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This article presents a multi-dot PIN photodiode structure that addresses the inherent trade-off between the light-sensitive area and capacitance in conventional planar photodiodes commonly used in optical communication systems. This structure is a combination of several connected cathode dots and with a shared anode. The radial distribution of the electric field surrounding each cathode dot facilitates both vertical and peripheral charge collection, and accordingly, enables the region beneath and between the dots to function as a light-sensitive area with fast carrier drift. The key innovation of this work lies in the flexibility of the multi-dot structure for easy enlargement of the light-sensitive area by expanding the dot array, while still maintaining a small capacitance. Experimental results show that a 5 × 5 multi-dot PIN photodiode with a pitch of 20 $\mu$m corresponding to an active area of 100 $\mu$m × 100 $\mu$m achieves a capacitance of 48.8 fF, a responsivity of 0.294 A/W at a wavelength of 675 nm, and a bandwidth of 660 MHz at an operating voltage of 10 V. With a pitch of 15 $\mu$m that provides a light-sensitive area of 70 $\mu$m × 70 $\mu$m, the bandwidth increases to 930 MHz.

Spot PIN photodiodes were integrated without any process modifications in a high-voltage 0.18 μm CMOS technology. These photodiodes are a combination of vertical and lateral PIN photodiodes using the P+ bulk wafer and a P-type ring at the surface as anodes. Devices with N+ cathode and N+/N-well cathode are compared. A small N+/N-well cathode spot reduces the capacitance to 1.47 fF and the N+ cathode spot leads to a capacitance of 1.07 fF. The light sensitive area of these photodiodes is 707 μm2. Simulated electric field distributions show the full depletion of the spot PIN photodiodes. Responsivities from 0.12 A/W to 0.16 A/W and from 0.50 A/W to 0.52 A/W for 405 nm and 675 nm, respectively, are achieved. The measured bandwidths for 675 nm light are from 520 MHz to 690 MHz at reverse biases from 15 V to 30 V.

We report on an investigation of dark current contributions from common microscale crystallographic defects in type-II InAs/GaInSb superlattice infrared PIN type photodiode structures grown on (100) GaSb substrates and have identified three general classifications. Defects on several wafers of varying design were examined from multiple perspectives to correlate electrical activity with structural properties, to develop the identification and classification scheme. Active defects were first identified by current density vs voltage (J-V) measurements and electron beam induced current (EBIC) scans of individual diodes with micrometer resolution. The EBIC scans were then correlated with plan-view optical and atomic force microscopy images, both before and after anisotropic etch-pit analysis using a newly developed etchant. The atomic scale structure of active and inactive defects was then compared using cross-sectional transmission electron microscopy (TEM) on vertical slices of defects extracted using focused ion beam milling. Analysis of the TEM images yielded important clues as to the structure and root causes of benign and active defects, in which only significant disruptions at the epi-substrate interface appear to play a key role in producing microscale defects that efficiently promote dark current. [ABSTRACT FROM AUTHOR]

In this paper, we propose a dual manipulation on wave-front in the X band based on a reconfigurable water-based metasurface. We design and test a metasurface integrated with a saline-water substrate and PIN diodes. We showed that the wave-front reflected by the metasurface can be modulated by both the degree of salinity and the diode pattern. With these two manipulating methods, the metasurface can not only control the amplitude of the scattered beams but also the beam deflection angles, which promises a more flexible and economical way to manipulate the wave-front. We provide two diode patterns to illustrate the performance. The experimental results agree well with our simulations, further verifying our designs. Superior than the conventional reconfigurable metasurfaces, the proposed metasurface combines both water salinity and diodes, which offers more possibilities in electromagnetic (EM) wave tailoring, as well as potential applications in sensing and detection. [ABSTRACT FROM AUTHOR]

A polarization-reconfigurable antenna is presented here with the help of an anisotropic reconfigurable reflective polarization converter (RRPC). Proposed design consists of a monopole antenna as a source and an electronically switchable polarizer. Depending on the conducting states of only eight PIN diodes, which are placed on the top surface of the polarizer, linearly polarized (LP) wave generated by the monopole can be converted into left-hand circularly polarized (LHCP), right-hand circularly polarized (RHCP), and LP wave. Proposed RRPC has a ground plane on the back side and it is positioned below the source antenna with an air gap of 0.13 λ0 where λ is calculated at the antenna's operating frequency of 3.5 GHz. Overall configuration of the antenna is compact with a dimension of (0.31×0.31×0.19) λ03. As fewer active elements are used in the proposed design, complexity of the circuit for biasing and losses would be less. To the best of authors’ knowledge, it is first time reported work on active reflective polarizer, which not only has LP-to-CP polarization conversion ability but also it possesses electronic polarization switching ability in between LHCP, RHCP, and LP states. [ABSTRACT FROM AUTHOR]

The results of electrical characteristics and alpha-particle energy spectrometry of 4H-SiC p-i-n diodes are reported. From the capacitance-voltage measurement, the effective doping concentration of the $80 ~\mu \text{m}$ lightly doped 4H-SiC epitaxial layer used in this work is calculated to be about $2\times 10\,\,^{{13}}$ cm $^{-{3}}$ , approaching the limit of the lowest doping level by the SiC epitaxial growth technique. The detector exhibits consistently low leakage current of picoampere level at a reverse bias of 100 V and superior thermal stability up to 150 °C. Resultantly, an energy resolution of 0.6% has been achieved within a 5486 keV $\alpha $ -particle spectrum, which is comparable to the high-resolution SiC Schottky barrier $\alpha $ -particle detector. Also, near 100% charge collection efficiency has been realized with reverse bias exceeding 25 V. This study thus provides a promising solution to high-performance 4H-SiC radiation detectors with low-voltage operation. [ABSTRACT FROM AUTHOR]

In this paper, a novel superjunction MOSFET with ohm contact in the termination region and dual Schottky contacts in the cell region is proposed and experimentally demonstrated. The dual Schottky contacts consisting of the N-type Schottky contact and the P-type Schottky contact suppress the hole injection in the cell region, thereby reducing the reverse recovery charge and enhancing the current density in the termination region. The high current density and the ohm contact in the termination region provide sufficient slowly extracted non-equilibrium holes during the reverse reduction period, which contributes to a significantly improved softness. Experimental results show that, in comparison with the conventional superjunction MOSFET, 66.2% reduction in reverse recovery charge and 137.5% improvement in softness factor can be obtained in the proposed superjunction MOSFET. [ABSTRACT FROM AUTHOR]

