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This study presents a novel implementation of vanadium dioxide (VO2) phase change material in an electromagnetic (EM) surface with beam steering capabilities. For the first time, we present the design, fabrication, and measurement of a globally actuated, VO2-based beamforming reflective EM surface. We propose a design featuring complementary unit cells that enable beam steering with a single excitation, marking a pioneering use of low-loss VO2 in creating a complementary EM surface for the mmWave band. The unit cells incorporating VO2 exhibit low-loss characteristics, with −0.92 and −1.9 dB in the hot state and −0.49 and −0.25 dB in the cold state, respectively. We incorporate both positive and negative phase variants alongside two temperature-independent phase unit cells. The complementary design enables us to utilize two beam operating states, effectively exploiting the otherwise unused cold state. We experimentally demonstrated beamforming at ±5° and ±10° from the broadside. In the case of ±10°, the measured gains at 35 GHz in the cold and hot states were 19.4 and 20.3 dB, respectively, which aligned well with the simulated gains of 20.9 and 21.5 dB. Manipulation of the electromagnetic wave direction with a single excitation has the potential for imaging, sensing, and communication applications. The complementary unit cell design methodology can be further adapted for mmWave beamforming, absorbing, and cloaking reconfigurable EM surfaces. Furthermore, the use of VO2 can be extended up to sub-THz frequencies due to the wideband, low-loss characteristics compared with conventional reconfigurable devices, such as PIN diodes or MEMS switches. [ABSTRACT FROM AUTHOR]

This work reports analysis of the reverse-bias breakdown characteristics of homojunction gallium nitride (GaN) p–i–n (PIN) rectifiers fabricated on bulk GaN substrates. Sub-bandgap photoluminescence mapping at room temperature as a contactless, non-destructive wafer inspection method was performed to analyze the impact of material properties on grown GaN PIN diodes and to study the correlation between defect types and breakdown characteristics of vertical GaN PIN rectifiers. Under the sub-bandgap excitation, yellow luminescence is dominant. The premature breakdown characteristics of the fabricated kV-class vertical GaN PIN rectifiers with nitrogen-implanted floating guard rings are found to be associated with material defects and deep level complexes. Photoluminescence mapping has demonstrated its effectiveness in quantitative analysis of dislocations and other types of defects. [ABSTRACT FROM AUTHOR]

An analytical device physics model is presented for determining the energy conversion efficiency of semiconductor nanowire array-based radial (core–shell) p-i-n junction betavoltaic cells for two- and three-dimensional radioisotope source geometries. Optimum short-circuit current density J sc , open-circuit voltage V oc , fill factor F F , and energy conversion efficiency η are determined for various nanowire properties, including dopant concentration, nanowire length, core diameter, and shell thickness, for Si, GaAs, and GaP material systems. A maximum efficiency of 8.05 % was obtained for GaP nanowires with diameter 200 nm (p-core diameter, i-shell, and n-shell thicknesses of 24, 29.4, and 58.6 nm, respectively), length 10 μ m , acceptor and donor concentrations of 10 19 and 5 × 10 18 cm − 3 , respectively, and a 3D source geometry. [ABSTRACT FROM AUTHOR]

A practical quantitative model is presented to account for the I–V characteristics of pin diodes based on epitaxial Ge-like materials. The model can be used to quantify how the different material properties and recombination mechanisms affect the diode performance. The importance of dislocations, non-passivated defects, and residual intrinsic layer doping in determining the qualitative shape of the I–V curves is discussed in detail. Examples are shown covering literature diodes as well as diodes fabricated with the purpose of validating the theoretical effort. [ABSTRACT FROM AUTHOR]

In this paper, a wideband polarization reconfigurable omnidirectional antenna (PROA) based on a single-substrate active metasurface is proposed. By controlling the states of the PIN diodes, the antenna can selectively radiate an omnidirectional linearly polarized wave and an omnidirectional circularly polarized wave. The reflection coefficient, axial ratio (AR), radiation pattern, and gain of the proposed antenna have been analyzed from the perspective of simulation and measurement. The measured results show that the PROA has a wide overlapped bandwidth from 2.87 to 3.67 GHz (relative bandwidth 24.46%). To the authors' best knowledge, this is the first reported wideband PROA based on a single-substrate reconfigurable polarization converter. This study not only offers a novel approach to design PROAs, but also greatly reduces the design complexity of the feed source compared with the traditional design method of PROAs. [ABSTRACT FROM AUTHOR]

It is a formidable challenge to find the minority carrier recombination lifetime in low-dimensional devices as low-dimensionality increases the surface recombination rate and often reduces the recombination lifetime to a scale of picoseconds. In this work, we demonstrated a simple but powerful method to quantitatively probe the minority carrier recombination lifetime in silicon nanowires or microwires by fitting the experimental photoresponses with our recently established analytical photoresponse principle of photoconductors. The nanowires were passivated with small molecules and Al2O3 to suppress surface recombination, which will increase the minority recombination lifetimes. As expected, the minority carrier recombination lifetime found by this approach increases by orders of magnitude. These wires were also made into PIN diodes, the leakage of which was reduced at least 1 order of magnitude after surface passivation by Al2O3. The minority recombination lifetime found from the leakage current of these devices is largely consistent with what we found from our analytical photoresponse principle. As a further step, we performed scanning photocurrent microscopy to find the minority diffusion length from which we found that the minority recombination lifetime is close to what we found from the analytical photoresponses. In short, this work validated that our analytical response principle is a reliable method to find the minority recombination lifetime in low-dimensional semiconductors. [ABSTRACT FROM AUTHOR]

In this paper, we report a reconfigurable multifunctional polarization converter (RMPC) based on positive-intrinsic-negative (PIN) diodes, enabling to achieve different functions in different bands and states. The simulations and experiments show that when the PIN diode is off, it acts as a broadband linear polarization (LP) converter at 9.12–15.93 GHz. Simultaneously, when the PIN diode is on, the LP incident wave is converted into a left-handed circular polarization wave at 8.69–11.41 GHz and a cross-polarization wave at 13.40–14.97 GHz, whereas full reflection is obtained at 12.05–12.54 GHz. The RMPC consists of two dielectric plates and three layers of metal copper plates. Finally, a sample was fabricated and measured, the simulated and experimental results were in good agreement. Compared with other works, the RMPC has more working states and wider operating frequency bands, which has an application potential in the field of radar stealth and satellite communication. [ABSTRACT FROM AUTHOR]

