A real time, low complexity algorithm is developed to steer a planar patch antenna array beam to the maximum received signal strength (RSS) direction for communication link enhancement. The beam steering towards the maximum incoming signal direction is based on an iterative technique utilizing a set of RSS measurements taken from specific locations in the search space, these locations collectively form an ellipse. The algorithm is denoted as ``elliptical peeking''. It was simulated for a flying unmanned aerial vehicle (UAV) as the vehicle tries to identify the maximum signal strength incoming direction of a stationary ground signal and it was tested on an embedded platform to validate its low demand for computational power. Such an algorithm is suitable for autonomous platforms due to its simplicity and low cost.

In this paper, a printed Vivaldi antenna with two pairs of eye-shaped slots is proposed for UWB applications. By using two pairs of eye-shaped slots, the side lobe levels of the radiation pattern are reduced, and the antenna gain is improved at low frequencies. To illustrate the effectiveness of the proposed design, a prototype of the proposed antenna is fabricated and measured. Experimental results show that the proposed antenna presents a measured impedance bandwidth, defined by |S₁₁| < -10 dB, from 3 to 12.8 GHz with a compact size (36 mm×36 mm). Good unidirectional radiation characteristics with a front-to-back ratio better than 10 dB are also achieved. The measured gain is better than 3.7 dBi in the operating frequency band. In addition, the measured group delay of the proposed antenna is around 1.2 ns with a variation less than ± 0.5 ns.

This study investigates snowfall detectability and snowfall rate estimation with NASA's CloudSat through the first evaluation of its newly released 2C-16 SNOW-PROFILE products using the National Mosaic and Multisensor QPE System (NMQ) snowfall products. The primary focus is on the detection and estimation of 18 surface snowfall. The results show that the CloudSat product has good detectability of light snow (snow water equivalent less than 1 mm/h) but degrades in moderate and heavy snow (heavier than 1 mm/h). The analysis suggests that the new 2C-SNOW-PROFILE algorithm is insufficient in correcting signal losses due to attenuation. Its underestimation is well correlated to snowfall intensity. Issues of sensitivity and data sampling with ground radars, which may affect the interpretation of the results, are also discussed. This evaluation of the new 2C-SNOW-PROFILE algorithm provides guidance for applications of the product and identifies particular error sources that can be addressed in future versions of the CloudSat snowfall algorithm.

A novel feed network based on the microstrip/slotline transition is proposed in this paper. This feed network not only has ultra-wide impedance bandwidth but also can improve space utilization and make the design of antenna array easier. Then an ultra-wideband (UWB) antenna array with four elements fed by the network is designed. The antenna array is simulated, manufactured and measured. The results show that: the impedance bandwidth with return loss under -10 dB is 88.76%, from 2.35 GHz to 6.1 GHz. Within the impedance bandwidth, the radiation performance is satisfactory, and the gain of the array is 2.1-7.1 dB, higher than that of the element. The cross-polarization level of the array is lower than -20 dB, just as the element. A reasonable agreement of results is achieved between simulation and measurement.

In optical region, the scattering center model is very useful in scattering analysis, target recognition and data compression. The method based on Hough transformation performs well in most cases. However, the algorithm extracts the scattering centers one by one via a clean method, which is time consuming. To solve this problem, a novel method is proposed in this paper to extract the scattering centers. By searching the estimated 1D scattering centers, the candidate positions for 3D scattering centers are extracted. Then the candidates are discriminated by a clustering based procedure. By employing the new algorithm, the 3D scattering centers can be extracted simply and the clean step is unnecessary, which makes the procedure efficient. The experiment results of the high-frequency-electro-magnetic data demonstrate the performance of the proposed method.

A simple and effective method of bandwidth enhancement for the printed meander line antenna (MLA) is proposed. This approach is characterized by symmetrically printing two meandering sections on both sides of a dielectric substrate and connecting them via shorting pins at the bottom of meandering sections, which are connected to a capacitive stripe for impedance matching. The illustrative equivalent circuit and the corresponding principle of bandwidth enhancement of this double-layered MLA are presented. The measured results of these double-layered and single-layered MLAs manifest the validity of our design approach.

In this paper, a rectangular metallic monopole antenna with normal rectangular stubs is presented for application in ultra-wide band communication systems. It is shown by computer simulations (HFSS and CST) and actual fabrication and measurement that the addition of protruding normal metallic stubs lead to the increase of impedance band width. The optimum design of geometrical dimensions of the antenna (consisting of the monopole plate and stubs) achieves up to 10 dB return loss in the UWB (3.1-10.6 GHz) frequency range. The radiation efficiency of antenna is better than 95%. Furthermore, the antenna provides linear polarization, with quite low cross-polarization levels.