This letter presents a folded reflectarray (FRA) capable of electrical beam steering in the Ka-band. The FRA consists of a low-profile feeding source, a dual-layer wire grid, and 36×36 polarization twisting reflective elements. An element of center shorted patch with two plated through holes is proposed where only two switches are required for polarization twisting and 1-bit encoding. A cavity is then introduced surrounding the element to improve the beam-steering performance. To verify the proposed element, two prototypes with 0° and 60° beam directions are designed and experimented where the metal stub and open circuit are used to model “on/off” states of PIN diodes for simplification. The measured peak gain of 0°FRA is 27.5 dBi with 2 dB gain bandwidth of 28–32 GHz (13.3%). A measured gain drop of 3.25 dB is achieved by the 60°FRA, which verifies the wide-angle beam-steering ability. The measured reflection coefficient of the feeding source is less than −15 dB over the operating band. The proposed FRA has a good potential to realize beam-steering with real PIN diodes for the satellite communications. [ABSTRACT FROM AUTHOR]

A miniaturized, vertically polarized (VP), pattern switchable/beam-steering antenna based on a metamaterial radiator is presented for sub-6 GHz applications. Different from the traditional split-ring resonator (SRR), the proposed T-shaped SRR can work as a miniaturized VP omnidirectional radiator. To steer the radiation beam, a novel switchable mushroom reflector with a low profile and low loss is explored and utilized. Multiple switchable mushroom reflectors are loaded around the T-shaped SRR radiator to obtain various steerable beams. To verify the proposed design principle, a VP beam-steering SRR-based antenna with a compact size of 0.36 λ0 × 0.36 λ0 × 0.07 λ0 is designed by loading four mushrooms. By controlling the off/on states of four switches, the proposed reconfigurable antenna can realize beam-steering in the horizontal plane (eight states with 45°-step). The measured overlapped −10 dB impedance bandwidth is wider than 3.40–3.80 GHz (11.1%), and the realized peak gain is larger than 5.3 dBi. Therefore, the proposed antenna is a good solution for the widely deployed fifth generation (5G)-NR and smart antenna applications due to its compact size, flexible beam-steering capacity, broad bandwidth, and good scanning coverage. [ABSTRACT FROM AUTHOR]

In this communication, a reconfigurable 2-bit leaky-wave antenna (LWA) is proposed for low-cost fixed-frequency beam-steering applications. The proposed antenna consists of a microstrip transmission line loaded with several branches, a series of 2-bit phase shifters, and a $1\times 8$ patch array. Each phase shifter is built by selecting the feed directions on the branch and introducing slot perturbation on the patch, thus no phase delay line is used. Only three p-i-n diodes are needed to control the 0°, 90°, 180°, and 270° states of the element. The reference phase $\varphi _{0}$ , namely the phase of the first element, is utilized to enhance the peak gain of the array. The stopband effect of broadside beam is eliminated due to the perturbation on the patches. The prototype is tested at 3.6 GHz. The measured peak gain is 13.54 dBi, and the main beam can steer from $- \mathrm{48}^{\circ }$ to $+ \mathrm{46}^{\circ }$. [ABSTRACT FROM AUTHOR]

Comprehensive analysis of small-signal equivalent circuit models for GaAs-based PIN diodes is performed in this article. The analysis provides the equivalent circuit models for PIN diode operation in four different operation modes. A compact nonlinear equivalent circuit model has been developed which takes into account the dc/ac frequency dispersion of the diode dynamic resistance. In order to verify the validity of the proposed circuit model, the comparison between the modeled and measurement data is given, good fitting is obtained for GaAs-based PIN diode. [ABSTRACT FROM AUTHOR]

The intelligent omni-surface (IOS) is a dynamic metasurface that has recently been proposed to achieve full-dimensional communications by realizing the dual function of anomalous reflection and anomalous refraction. Existing research works provide only simplified models for the reflection and refraction responses of the IOS, which do not explicitly depend on the physical structure of the IOS and the angle of incidence of the electromagnetic (EM) waves. Therefore, the available reflection-refraction models are insufficient to characterize the performance of full-dimensional communications. In this paper, we propose a complete and detailed circuit-based reflection-refraction model for the IOS, which is formulated in terms of the physical structure and equivalent circuits of the IOS elements, as well as we validate it with the aid of full-wave EM simulations. Based on the proposed circuit-based model for the IOS, we analyze the asymmetry between the reflection and transmission coefficients. Moreover, the proposed circuit-based model is utilized for optimizing the hybrid beamforming of IOS-assisted networks and hence improving the system performance. To verify the circuit-based model, the theoretical findings, and to evaluate the performance of full-dimensional beamforming, we implement a prototype of IOS and deploy an IOS-assisted wireless communication testbed to experimentally measure the beam patterns and to quantify the achievable rate. The obtained experimental results validate the theoretical findings and the accuracy of the proposed circuit-based reflection-refraction model for IOSs. [ABSTRACT FROM AUTHOR]

This work presents a D-band phase shifter which utilizes a one-bit phase inverter (PI), followed by two cascaded reflective-type phase shifters (RTPSs). The PI uses two identical cascode amplifiers and a triaxial balun for compact form factor and to provide identical loading in both states. The RTPSs use SiGe PIN diodes for their resonant loads due to their naturally high-Q and tuning range. The phase shifter is implemented in a 90-nm SiGe BiCMOS technology platform, and achieves insertion loss < 5.5 dB with a 360° phase shift range, for frequencies up to 145 GHz. By using dual voltage control, the insertion loss variation is kept within ±0.9 dB by selecting the appropriate points. This phase shifter achieves competitive performance in terms of insertion loss, power consumption, and amplitude error while operating over a wide bandwidth. [ABSTRACT FROM AUTHOR]

This letter proposes a co-designed millimeter-wave (mm-wave) and sub-6 GHz antenna system. The antenna system consists of four 28 GHz mm-wave arrays with reconfigurable radiation patterns and two sub-6 GHz antennas fed with two corner capacitive coupling elements (CCEs). Each corner CCE is formed by the connected ground planes of two mm-wave arrays in the shared-aperture configuration. The two CCEs are separately matched to cover two sub-6 GHz bands. Each mm-wave array consists of an active patch element and two parasitic patch elements loaded with PIN diodes, realizing 90° beam scanning range with two states of the PIN diodes. The measured results of the fabricated prototype show good agreement with the simulated ones. The prototyped mm-wave arrays cover the band 27.5–28.35 GHz, and each achieves 90° beam scanning at 28 GHz, with measured peak realized gain of 7.9 dBi. The CCE ports cover the two sub-6 GHz bands of 0.79–0.96 GHz and 1.7–5 GHz, with measured isolation of above 17 dB and 20 dB, respectively. The mm-wave band isolation is above 26 dB. [ABSTRACT FROM AUTHOR]

