Wide-band circular groove guide horn antenna

A novel horn antenna based on a circular groove guide is analyzed and measured at Ku-band and Ka-band, respectively. This horn antenna can cover a frequency range from 14 to 40 GHz. Its optimum dimension was obtained according to the maximum directivity. The antenna can be matched efficiently to free space through its large aperture. Moreover, its input VSWR is low. The theoretical radiation patterns are close to the measured ones.     

Performance characterization of polarimetric active radarcalibrators and a new single antenna design

Several topics associated with the use of a polarimetric active radar calibrator (PARC), which is a high radar-cross-section transponder with a known scattering matrix, are addressed. The first involves experimental measurements of the magnitudes and phases of the scattering-matrix elements of a pair of PARCs that operate at 1.25 GHz and 5.3 GHz. The measurements were conducted over a wide range of incidence angles (relative to the boresight direction) in the azimuth, elevation, 45°, and 135° planes. The 5.3-GHz PARC, which consisted of two antennas placed several wavelengths apart, exhibited symmetrical patterns with no ripples and excellent isolation between orthogonal polarization channels. The 1.25-GHz PARC, whose antennas were in very close proximity to one another, exhibited unsymmetrical patterns as well as ripples in the phase patterns, thereby introducing errors in the elements of the scattering matrix. To avoid this problem, a single-antenna PARC is designed,, using an orthomode transducer. The single-target calibration technique is extended so that it applies to the use of a PARC as well as reciprocal passive calibration devices such as spheres and trihedral corner reflectors     

Wide-band microstrip antenna with an H-shaped coupling aperture

Theoretical and experimental results of a wide-band planar antenna are presented. This antenna can achieve a wide bandwidth, low cross-polarization levels, and low backward radiation levels. For wide bandwidth and easy integration with active circuits, it uses aperture-coupled stacked square patches. The coupling aperture is an H-shaped aperture. Based on the finite-difference time-domain method, a parametric study of the input impedance of the antenna is presented, and effects of each parameter on the antenna impedance are illustrated. One antenna is also designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of 21.7%. The cross-polarization levels in both E and H planes are better than 23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results of S parameters and radiation patterns are presented and discussed     

Wide-band smart antenna design using vector space projection methods

We use vector space projection (VSP) methods to design wide-band adaptive and self-healing arrays. Rectangular arrays are assumed but the VSP algorithm can be applied to any configuration. In the VSP method, we formulate a set of design constraints and then iteratively improve on a trial solution by operations known as "alternating projections". When all of the constraint sets are convex and the intersection of these sets is not the empty set, we can meet the design specifications in a finite dimensional setting. In our simulations, we show that reasonable design constraints are readily met. We demonstrate that VSP is useful for broad-band self-healing, i.e., the reconfiguration of the array when some broad-band elements fail to operate. Finally we compare our results with a known design procedure for broadband antenna arrays.     

Wide-band characterization of current probes

The use of current probes for the injection of wide-band disturbance in electromagnetic compatibility applications requires their accurate characterization up to few gigahertz. While the representation of the current probe with a simple transformer is acceptable at low frequencies, the spectral content of fast signals requires models which are accurate even at gigahertz frequencies. This can be accomplished directly by measurements in the frequency domain (FD), making use of a S-matrix representation of the probe, or in the time domain (TD), recovering the transfer functions from the impulse responses measurement. Both techniques suffer limitations due to numerical and experimental problems; in particular, the FD approach leads to the solution of an inverse problem, with numerical instabilities in the high-frequency range, whereas the TD approach is not so accurate in the low-frequency range of the sought transfer function. The paper combines the two techniques to overcome these difficulties and achieve a better accuracy across the overall bandwidth. The characterization of a commercially available current probe allows comparison of numerical results with experimental measurements.     

Wide-band communication satellite antenna using a multifrequency primary horn

The design method of and experimental results obtained from a wide-band satellite antenna with a multifrequency primary horn is described. This antenna can be used in 4, 6, 20, and 30 GHz frequency bands. Some measured data of the primary horn and the antenna are reported. Consequently, the antenna efficiency is about 45-50 percent in all the above frequency bands.     

Wide-band network characterization by Fourier transformation of time-domain measurements

A novel method of measuring driving-point and transfer impedance over a wide spectrum rapidly and with good accuracy uses a digital computer to transform the pulse response of a network into the frequency domain. A sampling oscilloscope provides the time transformation needed for data acquisition. The method and laboratory technique are discussed. Experimental data show agreement within 12 percent between the data from a single pulse measurement and bridge measurements over a band of 40 harmonic frequencies, i.e., 25-1000 MHz. Fundamental accuracy and bandwidth are believed to be substantially greater than these figures.     