A generalization propagator method (GPM) is presented. It is the extension of traditional propagator method (PM). In order to make full use of the received data, many propagators are structured according to different block structures of array manifold. By these propagators, a high order matrix is obtained in a symmetric mode, and it is orthogonal with array manifold. Based on this matrix, a generalization spectral function is obtained to solve the problem of direction-of-arrival (DOA) estimation by spectral peak searching. Moreover, in order to avoid spectral peak searching, a generalization root-propagator method (GRPM) is also proposed, and shows excellent estimation precision. Numerical simulations demonstrate the performance of the proposed method.

A novel wideband sleeve antenna with capacitive annulus for wireless communication applications is presented in this paper. A sleeve structure is introduced to improve the impedance bandwidth through exciting a new resonate point. By loading capacitive annulus at the center of sleeve, an impedance bandwidth enhancement is achieved at the upper frequency band. The measured impedance bandwidth for VSWR≤2 about 142.8% ranging from 1.01 to 6.06 GHz is achieved, and monopole-like radiation patterns are presented. A prototype has been fabricated and tested, and the experimental results validate the design procedure. It is sufficient for accommodating recent wireless communication services such as DCS1800, PCS1900, IMT2000, WLAN, WiMAX2350/3500, etc.

In this paper, a quad-antenna system for laptop computers is studied. Because two dual-antenna systems can construct a quad-antenna system, the dual-antenna systems in the open literature are utilized. The mutual coupling between the two dual-antenna systems is analyzed and reduced. To validate the design of a quad-antenna system, the quad-antenna system, consisting of two dual-antenna systems proposed in the open literature and a decoupling element, is fabricated and tested. Its measured -10 dB impedance bandwidths are 200 MHz (2.33-2.52 GHz) and 1.62 GHz (4.5-6.12 GHz). The measured mutual couplings are below -15.5/-19 dB at the 2.4- and 5.2/5.8-GHz WLAN bands, respectively. The measured gains are better than 2.4/3.9 dBi with efficiencies higher than 70%/72% at the two bands, respectively. The envelop correlation coefficient is evaluated based on the measured results.

It is well known that MUltiple SIgnal Classification (MUSIC)-type algorithm produces a good result for the imaging of thin dielectric inhomogeneity in full-view inverse scattering problems. In contrast, it yields a poor result in limited-view inverse scattering problems. In this paper, we verify the reason for the above by establishing a relationship between a MUSIC-type imaging function and the Bessel functions of the integer order of the first kind. This verification is based on the asymptotic expansion formula for thin dielectric inhomogeneity. Various numerical examples are shown for confirming our verification.

Two novel short tapered leaky wave antenna (LWA) designs with a complementary split ring resonator (CSRR) structure are proposed in this paper. The CSRR structure is positioned at 1/4λ_g away from the open-end edge of the LWA. For one of the antenna designs, the CSRR is placed at the ground plane; for the other one, the CSRR is placed on the antenna plane. The reflected wave caused by the open-end edge of the LWA is cancelled by the reflected wave caused by the CSRR, thus, the back lobe can be effectively suppressed. The length of these two short tapered LWAs with CSRR design is only 1.2λ_g at 4.3 GHz. According to the measurement results, the impedance bandwidth is 650 MHz for 7 dB return loss, which covers the range from 4.3 GHz to 4.95 GHz. The back lobe can be suppressed effectively about more than 12 dB at the whole operating frequency band. The scanning range of the main beam is about 34˚, which covers the scanning angle from 10˚to 44˚.

The present article expounds a formalism for the representation of multi-port non-reciprocal antenna structures in an arbitrary surrounding linear medium. In the most general approach the antenna, the waveguides connected to it, as well as the surrounding medium may contain any distribution of anisotropic magneto-electric media. Furthermore, an arbitrary external field is taken into consideration which need not be of plane wave form. A reciprocally adjoint system is introduced to derive relations which describe the antenna under such general conditions. Since the antenna may contain media which prohibit the use of ordinary scattering, admittance or impedance matrices, an approach by means of generalized scattering matrices, or by a generalized admittance and a generalized impedance matrix, is applied. This leads to an n-port description of the whole waveguide-antenna environment where transfer operators render the interaction between the external field and the state of the ports. These operators are the generalizations of effective length vectors. For its importance the case of reciprocal reflection-symmetric waveguides is treated in detail, including a derivation of the consequences of abstract network reciprocity and complex power relation for voltage-current representations. The formalism is adequate for the description of radar and radio astronomy antennas, in particular when wave polarization plays a crucial role and/or a magnetized plasma environment is present (which is responsible for anisotropy and non-reciprocal conditions).

A modification in the structure of substrate has been carried out to reduce weight and improve the performance of microstrip patch antenna in X-band. A step profile is incorporated in the substrate along the radiating edges of the patch. The design is tested on both dielectric and magnetodielectric substrates. Return loss of antenna with varying step riser height and step tread length shows improvement in -10 dB bandwidth to 13.2% for the dielectric and to 12.3% for the magnetodielectric as compared to about 4.8% and 6.9% for unprofiled substrate geometry in dielectric and magnetodielectric respectively. As compared to the unprofiled planar antenna, maximum weight reduction for the stepped antenna on dielectric substrate is 54.75 % and for the magnetodielectric is 58.9% is observed. An equivalent circuit modeling for the stepped structure is carried out for the proposed structure.