The irregularly located element array within the antenna aperture can be applied to obtain narrow main lobe width and low sidelobe levels with fewer elements as compared with the traditional (periodic) array configurations. In this article, a reconfigurable reflectarray antenna (RRA) combined with hyperuniform disordered distribution is presented. Based on the theoretical radiation pattern of reflectarray, it has been found that the proposed array with reduced elements holds a similar radiation pattern as that of a corresponding periodic array. Meanwhile, the reflectarray avoids the design of complicated feeding network for the disordered phased array antenna. In addition, for a reconfigurable reflectarray to achieve beam scanning, active devices are necessary. In such case, the design of RRA with fewer elements is of particular importance. A 1 bit RRA of 64 elements prototype has been designed, fabricated, and measured. The side length of each element is $0.625\lambda $. Experimental results agree well with the full-wave simulations, and scan beams within ± 50° range have been obtained with a peak gain of 17.4 dBi at 12.5 GHz. [ABSTRACT FROM AUTHOR]

A dual-band fixed-frequency beam-scanning leaky-wave antenna (LWA) operating in C and Ka bands is presented in this article, exhibiting a large-frequency-ratio property. A microstrip line (MSL) is employed on the top layer to feed the patches operating in the low-frequency band, and an air-filled low-loss gap waveguide (GW) is introduced at the bottom of the antenna to feed the patches operating in the high-frequency band. By changing the biasing states of the soldered p-i-n diodes, the operation states of all the radiating patches for the low and high bands can be switched between on and off. Then, based on the holography theory, the hologram is generated on the radiating aperture of the LWA, which can be manipulated to produce expected radiation, and hence, the dual-band fixed-frequency beam-scanning property is realized. In addition, the presented antenna is fabricated and measured for validations. Good agreement can be found between the simulated and measured results, with a peak realized gain of 8.9 dBi at 4.85 GHz and 17.2 dBi at 27 GHz, showing a desirable dual-band operation ability with large frequency ratio. Scanning ranges of 100° are achieved in both bands, demonstrating that the developed antenna has great potentials to large-frequency-ratio microwave and millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A design method of programmable transmitarray antenna with independent controls of transmission amplitude and phase is proposed in C-band. The unit cell with cascaded structures mainly consists of four parts, including the receiving antenna, reconfigurable attenuator with p-i-n diodes, reconfigurable phase shifter with varactors, and transmitting antenna. Correspondingly, various manipulations of spatial electromagnetic (EM) fields are achieved by varying the bias voltages of p-i-n diodes and varactors in the transmitarray antenna. The fabricated unit cell is measured in a standard waveguide, and the whole array with $8\times 8$ unit cells is measured with two horns for calibration of the programmable EM features. The experimental results show that the transmission amplitude can range from −16 to −3.6 dB, and the transmission phase achieves 270° coverage independently at the operating frequency of 5.67 GHz under 16 bit programmable control. To further exhibit the capability and functionality of the proposed transmitarray antenna, the waveform engineering of adaptive beamforming and power-allocation beamforming is separately realized in the experiment. The measured results have good agreements with our theoretical calculations, verifying the validity of our design method. [ABSTRACT FROM AUTHOR]

The concept of dual-polarized reconfigurable reflectarray (RRA) featuring dual-polarized beam control is proposed and demonstrated using a dual-channel programmable metasurface. The p-i-n diodes are incorporated into each metasurface element as the active components to provide independent phase control in two orthogonal polarization channels. By altering the working states of each p-i-n diode, well-defined beam scanning can be obtained. Element design, focal diameter ratio selection, and discretized phase distributions are carefully optimized to ensure stable radiation performance of the proposed RRA. As verification, a prototype consisting of 20 $\times20$ elements is fabricated and measured, which is controlled by a field programmable gate array-based controller. Measured results show that wide-angle beam scanning up to ±40° can be obtained around 7.45 GHz, with peak gains of 21.13 and 20.89 dBi in dual channels, corresponding to aperture efficiencies of 16.35% and 15.47%. The proposed dual-polarized RRA brings a new freedom in polarization manipulations for versatile beam scanning, which provides promising applications in wireless communication and tracking/detecting systems. [ABSTRACT FROM AUTHOR]

We propose an innovative polarization reconfigurable high-gain Fabry–Perot cavity (FPC) antenna. The antenna can electrically select its polarization among three linear polarization (LP) modes of $x$ -, $y$ -, and 45°-direction with stable high gain. To achieve these properties, we devise a novel polarization conversion partially reflective surface (PCPRS) as a superstrate. The PCPRS plays two crucial roles simultaneously; it reconfigures antenna polarization and maintains high gain using an FP resonance between the PCPRS and a ground plane. The FP resonance, which is the key point in our antenna design, is essential to maximize both antenna gain and polarization reconfigurability. Therefore, in order to stably achieve the FP resonance for all three polarization modes, we have designed the PCPRS to keep its reflection behavior as constant as possible for all LP modes. To the best of our knowledge, this is the first FPC antenna introducing a partially reflective surface (PRS) which also functions as an active polarizer. Consequently, the proposed antenna attains remarkable polarization conversion performance with higher than 20 dB cross-polarization suppression level for all polarization modes. Moreover, in all modes, our antenna well maintains reasonably high gain of about 15 dBi with good impedance matching properties. Good agreement between measurements and simulations proves the validity of our design approach. [ABSTRACT FROM AUTHOR]

