In this paper we present a novel approach for calculating the torque between two filamentary circular coils with inclined axes whose centers are at the same plane. In this approach we use Grover's formula for the mutual inductance between two filamentary circular coils with inclined axes whose centers are at the same plane. The filament method is applied to the combination comprising a filamentary circular coil and a thin wall solenoid. As the comparative method we give the new formula for this coil's combination which is derived from Chester Snow's formula for two solenoids with inclined axes.

A pattern-synthesis approach previously described by the author is used here to develop Dolph-Chebyshev-like patterns for some unconventional array geometries. The approach is briefly summarized and then demonstrated for various non-uniformly spaced arrays and nonlinear geometries. Geometries discussed include a V-shaped array, and x-aligned arrays having non-uniform element spacing as well as having elements located off the x-axis in the x-y plane. Arrays having randomly located elements are also exploted. The goal is to show that patterns having equipple sidelobes can be produced by a variety of array geometries.

A cavity-backed crossed bowtie dipole antenna for wideband circularly polarization (CP) is proposed in this letter. By introducing four inverted L-shaped parasitic elements with sequentially rotated angles, two extra CP modes areexcited, thus greatly broadening the 3-dB Axial-ratio (AR) bandwidth (BW) of the antenna. The proposed antenna is simulated, fabricated and measured. Results show that the antenna generates a 10-dB impedance bandwidth (IBW) of 91.4% (1.2-3.22 GHz) and a 3-dB AR bandwidth of 74.1% (1.37-2.95 GHz). In addition, the antenna achieves a unidirectional radiation pattern with a stable gain of 6.52-9.27 dBi over the whole CP operating band.

In this paper, a method to miniaturize a stepped open-slot antenna (SOSA) for ultra-wideband (UWB) applications is proposed. The antenna consists of a stepped open slot, J-shaped slots, and two strip directors. A broadband microstrip-to-slotline transition with circular stubs is applied to feed the antenna. J-shaped slots are inserted on the ground plane of the antenna to create a new resonance in the low-frequency region, thereby miniaturizing the size of the antenna. Finally, two strip directors are appended above the stepped open slot in order to increase the gain in the middle- and high-frequency regions, as well as to enhance input impedance matching in the high-frequency region. A prototype of the miniaturized SOSA is fabricated on an FR4 substrate with dimensions of 30 mm×32 mm. It shows a measured frequency band of 2.99-10.87 GHz for a voltage standing wave ratio < 2, which ensures UWB operation, and the measured gain range is 3.2-7.3 dBi in the band with a front-to-back ratio > 8.7 dB.

In this paper, a novel compact ultra-wideband (UWB) power divider with triple-notched bands is investigated. Firstly, the initial UWB power divider is studied using a couple of square ring quad-mode resonators. Then, by embedding a pair of coupled triple-mode stepped impedance resonators (TMSIRs) into the initial UWB power divider, three desired notched bands are achieved. The central frequencies of the notched bands can be easily controlled by the electrical length of the TMSIRs. To validate the design theory, a novel compact UWB power divider with triple notched bands centered at frequencies of 3.7 GHz, 5.2 GHz and 7.8 GHz is designed and measured. The simulated and measured results indicate that it has a low insertion loss and good return loss performance at all the three ports and a high isolation between the two output ports across the UWB bandwidth from 3.1 to 10.6 GHz.

Because of the maneuvering of hypersonic target, the tracking of near space hypersonic target is difficult. In this paper, a new adaptive tracking algorithm based on aerodynamic model and improved square root cubature kalman filter is proposed. The adaptive piecewise constant Jerk model, gives the acceleration recursive process based on the dynamic model. Considering the non-linear characteristic of the target state model and the observation model, the improved square-root cubature kalman filter is applied to estimate target state. The simulation results under different maneuvers conditions indicate that the proposed method has higher accuracy than original aerodynamic model. The research provides a feasible solution to the further improvement of the real time tracking accuracy of near space hypersonic target.

A novel frequency reconfigurable antenna is proposed for WiMAX and WLAN applications. It has a simple structure and compact size of 0.44λ_g×0.37λ_g. The proposed approach is based on combining of double planar U-shaped antenna. Furthermore, to achieve a reconfigurable function, a PIN diode switch is introduced across the slot between the two U-shaped patches. By controlling the PIN diode, the antenna resonates at two modes of single and dual band (WiMAX 3.2/3.5 GHz, and WLAN 5.2/5.8 GHz). The obtained gain ranges from 2.3 to 3.9 dBi within the whole operating bands. The simple configuration and low profile nature of the proposed antenna is suitable for Wireless communication systems.

