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     

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.     

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     

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。     

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.     

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     

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.     

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     

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.     

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.     

Microstrip-fed quasi-Yagi antenna with broadband characteristics

A compact and uniplanar antenna with broadband characteristics is presented. The novel Yagi-like printed dipole array antenna is fed by a microstrip-to-coplanar strip transition, and uses the truncated microstrip ground plane as its reflecting element. An X-band prototype measures a bandwidth of 17%. With 6.5 dB gain, 18 dB front-to-back ratio, and lower than -15 dB cross-polarisation level at 10 GHz     

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.     

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     

Broadband RFID tag antenna with quasi-isotropic radiation pattern

A passive RFID tag antenna in the UHF band using two bent dipoles and a modified double T-matching network is proposed. The antenna was fabricated with a thin copper layer printed on a 50 /spl mu/m-thick PET substrate for low-cost production. The proposed antenna provided a quasi-isotropic radiation pattern and a fairly broad bandwidth S/sub 11/<-10 dB, 8.5%) for conjugate-matching with a commercial tag chip. The efficiency of the antenna was about 90% in the operating frequency band. The measured readable range was between 170 -240 cm for an arbitrary rotation angle of the tag.     

Routing characteristics of ad hoc networks with unidirectional links

Unidirectional links in an ad hoc network can result from factors such as heterogeneity of receiver and transmitter hardware, power control or topology control algorithms, or differing sources of interference or jamming. Previously proposed metrics for evaluating the difficulty of a unidirectional scenario are limited in scope and are frequently misleading. To be able to analyze ad hoc network routing protocol behavior in a complex networking environment, it is not sufficient to merely assign a single level of difficulty to a unidirectional network scenario; the many interrelated routing characteristics of these scenarios must be understood. In this paper, we develop a set of metrics for describing these characteristics, for example for characterizing routing scenarios in simulations, analysis, and testbed implementations. Based on these metrics, we perform a detailed simulation analysis of the routing characteristics of the three most common simulation models for generating unidirectional links in ad hoc networks: the random-power model, the two-power model, and the three-power model. Our findings enable protocol designers to better choose a set of network scenarios and parameters that truly explore a wide range of a routing protocol’s behaviors in the presence of unidirectional links, and to better understand the complex interplay between routing mechanisms and network conditions.     

具有三陷波特性的类Sierpinski分形超宽带天线

为避免窄带通信系统对超宽带(ultra-wideband,UWB)系统的干扰冲突,提出一款具有三陷波特性的类Sierpinski分形UWB天线.辐射贴片采用圆环与五角星形嵌套迭代的2阶类Sierpinski分形结构,并采用缺陷地结构接地板以实现良好的UWB特性.通过在分形结构的上部添加对称倒L形开路枝节,在微带馈线两侧添加对称L形开路枝节,并在馈线处刻蚀倒π形窄缝隙产生了4.5～4.8 GHz、7.2～7.8 GHz和8.0～8.5 GHz三个频段的陷波特性.仿真和实测结果表明,天线在3.1～18.1 GHz的频段内,可有效抑制国际卫星波段、X卫星波段和国际电信联盟波段等窄带系统的干扰.该天线除滤波频段内,在通带频段内有较稳定的增益和全向辐射特性,可用于各种UWB系统中.