A wideband 1 bit reconfigurable transmitarray antenna (RTA) with low-profile characteristic is presented. First, a wideband element for the RTA is designed by combining two centrally fed magnetoelectric (ME) dipoles. Two p-i-n diodes are integrated within the element to achieve 1 bit reconfigurable phase states. Next, the folded scheme is adopted to achieve multiple reflections between the feed source and the RTA, and thus, the height-to-diameter ratio (H/D) is reduced to about one-third of that of the conventional transmitarray. A reflective surface with polarization conversion function is designed beneath the RTA around the source, the unit cell of which is a special $C$ -shaped polarizer operating over a wide frequency band. Finally, a low-profile RTA with $12 \times \mathbf {12}$ elements is designed, fabricated, and measured. The whole structure has an aperture size of $\mathbf {5}.\mathbf {75} \boldsymbol {\lambda }_{\mathbf {0}}\times \mathbf {5}.\mathbf {75} \boldsymbol {\lambda }_{\mathbf {0}}$ , and H/D is 0.28. Measured results show that the proposed RTA has the beam-scanning capability to $\pm \mathbf {40}^{\circ }$ in both E- and H-planes over a bandwidth of 32%. The realized gain is up to 19 dBi and the peak aperture efficiency is 20.5%. [ABSTRACT FROM AUTHOR]

In the field of high energy particle imaging detection, there is an urgent requirement for detectors with radiation hardness and thermal resistance. Here, we design a 4H-SiC pixel detector based on a $4\times4$ p-i-n diode array. The thickness of sensitive region (epitaxial layer) is up to $90 ~\mu \text{m}$ , which could realize the detection of 6-MeV tritium. The active area of one p-i-n diode is 1.6 mm $\times1.6$ mm. With an excellent design of gradual doping space modulated (GDSM) junction termination extension (JTE), the reverse bias voltage is up to 5 kV, and the average leakage current is lower than 70 pA when the reverse bias voltage is 400 V. Based on a 16-channel readout electronic system, this detector shows good performance in the position resolution experiment for 5.4-MeV $\alpha $ particles. [ABSTRACT FROM AUTHOR]

Herein, based on a rounded rectangle p-i-n diode with the minimum radius allowed by the process and a 0.8- $\boldsymbol {\mu }\mathbf {m}$ thick I-layer, a high-power wideband monolithic limiter was realized by using GaAs p-i-n process. At 16 GHz, the maximum handling power of the monolithic limiter is up to 400 W (56 dBm), while the output power is less than 45 mW (16.5 dBm). Meantime, the insertion loss of the limiter is less than 0.55 dB and the return loss is better than −15 dB in the frequency range of 10–18 GHz, which has little effect on the signal of the receiver. It demonstrates that the limiter has a significant potential in high-frequency and high-power phased-array radars and communication systems. [ABSTRACT FROM AUTHOR]

In this letter, a switchable frequency selective surface is designed that can operate between rasorber and absorber having a wide passband characteristics. The structure has an extra advantage of being built on a single dielectric layer having lossy and lossless layer on the two opposite sides. The lossy layer comprises of lumped resistors, which assists in wideband absorption from 4.8 to 15 GHz. PIN diodes are mounted in the lossless layer to equip the structure with rasorber/absorber operation. Under the rasorber operation, a wide transmission bandwidth in between the absorption band from 9 to 11 GHz is obtained. The system is also simplified with the help of an equivalent circuit model. The structure is carefully designed so that it is immuned to polarization and angle sensitivity. Finally, the prototype is fabricated and measured, and the results are found to be in good agreement with the simulated ones. The proposed design is expected to find its application in all airborne technologies. [ABSTRACT FROM AUTHOR]

This letter exhibits a switchable double-sided absorber/reflector that realizes broadband performance. This structure effectively breaks the limitation of the absorption bandwidth due to the parasitic capacitance of the p-i-n diode through resonance cancelation. First, the LC parallel resonance is adapted to inhibit the interference of the parasitic capacitance by connecting the inductance in parallel with the p-i-n diode. Then, a gap capacitance is introduced to increase the resonance frequency and further expand the bandwidth. The double-sided design is applied to avoid the short-circuit phenomenon caused by the parallel connection of the inductor and the p-i-n in the single-sided design. To control the inductance value more precisely, the meander inductor is employed. Finally, the reflectivity of the proposed structure covers broadband of 3.91–9.77 GHz from reflection to below −10 dB under normal incidence by changing the working states. Furthermore, a sample of the proposed structure was manufactured and measured. The measurements are consistent with simulations. [ABSTRACT FROM AUTHOR]

In this work, a high performance GaN-on-Si quasi vertical PiN diode was demonstrated by the combination of a beveled sidewall and self-aligned fluorine plasma treatment. The didoes achieved a remarkable breakdown voltage ($\text{V}_{\text {BR}}{)}$ of 930 V and an ultra-low reverse leakage current. Meanwhile the didoes showed a low specific on-resistance ($\text{R}_{ \mathrm{\scriptscriptstyle ON},\textit {sp}}$) of 0.43 $\text{m}\Omega \cdot $ cm2, a high on/off current ratio ($\text{I}_{ \mathrm{\scriptscriptstyle ON}}/\text{I}_{ \mathrm{\scriptscriptstyle OFF}}$) of $10^{{11}}$ , and an excellent Baliga’s figure of merit (BFOM) of 2.01 GW/cm2. The measurement results of X-ray spectroscopy (XPS) and Kelvin Probe Force Microscopy (KPFM) proved the presence of F ions and the decrease of surface potential, which reduced the electric field peak and suppressed the leakage current. These results show a great potential of GaN on Si PiN diode for power applications. [ABSTRACT FROM AUTHOR]

We report Al0.1Ga0.9N p-i-n ultraviolet (UV) avalanche photodiodes (APDs) based on sapphire substrates with a record-high gain over $2 \times 10^{6}$. The devices fabricated with various mesa diameters present consistent avalanche behaviors and identical dark current distributions over multiple ${I}-{V}$ scans, which are comparable to the GaN APDs grown on free-standing GaN substrates. The quadratic fitting of the dark currents versus the mesa sizes reveals that the leakage current at the breakdown voltage is a mixture of surface leakage and bulk leakage, and the surface component is comparable to that of the bulk. Additionally, KOH surface treatment and SiO2 passivation are proven to be very effective in suppressing the leakage current and achieving robust avalanche performance. [ABSTRACT FROM AUTHOR]

