In this paper, we discuss two well known definitions of electromagnetic momentum, ρA and \epsilon₀[E x B]. We show that the former is preferable to the latter for several reasons which we will discuss. Primarily, we show in detail|and by example|that the usual manipulations used in deriving the expression \epsilon₀[E x B] have a serious mathematical flaw. We follow this by presenting a succinct derivation for the former expression. We feel that the fundamental definition of electromagnetic momentum should rely upon the interaction of a single particle with the electromagnetic field. Thus, it contrasts with the definition of momentum as \epsilon₀[E x B] which depends upon a (defective) integral over an entire region, usually all space.

In the forward modeling of the transient electromagnetic (TEM) method, a frequency-domain solution is usually obtained first, and the solution in the time domain is then calculated by a frequency-time transformation. At present, the three main fast frequency-time transformation methods are the Guptasarma algorithm, the sine and cosine numerical filtering algorithms, and the Gaver-Stehfest (G-S) algorithm. In recent years, with the increasing demand for fine detection at shallow depths, the small-loop TEM method has undergone rapid development. It is therefore important to evaluate whether the traditional forward modeling approaches can be directly applied to the small-loop method. In this paper, the principles of the three forward modeling methods and their limitations when being applied to the small-loop TEM method are discussed. Through a comparison with the analytical solution for a uniform half-space, we demonstrate that the accuracy of forward numerical calculation is affected by loop size and earth resistivity. When the Guptasarma, G-S, and cosine numerical filtering algorithms are used for small-loop TEM forward calculation, the overall calculation error becomes non-negligible, whereas the sine numerical filtering algorithm retains a high calculation accuracy. By studying the response of the frequency-domain solution, we analyze the cause of the error in the forward calculation. Generally, the sine numerical filtering algorithm is the most suitable method for fast and high-precision small-loop TEM forward modeling. The results obtained here should provide a foundation for high-precision forward modeling and inversion of the small-loop TEM method.

This paper presents a bidirectional coupler which is designed by combining nonuniform wiggly lines and the reflected power canceller (RPC) method. The combination not only brings about a high directivity but also makes a wideband structure with a compact size. Although, in the RPC method, an idle port is used to produce a reflected signal in order to achieve a high directivity, there are not any idle ports in the proposed coupler. The coupler was built on an FR4 substrate. The measurement results show that this structure is suitable to monitor forward and reflected signals in high power applications. The fabricated coupler has the directivity of more than 22 dB and the coupling flatness of ±0.12 dB in the forward and backward signals in a wide frequency range of 140 MHz-190 MHz.

A pattern reconfigurable patch antenna with dual band characteristic is investigated in this paper. Two substrates with an air layer of 2 mm is used to design the antenna. Two radiators are respectively printed on the top surfaces of the two substrates. The first radiator, which is the circular patch, is printed on the top surface of the upper substrate. Eight rectangular slots are also introduced to obtain directional radiation pattern with reconfigurable characteristic in low band by changing the current distribution, and no metal layer is printed on the bottom surface of the upper substrate. The second radiator, which is composed of a cross branch and four arc-shaped branches, is printed on the top surface of the lower substrate to provide weak coupling effect with the circular patch. A round ground plane and four symmetrical rectangular slots are printed on the bottom surface of the lower substrate to generate additional resonance point in high band with the characteristic of pattern reconfiguration. A total of 12 PIN diodes are installed in the rectangular slots to verify the accuracy of dual-band and pattern reconfigurable features. The measured result exhibits that the designed antenna has dual band characteristic, in which the low band f₁ is from 2.43 to 2.50 GHz with an average gain of 3.2 dBi and an average radiation efficiency of 73.5%, and the high band f₂ is from 4.83 to 5.03 GHz with an average gain of 5.24 dBi and an average radiation efficiency of 73.9%. Moreover, the measured radiation patterns show that the patterns can be reconfigured at 90-degree intervals simultaneously in two bands.

Conventional dielectric lenses rely on the accumulation of phase delay during wave propagation to produce a desired wavefront. By considering the required phase delay at each lens position, an `equivalent' transmitarray antenna can be obtained. Despite a lack of curvature as in conventional lenses, the phase delay in the transmitarray antenna is achieved via a periodic arrangement of unit cell elements to bend the incident waves in the desired directions. This paper presents the design and characterization of a 4-layer transmitarray antenna consisting of double square ring elements. The gap between the double square rings is varied as a fixed proportion of their dimensions, while keeping the widths constant. The transmitarray element can achieve a transmission phase range of 2350 with a loss of less than 3 dB. The performance of the transmitarray antenna is explicitly compared to that of a convex dielectric lens, both of which are operating at 8 GHz.

