Oblique incidence of small-amplitude electromagnetic wave on an anisotropic conductive collision semi-infinite turbulent plasma slab under the influence of a homogeneous magnetic field is considered. The conditions of both the ordinary and extraordinary waves' propagation along and transversal directions with respect to the external magnetic field in a homogeneous absorbing collisional magnetoplasma are obtained. Second order statistical moments of the spatial power spectrum of a scattered radiation in the polar ionosphere are calculated for the arbitrary correlation function of electron density fluctuations using the geometrical optics approximation. External magnetic field, oblique incidence of electromagnetic wave on a plasma slab, anisotropy of both ionospheric conductivity and dielectric permittivity, also elongated plasma irregularities in the auroral region of the terrestrial atmosphere are taken into account. The direction along which these asymmetric factors compensate each other is established. The conditions of the "Compensation Effect" are obtained: the spatial power spectrum not broadens, and its maximum is not displaced. Second order statistical moments of a scattered radiation: the shift of maximum and the broadening of the spatial power spectrum in the main and perpendicular planes are investigated analytically and numerically for the power law spectrum of the anisotropic ionospheric plasmonic structures using the experimental data.

This paper presents, time and frequency domain analysis of a compact tri-band notched UWB (ultra-wideband) antenna with integrated Bluetooth frequency for wireless applications. Modifications in radiating element and DGS techniques are used to achieve high impedance bandwidth. The antenna operates at UWB frequency band 3.1-10.6 GHz as well as bluetooth frequency 2.4 GHz. The band notch characteristics are at Wi-MAX (3.3-3.7 GHz), WLAN (5-6 GHz), X-Band Satellite communication (7.1-7.76 GHz). These notches are obtained by etching different slots in ground plane and in radiating element. Gain, group delay, pulse transmission and radiation patterns of the proposed antenna are also investigated. A prototype of antenna is fabricated and reflection coefficient is measured. A comparison has been made between proposed antenna and previously published UWB antennas.

In this work, we propose a liquid crystal (LC)-based double-dipole phase shifter. By manipulating the electric field, we change the resonant frequency and phase of the electromagnetic wave by deflecting the orientation of LC molecules. We made the LC-based device with a 30 × 30 array of two parallel unequal dipoles on a Quartz substrate. The substrate has an area and thickness of 4×4 cm² and 480 μm, respectively. The experimental results show that the phase shift of 0°-385.4° is achieved at 94 GHz by changing the applied bias voltage on the LC layer from 0 V to 8.4 V. The phase shift is greater than 360° in the range 91.75-94.85 GHz. When the LC molecules are most significantly affected by the electric field, the maximum precision of phase shift is 4.08° with a bias voltage of 2 mV.

With the technology of free space optical communication, information can be transmitted from the transmitter to receiver wirelessly without the necessity of fiber optic cables. This technology offers system security, extended bandwidth, high data rate, and simple installation. This work aims to improve the optical channel based on the optimization of different optical amplifiers and filters. Performance analysis is carried out using a rectangular optical filter (ROF) and two electrical amplifiers named automatic gain control (AGC) and transimpedance amplifier (TIA). The results are presented in terms of maximum quality factor as a function of link range. The proposed systems (represented by ROF and AGC) brought better performance than traditional one (represented by TIA) via the same link range and data rates used. The findings displayed the progress of the AGC which has better quality factor than TIA and ROF. For instance, at 5 m length, the AGC achieves a maximum Q-factor of 12.29, while the ROF and ATI reveal a Q-factor in the range of 9.8 and 7.01 respectively.

This letter proposes a differentially-fed broadband dipole and its 1×8 array. The antenna achieves cost-effectiveness by using a low-cost FR4 substrate. The antenna obtains surface mount capability due to the ball grid array (BGA) package. The measured results show that the proposed antenna array achieves a wide impedance bandwidth of 37.8% (24-35.2 GHz). The gain of the 1×8 array is greater than 10.1 dBi, and the cross-polarization level in the main beam direction is less than -20 dB. the radiation pattern of the 1×8 array is stable and unidirectional. The proposed antenna array covers the 5G N257 (26.5-29.5 GHz), N258 (24.25-27.5 GHz), and N261 (27.5-28.35 GHz) bands.

