven slits beside the radiating slot, the back lobe at the upper frequency bands can be reduced. Two pairs of three-element metal strips are utilized as a power director to increase the forward power and enhance the front-to-back ratio of the SI open-slot antenna. Compared to conventional unidirectional radiation antennas, the proposed antenna demonstrates improved wideband unidirectional radiation characteristics and relatively smaller size.     

偏馈FZP天线的远场辐射特性

利用物理光学法分析了偏馈FZP反射面天线的辐射特性，考察了喇叭馈源的最强辐射中心带来的影响，计算机模拟结果表明了该天线具有较好的辐射特性。     

Integrated active antenna array using unidirectional dielectricradiators

In this paper, design considerations and experimental investigations of an integrated active antenna for space power combining that makes use of unidirectional dielectric radiators (UDRs) are presented and discussed. Attractive electrical performance stemming from proprieties of nonradiating dielectric waveguide structures is used to design a prototype at a frequency of 14 GHz. A UDR feed circuit is implemented by microstrip lines and aperture-coupling is studied experimentally for arrays of two, four and eight radiators. Measurements show high coupling and radiation efficiencies of the proposed excitation method. A power-combining efficiency of 89% was measured and a gain of 23.1 dBi was achieved for an antenna with eight radiators and four amplifiers. It is also shown that such a circuit configuration allows the combination of planar Ku-band monolithic hybrid microwave integrated circuit and UDR components in flexible design of active array antennas     

Simple reconfigurable antenna with radiation pattern

A radiation pattern reconfigurable antenna is proposed. By controlling the switch states, the antenna can be worked as a monopole antenna with an omnidirectional radiation pattern or a dipole antenna with reflector, which has directional radiation pattern. Detailed design considerations of the proposed antenna, simulated and experimental results are presented and discussed.     

Wideband unidirectional patch antenna with Γ-shaped strip feed

A wideband unidirectional patch antenna composed of a shorted bowtie dipole with ?-shaped feed and an L-shaped electric dipole is designed. It achieves an impedance bandwidth of 87% for VSWR ? 2 in the range 2.2-5.6 GHz, stable peak gain of around 7 dBi, unidirectional radiation patterns and low cross-polarisation over the whole operating band. It is sufficient for accommodating recent wireless communication services such as 3G, WiFi, WiMax, Bluetooth, Zigbee, etc.     

A unidirectional semi-circle spiral antenna for subsurface radars

Specifications of an antenna for a subsurface radar are quite different from those of an ordinary antenna for telecommunication. The antennas for a subsurface radar are located very close to the interface between the air and the Earth's surface. The antennas for subsurface radars have mutually conflicting requirements such as low-frequency operation for better penetration, broadband characteristics for finer resolution, small size for pinpointing the antenna location, and sufficient sensitivity for good signal-to-noise ratio of the image. It is found that a semi-circle spiral antenna with a cylindrical waveguide can meet most of the above requirements. A practical structure is proposed, and a method of designing such an antenna is presented. The experimental results show the usefulness of the developed antenna     

Log-periodic antennas with modulated impedance feeders

The proper phasing of the active region of a log-periodic array can be obtained by means of a feeder without the conventional transposition of the wires. This is of practical importance for arrays of monopoles and slots where the transposition is not possible. However, the input impedance of such structures, when fed from a line with constant impedance, varies greatly with frequency. The impedance variation has been traced to reflections from a stop region between the antenna feedpoint and the active region. By introducing a step modulation of the characteristic impedance of the feedline, the reflections can be reduced and a stable impedance obtained.     

部分浸没于海水中天线阻抗及辐射效率分析

针对海洋环境中浮标天线的辐射性能问题,基于海水中短波、超短波频段高衰减的特性,提出了以海面为分界面,将天线分为水上、水下两部分考虑的假设,建立了部分浸没于海水中天线的理论计算模型,开展了天线输入阻抗测试实验,验证了假设和模型的正确性.应用该模型,确定了天线的水上、水下部分阻抗共轭匹配条件下的工作频率范围,分析了不同入水...     

Single feed antenna with radiation pattern diversity

A vehicle diversity antenna system comprising a single-fed element together with a loaded parasitic element is described. Different termination loads on the parasitic element give rise to variations in the radiation patterns that are comparable with a four-element diversity system. There was good agreement between measured parameters and simulations.     

