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Antennas using the active frequency selective surface (AFSS) can achieve fast beam‐scanning ability at a low cost. In this study, a switched beam antenna with a high gain and 360° coverage in the horizontal plane is proposed. Twelve columns of AFSS form a cylindrical cavity and are transmissive or reflective to the incident electromagnetic waves under the control of PIN diodes. Benefiting from a coaxial continuous transverse stub array placed at the cavity centre and using 4 units to generate a high gain omnidirectional radiation, the proposed antenna can realise a highly directive switched beam. An antenna prototype is designed, fabricated and measured. Results show that it achieves a |S11| < −10 dB bandwidth of 12.9% and is able to sweep its beam around the azimuth plane with a high gain up to 13.6 dBi at 5.8 GHz working frequency. [ABSTRACT FROM AUTHOR]

The radome absorber, always be defined as rasorber, is investigated based on the SiO $_{2{\text{f}}}$ /SiO $_{2}$ fiber-reinforced ceramic matrix composite (CMC) for high-strength environment. The prominent advantage of using CMC as the substrate is that it can significantly improve the power capacity and environmental tolerance of the rasorber. The surface roughness and the dielectric stability are considered key factors in the electromagnetic-material codesign. Silica sol is used to densify the surface of fiber CMC for screen printing, and the process is characterized by scanning electron microscopy. The passband can be controlled by integrating p-i-n diodes on the screen-printed silver paste. The equivalent ground condition for the bandpass reflector is theoretically analyzed, and ideal integration of absorbing and transmitting functions is achieved. Afterward, a CMC-based rasorber is manufactured. A dual-polarized transmission window at 1.6 GHz can be triggered, while a low radar cross section (RCS) band is designed from 2.7 to 4 GHz. Transmission and RCS characteristics of the CMC rasorber under 25–700 $^{\circ }$ C environment are both analyzed. The tensile, compressive, and flexural strength of the proposed CMC rasorber are tested, and the electromagnetic properties are verified using compact antenna test range. [ABSTRACT FROM AUTHOR]

Semi-analytical method for the determination of extrinsic and intrinsic model parameters for GaAs-based p-i-n diode is presented in this article. The main advantage is that the air-bridge interconnect inductance is regarded as an independent element and can be distinguished from the feedline effect. The detail model parameters extraction procedure is proposed, and the corresponding closed-form expressions are derived. Good agreement is obtained between the simulated and measured S-parameters up to 110 GHz to verify the validity of the approach. [ABSTRACT FROM AUTHOR]

The field effect diode (FED) is an attractive device to use in various digital and analog applications, but all previously proposed FEDs are based on the silicon-on-insulator (SOI) technology. In this article, a bulk version of FED (BFED) is proposed for the first time. Both SOI-FED and BFED are simulated using TCAD tools as a semiconductor drift-diffusion solver. The proposed bulk FED can operate as well as a regular SOI-FED. Most sensitive parameters in the design of the BFED are doping and thickness of $\text{p}^{+}$ -drain and $\text{n}^{+}$ -source. The effect of these parameters is investigated on the output characteristics of the BFED. [ABSTRACT FROM AUTHOR]

Miniaturized dual-band filtering switches are proposed in this article using multimode dielectric resonators (DRs). The planar printed circuit boards (PCBs) are utilized not only to construct the hybrid electromagnetic boundary for quad-mode DR, but also to offer the switchable multimode feeding structures with the p-i-n diodes. When the diodes are reversely biased, all the four modes are excited simultaneously by the mixed electric and magnetic couplings and controlled flexibly to construct the dual-band response. In this manner, extra losses from diodes are avoided, and low-loss transmission is realized. When the diodes are forward biased, all the four modes are shut off at the same time. Owing to the used mixed electric and magnetic couplings, the isolation is enhanced further by the cancellation of the electric and magnetic couplings between the feeding line and the resonant modes. For demonstration, both dual-mode and quad-mode filtering switches with dual-band operations are fabricated and tested. With only one quad-mode DR, high performance, including low-loss dual-band transmission and high-level isolation, is observed in the measurement, making the proposed switches promising in high-standard multiband time division duplex (TDD) systems. [ABSTRACT FROM AUTHOR]

In this article, a novel silicon carbide double-trench MOSFET with an integrated fully depleted P-base MOS-channel diode is proposed and investigated by calibrated TCAD simulations. The proposed silicon carbide (SiC) MOSFET features a fully depleted P-base region achieved by shrinking the source trench mesa in the ${z}$ -direction. Due to the significantly reduced conduction band energy in the fully depleted P-base region, a low potential barrier for electrons to flow through the JFET region to the N+ source region is formed. As a result, the proposed SiC MOSFET not only exhibits more than three times lower diode cut-in voltage than the body p-i-n diode but also successfully eliminates the bipolar degradation issues. Besides, a compact model based on Poisson’s law is developed to understand the origin of the barrier lowering effect. Calibrated TCAD simulation results indicate that the enhanced third quadrant performance would not comprise the other electric characteristics, which makes the proposed SiC MOSFET a highly promising candidate for high-frequency power applications. [ABSTRACT FROM AUTHOR]

