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A capacitive coupling dual‐band circular patch antenna for on‐/off‐body communications is proposed for 3.5 GHz world interoperability for microwave access band and 5.8 GHz industrial scientific medical band. The antenna has a compact structure with a single substrate made of polydimethylsiloxane which is flexible and easy to wear. To realise off‐body mode, the antenna adopted bias feeding. The on‐body mode is achieved by symmetrically loading four shorting vias on the edge of the patch to stimulate TM41 mode, which tends to bring a high gain of the antenna. The measured operating bandwidths of the antenna for off‐body and on‐body modes are 120 MHz (3.45–3.57 GHz) and 360 MHz (5.54–5.90 GHz) respectively. The peak gains are 5.99 dBi for off‐body mode and 5.46 dBi for on‐body mode. Moreover, the antenna displays robust performances when it is bended or closed to human bodies. Meanwhile, low specific absorption rate values are proving that the antenna is safe to wear on human bodies. [ABSTRACT FROM AUTHOR]

The research on reconfigurable antennas has some disadvantages such as low working frequency and large size. This paper presents a Ka-band patch antenna with pattern reconfigurability using RF MEMS switches. The antenna contains one main patch, two sub-patches, two parasitic patches, and two RF MEMS switches. By controlling the states of the RF MEMS switches, the antenna can achieve three different radiation patterns (−8°, 0°, and +8°) at 35 GHz. The pattern analysis was based on the electric field vector addition method. The analytical, simulated, and measured results agree well with each other. Due to its compact and thin structure of 3.7 mm × 5.2 mm × 0.4 mm, this antenna can be applied in fields such as satellites, smartphones, etc. [ABSTRACT FROM AUTHOR]

This paper describes the integration of a plate Luneburg lens with a microstrip patch antenna (MPA) with a complementary split ring resonator (CSRR) at 17 GHz frequency. The main advantage of the method is the compact size of the optimized MPA with CSRR such that the radiation pattern of the antennas successfully overlaps at −3 dB. The overlapping is achieved by positioning multiple MPA with CSRR structures around the plate Luneburg lens with 0.408λ distance between the elements. To test the performance of the lens, CST simulations are carried out using a classical WR62 open-ended waveguide to feed the structure, then adding more waveguides rotated at focal points of the lens. After that, the waveguide is substituted with the MPA with CSRR structure. The superiority of the proposed method over the conventional waveguide or regular patch antenna is confirmed by an overlap in radiation pattern at −3 dB with a narrow beamwidth of 10.9°. [ABSTRACT FROM AUTHOR]

An antenna synthesis application is presented by solving a highly oscillatory Fourier integral using a stable and accurate Levin's algorithm. In antenna synthesis, the current distribution is obtained by the inverse Fourier integral of the antenna radiation pattern. Since this integral is highly oscillatory, the Levin method can be used for its solution. However, when the number of nodes or the frequency increases, the Levin method becomes unstable and ineffective due to the large condition number of the interpolation matrix. Thus, an improved scheme of the method is used in an antenna synthesis application in which reproducing kernel functions are used as the basis of the approximation function. The accuracy of the new method is verified by a log-periodic antenna example. The error and stability analysis results show that the new method is more stable and accurate than other well-known kernels, especially for a large number of nodes. [ABSTRACT FROM AUTHOR]

Antenna array synthesis is quite a popular topic in electromagnetics and finding suitable array parameter values is a challenging nonlinear engineering problem in this field. In recent years, it has been realized that optimization algorithms can be used to achieve desired solutions in this area. Besides, improvements in the optimization algorithms make it possible to perform synthesis processes on different array structures and to obtain better results. In this paper, a method based on a combination of ant lion optimizer (ALO) and sequential quadratic programming (SQP) is proposed for the concentric circular antenna array (CCAA) synthesis. Excitation amplitudes of array elements are optimized for CCAAs with low maximum sidelobe level (MSL), narrow first null beamwidth (FNBW), and low dynamic range ratio (DRR). The results of proposed ALO‐SQP method are compared with those of 11 different algorithms: ALO, moth flame optimizer (MFO), SQP, symbiotic organisms search (SOS), biogeography based optimization (BBO), opposition‐based gravitational search algorithm (OGSA), cat swarm optimization (CSO), firefly algorithm (FA), evolutionary programming (EP), backtracking search optimization algorithm (BSA), and seeker optimization algorithm (SOA). The comparisons indicate that the CCAAs synthesis using the proposed method presents good MSLs, FNBWs, and DRRs. [ABSTRACT FROM AUTHOR]

An effective, probe‐compensated, phaseless Near‐Field‐Far‐Field (NF–FF) transformation technique with planar spiral scanning is presented. The phase retrieval problem is solved by a quadratic inverse process, whose data are the voltage squared amplitudes of the NF samples acquired on two scanning surfaces. The available information on the antenna under test and on the scanning geometry are used to provide efficient representations for both the unknowns and the data, thus improving the accuracy and reliability of the technique. Furthermore, disconnected apertures are dealt with by adopting two different sets of prolate spheroidal wave functions to represent the aperture fields. Experimental results are reported to assess the effectiveness of the proposed approach. A drastic reduction (about 90%) of the required NF samples, as compared to standard λ/4 measurements (λ being the wavelength), is observed. Aggregating the measurements on the two scanning surfaces, the technique uses less samples even when compared to the case of complex, λ/2 measurements performed on a single surface. Our approach exhibits an accuracy comparable to that achieved when adopting complex measurements with non‐redundant sampling or classical, λ/2 plane‐rectangular NF–FF transformations. [ABSTRACT FROM AUTHOR]

Given the problem that the communication distance and quality of the vehicle-mounted ultrashort wave radio are affected by ground attachments and topography in the actual combat environment, a radio wave propagation prediction model of vehicle-mounted ultrashort wave radio is established based on ray tracing and machine learning. The integrated modeling of armored combat vehicle and vehicle antenna is established to obtain the antenna radiation pattern, and combined with electronic images, the radio wave propagation simulation model based on ray tracing technology is established. Based on the machine learning algorithm of the random forest and data results for the simulation model, the radio wave propagation prediction model based on the random forest was established. Compared with traditional classical radio wave propagation models such as the Egli and Okumura-Hata models, the radio wave propagation prediction model based on the random forest has higher accuracy. The root mean square error reaches 2.190 1 dB, and the coefficient of determination reaches 0.960 1. It can accurately predict radio wave propagation in the tactical communication environment. [ABSTRACT FROM AUTHOR]