Summary: Developing wireless communication systems depends on reconfigurable microwave filters (MF) and dielectric resonator antenna (DRA) because the functionality of the various filters and antennas available for a wireless communication system is limited, and reconfigurable DRA and MF are utilized to overcome these limitations. The throughput of a multiantenna system can be achieved with reconfigurable DRA and filter. Various switching strategies and classifications of reconfigurable DRA and MF are presented. The electrical reconfiguration technique is most suitable for developing a reconfigurable DRA and filter among all the switching techniques. In this approach, reconfigurability may be accomplished by utilizing a PIN diode, a varactor diode, and a radio‐frequency microelectromechanical switch (RF‐MEMS). These switches are more reliable, highly efficient, and easily integrated with the microwave circuit. Reconfigurable DRA with machine learning is demonstrated. The application of reconfigurable DRA and filters in cognitive radio (CR) is also demonstrated. Also, the review article focused on the performance parameters, design, and challenges of reconfigurable antenna and MF. [ABSTRACT FROM AUTHOR]

Summary: This paper introduces a concept for designing a polarization reconfigurable transmitarray (PRT). The unit cell of the transmitarray utilizes Huygen elements, with dimensions measuring 0.6 λ0×0.6λ0 (λ0 corresponds to a frequency of 15 GHz). An equivalent circuit model is proposed for the unit cell based on the two‐port Z‐matrix. The proposed unit cells have a very low insertion loss of 0.5 dB at 15 GHz. The PRT is illuminated by a linearly polarized (LP) microstrip‐printed Yagi antenna. The transmitarray is designed using the 13×13 proposed unit cells with a two‐level phase quantization. The collimated LP radiation emitted by the transmitarray subsequently traverses a polarization reconfigurable converter (PRC). The resultant radiation from the PRC can be either LP or circularly polarized (CP), contingent on the configuration of the PIN diodes employed within the PRC. The proposed PRT demonstrates a measured gain of 16 dBi when operating in the LP mode while achieving a peak gain of 15 dBic in the CP mode. The overall size of the proposed PRT is compact owing to a small f/d ratio (0.58). The practicality of the design is validated through fabrication and measurement. This innovative antenna design holds potential applications in the realm of Ku‐band uplink satellite communication. [ABSTRACT FROM AUTHOR]

Active switching components are employed to propose a novel compact dual-band matching network (MN) with an adapted frequency in this paper. The design method involves the integration of active switching devices, stepped impedance resonator (SIR), and microstrip transmission line into the frequency response of a dual-band MNs. The PIN diode is employed as an active switching device in the proposed structure to increase the bandwidth of the MNs and attain the desired frequency. The dual-band MNs that are being proposed are fabricated and designed on the Rogers RO4350B substrate for use in Wireless Local Area Networks (WLANs). The simulation results demonstrate a high degree of congruence with the measurements. The maximal insertion losses and return losses in the first band are -1.3 and -24 dB, respectively. In the second band, they are -2.2 and -20.69 dB. The primary benefits of the proposed dual-band MNs are their high attenuation between two passbands, frequency matching capability, suitable return loss, and low insertion loss. [ABSTRACT FROM AUTHOR]

Switching of vertical 6.1 kV/4A NiO/Ga2O3 rectifiers from voltages up to 1.45 kV showed reverse recovery times of 75 ns, current slew rate of 39.0 A/μs, and energy loss of ∼105 μW. These are the highest switching voltages reported for Ga2O3 rectifiers. To place the results in context, commercial 3.3 kV/5 A SiC merged PiN Schottky diodes showed reverse recovery times of 20 ns, current slew rate of 47.5 A/μs, and energy loss of ∼67 μW. The validity of comparing unpackaged experimental Ga2O3 diodes with commercial Si or SiC diodes without considering their differences in chip size and consequently in capacitive charge and ON-resistance is restricted. However, the results show the rapid progress in these devices when compared to commercial SiC rectifiers. [ABSTRACT FROM AUTHOR]

This paper presents a novel bandpass filter with reconfigurable bandwidth or transmission zeros. The proposed filter is based on a multiple-mode stub-loaded resonator. Three PIN diodes are utilized as switching elements to achieve four switchable operating states. The measurement results indicate that the 3 dB fractional bandwidth (FBW) of the filter can be varied from 32.3% to 70% at the centre frequency of 2.2 GHz, and the stopband attenuation is higher than 35 dB. The filter size is only about 0.28λg × 0.19λg. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative design approach for a voltage‐controlled (variable) attenuator that allows continuous control of attenuation through analog voltage. Different from fixed attenuators, this work employs PIN diodes and compensated gold wire inductors to configure the attenuation network. It is based in imperfect matching theory, ensuring to obtain the acceptable S‐parameters over the operating band. Measurement results demonstrate effective performance of the attenuator within the voltage range of 0.7–1.03 V. Return losses of the attenuator are all better than 15 dB in the operating range of 10.5–19 GHz. The insertion losses exhibit continuous variation from 2 to 15 dB, requiring only a single controlled voltage to adjust the attenuation value. [ABSTRACT FROM AUTHOR]

This letter presents the theoretical investigation by a transmission line model and the physical implementation of a novel frequency reconfigurable microstrip antenna with switchable states. More specifically, by using voltage‐controlled PIN diodes, the antenna can be switched between a radiation state and a low‐scattering state. In the radiation state, the operation frequency of the antenna can be electrically modified between 1.5 and 2.3 GHz by acting on the voltage applied to the varactors. In the low‐scattering state, the antenna achieves a significant in‐band radar cross section reduction, with a maximum value of 26.7 dB. The proposed antenna is fabricated and measured. The validity of the proposed strategy is verified by the good agreement between simulated and measurement results. The antenna designed by the proposed approach has great advantages in the radiation performance, aperture size, profile height and design freedom. This work indicates the feasibility of employing the reconfiguration technique to mnipulate the scattering features of an antenna without deteriorating its radiation characteristics. [ABSTRACT FROM AUTHOR]