The present state-of-the-art of junction-based diamond electronic devices is limited by the challenges inherent to the synthesis of n-type layers, where the dopant itself forms defect complexes that are donor compensating centers. Recently, the fabrication of diamond Schottky p-i-n diodes (SPINDs) by chemical vapor deposition (CVD) of intrinsic diamond films followed by an n-type layer on p-type diamond substrates has been reported to demonstrate excellent diode-like behavior with high rectification factors and surface barrier height at elevated temperatures. However, due to the ultrawide bandgap of diamond and small contact area of the devices, it is challenging to characterize the defect centers that limit the performance of the SPINDs using conventional capacitance transient spectroscopy. In this article, we report the characterization of defect centers in the diamond SPINDs with a contact area of 280 $\mu \text{m}\,\,\times \,\,280\,\,\mu \text{m}$ using current transient spectroscopy (CTS), which measures thermally induced emission rates from trap centers through change in device current instead of junction capacitance. The CTS scans in the temperature range 80–800 K revealed the presence of five trap-related peaks. Results from density functional theory (DFT) calculations were used to identify the nature of the traps. While most of the detected traps were identified to be vacancy complexes coupled to phosphorus and hydrogen impurities, one trap has been identified as single carbon vacancy. Most of the phosphorus-related defect complexes were observed to be in neutral and/or negative charge states and were identified as acceptor-like states. [ABSTRACT FROM AUTHOR]

The concept of “coding metasurfaces” was first put forward in 2014 and has developed rapidly during the past few years, originating several intriguing ramifications. The essential underlying idea is to discretize the local geometry, constitutive parameters, and electromagnetic (EM) responses (e.g., the phase, amplitude, and polarization) so that they can be represented via sequences of digits (e.g., “0” and “1”). This concept breaks the boundaries between traditional analog and digital devices, bridging the physical and information worlds, and opens up new perspectives in the design of metasurfaces. [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]

This article presents the design, fabrication, and characterization of an active electromagnetic shield intended to dynamically protect optical and electromagnetic sensors against high intensity radiated fields. The shield exhibits high and constant optical transparency level over the entire visible light spectrum thanks to a micrometric mesh metal thin film printed on a glass substrate. The central micrometric mesh area is separated from the peripheral ground plane of the shield by a peripheral slot. This slot is fitted out with p-i-n diodes and resistors, connecting electrically the central micrometric mesh area and the ground plane. The aim of these components is to dynamically control the shielding effectiveness of the screen, by using the conducting (on) or blocking (off) states of the p-i-n diodes. Accordingly, the shielding effectiveness can be set at high level to protect the system against high intensity radiated fields, and conversely at low level to both prevent system electromagnetic self-perturbation and increase the sensitivity of the internal electromagnetic sensors. Dynamic control of the shielding effectiveness of the fabricated screen, whose optical transparency is close to 85% over the entire visible light spectrum, is fully demonstrated. A shielding effectiveness contrast ranging from 5 dB to 24 dB between the on and off diode states was measured in the 2–10.5 GHz frequency range in a reverberation chamber. [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]

A novel differential-fed dielectric patch (DP) antenna with beam steering capability is investigated in this communication. The TEmn mode in the DP resonator is theoretically analyzed to provide guidance for the subsequent antenna design. The high-order TE12 mode that can be differentially excited is selected as the operating mode to further enhance the gain. Based on this, three parallel coupling slots loaded with p-i-n diodes are used as a beam steering structure. By controlling the ON-/OFF-state of the p-i-n diodes to change the $E$ -field distribution of the TE12 mode, the main beam can be switched to five directions. The measured gain of each state is higher than 7 dBi, and the peak value reaches 8.1 dBi. The beam steering structure and differential-fed scheme show good coordination, which effectively suppresses the deterioration of cross-polarization caused by structural asymmetry. The cross-polarization of each state is lower than −26 dB. To further verify the scalability of the proposed ideal, a 1 $\times $ 4 array fed by two dual Marchand baluns is implemented, which well maintains the beam steering capability and low cross-polarization. Reasonable agreement is obtained between the simulated and measured results. The proposed DP antenna provides a suitable candidate for indoor wireless communication. [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]

A 2-bit double layer design structure with a tricharacteristic multifunction response is presented. The top layer incorporates resistive loop printed on the FR4 dielectric material. The bottom layer is an active multifunction design that comprises dipole elements etched on the F4BME dielectric material. The design employs polarization inversion and switching characteristics between the transmission, reflection, and absorption properties. The binary coded state “ $00$ ” furnishes transmission to the dual polarized plane wave around 2 GHz frequency and absorption peak at 4.2 GHz frequency. The fractional bandwidth, calculated at $-3$ dB, of this transmission band is 77%. The binary coded state “ $11$ ” furnishes reflection to dual polarized plane wave at low frequencies around 2 GHz and absorbs a higher frequency plane wave with absorption peak at 3.2 GHz. The binary coded states “ $01$ ” and “ $10$ ” control polarization inversion between the transmission, reflection, and absorption at the same frequencies selected by “ $00$ ” and “ $11$ ” binary coded states. A prototype of the proposed design structure with $20 \times 20$ elements is fabricated. Measurement of the S-parameters shows that the behavior of the prototype can be controlled by dc voltage fed to p-i-n diodes. The measured results affirm the credibility of the proposed design. [ABSTRACT FROM AUTHOR]

