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Viewshed analysis is an important research content of digital terrain analysis. The terrain viewshed refers to the range that can be seen at the current position, which varies with the nature of the observer. When the observer is a wireless signal tower, it is the communication viewshed, which refers to the area consisted of grid cells where the receiving antennas can receive the signals from a transmitting antenna set up on a grid cell of terrain. The core of base station location problem includes two aspects: combinatorial optimization and the calculation of the coverage rate of signal. The calculation of communication viewshed is an important research content for determining signal coverage range. In this article, we propose an accurate communication viewshed computation algorithm for wireless signal (CVCWS) using the projection curve of 3D Fresnel zone analysis based on DEM. The CVCWS method can calculate the signal reception quality at different locations more precisely. Besides, a signal attenuation model is proposed to compute the theoretical attenuation value according to the signal receiving quality index. The proposed algorithm is compared with the existing DEM‐based communication viewshed algorithms, and the theoretical attenuation values are compared with the measured values. The experimental results show that the theoretical values gained by the CVCWS algorithm are close to the measured values, indicating high accuracy of the CVCWS algorithm. The proposed method can provide theoretical support for communication tower location planning and other related applications. [ABSTRACT FROM AUTHOR]

Very‐low‐frequency (VLF) transmitting antennas have a crucial influence on the nearby electromagnetic environment. Commercial software packages, such as CST Studio Suite (CST) or Altair FEKO (FEKO), are always utilised to calculate the electric fields of VLF antennas, which consume considerable computing resources and time. The classical method of electric field calculation, the charge simulation method (CSM), is first applied to the calculation of electric field near the VLF transmitting antenna. The distribution characteristics of three‐dimensional electric fields were analysed. The electric field surrounding the antenna exhibited axial symmetry. The highest electric field strength was at the top of the antenna, and as the distance from the antenna increased, the electric field strength exponentially decreased. The comparisons are performed between the results of the CSM and those of commercial software, the average relative errors of CSM on two observation paths are very small, 2.20% and 2.21%, respectively. Meanwhile, the CSM shows considerable advantages in saving calculation resources and improving efficiency. Additionally, the comparison between CSM calculation and the measured data is carried out. The results show that this method can accurately calculate the electric field near VLF transmitting antenna and offer valuable insights and a new solution. [ABSTRACT FROM AUTHOR]

Digital coding and programmable metasurfaces stand out as promising candidates in future wireless communications due to their low costs and fast‐action reprogrammable capability. However, 2 significant obstacles, namely integration and power consumption, must be addressed before large‐scale engineering application of the programmable metasurface. This work proposes an easy‐integration and energy‐saving meta‐system and demonstrates its application in wireless communications. The meta‐system features a hybrid architecture and consists of a programmable feed array and a metasurface lens. The feed array comprises 3 subarrays, in which active elements are doped with passive elements and interconnected configurations are used to efficiently reduce the number of active elements by one‐third. The meta‐lens acts as a passive phase shifter to enhance the beamforming performance, further reducing the number of active elements. Moreover, the meta‐system can switch between different modes to achieve various functions. In particular, the maximum power consumption of the meta‐system is only 54 mW, which can be considered nearly passive. A wireless communication experiment is presented, where the meta‐system simultaneously serves as the direct digital modulator and the transmitting antenna. Owing to the low cost, high integration, and nearly passive and programmable features, the meta‐system has remarkable potential for future applications in wireless communications. [ABSTRACT FROM AUTHOR]

A characterization of near-field impulse responses based on electromagnetic (EM) near-field data from an EM solver to explore features of the propagation process on a well-known wideband traveling wave antenna—double-slot Vivaldi antenna—is presented in this article. The intensity, propagating time and partitional response characteristics facilitate interpretation of the propagation process and impacts of the antenna partitions on the process. The EM energy flows guided, reoriented and scattered along a sequence of antennas transmitting and radiating segments were recognized. The geometric features of near-field wavefront surfaces supported evaluation of the EM flow proportions and antenna directivity. Impact of the structural section on radiation was also assessed by the partitional far-field response characteristic in frequency and time domains. Supported by many complementary characteristics in the analyses, inherent features of the propagation process were emphasized and false flags were minimized. By this approach, the simplification for the near-field propagation model contributed to enhancing the insight of near-field propagation processes on the double-slot antipodal Vivaldi antennas and enabled optimizing the antenna structure details. [ABSTRACT FROM AUTHOR]

There is an urgent need to develop non-destructive testing (NDT) methods for infrastructure facilities and residences, etc., where human lives are at stake, to prevent collapse due to aging or natural disasters such as earthquakes before they occur. In such inspections, it is desirable to develop a remote, non-contact, non-destructive inspection method that can inspect cracks as small as 0.1 mm on the surface of a structure and damage inside and on the surface of the structure that cannot be seen by the human eye with high sensitivity, while ensuring the safety of the engineers inspecting the structure. Based on this perspective, we developed a radar module (absolute gain of the transmitting antenna: 13.5 dB; absolute gain of the receiving antenna: 14.5 dB) with very high directivity and minimal loss in the signal transmission path between the radar chip and the array antenna, using our previously developed technology. A single-input, multiple-output (SIMO) synthetic aperture radar (SAR) imaging system was developed using this module. As a result of various performance evaluations using this system, we were able to demonstrate that this system has a performance that fully satisfies the abovementioned indices. First, the SNR in millimeter-wave (MM-wave) imaging was improved by 5.4 dB compared to the previously constructed imaging system using the IWR1443BOOST EVM, even though the measured distance was 2.66 times longer. As a specific example of the results of measurements on infrastructure facilities, the system successfully observed cracks as small as 0.1 mm in concrete materials hidden under glass fiber-reinforced tape and black acrylic paint. In this case, measurements were also made from a distance of about 3 m to meet the remote observation requirements, but the radar module with its high-directivity and high-gain antenna proved to be more sensitive in detecting crack structures than measurements made from a distance of 780 mm. In order to estimate the penetration length of MM waves into concrete, an experiment was conducted to measure the penetration of MM waves through a thin concrete slab with a thickness of 3.7 mm. As a result, Λexp = 6.0 mm was obtained as the attenuation distance of MM waves in the concrete slab used. In addition, transmission measurement experiments using a composite material consisting of ceramic tiles and fireproof board, which is a component of a house, and experiments using composite plywood, which is used as a general housing construction material in Japan, succeeded in making perspective observations of defects in the internal structure, etc., which are invisible to the human eye. [ABSTRACT FROM AUTHOR]

