The use of radar micro-Doppler (m-D) signatures for human activities classification, surveillance and healthcare has become a hot topic in recent years. While m-D signals are always multicomponent, it is necessary to separate them into mono-components signals associated with individual body parts for easier features analysis and extraction. In this paper, a novel method called local time-frequency sparse reconstruction (LTFSR) is proposed to iteratively extract and separate m-D components one by one in a descending intensity order from a time-frequency (T-F) representation. For the current strongest m-D component, we first estimate its instantaneous frequency (IF) by dividing the signal into short overlapping time intervals and selecting the best matching chirp atom to approximate the local frequency in each time interval based on matching pursuit. Then, a T-F filtering is used to extract and remove the strongest component from the multicomponent signal. Repeat the above steps until all m-D components are separated. Simulations are given to validate the effectiveness and robustness of the proposed method.

A 4-port wideband Multiple-Input Multiple-Output (MIMO) antenna operating in the frequency band from 24.8 GHz to 27.6 GHz dedicated to 5G application is proposed in this manuscript. The MIMO antenna is implemented on a 23.75 × 42.5 × 0.508 mm³ Roger/Druoid 5880 substrate with relative dielectric constant ε_r = 2.2 and loss tangent 0.0009. Firstly, the design starts with a simulation and optimization of a single element antenna based on Minkowski fractal shape as Defected Ground Structures (DGSs) using CST Studio Suite. The single proposed element shows a 7 dBi gain and antenna efficiency of 85% at the operating frequency band. Secondly, to design a MIMO antenna with good isolation, three different configurations are used, and overall MIMO performances such as low Envelope Correlation Coefficient (ECC), high Diversity gain (DG), and low Channel Capacity Loss (CCL) are calculated and analyzed. Finally, fabrication and measurement are conducted to validate the concept for single and 2-port MIMO antenna performance.

This paper presents two novel different feeding and coupling schemes to solve the problem of generating transmission zeros (TZ) in lower stopband and their applications to design single-band filters. The designed two filters are based on substrate integrated waveguide (SIW) square cavity with orthogonal ports. In the design of Filter A, two L-shaped stubs are introduced to form an addition coupling path between two ports, which cause the generation of one TZ. Other two TZs are formed due to the resonance characteristics of L-shaped stubs and ports offset. Two metal vias are used to adjust center frequency slightly. In the design of Filter B, other two stubs are designed to form two additional coupling paths, thus forming a total of three coupling paths with the original path. Two TZs are obtained by utilizing the phase difference between different paths, and one TZ is generated for the resonance characteristics of the proposed stub 3. Simultaneously, an L-shaped slot is used to adjust center frequency. Both designed filters use the coplanar waveguide (CPW) structure to control bandwidth. Two filters are set to operate at 14.4 GHz with bandwidth of 800 MHz. Both filters are fabricated and measured. The simulation results of two filters are in good agreement with the measured ones.

In this paper, eigen analysis of the correlation matrix for an 8-element singly curved conformal antenna array with plane wave(s) incident at different angles is presented. The signal eigenvectors derived from the correlation matrix are used as the array weights to generate peak beams toward the directions of the signals, and the noise eigenvectors derived from the correlation matrix are used as the array weights to generate nulls in the directions of the signals. A 1 x 8 microstrip patch antenna array is embedded on an anhedral corner type structure with different amount of surface deformation to analyse the array pattern. The patch antenna elements in the conformal array are excited with attenuators (for amplitude control) and phase shifters (for phase control) to implement the complex signal eigenvectors practically. The simulated eigenbeams using conformal antenna array are in good agreement with the measurement results. Furthermore, the effects of surface deformation on gain and beamwidth of array main beam is discussed. The proposed eigenbeam conformal antenna array can be used in smart and adaptive array applications.