偶极子光电导天线结构对THz 辐射特性影响的研究

研究了GaAs工型偶极子光电导天线(PCA)结构参数对THz辐射特性的影响。首先利用DL(Drude-Lorentz)模型得到了光电导天线的电流解析解,结合时域有限差分(FDTD)进行半解析半数值仿真,有效地解决了纯解析解(通过光电流对时间求导数可以得到辐射的THz的相对强度)无法和PCA结构直接对应的仿真问题,也较直接全波FDTD方法计算效率高。接着,利用偶极子光电导天线的等效电路模型和等效源阻抗公式,结合实际的PCA参数,分别得到了PCA阻抗和源阻抗,说明了由于源阻抗很低,导致匹配效率较低。最后,综合考虑数值仿真结果和理论计算结果可证明,工型偶极子光电导天线的辐射效率会随着其长宽比的增加而相应增加,该结论与相关文献实测结果吻合,从而也验证了文中FDTD仿真结果、理论模型及计算结果的有效性。     

A circularly polarized octave-bandwidth unidirectional antenna using conical dipoles

A unique unidirectional octave-bandwidth reflector type circularly polarized antenna is described which uses crossed parallel connected conical dipoles operated near second resonance. The impedance characteristics of the antennas together with added series reactances gives the desired approximately quadrature current relation between the two dipoles. The axial ratio does not exceed 2 to 1.     

A broad-band, unidirectional, two-port microstrip patch antenna

Resonant microstrip antennas usually have very narrow impedance bandwidths. By simultaneously exciting two modes of a circular patch, a two-port patch radiator with image impedance that remains near constant over a wide band can be obtained. This result is achieved by adjusting the coupling so that the two modes present complementary impedances, one in series, the other in shunt, at the same point on the feeder. The patterns can be made unidirectional so that the antenna is well suited for use in series-fed, end-fire, or side-fire arrays. The patterns are stable over a wide frequency band. Hence, the operating bandwidth will probably be determined by efficiency or power gain rather than by impedance or patterns     

基于FDTD的太赫兹光导天线三维辐射特性计算方法

光导天线是目前产生和探测太赫兹波最常用的辐射源之一,在太赫兹成像、光谱检测等诸多领域有着广泛的应用前景。本文介绍了基于时域有限差分(FDTD)的太赫兹光导天线三维辐射特性计算方法,在分析光导天线辐射原理的基础上阐述了半导体漂移电流、扩散电流对电场及磁场的作用,并根据实际运用情况对漂移方程、连续性方程进行简化,最终求得电流密度、电场、磁场的迭代方程,给出了光导天线辐射特性计算流程。     

Human operator coupling effects on radiation characteristics of aportable communication dipole antenna

EM coupling effects of a human operator on antenna radiation characteristics, such as the antenna input impedance, radiation patterns, the radiation power (into free space), the power absorbed by the body, the radiation efficiency, etc., of a portable communication dipole antenna were investigated in detail. A realistically shaped 3D man model and an approximate linear dipole antenna were used to model this problem. Coupled integral equations (CIE) and the method of moments (MoM) were employed to numerically solve this antenna-body coupling problem. Numerical examples are presented for the antenna located in front of the head (distance ranging from 5 to 1 cm) or adjacent to the abdomen (0.6 cm distance) at 830 MHz. It is found that, when coupled with the operator body, the antenna input impedance will have significant deviation from those in free space and different positions. Due to the operator body absorption effect, the maximum attenuation of the H-plane antenna gain may reach about 15 dB for the antenna at the head position and 25 dB for the abdomen position, toward the direction of the body side. Also, the antenna radiation efficiency is reduced to the range from 0.72 to 0.29 for the head position and 0.15 for the abdomen position, respectively. Moreover, the cross-polarization field is significant, especially in the E plane of φ=90°. This is important for the antenna RF design and communication link budget consideration of portable radio systems     

Investigation of characteristics of planar leaky-wave antenna arrays designed for broadside radiation

The results of computer simulation and experimental investigations of new planar leaky-wave antenna arrays designed for microwave and EHF bands and for the mode of radiation normal to the aperture plane have been presented. These arrays comprise single-layer shielded dielectric waveguides and metal-strip periodic diffraction gratings. The specified antennas ensure the radiation efficiency of no less than 50% and the gain of about 28–30 dB within the 3–4% frequency band.