Most imaging modalities image an object's interior while all instrumentation, including sources and receivers, is externally located. One notable exception is ultra-sound (US), which can be miniaturized sufficiently to locate a US transducer within an object and gather data for image reconstruction. Another is cross-borehole geophysical imaging. The goal of any internal imaging modality is to provide images of greater fldelity while avoiding interfering structures. Due to the bulkiness of multi-coil magnetic induction tomography (MIT), transmitting and receiving coils are never placed within small targets (e.g., a human body). Here, we demonstrate a novel implementation of single-coil MIT that performs a scan all while the coil is located within the interior of a small, lab-created phantom consisting of salt-doped agarose. Phantom geometry is annular, consisting of a 6.0 cm diameter channel of depth 5.5 cm surrounded by a 3.0 cm thick cylindrical wall. A centrally located agarose gel annulus, 2.0 cm thick, is doped with sucient NaCl to elevate its conductivity above that of surrounding agarose. The resulting nearly axisymmetric phantoms consist of material having conductivity ranging from 0.11 to 10.55 S/m. A scan is accomplished robotically, with the coil stub-mounted on the positioning head of a 3-axis controller that positions the planar circular loop coil into 360 or 720 pre-programmed internal positions. Image reconstruction from gathered data is shown to correctly reveal the location, size and conductivity of the approximately axisymmetric inclusion.

The method of broadband Green's functions with low wavenumber extractions (BBGFL) is used to calculate Green's function for inhomogeneous waveguides filled with different dielectrics and with irregular boundaries. To construct the BBGFL modal solutions, we derive governing equations of the linear eigen-matrix problem and orthonormalization condition. In BBGFL, the Green's function is represented in modal expansions with convergence accelerated by higher order low wavenumber extractions. To obtain a linear eigenvalue problem for the modes, we use two BBGFLs of rectangular waveguides with two dielectric wavenumbers. The orthonormalized mode functions are used to construct the Green's function. Current wavenumber derivatives and Green's function wavenumber derivatives are computed by a single low wavenumber MoM impedance matrix. The wavenumber derivatives are used to accelerate the convergence of modal summations to 6th order. Numerical results are illustrated and compared with the direct MoM method of using free space Green's function. Results show accuracies and computation efficiencies for broadband simulations of Green's functions.

Defected ground structures (DGSs) are often utilized in planar filters and antennas for compactness and spurious frequency suppressions by creating defects or slots on the ground planes. One disadvantage of conventional DGS filters is that the overall dimension increases as the order of the filter increases. In this research, we proposed an asymmetric finger-shape DGS which created multiple equivalent LC resonators when combining with a capacitive microstrip gap on the top. In contrast to the conventional high-order DGS filter by generating many DGSs on the ground plane, the finger-shape DGS provided a high-order bandpass response with one single DGS due to the capacitances between the top metallic strip and the ground plane. Therefore, we developed a wide-band, high-order, and spurious frequency suppressed microstrip bandpass filter with a compact size. To achieve these features, different filter design techniques were exploited including stepped impedance resonator (SIR), series-coupled resonator, and nger-shape DGSs. The main advantage of our DGS filter was that it had a higher-order and wider bandpass responses than other harmonic-suppressed work. A prototype was designed, fabricated, and measured with a calibrated vector network analyzer (VNA) where the simulations matched with the measurements. The finger-shape DGS filter demonstrated a passband centered at 2.35 GHz with a fractional bandwidth of 72.3%, the spurious frequency suppression up to 8.5f₀ where f₀ was the center frequency of the passband, and a compact size of 0.034λ₀² where λ₀ was the wavelength corresponding to f₀.

This work describes the path loss of radio propagation for wireless sensor network in the outdoor fruit orchard which is one of the common agriculture environments. The measurement was conducted in the jackfruit orchard in the 2.45 GHz band. Unlike other studies conducted in the fruit orchard environments, the variation of path loss over the relative angles between the plant rows and the line-of-sight direction from the transmitter to the receiver is identified. The equivalent vegetation obstruction model is proposed as the function of the equivalent number of trees along the line-of-sight to better represent the angular path loss variation. This leads to the proposal of the path loss prediction approach at any point in the fruit orchard by using a few measurement efforts. This work also introduces the Monte Carlo simulation using the numerical electromagnetic scattering computation called hybrid T-matrix method to evaluate the relative angular vegetation loss of a single tree that is used as the input to determine the equivalent number of trees. The evaluation results suggest that it can further reduce the measurement workload required for the proposed path loss prediction approach.