This communication presents a novel compact, broadband, monopole-like endfire antenna with reconfigurable radiation patterns for 5G applications. Based on the mirror principle, a half-size monopole-like endfire structure with a wideband response is firstly proposed and analyzed. By switching the ON/OFF states of p-i-n diodes embedded in the passive stub lines, the monopole-like endfire structure achieves omnidirectional and endfire beam switching. Since the structure has a stable and broadband frequency response, a novel flexible pattern diversity antenna with omnidirectional coverage and directional scanned radiation is easily implemented by loading multiple stub lines. To validate the working principle, a nine-mode pattern reconfigurable antenna with a compact size of $0.31\,\,\lambda _{0}\,\,\times \,\,0.31\,\,\lambda _{0}\,\,\times \,\,0.19\,\,\lambda _{0}$ ($\lambda _{0}$ is the free space wavelength at 3.75 GHz, radiator only) is designed and fabricated. The measured overlapped −10 dB impedance bandwidth for the nine modes is from 3.30 to 4.20 GHz (>24.0%), which well covers the 5G N77/N78 band. Besides, their measured gain is greater than 4.0/5.30 dBi. The proposed antenna has the merits of a compact size, simple design, wideband, good radiation performance, and flexible multibeam switching capacity. It is a good candidate for 5G new radio and other sub-6 GHz applications. [ABSTRACT FROM AUTHOR]

A 2-D scanning phased array with large element spacing using pattern reconfigurable stacked patch antenna at Ka-band is presented. The pattern reconfigurable stacked patch antenna is composed of four patches on the top integrated with four p-i-n diodes and a driven patch on the lower layer, where the top patches are located along the diagonals of the proposed antenna. By switching the reverse/forward bias states of p-i-n diodes, the phase gradients in different directions are generated and beam steering on the E-, D-(diagonal), and H-planes can be delivered. Subsequently, a 2-D scanning $4\times 4$ phased array with large element spacing is proposed by applying the pattern reconfigurable stacked patch antenna. The 2-D space is divided into nine subsets and covered by nine states of the proposed antenna. The measured results show that a scanning range of ±55° on the E-, D-, and H-planes can be provided. The maximum realized gain is 20.9 dBi at 26.5 GHz with an aperture efficiency of 62.0%. Compared with conventional half-wavelength phased array, the complexity and cost can be reduced for 2-D scanning phased array by introducing the proposed pattern reconfigurable stacked patch antenna. [ABSTRACT FROM AUTHOR]

An $N$ -way reconfigurable Power Divider (PD) based on parallel reconfigurable-characteristic-impedance transformation lines is proposed in this article. The characteristic impedance of the transmission lines in the power division network is constant, making it suitable for realizing a multiway reconfigurable PD. The reconfigurable parallel characteristic impedance transformation lines are composed of coplanar waveguides and the p-i-n diodes. Reconfigurable star isolation networks with zero-phase transmission lines are used to improve isolation. By making the p-i-n diodes under different bias conditions, $2^{N} - 1$ states of $N$ transmission modes can be realized. For verification, a six-way simplified reconfigurable PD is designed and fabricated; 21 states of 6 transmission modes of the PD are realized. The measured insertion losses of the six-way reconfigurable PD in six transmission modes are less than 1.89 dB. The measured isolations between transmission ports and isolation ports are greater than 30.3, 32.8, 33.3, and 35 dB, while in those modes, the isolations between the input port and isolation ports are greater than 27.1, 29.1, 29.8, and 32.4 dB. The current study is restricted to the case of PDs with equal power-division action to be more specific. [ABSTRACT FROM AUTHOR]

Scalable modeling and parameter extraction of the millimeter-wave GaAs-based p-i-n diode for W-band switch design are presented in this article. A direct-extraction method based on the S-parameters on-wafer measurement is utilized to determine the extrinsic and intrinsic model parameters without any de-embedding test structures. Under turn-on and turn-off bias conditions, the modeled input reflection coefficients agree well with the measured data in the entire frequency ranges for GaAs-based p-i-n diode. The scalable normalization rules have been used to design W-band p-i-n diode switch successfully; good agreements are obtained between the simulated and measured data to verify the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

By the pulsed, heterodyned, and modulated laser illuminations, the impulse and noise responses of O-band germanium (Ge) p-i-n waveguide photodetector (WPD) with different transmission-line designs are characterized for receiving the NRZ-OOK data beyond 60 Gbit/s. The Ge lateral p-i-n WPD reveals an optical responsivity of 0.63-0.74 A/W at 1327.5 nm under −1.8 V bias.The noise equivalent power (NEP) is increased from 0.11 to 0.2 pW/√Hz by shrinking the transmission-line contact electrode length from 280 to 80 μm. After optimizing the transmission-line designs with shorter length and less right corner number (C⊥#) between PD and bonding pad, the Ge lateral p-i-n WPD improves its RLC response to suppress its switching time with broadened receiving bandwidth. Shrinking the connecting transmission-line length from 280 μm to 80 μm extends the flattened S11 spectral response from 51 to 57 GHz by up-shifting the inductor inductor-induced frequency notch from 58 to 61 GHz, as confirmed by the shrank spiral curve in the Smith chart with the decreased inductance by shortening the transmission-line electrode. The dual-wavelength optical heterodyne analysis demonstrates that the Ge p-i-n WPD significantly improves its analog receiving bandwidth from 29.5 to 44.3 GHz measured at 6-dB decay. The sub-ps laser pulse illumination observes that the Ge p-i-n WPD response shortens its impulse response from 23.14 to 19.92 ps by reducing the contact inductor length (by 200 μm) and right corner number (C⊥#) from 4 to 2) of its electrode. When receiving the optical NRZ-OOK data stream, the long-electrode (L = 280 μm, C⊥# = 4) device reveals only 53-Gbit/s receiving performance. The short-electrode (L = 80 μm, C⊥# = 2) Ge lateral p-i-n WPD with significantly reduced inductance successfully receives the NRZ-OOK data beyond 56 Gbit/s and 60 Gbit/s under error-free communication criterion of BER<10−12 and BER<10−9, respectively. [ABSTRACT FROM AUTHOR]

In this letter, a broadband switchable active frequency selective surfaces (AFSSs) is presented, and the proposed structure is comprised of three metallic layers and two Rogers RT5880 substrates. In order to realize broadband transmission, a second-order bandpass filter is constructed, and the multilayer coupling effect is utilized. A modified equivalent circuit model of the p-i-n diode is proposed to reduce the simulation error and improve the design accuracy. By controlling the bias voltage of the p-i-n diodes, two completely different functions are realized. At the function of dual-polarized shielding, the shielding bandwidth is 2–18 GHz, and the transmission bandwidth is 8.2–10.5 GHz with a fractional bandwidth of 24.6% at the function of dual-polarized transmission. A prototype has been fabricated and measured, and the measurement results are in good agreement with the simulation results, indicating that the AFSSs has good polarization stability for X-band radar applications. [ABSTRACT FROM AUTHOR]