In this paper, a compact triple-band bandpass filter using metamaterial (MTM) inspired structure with controllable transmission zero (TZ) position has been proposed. The gap between feed lines develops electrical coupling and provides series capacitance. An open loop rectangular ring resonator with meander line and rectangular stub develops electric and magnetic couplings separately. Defected ground structure (DGS) provides proper impedance matching and increases the passband. In order to validate metamaterial (MTM) behaviour of designed filter dispersion diagram has been plotted. The position of transmission zero can be controlled by electric and magnetic coupling. The measured operating frequency ranges of three passbands are 1.85-2.15 GHz, 3.55-3.73 GHz and 3.85-4.0 GHz with the 3 dB fractional bandwidth of 15.63, 4.94 and 3.82 percent, respectively. It has minimum insertion loss of 0.7 dB, 0.5 dB and 0.5 dB at the 1st, 2nd, and 3rd passbands, respectively. The electrical size of the proposed filter is 0.16λ_g×0.15λ_g, where λ_g is the guided wavelength at zeroth order resonance (ZOR) frequency of 1.92 GHz.

This paper presents the design investigation and experimental testing of a flux-focusing magnetic gearbox with a fully laminated rotor structure. The unique feature of this flux-focusing magnetic gearbox design is that the three rotors are each made of a single lamination stack, and the central modulation structure is retained in place without the use of a resin filler such as epoxy. Ferromagnetic bridges are used to connect individual pole pieces together. It is shown that the use of the ferromagnetic bridges reduces the calculated torque density from 156 Nm/L to 139 Nm/L (a reduction of 11%). The experimentally measured torque density is, however, only 97 Nm/L. The reason for this discrepancy is associated with the demagnetization of the magnets.

A phase diversity printed-dipole antenna element for patterns selectivity array application is designed in this paper. The antenna element consists of a printed dipole structure and two varactors. By changing the control voltage of each element, various radiation phases in the far field of each element is realized, that is, the peak gain direction of the array is changed. With this method, the structure designed is simple, and only two varactors are loaded. To verify the feasibility, an antenna prototype is experimentally characterized, which validates the proposed concept. The impedance bandwidth of array is 22.2% (3.2~4.0 GHz), in which the peak gain direction can be scanned during angles from -θ to +θ across broadside (θ = 13°~18° at different frequencies). It can be applied to phased antenna system.

To provide better care to the people, who are living in rural areas and whoever in need of emergency medical care, it becomes essential to develop remote monitoring health care applications. Body Area Networks (BAN) that are formed with wearable or implanted wireless sensor devices will play an important role to achieve the above task. Since the communication in BAN is of short communication distance and higher data rate, the Ultra-Wideband (UWB) radio signals make themselves as the right candidates due to their inherent characteristics. This requires more research in design and development of UWB transceivers, especially for implantable biomedical devices. This paper proposes a UWB antenna design and a numerical channel model to predetermine the path loss characteristics of an on-body to in-body channel in UWB. The proposed model has been developed using ray tracing procedures and includes the antenna polarization and radiation pattern. In addition, the predicted results have been validated by measurements conducted with honey based liquid phantoms.

Synthetic Aperture Radar (SAR) image registration is to establish reliable correspondences among the images of the same scene. It is a challenging problem to register the airborne SAR images for the instability of airborne SAR systems and the lack of appropriate geo-reference data. Besides, techniques for registering satellite-based SAR images relying on rigorous SAR geocoding cannot be directly applied to airborne SAR images. To address this problem, we present a coarse-to-fine registration method for airborne SAR images by combining SAR-FAST (Features from Accelerated Segment Test) feature detector and DSP-LATCH (Domain-Size Pooling of Learned Arrangements of Three patCH) feature descriptor, which only relies on the gray level intensity of SAR data. More precisely, we first apply SAR-FAST, which is an adapted version of FAST for analyzing SAR images, to detect corners with high accuracy and low computational complexity. To reduce the disturbance of speckle noise as well as to achieve efficient and discriminative feature description, we further propose an improved descriptor named DSP-LATCH to describe the features, which combines the Domain-size Pooling scheme of DSP-SIFT (Scale-Invariant Feature Transform) and the idea of comparing triplets of patches rather than individual pixel values of LATCH. Finally, we conduct a coarse-to-fine strategy for SAR image registration by employing binary feature matching and the Powell algorithm. Compared with the existing feature based SAR image registration methods, e.g., SIFT and its variants, our method yields more reliable matched feature points and achieves higher registration accuracy. The experimental results on different scenes of airborne SAR images demonstrate the superiority of the proposed method in terms of robustness and accuracy.