Bearingless switched reluctance motor can be used in aerospace and flywheel energy storage industry. Taking a 6/4/4 hybrid excitation double stator bearingless switched reluctance motor as an example, the motor adopts an E-block structure on the outer stator and is excited by permanent magnet and current. The loss calculation and thermal analysis of the motor is carried out by using finite element method. The result shows temperature distributions of the motor under natural air-cooling condition. The temperature change under different operating status is analyzed. Finally, the temperature change and transient temperature curve of each part of the motor are obtained through simulation, and the motor can run stably.

Conformal low profile antenna array has been widely used towards reduced radar cross section and good radiation characteristics. Being conformal, it has a number of advantages over planar antenna structure. This paper presents the radiation and scattering characteristics of a planar and conformal patch array with conventional and hybrid HIS-based ground plane on a low loss dielectric substrate. The use of a hybrid HIS layer instead of conventional metallic ground plane contributes to achieving wideband RCS reduction over 8 GHz-50 GHz, without degrading the radiation performance in terms of antenna gain, return loss and VSWR. The measurement results of the fabricated antennas are found in good agreement with the simulated ones. The radiation mode RCS of the conformal patch array has been analytically estimated and shown to be controlled in the operating frequency range. Such a low profile low RCS antenna array can be used as a subarray of phased arrays in fire control radars.

Study of Global Navigation Satellite System (GNSS) for various non-navigational applications is gaining importance day by day. Very recently, India's Navigation with Indian Constellation (NavIC) is a new entry in GNSS systems available worldwide such as GPS, GLONASS, Galileo and Beidou. One of the important non-navigational applications is the study of soil moisture with GNSS. NavIC is very much different from widely used and globally available GPS system. Therefore, in this paper we have analyzed and developed an algorithm for soil moisture retrieval with NavIC Carrier to Noise (C/No) ratio. Information of soil moisture is very beneficial for various applications such as groundwater estimation, management of agricultural, drought monitoring and prediction, weather forecasting and flood forecasting. Amplitude of multipath Carrier to Noise (C/No) ratio from the NavIC receiver at L−band has been utilized to determine the soil moisture from the smooth bare soil surface. The analyses of sensitivity of soil moisture have been carried out by observing the NavIC multipath data and measurement of in situ soil moisture content. The algorithm development focuses on the retrieval of multipath amplitude from the interference pattern created at the receiver due to direct signal and reflected/multipath signal. The 1st, 2nd, and 3rd order polynomials have been analyzed to detrend the signal before fitting it with sinusoidal variation. It was observed that the multipath amplitude retrieved after detrending the C/No data with the 1st order polynomial provides better correlation with observed soil moisture than the 2nd and 3rd order polynomials. An empirical relationship between multipath amplitude and soil moisture has been developed. This developed empirical relationship is capable of providing soil moisture with known multipath amplitude. The retrieved soil moisture with developed algorithm is in good agreement with observed soil moisture with RMSE of 1.43%. Obtained results indicate the promising potential for the estimation of soil moisture with NavIC C/No ratio.

We present a general theory of linear continuous circuits (microwave networks, waveguides, transmission lines, etc.) based on Lie theory. It is shown that the fundamental relationship between the low- and high-frequency circuits can be fully understood via the machinery of Lie groups. By identifying classes of distributed-parameter circuits with matrix (Lie) groups, we manage to derive the most general differential equation of the n-port network, in which its low-frequency (infinitesimal) circuit turns out to be the associated Lie algebra. This equation is based on identifying a circuit Hamiltonian derived by heavily exploiting the Lie-group-theoretic structure of continuous circuits. The solution of the equation yields the circuit propagator and is formally expressed in terms of ordered exponential operators similar to the quantum field theory's formula of perturbation theory (Dyson expansion). Moreover, the infinitesimal operators generating the per-unit-length lumped element local circuit approximation appear to correspond to operators (such as observables) in quantum theory. This analogy between quantum theory and circuit theory through a shared Hamiltonian and propagator structure is expected to be beneficial for the two separate disciplines both conceptually and computationally. Several applications are presented in the field of microwave network analysis where we introduce and study the Lie algebras of important generic classes of circuits, such as lossless, reciprocal, and nonreciprocal networks. Applications to the problems of generalized matching and representation theorems in terms of uniform transmission lines are also outlined using topological methods derived from our Lie-theoretic formulation and exact theorems on continuous matching are obtained to illustrate the potential practical use of the theory.

