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A compact single-layer, polarization-insensitive, and angularly stable frequency selective surface (FSS) based multi-stop band filter is reported for shielding three useful frequency bands covering 1.82–2.86 GHz Industrial, scientific, and medical (ISM), 3.52–4.06 GHz Worldwide Interoperability for Microwave Access (WiMAX), and 7.42–8.72 GHz (satellite downlink), centered at 2.4 GHz, 3.6 GHz, and 8.1 GHz, respectively. The proposed unit cell (15 mm × 15 mm) contains four equal-sized square-headed dumbbell (SHD) shaped resonators surrounded by two square ring resonators. The outer and inner square rings offer the first and second stop bands, while the SHD resonators provide the third stop band. A highly polarization-insensitive response is realized owing to the four-fold symmetry in the proposed structure. The unique arrangements of the SHD resonators help to realize higher angular stability under transverse electric (TE), transverse magnetic (TM), and diagonally polarized incident electromagnetic (EM) waves for incidence angles up to 80°, 80°, and 70°, respectively. A detailed analysis in terms of equivalent circuit and parametric variation is carried out to illustrate the higher to lower frequency band ratio. A prototype is fabricated and tested through a proper measurement setup to validate its performance, and it shows good agreement with the simulated results. The proposed FSS unit cell offers better angular stability under diagonally polarised incident waves, attenuation level, minimum higher to lower frequency band ratio, good fractional bandwidth, and compactness. So the designed multi-stopband FSS can be considered a potential candidate for shielding EM radiation across the useful bands

This paper presents the design and development of a mini-compact Wilkinson Power Divider (WPD) operating at 9.3 GHz, with a wide bandwidth of 200 MHz, for the Man-Pack Surveillance Radar (MPSR) application. The design of the WPD was carried out using Advanced Design System (ADS) software with a microstrip feeding technique. The substrate material used in this design was Duroid Roger 5880, which has a thickness (h) of 1.575 mm, dielectric constant (εr) of 2.20, and loss tangent (tan δ) of 0.0009. A WPD was designed, developed, and measured. The simulation results obtained included return loss (S11) -37.50 dB, (S22) -26.59 dB, (S33) -26.09 dB, insertion loss (S21) -3.61 dB and (S31) - 2.55 dB, and isolation (S32) -12.89 dB. Overall, the simulation result parameters worked at a frequency of 9.3 GHz. Furthermore, when the WPD measurement produces a measured return loss of (S11) -28.69 dB, (S22) -28.5 dB, (S33) -29.95 dB, insertion loss (S21) -6.61 dB, and (S31) -7.55 dB, and isolation (S32) -21.89 dB. The dimensions resulting from the realization were 20.5 mm x 20 mm.

Introduction. Conventional contact measurements of hydrographic parameters frequently fail to provide the necessary accuracy of data in the field of water area monitoring. This problem can be solved using coherent radars enabling direct measurements of surface current velocities.Aim. To establish the accuracy of surface current velocities measured by a Doppler radar using drifter data.Materials and methods. In June 2022, coastal operational oceanography studies were conducted at the hydrophysical test site of the Institute of Oceanology of the Russian Academy of Sciences in the Black Sea near Gelendzhik. Measurements were carried out using a coherent X-band radar installed on the Ashamba research vessel simultaneously with drifter experiments using Lagrangian drifters of the near-surface layer with an underwater 0.5 m sail. Coordinates were transmitted via mobile communication. The drifter data on the current velocity and direction were used to verify radar measurements. Measurements were taken onboard of the research vessel at a low speed and different distances from the shore, near the drifters. The tracks of the vessel and drifters were recorded simultaneously. Processing of the radar data involved obtaining Doppler spectra of signals to estimate the dynamic processes on the sea surface, including the current velocity.Results. Radial components of the near-surface current velocity were calculated. Then, the current velocity values obtained based on the drifter and radar data were compared.Conclusion. The present work makes a contribution to the advancement of methods for measuring surface currents from the board of a moving ship by Doppler radars. The obtained results confirm the suitability of the radar hardware and software and signal processing algorithms for measuring currents. The radar measurement data were found agree well with drifter data in the velocity range from 15 cm/s.

This research presents a concept, for an elliptical ring patch microstrip antenna (ERPA) which was created tested and produced Employing types of materials, with varying permittivity values. The antenna is meant for X band use. In this study the substrates employed are FR4 (Design (1)) and RT5880 (Design (2)) having permittivity values of 4.4 and 2.2 respectively and thicknesses of 1.6 mm and 1.575 mm. The ERPA design includes four rings, with holes of different sizes. The Ansoft HFSS, a high-frequency structure simulator, is utilized to model the antenna design, which is crucial for optimizing the design and accurately predicting its performance. Moreover, simulation tools were integral in optimizing antenna characteristics before physical testing. Curiously, there is a significant consensus over the comparative outcomes. The research primarily examines key characteristics, including radiation pattern gain, return loss, and input impedance, which have been shown to fall below acceptable thresholds. The results show that relative permittivity and difference in the thickness of the substrate materials have a substantial impact on both bandwidth and gain. The analysis of efficiency showed the superior efficiency of 85.70% by RT-5880 in contrast to 69.96% efficiency gained via FR-4 substrate. The bandwidth of both proposed antennas is greater than 2 GHz which is 2.420 GHz and 3500 GHz for Design (1) and Design (2) respectively. The gain 3 is observed in both the Designs 1 and 2. The higher bandwidth and gain makes RT5880 substrate more efficient, and provide better design for X- band applications. Maintaining the X-band frequency range the proposed antenna design can be applied to wide range of applications.