This paper proposes a full-duplex (FD) antenna design with passive self-interference (SI) suppression for the 28 GHz mmWave band. The reduction in SI is achieved through the design of a novel configuration of stacked Electromagnetic Band Gap structures (EBGs), which create a high impedance path to travelling electromagnetic waves between the transmit and receive antenna elements. The EBG is composed of stacked patches on layers 1 and 2 of a four-layer stack-up configuration. We present the design, optimization, and prototyping of unit antenna elements, stacked EBGs, and integration of stacked EBGs with antenna elements. We also evaluate the design through both HFSS (High Frequency Structure Simulator) and over-the-air measurements in an anechoic chamber. Through extensive evaluations, we show that (i) compared to an architecture that does not use EBGs, the proposed novel stacked EBG design provides an average of 25 dB of additional reduction in SI over 1 GHz of bandwidth, (ii) unit antenna element has over 1 GHz of bandwidth at −10 dB return loss, and (iii) HFSS simulations show close correlation with actual measurement results; however, measured results could still be several dB lower or higher than predicted simulation results. For example, the gap between simulated and measured antenna gains is less than 1 dB for 26–28 GHz and 28.5–30 GHz frequencies, but almost 3 dB for 28–28.5 GHz frequency band. [ABSTRACT FROM AUTHOR]

This paper proposes a compact design of dual-sense circularly polarized (CP) antenna for simultaneous transmit (Tx) and receive (Rx) communication systems. The primary radiating aperture of the proposed antenna is a 2 × 2 unit-cell metasurface (MS). The MS is excited by the asymmetric patch in the center, which acts as the CP source of the whole antenna structure. By properly tuning the feeding positions, dual-sense CP with high isolation can be achieved. For verification, an antenna prototype with compact dimensions of 0.36λ × 0.36λ × 0.02λ (λ is the free-space wavelength at the center operating frequency) is fabricated and measured. The measured operating bandwidth is 1.6% (2.45–2.49 GHz), in which the reflection and transmission coefficients are less than—10 dB and the axial ratio is lower than 3 dB. Within this band, the maximum isolation value is 39 dB, and the peak gain is 5.7 dBi. [ABSTRACT FROM AUTHOR]

Here, fast time‐varying channels of high‐mobility vehicle‐to‐vehicle communications for massive multiple‐input multiple‐output orthogonal frequency division multiplexing systems are considered. Large‐scale uniform linear arrays are configured at the transmitter and receiver to separate multiple angle domain Doppler frequency offsets based on transmit and receive beamforming with high spatial resolution. Then, each beamforming branch comprises only one dominant Doppler frequency offset. Next, the conventional channel estimation method is performed for each beamforming branch, and carry out maximum‐ratio‐combining for data detection. Power spectrum density and Doppler spread of the equivalent link between the transmitter and receiver are derived and regarded as the criterion for assessing the residual channel time variation caused by limited antennas in practice. Interestingly, a scaling law between the asymptotic Doppler spread and the number of transceiver antennas shows that asymptotic Doppler spread is proportional to the maximum Doppler frequency offset and decreases at the rate of 1NT2+1NR2$\sqrt {\frac{1}{{{N_T}^2}} + \frac{1}{{{N_R}^2}}}$, where NT${N_T}$ and NR${N_R}$ are the number of transmit and receive antennas, respectively. Simulation results confirm the validity of the proposed Doppler suppression framework in high‐mobility vehicle‐to‐vehicle communications. [ABSTRACT FROM AUTHOR]

A novel method based on machine learning is proposed to estimate the electromagnetic radiation level at the ground plane near fifth‐generation (5G) base stations. The machine learning model was trained using data from various 5G base stations, enabling it to estimate the electric field intensity at any arbitrary radiation point when the base station provides service to different numbers of 5G terminals which are in different service modes. The inputs required for the model include the transmit power of the antenna, the antenna gain, the distance between the 5G base station and 5G terminals, terminal service modes, the number of 5G terminals and the environmental complexity around the 5G base station. Experimental results demonstrate the feasibility and effectiveness of the estimation method, with the mean absolute percentage error of the machine learning model being approximately 5.98%. This level of accuracy showcases the reliability of the approach. Moreover, the proposed method offers low costs when compared with on‐site measurements. The estimated results can be utilised to reduce test costs and provide valuable guidance for optimal site selection, thereby facilitating radio wave coverage or electromagnetic radiation regulation of 5G base stations. [ABSTRACT FROM AUTHOR]

This study proposes a method for predicting the electric field strength in a nuclear power plant's main control room (MCR) using convolutional neural networks (CNN). The CNN model learns the electric field distribution using data from the ray tracing (RT) simulator or measurements and predicts the electric field strength for new conditions. The proposed method was validated by comparing the predicted electric-field strength with the results of the RT simulator by changing the position of the transmitting antenna in the MCR. The average errors were less than 5 %, confirming that the proposed method can effectively predict electric fields in environments such as nuclear power plants. [ABSTRACT FROM AUTHOR]