Summary: A novel pattern reconfigurable antenna is proposed in this letter. The overall dimension of the antenna is 11 × 11 × 0.787 mm. The proposed antenna is fabricated on Rogers RO4003C substrate. The antenna has two meandered monopoles and two straight monopoles. Two PIN diodes are connected between meandered monopoles and feed. The proposed design has three states of switching, that is, ON‐ON, ON‐OFF, and OFF‐ON. The antenna radiates from 18.5 to 26.25 GHz band with more than 5 GHz (−10 dB) bandwidth for all states. The proposed geometry exhibits 270° radiation beamwidth with 45° and 135° directions for ON‐OFF and OFF‐ON state, respectively. [ABSTRACT FROM AUTHOR]

High-voltage semiconductor devices are vulnerable to Single Event Burnout (SEB) as a result of interactions with Galactic Cosmic Rays (GCR). SEB is a permanent failure triggered by the passage of a single particle during the turn-off state of the device. This paper investigates SEB in a PiN diode induced by various ions in space through simulation. The Linear Energy Transfer (LET) of the ions studied was determined using SRIM. Additionally, the electrical properties of the device due to irradiation were analyzed using the Silvaco TCAD tool. The key indicator of SEB occurrence is the threshold voltage of SEB (VSEB). Therefore, the correlation between the ion's LET and VSEB was investigated. The results indicate that the most sensitive region is in the middle of the device, and SEB is caused by avalanche multiplication of ion-generated carriers. It was also observed that the VSEB decreased from 3200 V to 2100 V; as the LET increased from 0.19 to 58 MeV.cm².mg-1 for He and Ta, respectively. Consequently, ions with higher LET values can cause the device to burnout at a lower VSEB level, increasing the device’s sensitivity to SEB. [ABSTRACT FROM AUTHOR]

The Internet of things is increasingly focused on UAV-based long-range applications. This necessitates versatile, low-cost antenna designs for both ground stations and drones. This study proposes the design of a pattern reconfigurable parasitic element antenna system operating in the LoRa 868 MHz band and its on-field characterization. The electronic steerable parasitic array radiator (ESPAR) antenna consists of a single-fed shorted patch surrounded by four rectangular parasitic elements. The antenna system can develop four directive beams, each activated by one of four PIN diodes, and an omnidirectional pattern obtained when all diodes are turned off. The antenna has been characterized both in an anechoic controlled environment and in a practical on-field drone-to-ground packet transmission scenario. Results based on received signal strength indicator (RSSI) show that the pattern reconfigurability becomes increasingly relevant with the end-point distance and that pointing the beam at the end point always allows the highest RSSI level to be received. [ABSTRACT FROM AUTHOR]

Summary In today's intricate wireless communication environment, ensuring system quality demands the use of a reliable and versatile antenna system. This research article introduces a polarization reconfigurable antenna integrated with a 4 × 4 Artificial Magnetic Conductor (AMC) surface. The AMC unit cell exhibits a triple‐band reflection phase response at 1.8GHz, 4.5GHz, and 5.5GHz, demonstrating double negative metamaterial behavior. The antenna features two distinct C‐shaped metal strips connected to two PIN diodes, enabling dynamic current distribution adjustment. Consequently, the proposed antenna offers three reconfigurable states, facilitating seamless switching between dual circular polarization (left and right‐hand circular polarization) and linear polarization. With a frequency coverage ranging from 1.29 to 2.52GHz and 3.59 to 6.15GHz, the antenna boasts a maximum axial ratio (AR) bandwidth of 31.96%. Additionally, it achieves a maximum peak gain of 5.5 dB and maintains front‐to‐back ratio (FBR) values exceeding 25 dB, while recording a minimum specific absorption rate (SAR) value of 0.1059 W/kg. The integration of the AMC surface ensures enhanced performance of the antenna. Experimental results from constructed prototypes closely align with simulation outcomes, validating the effectiveness of the proposed antenna. Consequently, this antenna holds significant promise for next‐generation wireless applications. [ABSTRACT FROM AUTHOR]

The generation of terahertz radiation by heterostructure p-i-n AlxGa1−xAs/GaAs diodes excited by femtosecond optical pulses was studied experimentally and using the Monte Carlo method. It is shown that when the reverse bias varies, the terahertz generation mechanism changes. With a positive bias on the p-i-n diode, the THz generation mechanism is due to the reflection of the photoexcited electrons from the interface. With a large internal electric field, THz generation in the p-i-n diode occurs due to the acceleration of electrons at the ballistic stage of their movement in the electric field to velocities significantly exceeding the steady state velocity ("velocity overshoot"). The subsequent sharp decrease in velocity of electrons is associated with their inter-valley transitions from the Γ-valley to the L-valley of the conduction band. At electric fields less than 22 kV/cm, the effect of electric field screening by photoexcited carriers has a significant impact on the formation of photocurrent and, accordingly, on the THz generation mechanism. As the reverse bias decreases, this effect leads to a shift in the maximum of the THz pulse toward shorter times and it begins to dominate at electric fields less than 10 kV/cm. [ABSTRACT FROM AUTHOR]

A high-tuning range frequency reconfigurable dual-band compact cylindrical Dielectric Resonator Antenna (DRA) for 5 G Sub 6 GHz applications is presented in the proposed work. The work presented here provides compactness, frequency reconfigurability (FR), and dual-band. FR is obtained through two PIN diode switches, which operate in ON-ON, ON-OFF, OFF-ON, and OFF-OFF configurations and offer a maximum wide tuning range and a total spectrum of 44.44% and 71.49%, respectively. In the cylindrical DRA, the ${\rm{HE}}{{\rm{M}}_{11{\rm{\delta }}}}$HEM11δ and ${\rm{HE}}{{\rm{M}}_{12{\rm{\delta }}}}$HEM12δ modes create dual-band, while the hybrid structure and higher order mode excitation yield compactness. [ABSTRACT FROM AUTHOR]

