In order to analyze the working status of the underwater unmanned vehicle not fully surfaced, the optimal working frequency when the whip antenna radiates the maximum power is given. The input impedance of the antenna on the water is theoretically calculated. It is regarded as the load of the underwater part of the antenna, and the total input impedance of the whip antenna is obtained. The relationship between the antenna radiated power to the external field and the input power is analyzed, and the optimal operating frequency corresponding to the maximum radiated power is determined. Using simulation experiments and actual measurements, the radiated power of the 1 m whip antenna when being immersed in seawater at 0.25 m, 0.5 m, 0.75 m is obtained, and the corresponding optimal working frequency is calculated, which are in good agreement with the theoretical deduction results. The results show that as the depth of the antenna immersed in seawater increases, the power radiated from the antenna to the external field decreases, and the optimal working frequency increases accordingly.

In this paper, a high-performance microstrip diplexer is designed and manufactured. The design is based on two pairs rectangular open-loop resonators band-pass filters and a novel zigzag junction. It operates at 3.5 GHz for fifth-generation 5G sub-6-GHz and 5 GHz for Wi-Fi communications. The proposed diplexer is considerably miniaturized with a global compact size of 30×17 mm². In addition, it presents low insertion losses less than 0.5 dB at both channels in comparison with the previous diplexers. Moreover, the isolation is higher than 20 dB, and the return loss is better than 14 dB at the bandwidths. To confirm the simulation results, the presented diplexer is manufactured and measured where a good agreement is carried out.

This paper aims to design an ultra-wideband reflectarray using True Time Delay technique that depends on compensate for the path differences of the electromagnetic waves between the feed and reflectarray surface, and reradiate them in-phase as a planar wave. The reflectarray surface is composed of numerous radiating elements. The reflecting surface is divided into several concentric annular zones; each of them has equal path delays of the electromagnetic waves. The radiating elements in each zone are implemented with two-layer square-loop type Frequency Selective Surface (FSS) structures. A TTD reflectarray with a diameter of 250 mm fed with a centered ku-band pyramidal horn antenna is studied and designed and fabricated to operate at the center frequency of 15 GHz. The proposed reflectarray provides a gain of 26.42±2 dB in the 12-18 GHz range achieving a fractional bandwidth of 40%. The simulated radiation patterns are stable with cross-polarization level below -40 dB and side-lobes level below -15 dB over the entire operating frequency range. The simulated phase efficiency is about 56% at the center frequency of 15 GHz.

For the coexistence of SUT (System Under Test) radiative emission signal and ambient interference signal, the amplitude of SUT signal will be submerged by the amplitude of interference signal, so it is difficult to accurately measure the amplitude of SUT signal. In this paper, a two-level nested array is used as the receiving array antenna, and the mixed matrix estimation method based on Blind Source Separation (BSS) is used to separate the coherent groups of the signal. Then the Sparse Reconstruction method is used for the DOA (Degree Of Arrival) estimation of each coherent group of the signal. After the DOA information of each signal is obtained, beamforming method is used to form beams of the main channel and auxiliary channel. The beam of the main channel outputs without distortion in the direction of the SUT signal and forms zero traps in the direction of the coherent signals, while the beam of the auxiliary channel forms zero traps in both the direction of the SUT signal and the direction of the coherent signal. The data received by the array are respectively multiplied by the weights of the main channel and auxiliary channel to obtain the output signals of the two channels. The output signals of the two channels are respectively fed into the Adaptive Noise Cancellation (ANC) system, and the ANC method is used to suppress the ambient interference signals and restore the SUT signal. Simulation and experiment results show that this method can accurately estimate DOA of radiation emission signals, effectively suppress ambient signals and restore the signal of SUT in field measurement of radiation emission.