Precise knowledge of the antenna pointing direction is a key facet to ensure the accuracy of observations from scanning weather radars. The sun is an often-used reference point to aid accurate alignment of weather radar systems and is particularly useful when observed as interference during normal scanning operations. In this study, we combine two online solar interference approaches to determine the pointing accuracy of an X-band mobile weather radar system deployed for 26 months in northern England (54.517°N, 3.615°W). During the deployment, several shifts in the tilt of the radar system are diagnosed between site visits. One extended period of time (>11 months) is shown to have a changing tilt that is independent of human intervention. To verify the corrections derived from this combined approach, quantitative precipitation estimates (QPEs) from the radar system are compared to surface observations: an approach that takes advantage of the variations in the magnitude of partial beam blockage corrections required due to tilting of the radar system close to mountainous terrain. The observed improvements in QPE performance after correction support the use of the derived tilt corrections for further applications using the corrected dataset. Finally, recommendations for future deployments are made, with particular focus on higher latitudes where solar interference spikes show more seasonality than those at mid-latitudes. [ABSTRACT FROM AUTHOR]

A single-substrate-layer Frequency Selective Surface (FSS) is designed with a 1.6 mm thick FR4 substrate for triple band-stop frequency filtering applications, that are for Bluetooth, WLAN, WiMAX, and X-band. The proposed FSS unit cell consists of two polygon loops on the front side and a square loop with four annular rings attached to its corners on the backside. The offered design covers three frequency bands: 2.3-4 GHz, 5-6 GHz, and 8-12 GHz. There are three resonances at 3.3, 5.6, and 9.9 GHz. The equivalent circuit model of the proposed structure and the formulas of the LC parameters are presented. A prototype of this structure was manufactured in size of 26 × 26 cm2 and experimentally verified in the antenna and microwave laboratory. The software used for design and simulation is HFSS from Ansys, which uses the finite element method. A comparison with similar structures was performed to demonstrate the performance of the proposed structure. The advantages of the proposed filter include adequate bandwidth, simple structure, as well as small size. In addition, it is unaffected by variant angles of incidence for TE polarization and TM polarization. Furthermore, due to its symmetrical design, it shows a polarization-independent feature. Experimental results for both polarizations verify the merits of the proposed approach, as shown before in the simulation results as well. [ABSTRACT FROM AUTHOR]

Beam scanning devices in the X-band allow spatial reorientation of the beam, but this poses challenges for material and device design. To meet such challenges, the development of microwave dielectric materials and the design of special structures are crucial. Here, the microwave dielectric properties of Ca 5 Mn 4 V 6- x Nb x O 24 (x = 0.00–0.08) ceramics are systematically investigated by using first-principles calculations and microstructural analysis. The ceramic has the best microwave dielectric properties (ε r = 10.92 ± 0.14, Q × f = 50032 ± 1795 GHz (@10.52 GHz), τ f = −59.58 ± 3.81 ppm/°C) when x = 0.04 and T = 875 °C. As a concept demonstration for device applications, a frequency-controlled beam scanning device in the X-band is designed by using this ceramic and copper electrode. This device has a beam scanning space of 3.248° (from 27.143° to 32.371°) in the frequency range of 10–11 GHz while maintaining high reflectivity (≥0.6). This function is verified by simulation results for far-field amplitude and far-field phase. This work contributes to the application of microwave dielectric ceramics. [ABSTRACT FROM AUTHOR]

This paper presents design of a 4-element crescent-shaped two-sided multiple-input-multiple-output (MIMO) antenna, employing pattern and polarization diversity with improved element-to-element isolation, for UWB, X and Ku band wireless applications. The proposed crescent-shaped MIMO structure consists of two antennas on the top and remaining two antennas on the bottom sides of the substrate. The developed antenna operates in a frequency range from 2.8 to 15.2 GHz, covering the entire UWB 3.1–10.6 GHz, X-band and portion of Ku-band giving element-to-element isolation of more than 20 dB in most of the operating bands. Also, the proposed MIMO structure gives a maximum gain of 6.6 dBi with radiation efficiency from 75 to 95% in the operating band. The important MIMO parameters like envelope correlation coefficient (ECC < 0.005), channel capacity loss (CCL < 0.03 bits/s/Hz), mean effective gain (MEG < − 3 dB) and total active reflection coefficient (TARC < − 10 dB) are presented to estimate the performance of the developed UWB MIMO system. [ABSTRACT FROM AUTHOR]