To improve the threshold voltage and gate reliability of conventional enhancement-mode p-GaN-gated AlGaN/GaN high electron mobility transistors while maintaining a low on-resistance, an improved design solution for p-GaN HEMTs with P-I-N junction gate (PIN-HEMTs) has been proposed. Simulation results show that energy band modulation is achieved by adjusting the doping concentration and thickness of each layer of the PIN junction, and high-performance p-GaN gate HEMTs with adjustable threshold voltages ranging from 0.56 V to 4.75 V and gate breakdown voltages ranging from 19.8 V to 30.3 V would be prepared. The PIN-HEMT has a quasi-self-alignment property, which means that good gate control is independent of gate metal alignment. This not only improves the production efficiency but also solves the problems of weak gate control and electric field aggregation at the gate edge caused by the gate misalignment in conventional p-GaN gate HEMTs, thus realizing lower on-resistance and higher gate breakdown voltage, which demonstrates this proposed structure has excellent potentials for realizing effective and reliable high-power transistors. [ABSTRACT FROM AUTHOR]

This article proposes a dual mode dual-polarized antenna configuration for IRNSS and fifth generation (5G) applications, operating at a frequency of 3.5 GHz based on characteristic mode analysis (CMA), and aims to provide broadband dual-polarized functionality. The original design of the antenna is a traditional patch antenna, and its dual-polarized features are determined using characteristic mode analysis. The full-wave method is used to stimulate both orthogonal modes using a 50 Ω coaxial input line at 3.5 GHz. In this design, the circular patch has been extended into an elliptical patch through a process of mode separation. The circular patch exhibits resonance at a frequency of 2.5 GHz, whereas the extended elliptical radiator demonstrates two resonance modes at 2.5 GHz and 3.5 GHz. The operational mechanism is elucidated by modal analysis and characteristic angle. This antenna operates on two different frequencies at the 2.5 GHz IRNSS band with horizontal polarization and the 3.5 GHz 5G service with vertical polarization. The maximum gain achieved with these frequency ranges is 5.31 dBi and 4.72 dBi, respectively. A ring resonator is chosen to improve the axial ratio and impedance bandwidth of the suggested prototype. The antenna's ground plane is shaped like a rectangle and features a V-shaped slot in the radiating patch. The antenna's physical footprint is 50 mm × 50 mm × 1.6 mm and an FR4 dielectric substrate serves as its foundation. Through its interaction with a PIN diode, the diode modifies the polarization of the antenna. The antenna functions as a right-handed circular polarization (RHCP), when the diode is operational. The bandwidth from 4.3 to 7.5 GHz is covered. On the other hand, it generates linear polarization (LP) between 4.2 and 5.3 GHz. The experimental antenna is evaluated and examined for its performance characteristics. The simulations are carried out utilizing the CST simulator. A prototype antenna has been manufactured and its performance has been validated against simulated findings. [ABSTRACT FROM AUTHOR]

High‐quality quasi‐2D perovskites in a GaN nano‐wire matrix are grown to build a 3D hetero‐structure for high‐performance X‐ray sensing. In the 3D hetero‐structure, GaN nano‐wire matrix serves as an n‐type charge collector that can rapidly extract carriers through the bulk film of the perovskite layer. Together with a p‐type top electrode, a p–i–n diode with the 3D hetero‐structure is built, that exhibits a rectified current–voltage characteristic. After analyzing the interface energy alignment, it is found that the fermi levels of the perovskite and GaN are aligned in the dark, and a quasi‐fermi level splits upon illumination, introducing a built‐in electrical field at the interface. As a result, strong photo‐induced current is observed from the diode without an external field. Finally, the 3D diode for X‐ray detection demonstration is used, revealing a sensitivity of 308.9 µC Gyair−1 cm−2 at an exceptionally low applied field of 0.125 V µm−1. The X‐ray‐induced signal from the 3D diode is stable after 155 cycles of X‐ray irradiation under a constant electric field. This demonstration informs a new 3D architecture for high‐performance X‐ray sensing, and it shows that GaN is a robust n‐type interface for perovskite optoelectronic devices. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile reconfigurable antenna array capable of five radiation-pattern modes for vehicular communication applications. The antenna array consists of four antenna elements, each containing four square patches. Exciting one of the square patches generates a broadside radiation. A square parasitic patch is added at the rear of the excited patch, and two square parasitic patches are placed at the front. By optimizing the design of these parasitic patches, including the treatment of center slotting and addition of shorting pins, the antenna element achieves an end-fire beam with a certain tilt angle. On this basis, a reconfigurable feeding network is designed with 1:1 and 1:4 output modes. By connecting the reconfigurable feeding network to the four antenna elements and altering the on/off states of the PIN diodes in the feeding network, a reconfigurable antenna with four end-fire beams and one omnidirectional beam in its radiation pattern is realized. Measurement results demonstrate an excellent impedance bandwidth, radiation pattern, and gain performance in all modes. The four end-fire and one omnidirectional radiation characteristics make it highly suitable for vehicular communication applications. [ABSTRACT FROM AUTHOR]

The integrated design of radiation and stealth holds significant importance for radar communication and camouflage. Currently, radar systems primarily rely on radomes for off‐band stealth. However, achieving in‐band stealth by radomes and absorbing materials is challenging. Even more challenging is the dynamic control of both in‐band radiation and stealth. Therefore, a novel space‐time‐coding metasurface is proposed for radiation and stealth modes regulation. By adjusting the two PIN diodes loaded on the meta‐atom, switching between radiation and scattering modes can be achieved. A 1‐bit reflection phase can be achieved in the scattering mode. The stealth is achieved by controlling the scattering properties of the metasurface. In the radiation mode, 2‐bit phase modulation is achieved by separately controlling the PIN diodes on the meta‐atom and the 3 dB coupler. Additionally, by varying the size of the meta‐atom in the y‐polarization direction, a 1‐bit reflection phase also can be achieved. To validate the proposed radiation‐stealth metasurface characteristics, a 12 × 12 prototype is fabricated. This prototype demonstrates important functionalities, including dual‐mode radiation, amplitude‐phase co‐modulation space‐time‐coding stealth, and space‐coding stealth. [ABSTRACT FROM AUTHOR]