We present a wideband reflectarray antenna with electronic beam-steering capability. The beam-steerable reflectarray uses an electronically reconfigurable polarization-rotating unit cell (PRUC) that acts as a wideband 1 bit phase shifter. The unit cell consists of four metallic single-headed arrows placed above a ground plane. The four arrows are connected to the unit cell’s bottom surface, which contains two p-i-n diodes for switching and three lumped inductors for RF–DC isolation. Changing the bias states of the two antiparallel p-i-n diodes reconfigures the unit cell between two operating states that provide a +90° and −90° polarization rotation (PR). Simulation results for the unit cell show a wide frequency range of 8.5–11.5 GHz over which the reconfigurable unit cell provides dominant reflection coefficients of >−2 dB and relative phase shifts of 0° and 180° for the two operating states. The proposed unit cell was used to construct a 256-element, fully electronically reconfigurable reflectarray prototype with aperture dimensions of 192 mm $\times192$ mm to demonstrate the design concept. The digital control circuitry needed to individually control the unit cells was also designed and fabricated. Experimental characterization of the reconfigurable reflectarray demonstrated the 2-D beam scanning capability within the scan range of ±60° over a 30% bandwidth. [ABSTRACT FROM AUTHOR]

A wideband fixed-frequency beam-scanning leaky-wave antenna (LWA) operating at the millimeter-waveband is presented in this article. A groove gap waveguide (GGW) supporting base is introduced as a transmission structure of the antenna with a TE01-mode excitation, and two rows of longitudinal slots etched on top of the superstrate act as the radiating structures. Two rows of PIN diodes are soldered below the longitudinal slots, so that the long slots can be cut into a group of short slots. By controlling the PIN diodes, the working states of the slots can be switched between “ON” and “OFF.” Then, by selecting proper activation states, the fixed-frequency beam scanning can be obtained. In addition, the developed antenna is verified in practical fabrication and experiment. The experimental results have good agreements with that in simulations. The measured peak gain reaches at 16.8 dBi, and the beam-scanning range more than 70° from 23 to 29 GHz is realized. [ABSTRACT FROM AUTHOR]

The snappy reverse recovery (SRR) and failure of high-voltage nonpunch-through (NPT) PIN diodes under extreme working conditions are of great significance to the reliability evaluation of operating diodes in actual power electronic devices. In this article, the analysis of the physical mechanism of the diode SRR and the restrictions of the traditional PT-PIN diode model are made. Then, the traditional model for soft recovery is improved in order to accurately describe the diode SRR characteristics. Simulations of key dynamic performances of the established model agree well with the experimental results. Furthermore, a suppression method for diode SRR based on the optimal RC snubber circuit is proposed. A high-voltage NPT-PIN diode used in the dc−dc converter with different RC snubber circuits is simulated using the proposed diode snappy model and tested. The comparison results show good consistency between the simulated and measured voltage and current peaks and the diode SRR are suppressed effectively. The developed model and results are of much importance to the prediction of the safe operation area of the diode and to the reliability improvement of power electronic device. [ABSTRACT FROM AUTHOR]

Acircular polarization (CP)-reconfigurable antenna array with enhanced axial ratio (AR) bandwidth and high gain is proposed in this letter. By loading the tuning resistor on the annular coupling slot, the AR bandwidth of the initial design is significantly improved. Furthermore, the elliptical grid-slit patch is employed to mitigate the decreased AR performance caused by the parasitic effect from PIN diode switches while improving the gain. A prototype of a 2×2 array is developed, fabricated, and measured. Experiments show that the AR bandwidth is 31.6%, while the measured peak gain is up to 16.3 dBic. [ABSTRACT FROM AUTHOR]

Given the rapid development of advanced electromagnetic (EM) manipulation technologies, researchers have turned their attention to the investigation of smart surfaces for enhancing radio coverage. Simultaneously transmitting and reflecting (STAR) intelligent omni-surfaces (IOSs) constitute one of the most promising categories. Although previous research contributions have demonstrated the benefits of simultaneously transmitting and reflecting intelligent omni-surfaces (STAR-IOSs) in terms of wireless communication performance gains, several important issues remain unresolved, including practical hardware implementations and accurate physical models. In this article, we address these by discussing four practical hardware implementations of STAR-IOSs as well as three hardware modeling techniques and five channel modeling methods. We thus clarify the taxonomy of smart surface technologies in support of further investigating the family of STAR-IOSs. [ABSTRACT FROM AUTHOR]

In this communication, a pattern-reconfigurable filtering patch antenna is presented which consists of a driven patch, a stacked patch, an embedded filtering feeding line, and two vertical switchable elements with gaps from the suspended patches. Compared with the conventional stacked patch antenna, the proposed antenna does not increase the volume. A novel filtering feeding network is designed which consists of a hairpin-shaped resonator and a half-wavelength coupled microstrip line. It is used to generate the radiation nulls near the lower and higher passband edges. A U-shaped slot is etched on the driven patch to generate another radiation null. Three radiation nulls are excited to realize filtering performance. Meanwhile, the radiation beam of the proposed antenna can be reconfigured by switching the function of switchable elements between a director and a reflector using p-i-n diodes. Good radiation pattern reconfigurability, filtering, and wideband performance can be achieved simultaneously. The simulated and measured results show that the radiation beam can be switched to the directions of −33°, 33°, and 0°. The proposed antenna can maintain a wide operating bandwidth of 2.22–2.84 GHz (25%), out-of-band suppression of over 14 dB, and flat in-band gain of about 8 dBi in different states. [ABSTRACT FROM AUTHOR]

In this article, the thermally induced threshold voltage (${V}_{\text{TH}}$) shift was investigated on two types of normally- OFF p-GaN gate high-electron-mobility transistors (HEMTs), featuring either an Ohmic-type or a Schottky-type gate. A positive ${V}_{\text{TH}}$ shift in a Schottky-type device and a negative ${V}_{\text{TH}}$ shift in an Ohmic-type device were observed at elevated temperatures. Temperature-dependent gate current–voltage (${I}-{V}$) and the transfer-length-method (TLM) analysis revealed that the bias condition across the p-GaN/AlGaN/GaN heterostructures was changed in both Schottky- and Ohmic-type devices as temperature increased. We propose that: 1) temperature-enhanced hole injection through thermionic emission which lowers the knee voltage of the Ohmic-metal/ p-GaN contact in Ohmic-type devices and 2) thermally enhanced gate current which enlarges the bias voltage across the Schottky-metal/p-GaN junction in Schottky-type devices, resulted in the observed ${V}_{\text{TH}}$ instability characteristics. The photoluminescence measurements were conducted to verify the thermally-enhanced ionization of magnesium dopants in the p-GaN and the corresponding instability issues. [ABSTRACT FROM AUTHOR]