A compact (25×28×1.57 mm³) and wide-band multimode frequency tunable antenna with defected ground structure (FRDGS) for 4G and 5G conformal portable devices and multi-band wireless systems is presented in this article. In a previous study, frequency reconfigurable antenna designs only used the method of adding slots on the patch or ground. In this study, a combination of multiple slots, partial ground, and defective ground structure techniques were utilised to attain the advantages of compactness, wide impedance bandwidth, and steady radiation pattern. Multiple slots on the top layer of the substrate and F-shaped slot etched at the bottom makes the proposed antenna. Two PIN diodes are inserted in the F-shaped slot for frequency reconfiguration, allowing the antenna to switch between different resonances. Ansys high frequency structure simulator 15.0v is used to simulate the antenna parameters. This antenna performance is demonstrated using measured and simulated data. The simulated and measured results clearly show that the proposed antenna can switch between six dissimilar resonant frequency bands via various modes of operation across the frequency spectrum from 2.3 to 8.9 GHz. The antenna works in a variety of commercial bands, such as WLAN/Bluetooth (2.4-2.5 GHz), LTE/4G (2.3-2.7 GHz), S-band (2-4 GHz), Radio Navigation (2.7-2.9 GHz), and 5G/sub-6 (3.3-4.9 GHz), according to simulations and experiments. The proposed design features narrowband, wideband, and ultra-wideband properties with a consistent radiation pattern, adequate gain (1.6 to 5.8 dB), and high radiation efficiency (86 to 94%) in a small package. Furthermore, the performance comparison of the proposed antenna with that of the state-of-the-art antennas in terms of compactness, frequency reconfigurability, number of operating bands, and impedance bandwidth demonstrates the novelty of the proposed antenna and its potential application in multiple wireless applications.

The field of wireless body area networks (WBAN) has seen growing interest in recent years due to applications of wearable devices, such as in healthcare. Effective on-body antenna design is necessary to provide optimal performance in real-world scenarios. This study compares several wearable antenna types, which are the monopole, patch, and e-textile antennas, to determine how human body motion affects antenna performance using a human body phantom model and human volunteers. The monopole antenna overall outperforms the patch antenna at 915 MHz and the e-textile antenna at 2.45 GHz and a Weibull distribution can be used as a probability distribution for S₂₁ during an arm swing motion for all antenna types tested.

A novel compact dual-band bandpass filter with wide stopband using stub-loaded stepped-impedance resonators is presented in this paper. The characteristics of the dual-mode resonator are investigated by using even/odd mode analysis. The center frequencies and bandwidths of the two passbands can be controlled by adjusting the geometric dimensions of the stub-loaded stepped-impedance resonators. Moreover, the filter has been implemented with five transmission zeros to improve the selectivity. A prototype of a dual-band bandpass filter centered at 3 and 4.35 GHz has been designed and fabricated. The measured bandwidths are 8.3 and 4.6%, and the corresponding insertion losses are 1.7 and 1.6 dB, respectively. A compact dual-band bandpass filter with sharp roll-off rate of 113.3/56.7/56.7/170 dB/GHz, wide stopband of 5.3 GHz, and isolation between two passbands of 25 dB is achieved. The measured results are in good agreement with the simulated ones.

In phased array systems, beam pointing accuracy is one of the major issues for its great effect on radar communication. Regardless of the initial excitation error and the inherent mutual coupling between antenna elements, the anisotropy of antenna element's radiation pattern is the main reason for beam pointing error. In this paper, we propose a closed-form solution of compensating for beam pointing error with uniform linear arrays. It gives a theoretical explanation how beam pointing deviates from the desired angle when scanning angle and the number of elements vary. Then a numerical simulation validates the effectiveness of the proposed theory. Finally, an experiment with an X-band phased array verifies that the closed-form solution can be applied to practical phased array systems in the presence of mutual coupling.

A compact, two-port, oblong loop antenna producing two orthogonal waves for fifth-generation (5G) operation in the 3.4-3.6 GHz band with transmission coefficient (S₁₂) lower than -32 dB and excellent envelope correlation coefficient (ECC) less than 0.002 is introduced for laptop antenna applications. Unlike the conventional, probe-fed, dual-polarized patch antennas, the proposed design uses the loop antenna fed by the coaxial cables and has a coplanar structure. The loop antenna is placed 1 mm above the top edge of the display, has a compact size of 30 mm × 4 mm and two feed ports spaced merely 2 mm (about 0.02-λ at 3.4 GHz) apart. Port1 is designed as a coupling feed to the loop while port2 is a direct feed in the loop, all located along the loop's central line. With this feeding arrangement, port2 is located in the current-null region when port1 is excited, whereas maximum currents of port1 excitation are located in the current nulls of port2 excitation. These properties lead to two decoupled, orthogonal radiating waves with very low ECC. Additionally, due to the oblong structure of the loop, pattern diversity is also achieved. Details of the dual-polarized loop antenna for 5G applications are presented.

Nowadays, wireless charging for electric vehicles has become popular in numerous situations by reason of safety and convenience. In this article, a composite compensation network and the corresponding charging control strategy aiming at optimizing the transmitting efficiency of the system and achieving constant current (CC) output and constant voltage (CV) output are proposed. First, the composite compensation network is analyzed by the equivalent circuit model as a reference. Second, based on the realization of CC/CV output, by analyzing the relationship between charging current/voltage and duty cycles of both DC-DC converters, the optimal duty cycles of both converters can be found. The purpose is to obtain the maximum transmission efficiency. Finally, the experimental results show good agreement with theoretical analysis, proving that the proposal can realize CC/CV charging and optimize the transmission efficiency.