Wide-band high-efficiency printed loop antenna design for wireless communication systems

A new wide-band high-efficiency coplanar waveguide-fed printed loop antenna is presented for wireless communication systems in this paper. By adjusting geometrical parameters, the proposed antenna can easily achieve a wide bandwidth. To optimize the antenna performances, a parametric study was conducted with the aid of a commercial software, and based on the optimized geometry, a prototype was designed, fabricated, and tested. The simulated and measured results confirmed that the proposed antenna can operate at (1.68-2.68 GHz) band and at (1.46-2.6 GHz) band with bandwidth of 1 and 1.14 GHz, respectively. Moreover, the antenna has a nearly omnidirectional radiation pattern with a reasonable gain and high efficiency. Due to the above characteristics, the proposed antenna is very suitable for applications in PCS and IMT2000 systems.     

Wide-band photonically phased array antenna using vector sum phase shifting approach

In this paper, a wide-band photonically phased array antenna is demonstrated. The array configuration consists of a 4 /spl times/ 1 Vivaldi single-polarization antenna array and an independent photonic phasing system for each element. The phasing network of this array is implemented using two novel photonic phase shifters based on the vector summation approach. A vector sum phase shifter (VSPS), which exhibits a frequency-linear characteristic from dc to 15 GHz and can be continuously tuned from 0 to 100/spl deg/, is presented. A second-order VSPS (SO-VSPS), a modification of the VSPS that is capable of 0-430/spl deg/ phasing range, is also demonstrated. This paper presents the operation and characterization of each component of the array, including the radiating elements and the various photonic phase shifters and, finally, a demonstration of the combined system. A discussion on the practicality of this system for airborne applications is presented, along with suggestions for simplification and improvement.     

Wide-band nulling performance versus number of pattern constraints for an array antenna

The problem of wide-band pattern hulling for an array antenna is addressed, in particular the relation between the number of constraints imposed and the sidelobe suppression achieved. The two constraint methods considered are multiple nulling over a narrow angular sector and hulling of the pattern and its derivatives at a single point. To first order the sidelobe cancellation is shown to be independent of the actual pattern type and is determined by only two parameters: the number of null constraintsMand the number of sidelobesvto be cancelled. The latter parameter directly translates into a desired hulling bandwidthDelta f. A numerical solution to the problem is offered in the form of curves, from which the number of nulls required to suppress a jammer over a given bandwidth can be conveniently estimated. This number is indicative of how many degrees of freedom a conventional adaptive antenna system must allocate to attain a specific hulling performance.     

Relation between diagram correlation factors and s-parameters of multiport antenna with arbitrary feeding network

Antenna diversity demands a sufficiently low diagram correlation factor p. A universal relation between p and the scatter parameters of a multiport antenna is derived for arbitrary numbers of ports and radiating elements. It is shown that the diagram correlation factor depends significantly on the number of ports. While for a two-port antenna a vanishing correlation factor can be achieved with port matching only, this is not possible for multiport antennas with port numbers greater than two.     

Transient characterization of a novel ultrawide-band antenna: the scissors antenna

A new ultrawide-band (UWB) antenna named the "scissors antenna" has been designed specially for transient ultrawide-band applications. The scissors antenna, which is composed of conducting wires, radiates ultrashort pulses with very low dispersion. The radiation of this antenna has been characterized by a transient measurement method suitable for characterizing UWB antennas with very low dispersion. After a presentation of the scissors antenna, this measurement method is described. The last part of the paper presents a comparison between the radiation characteristics of the scissors antenna obtained by the transient measurements and those obtained by the classical harmonic measurements.     

