In the paper, a miniaturized wideband rat-race coupler with improved phase performance is designed and analyzed. Flat output ports phase differences are obtained by utilizing a component-loaded T-type transmission line (CLT-TL) with a stub-loaded short-circuited coupled line (SLS-CL). Let the CLT-TL and SLS-CL sections be equivalent to uniform 90° and 270° transmission lines, respectively. Design equations are derived, and an optimization is proceeded to obtain the circuit parameters. For validation, a prototype is designed, fabricated, and measured. Including the feeding lines, the circuit size is 0.31λ_g × 0.31λ_g. Under the criterion of return loss (RL) > 10 dB, the measured bandwidths for ports 1 and 3 excitations are both reach 48%. For amplitude imbalance (AP) < 0.5 dB, the overlap relative bandwidth is 46.88%. The measured bandwidths with 2° phase imbalance are 49.58% and 54.01% for ports 1 and 3 excitations, respectively.

This paper presents a set of statistical channel models based on 60 GHz radio measurements in a server room. The channel models are developed for possible use-cases, corresponding to potential deployment scenarios in wireless data centers (WDCs). A simple parametric channel model is used to model both the deterministic and stochastic channel parameters in the delay domain, within the 57-64 GHz unlicensed band. A simulation framework is accordingly provided to generate channel realizations for WDC use cases. The accuracy of the simulation framework is verified using the delay spread as a validation metric. The reported models are useful for practical system design and evaluation of WDCs millimeter-wave systems.

This paper presents the design of a compact triple band-notched ultra-wideband (UWB) two element multiple-input multiple-output (MIMO) antenna. For validation of the simulation results, the prototype of the design is fabricated and experimentally measured. From the experimental results, it is observed that the proposed design， operating in the frequency range 2.5-12 GHz, successfully rejects three interfering bands i.e. the WiMAX band, WLAN band, and satellite communication X-band, when a triple bandgap CSRR-loaded EBG structure is embedded close to the feedline of the UWB antenna. In the ground plane of MIMO antenna, a rectangular slot and a mirrored pair of F-shaped stubs are added to minimize the mutual coupling between the UWB elements. The proposed MIMO antenna has good wideband isolation between the elements (> 20 dB), high diversity gain (10 dB)， and low envelope correlation coefficient (< 0.02) over the entire UWB.

This paper presents a planar filtering magic-T with a simple structure. It consists of four half-wavelength microstrip resonators with one loaded with a shorted microstrip stub at its central location. The resonator loaded with a shorted microstrip stub has the even-symmetry resonant mode. Other three resonators have the odd-symmetry resonant mode. The planar filtering magic-T has four ports, which all adopt a tapped line structure. Its novelty lies in the simple structure. Compared with previous works in the literature, its inter-resonator coupling zones are apart away and have no influence on each other, which means a simple design. Furthermore, a different-properties coupling is not needed, and its filtering response can be easily extended to the high-order case. The operational mechanism and design method are introduced in details. A planar filtering magic-T with center frequency of 920 MHz was designed and fabricated. The measured results show that, at the center frequency, the return losses (S₁₁/S₄₄) is less than 20/12 dB; an isolation degree of 25 dB (S₄₁) can be observed; the insertion loss of the difference port (S₂₁/S₃₁) and sum port (S₂₄/S₃₄) are 4.5/4.7 dB and 4.3/4.6 dB; the phase unbalance is 8˚/7˚(Σ/Δ). Totally, these results can verify the effectiveness of the proposed novel planar fiiltering magic-T.

A compact 3-D, circular line matched dipole (CLMD) antenna is presented in this paper. The realization of the antenna is based on Laser Direct Structuring (LDS) plastronic technology, enabling metallization on plastic parts. Cylindrical holder is chosen to carry the dipole, which implies high bending constraints on the antenna. Miniaturization of the radiating element is obtained by an effective use of 3-D space, resulting in a very low profile length dimensions of 0.14λ × 0.14λ × 0.05λ operating at 868 MHz. Specific attention is paid to the input impedance change due to conformation. An equivalent circuit model is proposed to take into account the conformation and design the matching line. Both simulated and measured results demonstrate good performances, with a 30 MHz bandwidth (i.e., a relative bandwidth of 3.5% with S₁₁ < -10 dB) around the working frequency. The LDS prototype achieves a maximum gain of 1.2 dBi with a quasi-omnidirectional radiation pattern. This compact and conformed design presents a real interest for pervasive highly integrated ISM band IoT sensors.