Bandstop filters (BSFs) have many applications in suppressing interference signals and shielding specific bands. Among them, reconfigurable BSFs that cover more frequency bands by switching modes have great research value. In this paper, a novel synthesis approach for compact reconfigurable BSFs with controllable equal-ripple performance is proposed. By switching the ON/OFF state of the positive intrinsic negative (PIN) diode, the proposed reconfigurable BSF can be switched between single-BSF (S-BSF) and dual-BSF (D-BSF). Based on the synthesis approach, the equal-ripple levels of stopband and passband for S-BSF and D-BSF can be independently controlled. To verify, the equal-ripple levels of stopband and passband for S-BSF state and D-BSF state are independently controlled in four groups of examples. Finally, a reconfigurable BSF with a miniaturized size is designed and fabricated. The fabricated reconfigurable BSF behaves with 15 dB and 10 dB return loss (RL) in two different passbands of the D-BSF state, and 25 dB bandpass RL and controllable stopband rejection (SR) for the S-BSF state. The measured results are in good agreement with the electromagnetic (EM) simulation results. [ABSTRACT FROM AUTHOR]

A miniaturized ultra-wideband (UWB) antenna with quadruple reconfigurable characteristics is proposed in this paper. The first step involves the development of an elementary rectangular patch antenna of size 40 × 40 mm2, which is subsequently modified to demonstrate UWB properties. To incorporate quad-band notch features, the radiating surface of the patch antenna is etched with four Ushaped slots. The antenna has an impedance bandwidth ranging from 2.2 GHz to 12 GHz, with four specific notches located at 3.3 GHz (3.1-3.5 GHz), 3.8 GHz (3.6 GHz-4 GHz), 4.6 GHz (4.5 GHz-4.7 GHz), and 5.2 GHz (5.1 GHz-5.3 GHz). By incorporating four PIN diodes, the antenna is capable of attaining a range of sixteen reconfigurable states across the UWB spectrum. The design of this system successfully addresses the issue of interference caused by WiMAX, downlink C-band, Indian national satellite system, and Wireless LAN. A prototype is fabricated and tested. The simulated and experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

A broadband reconfigurable metasurface consisting of perpendicular metallic gratings and a PIN diode-driven split circular ring for polarization and propagation modes control is demonstrated. The designed metasurface possesses tunable properties in two propagation modes. In the "OFF" state, it can convert incident linear-polarized waves into transmitted cross-polarized waves with full transmission. In the "ON" state, it can reflect incident linear-polarized waves into co-polarized waves with full reflection. Without the increasing number of active elements commonly utilized in chirality-type metasurface polarizers, the equivalent transformation of the split circular ring can be achieved by switching the single PIN diode, and high polarization-conversion efficiency is guaranteed. A metasurface array with 10 × 10 unit cells is fabricated and measured. The experimental results show that the tunable transmission, reflection, and polarization properties of the proposed reconfigurable metasurface can be achieved from 4.9 to 7 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a transmissive reconfigurable polarization converter (RPC) based on an active metasurface is proposed, which can regulate the ideal plane wave and the spherical wave as a cladding of the horn antenna. The metasurface unit is composed of a single-layer F4B dielectric substrate and two double-cross metal strips with a p–i–n diode on the top and seven vertical metal strips on the bottom. One RPC prototype with 15 × 15 units has been fabricated and measured when it regulates an ideal plane wave. By controlling the states of diodes, the RPC can realize the linear-to-circular polarization conversion (LCPC) or the linear polarization maintaining (LPM) function from 2.5 to 3.64 GHz. Furthermore, the RPC is used as the cladding of a horn antenna for high integration in practical applications. The measured results show that this RPC-antenna system can still achieve LCPC or LPM function from 3.1 to 4.5 GHz. It is worth mentioning that the 3 dB axial ratio beam width of RPC can cover from −65° to 65° in LCPC. The proposal has advantages of a wideband, simple biasing network, and easy fabrication and integration, which can be widely applied in modern wireless communication systems. [ABSTRACT FROM AUTHOR]

PIN diodes, due to their simple structure and variable resistance characteristics under high-frequency high-power excitation, are often used in radar front-end as limiters to filter high power microwaves (HPM) to prevent its power from entering the internal circuit and causing damage. This paper carries out theoretical derivation and research on the HPM effects of PIN diodes, and then uses an optimized neural network algorithm to replace traditional physical modeling to calculate and predict two types of HPM limiting indicators of PIN diode limiters. We proposes a neural network model for each of the following two prediction scenarios: in the scenario of time-junction temperature curves under different HPM irradiation, the weighted mean squared error (MSE) between the predicted values from the test dataset and the simulated values is below 0.004. While in predicting PIN limiter's power limitation threshold, insertion loss, and maximum isolation under different HPM irradiation, the MSE of the test set prediction values and simulation values are all less than 0.03. The method proposed in this research, which applies an optimized neural network algorithm to replace traditional physical modeling algorithms for studying the high-power microwave effects of PIN diode limiters, significantly improves the computational and simulation speed, reduces the calculation cost, and provides a new method for studying the high-power microwave effects of PIN diode limiters. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative and cost-effective approach for developing a millimeter-wave (mmWave) frequency-reconfigurable dielectric resonator antenna (DRA), which has not been reported before. The antenna integrates two rectangular DRA elements, where each DRA is centrally fed via a slot. A strategically positioned PIN diode is employed to exert control over performance by modulating the ON–OFF states of the diode, thereby simplifying the design process and reducing losses. In the OFF state, the first DRA, RDRA-I, exclusively supports the TE311 resonance mode at 24.3 GHz, offering a 2.66% impedance bandwidth and achieving a maximum broadside gain of 9.2 dBi. Conversely, in the ON state, RDRA-I and RDRA-II concurrently operate in the TE513 resonance mode at 29.3 GHz, providing a 2.7% impedance bandwidth and yielding a high gain of up to 11.8 dBi. Experimental results substantiate that the proposed antenna presents an attractive solution for applications necessitating frequency-reconfigurable and high-performance mmWave antennas in 5G and Beyond 5G (B5G) communication systems. [ABSTRACT FROM AUTHOR]