The use of beryllium as both an i-layer and current spreading layer (CSL) dopant in GaN quasi-vertical p-i-n diodes on sapphire was investigated. With the inclusion of the Be CSL, the current uniformity dramatically improves from $\sim 40$ % of the p-contact radii to 100% resulting in higher breakdown performance and reduced leakage currents. Metal modulated epitaxy (MME) GaN p-i-n diodes on sapphire templates with beryllium-doped GaN (GaN:Be) i-layer thicknesses in the range of 1– $10~\mu \text{m}$ are reported. Additionally, a GaN:Be CSL sandwiched between two conductive Si-doped GaN layers is used to achieve a high quasi-vertical p-i-n diode breakdown voltage of 375 V and a breakdown field of 1.875 MV/cm for the $2~\mu \text{m}$ i-layer p-i-n diodes. At room temperature, the diode with a mesa diameter of $100~\mu \text{m}$ showed a differential ON-resistance (${R}_{ \mathrm{\scriptscriptstyle ON}} \,\,=\,\,\text{d}{V}/\text{d}{I}$) as low as 0.3 $\text{m}\Omega $ -cm2 for a $10~\mu \text{m}$ GaN:Be i-layer diode. A Baliga’s figure of merit (BFOM) ($\text {V}_{\text {Br}}^{{2}}/{R}_{ \mathrm{\scriptscriptstyle ON}}$) of 363 MW/cm2 was achieved for the $10~\mu \text{m}$ i-layer p-i-n diode. This is the highest reported BFOM for GaN p-i-n diodes on foreign substrates. Additionally, the leakage current density is very low: $1\times 10^{{-{9}\,\,{ }}}$ kA/cm2 at 300 V reverse bias for the 5 and $10~\mu \text{m}$ GaN:Be i-layer devices. These devices exhibit a current ON/ OFF ratio ten orders of magnitude. Given the low particle environment, rapid growth rates, ease of compatibility with the toxic dopant Be, and high device performance, the use of Be as a dopant is very useful for high-power devices. [ABSTRACT FROM AUTHOR]

Aiming for 5G-NR vehicular applications, this paper proposes two miniaturized wideband pattern reconfigurable antennas with different pattern steering capabilities. They are inspired by an end-fire structure that could be easily mounted on cars. This newly proposed planar pattern reconfigurable end-fire structure is firstly presented and studied by current distribution and equivalent circuit analysis. By turning the ON / OFF state of the PIN diodes on the passive dipole, a planar reconfigurable antenna with one omnidirectional and two end-fire beams is implemented. Additionally, a low-profile pattern diversity antenna with a compact size of 0.311 λ0 × 0.244 λ0 × 0.106 λ0 is implemented by loading a reactive metasurface, its main lobe can be steered in the broadside direction (35°, 0°, and −35°). Both antennas achieve a wideband response over 3.30 to 4.20 GHz (24.0%) range and good radiation efficiency of 84.0%. They feature the advantages of a miniaturized size (low-profile), structurally simple and fabrication friendly design, wideband, good radiation efficiency (low-loss), and flexible multi-beam switching capability, which are well suited for the coming sub 6 GHz vehicular applications in different scenarios. [ABSTRACT FROM AUTHOR]

A transmissive frequency-reconfigurable cross-pola- rization conversion surface is presented. First, two static cross-polarization conversion unit cells are proposed. Results indicate that they are both capable of transforming incoming linearly polarized waves into their cross-polarized counterparts effectively, but at different operating frequencies. Second, PIN diodes are employed to construct an active unit cell, imitating the behavior of each static unit cell, as the PIN diodes are on or off, respectively. Finally, a prototype containing 10 × 10 unit cells is designed, manufactured, and measured. Measurements show that with the PIN diodes in off or on state, a switchable cross-polarization converting band around 4.17 and 6.73 GHz is achieved, validating the proposed concept. [ABSTRACT FROM AUTHOR]

This work reports an optimal design and modeling of a high-performance normal-incidence GeSn homojunction p-i-n PDs on p-doped silicon (Si) substrate via Intrinsic-Si buffer. Specifically, we optimize the Sn concentration and the absorption layer thickness to simultaneously achieve high-speed, responsivity, detectivity, and low-noise in the mid-infrared (MIR) spectral range (2- $5 ~\mu \text{m}$). We also show that a reduced defect density due to the homojunction GeSn layer can lead to a suppressed dark current. The photoresponse of the designed device was studied for the range between 1500–3000 nm, and the calculated responsivity is 3.26 A/W and 1.27 A/W at 2000 nm and 2500 nm, respectively for Sn = 9%. A specific detectivity, linear dynamic range (LDR), noise-equivalent power (NEP), and the signal-to-noise ratio (SNR) of $2.5\times 10^{10}$ Jones, 105.5 dB, $40.9\times 10^{-15}\text{W}$ Hz−0.5, and 100.9 dB, respectively, were achieved at 2500 nm for Sn = 9%. Furthermore, the impact of intrinsic layer thickness and incident optical power was also studied in detail. The calculated results show that larger absorption layer thickness enhances the photocurrent, detectivity, LDR and SNR, however, the speed of the device degrades significantly. The increased incident optical power results in an increase in SNR and LDR of the device due to an increased photocurrent. The 3dB bandwidth was also calculated for varying Sn concentration and intrinsic layer thickness. The calculated result shows a 3dB bandwidth of > 26.2 GHz at −3V. All the calculated results show that the proposed device has significant potential applications in the MIR range. [ABSTRACT FROM AUTHOR]