An 8-element/8-port antenna with four resonating dual-polarized slot radiator elements for sub-6 GHz 5G multiple-input multiple-output (MIMO) applications is proposed in this paper. The proposed MIMO design comprises four annular slot radiators with dual-polarized characteristic and has rectangular micro-strip line feeds. The designed elements operate in the frequency bands 2.73-3.12 GHz and 4.33-4.68 GHz providing an acceptable characteristic for dual-polarizations. The isolation improvement and reduction in mutual coupling factor are achieved by using split ring resonator (SRR) structures on the top layer along the slot radiator. The proposed design has a -10dB wide impedance bandwidth in both bands, considerable realized peak gain around 4 dBi, and better efficiencies around 80\% with ECC < 0.004 which has enhanced the performance of the MIMO array in terms of diversity. The antenna is fabricated, characterized, and it is shown that the measured results are in good agreement with the simulated ones. The proposed MIMO design has been analyzed for SAR functions and the radiation coverage in the vicinity of the user human head. The SAR values studied are found to be less than `2' which is quite desirable. All the features achieved in the proposed MIMO design suggest it to be suitable for 5G mobile terminal applications.

In this paper, a Rectangular Monopole Antenna (RMPA) with offset microstrip feed is presented. The structure is fabricated on an FR4 substrate with a dimension of 28 x 32 x 1.6 mm³. The proposed structure achieves multiband operation by engraving 2 Complementary Split Ring Resonators (CSRRs) and a C-Shaped slot. Also, 2 Split Ring Resonators (SRRs) are printed on the adjacent sides of the radiating element. The parametric analysis is used to determine the optimum position of the feed and other critical parameters. The proposed structure operates at 2.25 GHz, 3.86 GHz, 4.60 GHz, 5.64 GHz, 5.86 GHz, 6.94 GHz,7.48 GHz, and 9.47 GHz. The permeability of the SRR and permittivity of the CSRR are extracted and presented. The proposed antenna is fabricated and measured. The measured results of S11, radiation pattern, and gain are on par with the simulated results. The proposed antenna's simulated surface current and efficiency are also presented to validate the performance. Simple structure, stable radiation patten, multiband operation, reasonable gain, and efficiency are the significant features of the proposed RMPA.

In this article we give an analytical formula for calculating the self-inductance for circular coils of rectangular cross-section which has a non-uniform current density. Recently, the formula for calculating this important electromagnetic quantity was published in the form of the single integral whose kernel function was asum of elementary functions. However, a new formula is obtained in the form of elementary functions, single integrals, and the complete elliptic integral of the first, second and third kind. Although its development looks tedious, we obtain a rather user-friendly expression for the calculation. From the general case, the self-inductance of the thin disk coil (pancake coil) with the nonuniform current is obtained in a remarkably simple form. The results of this work are compared with different known methods, and all results are in the excellent agreement. Our approach has not been found in the literature.

This paper presents a new design concept of dual bandpass filter. Based on the strong coupling between two resonators, a dual 1-pole band-pass filter is designed and is used as the basic building block. By providing appropriate weak coupling between these building blocks, a higher-order dual bandpass filter can be realized. In addition, these building blocks can be stacked vertically and/or horizontally to construct a compact filter. In this way, by using 3D full wave EM and circuit co-simulation, the simulation time required in the design stage can be reduced. In addition, it also provides a way to post-tune each building block individually and further reduces the time required in prototype post tuning process. For demonstration, an L-band dual 4-pole bandpass filter is designed with passband frequencies of 1.23 GHz~1.255 GHz and 1.55 GHz~1.6 GHz. In order to reduce the size of the filter and obtain a wide stopband bandwidth, a suitable evanescent mode cavity is used to realize the resonant structure. The measurement result shows that the insertion losses of the low passband and high passband are 1.03 dB~2.00 dB and 1.02 dB~1.75 dB, respectively; the return loss of both passbands is better than 15 dB. Furthermore, up to 5 GHz (> 3fo, where fo is at 1.39 GHz), the stopband rejection level is better than 80 dB.

In this work, a novel 4 element Multi-Input Multi-Output (MIMO) antenna is reported. The proposed antenna has a size of 50x50x1.6 mm³ is printed on the FR-4 substrate having dielectric constant ε_r = 4.4 and loss tangent (tan δ = 0.02). The four antenna elements are positioned in each corner of the PCB board in an orthogonal manner such that they can provide better isolation between antenna elements. The proposed MIMO antenna is designed to operate in frequency bands of 2.25 GHz to 2.4 GHz and 4.7 GHz to 6.3 GHz. The lower band ranges from 2.25 GHz to 2.4 GHz and covers 2.3 GHz WiBro applications while the upper band ranging from 4.7 GHz to 6.3 GHz is useful for Hiper LAN and Wi-MAX applications. The proposed antenna acquires return loss less than -10 dB and isolated by more than 16 dB throughout the dual operating bands. The structure exhibits stable gain and radiation patterns. Various diversity performance metrics including envelope correlation coefficient (ECC), diversity gain (DG), and mean effective gain (MEG) are evaluated and are within acceptable limits.