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technological support for the simultaneous and frequent access by a large number of users to radio resources. For 5G cellular systems, this exhaust is not enough to provide physical layer services. An appropriate Peak-to-average power ratio (PAPR) minimization principle, which maximizes data capacity and channel utility, has been used to address this issue. In this paper, mainly focus on minimize the high PAPR of the candidate sequence of the OFDM sub-block using modified enhancement asymmetric arithmetic coding scheme (M-EAAC). According to this, circular shifting of the candidate sequence is established in the spatial circular shifting and temporal interleaving (SCS-TI) form to generated different set of conjugated phases which is multiplied with candidate sequence. Then, the transmitting antenna is identified the best lowest PAPR of the candidate sequence is chosen for entire OFDM data transmission. The simulation results conveys that the proposed SCS-TI method provide acceptable improvement in the PAPR reduction as compared with conventional selective mapping (SLM) and pseudo-random SLM (PR-SLM). Moreover, the complexity evaluation which ensure the proposed method provides better improvement at three important stages includes inverse fast Fourier transform (IFFT) operation, optimization process, and PAPR calculation at each candidate sequence. [ABSTRACT FROM AUTHOR]

This work addresses the evolving landscape of internet of things (IoT) applications and large antenna array systems, where optimizing spectral efficiency and simplifying design complexities are crucial. Focusing on two key challenges, the study introduces a novel hybrid analog-digital transceiver strategy tailored for frequency-selective channels. By integrating Shannon and Hartley theorems, the approach enhances data transfer rates, thereby optimizing radio frequency (RF) chain utilization in large-scale antennas. To achieve a balance between transceiver performance and hardware complexity, the study employs a decentralized alternating direction method of multipliers (ADMM) framework. The proposed hybrid consensus ADMM algorithm (HC-ADMM) ensures efficient convergence in decentralized optimization scenarios. Comparative analyses with ADMM and existing system transceiver optimization (ESTO) models highlight HCADMM's superior performance across key metrics such as spectral efficiency, efficiency per cell, total efficiency, and optimal scheduling of user equipment (UEs). Particularly notable is HC-ADMM's advanced optimization capabilities as the number of transmit antennas increases, positioning it as a promising approach for enhancing overall communication network performance. [ABSTRACT FROM AUTHOR]

We report on the theoretical design and experimental verification of a high efficiency microwave wireless power transmission (MWPT) system operating in the Fresnel region. To achieve high conversion efficiency over a transmit distance of 11 meters, the transmit reflector antenna was optimized to locate the focal point at 11 m. The size of the receive antenna was decided by calculating the field distribution and the received power at different positions in the receive antenna aperture. Furthermore, an accurate model of the diode is presented, which was imported into the ADS software for high-precision rectifying circuit design. As a result, an overall DC-DC conversion efficiency of 20% was achieved, as measured in an anechoic chamber at a given distance of 11 m. The experimental results validated the proposed method. [ABSTRACT FROM AUTHOR]

The paper examines the application of adaptive antennas in wireless communication systems with particular attention to how well they can transmit and receive signals by dynamically adjusting radiation patterns. The review covers a range of artificial intelligence (AI) approaches that have been used to enhance adaptive antenna performance in beamforming, channel estimation, interference mitigation, and spectrum utilization. Besides adaptive antennas' potential to improve wireless communication systems, the paper also discusses their limitations, including computational complexity, interference sensitivity, and the significance of precise channel state information (CSI) estimates. [ABSTRACT FROM AUTHOR]

In satellite remote sensing (SRS), there is a demand for large-power microwave components. A Butler matrix is essential to a transmitting antenna array in SRS. This article illustrates the electrical and mechanical design, simulation, and test results of a large-power planar beamforming network for SRS at C-band. It is a 4 × 4 Butler matrix based on square coaxial lines. Short-ended stubs are used in the Butler matrix to broaden its bandwidth by 10%, support inner conductors, and enhance heat transfer in vacuum environments. The simulation results are consistent with the measured results. The reflection coefficient is less than −18 dB, and the isolation is more than 23 dB from 3.8 GHz to 4.2 GHz. The insertion losses are less than 0.6 dB, and the phase errors are better than ±6°. The measured peak microwave power of the proposed Butler matrix is 9 kW. Its size is 440 × 400 × 40 mm3. The proposed Butler matrix beamforming network can be applied to SRS systems. [ABSTRACT FROM AUTHOR]

In this paper, channel estimation capabilities of a multiple-input multiple-output (MIMO) system using superimposed training sequences are investigated. A new expression for estimation-error variance is derived. It is shown that the training sequences must be balanced and must have specific correlation properties. The latter are required only in a specific zone. Sequences that satisfy these criteria exist and are referred to as zero-correlation zone (ZCZ) solutions. Consequently, by using balanced ZCZ sequences, harmful direct current (DC) offset can be removed. Owing to their zero-cross correlation, interference from other transmitting antennas may be eliminated. Furthermore, a closed-form expression of the estimation-error variance can be obtained due to their impulse-like autocorrelation. To increase the number of antennas in the MIMO system, a new construction of ZCZ sequence set is proposed, in which all sequences are balanced. [ABSTRACT FROM AUTHOR]