This paper presents a dual-band bandpass filter (BPF) operating at 9.5 GHz and 11 GHz using a substrate integrated waveguide (SIW) technology. The filter was designed on the diplexer structure to enable the flexible control of the spacing of two passbands. By carefully designing the input/output cavities, spacing between two passbands can be adjusted freely. In addition, thanks to the design of each branch cavity, performance of each band is able to tune easily. The filter was designed on a cost-effective RO4003C substrate and simulated using a CST Microwave Studio 2019 simulator based on the time-domain analysis. The simulated insertion losses at 9.5 GHz and 11 GHz are 2.0 and 1.9 dB, respectively whereas the return losses at these two center frequencies are -15.7 dB and 32.8 dB, respectively. The fractional bandwidth of 1-dB insertion loss is 3.7 % and 3.6 % at the two passbands. The total size of the filter is just 2.4 x 3.5 mm² . The proposed filter aims at using for next-generation wireless communications such as satellite communication, 5G, 6G and beyond. [ABSTRACT FROM AUTHOR]

This research presents a coplanar waveguide fed elliptical-based second iterative antenna for dual-broadband applications. The antenna radiator is formed after implementing two iterations of an elliptical-shaped patch in a tree-shaped manner and a modified semi-elliptical CPW plane. The antenna provides a bandwidth of 1.87 GHz (2.49–4.36 GHz) in the lower resonating band and 1.96 GHz (7.96–9.92 GHz) in the upper resonating band with peak gains of 2.84 and 6.15 dBi, respectively. An augmented gain of 9.48 dBi is obtained by implementing a single-layer FSS (frequency selective surface) beneath the designed antenna. The simulated and experimental results of the antenna with and without FSS are very similar regarding gain, impedance bandwidth, and directional radiation patterns. The antenna described in this article is simple, inexpensive, and low profile in nature. It can be used for Wi-MAX, lower sub-6 GHz 5G (n78), and x-band applications. [ABSTRACT FROM AUTHOR]

This study presents an original parallel connected hybrid microstrip-substrate integrated waveguide (PCHMSIW) bandstop filter. A low-pass filter implemented on a microstrip structure and a SIW-based high-pass filter are connected in parallel to each other. In this way, the aim is to obtain a bandstop filter in the novel hybrid design. The parallel connected hybrid microstrip-substrate integrated waveguide (PCHM-SIW) bandstop filter is synthesised, simulated, and produced. The effects of connecting filters in parallel are discussed. It is seen from the results of CST Studio Suite simulation that PCHM-SIW bandstop filter has a bandwidth of 2.85 GHz and a center frequency of 4.26 GHz. The frequency change rate of the center frequency between simulation and measurement is 7.02 % where it is just 3.76 % for the deviation in bandwidth. The results of the simulation and those of the measurement are close to each other. These results converge to ideal analytical results. [ABSTRACT FROM AUTHOR]

A dual-port multiple-input multiple-output (MIMO) filtenna with minimal sizes of 80 × 45 mm2 is set up in this study. Each element in this MIMO filtenna is positioned orthogonally to the one next to it to improve isolation. For the MIMO element to achieve high-frequency selectivity and compact size, a frequency-reconfigurable filtenna that was created by fusing a band-pass filter and a monopole radiator was used. The suggested filtenna can switch between its C-band and X-band operating states with ease. On build the filtenna circuit, a band-pass filter based on defective microstrip structure is inserted to a circular monopole radiator. The developed filtenna operates in the C-band frequency range of 6.5–8 GHz and the X-band frequency range of 8–12 GHz. It is possible to use the X-band operating state for communication in a cognitive radio environment. Used as a decoupling structure, metamaterial structures can increase isolation to more than 40 dB across the bandwidth. The suggested MIMO filtenna system has an envelope correlation coefficient of 2.4e−6, a peak gain of 6 dBi, and an impedance bandwidth of 7.4–7.75 GHz. The MIMO filtenna is constructed and measured, and the findings of the measurement and simulation are in good agreement. [ABSTRACT FROM AUTHOR]

In this study, spinel Ni 0.5 Zn 0.5 Fe 2 O 4 doped with transition metal ions as well as rare-earth ions Ni 0.4 Zn 0.4 M′ 0.2 Fe 2 O 4 (M′ = Cu, Dy, Gd and Lu) and M″ 0.5 Zn 0.5 Fe 2 O 4 (M″ = Ni, Mn and Co) are developed using the sol-gel auto-combustion route, and the role of substitution on electromagnetic properties is investigated. The powder X-ray diffraction accompanied by Rietveld refinement signifies a single-phase spinel ferrite that belongs to Fd- 3 m space group for all the compositions. Rietveld refinement confirms that doped Cu2+, Dy3+, Gd3+ and Lu3+ ions are at random distribution between spinel tetrahedral and spinel octahedral sites against their preferential occupancy. The saturation magnetisation (M S) of Ni 0.5 Zn 0.5 Fe 2 O 4 (M S = 50.5 emu/g) increased with partial doping showing M S = 60.08 emu/g for transition-metal doped Ni 0.4 Zn 0.4 Cu 0.2 Fe 2 O 4 and M S = 109.7 emu/g for rare-earth doped Ni 0.4 Zn 0.4 Dy 0.2 Fe 2 O 4 , which was the highest among all the doped compositions. Doping enhances the dielectric permittivity of Ni 0.5 Zn 0.5 Fe 2 O 4 from 4.2 to 6.5 for Ni 0.4 Zn 0.4 Cu 0.2 Fe 2 O 4 and 7.7 for Ni 0.4 Zn 0.4 Dy 0.2 Fe 2 O 4. Further, the reflection coefficient (R L) of all the doped compositions of Ni 0.4 Zn 0.4 M′ 0.2 Fe 2 O 4 (M′ = Cu, Dy, Gd and Lu) was less than −8 dB (85% absorption) throughout the frequency band of 8–12 GHz with an optimum material thickness of 3.5 mm. Transition metal ion doped Ni 0.4 Zn 0.4 Cu 0.2 Fe 2 O 4 resulted in further improvement of its absorption characteristics of the incident EM waves with reflection coefficient (R L) less than −10 dB (between 84.15% and 90%) between 10 and 12 GHz at a material thickness of 3.5 mm in the X-band frequency range. [ABSTRACT FROM AUTHOR]