Holographic imaging as one of promising image techniques reconstructs object image using the amplitude and phase information scattered from objects. Programmable metasurface composed of digitally coding unit cells can arbitrarily manipulate amplitude and phase of the scattering wave by tailoring operation states of the unit cells, and thus achieves high‐resolution imaging reconstruction. However, the conventional metasurface can only achieves a desired holographic image on an imaging plane. This paper presented a time‐space coding 2‐bit metasurface to overcome this challenge. By rapidly switching PIN diodes loaded in metasurface unit cell according to the customized time sequences, the magnitude and phase of the ±1st order harmonic fields can be fully controlled, achieving the hologram imaging at the higher order harmonics. The proof‐of‐concept measurements are given to demonstrate the versatile holographic imaging functions at the ±1st order harmonics including two different holographic images on an imaging plane, holographic imaging and beam scanning, and holographic imaging and orbital angular momentum (OAM) wave generation, which undoubtedly enriches the applications of the programmable metasurfaces in the field of the holographic imaging. [ABSTRACT FROM AUTHOR]

A miniaturized edge-fed multi-band wideband (WB) sensor complementary split ring resonator (CSRR) and two folded pedal arms loaded antenna for wireless, ISM, military, Radar, and satellite applications is fabricated, tested, and investigated. The reduced ground plane at the bottom to makes the gain positive and leads to improvement in the radiation efficiency. Loading of antenna patch with two folded bicycle pedal-shaped arms results in an increased total electrical length and hence antenna could be tuned up to higher frequency bands. The appended two folded pedal arms enhance the value of gain and CSRR loading introduces additional resonant frequencies below −10dB reflection coefficient. The symmetrical ground width compression results in total antenna size miniaturization to 43.33% concerning the conventional circular microstrip antenna designed at a frequency of 2.45GHz. The antenna has a bidirectional radiation pattern with a gain of 5.21dBi and a radiation efficiency of 90.50%. The antenna exhibits four bands (2.13–2.58GHz), (2.77–3.89GHz), (5.65–6.56GHz), and (7.77–12.98GHz) within a frequency sweep of 1–15GHz, therefore it, is the most suitable element for Bluetooth, PCS, ISM band, 3G/4G/5G, Wi-MAX/WLAN/ Wi-Fi, and wireless, satellite, military, and RADAR applications. These bands are frequency reconfigured by two BAP64-02V PIN diodes in the pedal-arms fold locations with four switching combinations. The measured (frequency sweep: 1–23GHz) and simulated antenna reflection coefficient values are found in match except for a frequency range of 12–14 GHz. The antenna was fabricated on a low-cost FR-4 that holds well <12 GHz frequencies, and >12 GHz frequencies values this shows nonlinear and frequency dispersion. [ABSTRACT FROM AUTHOR]

Maintaining acceptable radiation performance over the entire operation bandwidth is a significant challenge in development of a miniaturised reconfigurable antenna. To address this issue, a new Substrate Integrated Waveguide (SIW) based reconfigurable antenna using slow wave structure is presented in this study. The proposed SIW antenna is based on a layered construction with metallic blind vias connecting to ground plane of SIW. The multi-layer structure of SIW with blind vias helps to separate magnetic and electric fields in the SIW cavity. Thus, a slow wave effect is also utilised and it leads to 36% reduction in the antenna size as compared to conventional SIW cavity. To attain the polarisation and frequency reconfiguration, a cross slot is introduced in the top metallic layer of the SIW cavity and four PIN diodes are connected into the cross-slot arms. Experimental results exhibit frequency reconfigurability in different operating regions with resonant frequencies 4.35, 5, 5.8, 6.4, and 9.6 GHz. The polarisation reconfigurability of the proposed antenna is achieved at 5 GHz with LP/RHCP/LHCP. The proposed antenna exhibits 3-dB axial ratio bandwidth of 4.8 to 5.2 GHz with peak gain of 4.2 dBi. [ABSTRACT FROM AUTHOR]

A frequency and beam reconfigurable antenna based on encoded reflectors for Wi-Fi and IoT applications is proposed in this paper. By modifying the traditional Alford antenna, extending the transmission line, adding radiation arms, and loading PIN diodes, the frequency reconfigurable function can be realized. Then, the three-layer reflectors are loaded around the antenna. The pattern reconfigurable function of the antenna can be achieved by encoding the operating states of the PIN diodes on the reflectors. The antenna is fed from the bottom via a coaxial transmission line, and the dimension of the antenna is 0.99λ0 × 0.99λ0. The simulated and measured results show that the working frequencies of the antenna can be switched between 1.65, 2, and 2.4 GHz with bandwidths of 2.4%, 4.4%, and 1.2%, gains of 3, 4.5, and 2 dBi, and efficiencies of 48.8%, 75.0%, and 49.6% in directional mode, respectively. The antenna works in omnidirectional radiation mode with a scanning accuracy of 10°, bandwidths of 6.6%, 4.9%, and 0.8%, gains of 0.3, 0.52, and −2.8 dBi, and efficiencies of 73.1%, 74.1%, and 51.9% at 1.65, 2, and 2.4 GHz, respectively, when the PIN diodes are tuned in off states. The antenna proposed in this paper offers several advantages, including a wider frequency band, a broader angular range, and higher precision compared to other frequency and pattern reconfigurable antennas. The antenna can be utilized for Wi-Fi and IoT communication, thereby reducing the number of antennas, enhancing communication quality and accuracy, and improving device integration. [ABSTRACT FROM AUTHOR]