Spatial modulation (SM) has the potential to meet the requirements of 5G and beyond communication systems with features such as reduced hardware complexity and good trade-off between spectral efficiency and energy efficiency. In this study, an efficient non-square differential spatial modulation (DSM) scheme is presented in which the number of time slots is one more than the number of transmit antennas. The introduced scheme includes one empty time slot. At the other time slots, the time slots of the conventional DSM (CDSM) are used (the Gray code order (GCO) can also be used). There is one active antenna at each time slot of the proposed scheme. The index of empty time slot conveys information. Thus, in comparison with CDSM (or GCO), for the same number of transmit antennas, the introduced scheme has more energy-free bits (index bits). It is free of pilot overhead, channel estimation complexity, and potential channel state information (CSI) estimation errors. Further, a detector with no error propagation is presented. Analytical expressions for the bit error rate (BER) are derived at high signal-to-noise ratios (SNRs) and high SNRs per bit (SNRbs). Simulation results verify the theoretical evaluation and demonstrate the efficiency of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a novel optimized-Goppacoded cooperative generalized spatial modulation (OGCCGSM) scheme for short-to-medium information block transmission. In the proposed OGCC-GSM scheme, an efficient Goppa polynomial selection approach is designed to ensure that the selected Goppa codes applied in the source and relay nodes both have the largest minimum Hamming distance (MHD) and the optimal weight distribution. Compared to conventional coded cooperation (CC) with a single antenna, the proposed scheme employs the generalized spatial modulation (GSM) technique to achieve more diversity gains, where each node is equipped with multiple antennas and more than one transmit antenna (TA) is activated at each time-instant transmission. As a benchmark comparison, the OGCC spatial modulation (OGCC-SM) scheme is also investigated with a single TA active. Moreover, the reduced-complexity transmit antenna combination (RC-TAC) selection algorithm utilized in GSM is first developed with the aid of the channel state information (CSI) to reconcile computational complexity and system performance. In addition, joint decoding is conducted on the destination terminal to further enhance the performance of the proposed scheme. The simulated results indicate the performance of the proposed OGCCGSM scheme is superior to that of its benchmark OGCC-SM scheme, with a substantial reduction in the number of TAs. Besides, Monte Carlo simulations demonstrate that the proposed OGCC-GSM scheme prevails over its counterparts by a margin of over 4.2 dB under identical conditions. [ABSTRACT FROM AUTHOR]

This paper presents the development of a four-port dual-band dual-polarized antenna for transmitting/receiving (Tx/Rx) applications in Ku-band satellite communications. The antenna consists of two antenna elements sharing a common radiating aperture, a low-band element formed by an L-probe proximity-fed square-ring radiator for operation at the Rx band of 10.7–12.75 GHz, and a high-band element realized by a stacked-patch radiator for operation at the Tx band of 13.75–14.5 GHz. Within a compact multilayer structure, the antenna achieves wide dual-band operation, with each band having the ability to simultaneously operate with dual polarization. An antenna prototype is fabricated and tested to verify its performance. The experimental results show that the proposed antenna achieves an impedance bandwidth of 9.28–12.96 GHz (13.21–15.32 GHz), an isolation value between two orthogonal polarizations of 12 dB (12.4 dB), and a peak gain of 6.63 dBi (5.42 diBi) at the low band (high band). Tx/Rx isolation of more than 14 dB is achieved in both the Rx band and Tx band. [ABSTRACT FROM AUTHOR]

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As the transmitter and receiver (Tx and Rx, respectively) are located in close proximity during a typical ground‐penetrating radar (GPR) survey, the powerful signal generated by the Tx and which is then recorded by the Rx at various time delays, can be saturated at early times (i.e., this is the direct wave (DW) signal reaching the Rx). This often causes the masking of shallow targets, complicating data interpretation. In this study, our aim is to examine the spatial distribution of the electromagnetic signals around the Tx, attempting to locate areas where the DW becomes minimum, whereas the signal strength from subsurface targets (i.e., reflected wave – RW) remains ideally unchanged. The position of these local minima in the DW signal could give rise to advantageous Tx–Rx configurations, where clear reflections from subsurface targets lying at shallow depths can be obtained with the least possible involvement of the DW. To perform such a study, we carried out static field measurements over a flat lying reflector as well as numerical simulations in a reflection, common‐offset mode around a transmitting antenna. In the field, we also collected wide‐angle reflection–refraction data to determine the GPR wave velocity in the uppermost layer. GPR signals were recorded by the Rx around the Tx in three concentric circles of various radii (i.e., varying the Tx/Rx separation), using a specific angular step and varying the Tx/Rx polarization each time. The synthetic data were produced using a three‐dimensional finite‐difference time‐domain modelling tool. Field and numerically simulated data were analysed and compared to study the behaviour of both the DW and RW events around the Tx when changing the Tx/Rx distance, their respective angular position, as well as their relative polarization/orientation. [ABSTRACT FROM AUTHOR]

Time-domain effects of UWB disc monopole antenna as transmit antenna, receive antenna, and transmit–receive antenna pair have been investigated using different types of signal excitations. Several noted literature have performed the same by calculating either first or second-order derivatives of the input, thereby creating an ambiguity of computational approaches. The response is also reported to change with a change in pulse width. This paper aims to obviate the ambiguity in time domain response from the transfer function perspective. The concept is established in the paper by implementing a co-planar waveguide (CPW) fed disc monopole antenna with upconverted and baseband input excitation. Findings reveal that the uniqueness of frequency response in determining the effect of antenna rather than the conventional method, and the existing jeopardy of the temporal derivative is henceforth removed. Subsequently, the singularity expansion method has been applied to characterize and optimize the antenna. [ABSTRACT FROM AUTHOR]

Massive MIMO (M-MIMO) devices are the key tool to meet the performance stards established for 5G-wireless communication. However, more Radio Frequency (RF) chains needed in base station (BS) with a huge count of transmitting antennas, involve expensive hardware and computing complexities. In order to decrease the RF chains needed in BS, this work intended to use the optimal transmit antenna selection (TAS) strategy. This strategy is gaining a lot of interest since the optimization algorithm aids in the ability to enhance the system performance considerably the efficiency and secrecy rate. This work proposes a novel Coati Adopted Pelican Optimization (CA-PO) for choosing the optimal TA by considering efficiency as well as secrecy rate. In addition, the CA-PO algorithm makes the decision on which antenna to be elected. At last, the supremacy of CA-PO-based TAS is proven from the analysis regarding secrecy rate and EE analysis. Accordingly, the proposed CA-PO method for MF for set up 2 has attained a higher EE of 0.976; whereas, the DMOA, COA, MRFO, POA and BEA techniques have got a relatively lower EE of 0.968. [ABSTRACT FROM AUTHOR]

