In this paper, we propose a very simple technique that offers an extra degree of freedom to optimize the design of a tire dust-based absorber with reduced height. Cladding is a technique that is used to enhance the surface properties of a part, and it has been used in many applications for many years. In this technique, a clad layer is created on the core material, and the composition of the clad layer is adjusted to enhance the performance of the core material. We use a rice husk-clad layer to enhance the impedance matching characteristics of the low-loss, tire-dust core, microwave absorber. The overall design is a two-layer, geometrically-tapered, pyramidal structure composed of two lossy waste materials. Our main goal was to make the front surface less reflective (impedance matched), hence the material of the outer layer (clad) of the absorber was selected on the basis of the analysis of the dielectric properties of the candidate materials. Optimum thickness of the clad was obtained by using CST simulation software and found to be 12 mm, for which a reflectivity performance of less than -20 dB was achieved in the frequency range of 4 to 20 GHz. The results were found to be better than those provided by an earlier design of the absorber, which was composed of a mixture of tire dust and rice husks.

The design of an efficient quasi-optics Frequency Selective Surface (FSS) filter which is required to provide a -3 dB pass band from 405 GHz to 441 GHz is presented. For atmospheric remote sensing application, this space-borne spatial device consists of a silicon layer and a thin copper layer which is perforated with periodic arrays of resonant dipole slots and circular apertures. FSS unit cell has a dimension much smaller than its operating wavelength. Unique features of this complex dense FSS structure include wide pass band properties with superb performance of frequency response and incident angles independence for TE polarization. Floquet mode analysis and finite element method (FEM) models are used to establish the geometry of the periodic structure and predict its spectral response.

Azimuth multichannel is a promising technique of realizing high resolution and wide swath for synthetic aperture radar (SAR) imaging, which consequently leads to extremely high data rate on satellite downlink system and confronts serious ambiguity in subsequent processing due to its strict limitation of pulse repetition frequency (PRF). Ambiguity suppression performance of conventional spectrum construction is disappointing when the samples are approximately overlapped. To overcome these weaknesses, a novel sparse sampling scheme for displaced phase center antennas based on compressed sensing (CS) is proposed in this paper. The imaging strategy sparsely sampled in both range and azimuth direction, leading to a significant reduction of the system data amount beyond the Nyquist theorem, and then operated the CS technique in two dimensions to accomplish target reconstruction. Effectiveness of the proposed approach was validated through simulation and real data experiment. Simulation results and analysis indicated that the new imaging strategy could provide several favorable capability than conventional imaging algorithm such as less sampled data, better ambiguity suppression, higher resolution, and lower integrated side-lobe ratio (ISLR).

A new design of broadband circularly polarized antenna is proposed. The antenna is composed of a square patch and a horizontal L-shaped stripline that feeds the patch at two orthogonal directions by two probes. The L-shaped feeding structure provides excitements of approximately equal amplitude and 90° phase difference and then good circularly polarized characteristics are obtained. Measured results show that the proposed antenna has 10-dB impedance bandwidth of 14.3% (2.27-2.62 GHz) and 3-dB axial-ratio bandwidth of 13.1% (2.3-2.62 GHz). Moreover, the measured gain is over 7 dBic within the effective band.

This letter presents a dual-band bandpass filter (BPF) using interdigital coupling lines with a new defected ground structure (DGS) pattern. Traditional DGS structures are mainly used to realize wide bandstop characteristics. In this letter, by introducing a pair of coupling stubs in the aperture of the DGS, a narrow passband can be achieved within a wide stopband, so a dual-band bandpass filter can be implemented. An equivalent circuit model is derived to describe the filter. And the circuit simulation result agrees well with the EM simulation one. The position and bandwidth of the two passbands can be designed and adjusted independently. In order to verify the theory, a dual-band bandpass filter is designed, fabricated and measured. The simulated and measured results are in good agreement.