A low-profile, compact size and light weight wide band BPF prototype is presented for satellite communication applications (Ku-band). The proposed wideband BPF satisfies the International Telecommunication Union's (ITU) region 3 spectrum requirement. Direct broadcast service (DBS) and fixed satellite service (FSS) in transmitting mode, respectively, employ the frequency band 11.41-12.92 GHz. The proposed filter offers an impedance bandwidth of 1.5 GHz and group delay of 0.2 ns. The proposed wideband BPF is fabricated, and various parameters such as return loss, insertion loss, group delay and quality factor are measured. Miniaturization of filter size reveals the filter's suitability to use on smaller platforms with smaller surfaces.

A novel 4-element UWB MIMO (multiple-input multiple-output) slot antenna with triple band-notched characteristics is designed and fabricated. It is composed of four rectangular slot antennas with two C-slots and a T-slot. To improve the isolation, cross-shaped branches are added. The measured results demonstrate that the antenna can operate ranging 2.51-11.07 GHz with the impedance bandwidth (S₁₁ < -10 dB) of 856 MHz except three rejected bands, including 3.02-4.07 GHz, 4.54-5.83 GHz and 7.88-9.38 GHz, and the inter-element isolation of antenna in the range of UWB band is higher than 21 dB. The presented antenna can filter the interference of WiMAX (3.3-3.7 GHz), WLAN (5.15-5.825 GHz) and X-band (7.9-8.4 GHz). What's more, the parameters of diversity performance like envelope correlation coefficient (ECC), diversity gain (DG), efficiency, gain, channel capacity loss (CCL), mean effective gain (MEG) and total active reflection coefficient (TARC) have been analyzed. Based on the analysis on simulated and measured results, the proposed MIMO antenna is competent for UWB applications with notched bands for WiMAX, WLAN and X-band.

Reconfigurable antennas are devices that can dynamically alter their geometry and/or electromagnetic properties tofacilitate different behaviors. Numerous approaches for achieving reconfigurability have been studied over the past 20 years, mainly consisting of mechanical, electrical, optical, and metamaterial methods. This review presents the most notable works and advancements in this field while placing a significant focus on antennas with explicit practical applications in the emerging areas of millimeter waves, 5G/6G communications, Internet-of-Things (IoT), high-throughput satellites and miniaturized systems among several others. The various reconfiguration methods mentioned will be compared, and their benefits and drawbacks discussed.

The unique bow-tie shaped pentagonal slit microstrip patch antenna has been particularly developed, manufactured, and tested for defense applications such as gunner training systems. The substrate is made of 3.2 mm thick FR4 material with a dielectric constant of 4.3. With a conductivity of 5.96×10⁷ Siemens/m copper is used as a pentagonal bow tie patch. During the training period of MANPADS, previously wired system is used, and it is replaced by a completely wireless system with a specially designed antenna along with an ultrasonic sensor and processor unit. The innovation of antenna is pentagonal slit created on patch, and it increases fringing effects. It attains 6.523 GHz with a return loss of -22.5 dB, maximum gain of 5.84 dB, and better VSWR of 1.16. CST Microwave Studio 2016 simulates the proposed antenna characteristics such as gain, return loss, radiation pattern, and VSWR.

This letter proposes a two element multiple-input multiple-output (MIMO) antenna with compact decoupling structure for 5G wireless communication applications. A compact decoupling structure was developed based on the elliptic curve, achieving isolation between the two antenna elements with a wideband response. The proposed concept is discussed and verified numerically and experimentally. The MIMO antenna system has demonstrated a wideband impedance matching with high isolation capability, while maintaining a good far-field and MIMO performance.

This paper presents a novel design structure of a series fed array antenna for desired shaped beam pattern synthesis. The desired beam shape is obtained by varying the width of patch elements. A uniform array is designed for the desired frequency, and then the proportionate values of the widths are calculated using amplitude coefficients obtained from the Woodward Lawson array synthesis method, while keeping excitation phase and inter element spacing constant. The proposed antenna is designed and simulated in HFSS. A prototype is fabricated on FR-4 epoxy dielectric material and tested at 12.5 GHz. The overall antenna has a compact size of 112 mm x 34 mm x 0.8 mm. The array structure exhibits impedance bandwidth of 1.8 GHz from 11 GHz to 12.8 GHz frequency range with return loss of -27.1 dB and high gain 14.2 dBi. The series fed configuration results in a VSWR of 1.38 and considerably low side lobe level of -24 dB in H-plane. There is a fine similarity between simulation and fabrication measurement parameter values such as return loss, VSWR, gain, and bandwidth.