A new compact topology of rectenna, which combines a miniaturized wideband printed antenna and a rectifier integrated on the radiating surface, is reported in this paper. The rectenna is designed for ISM 900 MHz band and applied to wireless power transmission and energy harvesting to supply Ultra-Wideband tags for 3D indoor localization. The rectenna allows activating a DC-DC boost converter that supplies power to the tags. It exhibits a minimum conversion efficiency of 25% for very low microwave power densities (>0.18 μW/cm²) on the non-optimal loading impedance (of about 10 kΩ) of a commercial DC-to-DC boost converter and power management unit. The harvested DC voltage obtained from this novel rectenna exceeds 330 mV for microwave power density of 0.22 μW/cm². This measured DC voltage is in the range of the cold turn-on/start-up voltage of nowadays commercial off-the-shelf DC-to-DC boost converters and power management units. The proposed rectenna is also very compact, as its surface (10.5x6 cm²) is of 0.05λ² at the operating frequency (860 MHz).

In this paper we present a new compact microstrip lowpass filter using a П-H-П-DGS resonator etched in the ground plane and two patches compensated capacitors placed on the top layer. Two DGS shapes are electromagnetically coupled. The proposed lowpass filter has shown improvement by adding a square microstrip to the single DGS resonator. The design procedure is validated using the commercial full-wave EM MoM simulator Microwave Office. Simulated as well as measured results exhibit sharp roll-off (ξ) of 34 dB/GHz and create a transmission zero at around 4 GHz with attenuation level -34 dB near the passband. On the other hand, the proposed LPF has shown wide stopband bandwidth with rejection better than -20 dB from 3.5 GHz up to 11.5 GHz, while the size of the whole structure is smaller (20 mm x 20 mm). Finally, the proposed filter structure was fabricated and measured. The measurements are in a good agreement with the simulated results.

Slot skew is applied as a method to increase the armature winding voltage waveform quality of synchronous hydro generators. Skew that matches the region of one slot pitch can effectively damp stator slot harmonics. However, achieving this condition can be difficult I some manufacturing cases, especially for the machines with greater axial length. That is why other methods are commonly used to increase the voltage waveform quality of large hydro generators. One such method is based on the damper winding slot pitch choice which ensures reduction of stator slot harmonics from the main magnetic field. Appropriate placement of damper bars over the pole shoe does not represent a significant technological problem and is much simpler to manufacture in compare with the slot skew or the fractional armature winding methods. The downside of damper slot pitch adjustment method is the damper bar currents incensement in steady state condition of the generator, which increases damper winding losses and also the rotor temperature. In order to decrease damper winding current for long term operating and enable the generator pole shoe design with smaller cross section damper bars, a combination of damper slot pitch and partial slot skew can be utilized. This paper gives insight on consequences that can occur for voltage waveform if slot skew does not not fully match the stator slot pitch and the advantages of above mentioned combined method for the design optimization of salient pole synchronous generator.

Two different designs of orthomode transducers for the coming Ku-band receiver of the Italian radio telescope in Medicina are presented and compared, showing design details, describing numerical simulations and discussing manufacturing and test results. Such orthomode transducers provide a tradeoff between low-loss and phase-matching, according to different initial requirements where the final receiver architecture has to be frozen. Both designs show high performance over the operative 13.5-18.1 GHz Ku-band. One of the OMT designs has been fabricated and tested, showing results in very good agreement with simulations.

Hybrid beamforming systems are a cost and energy efficient architectural approach for large-scale antenna arrays operating at millimetre-wave frequencies. The separation of the beamforming process into an analogue beamforming network and a digital precoding part enables the reduction of digital channels, while preserving a precise beam steering capability. Especially subarray-based hybrid beamforming systems distinguish them due to a low complex analogue beamforming network. However, to determine the ideal analogue and digital precoding matrices the channel state information has to be estimated. This estimation process is hampered by the electrical interconnection of different antenna elements within the analogue beamforming network. Hence, a separation of the antenna elements of the subarrays in the digital domain is not possible. Furthermore, actual channel estimation methods for hybrid beamforming systems are based on beam training techniques, which suffer from long estimation times. To overcome these problems we developed a two-stage channel estimation method for subarraybased hybrid beamforming systems using sparse array estimations. In the first stage, only one antenna element of each subarray at the transmitter is active during the channel estimation, resulting in a sparse array estimation. To distinguish the transmitters at the receiver side the transmitters are separated in the frequency domain using different orthogonal frequency division multiplexing subcarriers. For recovering the full-dimensional channel matrix we present two algorithms. The first algorithm is based on a two-dimensional interpolation of the channel matrix, while the second algorithm uses multiple subsequent channel measurements. The presented estimation method enables thereby a direct determination of the channel matrix with only one or a few measurements.