In this article, a high gain Circularly Polarized (CP) dual band 2 × 2 antenna array using sequential phase rotation technique for wireless applications is designed and investigated. The feed network utilizes four rectangular lines of equal width and three 90° arcs. The length of all elements is equal to λg/4 to provide 0°, 90°, 180° and 270° phase differences at the four outputs of feed network to increase Axial Ratio (AR) bandwidth and purity. Four corner truncated patch elements are connected to the feed network to complete 2 × 2 antenna array design. The proposed antenna array operates at two different frequency bands of 4.9–6 and 7.9–8.3 GHz (S11 < −10 dB) and also shows CP behavior at 5–5.8 and 8–8.4 GHz (AR < 3 dB) frequency bands. Very good similarity is attained between the axial ratio and impedance bandwidths. The maximum gain of the antenna array is 9.1 dB. The antenna array was prototyped and tested to validate its performance. This array is well suitable for WLAN, Wi-Fi and X-Band uplink satellite communication applications. [ABSTRACT FROM AUTHOR]

Variation in canopy water content (CWC) that can be detected from microwave remote sensing of vegetation optical depth (VOD) has been proposed as an important measure of vegetation water stress. However, the contribution of leaf surface water (LWs ), arising from dew formation and rainfall interception, to CWC is largely unknown, particularly in tropical forests and other high-humidity ecosystems. We compared VOD data from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) and CWC predicted by a plant hydrodynamics model at four tropical sites in Brazil spanning a rainfall gradient. We assessed how LWs influenced the relationship between VOD and CWC. The analysis indicates that while CWC is strongly correlated with VOD (R2  = 0.62 across all sites), LWs accounts for 61-76% of the diurnal variation in CWC despite being < 10% of CWC. Ignoring LWs weakens the near-linear relationship between CWC and VOD and reduces the consistency in diurnal variation. The contribution of LWs to CWC variation, however, decreases at longer, seasonal to inter-annual, time scales. Our results demonstrate that diurnal patterns of dew formation and rainfall interception can be an important driver of diurnal variation in CWC and VOD over tropical ecosystems and therefore should be accounted for when inferring plant diurnal water stress from VOD measurements.

A porous 3D cross-linked conductive network pierced by multi-wall carbon nanotubes (MWCNTs) was successfully designed from zeolitic imidazolate framework-8 (ZIF-8). Zn@NPC@MWCNTs composites were tailored by the facile regulating the mass ratios and thermal annealing treatment. Due to the combination of less eddy current loss and dielectric loss together with multiple reflection attenuation caused by a unique structure. With a 10 wt% filler loading, the Zn@NPC@MWCNTs composites carbonized at 800 °C show two high reflection loss (RL) values with different thicknesses. An RL value is −53.18 dB with 4.09 mm thickness in the C-Band (4–8 GHz), and a minimum RL can reach −74.83 dB (10.8 GHz) with a matching thickness of 2.749 mm. The effective absorption bandwidth is 4 GHz (from 8 to 12 GHz, RL ≤ −10 dB), which just covers the full X-band. Low cost and easy preparation can also provide advantages to develop MOF-based materials as effective EMW absorbents.

A compact single-layer, polarization-insensitive, and angularly stable frequency selective surface (FSS) based multi-stop band filter is reported for shielding three useful frequency bands covering 1.82-2.86 GHz Industrial, scientific, and medical (ISM), 3.52-4.06 GHz Worldwide Interoperability for Microwave Access (WiMAX), and 7.42-8.72 GHz (satellite downlink), centered at 2.4 GHz, 3.6 GHz, and 8.1 GHz, respectively. The proposed unit cell (15 mm x 15 mm) contains four equal-sized square-headed dumbbell (SHD) shaped resonators surrounded by two square ring resonators. The outer and inner square rings offer the first and second stop bands, while the SHD resonators provide the third stop band. A highly polarization-insensitive response is realized owing to the four-fold symmetry in the proposed structure. The unique arrangements of the SHD resonators help to realize higher angular stability under transverse electric (TE), transverse magnetic (TM), and diagonally polarized incident electromagnetic (EM) waves for incidence angles up to 80°, 80°, and 70°, respectively. A detailed analysis in terms of equivalent circuit and parametric variation is carried out to illustrate the higher to lower frequency band ratio. A prototype is fabricated and tested through a proper measurement setup to validate its performance, and it shows good agreement with the simulated results. The proposed FSS unit cell offers better angular stability under diagonally polarised incident waves, attenuation level, minimum higher to lower frequency band ratio, good fractional bandwidth, and compactness. So the designed multi-stopband FSS can be considered a potential candidate for shielding EM radiation across the useful bands. [ABSTRACT FROM AUTHOR]