The emergence of 5G technology is expected to significantly impact high-bandwidth wireless applications, making efficient antenna designs essential. This research paper presents an equivalent circuit for a square-slotted patch antenna design for 5G cellular applications. Indeed, the equivalent circuit for an antenna can be represented by a simple circuit model, such as a resonant LC circuit or a transmission line model. These models can be used to determine the resonance frequency, bandwidth, and radiation pattern of the antenna. Matching networks can also be designed using the equivalent circuit to match the antenna and receiver impedances. This analysis of the antenna can offer valuable insights into its behavior, serving as a foundation for a more extensive investigation. The antenna has been designed and simulated on an FR4 substrate featuring a relative permittivity ξr of 4.3, and it is sized at 4.5 x 5.2 x 0.3 mm³. In the proposed design, a 50Ω microstrip line feeds a square-slotted radiating patch, and power dividers join the two elements. As part of 5G technology, it is crucial to achieve high bandwidth with reduced losses and improved gains. This study employs AWR and HFSS to simulate and design the square-slotted microstrip patch antenna, and in terms of gain and S11, the results are compared. The proposed design has the potential to contribute to the development of high-performance 5G antenna systems. [ABSTRACT FROM AUTHOR]

In this study, an inset fed rectangular patch antenna is designed for 5G application. The proposed antenna has been designed by utilizing a U-shaped lot loading technique introduced on ground plane for bandwidth improvement. The designed antenna is integrated with parasitic patch as FSS unit cell in order to obtain gain improvement. FR-4 substrate with (εr = 4.4 and tanδ = 0.02) is used to design the antenna. The bandwidth and gain parameters are improved by altering the length of the ground plane initially and frequency selective surface (FSS) placed at the back of the substrate to enhance the radiation property of the antenna. Bandwidth improvement of 30 % is obtained for proposed wideband high gain antenna compare to conventional inset feed patch antenna. Maximum gain obtained for proposed wideband high gain antenna is 6 dB at 25 GHz. The obtained return loss is also well below 10 dB range from 24.57 GHz to 27.57 GHz. Bandwidth obtained for the proposed antenna is 3.0 GHz. Slot loading technique with ground optimization is useful for bandwidth improvement without affecting radiation pattern of the antenna. Further FSS integration is an efficient approach to improve the gain of convention antennas. The proposed antenna features good characteristics in terms of return loss, gain and bandwidth which makes it highly suitable for 5G applications in mm-wave band. [ABSTRACT FROM AUTHOR]

In order to properly cover different scenarios, radiation patterns of antennas should be accordingly designed. However, most antennas are unable to provide either broadside beams or designable conical beams, which are the typically used radiation patterns for radio coverage, based on one single-structure format through adjusting parameters before fabrication. In this paper, a planar circular polarized (CP) annular leaky-wave antenna (LWA) is proposed, which is realized on an annular substrate-integrated waveguide (SIW). A broadside beam or a conical beam could be easily obtained through fabricating the LWA with different structural parameters. The operating frequency is 5.75 GHz. The LWA allows only the −1st spatial harmonic to radiate, while the fundamental wave and other spatial harmonics are suppressed in slow wave mode. In order to validate the design effectiveness, two examples for broadside beam and conical beam radiation are fabricated and measured. The measurement results show good agreement with the simulation results. The broadside beam LWA shows a gain of 9.75 dBic and the conical beam LWA with a beam angle of 13° has a gain of 7.93 dBic. The proposed LWA presents promising radiation performance and is a good candidate for wireless communication applications. [ABSTRACT FROM AUTHOR]

A new miniaturized patch antenna based on a metal strip is proposed in this paper. The antenna is designed by adding a middle metal strip layer to the substrate of a traditional rectangular patch antenna. By increasing the length of the metal strip, the working frequency of the patch antenna can be continuously reduced without significantly impacting the radiation pattern. The simulation results indicate that as the metal strip length increases from 5mm to 25 mm, the working frequency of the patch antenna decreases from 2.39 GHz to 1.84 GHz, and its gain decreases from 6.72 dBi to 5.4 dBi. Two antenna samples with metal strip lengths of 5mm and 20mm are fabricated. The experimental results indicate that their working frequencies are 2.64 GHz and 2.43 GHz, respectively. And the radiation patterns of two antennas are consistent with the simulated results. All results confirm the effectiveness of the proposed miniaturization method. [ABSTRACT FROM AUTHOR]

This paper proposes a compact planar Wi-Fi antenna with optimized radiation patterns for small uncrewed aerial vehicle (UAV) applications in both urban and open areas. It is suitable for mounting on the outermost side of the non-metallic wing of small UAVs. It has small dimensions of 16.5 mm (L) by 30.3 mm (W) by 1.6 mm (h), and the measured results of its prototype are in agreement with simulated data. Its impedance bandwidths over the two frequency ranges are 2.11 to 2.58 GHz and 5.06 to 7.5 GHz ( S 11 ≤ - 10   d B ). At 5.8 GHz, it has stronger radiation below the small UAV to reduce interference from rare-use directions. Its maximum radiations, the directions of the maximum radiation in each elevation plane, are below the UAV and between 14° and 29° from the horizontal plane. At 2.4 GHz, it has quasi-omnidirectional radiation to ensure a stable link in all directions, and its maximum radiations are near the horizontal plane. The optimized radiation patterns at 5.8 and 2.4 GHz can provide more antenna gain when the small UAV flies farther in urban and open areas, respectively. In addition, it has good vertically polarized radiation for long-distance applications. [ABSTRACT FROM AUTHOR]

The study carried out a new approach to modeling an antenna system with metamaterials, which is used to form reflectors. Through the use of high-frequency switches, it is possible to achieve fast switching of different antenna characteristics. The use of the proposed design of the antenna makes it possible to provide directional communication with high protection against spurious radiation, which adversely affects the noise immunity of the channel. In the process of research, modeling methods based on the finite integration method were used. The proposed design of the antenna makes it possible to solve the problem with the formation of directional radiation, since it is not required to perform mechanical rotation of the antenna, but only to provide switching of switching devices, which increases reliability and simplifies the installation of the antenna structure. In this paper, it is proposed to use a broadband opto-controlled active metamaterial, which allows you to control the characteristics of the radiation pattern of the simplest antenna - a half-wave dipole. The use of the proposed design makes it possible to implement an active antenna with a controlled radiation pattern, and the control is carried out by performing electrical switching of the layers, which makes it possible to increase the speed of the device, to achieve an increase in the reliability of the structure. In this case, the half-wave dipole is an example of the used emitter, which can be replaced by another one with an omnidirectional radiation pattern, which is possible due to the broadband nature of the metamaterial used. [ABSTRACT FROM AUTHOR]