In this paper, we developed a 3-dimensional (3D) ray-tracing simulator using MATLAB for establishing the viability of heating, ventilation, and air conditioning (HVAC) ducts as a reliable communication channel for indoor communication at millimeter-wave (mm-wave) frequencies. We present theoretical analysis of image theory ray-tracing and provide the equations for total electric field due to different rays undergoing reflections at the duct walls. We also computed the received signal strength indicator (RSSI) for the dry and moisture-laden air flowing through the HVAC ducts. The ray-tracing results are compared with the experimental and theoretical results we obtained for the HVAC ducts. With transmitter effective isotropic radiated power (EIRP) of 7 dBm, we obtain RSSI which varies between -34 dBm and -53 dBm for dry atmospheric pressure and temperature of 1013.25 hPa and 294.26 K, respectively, and duct lengths of up to 8 m at 60 GHz.

This research paper presents a wideband hook shaped aperture coupled circularly polarized antenna for 5G application. It consists of three layers; a radiating copper plate (0.5 mm) as a top layer, a foam material of 2 mm thickness as a middle layer, an FR4 substrate with hook-shaped apertures in the ground plane, and a bent feed line as the bottom layer. The performance characteristics of the proposed design are improved by feeding mechanism, which entails the use of a bent shape microstrip line coupling through four hook shaped slots to generate four sequentially phased sources to excite the single layer patch antenna. The proposed antenna exhibits return loss bandwidth of 29.10% (2.8-3.81 GHz), axial ratio bandwidth of 13.47% (3.61-4.11 GHz), and cross polarization level is 20 dB which is attained at boresight and Gain of 4.08 dBic at the resonant frequency of 3.47 GHz. The proposed antenna design is fairly applicable to 5G radio band and discussed about the azimuth, elevation patterns and surface current distribution in frequency band of interest. The proposed design is simulated using High frequency structure simulator (v.13), and measured results are in good agreement with simulated ones.

In order to improve the performance of decoupling control for an interior permanent magnet synchronous motor (IPMSM), a recursive least square algorithm with fuzzy forgetting factor is proposed to identify IPMSM parameters. Firstly, the problems of coupling and parameter identification of IPMSM are analyzed. Secondly, the identification process of resistance and flux linkage is analyzed, and the static parameters are identified as the initial value or constant value. Thirdly, fuzzy control is used to dynamically adjust the forgetting factor in the recursive least square algorithm to make the identification of direct axis and quadrature axis inductance parameters more accurate. Finally, the effectiveness and accuracy of the proposed parameter identification algorithm are verified on the platform, and the good performance of the proposed algorithm in decoupling control is verified. The experimental results show that the identification method can accurately identify the motor parameters in static state and dynamic state. At the same time, the forgetting factor is dynamically adjusted to improve the parameter identification effect and decoupling control performance of the motor.

In this letter, two cost-effective surface-mount patch antenna elements for millimeter-wave (mmWave) systems using ball grid array (BGA) packaging are presented. A single-layer substrate based on FR4 is used to meet the low-cost requirements. The BGA packaging makes the proposed antenna element compact and easy to integrate. A U-slot is added to the patch to improve the impedance bandwidth of the patch antenna, and a vertical transition is designed to transmit the excitation signal by using a plated through-hole (PTH). The design process of the antenna is illustrated in detail. The antenna prototype has been simulated, fabricated, and measured to validate the design. The size of the fabricated prototype is 5 mm × 5 mm × 1.3 mm, which is very suitable for integration into a mmWave system.

In this paper, a wide 3-dB gain bandwidth transmitarray (TA) antenna with low focal length to diameter ratio (F/D) is presented. The TA comprises four identical metasurface layers, and the metasurfaces are printed on thin dielectric substrates, which are separated by air gaps. The unit cells of the metasurfaces are constructed by etching slots on the metal layers, which include a serrated crevice and two disjunct slots. The F/D of the TA is designed as 0.48 to accommodate the applications required low profiles. A TA is constructed by arranging high transmission elements at the center and the other elements in the external of the aperture. A transmitarray antenna (TAA) operating at 9~13 GHz is designed by applying a horn antenna to the TA, which achieves a measured 1-dB gain bandwidth of 10.5% (3-dB gain bandwidth of 23.3% and measured maximum gain of 22.48 dBi at 10.5 GHz) and a maximum measured aperture efficiency of 38.4%. Compared to the reported works, the proposed TA has outstanding F/D and wide 3-dB gain bandwidth.