Inspired by the recent progress of metasurfaces, a novel wideband and high-efficiency electronically reconfigurable transmitarray (TA) is presented that can enable two-dimensional (2-D) beam steering and multiple beam mode switching in a digital manner. The proposed unit cell consists of a reconfigurable anisotropic metallic resonator, which locates between a pair of orthogonally oriented subwavelength metal gratings. One-bit phase quantization is obtained by controlling the ON or OFF state of two positive-intrinsic-negative (p-i-n) diodes integrated on the anisotropic metallic resonator layer. To choke the radio frequency (RF) signal effectively, a bias layer is connected by the metallic via hole to the center of the resonator, where the electric field is minimal. The simulated results show that the proposed unit cell can achieve a low insertion loss of 1 dB from 9.3 to 10.9 GHz for two phase states. Then, the radiation performance of a 10 $\times\,\,10$ element array fed by a pyramidal horn antenna is theoretically calculated, simulated, and measured. The measured maximum gain is 19.1 dBi at 10.0 GHz with an aperture efficiency of 25.8% and a 3 dB gain bandwidth of 15.9%. The measured results demonstrate the 2-D beam scanning capability within the 50° range. [ABSTRACT FROM AUTHOR]

Polarization reconfigurable antennas at millimeter-wave (mm-wave) frequencies are important technologies for 5G and beyond wireless communications systems. This article presents an mm-wave multi-linear polarization (LP) reconfigurable antenna. It employs a resonant TM510-mode air-filled cavity as the base, and a circular array of slots is uniformly etched on its top surface to provide a rotationally symmetrical “excitation” for the multi-LP antenna. An upper substrate printed with engineered patch layers is introduced above the slots for an in-phase high-gain composition, and it is mechanically rotated to facilitate the multi-LP reconfiguration. Each slot radiation is separately monitored and analyzed by using single-slot cavity models. A final multi-LP antenna that can switch among five LP states at mm-wave band was constructed. To overcome the classic high sidelobe problem associated with circular arrays, a modified bottom layer is introduced to the multi-LP antenna. The measured overlapped bandwidth of the optimized multi-LP antenna ranges from 28.58 to 28.99 GHz. For all of the five LP states, the simulated and measured sidelobe levels are −13 and −10 dB, respectively. The measured realized gains are varied from 15.5 to 16.8 dBi in the overlapped operating bandwidth. This is the first time to report an mm-wave multi-LP reconfigurable antenna. [ABSTRACT FROM AUTHOR]

In this letter, a planar antenna withreconfigurable radiation pattern is investigated for smart Wi-Fi systems. The design incorporates one pair of folded dipoles, a microstrip-to-via feeding balun and two reconfigurable parasitic strips which are near-field excited by the dipole pair. By controlling the states of two Pin diodes embedded in two reconfigurable printed lines, the proposed antenna can switch between one omnidirectional mode and two unidirectional endfire radiation modes. This optimized antenna exhibits a decent size of 0.5 λ0 × 0.38 λ0 ×0.004 λ0 (where λ0 is free space wavelength at 2.45 GHz). Good agreement is observed between the simulated and measured results. The overlapped impedance bandwidth with |S11| < −10 dB for the three pattern modes is from 2.34 to 2.6 GHz in the measurement. Throughout the overlapping bandwidth, the front-to-back ratios are higher than 15 dB for the two unidirectional radiation modes and out-of-roundness is less than 1.2 dB for omnidirectional radiation mode. The measured peak realized gain of the proposed pattern-reconfigurable antenna is 6 dBi. This proposed Wi-Fi antenna is well poised for intelligent Wi-Fi communication systems. [ABSTRACT FROM AUTHOR]

Electrical and optical properties deterioration of P-GaN films under 150 keV proton irradiation were investigated. Through the Hall measurement method, as the irradiation fluence increasing, the carrier concentration of P-GaN films decreases from 1.23 $\times \,\,10^{{17}}$ to $-8.24\,\,\times \,\,10^{{16}}$ cm−3, and the carrier mobility change from 5.64 to 295.84 cm2/V/s. And through the circular transmission line model method, the sheet resistance and specific contact resistance for P-GaN films increased first and then decreased slightly under the proton irradiation. Radiation-induced $\text{V}_{\mathrm {N}}$ , $\text{Ga}_{\mathrm {i}}$ , $\text{V}_{\mathrm {Ga}}$ , and $\text{N}_{\mathrm {i}}$ were found to be responsible for the degradation of P-GaN films. It was confirmed that P-GaN has been transformed into N-GaN under the fluence of 1 $\times \,\,10^{15}$ p/cm2. The optical properties of the P-GaN films were characterized by examining changes in the photoluminescence spectrum. In addition, the electrical characteristics of Schottky barrier diode (SBD) and p-i-n diodes with the same structure (except for 0.5 $\mu \text{m}$ P-GaN of p-i-n diode) were used to study the effect of P-GaN degradation on electronic device performance. When P-GaN was transformed into N-GaN, p-i-n diodes lost the electrical characteristics of the p-n junction and the ${I}$ – ${V}$ curves of p-i-n diode are similar to that with SBD. [ABSTRACT FROM AUTHOR]

Integrated silicon microwave pin diodes are exposed to 10-keV X-rays up to a dose of 2 Mrad(SiO2) and 14-MeV fast neutrons up to a fluence of $2.2\,\,\boldsymbol {\times }\,\,10\,\,^{\mathrm{ 13}}$ cm−2. Changes in both dc leakage current and small-signal circuit components are examined. Degradation in performance due to total-ionizing dose (TID) is shown to be suppressed by non-quasi-static (NQS) effects during radio frequency (RF) operation. Tolerance to displacement damage from fast neutrons is also observed, which is explained using technology computer-aided design (TCAD) simulations. Overall, the characterized pin diodes are tolerant to cumulative radiation at levels consistent with space applications such as geosynchronous weather satellites. [ABSTRACT FROM AUTHOR]

In this letter, a wideband high-efficiency 1-bit 16 × 16 reconfigurable reflectarray antenna (RRA) is proposed. First, a wideband and low loss 1-bit RRA element is designed. It consists of double-layer patches printed on two dielectric substrates, respectively, forming a multiresonant behavior to expand the bandwidth.Due to the relatively thin thickness of the double-layer dielectric substrate (0.05 λ0), the element has low reflection loss. Therefore, the high efficiency and wide bandwidth performances can be obtained simultaneously. The phase difference between the two states of the RRA element is stable within 180 ± 20° in the frequency range of 12.9–16.5 GHz. Based on the broadband RRA element, a 16 × 16 RRA was fabricated and measured. Tested results show that the proposed RRA achieves 22.5% of 1 dB gain bandwidth and 25% of maximum aperture efficiency. [ABSTRACT FROM AUTHOR]