A balloon shape super wideband (SWB) Terahertz monopole antenna and its pattern diversity configuration are presented in this paper. In order to enhance the impedance bandwidth, the feedline is tapered. It improves impedance matching and results in large impedance bandwidth. Both antenna element and diversity configuration offers an almost equal impedance bandwidth of about 186% for |S11| = -10dB. In the case of the antenna element, the lower edge of frequency response is at 2.11 THz whereas, in the diversity case it is 2.17 THz. However, the upper edge of the frequency point is the same (60 THz) in both cases. Besides, isolation of more than 25 dB throughout the band is achieved between antenna elements. The overall antenna element and MIMO configuration size are 24×41.8 µm2 and 70.8×42 µm2, respectively. The parameters like Diversity Gain (DG), Envelop Correlation Coefficient (ECC), Channel Capacity Loss (CCL) and Mean Effective Gain (MEG) are calculated to characterize the diversity performance and all are found in the acceptable limit. [ABSTRACT FROM AUTHOR]

A compact frequency reconfigurable beam switching antenna based on a single‐layer frequency selective face (FSS) is proposed in this paper. The proposed antenna consists of a dual‐band dipole antenna and a single‐layer FSS with hexagonally arrangement. The omnidirectional radiation pattern of the dipole antenna designed as a radiation source and surrounded by the FSS can be converted into directional radiation pattern sweeping along the entire azimuthal plane at two single frequency of 2.4 or 5 GHz. The frequency selection is achieved by controlling the diode state of the FSS unit, and the beam switching is realised by a specific combination of electromagnetic wave reflection or transmission from the hexagonal FSS. The novelty lies in applying the hexagonal arrangement to a dual single‐frequency single‐layer FSS unit. This will not destroy the reflection or transmission characteristics of the FSS unit, but also contribute to reduce the antenna size and achieve a low cost. To validate the design, a prototype is fabricated and measured. The single‐layer FSS antenna with a volume of 57 mm × 57 mm × 58.5 mm can be scanned in 12 steps along the azimuth plane at 2.4 and 5 GHz, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a printed monopole antenna with high-gain and dual-band characteristics for applications in wireless local area networks and the internet of things sensor networks is presented. The proposed antenna consists of a rectangular patch with multiple matching stubs surrounded to improve the impedance bandwidth of the antenna. The antenna incorporates a cross-plate structure which is seated at the base of the monopole antenna. The cross-plate consist of metallic plates aligned perpendicularly which enhances the radiations from the edges of the planar monopole to maintain uniform omnidirectional radiation patterns within the antenna's operating band. Furthermore, a layer of frequency selective surface (FSS) unit cells and a top-hat structure is added to the antenna design. The FSS layer consist of three unit cells printed at the back side of the antenna. The top-hat structure is placed on top of the monopole antenna and comprises of three planar metallic structures arranged in a hat-like configuration. The coupling of both the FSS layer and the top-hat structure presents a large aperture to increase the directivity of the monopole antenna. Thus, the proposed antenna structure realizes a high gain without compromising the omnidirectional radiation patterns within the antenna's operating band. A prototype of the proposed antenna is fabricated where good agreement is achieved between the measured and full-wave simulation results. The antenna achieves an impedance bandwidth |S11| < − 10 dB and VSWR ≤ 2 for the L and S band at 1.6–2.1 GHz and 2.4–2.85 GHz, respectively. Furthermore, a radiation efficiency of 94.2% and 89.7% is realized at 1.7 and 2.5 GHz, respectively. The proposed antenna attains a measured average gain of 5.2 dBi and 6.1 dBi at the L and S band, respectively. [ABSTRACT FROM AUTHOR]

Airborne array tomographic synthetic aperture radar (TomoSAR) can acquire three-dimensional (3D) information of the observed scene in a single pass. In the process of airborne array TomoSAR data imaging, due to the disturbance of factors such as inconsistent antenna patterns and baseline errors, there are spatially varying amplitude-phase inconsistency errors in the multi-channel Single-Look-Complex (SLC) images. The existence of the errors degrades the quality of the 3D imaging results, which suffer from positioning errors, stray points, and spurious targets. In this paper, a new calibration method based on multiple prominent points is proposed to calibrate the errors of amplitude-phase inconsistency. Firstly, the prominent points are selected from the multi-channel SLC data. Then, the subspace decomposition method and maximum interference spectrum method are used to extract the multi-channel amplitude-phase inconsistency information at each point. The last step is to fit the varying curve and to compensate for the errors. The performance of the method is verified using actual data. The experimental results show that compared with the traditional fixed amplitude-phase inconsistency calibration method, the proposed method can effectively calibrate spatially varying amplitude-phase inconsistency errors, thus improving on the accuracy of 3D reconstruction results for large-scale scenes. [ABSTRACT FROM AUTHOR]

Three new species of entomobryid springtails (Collembola) from China are described here. Homidia pseudozhangi sp. nov. is characterised by a narrow irregular longitudinal stripe on the body, smooth chaetae e and l1 of the labial base, and the relative position of the specialized microchaeta on Abd. I; H. qianensis sp. nov. by its colour pattern on the antennae and nine sutural macrochaetae on the head; and Entomobrya shaanxiensis sp. nov. by its colour pattern, labral papillae and the lateral process of labial papilla E. Specimens of Akabosia matsudoensis Kinoshita, 1919 from China are redescribed, including description of some characters for the first time. [ABSTRACT FROM AUTHOR]

A prestressed cable net structure is applied to shape and support the reflective surface of mesh antennas. The radiation pattern of an antenna highly depends on the positions of the cable net nodes. The pretension force and node positions of the cable net structure are strongly coupled. The deformation of the flexible support frame changes the positions of the cable net nodes, causing the radiation pattern to deteriorate. To achieve high node position precision, this study proposes the pretension design method of a cable net structure with flexible supports. To improve calculation efficiency, finite element method and force density method are combined to calculate structural deformation directly and accurately. Furthermore, a pretension optimization model is established by considering the rigid body displacements of the nodes. This model is solved iteratively. Numerical results show that the proposed pretension design method can achieve high design accuracy for a flexible support cable net structure and significantly improve the mechanical properties of a support frame. [ABSTRACT FROM AUTHOR]