This research article proposes a Defected Star-Shaped Microstrip Antenna (DSSMSA) for wideband applications. A designed monopole antenna has a defected star-shaped tuning stub with a defected ground structure energised with a microstrip feed line. An appropriate tuning of resonating modes wideband frequency effect has been achieved by optimising the dimensions of the tuning stub and the dimensions of the defected ground and its notch. Surface current distribution plays a vital role in optimising the antenna geometry and developing mathematical resonating frequencies equations. The simulated and experimental results show that the DSSMSA radiates under the frequency band from 1.6638 GHz to 6.652 GHz with measured fractional bandwidth of 119.9692% for |S₁₁| < -10 dB. Optimised DSSMSA resonates at frequencies 2.05 GHz, 3.382 GHz, and 5.494 GHz. As the geometry of DSSMSA is symmetrical, the symmetric far-field pattern has been found in the far-field.

In this paper, a textile based fractal monopole antenna is proposed with a defected ground structure for wearable application. The proposed antenna is designed on Flannel fabric with a thickness of 1 mm, which translates to 0.03λ at 10 GHz. The total dimensions of proposed antenna is 60 x 40 x 1 mm. The measured fractional bandwidth of the antenna is 110.1%. The proposed flannel based conductive ink antenna is characterized, and the results for washable fabric are illustrated. Both simulated and measured results are presented. The concept of application of low cost conductive ink on flannel fabric is demonstrated using conventional screen printing method. The antenna is characterized for commercial wash ability; the measurement results are invariant with the machine wash of the flannel fabric indicating robustness of the proposed method of fabrication of the antenna element.

In this paper, a low-profile flexible antenna using a flexible substrate is presented. The proposed antenna has concentric circle-shaped radiating elements with circular slots to achieve an ISM band. The flexible antenna having dimensions (33 mm x 18 mm x 2 mm) is designed and fabricated on a silicon rubber-based substrate, and measurements were performed to validate the simulation results. The measured and simulated results demonstrate that the antenna radiates at 2.45 GHz center frequency, with a return loss of -24.54. The operating frequency of 2.45 GHz, flexible substrate, and low SAR of 0.0658 W/Kg confirm that the proposed antenna is suitable for medical telemetry applications.

This article reports an SDR (software-defined radio) operating as a receiver for near-field measurement, aiming at EMC pre-compliance tests. The SDR replaces professional-grade RF instrumentation with benefits, with the lower costs. Its software application is based on Open-source GNU-Radio, which grants a higher versatility to the signal processing and visualization, requiring a single laptop to analyze the data and control the whole system, in real time. Reported tests used two commercial PCB magnetic field probes, and a proof-of-concept near-field imaging is performed in an S-shaped transmission line at 1100 MHz.

In this paper, a new Surface Wave (SW) diplexer in frequency bands of 11.6 GHz and 19.3 GHz is presented based on the frequency variations of the refractive angle when an SW enters from a Scalar Impedance Sheet (SIS) to a Tensor Impedance Sheet (TIS). In this structure, a SIS has been placed alongside a TIS, and using three launchers, SW is excited and received on them. To achieve an SW diplexer, the structure is designed in a way that the refractive angle changes in the expected range when SW enters from SIS to TIS. Finally, the proposed structure is fabricated and measured by printed circuit technology. The measurement results at 11.6 GHz and 19.3 GHz show that this structure has 3.6 dB and 4.1 dB insertion losses and 33.5 dB and 37 dB isolations in the two bands, respectively. These measurements are in good agreement with mathematical modelling and simulations.

A compact and broadband uniplanar Microstrip Antenna (MSA) is proposed for endfire radiation at sub-6 GHz 5G frequency band. The proposed antenna consists of a semi-elliptical radiating element and a U-shaped ground plane. The use of semi-elliptical radiating element results in a wide impedance bandwidth (BW) and compact size. The U-shaped ground plane further improves the bandwidth due to the increased coupling from radiating element to ground. An endfire radiation pattern, 3.8 dBi peak gain, and 49.8% bandwidth (BW) are achieved while a compact size of 0.47λ₀×0.13λ₀×0.008λ₀ (where λ₀ is the wavelength in free space at the center frequency) is kept. A parametric study based on CST-MWS simulations is also presented together with an equivalent circuit analysis to see the effects of various dimensional parameters of the uniplanar MSA with an elliptical radiating element. To validate the simulation results, prototype of the proposed antenna was fabricated and tested. The measured results are in good agreement with the simulated ones.