This paper proposes a planar wideband microstrip feedline to a slot-line-based patch antenna for high-frequency pattern diversity applications. The antenna consists of two adjacent rectangular patches separated by the ground slots, with a directive patch slot along the edge of the substrate. A compact common feedline-to-slot configuration is used to miniaturize the antenna. The antenna is designed in stages, starting with an in-phase feedline, followed by a slot line structure, with two radiating patches on top and a director on the side. This creates radiation diversity with directive radiation patterns. The antenna was fabricated and analyzed inside a far-field anechoic chamber. The experimental results validate the return loss, gain, and radiation performance. The measured results of the antenna within a frequency range of 8.5 to 11 GHz show good agreement with the simulation. The antenna has a maximum gain of 9.2 dBi and has the potential to be beneficial for beam steering and X-band applications due to its low profile, broad bandwidth, high gain, and good directivity. [ABSTRACT FROM AUTHOR]

Electromagnetic pollution has become a major problem affecting human health, which requires the scientific community to characterise materials that can solve this problem. In the present work, we studied the microwave absorption properties and complex permittivity of ZrB2/Al2O3 ceramic composites in the X-band by simulation. The composites studied are based on alumina and reinforced with ZrB2 particles. The concentration of ZrB2 particles by volume in these composites are 0%, 5%, 10% and 15%. The results obtained show, on the one hand, that the complex permittivity depends on the frequency, and on the other hand, the high content of ZrB2 remarkably increases the complex permittivity and improves the microwave absorption properties. The ZrB2/Al2O3 composite with 5% by volume of ZrB2 particles has better microwave absorption property than others. In this case, the minimum reflection loss is −26.36 dB at 11.5 GHz. For this composite, the RL bandwidth of less than −10 dB is 1.72 GHz, and it is obtained in the frequency range from 9.4 GHz to 10.5 GHz. The simulation results are in good agreement with the published experimental results. In addition, they indicate that the composites studied are favourable for microwave absorption applications in the X band. [ABSTRACT FROM AUTHOR]

The article presents the design and development of a metamaterial-based microwave absorber having polarisation insensitivity, broad angle of incidence, low profile, and compactness in the microwave frequency range. The unit cell focuses to achieve maximum absorption at C-, X- and broad Ku-bands. The structure is simulated and the results are analysed for different angles of polarisation and angle of incidence. The dimension of the proposed structure is ultrathin and compact having an overall dimension of 8 mm × 8 mm × 0.8 mm. The dimensions are optimized in such a fashion to achieve three different peaks at three different bands thereby making the triple-band behaviour of the metamaterial absorber possible. The structure is providing absorption of 99.14% absorption at 6.08 GHz (C-Band) while absorption of 98.29% is achieved at 9.49 GHz (X-band) and 265 MHz bandwidth with above 95% absorption from 16.57 GHz to 16.83 GHz (Ku-Band) in the microwave regime. The absorber patch is a composition of square ring patches and a central square ring annexed with triangles on four sides, the split ring providing a combinational effect witnessing the desired absorption at designated frequencies. The unit cell dimension at a lower cut-off frequency is 0.162 λlowest. The proposed structure is verified for polarisation sensitivity and has a wide angle of incidence. The structure is experimentally verified for results and is found to be in close agreement with simulated ones. The compactness of structure with the attainment of the highest form of absorption in different bands including the 265 MHz high absorption band provides the scope of applicability in various engineering applications at microwave regimes. [ABSTRACT FROM AUTHOR]

Artificially designed anisotropic materials are gaining momentum in the microwave region to cater for various wideband applications such as 5G communication, microwave imaging, etc. In this work, a metasurface-based single-layer reflective cross-polarization rotator with 90% polarization conversion has been demonstrated. The proposed structure has been examined for both transverse electric (TE) and transverse magnetic (TM) wave incidences, and the physical mechanism has been thoroughly examined using the surface current distribution. The metasurface structure has been fabricated and measured in a compact range anechoic chamber. The simulation and measurement results show a polarization conversion ratio (PCR) of above 0.9 from 6.07 GHz to 13.77 GHz. Additionally, the generalized sheet transition condition (GSTC) has been used to calculate the structure's effective electric and magnetic surface susceptibility. The proposed metasurface can be used for monostatic radar cross-section reduction, low scattering antennae, and as an antenna polarization converter. [ABSTRACT FROM AUTHOR]

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A novel metamaterial-based MIMO antenna designed with low mutual coupling and good resolution for object detection using a machine learning model (ML). This proposed design analyzed the azimuth angle variation with gain in the field of view for object detection and isolation variation with the distance between antenna elements. The machine learning model for antenna parameter optimization is discussed. The MIMO antenna used Defected Ground Structure (DGS) and metamaterial unit cell to reduce mutual coupling and bandwidth tuning. This work's originality resides in designing a miniaturized MIMO antenna and optimizing antenna parameters using a machine-learning model. It is implemented on FR4 Epoxy with 1.6mm of thickness and a size of 15 × 25mm2 with a 3.5mm distance between antenna elements. The proposed antenna operates from 7.53 to 12.58GHz with maximum isolation of -26dB at 9.5GHz and maintained above 20dB throughout the operating band. The efficiency, gain, and Miniaturization of the proposed antenna 96%,4.4dB, and 62% were achieved compared to previous works. The performance parameters of the MIMO antenna, return loss, mutual coupling, and envelope correlation coefficient (ECC) are evaluated using HFSS. The prototype of the MIMO antenna is fabricated, and the results are good arrangement with the simulated. [ABSTRACT FROM AUTHOR]