This publication proposes a fabricated multiple input multiple output (MIMO) antenna geometry of multiple dipole arrays and its numerical findings through simulations. The role that antenna resonators have in antenna performance is explored. The antenna's characteristics have been studied, such as its return loss, peak gain, bandwidth, polar plot, and electric field distribution. The proposed antennas described in the study can produce three to seven resonance bands, making them suitable for multiband, wideband, and short-band settings. With the radiator placed in a mirror image, a gain of ~ 27 dBi is seen in the design. This layout is successful at achieving a bandwidth of 0.98 GHz. The maximum bandwidth of 7.44 GHz was achieved in antenna design when the antenna was inverted and mounted vertically. We measure a peak gain of ~ 4.1 dBi for this antenna configuration. In addition, the suggested antenna may provide a multi-beam antenna radiation pattern, capable of producing both a narrow beam of 10° and a wide beam of 250°. The proposed antenna has numerous potential uses; the study's findings can be applied to various wireless networking and telecommunications technologies, including Zigbee, WiFi, WiMAX, satellite, and 5G. [ABSTRACT FROM AUTHOR]

Against the background of the intensive development and implementation of satellite technologies for position determination, navigation, and time synchronization, one of the central threats to critical industries is the creation of intentional interference to the signals of global navigation satellite systems. It is shown that the use of small-sized antenna arrays in navigation systems consisting of satellite constellations of GPS, GLONASS, GALILEO, BEIDOU, QZSS, or their combinations makes it possible to detect and suppress interfering signals by forming zeros of the antenna array directional pattern in the directions of their arrival. The interfering signal suppression is supplemented with detection procedures while maintaining the ability of navigation by using from one to four satellite systems according to criteria of the required number of satellites in the line of sight and the permissible geometric factor. The process of suppressing the interfering signal from four directions is illustrated by three scenarios, the initial data for which are signals from 35 satellites in the line of sight collected in real-time from five systems. It has been shown that the use of five systems and 35 satellites ensures the suppression of the interfering signal. At the same time, 22 satellites are involved in solving the navigation problem, 13 satellites are below the detection threshold, and the geometric factor is 1.18. When using GPS, GLONASS, and 19 satellites, the interfering signal is suppressed. In this case, 10 satellites are involved in solving the navigation problem, 9 are below the detection threshold, and the geometric factor is 2.1. When using only GPS, the interfering signal suppression is also ensured. This time 7 satellites are involved in solving the navigation problem, 4 are below the detection threshold, and the geometric factor is 1.76. [ABSTRACT FROM AUTHOR]

In antenna design, the low side lobe level (SLL) of the antenna radiation pattern plays a crucial role in communication systems as it reduces signal interference along the entire side lobes of the radiation pattern. This paper presents an effective technique to minimize the SLL and thus improve the radiation pattern of the concentric circular antenna array (CCAA) using an advanced marine predator algorithm (AMPA). The AMPA is inspired by the predator-prey relationship in aquatic ecosystems, and it incorporates an improved adaptive velocity update strategy and a chaotic sequence parameter. In this work, the AMPA is applied to synthesize two examples of CCAA (4,6,8-CCAA elements and 8,10,12-CCAA elements) under two different instances (without and with a centre element). The simulation results achieved a significant improvement in SLL minimization as compared to the uniform array, standard marine predator algorithm (MPA), and some other nature-inspired metaheuristic algorithms. [ABSTRACT FROM AUTHOR]

This paper presents a Track-Before-Detect (TBD) approach to search and localize a radioemitted target in a wide marine environment using just the received signal strength (RSS) measurements. In this problem, the lost target transmits radio signals, and the unmanned aerial vehicle (UAV), guided on a search path, receives the target transmitted signal strength by its mounted antenna. The guidance law directs the UAV to the best detection points where the probability of target detection is maximum. At the same time, the estimation module evolves the posterior distribution of the radio target states, including the target position, heading, and transmitter power. The best detection points are calculated based on this evolved target's states' posterior. The superiority of the proposed method is due to the consideration of the antenna radiation pattern, which is accurately modeled in this paper and ensures the strength of the filter against the uncertainties of the measurement model and the target model. The simulation results validate the performance of the proposed method in the autonomous localization of a lost moving target. [ABSTRACT FROM AUTHOR]

Slanting of subarrays in a hybrid MIMO configuration is known to mitigate loss from directional antenna elements typical of mmWave integrated circuit arrays, under the line-of-sight (LOS) plane wave model (PWM) of propagation. This paper considers optimal slanting of subarrays under the spherical wave model (SWM) of propagation, because the SWM is known to be more appropriate than PWM for short-range LOS MIMO channels. The capacity of MIMO under the LOS SWM is known to depend on subarray spacing for non-slanted subarrays, so this paper derives the optimal spacing for slanted subarrays, which is shown to be the same as for non-slanted subarrays. The paper goes on to show that slanting only degrades hybrid MIMO capacity under the SWM model. By comparing the capacities under the PWM and SWM, the authors explain why slanting is beneficial under one model and not under the other.

Antenna arrays have various applications, such as radar, military systems, and wireless communications. The performance of the communication system depends heavily on the antenna array design process. The major challenges in designing such arrays are the high sidelobe levels and the enormous number of elements. Recently, optimization techniques that exploit the evolutionary algorithms have been used extensively for thinning the antenna arrays to reduce power consumption and improve the radiation pattern by decreasing the sidelobe levels. However, due to the stochastic nature of the resolution algorithms, achieving a global optimal for such algorithms is not assured. Based on the combination theory, this paper adopts an element-by-element removing strategy for thinning planar arrays. Without loss of generality, a uniformly excited 25 elements rectangular array with isotropic elements is investigated as an example. The proposed thinning method examines all the possible arrangements of the placements of 25 elements in the phased array aperture. The optimum position of elements is selected to achieve the desired characteristics of the radiation pattern. The results show that with the 40% thinning percentage, the same radiation pattern for the full array (without thinning) can be witnessed. Consequently, a considerable reduction in resource utilization can be achieved in terms of power consumption, the number of phase shifters, and the number of attenuators.

Modern communication demands a low-profile, versatile antenna. In this paper, a low-profile antenna of size 38 × 40 × 0.787 m m 3 is proposed to reconfigure frequency and radiation pattern. The Rogers RT Duroid 5870 of dielectric constant 2.33 is used as a substrate. Frequency reconfiguration is achieved by connecting patches of different lengths corresponding to the resonant frequencies through three PIN diode switches. Switching on/off these three diodes results in frequency switching between four distinct frequency bands. The Yagi-Uda principle is utilized to alter the radiation pattern. Simple parasitic elements are loaded on either side of the radiating structure. Changing the electrical lengths of the parasitic elements using PIN diode switches facilitates pattern reconfiguration by making them behave as a reflector/director. The presented structure resonates at four distinct frequencies (5.3 GHz/3.82 GHz/2.77 GHz/2.2 GHz) with a maximum of three beam tilt angles for each resonating frequency. SMP1345-079LF PIN diode is used for switching operation. Biasing circuit has been designed to ensure RF and DC isolation. The proposed antenna offers acceptable radiation performance in all the switching states. The average measured gains are 2.43 dBi, 2.42 dBi, 3.5 dBi, and 3.29 dBi at 5.3 GHz, 3.82 GHz, 2.77 GHz, and 2.2 GHz, respectively. On an average, the proposed antenna exhibits the simulated efficiency of 81%. The proposed antenna is suitable for 5G communication as its bandwidth covers band 1, band 7, band 46, and band 77 of the 5G new radio (NR) standard. Fabrication and testing are done to validate the results. [ABSTRACT FROM AUTHOR]