Parallel imaging is one of the key MRI technologies that allow reduction of image acquisition time. However, the parallel imaging reconstruction commonly leads to a signal‐to‐noise ratio (SNR) drop evaluated using a so‐called geometrical factor (g‐factor). The g‐factor is minimized by increasing the number of array elements and their spatial diversity. At the same time, increasing the element count requires a decrease in their size. This may lead to insufficient coil loading, an increase in the relative noise contribution from the RF coil itself, and hence SNR reduction. Previously, instead of increasing the channel number, we introduced the concept of electronically switchable time‐varying sensitivities, which was shown to improve parallel imaging performance. In this approach, each reconfigurable receive element supports two spatially distinct sensitivity profiles. In this work, we developed and evaluated a novel eight‐element human head receive‐only reconfigurable coaxial dipole array for human head imaging at 9.4 T. In contrast to the previously reported reconfigurable dipole array, the new design does not include direct current (DC) control wires connected directly to the dipoles. The coaxial cable itself is used to deliver DC voltage to the PIN diodes located at the ends of the antennas. Thus, the novel reconfigurable coaxial dipole design opens a way to scale the dynamic parallel imaging up to a realistic number of channels, that is, 32 and above. The novel array was optimized and tested experimentally, including in vivo studies. It was found that dynamic sensitivity switching provided an 8% lower mean and 33% lower maximum g‐factor (for Ry × Rz = 2 × 2 acceleration) compared with conventional static sensitivities. [ABSTRACT FROM AUTHOR]

A novel, high-gain reconfigurable antenna with a metasurface (MS) superstrate-based configuration is proposed in this research article. The design utilizes a concentric octagonal-shaped patch as a base antenna. Four SMP1345-079LF PIN diode switches are incorporated in the base antenna to facilitate frequency reconfiguration. When all four of the diodes are in OFF condition, the designed antenna resonates at 5.8 GHz. Switching ON the diodes switches the resonating frequency to 5 GHz. A novel MS unit cell of shape like '8' has been designed and analyzed. The designed unit cell exhibits properties of the metamaterial in the operating frequencies. An MS superstrate of a 5 × 5 array has been designed and connected to the base antenna through Teflon rods. Further, the proposed reconfigurable antenna with MS has been analyzed for air and foam medium (medium between antenna and superstrate). The proposed structure offers better performance for the air medium with a gain enhancement of 4.23 dBi and 1.55 dBi at 5 GHz and 5.8 GHz respectively. Fabrication and testing processes are undertaken to validate the proposed antenna's performance. [ABSTRACT FROM AUTHOR]

Silicon photonic integrated circuit foundries enable wafer-level fabrication of entire electro-optic systems-on-a-chip for applications ranging from datacommunication to lidar to chemical sensing. However, silicon's indirect bandgap has so far prevented its use as an on-chip optical source for these systems. Here, we describe a fullyintegrated broadband silicon waveguide light source fabricated in a state-of-the-art 300-mm foundry. A reverse-biased p-i-n diode in a silicon waveguide emits broadband near-infrared optical radiation directly into the waveguide mode, resulting in nanowatts of guided optical power from a few milliamps of electrical current. We develop a one-dimensional Planck radiation model for intraband emission from hot carriers to theoretically describe the emission. The brightness of this radiation is demonstrated by using it for broadband characterization of photonic components including Mach-Zehnder interferometers and lattice filters, and for waveguide infrared absorption spectroscopy of liquid-phase analytes. This broadband silicon-based source can be directly integrated with waveguides and photodetectors with no change to existing foundry processes and is expected to find immediate application in optical systems-on-a-chip for metrology, spectroscopy, and sensing. On-chip optical sensing and metrology systems are rapidly progressing, but CMOS-compatible silicon light sources remain a challenge. This work demonstrates a broadband, foundry integrated silicon waveguide emitter and the theory that describes it. [ABSTRACT FROM AUTHOR]

Metasurfaces have shown unparalleled controllability of electromagnetic (EM) waves. However, most of the metasurfaces need external spatial feeding sources, which renders practical implementation quite challenging. Here, a low‐profile programmable metasurface with 0.05λ0 thickness driven by guided waves is proposed to achieve dynamic control of both amplitude and phase simultaneously. The metasurface is fed by a guided wave traveling in a substrate‐integrated waveguide, avoiding external spatial sources and complex power divider networks. By manipulating the state of the p‐i‐n diodes embedded in each meta‐atom, the proposed metasurface enables 1‐bit amplitude switching between radiating and nonradiating states, as well as a 1‐bit phase switching between 0° and 180°. As a proof of concept, two advanced functionalities, namely, low sidelobe‐level beam scanning and Airy beam generation, are experimentally demonstrated with a single platform operating in the far‐ and near‐field respectively. Such complex‐amplitude, programmable, and low‐profile metasurfaces can overcome integration limitations of traditional metasurfaces, and open up new avenues for more accurate and advanced EM wave control within an unprecedented degree of freedom. [ABSTRACT FROM AUTHOR]

This study focuses on improving data rates in wireless networks through the design, simulation and measurement of a frequency reconfigurable four port MIMO antenna. The antenna is specifically developed for Wi-Fi, wireless local area network, and Industrial, scientific and medical applications. The antenna design has microstrip patch components, a closely built decoupling structure, an electromagnetic band gap structure, and a defective ground structure. These features enhance the antenna's MIMO performance at specific frequencies of operation and minimize radiation losses. The antenna design includes an RF PIN diode to allow for reconfigurability. This enables the antenna to operate at resonating frequencies between 2.39 and 5.36 GHz while the diode is in the ON and OFF states, respectively. The MIMO antenna under consideration is assessed on a FR4 substrate of 70 × 65.5 mm 2 and the wavelength is 0.56 × 0.53 λ 0 . It achieves a peak gain of 7.3 dBi at 2.39 GHz and 8.2 dBi at 5.36 GHz. The simulated results are implemented using HFSS and measured using network analyser KEYSIGHT N9951A. The bandwidths achieved are 0.07 at 2.39 GHz and 0.53 at 5.36 GHz. The experimental results on analysing various antenna characteristics are observed as Total active reflection coefficient value less than 0 dB, envelope correlation coefficient less than 0.5, Mean effective gain value less than − 3 dB, etc. The gain of the proposed four port reconfigurable MIMO antenna is 10% improvement when compared with existing works. The results from the simulated and measured matches well within the two operating bands, indicating that the suggested topology could be used for 5G communications. [ABSTRACT FROM AUTHOR]