In this paper, a wideband 1-bit reconfigurable transmit array antenna (RTA) is proposed. The 1-bit RTA element consists of a passive receiving antenna and a reconfigurable radiating antenna, which adopt a proximity-coupled feed method to broaden the transmission bandwidth. Two p-i-n diodes are integrated into the reconfigurable receiving antenna to control the current distribution. By switching the states of the p-i-n diodes, the reconfigurable radiating antenna can achieve a 1-bit phase shift. Element simulation results show that the proposed RTA element can achieve a 3 dB transmission bandwidth of 21.5%. A 100-element RTA prototype with 200 p-in diodes is designed, fabricated and measured. The measured results show that the peak gain is 18.8 dBi at 5.05 GHz, corresponding to an aperture efficiency of 20.8%, and the 3 dB gain bandwidth is 17.1%. Furthermore, the scanned beams can reach −32° and −36°, respectively, in the E- and H-planes. [ABSTRACT FROM AUTHOR]

Accurate information about the satellite transmit antennas is essential for high-precision GNSS applications. Such metadata of the GPS III satellites were publicly made available by the manufacturer Lockheed Martin. They comprise phase center offsets (PCOs), phase patterns, and directivity patterns. These calibrations are validated with ground-based measurements of a global GPS tracking network and observations of a high-gain antenna. Phase center offsets and patterns are estimated from dual-frequency observations of a ground tracking network. The ionosphere-free L1/L2 z-PCOs show a 10 cm offset w.r.t. the manufacturer calibrations due to already known inconsistencies with the ITRF2020 scale fixed in the estimation. The standard deviation of the differences between estimated and calibrated z-PCOs is 2.7 cm. The estimated phase patterns have a 0.7 mm RMS consistency with the manufacturer calibrations after minimizing the raw patterns for nadir angles between 0° and 14°. The directivity patterns are validated with the effective isotropic radiated power (EIRP) measured with a 30 m high-gain antenna. The measured EIRP for the L1 and L2 band is affected by M-code transmission from a distinct antenna. When modeling the additional contribution of this antenna, the nadir-angle variation of the EIRP matches the calibrated directivity patterns with a precision of 0.1 dBW. Representative transmit power values of the main navigation antenna amount to 125 W, 30 W, and 85 W in the L1, L2, and L5 bands, while the L1 and L2 M-code signals are transmitted with about 30 W and 25 W, respectively. [ABSTRACT FROM AUTHOR]

As an extension of spatial modulation (SM) technology, generalized spatial modulation (GSM) systems can achieve higher data transmission rates with limited spectrum resources due to activate multiple transmit antennas to send data in each time slot. Simultaneously activating multiple transmit antennas increase the difficulty of signal demodulation at the receiver in GSM systems. To reduce the high computational complexity of the maximum likelihood (ML) detection algorithm in GSM systems, a low-complexity GSM detection algorithm is proposed, which combines the iterative zero forcing (IZF) algorithm and the minimum mean square error (MMSE) equalization processing detection algorithm. Firstly, the zero forcing (ZF) algorithm is used to iteratively detect all transmit antenna combinations to obtain multiple unlikely transmit antenna indices. Then the number of search antenna combinations is reduced by removing these antenna combinations. Next, MMSE equalization detection and symbol quantification on the new search set are performed. Finally, the ML algorithm is used to estimate the transmit antenna combination and transmit symbols. The effectiveness of the proposed algorithm is verified by simulation experiments. The simulation results show that the computational complexity of the proposed algorithm is much lower than that of the ML algorithm, and the bit error rate (BER) performance is close to that of the ML algorithm. [ABSTRACT FROM AUTHOR]

A 2.45 GHz high-efficiency rectifying circuit for a wireless radiofrequency (RF) energy collection system is proposed. The RF energy collection system is composed of a transmitting antenna, a receiving antenna, a rectifying circuit and a load. The designed receiving antenna is a kind of dual-polarised cross-dipole antenna; its bandwidth is 2.3–2.5 GHz and gain is 7.97 dBi. The proposed rectifying circuit adopts the technology of an output matching network, which can suppress the high-harmonic components. When the input power at 2.45 GHz is 13 dBm and the load is 2 kΩ, the highest conversion efficiency of RF-DC is 74.8%, and the corresponding maximum DC output voltage is 4.92 V. The experiment results are in good agreement with the simulation results, which shows a good application prospect. [ABSTRACT FROM AUTHOR]

In the fast-changing world of wireless communications, the combination of extremely large antenna arrays (ELAAs) and energy-efficient transmission methods is envisioned for the 6G. The application of directivity in the transmitted constellation can increase physical layer security (PLS) and promote the energy efficiency of transmission. In such scenarios, large constellations can be divided into multiple binary phase shift keying (BPSK) components, with each component being individually amplified and transmitted by an antenna. In this work, we consider an ELAA acting as a transmitter and constellation decomposition at the sub-array level. We investigate the impact of considering a near-field channel model in terms of secrecy rate and mutual information. In addition to the energy efficiency of the constellation decomposition, it is demonstrated that the particularities of near-field beamforming increase the PLS, namely in terms of robustness to eavesdropping. [ABSTRACT FROM AUTHOR]

Although the classic radar equation has been widely used to analyze the link budget of an automotive radar, it is valid only when the targets are located in the far-field region of the transmitted field and the receiving antenna is located in the far-field region of the scattered field. This paper confirms this hypothesis using measured and simulated data for short-range radars. Furthermore, a novel radar equation based on the Fresnel diffraction formula is proposed for application in situations where the receiving antenna is located in the radiative near-field region (or Fresnel region) of a target, but the target is situated in the far-field region of the transmitting antenna. In addition, the proposed radar equation is assessed by comparing the measured and simulated data. [ABSTRACT FROM AUTHOR]