The paper explores an omnidirectional antenna configuration composed of a reflector fed by a shaped dielectric lens associated with a coaxial TEM horn. A simple formula describes the lens shape obtained by applying Fermat's principle to control the rays' caustic emerging from the dielectric interface. Based on geometrical optics (GO) principles, a synthesis technique defines the reflector shape to control the antenna radiation pattern in the vertical plane. Concatenated conic describes the reflector generatrix. The study employs a full-wave analysis to validate the designs and explores the proposed configuration to attend two distinct far-field specifications. [ABSTRACT FROM AUTHOR]

Slotted waveguide antennas have received much attention due to features such as low loss, high efficiency, and high power capacity. In this article, a 2-D slot array antenna based on a ridged waveguide with a low level of side lobe is synthesized. The antenna consists of four slotted ridged waveguides, each of which consists of eight slots as the radiating elements. A fast and easy way is proposed to synthesize the aperture distribution in the H-plane. Further, a corporate feed network based on ridged waveguide is designed to feed the antenna. The feed network is designed such that the desired aperture distribution in the E-plane is achieved. A prototype of the antenna is fabricated and measured. The measured sidelobe levels in the H- and E-planes are, respectively, -24.5 dB and -23.9 dB, and the reflection coefficient of the antenna is -19 dB at the design frequency, indicating the accuracy of the design procedure. The measured antenna gain is approximately 20.4 dBi at the entire frequency band. The stable radiation pattern of the antenna makes the antenna suitable for radar applications. [ABSTRACT FROM AUTHOR]

The directional multiple signal classification (Dir-MUSIC) algorithm based on the antenna gain array manifold has been proposed to find the direction of the partial discharge (PD) source in substations. However, PD signals are wideband signals and the antenna gain pattern functions are always different at different frequencies; therefore, the accuracy can be improved using a wideband Dir-MUSIC algorithm. In this paper, wideband Dir-MUSIC algorithms are discussed and a novel wideband Dir-MUSIC algorithm using the strength proportion (DirSP) is proposed. This algorithm estimates a focusing PD signal at a certain frequency using the strength proportion among different directions, and then the Dir-MUSIC algorithm can process the focusing PD signal at this frequency. In simulations, when the antenna gain functions among different frequency bins are quite different, the Dir-MUSIC algorithm loses accuracy; meanwhile, DirDP performs very well. In the experiments, we deal with six sets of samples, and the mean error and standard deviation are both smaller than 4 ° better than other methods. [ABSTRACT FROM AUTHOR]

The existence of significant cross-polar antenna patterns, as well as the scan-dependent measurement biases, inherent to the polarimetric phased array radar (PPAR), are among the most important risk factors for using this technology in weather observations. The cross-polar patterns on receive induce cross coupling between returns from the two orthogonal fields causing biases in polarimetric variable estimates. Furthermore, the electromagnetic coupling in hardware may exacerbate the cross-coupling effects. To address this problem, a pulse-to-pulse phase coding in either the horizontal or vertical ports of the transmission elements has been proposed. However, it does not affect the scan-dependent system biases in PPAR estimates, which require corrections via calibration mechanisms. Further, the cross-coupling signals are proportional to the cross-polar pattern power levels, rendering mitigation effective only at steering angles where these levels are sufficiently low (e.g., approximately less than −25 dB). In that regard, any approach that augments the number of such steering angles benefits the cross-coupling mitigation effectiveness. Herein, a simple approach that has a potential to achieve this via antenna tilt is presented. Significance Statement: The issue of biases caused by cross coupling (due to significant cross-polar patterns in PPARs) is one of the biggest challenges for their weather observation applications. Numerous approaches have been proposed to address this issue, but none has been comprehensive. This suggests that the solution to the cross-coupling issue should be a combination of various mitigation approaches. In that regard, it is suggested in this work that a small antenna tilt can aid in the mitigation of the cross-coupling issue. [ABSTRACT FROM AUTHOR]

Sensors in the electronic world are parts that are used to detect changes in the physical or chemical environment. The output from the sensor is converted into an electrical quantity that represents the change in the environment. Sensors are widely used in agriculture, especially to detect changes in the physical or chemical environment related to plant growth, for example: temperature sensors, light sensors, soil moisture sensors, and so on. In agricultural applications that have a large area, the problem of location and distance from the sensor to the control center is a problem in itself. To solve this problem, a sensor system is designed that does not use wired (wireless) connections. In the application of wireless communication systems there is an antenna part which is very important which can affect the rate of sending sensor data. To improve the performance of wireless sensors in sending data, it is necessary to integrate the appropriate antenna with the sensor transceiver system. So this research was conducted to integrate circular polarized antennas with sensors to increase the gain in the transmission. From this integration, measurements are then taken to obtain the value of the radiation pattern, gain and bandwidth. From the resulting measurements, it can be seen that there is an increase in the gain of the wireless sensor transmission using the 2.4 GHz frequency. [ABSTRACT FROM AUTHOR]

The antenna is one of the key components of satellite communication load. To address the evolving requirements of future satellite communication systems, the sparse planar array has become an important device for transmitting and receiving electromagnetic waves in emerging antenna systems. The advantages of this technology include low cost, low system complexity, and robust anti-interference ability, which have attracted widespread attention within the industry. In this paper, we investigate an optimization design of sparse planar arrays in satellite communication scenarios. Firstly, we introduce the mathematical foundation of the array antennas and establish the optimization design model of the sparse planar array. Secondly, we analyze and compare the impact of different array layout methods on the sparse planar array antenna pattern, and then introduce the latest design trend of array material design. Thirdly, we review some classical optimization methods for optimizing sparse planar arrays and the recent research advancements in promising and novel methods. Lastly, on the basis of the present research status, we propose three future research directions and two critical challenges for optimal design of sparse planar arrays in satellite communication scenarios, which can facilitate the development and realization of array technology under future B5G and 6G wireless networks. [ABSTRACT FROM AUTHOR]