Aiming at the focusing of near-field electromagnetic (EM) energy, a design approach of multi-type focusing (MTF) based on 1-bit metasurface is proposed in this paper. The surface electric field required for multi-focus is actually obtained by the superposition of the surface electric field of each single focus. This method can flexibly design the number, position, and energy distribution ratio of the focus according to the phase arrangement of the metasurface. Dipole structure is used as ``0'' and ``1'' unit of 1-bit metasurface. The phase difference of reflection is 180°, and the reflection coefficient is over 90% in 7.4-21.9 GHz. Using this 1-bit unit, the linear focus metasurface, multi-focus metasurface and metasurface generating two foci with different energy distribution are realized respectively. The energy distribution metasurface was manufactured and measured, and the measured results are consistent with the simulations. The design method used in this paper is simple and effective to realize multi-focus metasurface design and has potential application value in microwave imaging, radio frequency identification (RFID), and wireless power transmission.

Utilizing the special physical characteristic of a high impedance surface, a radio frequency identification tag antenna working at 920 MHz for metallic ground is proposed. The antenna not only overcomes the problem of impedance mismatching when placing on a metallic object, but also exhibits a low-profile antenna structure.

Low power, near-field (NF) radar imaging techniques have been proposed for breast cancer detection and long-term monitoring. It is important to optimize the data processing paths required for NF image reconstruction given the inherent resolution limitations of microwave compared to MRI or X-ray imaging. A key limitation in obtaining internal tumour and breast feature information is the reflection from the skin surface physically close to the antenna. Typically, algorithms to remove this dominant reflection involve subtracting an estimate of the time domain signal for the skin reflection from one antenna location using information from other locations. A key challenge in these approaches is determining the portion of the signal, the skin dominant window (SDW), to use to determinethe weights applied to nearby antenna signals when calculating the skin reflection estimate. Equipment limitations and breast characteristics impact the amount of data that can be captured, leading to the well-known Gibbs' ringing distortionsin the time domain signals. We suggestthat the Gibbs' ringing from the magnitude larger skin reflection has caused the length of the SDW to be over-estimated in previous determinations. Since this distorted signal now overlaps the time signals from the tumour and breast responses, removing the skin reflection estimatemay result in attenuation of tumour responses. In this contribution, two alternative strategies for designing the SDW are proposed. One minimized the first skin peak in the SDW, i.e., the furthest from the breast feature signals, and the other minimized the main, i.e., largest, skin peak within the SDW. Both new approaches were shown to effectively suppress the skin signal on simulated and patient data while allowing recovery of the missing portions of the desired internal breast feature signals leading to an increase in the overall intensity of the images and preserving the tumour response. However, we provided reasons why we considered that basing the suppression on the largest skin signal peak would provide a more consistent improvement in the breast feature signals.

In recent years, additive manufacturing has found increasing interest in fabrication of dielectric antennas. Using additive manufacturing brings significant advantages such as design flexibility, compactness, fast and low-cost manufacturing compared to traditional fabrication methods. Dielectric antennas having dense material allow high power transfer efficiency through the lens. However, a successful 3D printing process with dense dielectric materials is a great challenge. In this paper, impact of main process parameters during 3D printing; namely printing speed, process temperature and layer height on the resulted relative electrical permittivity values of a dense dielectric material is investigated. Test samples are printed with a dielectric material having ε_r = 10, and relative permittivity variations of these samples are measured with a vector network analyzer in X-band (8.2-12.4 GHz). In this way, optimum printing parameters are determined. Influence of dielectric constants of printed materials on the antenna radiation characteristics are inspected for an extended hemispherical lens antenna by a full-wave computer-aided design tool. Results demonstrate that an additively manufactured dense dielectric antenna will act as a traditionally manufactured dielectric antenna if and only if it is manufactured with optimum printing parameters.

Beamforming at mm-Wave and beyond is expected to be a critical need for many emerging applications such as Internet of Things (IoT), vehicular networking systems, and unmanned aerial navigation systems as well as 5G/6G backhaul communications. A new technique is proposed using quasi-optical beamforming that will address the shortcomings of existing beamforming approaches. These structures are passive (or nearly passive) having low cost, low power consumption, compact size and weight, have bandwidth advantages, and are expected to be able to operate at higher frequencies. The proposed structures give sufficient degrees of freedom to control the beamsteering angles by varying the dielectric constants and geometries of these structures and can form simultaneous multiple low overlapping beams. This approach increases the gain of the radiating source resulting in highly directive beams; our studies suggest that sufficient dielectric and shape parameters are available so that electrical tuning of beamformer parameters is possible. These structures are designed for a 1x3 microstrip patch antenna to demonstrate the formation of three simultaneous low overlapping beams. The effects on bandwidth are negligible upto 4.4%, and scanning angle of 180° has been achieved by using vertically oriented dielectric wedges. 6 dB gain enhancement and the capability to scale to larger 2D arrays have also been demonstrated. Full wave simulation results in Ansys HFSS are provided to demonstrate the proposed techniques, and validation is done in CST MWS.