In this paper, a circularly polarized slot-patch antenna for nanosatellite is presented. The novel design of the circularly polarized wave conducted by two asymmetrical rectangular-truncation techniques implemented on a circularly-slotted-patch on the front side and a deformed-shifted-feedline on the back side of the substrate. The antenna is printed on substrates with the dielectric constant of 2.17 and thickness of 1.6 mm. The resonant frequency of the proposed antenna is set at 2.2 GHz with the minimum requirement of the axial ratio bandwidth (ARBW) of 300 MHz. The proposed antenna produces under -10 dB impedance bandwidth (IBW) 1.2765 GHz or equal to 58% (1.7235-3 GHz) with Left-Handed Circular Polarization (LHCP). The average antenna gain reaches 4.5 dBic at 2.2 GHz and the ARBW 327.5 MHz or about 14.88% (2.0275-2.355 GHz). This paper includes the description and presentation of the completed discussion.

Due to the existence of power coupling the virtual synchronous motor (VSG) will lead to overshoot fluctuations in the power adjustment process, thus affecting the control performance. Compared to the traditional direct current control inverter based on coordinate transformation, VSG model is more complex and difficult to achieve decoupling. This paper presents a dynamic power decoupling method by studying the coupling relationship between active power and reactive power of VSG. Firstly, the inverter grid-connected model is established, and the power expression is analyzed when the inverter output impedance is negligible. Then the virtual active power and reactive power expressions are obtained through coordinate transformation. Several key state equations and virtual states of the VSG are obtained. The power expression performs small signal perturbation to obtain the dynamic model of the VSG. From this, the dynamic model of the VSG can be analyzed to obtain the coupling relationship between the dynamic powers, and the series power compensation is used to decouple the dynamic power coupling. Finally, the correctness of the theoretical analysis and the effectiveness of the decoupling method are verified by simulation and experiments.

In this letter, a wideband dual-polarized dipole antenna is proposed for base station applications. By bending the arms of the dipole, the radiator size is reduced. Meanwhile, a new resonant mode occurs at high frequency. Besides, four shorting stubs are employed to improve the impedance matching. Finally, a wide operating bandwidth is realized by combining all resonant modes. A prototype of the proposed antenna is fabricated and tested. Experimental results show that the antenna has a wide impedance bandwidth of 53% (1.65-2.84 GHz) for VSWR<1.5 at two ports and a high port isolation of 26 dB. Also, a stable antenna gain around 7.9±0.5 dBi and a stable radiation pattern with 3-dB beamwidth of 67.5°±3.5° are obtained within the entire band of operation.

This work proposes an approach to retrieve the ferrite's electromagnetic properties in a single compact configuration, simpler than the traditional measurement systems. The ferrite under test is fully inserted into a rectangular waveguide with a magnetic bias. The complex scattering parameters are theoretically analyzed under the consideration of modal effect at isotropy-anisotropy interfaces. Extraordinarily sharp Fano resonances are observed in the scattering spectra, originating from the multimode interference inside the magnetized ferrite. There is good agreement among theoretical, experimental, and full-wave simulation results. This model can be further utilized to simultaneously retrieve all ferrite properties, including permittivity (ε), saturation magnetization (4πM_s), and magnetic linewidth (ΔH) from the measured scattering parameters, facilitating the designs and applications of ferrite devices.

A Direction Finding (DF) algorithm for small aperture DF systems is proposed. Traditionally, small aperture DF systems lack of beamforming capabilities and therefore require manual rotation, which may affect the Angle of Arrival (AOA) estimation accuracy. Based on Characteristic Mode (CM) Analysis, a Multi-Feed Structural Antenna (MFSA) is developed that utilizes an electrically small platform as a radiator. This paper chooses a Small Unmanned Aerial Vehicle (SUAV) as a design platform. The overlap of all Individual Element Radiation Patterns (IERPs) of the proposed MFSA covers the entire azimuth plane. In this way, beamforming and null steering of the MFSA on the azimuth plane can be achievedby linearly combining all weighted IERPs. A new method based on Vector Singular Value Decomposition (SVD) is proposed to determine the weight vector of beamforming (``Sum'' pattern) and null steering (``Difference'' pattern) in a specific direction. Based on the ``Sum-Difference'' delta method, the AOA of the Radio Frequency (RF) signal source can be estimated. A small aperture VHF DF system with a multi-channel digital-IF receiver is developed to experimentally verify the proposed concept. The evaluation results show that the AOA estimation RMS error is 1.55°, and the false detection rate is significantly improved.