Usually, omnidirectional radiation pattern antenna is used in the mobile ad hoc network (MANET) which causes neighbor node interference, consumes more power, and supports only limited range of transmission. To overcome these problems, smart antennas are used. A lot of medium access control (MAC) protocols are proposed using smart antennas. Existing works addressed various problems such as hidden terminal problem, hidden beam problem, deafness of nodes, and head of line blocking problem. However, certain factors including determination of weight vector and conveying it to the neighbor nodes for distortion-free transmission are not considered. In this study, nullifying MAC (NULLMAC) framework is proposed using an adaptive antenna array (AAA) for improving network performance in MANET. NULLMAC framework uses channel information for achieving high throughput and spatial reuse through integrated physical and MAC layer. Before the transfer of data packets, the receiver initially determines its weight vector and conveys it to the transmitter through control packets. Then, the transmitter computes its weight to nullify the dynamic receivers present in the neighborhood region to find the desired receiver. Beamformer weights are determined through channel coefficients between a transmitter-receiver pair to establish distortion-free transmission. Extensive simulations are performed using OPNET integrated with MATLAB. NULLMAC framework achieves 27.22% more throughput and 40.46% increase in signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Graphene is emerging as an ideal material for new-generation optoelectronic devices. In this paper, a novel graphene metasurface-based electrically switchable and tunable infrared light modulator has been proposed and theoretically studied. The functional modulator comprises a monolayer graphene sheet sandwiched in a Fabry–Perot (FP) like nanostructure consisting of a metal reflector, a dielectric spacer, and an ellipse patterned anisotropy antenna layer. As a result of the photon localization effect of the guided-mode resonance (GMR) in the FP structure, the graphene electroabsorption can be significantly enhanced to enable a high-performance light modulator. By fine-tuning the Fermi energy (Ef) of graphene via controlling its bias-gate voltage, the proposed modulator can switch between a perfect absorber and a reflective polarization converter of high conversion efficiency (i.e., >90%) at 1550 nm. The conversion mechanism and the geometric dependences of the infrared light modulator have been investigated. We further demonstrated the tunability of the highly-efficient polarization converter over a broad spectrum by adjusting the real dispersion of Ef. Our design concept provides an effective strategy for customizing novel optoelectronic devices by combining an electrically-tunable 2D material with a functional metasurface. [ABSTRACT FROM AUTHOR]

This paper investigates a low-Earth orbit (LEO) satellite downlink for high-speed data communication in interference situations. A choke ring horn type antenna is used as the data transmitting antenna with an isoflux pattern in the LEO satellite, which has a beam coverage of ±51.6° and a bore-sight gain of 4.4 dBi at 8 GHz. The receiving antenna on the ground station is a parabolic type antenna with a diameter of 11.3 m, and it has a half-power beam width (HPBW) of 0.2° with a maximum gain of 59 dBi at 8 GHz. The jamming-to-signal ratio (J/S) is calculated assuming that the LEO satellite transmits signals to the ground station, and an elevation angle of the interference source varies from 0° to 90° at an altitude of 10 km. Applying antenna characteristics, such as HPBWs and side lobes, to the calculated space wave path loss makes it possible to predict the J/S results according to the location of the interference source and the satellite. The results show that it is necessary to consider the space environment to accurately analyze the LEO satellite downlink, especially at the low elevation angle of the satellite. [ABSTRACT FROM AUTHOR]

Multicarrier technology is widely used for improving the performance of beampattern synthesis in frequency diverse array multiple‐input and multiple‐output (FDA‐MIMO) Radar. However, how to use multicarrier technology to achieve highly focussed beampattern synthesis is still an open problem. To this end, the authors first establish the system model of FDA‐MIMO radar with multicarrier transmission and analyse the parameters influencing beampattern synthesis by Cramér–Rao lower bound derivation. It can be recognised that frequency increments and multicarrier distribution are key parameters hindering highly focussed beampattern synthesis. On top of the investigation, a simple yet effective Multidimensional Non‐linear Frequency Component, named multidimensional frequency components (MNFC), is proposed for forming a highly focussed beam. Specifically, MNFC is a two‐dimension frequency component for FDA‐MIMO radar. The first dimension is the frequency increment weighted by the Dynamic Taylor Window Function that effectively decouples the joint‐range‐angle beampattern. The second dimension is a non‐linear multicarrier weighted by Log with a Linear Coefficient for further optimising dot‐shaped beampatterns for target indication with high precision. Finally, numerical simulations and comparative experiments are performed to validate the superiority of the MNFC in beampattern synthesis. [ABSTRACT FROM AUTHOR]

The advancement of communication and radar systems has triggered the demand for in‐band full‐duplex (IBFD) operation. IBFD is regarded as one of the most outstanding technologies in terms of its ability to improve spectral efficiency and data rate. IBFD operation has the potential not only to enable communication or radar systems separately, but to help realising radar sensing and communication at the same time, known as Joint Communication and Sensing (JC&S) technology. In realisation of IBFD and JC&S systems, self‐interference (SI) is the key challenge for antenna designers. In this article, a comprehensive survey on SI reduction techniques in the antenna domain is provided and the advantages and disadvantages of each technique are studied. SI reduction techniques have been proposed separately but an elaborated review of relevant techniques with a comparative study has not been presented yet. For the first time, a systematic comparative study of different SI reduction techniques is graphically presented to cover a comparison based on isolation, gain, and impedance bandwidth in terms of before and after SI reduction techniques. Moreover, this study also explores how antenna isolation characteristics vary with respect to the thickness and the permittivity of the substrate without any SI reduction technique. [ABSTRACT FROM AUTHOR]

A low‐profile planar end‐fire broadband antenna with wide beamwidth is presented. The proposed antenna consists of a grounded coplanar waveguide (GCPW), an antipodal dipole, and a pair of directors. A transition from the GCPW to the substrate integrated waveguide (SIW) with tapered coupling slots is designed to achieve a wide impedance bandwidth. Wide beamwidths of the proposed antenna are realised through the antipodal dipole with bilaterally symmetrical sector arms. A pair of directors are symmetrically located on both sides of the sector arms to further widen the beamwidth. An antenna prototype operating at Ka band with a size of 2.18 λ0 × 0.77 λ0 × 0.06 λ0 (λ0 is the wavelength of the centre frequency) is fabricated based on the conventional printed circuit board process. The measurement results show that the reflection coefficient is lower than −12.5 dB in the frequency range of 32.2–37.0 GHz. At 35.5 GHz, the peak gain is 3.8 dBi, and the half‐power beamwidths (HPBWs) in E‐plane and H‐plane are 116° and 215°, respectively. [ABSTRACT FROM AUTHOR]