A frequency reconfigurable microstrip patch antenna with two asymmetric L-slots is proposed in this article. Two RF pin diodes inserted on the asymmetric L-slots are used to switch the operating frequency over the C band. Design and optimization of different physical parameters of the antenna viz. slot dimensions, feed location, notch size and pin diode positions are carried out using High Frequency Structure Simulator Version 13.0. The design is implemented on an FR4 substrate (ε_r = 4.4) of dimension (35×40×1.6) mm³. DC bias circuitry for RF PIN diode activation is also integrated with the antenna. Switching combinations of two PIN diodes offer four reconfiguration modes of operation at 4.75, 5.05, 5.11 and 5.18 GHz. In all the states, the -10 dB bandwidth shows minimal changes with average variations of 15.8% with respect to the state when both PIN diodes are OFF. The gains of the antenna for different modes of operation are found almost stable with an average of 6.64 dBi.

Monitoring the prestress of prestressed steel strands is important but difficult. The magnetoelastic inductance (MI) method is used to monitor the prestress. A coupling model was established to describe the correlation among stress, magnetism, and inductance. A prestress monitoring system based on the MI effect was proposed. To verify the feasibility of the method, experiments were carried out. The results showed that influenced by the hydration heat of the grouting materials, the fluctuation range of the inductance was 1.033%. When the hydration came to an end, the inductance approached the initial inductance. For internal steel strands, the obtained inductance-prestress relationship was similar to the relationship of external steel strands. Thus, the prestress of the internal steel strands could be monitored by the MI method.

In this letter, a surface-mount planar inverted-F antenna (PIFA) is proposed for the 5G mmWave system using ball grid array packaging (BGA). To meet the requirement of cost-effectiveness, the proposed antenna element is designed on a single FR4 layer to achieve low cost. To achieve a compact size, the BGA packaging is used on the proposed antenna element. Finally, the size of the antenna prototype is only 4.5 mm × 4.5 mm × 1.3 mm. Besides, the surface-mount feature allows the proposed antenna to be integrated with other devices in the same system package. The simulation and measurement results are discussed in detail. The measurement results show that the impedance bandwidth of - 10 dB is 15.3 % (24.7-29.6 GHz), and the peak gain is 5.85 dBi at 28 GHz. The proposed PIFA can be used in the 5G NR bands N257 (26.5-29.5 GHz), N258 (24.25-27.5 GHz), and N261 (27.5-28.35 GHz).

This paper describes the ramifications in the capacity of Multiple Input Multiple Output (MIMO) wireless links when the antenna systems involved are mischaracterized and contain phase errors. Errors in simulated as well as measured radiation patterns are considered. Also, simple deterministic Line of Sight and stochastic propagation environments are examined. The analyses are carried out on a 2×2 MIMO system. Results show that the resultant error in capacity depends on the degree of the phase error between the antenna ports, the type of propagation environment, as well as the degree of the illumination Signal to Noise Ratio (i-SNR).

Transparent conducting materials with the ability of broadband electromagnetic shielding have a widespread range of applications in aerospace, medical equipment and electronic communications. Achieving enhanced electromagnetic shielding effect without sacrificing much optical transparency is the technical trend in both academia and industries. Here, we experimentally propose a flexible hybrid film constructed by nano-printing based metal meshes and a graphene coating for the transparent electromagnetic shielding application. Numerical analysis is carried out to investigate optimal balance between electromagnetic shielding and optical transparency. In the experiment, enhanced shielding ability of hybrid film is observed without excessively sacrificing optical transmittance, compared to the reference group (the case only with metal mesh). Our work provides a hybrid platform for the high-performance optically transparent shielding materials for electromagnetic environment safety protection.

A low loss propagating electromagnetic wave is shown to exist at a gradual interface between two lossy conductive media. Such a surface wave may be guided by a seafloor-seawater interface and it may be used in radio communication and imaging underwater. It should allow communication distances of the order of 500 m at 10 kHz along a sandy seabed. Similar surface waves may also be guided by various tissue boundaries inside a human body. For example, such surface wave solutions may exist at planar interfaces between skull bones and grey matter inside a human head at 6 GHz.