The design of a 64-QAM I/Q modulator based on load modulation is presented. The modulator is designed to operate at 3 GHz. In any standard M-QAM modulation, the RF circuitry of the voltage source generates currents on the antenna corresponding to the transmitted signals. With load modulation, the waveforms of the M-QAM constellation points are generated by changing the internal parameters of the load modulator connected to the antenna. At the same time, the voltage source is kept constant. Thus, the power amplifier amplifies a constant signal all the time and does not need to operate in the back-off region. An optimization algorithm is developed to find the design parameters of the load modulator circuit. The design parameters obtained from the algorithm have been used in the advanced design system (ADS) software to design, simulate, and fully characterize the RF load modulator circuit. The hardware prototype of the load modulator circuit is realized using microstrip lines and a diode-based switching circuit. The measurements show that the load modulator can generate outputs on the $S_{21}$ -parameter complex plane matched to the 64-QAM constellation diagram. A microcontroller is programmed to serve the required bias voltages to the p-i-n diodes in the load modulator based on a predetermined lookup table (LUT). The proposed architecture does not require a digital-to-analog converter (DAC). A credible agreement between the simulation results and measurements is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a dual-polarized bidirectional electronically reconfigurable beam-steering array (DBSA) for the first time, which integrates the beam-scanning capabilities of both dual-polarized reconfigurable transmitarray and dual-polarized reconfigurable reflectarray. First, a novel phase and direction reconfigurable dual-polarized element is proposed. Four PIN diodes are soldered onto the symmetric transmitting patches to tune the 1-bit transmission phase, while two PIN diodes are soldered onto the reflecting patches to tune the 1-bit reflection phase. By controlling the states of the PIN diodes, the DBSA element can achieve 1-bit reconfigurable phase in both transmission and reflection modes. Second, based on the proposed element, a 100-element DBSA prototype is fabricated and measured. At dual-polarization, the angles of the scanned beams can reach 45 ∘ and 222 ∘ in forward- and backward-spaces. Therefore, the proposed novel method opens a new avenue to designing a dual-polarized electronically reconfigurable spatially fed array antenna with full-space beam-scanning capabilities, and the proposed design is suitable for dual-polarized bidirectional wireless communication applications. [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]

High-voltage p-i-n diodes for space applications are sensitive to single event burnout (SEB), which may cause the failure of the entire electronic system. This article describes the SEB failure mechanism of high-voltage p-i-n diodes with field limiting rings (FLRs) termination structure, based on the electro-thermal coupled transient simulation model in the Sentaurus TCAD simulator. The simulation results show that the catastrophic failures result from the intense local heating at the edge of the main junction, because the high electric field strength at this region induces strong impact ionization of the charge carriers. The strike at the edge of the main junction shows the strongest sensitivity to SEB since the energetic particle-induced carriers are deposited exactly at the high electric field region. Then, a novel SEB hardening technique of localized carrier lifetime control at the edge of the main junction region is proposed based on the analysis on the failure mechanism. Our simulation results demonstrate that the reduction of the localized carrier lifetime can alleviate the peak electric field and reduce the local heat accumulation, thereby improving the SEB performance of high-voltage p-i-n diodes. [ABSTRACT FROM AUTHOR]

A diamond Schottky p-i-n diode (SPIND) with the highest reported current density to date of ~116 kA/cm2 is demonstrated, carrying a total current of ~1.32 A through a $50-\mu \text {m}$ wide pseudo-vertical diode structure. The diamond SPIND also provides a maximum power handling capacity of ${1.85}~ \text {MW/c}\text {m}^{{2}}$ and a low specific ON-resistance ${R}_{ \mathrm{ON}}S$ of ${0.05}~ \text {m}\Omega \cdot \text {cm}^{{{2}}}$ at a forward bias of ~16 V. The diamond Schottky p-i-n (SPIN) diode also shows excellent rectification characteristics with a current ON– OFF-ratio of $\sim {6} \times {10}^{{12}}$. An analytical model including thermionic emission and space charge limited (SCL) current is presented together with Silvaco ATLAS Technology Computer Aided Design (TCAD) simulations to accurately reproduce the experimental ${J}$ – ${V}$ characteristics using multiple single-trap levels and other physical models emulating a real device. Theoretical calculations from the analytical model show that further improvement in the device turn on voltage and ${R}_{ \mathrm{ON}}{S}$ can be achieved by reducing the defect density and contact resistance in order to approach the ultimate performance in the Mott–Gurney SCL current regime. [ABSTRACT FROM AUTHOR]

Usually, Radar signature of an object is reduced using microwave absorber surface. Recently, another approach based on time‐modulated frequency‐selective surfaces has been developed to deceive Radar detection by selectively generating harmonics/sidebands. Here, a polarization‐insensitive time‐modulated frequency‐selective surface is proposed that works over a broad frequency range. The design employs a PIN diode‐based switchable frequency‐selective surface to switch between the two states of reflection coefficient. Monochromatic incident electromagnetic (EM) wave, upon reflection from the surface is modulated by a periodic time‐varying reflection coefficient to generate several harmonics/sidebands along with the incident frequency. In the frequency spectrum of the reflected EM wave, the power of the incident frequency component is suppressed below that of the sidebands. The time‐modulated frequency selective surface has the capability to suppress the incident frequency component for any incident EM wave in 2–4 GHz that is S band, as well as generate spurious reflection sidebands. [ABSTRACT FROM AUTHOR]

An electrically small, planar, frequency-agile, beam-switchable Huygens dipole antenna is investigated in this article. The near-field resonant parasitic (NFRP) design incorporates an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL) that function as the electric and magnetic NFRP elements, respectively. A varactor diode is integrated into each of these NFRP elements to facilitate simultaneous tuning of its operating frequency and switching its main beam direction. By changing the capacitance values of these two varactor diodes, the antenna realizes two independent, antipodal, unidirectional endfire radiating states with similar realized gain (RG) and front-to-back ratio (FTBR) values within virtually the same frequency-agile ranges. The experimental results demonstrate that the developed antenna exhibits a 5% frequency-agile fractional impedance bandwidth in both of its two oppositely directed endfire states. The antenna is electrically small at the highest frequency of this bandwidth (${ka}_{high} < 0.86$) and has measured relatively high radiation efficiency (RE >67.7%), peak RG (2.1–3.19 dBi), and FTBR (5.61–13.4 dB) values, together with stable and uniform radiation patterns, over this frequency-agile range. [ABSTRACT FROM AUTHOR]