A monopole antenna with dual (linear/circular) polarization reconfigurability for X-band applications is presented in this paper. The antenna consists of a bent arm cross-shaped (BACS) slot created on the inverted triangular staircase fractal (ITSF) shaped patch. Two PIN diodes are embedded on the opposite side of the horizontal arm of the BACS slot for electronic switching between two different polarization states. By varying the biasing conditions of PIN diodes, the measured antenna’s 3 dB axial ratio (AR) operational band for left-hand circular polarization (LHCP) is observed from 9.88 GHz to 11.06 GHz, whereas linear polarization (LP) is achieved from 7.95 GHz to 12.64 GHz. The measured peak gain of the antenna is 5.71 dBi, whereas the average peak gain is obtained as 4.97 dBi. The size of the antenna is $1.57\mathrm {\lambda }_{\mathrm {g}}\times 1.25\mathrm {\lambda }_{\mathrm {g}}$ where, $\mathrm {\lambda }_{\mathrm {g}}$ is guided wavelength at the lowest cutoff frequency, 7.95 GHz. The proposed monopole antenna’s progressive design steps, an equivalent lumped circuit model analysis, and a comparative study between electromagnetic (EM) simulation and measured results are carried out to validate the antenna’s performance.

A dual-functionality printed dipole array antenna is proposed in this study with a fan-beam property. An integrated balun structure cooperation with the dipole arms creates a resonance in the X-band for the antenna. Adding Single-Ring Split-Ring Resonator (SR-SRR) next to the feed line allows another resonance in the C-band. This way, a dual-band dipole array antenna with identical radiation properties is accomplished. Considering the distance between the two resonances of the antenna, the main contribution of this work is the similar radiation pattern in the two frequency bands of the antenna. According to the experimental results, the introduced antenna can cover the frequency band of 4.52-5.83 GHz for C-band applications (such as; satellite communication and microwave relay) and 9.08-9.66 GHz for X-band applications (such as; weather mapping and detecting and long-range tracking radar) with peak gains of 9.05 dBi and 11.30 dBi respectively and similar fan-beam radiation patterns in two frequency bands.

In this paper, a quad-band polarization- and incident-angle independent low-profile metamaterial absorber is proposed. The design consists of three square rings one into another and one plus-shaped slot structure. The size of the unit cell is 11 × 11 mm2 and is printed on an FR-4 substrate having a thickness of 1 mm. It provides 99.2%, 97.6%, 99.3%, and 99.9% absorption at 3.55 GHz, 5.27 GHz, 7.57 GHz, and 11.57 GHz, respectively, thus covering the S, C, and X bands. The surface current distribution of the proposed absorber is also shown at the four resonating frequencies to get a better insight into the design. Moreover, the stability of the proposed design is also validated with different incident angles (for both TE and TM modes) and polarization angles. In addition, a prototype of the proposed absorber structure is also fabricated and then verified experimentally. [ABSTRACT FROM AUTHOR]

Metamaterials are frequently employed as sensors in a wide range of applications because of their special qualities that are not present in nature. This study focus on the design, fabrication and measurement of a novel shape metamaterial absorber for moisture-sensing applications. The proposed metamaterial absorber consists of modified cross along with split square resonator shape conductor on top of a 0.6 mm thick substrate. Parametric studies are also performed on the different design parameters, such as the thickness of the substrate and split square resonator etc. to figure out the optimal value of design variables. The simulated results of the proposed absorber illustrate the maximum reflection coefficient at 9.9 GHz. The obtained reflection coefficient value is − 30.5 dB at the resonant frequency The measured results of the absorber also show good agreement with the simulated results. Furthermore, the proposed metamaterial-based absorber utilize as a sensor. The proposed sensor design demonstrates excellent results in terms of resonance shift, sensitivity, linearity, Q factor, and figure of merit, making it a good candidate for moisture-sensing applications. [ABSTRACT FROM AUTHOR]

Developing flexible electromagnetic interference shielding (EMI SE) materials is an effective strategy to protect humans from being harmed by electromagnetic radiation from electronic devices. Though the EMI SE property of such materials as graphene can exceed 100 dB, it remains a challenge to achieve high-efficiency EMI SE performance while having excellent flexibility to allow them to be wearable. Herein, we designed theoretically and fabricated experimentally the flexible multilayer structure of the poly-(vinylidene fluoride)/graphene-poly-(vinylidene fluoride) (PVDF/GNP-PVDF) composite films. The experimental results show that the film thickness and layer number play an important role in determining the EMI SE performance, and the multilayer film with a thickness of 0.3 mm and a layer number of 6 exhibits not only high EMI SE performance (69.7 dB on average in X-band) but also excellent flexibility and stability (98.85% EMI SE retention after bending of 60° for 1000 cycles). The theoretical study via COMSOL software matching well with the experimental data reveals that multiple reflection and absorption of electromagnetic waves between layers is responsible for the high EMI SE performance of the PVDF/GNP-PVDF multilayer film at a relatively low thickness that ensures flexibility. This work highlights the significance of designing the multilayer architecture via theoretical simulation for improving the EMI SE performance and also demonstrates the high EMI SE application prospect of PVDF/GNP-PVDF films in wearable electronic devices. [ABSTRACT FROM AUTHOR]