A revision of main propagation mechanisms of radio waves for wireless sensor networks is presented in this paper. In order to address this topic, the free space model is firstly taken as a reference. Classical concepts like ground reflection, diffraction, and surface waves are included from a theoretical point of view, and some aspects related to wireless sensor networks are analyzed for each subject. A key parameter is the height of antennas which plays an important role on distinct formulations like reflection coefficient of the ground surface. From there, when antennas are very close to ground surface, the far field conditions could be different from that typical expression. Hence, some of propagation models involve a characterization of far field conditions, and practical settings of antennas for wireless sensor networks are analyzed by electromagnetic simulation. Attenuation due to vegetation is also reviewed, and models suitable for these networks are exposed.

A novel design to enhance the bandwidth of a low-profile substrate integrated waveguide (SIW) cavity antenna is presented. Distinct from traditional antennas with unilateral slots, bilateral slots are utilized as radiating elements in the proposed design. By etching an additional slot at the bottom plane, a new resonant mode is introduced, and quality factors of two original modes are significantly reduced. Antenna's bandwidth can be dramatically enhanced by merging these three modes within a single operating band. A prototype is fabricated and measured. With the height of 0.018λ₀, the measured 10-dB bandwidth is 410 MHz (3.24-3.65 GHz), corresponding to 11.9% fractional bandwidth. The measured gain is higher than 4.3 dBi, and the measured efficiency is around 75% within the operation band. Those attractive features, e.g. low profile, enhanced bandwidth and moderate radiation performance, make the proposed antenna suitable for future 5G systems.

We present a rigorous solution of a two-dimensional problem of stationary electromagnetic plane wave diffraction by a slot in a perfectly conducting screen having finite thickness in the presence of a plane dielectric layer behind the screen. For obtaining this solution, the method of additive regularization of singularities for field diffraction integrals is developed. This method is suitable for the cases of transparent, absorbing and amplifying dielectric. It reduces to explicit extraction of singularities in the form of supplementary singular integral terms, which describe waveguide modes of a dielectric layer. On the bases of the obtained solution, the conditions of optimum diffraction excitation for such modes are investigated in dependence of geometrical parameters of the problem for the cases, when these parameters are of the order of the radiation wavelength.

An X-band pyramidal horn antenna with a fourth order Chebyshev filtering function is presented in this paper. Four resonators are implemented in linear rectangular waveguide in the filter design. The last stage resonator provides not only resonance pole but also radiation function. To achieve high directivity, a pyramidal horn is attached to the filter output port, with negligible effect on the filter performance. Theoretical results are calculated based on the coupling matrix between the resonators. Finally, a pyramidal horn antenna operating at 10 GHz is designed and fabricated for demonstration. The measured results have found to be in good agreement with the simulated ones.

In this work, we propose a balun embedded driver stage to enhance the bandwidth and minimize the chip size of a differential CMOS power amplifier. By removing the passive input transformer, the bandwidth and chip size are improved. The proposed driver stage acts as an input balun as well as the driver stage for the power stage. The proposed driver is composed of a cascade connected PMOS, an inductor, and NMOS to generate the differential output signal. For the function of the input balun, the gate of the PMOS is connected to the drain of the NMOS. To verify the feasibility of the proposed balun embedded driver stage, we design a differential CMOS power amplifier for 5-GHz IEEE 802.11n WLAN applications. The designed power amplifier is fabricated using the 180-nm SOI RF CMOS process. The measured 3-dB bandwidth is approximately 2.5 GHz. The chip size of the fully integrated power amplifier, including input and output matching networks and test pads, is 0.885 mm². The measured maximum output power is 20.18 dBm with a PAE of 10.16%.

This work presents a novel structure of semi-circular floral shape slotted antenna for an ultra-wideband (UWB) including WCDMA, Bluetooth and Wi-Max applications. Initially, a semi-circular floral shape radiator is designed by inserting an elliptical slot in patch with partial rectangular ground plane. Further, three rectangle symmetrical stepped slots are inserted in ground below 50 ohm micro-strip (MS) feed line which is integrated with stepped quarter wave transformer to achieve an ultra-wide impedance bandwidth. The proposed antenna structure achieves UWB of 4-18 GHz which cover 127% (S₁₁<-10 dB) fractional bandwidth (FBW). Furthermore, ground plane is modified by loading three asymmetrical capacitive folded strip resonators (CFSR), which provide an additional lower frequency communication bands 2100 MHz (2-2.2 GHz), 2400 MHz (2.34-2.47 GHz), and 2700 MHz (2.69-2.75 GHz) for applications of WCDMA, Bluetooth, and Wi-Max, respectively. An optimized dimension of the proposed antenna is 30×30 mm² (1.1λ₀ ×1.1λ₀), which is designed and fabricated on an FR-4 substrate having thickness 1.6 mm and dielectric constant 4.3. The proposed design is computed by Electromagnetic (EM), ADS simulator, and simulation results are validated with measured results.