The effect of radiation damage on the minority carrier lifetime in the 4 H‐SiC epilayers forming the n‐base of the power p–i–n diodes is presented. Irradiation with fast neutrons and MeV protons is used for uniform and local lifetime reduction. Deep‐level transient spectroscopy in combination with open‐circuit voltage decay measurement shows that the carrier lifetime is reduced by increased carrier recombination on Z1/Z2, EH3, and possibly RD4 levels. The lifetime degrades swiftly and the ON‐state carrier modulation capability of high‐voltage devices can be easily lost already at very low fluences. The results further show that the proton irradiation provides an excellent tool for local lifetime tailoring. The carrier lifetime can be easily set by proton fluence and localized by proton energy. The proper local lifetime reduction speeds up diode recovery without an undesirable increase in the forward voltage drop. However, attention must be taken to properly locate the damage maximum so as not to increase device leakage. [ABSTRACT FROM AUTHOR]

This article investigates the reliability issues of silicon carbide (SiC) merged p-i-n Schottky (MPS) diodes. Aiming at the current imbalance issue in surge event and electric field crowding issue under avalanche shock for MPS diodes, plasma spreading layer (PSL) structure is proposed and its performance in alleviating such issues are studied via simulation and experiments. From the simulation, the PSL structure can provide an interconnection between P+ hexagonal islands and P+ rings, and allow bipolar current to spread from the wide P+ region to the other parts of the device during the surge pulse. Under avalanche shock, the PSL structure can relieve the electric field crowding at the corners of the P+ hexagonal island/ring. In both cases, it can relieve the current crowding issue and increase the effective energy dissipating area. It is demonstrated by the experimental results that adding PSL structure can improve both surge and avalanche reliability. Different configurations of PSL (i.e., P+ cross lines and P+ diagonal lines) are studied. The P+ cross-line configuration is proved to have ~20% improvement in surge capability, and the other one achieves ~11% improvement in avalanche capability. The PSL concept can also be applied to optimizing P well/P+ layers in SiC MOSFET for its robustness enhancement. [ABSTRACT FROM AUTHOR]

This article presents a fully integrated terahertz (THz) comb/pulse radiator and a broadband frequency-comb heterodyne receiver for sensing and imaging applications. The chipset is fabricated in the GlobalFoundries 90-nm SiGe BiCMOS process. The comb radiator utilizes p-i-n diode sharp reverse recovery to generate THz frequency comb/pulses. The repetition rate of the radiated pulses is locked to a stable off-chip source, which can be adjusted to as high as 15 GHz. By using a low-phase noise off-chip source rather than an on-chip oscillator, low phase noise and high-frequency stability are achieved. The phase noise of 405-GHz tone is −82 dBc at a 10-kHz offset frequency. The radiated tones are characterized from 220 GHz up to 1.1 THz using VDI SAX modules with the measured EIRP of −11, −15, and −36 dBm at 405, 500, and 750 GHz, respectively. In addition, a THz frequency comb detector using a Schottky barrier diode passive mixer is presented. The detector uses a broadband comb as LO for heterodyne detection of any arbitrary spectrum in mm-wave/THz band by adjusting the spacing of the LO comb from 100 s of MHz up to 15 GHz with a resolution of 2 Hz. The receiver chip is characterized from 220 up to 500 GHz with the measured NF of 24.5, 36, and 44 dB at 270, 405, and 495 GHz, respectively. Moreover, a dual-comb technique using the radiator and receiver chips is demonstrated, promising a compact low-cost solution for dual-comb sensing applications. The radiator and receiver chips consume a dc power of 40 and 38 mW, respectively. [ABSTRACT FROM AUTHOR]

A continuously tunable true-time-delay phase-shifter topology based on switchable varactor-tuned transmission lines is presented. By introducing p-i-n diodes to switch different varactor-tuned transmission lines, the phase shift tuning range can be doubled compared with the conventional design, which results in 50% size reduction. For verification, two cascaded four-unit and eight-unit microstrip phase shifters are designed and fabricated on a 0.787-mm-thick Rogers RT/Duroid 5880 substrate with $\varepsilon _{r} =2.2$ and tan $\delta =0.0009$. The measured microstrip phase shifts of the four-unit and eight-unit phase shifters are about 107° and 191° at 4 GHz, respectively, with insertion loss of less than 2.4 and 3.6 dB. The return loss is better than 15 dB from 0.5 to 4.65 GHz for all states. [ABSTRACT FROM AUTHOR]

A switchable polarisation conversion/in‐phase reflection metasurface (PCIPR‐MS) based on a Pin diode is proposed in this study. By changing the working state of the Pin diode, the PCIPR‐MS can be used as a polarisation conversion metasurface (PCM) and an artificial magnetic conductor (AMC), respectively. Furthermore, the designed PCIPR‐MS can be arranged into a checkerboard surface to integrate with the antenna, which means that the PCIPR‐MS can be flexibly switched to control the radiation and scattering characteristics of the antenna in a time‐sharing manner. The simulation results show that the 3‐dB axial ratio (AR) bandwidth is 4.31 to 6.14 GHz (35%) with the application of the AMC as the metal ground plane of the antenna in the radiation state, and the right‐hand circularly polarised (RHCP) gain is enhanced by more than 1.5 dB from 4.65 to 5.80 GHz in a low‐profile compared with the reference antennas. By using the PCM, phase cancelation is achieved in the scattering state of the antenna to realise the low‐RCS characteristics. [ABSTRACT FROM AUTHOR]