MIMO (Multi-input, Multi-output) systems are a key technology for achieving 5G wireless communications' performance goals. They achieve significant levels of various acquisition, consistency, and efficiency. Nonetheless, for more transmit antennas; more radio frequency (RF) chains are necessary, which may result in increased computational complexity and expenses. As a result, selecting the optimal transmit antennas is critical for improving system performance. This paper offers a new Fitness-based Elephant Herding Algorithm (F-EHA) for selecting the optimal broadcast antenna by specifying many criteria such as secrecy rate and efficiency. In addition, the system provides a recommendation for which antenna to use. Finally, the suggested model's advantage over existing techniques in terms of EE (Energy Efficiency) and secrecy rate is demonstrated. [ABSTRACT FROM AUTHOR]

Conventional low-frequency electromagnetic wave (LFEM) transmitting antennas are enormous in size, which limits the application of LFEM in underground space. Rotating-magnet Based Mechanical Antennas can realize the miniaturization of low-frequency antennas, which is expected to bring new possibilities for underground electromagnetic detection or ground penetration communication. Firstly, this paper establishes a synthetic field method for solving the electromagnetic field of a rotating permanent magnet in the air-earth cross-domain case. The method equates the magnet as an orthogonal superposition of vertical and horizontal dipole sources, and the phase difference between vertical and horizontal dipole sources is /2. Based on the half-space theory of multilayer planar media, the quasi-analytical solution of the electromagnetic field of the magnetic dipole in the case of air-earth trans dimensionality can be found by superposition. Secondly, based on the finite element numerical model, the trans-earth propagation characteristics of the electromagnetic field excited by the rotating permanent magnet across the air-earth dual domain are studied. At the same time, the radiation characteristics in the rotating plane of the permanent magnet are also studied. Again, this paper systematically investigates the influence of parameters such as earth conductivity, emission frequency, and propagation distance on the electromagnetic field propagation. Finally, the principle prototype is developed and experiments are carried out. The results show that the finite element numerical model established in this paper is correct, the experimental results are consistent with the theoretical values, and a field strength signal of 0.9 nT can be received at 20 m. The research work in this paper lays the foundation for the future use of mechanical antennas for electromagnetic detection and ground penetration communication. [ABSTRACT FROM AUTHOR]

This paper presents a pre-coding scheme for recently proposed differential spatial modulation (DSM) systems. It employs a lattice reduction (LR) aided pre-coding approach. An approximated upper bound on average bit error rate (BER) is semi-analytically derived. It is analytically shown that it can achieve a full diversity gain. That is, the performance analysis demonstrates that the LR-aided pre-coding DSM (LR-PDSM) systems with $ {N_T} $ N T transmit antennas and $ {N_R} $ N R receive antennas can achieve the maximum transmit diversity order of $ {N_T} $ N T . Meanwhile, it is well-known that the diversity order attained by the conventional zero-forcing (ZF) pre-coding is given as $ {N_T} - {N_R} + 1 $ N T − N R + 1. Simulation results verify the approximated theoretical analysis and show that LR-aided ZF pre-coding is capable of improving the BER performance of the conventional ZF pre-coding based DSM systems under the same spectral efficiency. [ABSTRACT FROM AUTHOR]

In antenna sequence spatial modulation (ASSM), the spatial and symbol domains are both used to encode information. The sequencing of the antennas' transmissions within given time slots and the symbol carried in those time slots represent information in the spatial and symbol domains, respectively. The receiver's task is to decode this sequence of transmission and to detect the symbol carried in the time slots, equal to the number of antennas. For better energy efficiency and greater security, we propose a generalized ASSM, GASSM. In the GASSM, while the information is contained in both the sequence and the symbols transmitted, different symbols can be transmitted within the time slots forming the frame. This expands the code domain since the symbol and the spatial information represent a longer code in the mapper table. As a special case, we present the case of three transmit antennas, transmitting within three time slots. A combination of the antennas' sequence and the symbol carried in the time slots is used as a code for a bit sequence. Results obtained from simulation and analysis of the bit error rate performance and secrecy capacity are contrasted and presented. Comparing the GASSM to the standard spatial modulation (SM) and the ASSM, we deduce that the GASSM has a higher secrecy capacity and higher energy efficiency per bit and unlike conventional SM allows utilization of odd number of antennas. [ABSTRACT FROM AUTHOR]

In this work, we present the preliminary results of radar observations of Near-Earth Objects (NEOs) carried out by European radio telescopes in the framework of the European Space Agency (ESA) project "NEO observation concepts for radar systems", aimed at deriving the functional requirements of a planetary radar system, evaluating the available European assets to perform NEO radar observations, and carrying out test radar campaigns. In the first part of the project, we executed the performance analysis of a possible European planetary radar system. Instrumental features, as much as issues like the impact of weather conditions on signal propagation at different radio frequencies, were considered. This paper focused on the test campaigns, performed in the years 2021–2022 in collaboration with the Jet Propulsion Laboratory (JPL), which led to the observation of several asteroids including 2021 AF8, (4660) Nereus, and 2005 LW3, which allowed us to derive astrometric measurements, as well as to measure physical properties, such as rotation periods, and observe how one of the targets is actually a binary asteroid. The obtained results demonstrated that European radio astronomical dishes, although employed only as receivers (in bistatic or multistatic configurations) and for a limited amount of time, are able to provide a significant contribution to the constitution of a European network to increase the opportunities for NEO monitoring and studies, if a transmitting antenna—equipped with a suitable high-power transmitter—were made available. [ABSTRACT FROM AUTHOR]

This study investigates the synthesis of a two‐dimensional transmitting planar antenna array for a wireless power transmission system. The antenna synthesis problem is transformed into an optimization problem under multiple constraints. Accordingly, a brainstorming optimization algorithm is utilized to optimize the element position of the planar antenna arrays under the constraints of aperture size, array spacing, and side lobe level. A numerical simulation of the beam collection efficiency is conducted under different receiving region shapes. The simulation results confirm the effectiveness of the proposed method in optimizing the two‐dimensional transmitting planar antenna array for wireless power transmission systems. [ABSTRACT FROM AUTHOR]