A conformal metamaterial absorber operating at the quad band is analyzed in this paper. The proposed structure is fabricated on a 0.5 mm thick, flexible polyester dielectric substrate. The proposed structure works at the chosen frequencies 4.11 GHz, 5.37 GHz, 7.39 GHz and 8.4 GHz with the absorptivities of 96%, 95%, 90% and 94%, respectively. The structure has essential novelty of miniaturization of λ/146 in the thickness, which is an exceptionally flexible material for Radar applications. Quad band excitation can also be analyzed by the iteration of the proposed structure as well as circuit analysis. The flexible polyester material is etched with silver coating for the development of the fabricated structure. The simulated results can also be associated with the measured ones from the planar as well as a cylindrical surface to realize flexibility for stealth technology. It can be accomplished by the free space measurement technique in an anechoic chamber.

A coplanar tri-band wearable antenna combined with an electromagnetic bandgap (EBG) structure is described for sub-6 GHz 5G and wireless local area network (WLAN) applications. The proposed antenna is fully implemented in textile materials thus offering a robust, compact, and discreet solution to meet the requirements of wearable applications. The addition of the EBG structure increases the textile antenna performance in terms of radiation patterns in the presence of the human body. The experimental results show that the proposed design exhibits tolerance to various bending conditions as well as loading by body tissues. In addition, to ensure the safety of the design for human health, the values of the specific absorption rate (SAR) have been reduced by more than 95%, which complies with the international standard. This design could thus be considered as a good candidate for IoT applications compared to the current state of the art while having a tri-band behavior and smaller volume.

In this article, a compact dielectric resonator antenna (DRA) with partial ground plane for wireless applications is examined. The exhibited structure is fed by a microstrip line. To demonstrate the functionality of a tri-band, a circular dielectric resonator antenna with concentric circular rings is created. The developed antenna parametric analysis has been performed on HFSS platform. The configured design operates at three frequency bands, i.e. 1.98-2.59 GHz (ISM), 3.24-3.85 GHz (Wi-max), and 4.85-5.85 GHz (WLAN), with the fractional bandwidths of 26.6%, 20.4%, and 18.67%, respectively. The customized concentric rings are placed onto the substrate to reinforce the antenna appearance and also miniaturize the size. The measured outcomes are strongly in accordance with the simulated results. The designed model can be customized with certain attributes to wireless applications.

A compact dual-mode band-pass filter (BPF) with 7th-order harmonics suppression is proposed. The proposed dual-mode BPF is designed using a three-section stepped-impedance-variable feeding line (SIVFL) and a square resonator. The high-order harmonics suppression is achieved by the SIVFL structures, and the size reduction is achieved using meandered lines and a resonator with two degenerate modes. The proposed BPF has a wide stopband up to 7th-order harmonics and a compact size of only 7 x 7 x 0.3 mm. The proposed BPF is suitable for the fifth-generation (5G) N77 band applications due to its working frequency, compact size, and good performance. Comparison and discussion are implemented as well.

In this paper, two variable leakage flux permanent magnet (VLFPM) machines are proposed. The keys are to adopt the rotor with single-layer and double-layer PMs and intentionally create leakage flux paths to extend the operating speed range and increase the machine efficiency. The characteristics of the variable leakage flux of the proposed machines are investigated. In order to improve the performances of the VLFPM machines, the Multi-Objective Genetic Algorithm (MOGA) method is applied for achieving the multi-objective optimizations of variables. Then, the performances of the double-layer permanent magnet variable leakage flux motor (DLPM-VLFM) and the single-layer permanent magnet variable leakage flux motor (SLPM-VLFM) are analyzed and compared with conventional interior PM machine (CIPMM) in detail. The performances mainly include flux linkage and torque, flux-weakening capability and efficiency. Finally, it is shown by analysis and comparison that the DLPM-VLFM can have a wider range of speed and high efficiency.

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.