This article presents a single-layer, ultra-thin and multifunctional polarization converter (PC) design using metasurface. The PC, which is proposed as a single layer, consists of a metal metasurface on the front side of a easily accessible FR-4 material and a metal termination on the back surface. The suggested PC features linear polarization (LP) characteristic within a frequency ranges of 5.21 - 5.41 GHz and 7.53 - 8.08 GHz in C-band, also 10.59 - 10.84 GHz in X-band under normal incidence. It indicates the conversion performance of linear polarization to circular polarization (LP-CP) that has the properties of left-handed circular polarization (LHCP) in frequency range of 5.74–7 GHz in C-band and right-handed circular polarization (RHCP) in frequency range of 8.63 - 10.15 GHz in X-band. Besides, the suggested PC provides more than 90 % polarization conversion ratio (PCR) value in case of normal incidence (0 ∘ ) and over 80 % PCR value in case of oblique incidence up to 45 ∘ . Again, the suggested PC offers the same CP feature in two frequency regions where CP conversion takes place under normal incidence for angle of incidence up to 60 ∘ . A prototype of suggested PC was produced, measured, and a good match was found between the results simulated via a commercial electromagnetic (EM) simulation program. Finally, the performance of suggested design is compared with existing studies in literature with its high aspects. In this context, the suggested PC may be useful for C- and X-band applications due to its simple structure, ultra-thin and compactness, low-cost, and performance of LP and CP conversion under wide oblique angles. [ABSTRACT FROM AUTHOR]

The proposed paper presents a flexible antenna that is capable of operating in several frequency bands, namely 2.45 GHz, 5.8 GHz, and 8 GHz. The first two frequency bands are frequently utilized in industrial, scientific, and medical (ISM) as well as wireless local area network (WLAN) applications, whereas the third frequency band is associated with X-band applications. The antenna, with dimensions of 52 mm × 40 mm (0.79 λ × 0.61 λ), was designed using a 1.8 mm thick flexible kapton polyimide substrate with a permittivity of 3.5. Using CST Studio Suite, full-wave electromagnetic simulations were conducted, and the proposed design achieved a reflection coefficient below −10 dB for the intended frequency bands. Additionally, the proposed antenna achieves an efficiency value of up to 83% and appropriate values of gain in the desired frequency bands. In order to quantify the specific absorption rate (SAR), simulations were conducted by mounting the proposed antenna on a three-layered phantom. The SAR1g values recorded for the frequency bands of 2.45 GHz, 5.8 GHz, and 8 GHz were 0.34, 1.45, and 1.57 W/Kg respectively. These SAR values were observed to be significantly lower than the 1.6 W/Kg threshold set by the Federal Communication Commission (FCC). Moreover, the performance of the antenna was evaluated by simulating various deformation tests. [ABSTRACT FROM AUTHOR]

Synthetic aperture radar (SAR) systems are one of the best resources to gather information in polar environments, but the detection and monitoring of sea ice types and icebergs using them is still a challenge. Limitations using single-frequency images in sea ice characterization are well known, and using different SAR bands has been revealed to be useful. In this paper, we present the quantitative results of an intercomparison experiment conducted by the Argentine Naval Hydrographic Service (SHN) using X-, C-, and L-bands from COSMO-SkyMed, Sentinel-1, and SAOCOM satellites, respectively. The aim of the experiment was to evaluate SAOCOM for its use on SHN products. There were 25 images with different SAR parameters that were analyzed, incorporating the diversity in the information that everyday Ice Services attend to. Particularly, iceberg detections, fast first-year ice, and belts and strips were studied in the Antarctic Sound, the surroundings of Marambio Island, and Erebus and Terror Gulf. The results show that the HV polarization channel of the L-band provides useful information for iceberg detection and fast first-year ice surface feature recognition and is a promising frequency for the study of strip identification under windy sea conditions and snow accumulation on first-year ice.

The quality of weather radar affects the reliability and effectiveness of monitoring severe convective weather. Therefore, rigorous calibration and validation are the foundation for the quantitative application of weather radar. Among the available methods, radial velocity validation is of great significance for reducing the false alarm rate in the identification of tornadoes and thunderstorms. Based on the traditional method that utilizes internal and external instrument radar velocity measurements, we propose a weather radar radial velocity validation method that uses RTK UAV to simulate external targets. In addition, according to the characteristics of the UAV application scenarios, we introduce the evaluation parameter of optimal absolute accuracy to supplement the original parametric system. The experimental results show that the evaluation parameter of optimal absolute accuracy can effectively reduce the interference caused by the systematic deviation of the UAV due to the internal and external environment, which can affect the validation results. When the UAV velocity is not greater than 10 m/s, the optimal absolute accuracy of the radial velocity validation is less than 0.05 m/s, which is essentially consistent with the external instruments’ measurement results. This method can be effectively applied to the procedural handling of weather radar radial velocity validation. It is significant for ensuring the accuracy and quality of weather radar radial velocity measurements and improving the effectiveness of radar velocity data applications.