A direct synthesis approach is presented to realize in-line topology filters with adjacent frequency-variant couplings implementing a transmission response with the same number of finite transmission zeros as poles. The proposed method starts with an N-order fully canonical filter response definition. A non-resonant node (NRN) is incorporated into the transversal network to make room for an extra coupling, and as a consequence of the extended similarity transformation applied, the NRN is transformed into a resonant node. The result is a network with N poles and N transmission zeros implemented with N+1 resonant nodes and N FVC, being able to describe a fully canonical response with an inline network without cross couplings.

In this paper, a compact tri-band flexible MIMO antenna based on liquid crystal polymer (LCP) is designed to operate in WLAN and WiMAX bands. The antenna consists of two identical antenna elements. The isolation structure includes a ground slot, two I-shaped branches, and a parasitic strip. The measured results show that the impedance bandwidth (S₁₁ < -10 dB) covers three frequency bands of 2.38-2.55 GHz, 3.37-3.60 GHz, and 4.92-5.37 GHz, and the S₂₁ of working bands is basically better than -19 dB. Moreover, the flexibility of the MIMO antenna is analyzed at different bent cases. The specific absorption ratio (SAR) values are obtained by simulating the model of antenna approaching human body. The simulated results show that the SAR value of the antenna meets the European Union (EU) standard. The proposed antenna demonstrates the characteristics of satisfactory radiation, high isolation, sound gain in working bands and flexibility, which has good application prospects in the wearable field.

A problem of electromagnetic waves radiation diffracted at a narrow rectilinear arbitrarily oriented slot cut in an end wall of a semi-infinite rectangular waveguide is solved by an asymptotic averaging method. The slot radiates into a half-space over an infinite perfectly conducting plane. An influence of slot inclination angle upon energy and spatial characteristics is numerically studied. Theoretical results are compared with experimental data. A numerical-analytical problem of a narrow rectilinear slot radiating into the space above an infinite impedance plane is also presented. The asymptotic solution for the slot magnetic current was obtained by a generalized method of induced magnetomotive forces (MMF) by using Green's functions of a space above the impedance plane. The effect of the plane with impedance coating on the slot is reduced taking into account an additional term to the slot external conductivity, for which the expressions were obtained in an analytical form.

Over the past few years, the continuous evolution of embedded electronic systems has increased electromagnetic interferences problems. It has also generated a new design constraint on electromagnetic compatibility. Hence, predicting the electromagnetic field behavior in the vicinity of the electronic components and systems becomes a priority to avoid the potential for unwanted coupling occurrence, as well as to ensure the electromagnetic compatibility compliance for those components and systems which are embedded in a confined space. As a result, the designers of electronics' equipment are extremely interested in radiated emission models. This paper reports a comparative study in which two different methods will be applied: the equivalent source method and plane wave spectrum method. These two methods will be used to predict the magnetic field behavior in the vicinity of a microstrip patch antenna. The latter works in ISM band for Wi-Fi and Bluetooth applications. The two applied models are constructed from the tangential magnetic fields cartographies of the antenna obtained from HFSS® at 3.5 mm and validated by comparing the HFSS® results with those of the models at a higher elevation. Furthermore, the relative error between the simulated field of the antenna and those of the equivalent source model according to the dipoles number is presented to determine the minimum number of dipoles that allow users to obtain the results with better accuracy. Subsequently, the relative error as function of different elevations along the z axis together with the two methods comparison results is presented.

In this paper, a modified circular loop FSS with a slot antenna is proposed for sub-6 GHz 5G applications. The proposed FSS reduces the resonant frequency to towards lower bands of conventional circular FSS without change in its size. The operating bandwidth (-10 dB) of proposed antenna loaded with polarization insensitive single-layer FSS varies from 3.6 GHz to 6.1 GHz with an average gain of 7-7.5 dB and a maximum realized gain of 7.87 dB. An FSS superstrate is loaded onto a slot antenna to increase the realized gain of 4 dB, where the FSS shows desirable electromagnetic wave reflection characteristics over operating bandwidth and can be used in 5G sub-6 GHz band applications.