The goal of the present paper is on retrieving the electrical and geometrical parameters of a stratified medium with two rough interfaces. The inversion problem is formulated as a cost function optimization problem, and it is solved using the simulated annealing algorithm. The cost function consists in the integrated squared deviation between the co-polarized incoherent intensities obtained from the Small Slope Approximation and those obtained from the Small Perturbation Method. The inversion scheme is applied to the electrical and geometrical parameters involved into the analytical expressions of the incoherent intensities given by the SPM. We study the influence of the shape of the autocorrelation function and the isotropy factor upon the estimation of parameters. We test the sensitivity of the inversion scheme to noisy synthetic data. The study is applied to snow-covered soils in L-band. For the configurations under study, we show that the inverse method is efficient for eight-parameter or ten-parameter predicting problems.

As the advanced technology in the Internet of Things (IoT), ultra-high frequency radio frequency identification (UHF RFID) tag has broad application prospects and significant research value. However, the transmission performance of UHF RFID on the metal surface and embedded in metal is severely impaired, bringing new challenges to its application for long-distance reading and writing. On this basis, an embedded metal UHF RFID tag design method is proposed in this paper. A planar inverted F antenna (PIFA) structure is optimized to enhance the anti-metal performance of the tag. The embedded feed design is adopted to achieve preferable impedance matching between antenna and chip. Besides, a series of electromagnetic simulations were investigated to optimize the performance of the tag, which can ultimately achieve the maximum gain of -9.7 dB in the metal groove, with the reduced volume of 19.8 mm×25.8 mm×2 mm by employing the meandering technology and the method of adding metal via holes. Finally, when the self-made tag is embedded in the metal groove, the experimental results demonstrate that the maximum reading distance can reach 1.26 m, indicating that the tag developed in this paper has significant practical value in the case of embedded metal.

A MIMO antenna for smartphones with radiation diversity is presented in this article. The proposed design consists of dual-fed Complementary Split Ring Resonator metamaterial antenna components design, which is located at the edges of an FR-4 substrate. The total dimension is 75 mm x 150 mm x 1.6 mm. 50-ohm dual microstrip feed lines placed orthogonal to each other are used to feed the SRR. Due to this orthogonality, radiation diversity is easily achieved. The proposed structure is operated in dual bands from 3.43 GHz to 3.62 GHz and 4.78 GHz to 5.04 GHz. In both, the band's good impedance bandwidth with a reasonable gain is achieved. The entire structure is simulated using CST EM software. All the simulated results are presented, which clearly show that the proposed structure is a good candidate for the future smartphone massive MIMO application.

A multiband circularly polarized microstrip patch antenna including a Minkowski fractal slot for wireless communication applications in the frequency bands 1.39 GHz, 2.45 GHz (WLAN band), 3.48 GHz (Mobile Wi-Max), 5.8 GHz (U-NII high-band) and 6.29 GHz has been proposed. The proposed antenna consists of two substrates mounted on top of the ground plane. The antenna has been fed with a 50 Ω microstripline which is etched on top of the lower substrate. The second iteration Minkowski fractal slot is etched on the truncated square patch which is on top of the upper substrate. The substrate has a size of 80 mm x 82 mm x 1.6 mm. The measured results show that the proposed antenna could excite for five resonant bands of 1.35 GHz, 2.45 GHz, 3.5 GHz, 5.8 GHz and 6.25 GHz and has reflection coefficients of -15 dB for 1.35 GHz, -16 dB for 2.45 GHz, -22 dB for 3.5 GHz, -23 dB for 5.8 GHz and -13 dB for 6.25 GHz as well as an axial ratio bandwidth of 3.42 GHz-3.47 GHz. The maximum gains of the antenna are 5.92 dBi for 1.39 GHz, 6.15 dBi for 2.45 GHz, 8.36 dBi for 3.48 GHz, 9.64 dBi for 5.8 GHz and 6.69 dBi for 6. 29 GHz. The simulations and optimizations have been carried through Computer Simulation Technology Microwave Studio (CST-MWS) software.