A major challenge in UWB signal processing is the requirement for very high sampling rate under Shannon-Nyquist sampling theorem which exceeds the current ADC capacity. Radar signal is essentially a delayed and scaled version of the transmitted pulse, determined by sparse parameters such as time delays and amplitudes. A system for sampling UWB radar signal at an ultra-low sampling rate based on the Finite Rate of Innovation (FRI) and the estimation of time delays and amplitudes to detect UWB radar signal is presented in the paper. This sampling scheme which acquires the Fourier series coefficients often results in sparse parameter extraction for UWB radar signal detection. The parameters such as time-delays and amplitudes are estimated using the total variation norm minimization. With this system, the UWB radar signal can be accurately reconstructed and detected with overwhelming probability at the rate much lower than Nyquist rate. The simulation results show that the proposed approach offers very good recovery performances for noisy UWB radar signal using very small number of samples, which is effective for sampling and detecting UWB radar signal.

This paper presents a compact dual-band multiple input multiple output (MIMO) antenna with low mutual coupling, operating in the 2.4 GHz band (2.4-2.485 GHz) and 5.5 GHz band (5.15-5.85 GHz). The proposed antenna system consists of two antenna elements located at the top two corners of FR4 substrate (PCB). Each element dimension is reduced substantially by employing a folded structure and slots on the top patch plate, so that it takes up a small volume of 12 × 9 × 6 mm³. To enhance port-to-port isolation and efficiency of each antenna, an additional non-radiating folded shorting strip is connected between each antenna element and ground plane of PCB. The measured isolation values are lower than -28 dB over the lower WLAN band (2.4-2.485 GHz) and better than -26 dB (-30 dB in most of the band) across the higher WLAN band (5.15-5.85 GHz). The improvement in antenna's efficiency caused to raise up 1 dB of effective diversity gain of MIMO system. Furthermore S-parameters, radiation patterns and diversity performance characteristics are provided.

This paper proposes a new logging while drilling (LWD) method to evaluate rock moisture content and reservoir hydrocarbon saturation. Transient signal with broadband spectrum covering the sensitive range of fluids contained formation was used as excitation signal in the near-bit MWD system. Continuous measurement in the whole spectrum with both fluid type and saturation changes caused differences in frequency distribution of response signals and achieved integrated evaluation of formation hydrocarbon and water saturation. Linear system analysis was optimized by adding oil/water saturation parameters, and analytic calculating results were presented to verify the performance of the proposed transient MWD system. Compared with conventional wireline and LWD tools, the method presented in this paper provided higher resolution and signal intensity.

This paper presents the analysis of novelistic fractal optical antenna arrays in a conceptual manner. Fractal antennas are array antennas with converging and diverging growth of basic element or elements for multi-wideband capturing of the electromagnetic waves. Most of these antennas relay on two components for their characteristics. First one is the basic stage shape and second one is the number of stages of growth. For computing the direction of radiation the well-defined fractal array manifold and a good estimate of the covariance matrix of the fractal array response is needed.

In this paper, a novel triangular metamaterial (TMM) structure, which exhibits a resounding electric response at microwave frequency, is developed by etching two concentric triangular rings of conducting materials. A finite-difference time-domain method in conjunction with the lossy-Drude model was used in this study. Simulations were performed using the CST Microwave Studio®. The technique of specific absorption rate (SAR) reduction is discussed, and the effects of the position of attachment, the distance, and the size of the metamaterials on the SAR reduction are explored. The performance of the novel TMMs in cellular phones was also measured in the cheek and the tilted positions using the COMOSAR system. The TMMs achieved a 50.82% reduction for 1 gm SAR. These results provide a guideline to determine the triangular design of metamaterials with the maximum SAR reducing effect for a cellular phone.