Phase switched screen (PSS) has been proposed for more than two decades for its applications on radar cloaking. However, the PSSs in most publications need a thickness of one-quarter wavelength to realize perfect cloaking at the operating frequency of the incident radar-detecting wave, which seems too thick for engineering. In this article, a new design of the dual-band artificial magnetic conductor (AMC) is proposed in which the electromagnetic band gaps are shifted among two bands by adjusting the biasing current on the four p-i-n diodes. By controlling the states of the diodes between on and off, the in-phase reflection frequency of the AMC can switch from 2.5 to 5.3 GHz. Based on the AMC structure above, a potential dual-band PSS is realized through different switching schemes and, therefore, achieves good stealth effects during the two bands above. [ABSTRACT FROM AUTHOR]

This article presents a simulation model of silicon carbide (SiC) power MOSFET that accurately predicts both the static and dynamic third-quadrant behavior without compromising the first-quadrant's accuracy. Unlike existing models, this model features an asymmetric third-quadrant behavior for MOSFET characteristics necessary for the accurate synchronous rectifier simulations. Moreover, it includes the gate-dependent body diode behavior, essential for the accurate prediction of freewheeling high-side device behavior in half-bridge configurations with significant gate voltage oscillation. The model also includes reverse recovery characteristics for the accurate overshoot and power loss prediction. Despite having these added features, the model demonstrates good convergence and efficiency due to the replacement of conditional piecewise equations with continuous ones consisting of weighted variables. The model's convergence capability and efficiency have been verified by simulating a five-level cascaded H-bridge multilevel inverter. The model's superior efficiency and accuracy have been validated by comparing it with an established SiC power MOSFET model. Also, an easy-to-follow parameter extraction procedure is documented that only requires data commonly available in commercial datasheets for broader utility. Considering accuracy, efficiency, and convenience, the model is useful for all power electronics converter applications. [ABSTRACT FROM AUTHOR]

This article introduces a multifunctional polarization insensitive frequency selective rasorber (MF-FSR) comprised of periodic metallic patterns printed on two dielectric substrates and separated by an air-spacer. The novelty of the proposed MF-FSR lies in its combined feature of mode switching and frequency tuning characteristics. This uniquely offers a real-time and multifunctional capability to switch from “rasorber mode (FSA-T)” into an “absorber with notch band (FSA-N)” mode where both modes support continuous tunability of their “transmission” or “notch” band. By controlling the reverse bias voltage of the embedded varactor, the transmission band in FSA-T mode can be tuned from 3.76 to 4.26 GHz with a very low insertion loss in the range of 0.62–0.95 dB. In complementary FSA-N mode, the notch band is also tunable from 4.17 to 4.71 GHz. Moreover, the same varactor set can control the tuning of transmission or the notch band depending upon MF-FSR’s basic state of operation which is further independently controllable by the p-i-n diode. Equivalent circuit models are also thoroughly examined. Finally, a prototype is fabricated and experimentally tested, showing a good agreement with the predicted results. [ABSTRACT FROM AUTHOR]

The open-circuit voltage decay (OCVD) method is a well-known technique for conducting electrical measurements of carrier lifetime: the main advantages lie in the simple setup and the possibility of carrying out measurements in commercial devices without the need of removing the package, as for optical methods. Despite several researchers having reported carrier lifetimes measured by the OCVD method in different devices, there has been little discussion about the potential effect of the experimental setup on the obtained results. By comparing the outputs of the experimental measurements with those of numerical simulations, this study investigates the overlooked effect of the OCVD measurement setup on the former. Due to the growing importance of SiC-based devices, the analysis is applied to a 4H-SiC p-i-n diode. Two main points are addressed: 1) the effect of circuit setup on the ambipolar lifetime is discussed and a method, originally developed for improving the estimate of low-level carrier lifetime in OCVD measurements, is used to correct the measured lifetime for this influence; 2) the origin of the local minimum eventually appearing in the lifetime versus time curves is also investigated. It is found that the minimum can also be related to the time constant of the experimental setup, giving rise to doubts about the usual interpretation of this minimum as the minority carrier lifetime. A method is thus proposed to help discriminate between the two interpretations. [ABSTRACT FROM AUTHOR]

A novel active frequency selective surface (AFSS) is proposed in this communication which not only can achieve electromagnetic (EM) switching between the transmission and absorption modes but also has the capability of dynamically modulating the amplitudes for the above two modes. The designed AFSS consists of a periodic metallic structure layer and a graphene capacitor layer. The periodic metallic structure plays the role of the EM switching for the mode selection of transmission/absorption by regulating the bias states of the loaded p-i-n diodes, while the corresponding amplitudes of the transmission/absorption can be further tuned by changing the effective sheet resistance of graphene through an electrostatic field bias. An equivalent circuit model is introduced to explain the EM switching and amplitude tuning behaviors of transmission/absorption. In addition, the designed AFSS is also demonstrated to perform well under circumstances of oblique incidence and different polarizations. The AFSS prototype is fabricated and measured. In the transmission mode, the transmission loss can be tuned from −4.8 to −1.1 dB at the band of 6–7 GHz, while in the absorption mode, the average value of absorptivity can be controlled between 0.65 and 0.95 at the band of 5–8.4 GHz. The measurement results agree well with the simulation ones, which demonstrate the great performance of our AFSS. [ABSTRACT FROM AUTHOR]