The classification algorithms of polarimetric synthetic aperture radar (PolSAR) imagesare generally composed of the feature extractors that transform the raw data into discriminative representations, followed by trainable classifiers. Traditional approaches always suffer from the hand-designed features and misclassification of boundary pixels. Following the great success of convolutional neural network (CNN), a novel data-driven classification framework based on the fusion of CNN and superpixel algorithm is presented in this paper. First, the region-based complex-valued network utilizes both the intensity and phase information to predict the label of each pixel and constructs the label map based on spatial relations. Second, superpixel generating algorithm is adopted to produce the superpixel representation of the Pauli decomposition image, and the contour information which reflects the boundary of each category is preserved. Finally, the original label map and contour information are fused to make the decision of each pixel, outputting the final label map. Experimental results on public datasets illustrate that the proposed method can automatically learn the intrinsic features from the PolSAR image for classification purpose. Besides, the fusion of the superpixel features can effectively correct the misclassification of the boundary and singular pixels, thus achieving superior performance.

Most of space-time adaptive processing methods have the excellent ability to suppress interferences when the space-time covariance matrix is perfectly estimated. Unfortunately, these methods may have calculation error of the covariance matrix in the case of fewer snapshots, which may lead to remarkable performance degrading. To solve the aforementioned problem, a space-frequency domain anti-jamming algorithm based on the compressed sensing theory (CS-SFD) is presented. Firstly, the proposed method utilizes less sampled data to form a space-frequency two-dimensional sparse representation for the narrowband interference signals. Secondly, the interference covariance matrix estimation problem is modeled as a sparse reconstruction problem which can be efficiently solved by the orthogonal matching pursuit algorithm. Furthermore, the diagonal loading method is used to modify the interference plus noise covariance matrix. Finally, the weight vector is given by the minimum output power criterion. Compared with the previous work, the presented method has better robustness and more effectively anti-jamming performance in the case of fewer snapshots. Simulation results show the effectiveness of the proposed algorithm.

The Cramer-Rao lower bound (CRLB) for calculating errors and accuracy of direction-of-arrival (DOA) estimation is discussed for a number of planar waves arriving on an antenna array. It is well known that the geometry of antenna arrays imposes restrictions on the performances of the direction-of-arrival estimation. In particular, the influence of the directivity factor of the individual antenna elements on the accuracy of the DOA estimation of the radio emission sources for circular (cylindrical), cubic and spherical antenna arrays consisting of the directional antenna elements is investigated. The directivity factor of antenna elements is changed within wide limits in order to determine the values at which the high accuracy of the direction-finding can be achieved. It is shown that further increasing the directivity factor of each antenna element makes the mean square error in the determination of the coordinates of the signals increase as well. The exact expression for the Cramer-Rao lower bound for the DOA-estimation variance calculation depending on the antenna directivity and the geometry is presented. The obtained exact equation shows the most important factors that the direction-of-arrival estimation accuracy is dependent on. A technique of obtaining antenna arrays with optimal directional elements locations is proposed. Those arrays allow increasing DOA estimation accuracy by several times.

This paper presents a reconfigurable, wide-beam antenna with a modular main radiator for base station applications. The addition of new spectrum and the path to 5G create unique antenna requirements in terms of patterns and impedance matching capabilities. The antenna in this paper exhibits a wide azimuth beamwidth up to approximately 180^o, and implements a modular approach where the antenna can be recongured for impedance matching requirements. Two congurations of the wide-beam antenna are presented; the rst conguration covers the 1.7-2.7 GHz band for 3G/4G/LTE applications where multiple wireless carriers would use the same antenna as a neutral site. This antenna provides wide-beam operation and a 10-dB return loss from approximately 1.64-2.76 GHz. The measured return loss over the 1.7-2.7 GHz band is better than 13 dB. A second conguration of the antenna is tuned for performance from 1.9-2.4 GHz where measured return loss better than 19 dB is achieved in this band. Simulated and measured return losses and patterns are presented that show very good agreement between simulation and measurement, and thorough parametric pattern analysis is presented for the baseline antenna configuration.

A general synthesis approach is proposed for reflectarrays using second order Phoenix cells. It relies on an original spherical representation that transforms the optimization domain in a continuous and unbounded space with reduced dimension. This makes the synthesis problem simpler and automatically guarantees smooth variations in the optimized layout. The proposed mapping is combined with an Artificial Neural Network (ANN) based behavioral model of the cell and integrated in a min/max optimization process. Bi-cubic spline expansions are used to decrease the number of variables. As an application, a contoured beam for space communication in the [3.6-4.2] GHz band is considered. The gain improvement compared to an initial Phase Only synthesis (POS) is up to 1.62 dB at the upper frequency. Full wave simulation of the final array is provided as a validation.