In this paper, a novel dual-band RF-harvesting RF-DC converter with a frequency limited impedance matching network (M/N) is proposed. The proposed RF-DC converter consists of a dual-band impedance matching network, a rectifier circuit with a villard structure, a wideband harmonic suppression low-pass filter (LPF), and a termination load. The proposed dual-band M/N can match two receiving band signals and suppress the out-of-band signals effectively, so the back-scattered nonlinear frequency components from the nonlinear rectifying diodes to the antenna can be blocked. The fabricated circuit provides the maximum RF-DC conversion efficiency of 73.76% and output voltage of 7.09 V at 881 MHz and 69.05% with 6.86 V at 2.4 GHz with an individual input signal power of 22 dBm. Moreover, the conversion efficiency of 77.13% and output voltage of 7.25 V are obtained when two RF waves with input dual-band signal power of 22 dBm are fed simultaneously.

This paper presents a new design for wide slot circularly polarized (CP) antenna (WSCPA). The proposed design possesses much larger return loss bandwidths and CP bandwidths than existing WSCPA. The main features of the antenna structure include a modified CPW feeding line and a wide and symmetric ellipse-aperture along the diagonal axis. By properly tuning axial ratio of ellipse-aperture and parameters of feeding line, wideband return loss and CP radiations can be achieved. The measured bandwidths of 10-dB return loss and 3-dB axial ratio (AR) are as large as 112.5% (2.1-7.5 GHz) and 109% (2.3-7.8 GHz), respectively. The improvement process of the AR and S₁₁ properties is completely presented and discussed in this paper.

In this paper, we propose a novel frequency selective surface (FSS) with stable performance under large incident angles. The FSS is composed of hexagon metallic lines and hexagon patches. Using such a hexagon arrangement, the periodicity size could be miniaturized and thus the FSS unit cell is compact. The composite FSS has an excellent stability under large incident angles. In the passband 10.58-11.06 GHz, the insertion loss is still less than -1 dB for both TE and TM polarizations, even under incident angle up to 85 degree. Both the design procedure and experimental results of the novel FSS are presented and discussed.

A novel double-ridge loaded folded waveguide (FWG) traveling-wave tube (TWT) amplifier for sheet electron beam working at 140 GHz is proposed in this paper. The dispersion relation and interaction impedance characteristics have been analyzed based on the equivalent circuit method. The transmission properties and nonlinear interaction are investigated. The simulation results reveal that the double-ridge loaded FWG-TWT with sheet electron beam can make full use of relatively large electronic fields, and the average output power can be over 110 W at 140 GHz when the electron beam voltage and the current of the sheet beam are set to 12.7 kV and 150 mA, respectively. Meanwhile, the maximum gain and interaction efficiency can reach 34 dB and 12%, respectively. Compared with the traditional FWG-TWT, the novel FWG-TWT has the advantages of much higher efficiency and bigger output power.

The selection of a near-field or far-field ground-penetrating radar (GPR) model is an important question for an accurate but computationally effective characterization of medium electrical properties using full-wave inverse modeling. In this study, we determined an antenna height threshold for the near-field and far-field full-wave GPR models by analyzing the variation of the spatial derivatives of the Green's function over the antenna aperture. The obtained results show that the ratio of this threshold to the maximum dimension of the antenna aperture is approximately equal to 1.2. Subsequently, we validated the finding threshold through numerical and laboratory experiments using a homemade 1-3 GHz Vivaldi antenna with an aperture of 24 cm. For the numerical experiments, we compared the synthetic GPR data generated from several scenarios of layered medium using both near-field and far-field antenna models. The results showed that above the antenna height threshold, the near-field and far-field GPR data perfectly agree. For the laboratory experiments, we conducted GPR measurements at different antenna heights above a water layer. The near-field model performed better for antenna heights smaller than the threshold value (≈29 cm), while both models provided similar results for larger heights. The results obtained by this study provides valuable insights to specify the antenna height threshold above which the far-field model can be used for a given antenna.