A novel approach to inactivate the body p-i-n diode of silicon carbide (SiC) MOSFET is proposed in this article. It features a normally-OFF JFET structure embedded medially between the two p-well regions in the z-direction. When the SiC MOSFET operates in the first quadrant, the normally-OFF JFET is pinched-off, guaranteeing the excellent fundamental performance of the SiC MOSFET. While when the SiC MOSFET serves as the freewheeling diode, the channel of the normally-OFF JFET is turned on, which provides a unipolar current conduction path with low cut-in voltage, thereby inactivating the body p-i-n diode. TCAD simulation results show that, in comparison with the double trench SiC MOSFET, the cut-in voltage and the reverse recovery charge of the proposed SiC MOSFET could be reduced by 51.6% and 52.2%, respectively. [ABSTRACT FROM AUTHOR]

This article proposes a novel inverted-E topology for the design of phase shifters and multibit phase shifters. The novel phase shifter consists of a 50 Ω main transmission line (MTL) symmetrically loaded with equally spaced three open-/short-circuited stubs via P-I-N switching diodes. The stubs provide the needed susceptances to achieve a phase shift with large value range. Thanks to the design flexibility of the topology, 2N-1 sets of stubs can share the same MTL, providing 2n phase states of an N-bit phase shifter. Design theory and performance analysis of the design variables are presented, followed by the analysis and simulation of four 22.5°, 45°, 90°, and 180° phase shifters. For validation and comparison, two typical 45° and 90° phase shifters and a 3-bit phase shifter, providing eight distinct phase states, have been fabricated and measured. The measured results show good agreement with analysis and simulation. In comparison to its traditional counterparts, the novel design yields a highly compact phase shifter because the separation between the loading elements on the MTL can be less than quarter wavelength, whereas low insertion loss is achieved because the diodes are loaded to the branches. In addition, multibit phase shifter in single unit can be realized with much shorter length and lower insertion loss. [ABSTRACT FROM AUTHOR]

The temperature dependence of the electron and hole impact ionization coefficients in GaN has been investigated experimentally. Two types of p-i-n diodes grown on bulk GaN substrates have been fabricated and characterized, and the impact ionization coefficients for both electrons and holes have been extracted using the photomultiplication method. Both the electron and hole impact ionization coefficients decrease as the temperature increases. The Okuto–Crowell model was used to describe the temperature dependence of the electron and hole impact ionization coefficients. Based on the measured impact ionization coefficients, the temperature dependence of the breakdown voltage of GaN non-punch through p-n diodes can be predicted; good agreement with experimentally reported results is obtained. [ABSTRACT FROM AUTHOR]

A novel wide-angle and broadband rasorber is presented incorporating several advances. To broaden the bandwidth, we introduce a new type of frequency selective surface (FSS) in the bottom layer of the rasorber. This strategy increases the upper and lower absorption bandwidths while reducing the insertion loss at transmission window. Furthermore, a new top resistive layer is proposed via the loading of electric field coupled resonator elements on a cross-dipole structure. The proposed design offers both, an angularly stable performance and a thin structure that can be fabricated on a single dielectric substrate. To enable switchability, p-i-n diodes are employed and a reconfigurable rasorber/absorber is designed where a new concept of “lossy/lossless” top layer is investigated and established as the best choice among other switchable designs. Equivalent circuit models are constructed for both active and passive designs to provide physical insight into their operation. Finally, to enable deployment of the rasorber over curved geometries, these advances are incorporated into a conformal structure. Three separate prototypes are fabricated and good agreement is obtained between design predictions and experimental results. [ABSTRACT FROM AUTHOR]

A low profile circularly polarized (CP) antenna with reconfigurable polarization is designed and presented, which can radiate omnidirectional patterns that can be switched between left‐hand circularly polarized (LHCP) and right‐hand circularly polarized (RHCP). A pair of arc‐shaped complementary dipoles is acted as reconfigurable elements by bridging four pin diodes at the dipole arced arms. A meander phase shift line is employed to connected the arc dipole arms and plate cavity to adjust the phase relationship of two sources. The proposed antenna exhibits the omnidirectional radiation pattern by combining six identical elements placed in a circular array configuration. 24 p‐i‐n diodes are exploited to six elements, by manipulating the dc bias voltage across the diodes, the polarization state of the antenna can be switched. The patterns of the antenna are similar to that of a dipole, but its size is only about Φ0.87 × 0.029λ0 at 5.8 GHz. The overlapped bandwidth of measured 3‐dB axial ratio (AR) and 10‐dB return loss is 5.724‐5.87 and 5.738‐5.91 GHz for two polarization states, which are right on the target of ISM band. It can be well adapted to medical diagnosis systems. [ABSTRACT FROM AUTHOR]

In this article, the ON-state performance limits of 4H-silicon carbide (SiC) IGBTs in field-stop technology are theoretically estimated for the first time and compared against silicon counterparts. The theoretical analysis is based on static modeling of a high-current p-i-n diode and the calculation results are examined with TCAD simulations. Owing to conductivity modulation effect, the ON-state losses of 4H-SiC IGBTs do not show any significant increase with the increase in breakdown voltage (BV). However, the large built-in potential of SiC poses an inherent limit on the reduction of ON-state voltage drop. Compared with 4H-SiC IGBTs, the silicon-based IGBTs exhibit superior ON-state performance limits within the BV range considered, although their drift layer thicknesses are ten times higher than that of 4H-SiC IGBTs. Therefore, silicon IGBTs remain as efficient technologies for enhancing high power conversion efficiency. [ABSTRACT FROM AUTHOR]