In this paper the scanning properties of dual reflector antenna systems constituted by two confocal paraboloidal reflectors fed by a planar array are investigated. This antenna architecture combines the interesting features of reflectors and array antennas. Because of the offset configuration the radiation pattern exhibits an anomalous deviation in the beam pointing when the beam is scanned out of the boresight direction. Heuristic equations, representing an extension of the linear equations available in the literature, are derived, which permit predicting the pointing direction of the overall system as a function of the pointing direction of the feeding array in a significant field of view.

Micro-Doppler (MD) caused by the motion of the ballistic missile can contribute to successful recognition of the ballistic missile. Considering the real observation scenario. This paper proposes a method to derive the MD image of the ballistic missile by applying the range-Doppler algorithm (RDA) based on the real flight scenario and analyzes the factor for the real-time MD imaging. Simulation results using the flight trajectory constructed using the real target parameter demonstrate that we need a new cost function for phase adjustment and a new method for range alignment. In addition, matched-filtering needs to be performed in the baseband, and a sufficient PRF is required to prevent discontinuity of the MD image. Dechirping of MD and filtering of the random movement are also needed for a clear MD image.

This paper reports a 2.45 GHz, low power dual circularly polarized (DCP) and dual access rectenna. It contains two dc-recombined rectifiers and a cross-slot coupled square patch antenna fed by a microstrip line. A judicious dc recombination scheme allows to minimize the RF power imbalance between accesses caused by multipath effects and consequently arbitrary polarized incident waves. The proposed rectenna is then able to harvest linearly polarized, right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic waves, with nearly stable performances. The rectenna has been optimized at -15 dBm per access and dedicated to remote and contactless supply low consumption sensors. It has been experimentally tested with very low power densities from 0.057 μW/cm² (E_rms=0.46 V/m) to 2.3 μW/cm² (E_rms=2.95 V/m). At 1.49 μW/cm² (-15 dBm on each rectifier), the structure exhibits an output dc voltage and a global efficiency of 189 mV and 37.7%, respectively when the azimuthal angle (Φ) of the incident field is equal to 0°. Due to the nearly constant total gain of the DCP antenna and an appropriate dc recombination of the two rectifiers, the global efficiency slightly varies between 37.7% and 41.4% when the azimuthal angle (Φ) varies between -90 and 90°.

The scenarios of achieving effective ionospheric modification are summarized, and the likely physical processes engaging linear and nonlinear mode conversions through plasma inhomogeneity and nonlinearity are revealed. Parametric instabilities, which are the directly relevant processes to achieve effective heating of the ionospheric F region, are formulated and analyzed. The threshold fields and growth rates of instabilities are obtained. The nonlinear Schrodinger equation governing the nonlinear evolution of Langmuir waves is derived and analyzed. The nonlinear periodic and solitary solutions of the equation are obtained. The analyses illustrate the conditions for the generation of Langmuir soliton and nonlinear periodic Langmuir waves.

In this paper, we propose a modified version of the Random Sample Consensus (RANSAC) method for Interferometric Synthetic Aperture Radar (InSAR) image registration based on the Scale-Invariant Feature Transform (SIFT). Because of speckle, the ``maximization of inliers'' criterion in the original RANSAC cannot obtain the optimal results. Since in InSAR image registration, the registration accuracy is in inverse proportion to number of residues. Therefore, we modify the old criterion with a new one --- minimization of residues --- to obtain the optimal results. We tested our method on a variety of real data from different sensors, and the experimental results demonstrated the validity and robustness of the proposed method.

Given the emphasis on increasing wireless network usage for healthcare application, e.g. Wireless Body Area Network (WBAN), the need for high-rate physical layer has become a genuine concern from research and industrial community. The use of the Ultra-Wideband (UWB) is looking especially bright for such systems given its lower energy consumption and performances towards frequency-selective channels. However, the Multi-Band-OFDM-based UWB technique has some inherent limitations as loss in spectral efficiency due to the use of Cyclic-Prefix (CP). In this paper, a new physical layer scheme for high-rate wireless body area networks based on MB-OFDM with Offset Quadrature Amplitude Modulation (OQAM) modulation is presented. The proposed MB-OFDM/OQAM can achieve high spectral and power efficiency than conventional MB-OFDM system. Moreover, the use of the CP Interval in the conventional MBOFDM removes efficiently the Inter-Symbols Interferences (ISI) but remains ineffective towards the Inter-Carriers Interferences (ICI) caused by the channel frequency offset (FO). The performances evaluation of the proposed technique will be carried-out in realistic UWB-WBANs channels with various scenarios, which will be also presented and studied herein.