In this paper, a 3-bit circularly polarized reconfigurable reflectarray is proposed. The array consists of 64 units in an 8 × 8 configuration, with each unit containing a circular metal patch loaded with phase-delay lines and eight PIN diodes. To independently control each unit, a corresponding DC control circuit was designed and tested with the array. In the bandwidth of 3.43–3.71 GHz, the circularly polarized reconfigurable reflectarray achieved a gain of 16 dB, an aperture efficiency of 27%, an axial ratio of ≤3 dB, an operating bandwidth of 8%, and a beam scanning range of ±60°. The circularly polarized reconfigurable reflectarray can also achieve a good dual-beam radiation performance after testing. The 3-bit circularly polarized reconfigurable reflectarray proposed in this paper offers several advantages, including low loss, high aperture efficiency, a wide beam scanning range, and excellent stability in wide-angle oblique incidence. It has potential applications in low-cost phased array, satellite communications, and deep space exploration. [ABSTRACT FROM AUTHOR]

In this paper, we present a comprehensive comparison study between p-n and p-i-n vertical diodes employing diverse heterojunction configurations under dark conditions. The diodes are fabricated utilizing p-PMItz as the organic semiconductor layer interfacing with different inorganic substrates, including n-Si (n-type silicon), n-4HSiC (n-type 4H silicon carbide), and incorporating an intrinsic SiO2 (silicon dioxide) layer in the p-PMItz/i-SiO2/n++-Si configuration. The current–voltage and dielectric characteristics are analyzed to discern the performance discrepancies among these diode configurations. The influence of heterojunction interfaces and band alignments on device behavior is investigated, shedding light on the charge transport mechanisms within these structures. Our findings reveal distinct trends in device characteristics for p-n and p-i-n diodes, highlighting the significance of heterojunction design in optimizing device performance. This comparative analysis offers valuable insights for the development of efficient organic–inorganic hybrid diodes tailored for various optoelectronic applications. [ABSTRACT FROM AUTHOR]

A reconfigurable metamaterial multiband antenna operating an octa-band resonating mode is designed for IoT wireless applications. Metamaterial cell split ring resonator (SRR) and quasi-complementary split ring resonator (CSRR) are printed on the back and front sides of the proposed antenna design to achieve the multiband characteristics. The PIN diode is implemented in a slotted ground section of the antenna structure to get different wireless standards by switching the diode ON/OFF. During reverse biased (OFF) mode of diode antenna operating at eight resonant frequencies 2.42, 4.34, 5.81, 8.45, 11.02, 13.98, 16.12, and 18.87 GHz covering the IoT wireless standards such as S, C, X, Ku, and K band to identify a variety of wireless applications such as WLAN, WAIC, ITU, Satellite, and radar communication. Simple structure, stable radiation pattern, multiband operation, frequency band reconfigurability feature, reasonable gain, and efficiency are the significant features of the proposed metamaterial multiband antenna. [ABSTRACT FROM AUTHOR]

In this article, an ultra-wideband (UWB) antenna featuring two reconfigurable quasi-perfect stop bands at WLAN (5.25–5.75 GHz) and lower 5G (3.4–3.8 GHz) utilizing electromagnetic bandgaps (EBGs) and positive-intrinsic-negative (P-I-N) diodes is proposed. A pair of EBG structures are applied to generate sharp notch bands in the targeted frequency spectrum. Each EBG creates a traditional notch, while two regular notches are combined to make a quasi-perfect, sharp, notch band. Four P-I-N diodes are engraved into the EBG structures to enable notch band reconfigurability. By switching the operational condition of the four diodes, the UWB antenna can dynamically adjust its notching characteristics to enhance its adaptability to various communication standards and applications. The antenna can be reconfigured as a UWB (3–11.6 GHz) without any notch band, a UWB with a single sharp notch (either at WLAN or 5G), or a UWB with two quasi-perfect notch bands. Moreover, the antenna's notch bands can also be switched from a traditional notch to a quasi-perfect notch and vice versa. To confirm the validity of the simulated outcomes, the proposed reconfigurable UWB antenna is fabricated and measured. The experimental findings are aligned closely with simulation results, and the antenna offers notch band reconfigurability. The antenna shows a consistently favorable radiation pattern and gain. The dimension of the presented antenna is 20 × 27 × 1.52 mm3 (0.45 λc × 0.33 λc × 0.025 λc, where λc is the wavelength in free space). [ABSTRACT FROM AUTHOR]

In this study ion‐implanted lateral 4H‐SiC pin diodes are reported, which show an unexpectedly high room temperature in‐plane magnetic field sensitivity approaching 100 % at 0.5 Tesla. Using dedicated TCAD simulations the underlying transduction mechanism is studied, and the effect of implantation‐induced carrier traps on the observed high sensitivity is unraveled. The study shows how such traps can greatly control the injection conditions at the highly doped implant regions providing a plausible explanation for an observed portion in the IV‐characteristics of the pin diodes exhibiting the aforementioned high magnetic field sensitivity. [ABSTRACT FROM AUTHOR]

We propose a programmable topological metasurface to integrate intelligent modulations of spatial and surface waves. A general design method is presented to design the programmable metasurface elements with PIN diodes. The surface waves can be controlled to propagate along the topological domain-wall interface by programming the C3-symmetry elements, while the spatial waves are modulated by the patterns of C6-symmetry elements. By independently controlling the bias voltages of meta-elements, the programmable topological metasurface can generate different coding patterns with distinct combinations of C3- and C6-symmetries in real time, respectively achieving the dynamical manipulation of the surface- and spatial-wave by using distinct element states in a time-division manner. To validate the modulation performance, we perform both near- and far-field tests with different coding patterns. Experimental results demonstrate good agreement with numerical simulations, thereby showcasing the flexible manipulations of surface waves and spatial waves by the topological metasurface. The proposed metasurface opens up new possibilities for multifunctional metadevices, which hold great potentials for future wireless communications and smart sensing systems. [ABSTRACT FROM AUTHOR]