The dynamical properties of cos-Gaussian beams in strongly nonlocal nonlinear (SNN) media are theoretically investigated. Based on the moments method, the analytical expression for the root-mean-square (RMS) of the cos-Gaussian beam propagating in a SNN medium is derived. The critical powers that keep the RMS beam widths invariant during propagation in a SNN medium are discussed. The RMS beam width tends to evolve periodically when the initial power does not equal to the critical power. The analytical solution of the cos-Gaussian beams in SNN media is obtained by the technique of variable transformation. Despite the difference in beam profile symmetries and initial powers, a cos-Gaussian beam always transforms periodically into a cosh-Gaussian beam during propagation, and the transformation between the two beams revives after a propagation distance.

Derivation is presented for analysing the shielding effectiveness of an enclosure with apertures and inner windows with Transmission Line Method (TLM). Theoretical values of shielding effectiveness are in good agreement with the simulation results. Results indicate that the capacitive window lowers the resonance frequency while the inductive window enhances the resonance frequency, and both of them improve the shielding effectiveness of the enclosure. The effects of location of the inner windows is discussed. Moreover, the present method can also be used in the condition that the enclosure has both inductive and capative windows.

A coherent processing method for subband signals of distributed multi-band radar data is proposed and tested. The method uses de-noising cross-correlation (DNCC) algorithm and statistical method to obtain phase incoherent parameters (ICP) between subband signals. After compensating the phase ICP, a coherence function is defined and combined with statistical method to find amplitude ICP. Finally, data fusion method via two-dimensional gapped-data state space approach (2-D GSSA) is applied to subband signals and high-resolution imaging of target is achieved. The advantage of this method lies in that it can be used to process subband signals of different bandwidth and different gaps between them. To validate our work, electromagnetic calculation target and real target measured in microwave chamber are analyzed and used for testing different mutual-coherence and data fusion algorithms. Experimental results demonstrate the superiority of the proposed method over previous approaches in terms of improved imaging quality and performance.

This paper presents a neural network based technique for the analysis of various stacked patch antennas, those can be applied for satellite and wireless local area network (WLAN) applications. In order to show the diversity of artificial neural network (ANN) modeling technique, two different trained neural networks were developed with different number of antenna geometrical parameters as inputs. These trained networks locate the operational resonance frequencies with their bands for stacked patch antennas (SPA) operating in the X-Ku (8 GHz-18 GHz) bands and WLAN bands (2 GHz-6 GHz). These frequency bands are useful for satellite communication and indoor wireless communication applications respectively. First ANN model takes design (geometrical) parameters of antenna like lower patch dimension, upper patch dimension, and height of air gap, as a input, whereas other NN model includes feed point location also as a input. The validity of the network is tested with the simulations results obtained from the full-wave Method of Moment (MoM) based IE3D and few experimental results obtained in the laboratory.

An LTE smart mobile antenna with multiband operation is proposed to work in the bands of LTE, GSM, DCS, PCS, PHS, UMTS, Bluetooth, and WLAN. Compared with those reported in the literature, the proposed antenna features a simple and straightforward design procedure, which is composed of three easy steps. Firstly, A three-dimensional meandering monopole antenna is constructed along the edge of a rectangular PCB to act as the main radiator, resulting in the bands of LTE, DCS, and PCS, PHS, and UMTS. Secondly, a shorted stub is fabricated to excite the GSM band, and also to improve the impedance matching in the bands of LTE and GSM. Finally, the second shorted stub is added to radiate in the band of WLAN. The numerical results show that the -6 dB return-loss bandwidths are from 0.7 GHz to 0.985 GHz (0.285 GHz, 34%) in the lower band and from 1.64 GHz to 2.535 GHz (0.895 GHz, 43%) in the higher band. The corresponding measured data are from 0.7 GHz to 1.03 GHz (0.33 GHz, 38%) in the lower band and from 1.64 GHz to 2.55 GHz (0.91 GHz, 43%) in the higher band. The measured antenna gains are about 2 to 3 dBi in the lower and higher bands, respectively.