To address the limitations of poor environmental adaptability, unsatisfactory bit-error performance, and high complexity of conventional antenna selection algorithms applied to a multi-array visible-light optical generalized spatial multiplexing–multiple-input multiple-output (OGSMP-MIMO) system, an OGSMP-MIMO system based on Pearson coefficient antenna selection is proposed. The algorithm adopts the correlation of Pearson coefficients among photoelectric detector (PD) terminals at different positions and active transmit antennas to select the optimal antenna combination without relying on the accuracy of channel estimation, for realizing the multiplexing of the time and space domains, and to improve the bit-error performance. Finally, experiments were conducted to verify the feasibility of the antenna selection algorithm, based on the Pearson coefficients. The results indicated that when the bit-error rate reached 10−6, using the antenna selection algorithm based on the Pearson coefficient, the signal-to-noise ratio was improved by 2.7 dB and 3.7 dB when compared with the norm-based antenna and random selection algorithms, respectively. In addition, increasing the number of active transmitting antennas can improve the transmission rate; however, the bit-error performance will be compromised. In the same modulation mode, increasing the number of transmitting antennas will reduce the bit-error performance. [ABSTRACT FROM AUTHOR]

Reverberation chambers (RCs) were recently reported as a low-cost alternative to anechoic chambers (ACs) to perform radar cross-section (RCS) pattern measurements. The method consists of using transmitting and receiving antennas pointing towards a target under test placed on a rotating mast. As a classical RCS characterization, the echo signal is analysed based on two measurements with and without the target in the RC. In the hypothesis of an ideal diffuse field generated in the RC, this signal difference appears as the echo signal hidden in a Gaussian noise. In case of a point-like backscattering target, observing this signal over a given frequency bandwidth allows the identification of the target response as a sinusoidal signal over this bandwidth whose period is related to the antennatarget distance measured from the measurement calibration plane positions. Therefore, the extraction of the magnitude of this sinusoidal signal requires a proper estimation of this distance. Furthermore, a sinusoidal regression processing relies on the approximation of a constant envelope over the selected frequency bandwidth, imposing some restrictions. In this paper, we introduce a two-step method that consists in identifying the most appropriate distance according to the target's orientation before estimating the magnitude of the sinusoidal signal. We highlight the improvement of RCS estimation on a point-like back-scattering target compared to the one-step procedure applied so far. In addition, it is shown that the analysis performed regarding the estimated distance provides a physical insight into the position of the equivalent backscattering point. [ABSTRACT FROM AUTHOR]

A simulated satellite communication system was constructed by introducing a phased array antenna based on liquid crystal (LC) technology to achieve communication with the transmitting antennas at various alignment angles. The 16 × 16 phased array antenna serves as the receiving antenna and employs tunable microwave LC material as the reconfigurable component to achieve 360° phase shift. The algorithm for controlling the wave is integrated into the FPGA to drive the antenna array and achieve the target beam deflection to maintain communication. [ABSTRACT FROM AUTHOR]

Summary: In practice, hardware impairments (HIs) often exist in wireless devices, especially in low‐cost device systems. However, previous reports usually ignored HIs due to the computational complexity in mathematical derivations, particularly in millimeter‐wave (mmWave) communications. This article proposes the usage of transmit antenna selection (TAS) and multiple reconfigurable intelligent surfaces (RISs) to address HIs in mmWave communications. In particular, TAS is utilized at the source to increase the received signal power at the destination and reduce the effects of HIs. Multiple channel gains from RISs are combined with the classical source‐destination channel gain at the destination. The symbol error probability (SEP) expression of the mmWave communications with TAS and RISs under the effects of HIs (shortened as the TAS‐RISs‐HIs communications) is formulated over Nakagami‐ m channels and verified through Monte Carlo simulations. The effects of HIs on the SEP of TAS‐RISs‐HIs communications are demonstrated through numerical illustrations. Specifically, the SEP of the TAS‐RISs‐HIs communications is significantly higher than the SEP of the ideal hardware communications with TAS and RISs, especially in the high transmit power regime. As a result, ignoring HIs when evaluating the SEP of the mmWave communications can result in some inappropriate conclusions. Moreover, the joint and separate advantages of TAS and RISs are thoroughly analyzed when comparing the SEPs in the cases with and without TAS, with and without RISs. [ABSTRACT FROM AUTHOR]

Automatic protection of EM detecting systems from unexpected high-power incidence is important to the robustness and life of a passive detecting system. In this paper, an adaptive metamaterial radome which automatically shields the receiving antenna from strong incident wave is designed. Based on standard wire medium, PIN diodes are added between adjacent wires. When the incident EM wave is weak, the diodes are in "off" state and affect little to the transmission of the wire medium. When the incident EM wave is strong enough to turn the diodes to "on" state, electric currents will be automatically formed in the diodes and the power transmitted to the antenna will be largely reduced. The adaptive transmission of the proposed radome is validated by the simulation and measurement results. [ABSTRACT FROM AUTHOR]