In this article, a fully reconfigurable frequency selective rasorber (FR-FSR) is presented. To establish systematic design guidelines, initially the conditions for full reconfigurability are derived. Then, a specific equivalent circuit model (ECM) is proposed which satisfies all the derived conditions. The circuit model is separately simulated to verify the proposed concept and further extensively analyzed to provide an in-depth design methodology for all three modes of operation. The ECM is further synthesized into a simple planar structure to obtain the design of the rasorber. In the proposed rasorber, both layers are independently reconfigurable with p-i-n diodes embedded in the top layer and varactors in the bottom layer, all symmetrically mounted to achieve polarization insensitivity. P-i-n and varactor diodes are seperately operated to achieve the desired mode of operation with minimum insertion loss. A simple and efficient bias network is proposed in such a way that it does not affect the performance of the rasorber. The sample prototype is also fabricated and experimentally tested where a good agreement between simulated and measured result is obtained. [ABSTRACT FROM AUTHOR]

This article reports trap-related forward conduction instability of GaN quasi-vertical p-i-n diodes grown on a Si substrate. Three hole traps with activation energies of 0.38, 0.60, and 0.70 eV together with one electron trap with an energy level of 0.26 eV under the conduction band were revealed by deep-level transient spectroscopy (DLTS). Pulsed I – V measurements were performed on a device whose traps were prefilled. The rest time durations and OFF-state bias levels and periods were varied to investigate the forward I – V recovery phenomenon, which was highly correlated with the carrier detrapping process inside the device. The detrapping process could be greatly accelerated by a reverse bias or a lifted temperature. An “on-the-fly” resistance characterization was carried out to study the time-dependent carrier release process using short positive voltage pulses. The device was further submitted to switch-on transient assessment to investigate the time-resolved dynamic RON evolution. The initial dynamic RON ratio was proportional to the reverse bias level and duration and was gradually decreased after continuous carrier injection until the trapping effects were overwhelmed. With a forward voltage slightly higher than the threshold voltage, it took dozens of milliseconds for the dynamic RON to be equal to its static counterpart. It was found that at 350 K, the ON-resistance ratio could reach unit more rapidly than the room temperature case, indicating mitigation of current collapse of p-i-n diodes and their great potential for high-temperature switching applications. [ABSTRACT FROM AUTHOR]

A novel resistance model of silicon-carbide-merged p-i-n Schottky diodes is presented in this article. With this model, the device characteristics and power dissipation can be predicted. The ON-resistance in the three operating modes, namely, unipolar, low-injection, and high-injection modes, is calculated. In the unipolar and low-injection modes, the effect of temperature on carrier mobility and conduction angle are added to the factors that need to be considered, whereas the influence of current density is considered in the high-injection mode. The carrier distribution in the high-injection mode is analyzed and applied to determine the resistance. And this resistance model is applied to the research of a forward characteristic model. The model is verified experimentally via the comparison of the calculated and measured characteristics. The experimental results prove that the model can not only predict the resistance in each working mode, but also accurately predict the forward current and voltage characteristics. [ABSTRACT FROM AUTHOR]

In this article, the avalanche capability of the 1.2-kV 4H-SiC junction barrier Schottky (JBS) and merged p-i-n Schottky (MPS) diodes is investigated through simulation and experiments. For MPS diodes, the width of the wide P+ region (W) is found to have great effects on the device avalanche capability. MPS diodes with varied W-values (3–20 μm) and JBS diode are designed and fabricated, and their avalanche energy/current capability is tested with unclamped inductive switching tests. The experimental results show that the MPS diode has an optimized avalanche capability at W = 8 - μm design. Simulation study reveals that the avalanche current is mainly distributed at the edges of the P+ regions in the JBS/MPS diodes as a result of the curvature-effect-induced electric field crowding. The localized current crowding and unbalanced current distribution in the avalanche mode contribute to a reduced effective power dissipation area and a weaker avalanche capability. The current nonuniformity coefficient (k) is used to characterize the severity of the current unbalance, and it is found that k declines as W increases when W = 3−8~μm and then gets increased when W exceeds 8~μm. Both the experimental and simulation results indicate that the MPS diode is superior to the JBS diode in avalanche capability, and the width of the wide P+ region in the MPS diode has an optimal design (8~μm in this article) which corresponds to the alleviated current crowding issue and 9%–19% improvement of the avalanche capability. [ABSTRACT FROM AUTHOR]

We demonstrate edge termination for vertical GaN p-n diodes using step-etched triple-zone junction termination extension (JTE). The technique was found to yield high breakdown efficiency without degradation of forward characteristics. The electric field distribution at various JTE thicknesses was simulated, and the experimental results were well matched to the simulation results. The fabricated GaN p-n diode with step-etched triple-zone JTE shows a breakdown voltage of 550 V corresponding to a junction termination efficiency of 75%, with a turn-on voltage of 3.1 V, a specific ON-resistance of 1.3 mΩ ⋅ cm2, and leakage current at −200 V of 80 nA/cm2. The multistep JTE strategy demonstration could be important for future applications for multikilovolt-class GaN vertical power devices. [ABSTRACT FROM AUTHOR]