A dual-band google lens logo-based patch antenna with defected ground structure was designed at 5.3 GHz for wireless applications and 7.4 GHz for wi-fi application. The designed antenna consists of a rounded rectangular patch antenna with a partial ground structure fed by a 50 Ω microstrip line. A google lens shaped logo is subtracted from the rounded rectangular patch and some regular polygon shaped slots are subtracted from the ground plane to obtain good dual-band characteristics and better results in terms of gain, VSWR, and return loss. The proposed antenna has a measurement of 20 × 20 × 1.6 mm3 and provides wide impedance bandwidths of 0.23 GHz (5.17‒5.40 GHz) and 0.16 GHz (7.33–7.49 GHz) at center frequencies of 5.3 GHz and 7.4 GHz, respectively. The antenna was designed and simulated using an ANSYS Electronics Desktop. Fabrication of the antenna was obtained using chemical etching and the results were measured by using an MS2037C Anritsu combinational analyzer. The return loss characteristics for dual bands are -20.56 dB at 5.3 GHz and -19.17 dB at 7.4 GHz, respectively, with a VSWR < 2 at both the frequencies and a 4 dB gain is obtained. [ABSTRACT FROM AUTHOR]

As the same device may be used for various types of applications, antennas must have the capacity to perform multiple functions. Reconfiguring the polarization, operational frequency, and radiation pattern can create an outcome of multi-functionality. A hybrid, frequency- and pattern-reconfigurable antenna with two V-shaped extrudes in a patch is proposed. To increase the bandwidth of the proposed antenna, the defected ground structure (DGS) phenomenon is presented, which is significant in the bandwidth of 3200 MHz from 2.7 GHz to 5.9 GHz, providing a gain of 3.5 dB. For this design, an FR-4 material was chosen as the substrate, and CST software was used for simulation. Using two p-i-n diodes, the projected antenna illustrates switching for multi-frequency bands such as 1.5, 2.6, 3.2, 5.1, and 8.1 GHz, with a constant radiation pattern and a main lobe direction of 155 degrees. It has C-band, WLAN, cognitive radio (CR), and Bluetooth applications. The proposed antenna displays radiation pattern switching at 3.5 GHz, showing variation between 7°, 158°, 173°, and 175°, and at 4 GHz, it demonstrates switching between 11°, 15°, 165°, and 344°, which defines the hybrid reconfiguration. [ABSTRACT FROM AUTHOR]

A low-profile and wide-angle radiation pattern reconfigurable antenna is designed, analyzed, and fabricated for wireless sensor network (WSN) applications, which operate at a 2.5-GHz frequency. This work aims to minimize the number of switches and optimize the parasitic size and ground plane to achieve a steering angle of more than 30° using a low cost-high loss FR-4 substrate. The radiation pattern reconfigurability is achieved by introducing four parasitic elements surrounding a driven element. In this work, the single driven element is fed by a coaxial feed, while other parasitic elements are integrated with the RF switches on the FR-4 as the substrate with dimensions of 150 × 100 mm (1.67 × 2.5 λo). The RF switches of the parasitic elements are surface mounted on the substrate. By truncating and modifying the ground plane, the beam steering can be achieved at more than 30° on the xz plane. Additionally, the proposed antenna can attain an average tilt angle of more than 10° on the yz plane. The antenna is also capable of attaining other important results, such as a fractional bandwidth of 4% at 2.5 GHz and an average gain of 2.3 dBi for all configurations. By adopting the ON/OFF condition on the embedded RF switches, the beam steering can be controlled at a certain angle, thus increasing the tilting angle of the wireless sensor networks. With such a good performance, the proposed antenna has high potential to serve as a base station in WSN applications. [ABSTRACT FROM AUTHOR]

In this paper, a miniaturized textile microstrip antenna is proposed for wireless body area networks (WBAN). The ultra-wideband (UWB) antenna used a denim substrate to reduce the surface wave losses. The monopole antenna consists of a modified circular radiation patch and an asymmetric defected ground structure, which expands impedance bandwidth (BW) and improves the radiation patterns of the antenna with a small size of 20 × 30 × 1.4 mm3. An impedance BW of 110% (2.85–9.81 GHz) frequency boundaries was observed. Based on the measured results, a peak gain of 3.28 dBi was analyzed at 6 GHz. The SAR values were calculated to observe the radiation effects, and the SAR values obtained from the simulation at 4/6/8 GHz frequencies followed the FCC guideline. Compared to typical wearable miniaturized antennas, the antenna size is reduced by 62.5%. The proposed antenna has good performance and can be integrated on a peaked cap as a wearable antenna for indoor positioning systems. [ABSTRACT FROM AUTHOR]

5G demands a significant increment in the number of connected devices. As a result, gNodeBs are constantly pushed to serve more spectrum and smaller sectors. These increased capacity demands are met by using multiband antennas in base stations. One of the key challenges with multiband antennas is the pattern distortions due to the presence of other surrounding antenna element structures. This work provides a novel approach to address the challenge of pattern distortion in the lower frequency band 690–960 MHz due to common-mode (CM) currents in the high- frequency-band antenna element operating in the 1810–2690 MHz band. A common-mode suppression circuit is integrated with the impedance matching network of the high-band antenna element to reduce these common-mode currents. The experimental results verified that the common-mode suppression circuit reduces the common-mode currents at low-band frequencies by moving the common-mode resonance frequency outside the low frequency band, resulting in cleaner low-band patterns meeting pattern specifications. [ABSTRACT FROM AUTHOR]

An integrated solution providing a bi-stable antenna with reconfigurable performance and light-responsive behavior is presented in this paper for the first time. The proposed antenna includes a radiation layer with conductivity, which is integrated onto the bi-stable substrate. First, the effect of the radiation layer material and substrate layer parameters on antenna performance was studied. The experiment showed that an antenna with CNTF has a wider impedance bandwidth than one with CSP, namely 10.37% versus 3.29%, respectively. The resonance frequency increases gradually with the increase in fiber laying density and fiber linear density. Second, the influence of state change of the substrate layer on the antenna radiation pattern was studied. The measured results showed that the maximum radiation angle and gain of states I and II are at 90°, 1.21 dB and 225°, 1.53 dB, respectively. The gain non-circularities of the antenna at states I and II are 4.48 dB and 8.35 dB, respectively, which shows that the antenna has good omnidirectional radiation performance in state I. The display of the array antenna, which shows that the array antenna has good omnidirectional radiation performance in state A, with gain non-circularities of 4.20 dB, proves the feasibility of this bi-stable substrate in reconfigurable antennas. Finally, the antenna deforms from state I to state II when the illumination stimulus reaches 22 s, showing good light-responsive behavior. Moreover, the bi-stable composite antenna has the characteristics of small size, light weight, high flexibility, and excellent integration. [ABSTRACT FROM AUTHOR]