The manufacturing of active RF devices like klystrons is dominated by expensive and time-consuming cycles of machining and brazing. In this article, we characterize the RF properties of X-band klystron cavities and an integrated circuit manufactured with a novel additive manufacturing process. Parts are 3D printed in 316 L stainless steel with direct metal laser sintering, electroplated in copper, and brazed in one simple braze cycle. Stand-alone test cavities and integrated circuit cavities were measured throughout the manufacturing process. The un-tuned cavity frequency varies by less than 5% of the intended frequency, and Q factors reach above 1200. A tuning study was performed, and unoptimized tuning pins achieved a tuning range of 138 MHz without compromising Q. Klystron system performance was simulated with as-built cavity parameters and realistic tuning. Together, these results show promise that this process can be used to cheaply and quickly manufacture a new generation of highly integrated high power vacuum devices.

The paper considers the possibilities of 3D printing technology for the manufacture of X-band waveguide photonic crystals. The photonic crystals for an EIA WR-90 standard rectangular waveguide with a cross section of 22,86 10,16 mm2 in the X-band were designed and manufactured. Numerical modeling of the reflection characteristics of photonic crystals of several designs in the OpenEMS software package was carried out. Based on the simulation results, the best types of the structures were selected, which were manufactured using the physical modeling technique by the fusion method of PETG plastic. Experimental study of the manufactured layouts and comparison of the experimental data with the numerical simulation data were performed. The best types of manufactured models of waveguide photonic crystals showed transmittance and reflection drop in the corresponding frequency bands of the order of 1520 dB, which is acceptable for technical applications. The numerical modeling results are in good agreement with experiments, thus indicating the high efficiency and good control of the topology and dimensions of the manufactured photonic crystals structural elements in the used type of 3D printing technology.

Herein, the PMMA/MWCNT/Ag hybrid composite films are prepared by solvent casting method to be used in an electrical application. The AC conductivity and dielectric characteristics have been investigated at room temperature. The electrical conductivity of the hybrid composite reaches a percolation critical concentration of 2.14×10-4 S/cm by Ag doping. For all PMMA/MWCNT/Ag hybrid composites, the frequency-dependent dielectric constant decreases as the frequency area widens. As the concentrations of MWCNT and Ag increase, the AC conductivity exhibits an increasing trend. The MWCNT and Ag content was found to significantly affect the SE of the given composites. A high electromagnetic (EM) shielding efficiency (SE) was achieved between 8.2 and 12.4 GHz (X-band). The highest EM attenuation of 18 dB at 12 GHz was achieved using 0.5 wt% MWCNT and Ag. The thermal analysis of the formed PMMA/MWCNT/Ag hybrid composites showed that exothermic reactions with the greatest weight loss took place between 200°C and 300°C. FESEM show that PMMA/MWCNT/Ag hybrid composites had uniform dispersion of the carbon nano tube and silver particles within the PMMA matrix .

ABSTRAK Jalan kelas IIIC memiliki struktur yang lebih sempit dan biasanya dibangun didekat permukiman penduduk untuk penggunaan pejalan kaki. Selain pejalan kaki, kendaraan motor roda dua juga dapat mempergunakaan jalan tersebut. Permasalahan mulai timbul saat kendaaraan bermotor memiliki kecepatan yang cukup tinggi sehingga membahayakan pengguna jalan lainnya khususnya pedestrian. Untuk mengatasi hal tersebut, pada penelitian ini dilakukan pengembangan X-band speed detector berbasis efek pergeseran doppler untuk kendaraan motor roda dua di jalan kelas IIIC. Detektor yang dibangun mengimplementasikan sensor HB100 dengan frekuensi 10 GHz Adapun efek pergeseran doppler diproses menggunakan Arduino. Parameter yang dijadikan perhitungan diantaranya kecepatan, pergeseran doppler, dan jarak detektor. Hasil pengujian menunjukan bahwa sistem berhasil memiliki akurasi diatas 95% (atau error

Summary: This work proposes an electrical compact triple‐bands antenna founded on a composite left‐/right‐handed approach. This structure contains a rectangular patch combined with two unit cells based on the metamaterial properties that are used to produce wide electrical lengths in miniature physical sizes. Thus, the presented antenna is designed with a lower resonant frequency and miniature physical dimensions compared to conventional antennas. The suggested antenna has been produced on top of the FR4 substrate having tan δ = 0.022, εr = 4.58, and a size of 28 × 16 × 1.6 mm3. This structure provides three bandwidths of (2.391–2.54 GHz), (3.42–3.56 GHz), and (5.02–11.40 GHz). Additionally, a multi‐input multioutput (MIMO) antenna is designed by placing two similar radiating patches in a perpendicular shape. Therefore, this design approach has been used to achieve an important isolation among ports and less than −30 dB at frequency bands. The results of radiation patterns, envelope correlation coefficient, diversity gain, and channel capacity loss are below to 0.06, 10 dB, and 0.4 b/s/Hz respectively, which confirms that the MIMO antenna is compatible with wireless MIMO devices. These antennas have been modeled and experimentally confirmed, and the results have proven that the suggested antennas are useable and can support multi‐standard wireless applications. [ABSTRACT FROM AUTHOR]