This paper presents the resonant properties of a new Asymmetric Single Split Resonator (ASSR) structure for metamaterial applications. The compact uniplanar structure is an asymmetric single split ring resonator with two non-concentric rings. The prototype is fabricated on a substrate of dielectric constant 4.4, loss tangent 0.025, and thickness 1.6 mm and analyzed based on reflection and transmission coefficients and unit cell simulations. The fabricated unit cell of miniaturized ASSR has a footprint area of 0.163ƛ₀ x 0.163ƛ₀ where ƛ₀ is the measured free-space wavelength corresponding to 1.63 GHz. The negative permeability meta-particle is best suited for high-performance multiband bandstop filters, sensors, and RFID applications in advanced communication systems. The paper presents the electric and magnetic responses of ASSR with its constitutive parameters for different field orientations in normal incidence.

An all-in-one UHF RFID tag antenna using nonuniform meandered lines for retail garments in the textile industry is presented. The all-in-one antenna offers relatively low cost, wide band, compactness, and good conjugate matching in the presence of its robust housing with good dipole-like read range. Results show an antenna with a wide bandwidth of 900MHz and a long read range of 10.2 m making the UHF RFID tag antenna using nonuniform meandered lines a potential candidate for retail garments in the textile industry. Simulations are corroborated by measurements and are in fair agreement.

In this paper, the performance analysis of a reconfigurable intelligent surface (RIS) assisted underwater optical communication (UWOC) system with a decode-and-forward (DF) relaying protocol is presented. The radio frequency (RF)-RIS link is subjected to Rayleigh fading while the optical UWOC link experiences mixture Exponential-Gamma distributions subject to heterodyne detection and intensity modulation with direct detection (IMDD). In order to obtain a traceable closed-form expression, the statistical distribution of the RF-RIS link is derived in terms of Meijer-G function. Thus, the exact closed-form expressions for system end-to-end outage probability and average bit error rate (ABER) for different modulation schemes are then derived. To gain further insight about the derived analytical expressions, asymptotic expressions for the system are derived at high signal-to-noise ratio (SNR) through which the diversity gain is obtained. The findings show the significant impact of the number of RIS elements, detection technique, and the UWOC optical turbulence on the system performance. Finally, Monte-Carlo simulation is used to justify the accuracy of the derived analytical results.

A novel two-step synthesis method of sparse nonuniform-amplitude concentric ring arrays (SNACRAs) to maximize the beam collection efficiency (BCE) for microwave power transmission (MPT) is proposed in this paper. In the first step, beetle antennae search (BAS) algorithm is used to optimize the radius of each ring of the SNACRA, to obtain the maximum BCE and the equivalent continuous excitation of each ring. In the second step, we find the least array element on each ring to discretize the continuous excitation on each ring by using the binary search (BS) algorithm directly under the restriction conditions and then find the excitation of each element. Through the above two steps of optimization, the optimal synthesized parameters of the SNACRA, including the maximum BCE, layout, excitation and power pattern, can be obtained highly efficiently. Many representative numerical results under different ring numbers, apertures, and receiving areas are presented. Comparing these numerical results with those of other three arrays for MPT, it is proved that the SNACRA synthesized by the two-step method can get higher BCE with less elements and have a relatively simple feed network.

A novel class of dual-mode filters with improved high frequency sideband suppression response making use of coplanar waveguide (CPW) square loop resonator is presented. The resonator is placed on the bottom plane and inside the defected area of the ground. The resonant property of the CPW square loop resonator as well as the coupling property between two degenerate modes with different patch perturbation is studied in the paper. Two T-shaped orthogonal feed lines are arranged on the top plane, which not only provide proper excitation to the resonator, but also introduce an additional source-load coupling, so the proposed filter is found to have two transmission zeros at high frequency sideband and takes on asymmetric frequency response. Such a compact dual-mode CPW square loop resonator filter operating at 2.68 GHz is designed and fabricated.

A methodology for designing planar spiral antennas with a feeding network embedded within a dielectric is presented. To avoid a purely academic work which may not be manufactured with available standard technologies, the approach takes into account manufacturing process requirements by choice of used materials in the simulation. General design rules are provided. They encompass amongst others, selection criteria for dielectric material, aspects to consider when sketching the radiating element design, as well as those for the implementation of the feeding network. A rule of thumb, which may be helpful in the determination of the antenna supporting substrate's height, has been found. The appeal of the method resides in the fact that it eases up the design process and helps to minimize errors, saving time and money. The approach also enables the design of compact and small-size spiral antenna as antenna-in-package (AiP), and provides the opportunity to assemble the antenna with other RF components/systems on the same layer stack or on the same integration platform.