D-Fiber antenna characterization using finite-element analysis

An all-fiber antenna using piezoelectric polymer coated circular core D-fiber has been characterized using finite-element analysis. The response of the D-fiber antenna was determined over a wide frequency range from 1 MHz to 2 GWz. The modeling predicts an electric field induced phase shift of 2.43×10^-6 rad/(V/m) per meter at 5 MHz. At frequencies higher than 8 MHz, the optical response is dominated by radial resonances of the D-fiber/coating composite. Using the simulation results, a minimum detectable electric field of 41 μV/m has been achieved using a 1 km length of coated D-fiber. In addition, a D-fiber antenna network intended for microcellular communications has been analyzed using shot noise limited detection. The D-fiber antenna has potential applications in areas such as electromagnetic compatibility testing and radio-over-fiber networks where it provides a convenient means of optically generating radio signals     

海面角反射器的极化旋转域特性研究

为满足各向异性雷达散射截面积（radar cross section,RCS）角反射器的目标需求,本文设计了一种异型多面体雷达角反射器,并对其电磁散射特性进行了分析. 该结构在不同电磁波入射方向下具有不同的电磁散射特性,在不同威胁探测方向上具有不同的干扰效果,其最大RCS能够达到281.84 m². 异型多面体角反射器可以应用于多种场景下,将其配置在被保护重点目标区域附近,以特定的排列方式进行布设,当保护目标受到威胁时将会在被保护目标周围产生多个假目标,干扰敌方雷达制导武器.

     

ASK multiport optical homodyne receivers

Several types of ASK multiport homodyne receivers are investigated, and the impact of the phase noise and of the shot noise on these receivers is analyzed. The simplest structure is the conventional multiport receiver with a matched filter in each branch. This structure can tolerateDeltavT[deltavis the laser finewidth andTis the bit duration) of several percent with a small power penalty (3.6 percent for 1-dB penalty and 5.2 percent for 2-dB penalty). Optimization of branch filters of conventional multiport receivers does not help when the linewidth (and the penalty) is small but does improve the receiver performance for larger linewidths. The most important point of the paper is the novel wide-band filter-rectifier-narrow-band filter (WIRNA) structure, proposed and investigated here for the first time for optical communication systems. It is shown that the optimized WIRNA homodyne receivers are extremely robust with respect to the phase noise: the WIRNA tolerable value ofDeltavTis 3.6 percent for 1-dB penalty and more than 50 percent for 2-dB penalty. Thus, the WIRNA structure opens, for the first time, the possibility of constructing homodyne receivers operating at several hundred megabits per second with conventional DFB lasers without complicated external cavities. Under no-phase-noise conditions, all the multiport receivers investigated here have the same performance, which is identical to that of heterodyne ASK receivers. In addition, the optimized WIRNA receivers can tolerate tapproximately) the same laser linewidth as the heterodyne ASK receivers. Thus, the main difference between the WIRNA multiport homodyne and heterodyne receivers is that the former shifts the processing to a lower frequency range, in return for a more complicated implementation. This difference makes the WIRNA multiport homodyne receivers particularly attractive at high (say, several gigabit per second) bit rates.     

Wide-band measurements and characterization at 2.1 GHz while entering in a small tunnel

The wide-band complex transfer function and propagation characteristics in a small passageway tunnel for nonline-of-sight are studied in this paper. A two-dimensional wide-band model based on the uniform theory of diffraction (UTD) and geometric optics (GO) is implemented and a network analyzer is used to perform measurements. In order to obtain the power delay profile, a correction factor is used, which adjusts the deviation caused by the windowing and zero padding performed in frequency domain. The UTD model predicts quite well the averaged path loss, power delay profile, root-mean-square (rms) delay spread and coherence bandwidth, even when the curved tunnel is approximated to two straight lines. Furthermore, it is shown that the position of the transmitter is crucial in the performance of the system: the path loss slope and rms delay spread are increased when the inclination of the transmitter is increased. In all cases, the rms delay spread is lower than 40 ns, where the coherence bandwidth decreases to 20 MHz. This parameter is proposed to estimate the excitation zone inside a tunnel.     

土壤偏振光谱二向反射影响研究

实验测量了土壤在400～720 nm内的光谱二向反射分布函数(BRDF),并分析了偏振BRDF强度分量与实验观测角及波长的关系.由于Hapke模型能很好地描述入射辐射与地物之间的相互作用过程,利用Hapke二向反射模型实现土壤在可见光波段的BRDF强度分量建模.通过比较模型预测值与实验观测值可以看出,所采用的强度模型能...     

Wide-band orthomode transducers

A summary of the results of a mainly experimental investigation into the development of wideband orthomode transducers (OMTs) is presented. It is shown that satisfactory performance for many applications is possible over bandwidths in excess of 2:1. The wideband return loss and cross-polarization behavior are given where the OMT used is measured in conjunction with a wideband corrugated horn. Two types of OMT are considered: one based on a finline technique and the other on a quad-ridged waveguide geometry. Overall, the latter design gives superior performance