Crosstalk between interconnected lines is considered from two perspectives in this study. From a physical space perspective, the four transmission lines are reduced to two transmission lines. Meanwhile, the replacement of signal transmission of four-channels 2PAM (Pulse Amplitude Modulation) with signal transmission of two-channels 4PAM can reduce the quantity of transmission line and increase the space between the transmission lines. Thus, it can reduce the crosstalk. Under the same signal-to-noise ratio (SNR), the change in symbol error rate (SER) after signals of four-channels 2PAM are changed to those of two-channels 4PAM is given. Results show that the latter has an advantage in anti-crosstalk compared with the former in terms of the influence of crosstalk on SER. From the signal space perspective, applying signal linear combination transformation can convert the multiplexing signals in the interconnects into orthogonal mode. This process can cancel the crosstalk. In this study, the two methods are combined to save wiring while reducing crosstalk. ADS simulation results show that the eye pattern of 4 PAM signal recovers well by saving half the number of transmission lines.

A compact substrate integrated folded waveguide (SIFW) H-plane horn antenna array with simultaneous omnidirectional and directional radiation characteristics for potential utilization to high-speed wireless communication is presented in this article. The realization of the proposed design has been accomplished by placing the apertures of nine exponentially tapered SIFW H-plane horns towards the circumference of a cylindrical substrate with an angular separation of 40˚ between the horns. Every horn flaring includes a column of three slots. Centre probe feed technique has been used to excite the antenna. The radiation of the field by the horn apertures and through the slots of the horns flaring, respectively, results in an omnidirectional and a directional radiation pattern at 13.8 GHz and 18.42 GHz, with the gain of 7 dBi and 10.92 dBi. The proposed antenna has performed well and is in good agreement between simulation and measurement. The dimension of the antenna is 37.3 mm (diameter) × 1 mm (height) (1.71₀×0.046₀ at 13.8 GHz and 2.29λ₀×0.061λ₀ at 18.42 GHz). SIFW technology makes low profile antenna. The proposed design can be a promising option to be used as a low-profile antenna for high-speed wireless communication.

An ultra-compact fiber tip Michelson interferometer (MI), primarily aimed for a reproducible and stable high-temperature sensing probe, is developed and demonstrated. Both single-mode fiber (SMF) and polarization maintaining fiber (PMF) are considered and compared. The tip MI is fabricated by only using a one-step partial-polishing technique, which forms a half oblique and half vertical end face and functions as a beam splitter. A wide spectra analysis proved that the interferometer has an optical path difference (OPD) that is consistent across samples. When the lead-in fiber suffers from bending or twisting, the interference spectrum for the PMF case is more stable than that for the SMF case. Experimental results show a linear average temperature sensitivity of 15.15 pm/˚C in the range of 100˚C to 1000˚C for three tested PMF samples, and the difference between the sensitivities of the samples is less than 4.0%. The ease of fabrication, highly compact structure, reproducibility, and excellent resistance to mechanical disturbance performance suggest that the proposed PMF tip MI is highly promising as a high temperature sensing probe with high spatial resolution.

This paper presents analytical and numerical studies of electromagnetic wave propagation through an interface between a regular right-handed material (RHM) and a left-handed metamaterial (LHM). The interface is graded along the direction perpendicular to the boundary plane between the two materials, chosen to be the x-direction. The permittivity ε(ω, x) and permeability μ(ω, x) are chosen to vary according to hyperbolic tangent functions. We show that the field intensities for both TE- and TM-cases satisfy the same differential equations, and we obtain remarkably simple exact analytical solutions to Helmholtz' equations for lossy media. The obtained exact analytical results for the field intensities along the graded RHM-LHM composite are in line with the expected properties of RHM-LHM structures. Finally, we perform a numerical study of the wave propagation over an impedance-matched graded RHM-LHM interface, using the software COMSOL Multiphysics, and obtain an excellent agreement between the numerical simulations and analytical results. The results obtained in the present paper are not limited to any particular application, and are generally useful for all cases of wave propagation over impedance-matched two- and three-dimensional interfaces between RHM and LHM media. The advantage of the present method is that it can model smooth realistic material transitions, while at the same time including the abrupt transition as a limiting case. Furthermore, unlike previously existing solutions, the interface width is included as a parameter in the analytical solutions in a very simple way. This enables the use of the interface width as an additional degree of freedom in the design of practical RHM-LHM interfaces.