In this paper, a novel miniaturized frequency selective surface (MFSS) with capacitive loading is proposed; it has characteristics of low profile, second-order, wide-band, and remarkable wide stop-band properties. In a specific frequency band, the proposed MFSS has a second-order filter function characteristic. The proposed MFSS is composed of three metallic layers separated by two dielectric substrates, which offers the spatial form of the second order microwave filter. The band and operating frequency can be controlled by the thickness of dielectric substrates and the gaps between the capacitive loading structures. The element size is smaller than 0.05λ x 0.05λ. The element thickness is less than λ/30, where λ is the free space wavelength at the resonant frequency. The frequency response produced by the proposed MFSS had very good stability when the plane wave incidence angles varied from 0 to 60 degrees. The fundamental frequency f₀ is 2.45 GHz; the relative bandwidth δ is 10%; and the stop-band is from 3 GHz to 39.6 GHz. The frequency response demonstrates the excellent filtering performance.

This paper presents a new saw-tooth shaped sequentially rotated fractal boundary (SRBF) square microstrip patch antenna (SMPA) for wireless application. The square shape is rotated by an angle `θ' and superimposed, realizing fractal like geometry at boundary. The rotation of square shaped patch is divided in equal number of scaling angles θ_n such that for every iteration of angle θ, fractal boundary geometry has been realized. The square shape is modified into a circular shape patch resonating at 2.5 GHz. A 450 tilted rectangular slot is cut inside the radiating element to achieve circular polarization at 2.45 GHz. The antenna is fabricated using an RT Duroid 5880 substrate, having size of 70 mm x 70 mm. The antenna offers measured impedance bandwidth (VSWR < 2) of 50 MHz (2%) with simulated peak gain about 7 dBi. The fabricated antenna is tested, and measured results are in close agreement with simulated ones.

A novel CPW-fed circular polarized slot printed monopole antenna for 5G application is presented. The proposed slot monopole antenna occupies a small area of 0.23λ_o x 0.35λ_o x 0.019λ_o, and the wavelength has been obtained for the center frequency of 3.4 GHz to 3.8 GHz range. First, two square slots are inserted on either side of the feed line and to provide two orthogonal electric fields, a spiral stub is embedded in one of the slots. In order to improve the axial ratio bandwidth of the proposed antenna, it is possible to etch another spiral stub on the other side of the feed line. The proposed antenna provides circular polarized radiation such that the reflection coefficient bandwidth (below -10 dB) is about 1.4 GHz (from 2.9 GHz to 4.3 GHz) or 38.89%, and the axial ratio bandwidth below 3 dB is about 400 MHz, from 3.4 GHz to 3.8 GHz. This is 11.1% at center frequency of 3.6 GHz. This antenna covers the useful frequency bandwidth for 5G application. Simulation and measurement results are presented.

According to the orthogonality of each sub-carrier in the multi-carrier phase-coded (MCPC) signal, this paper focuses on anti-interrupted sampling repeater jamming (ISRJ) and creatively proposes a novel radar signal based on time-frequency random coded (TFRC) method, namely TFRC-MCPC signal. Based on the perspective of waveform design, the TFRC-MCPC signal adopts a chaotic sequence with good pseudo-random to code each chip in time-domain and each subcarrier in frequency-domain. The TFRC method increases the pseudo-randomness of radar waveform pulses and reduces the correlation between radar echo and ISRJ, thereby effectively suppressing the interference of false targets. The TFRC-MCPC method and common filter design methods do not conflict with each other and can be used in combination. The simulation experiment results show that under the typical parameters described in the paper, compared with the traditional MCPC signal and LFM signal, the signal-jamming ratio (SJR) improvement factor of the TFRC-MCPC signal is optimized by 1-2dB after pulse compression, which verifies its feasibility and effectiveness.

The present work describes a new wideband circularly polarized MIMO rectangular antenna in cube form for X-band application (8 to 11.8 GHz). Proposed antenna structure shows pattern diversity in whole 360° angle with polarization diversity. The isolation between the antennas is more than -14.5 dB. The impedance matching bandwidth (IMBW) is 3.8 GHz, and 3 dB axial ratio bandwidth is 2.91 GHz. The envelope correlation coefficient is less than 0.035, and its diversity gain is 10 dB. A copper metallic cylinder is placed inside the cube antenna to reduce the mutual coupling between the antennas.