Taking advantage of multimaterial additive manufacturing, this work demonstrates a kind of polarization‐maintaining metasurface (MS) for spin‐decoupled beam shaping. The wavefronts of the two spin states, i.e., the left‐hand circular polarization (LHCP) and the right‐hand circular polarization (RHCP), can be independently manipulated while the output spin state remains the same as the input. The meta‐atom is implemented with dual‐polarized antennas at the top and the bottom with phase delay lines connecting them. The dual‐polarized antenna on the receiving side is fixed to receive the LHCP/RHCP incident waves, while the dual‐polarized transmitting antenna is rotated, providing the opposite phase shifts for the LHCP and RHCP. The absolute value of the phase shift is the same as the transmitting antenna's rotation angle. Meanwhile, varying the length of phase delay lines introduces 2π phase shifts for both LHCP and RHCP inputs. Thus, combining the two phase‐shifting degrees of freedom, the LHCP and RHCP wavefronts can be independently controlled while the polarization is not flipped after transmitting through the MS. One MS produces vortex beams with different topological charges for LHCP and RHCP. The other achieves spin‐decoupled focusing. The multilayered MSs are conveniently printed using multimaterial additive manufacturing without postprocessing. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the traditional physical layer technology cannot realize secure transmission due to the large number of users and wide dispersion in the multicast system, a layered transmission method is proposed, and a scheme for the secure transmission of the multicast group physical layer is designed. Firstly, the hierarchical transmission system model is established. Then, the array weighted vector of each layer is optimized according to the design criterion of maximizing the artificial noise interference power. At the same time, in the case where the number of users in a single multicast group is greater than the number of transmitting antennas, a multicast grouping strategy is introduced, and the singular value decomposition and Lagrange multiplier algorithms are utilized to obtain the optimal solution. Simulation results show that the proposed method can realize the secure communication of users with different distances in the same direction and can distinguish the multicast users with the same direction angle and different distances under the premise of mutual non-interference, thus realizing the secure communication of large-scale multicast users. [ABSTRACT FROM AUTHOR]

In this study, a space–time transmission scheme is proposed to tackle the limitations of channel estimation with orthogonal pilot information in colocated multiple‐input multiple‐output systems with several transmitting and receiving antennas. Channel information is obtained using orthogonal pilots. Channel estimation introduces pilot heads required to estimate a channel. This leads to bandwidth insufficiency. As a result, trade‐offs exist between the number of pilots required to estimate a channel versus spectral efficiency. The detection of data symbols is performed using the maximum likelihood decoding method as it provides a consistent approach to parameter estimation problems. The moment‐generating function of the instantaneous signal‐to‐noise ratio is used to drive an approximate expression of the symbol error rate for the proposed scheme. Furthermore, the order of diversity is less by one than the number of receiver antennas used in the proposed scheme. The effect of the length of a pilot sequence on the proposed scheme's performance is also investigated. [ABSTRACT FROM AUTHOR]

A broadband antenna can transmit and receive radio signals across a broad frequency spectrum. The use of broadband millimeter-wave (mmWave) band antennas has garnered significant interest in wireless communication research. As a result, this type of antenna finds applications in television, radio broadcasting, and radar communication. The millimeterwave broadband antenna covers an extensive range of frequencies, leading to distinct design methodologies for such structures. The primary focus of this manuscript is to present a comprehensive overview of the recent developments in millimeter-wave antenna design, encompassing an in-depth analysis of the working principles of broadband antennas and their associated design characteristics. This review aims to shed light on the challenging path for antenna researchers and the potential enhancements achievable through broadband antenna technologies. Various applications, including enhanced wireless communication, high-definition and ultra-high-definition multimedia, and security signal intelligence, necessitate high data rates and significantly greater bandwidth. Consequently, a substantial demand for millimeter-wave broadband antennas can cater to these requirements. [ABSTRACT FROM AUTHOR]

In this paper, a novel optimal two-way amplify and forward (AF) differential beamforming method for wireless sensor network is proposed. The proposed method is an advanced signal processing technique used to enhance the performance and reliability of the communication link by exploiting the diversity provided by multiple antennas. Unlike current state-of-the-art methods which require the knowledge of channel state information (CSI) at both transmitting and receiving antennas or at least at the receiving antennas, the suggested method does not need CSI at any transmitting or receiving antenna. Moreover, the proposed method enjoys high error performance with high diversity and coding gain and has a very low encoding and decoding complexity. Through our simulations, the proposed method is proved to outperform the best known non-coherent multi-antenna methods. [ABSTRACT FROM AUTHOR]

Radar is an important sensing technology for three-dimensional positioning of aircraft. This method requires detecting the response from the object to the signal transmitted from the antenna, but the accuracy becomes unstable due to effects such as obstruction and reflection from surrounding buildings at low altitudes near the antenna. Accordingly, there is a need for a ground-based positioning method with high accuracy. Among the positioning methods using cameras that have been proposed for this purpose, we have developed a multisite synchronized positioning system using IoT devices equipped with a fish-eye camera, and have been investigating its performance. This report describes the details and calibration experiments for this technology. Also, a case study was performed in which flight paths measured by existing GPS positioning were compared with results from the proposed method. Although the results obtained by each of the methods showed individual characteristics, the three-dimensional coordinates were a good match, showing the effectiveness of the positioning technology proposed in this study. [ABSTRACT FROM AUTHOR]

In this paper, we present the MU (multi-user) MIMO (multiple-input & multiple-output) system which is capable to serve the maximum number of users without additional bandwidth or power budget. MIMO systems maximize the channel capability as per the DPC scheme (Dirty Paper Coding). According to DPC, several antennas distributed over the base station are used for serving multiple users simultaneously. Nevertheless, DPC is a comprehensive search algorithm employing sequences of encoded user data for transmitting information to multiple users. Due to increased user density and subsequent transmit antennas in the MU-MIMO system, the exhaustive search (i.e. DPC) becomes cumbersome with the expanded search space domain. This search task would not be completed within a coherence time frame of the packet data communication system. The required objective is to consider this as a cost function for optimization to maximize the realizable sum-rate (throughput) of the MU-MIMO systems. This paper illuminates the joint antenna and user scheduling (JAAU) process with binary artificial bee colony (binary ABC) accomplishing nearly 98–99% of system throughput with the suggestively decreased figure in computation complexity and run time. Binary ABC is observed to have the global optimum value swiftly within the stipulated packet time frame of next-generation wireless data communications. Moreover, binary ABC achieves an appreciable system capacity for MU-MIMO systems as compared with DPC (which attains the maximum system throughput with the highest complexity). These findings are corroborated with exhaustive simulation results presented in this article. [ABSTRACT FROM AUTHOR]