In this paper, a novel ultrathin five-band polarization insensitive Metamaterial Absorber (MA) is proposed. The proposed structure consists of a periodic array of six arrows with two concentric hexagonal rings, having novel hexagonal 2D-bravais lattices on a grounded FR-4 dielectric substrate (ε_r = 4.25, loss-tangent tanδ = 0.02). The simulated result shows five discrete absorption peaks. The near unity absorption occurs at 2.7, 6.9, 7.3, 13.6 and 16.9 GHz with peak absorptivity of 88.99, 94.45, 87.58, 93.06 and 90.42% respectively. The proposed absorber is ultrathin with thickness of 0.056λ₀ corresponding to the highest frequency of absorption. In order to analyze the absorption mechanism of the structure electromagnetic parameters such as effective permittivity (ε_eff) and effective permeability μ_eff) are retrieved and plotted. Wave absorption phenomena are explained by comparative tabulation of real and imaginary parts of electromagnetic parameters. Absorption is further explained by the characteristics impedance and surface current distribution. The structure, being a six-fold symmetric, has been found to be polarization-insensitive under normal incidence. For the oblique incidence of waves, it also achieves high values of absorption for both TE and TM polarizations. The proposed absorber is fabricated, and scattering parameters are measured. Simulated and measured results are in close agreement. Performance of the proposed MA is further investigated by calculating Fractional Bandwidth (FBW). This absorber can find its applications in phase imaging, photo-detector, hyper-spectral imaging, micro-bolometer, spectroscopic detection, surveillance radar and other defence applications.

The celebrated Sommerfeld wedge diffraction solution is reexamined from a null interior field perspective. Exact surface currents provided by that solution, when considered as disembodied half-plane laminae radiating into an ambient, uniform space both inside and outside the wedge proper, do succeed in reconstituting both a specular, mirror field above the exposed face, and a shielding plane-wave field of a sign opposite to that of the incoming excitation which, under superposition, creates both the classical, geometric-optics shadow, and a strictly null interior field at the dominant, plane-wave level. Both mirror and shadow radiated fields are controlled by the residue at just one simple pole encountered during a spectral radiative field assembly, fixed in place by incidence direction φ₀ as measured from the exposed face. The radiated fields further provide diffractive contributions drawn from two saddle points that track observation angle φ: Even these, more or less asymptotic contributions, are found to cancel exactly within the wedge interior, while, on the outside, they recover in its every detail the canonical structure lying at the base of GTD (geometric theory of diffraction). It is earnestly hoped that this revised scattering viewpoint, while leaving intact all details of the existing solution, will impart to it a fresh, physically robust meaning. Moreover, inasmuch as this viewpoint confirms, admittedly in an extreme limit, the concept of field self-consistency (known in rather more picturesque language as Ewald-Oseen extinction), perhaps such explicit vindication may yet encourage efforts to seek exact solutions to scattering/diffraction by electromagnetically permeable (i.e., dielectric) wedges, efforts that harness integral equations with polarization/ohmic currents distributed throughout wedge volumes as sources radiating into an ambient, uniform reference medium.

The results of experimental research and development of the diffraction radiation oscillator with a periodic structure in form of a reflective double comb and with frequency tuning on mutual coupled modes in its open resonant system were presented. As an operating mode we chose the mutual coupled modes TEM₀₀₂ → TEM₁₀₁, which arise in the open resonant system with the shift between mirrors symmetry planes. To analyse its features, a rigorous electrodynamical 2-D model of the open resonant system was used, and the optimal shift width was established. As a result, the operation on the mutual coupled modes allowed to extend the frequency tuning range without failures in output power and to exclude the influence of higher-order modes (TEM_20q, TEM_30q etc.) on the output characteristics of the oscillator. The research has been carried out in Ka band.