Summary: This paper presents an optimization‐based approach to compensate for the mutual coupling effect and to reduce the sidelobe level (SLL) of the normalized radiation pattern by optimizing the current excitation amplitude of the antenna array elements. Due to the mutual coupling effect, the SLL of the radiation pattern is increased, and thereby, the field pattern of the antenna array is severely degraded. This causes interference with other communication systems working at the same frequency. Toward the compensation of the mutual coupling effect and reduction of SLL, the Cat swarm optimization (CSO) algorithm is employed, and the excitation amplitudes of the antenna elements are optimized. In this regard, optimizing the cost function is defined by introducing the impedance factor (IF), calculated by using the self‐impedance and mutual impedance of the antenna elements. The proposed method for the synthesis of a mutually coupled linear antenna array is less expensive, simpler to use, and more effective. Array sets of 4, 6, 8, and 10 elements are considered for optimization. [ABSTRACT FROM AUTHOR]

In precision agriculture, information technology is used to improve farm management practices. Thereby, productivity can be increased and challenges with overfertilization and water consumption can be addressed. This requires low-power and wireless underground sensor nodes for monitoring the physical, chemical and biological soil parameters at the position of the plant roots. Three ESP32-based nodes with these capabilities have been designed to measure soil moisture and temperature. A system has been developed to collect the measurement data from the sensor nodes with a drone and forward the data to a ground station, using the LoRa transmission standard. In the investigations of the deployed system, an increase in the communication range between the sensor node and the ground station, from 300 m to 1000 m by using a drone, was demonstrated. Further, the decrease in the signal strength with the increasing sensor node depth and flight height of the drone was characterized. The maximum readout distance of 550 m between the sensor node and drone was determined. From this, it was estimated that the system enables the readout of the sensor nodes distributed over an area of 470 hectares. Additionally, analysis showed that the antenna orientation at the sensor node and the drone influenced the signal strength distribution around the node due to the antenna radiation pattern. The reproducibility of the LoRa signal strength measurements was demonstrated to support the validity of the results presented. It is concluded that the system design is suitable for collecting the data of distributed sensor nodes in agriculture. [ABSTRACT FROM AUTHOR]

The radiation and propagation characteristics of a plasma column is theoretically studied in isothermal/non-isothermal regimes. The Boltzmann and Maxwell equations are employed to derive the radial profile of the electron temperature, electron density and the field components. It is found that by increasing the plasma density the plasma system goes toward the non-isothermal regime. It is shown that for the high values of the electron density, the isothermal approach would be violated and it must be replaced with the non-isothermal approach. This model is applicable to the plasma column with azimuthally symmetric plasma density. The present results are important from practical point of view and can be used in design and tuning of the plasma antennas. [ABSTRACT FROM AUTHOR]

New GNSS applications demand resilience against radio interference and high position accuracy. Separately, these demands can be fulfilled by multi-antenna systems using spatial filtering and carrier-phase positioning algorithms like real-time kinematic (RTK), respectively. However, combining these approaches encounters a severe issue: The spatial filtering induces a phase offset into the measured carrier phase leading to a loss of position accuracy. This paper presents a new approach to compensate for the phase offset in a blind manner, (i.e., without knowing the antenna array radiation pattern or the direction of arrival of the signals). The proposed approach is experimentally validated in two jamming scenarios. One includes a jammer with increasing power and the other includes a moving jammer. The results demonstrate that the approach successfully compensates for the phase offset and, hence, allows for the combined use of RTK positioning and spatial filtering even under jamming. [ABSTRACT FROM AUTHOR]

SAR data products for Sentinel-1 have been freely available and delivered operationally on behalf of the European Space Agency since the routine operation of Sentinel-1A in 2014. These products were delivered using the best knowledge at their processing time, in particular with respect to the radiometric calibration. As reprocessing of SAR data products is not foreseen in the nominal processing chain of Sentinel-1, changes of applied processing parameters impact the SAR data quality and can be a disturbing factor for long-term monitoring of radiometric features. In particular, antenna pattern updates produce artificial radiometric steps which are visible in radar backscatter time series, especially in case of monitoring radiometric stable reference targets. This paper introduces a method for correcting changes due to such updates without the need of reprocessing SAR data products. The method was applied to long-lasting time series of data acquisitions which are used to monitor the radiometric performance with reference targets at the DLR calibration site. It has been shown that artificial steps due to antenna pattern updates disappear in backscatter timelines after correct application. Furthermore, the derived absolute radiometric accuracy was improved for the joint observation period of S1A and S1B for almost five years until December 2021. [ABSTRACT FROM AUTHOR]

The Calibration Microwave Radiometer (CMR) is a three-band radiometer deployed on the HY-2C satellite in a near-Earth orbit, and since it launched, there are few studies presented on the performance of CMR to date. Therefore, this paper focuses on providing an assessment of HY-2C CMR brightness temperature and wet troposphere correction (WTC). CMR works at 18.7 GHz, 23.8 GHz and 37 GHz in a nadir-viewing direction, aligned with the HY-2C radar altimeter. The wet troposphere path delay of the radar altimeter signal caused by water vapour and cloud liquid water content can be monitored and corrected by CMR. In this paper, guided by the concept of antenna pattern correction algorithm and a purely statistical method, we directly establish the function between the CMR antenna temperature and the model-derived WTC calculated by the European Centre from Medium-Range Weather Forecasting (ECMWF) Reanalysis data, which can obtain the brightness temperature and the WTC of CMR simultaneously. Firstly, the algorithm principle of CMR to establish the function between the antenna temperature and the model-derived WTC is introduced, and then the brightness temperature of CMR is evaluated using reference brightness temperatures of the Advanced Microwave Radiometer 2 (AMR-2) on Jason-3 satellite at crossover points. Furthermore, the performance of the CMR WTC is validated in three ways: (1) directly comparing with the colocated WTC measured by Jason-3 AMR-2, (2) directly comparing with model-derived WTC from ECMWF, which allows a rapid check at a global scale, (3) comparing the standard deviation of the Sea Surface Height (SSH) difference at crossover points using different WTC retrieval methods. The linear fit with Jason-3 brightness temperature and WTC in all non-precipitation conditions demonstrated a good agreement with Jason-3. In addition, the WTC of CMR has an obvious decrease in the standard deviation of the SSH difference compared with model-derived WTC, indicating the CMR can significantly improve the accuracy of the HY-2C SSH measurements. All the assessments indicate that the CMR performances are satisfying the expectations and fulfilling the mission requirements. [ABSTRACT FROM AUTHOR]