This article investigates the stability of hydrogenated amorphous silicon (a-Si:H) p-i-n junctions employed as temperature sensors in lab-on-chip (LoC) applications. The devices have been tested under forward current injection and different temperatures (from room temperature up to 90 °C) in order to reproduce the practical operating conditions. Two sets of devices with different diborane concentrations in the p-doped layer have been investigated as a case study. For both sets, a temperature-drift error of 0.05 °C/h and a sensitivity around 3 mV/°C in the range between 30 °C and 90 °C have been achieved. These results demonstrate the device suitability as a thin-film temperature sensor integrated into LoC systems that implement thermal treatment of the biological samples as, for example, DNA amplification. [ABSTRACT FROM AUTHOR]

To effectively analyze the electro-thermal characteristics of a semiconductor p-i-n diode in the microwave limiter circuit, a cosimulation algorithm of the time-domain impulse response technique and physical-model-based semiconductor solver is proposed in this article. The physical-model-based semiconductor solver algorithm is based on the drift diffusion model (DDM). First, the multiphysical field coupling equations of the drift diffusion model and heat conduction model are used to analyze the electro-thermal behavior of a semiconductor p-i-n diode. Second, the time-domain impulse response technique based on the field–circuit coupling algorithm is used to extract the time-domain impulse response at each port of the electromagnetic field structure. Finally, the time-domain impulse response is combined with the volt–ampere characteristic relationship of the physical-model-based p-i-n diode. As a result, an efficient computation of the time-domain electro-thermal coupling characteristics of p-i-n diode in the microwave limiter can be obtained. The simulation results are in good agreement with those by the commercial software (COMSOL). The computation time and the memory requirement of the proposed algorithm are significantly reduced when compared with COMSOL. [ABSTRACT FROM AUTHOR]

This article presents a pattern-reconfigurable saber-like antenna with low wind drag for the onboard communication application, under the requirement of upper hemispherical coverage. The compact antenna mainly consists of a segmented loop and a $\Pi $ -shaped polygon, which are closely integrated for compact size. By controlling the OFF/ON states of a p-i-n diode embedded in the segmented loop, the proposed antenna can be operated at dipole/monopole modes. An upper hemispherical coverage area can be achieved since broadside and omnidirectional patterns are obtained at dipole and monopole modes, respectively. To validate the design strategy, a prototype was fabricated and tested. A good agreement between the simulated and measured results is achieved. The measured −8 dB reflection coefficient common bandwidth of two modes is from 2.16 to 2.63 GHz with the relative bandwidth of 19.6% while keeping a smaller size of $30.5\times 32.5\times 0.6$ mm3 ($0.24\,\,\lambda _{0} \times 0.26 \lambda _{0}\times 0.005 \lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at the center frequency). We portend that the proposed design scheme, with merits of low wind drag, metal ground compatibility, and upper hemispherical coverage, has the potential for airborne application. [ABSTRACT FROM AUTHOR]

This communication presents the design, optimization, fabrication, and characterization of an electronically steerable transmitarray (TA) with 2 bits of phase quantization per unit cell. The proposed TA operates in linear polarization at Ka-band and is composed of $14\times14$ reconfigurable unit-cells. Four p-i-n diodes are integrated on each unit-cell to control the radiated field phase distribution across the TA aperture. The prototype demonstrates experimentally pencil beam scanning over a $120^{\circ } \times 120^{\circ }$ window, a maximum gain at broadside of 19.8 dBi, and a 3 dB fractional bandwidth of 16.2%. [ABSTRACT FROM AUTHOR]

In this article, we investigated the destructive behavior of the latest power diode when operating a hard-switching process. From the numerical simulation analysis, the destruction behavior originates in the enhanced impact ionization at the p-n junction on the anode side and current filament in the active region. A relaxing electric field on the anode side and a moderated electric field on the cathode side prevent the above-mentioned behavior. These improvements result from controlling the carrier-plasma layer in the n-buffer layer on the cathode side. This article demonstrates the effective n-buffer technology for the power diode that achieves superior dynamic robustness and high operating temperature over 448 K. [ABSTRACT FROM AUTHOR]

In this article, a trench-field-plate (TFP) high-voltage power MOSFET is proposed. Instead of using a conventional n− drift region, the TFP power MOSFET features benzocyclobutene dielectric in the sidewall of deep trenches in the drift region and a sloped field plate (FP) inside each of the trenches. The TFP structure employed in the drift region modulates the electric field in the OFF-state, resulting in a higher breakdown voltage (BV) than that of conventional power MOSFETs. Simulation results show that the specific ON-resistance of the TFP power MOSFET is approximately one-third that of the conventional power MOSFET and about 50% lower than that of the silicon limit for the same BV. In addition, compared with superjunction devices, the TFP power MOSFET is able to provide better reverse recovery characteristics, including a reduction in peak reverse recovery current (IRRM) and reverse recovery charge (QRR) by 24% and 37%, respectively. Moreover, a p-i-n diode employing the TFP structure is fabricated, which is essentially identical to a power MOSFET in the OFF-state, to demonstrate the BV characteristics. The fabricated TFP p-i-n diode has a BV of 522 V, which is 2.3 times that of a conventional p-i-n diode fabricated on the same substrate. [ABSTRACT FROM AUTHOR]

A p-i-n diodes-controlled radiation-pattern reconfigurable phased array for fifth-generation (5G) handsets is proposed in this article. The proposed beam scanning and switching hybrid system can significantly reduce the number of arrays and transmit–receive (TR) components when compared with multiarray systems while keeping the same spatial coverage. The array has wide working band from 24 to 27.5 GHz, which can cover the allocated 5G band for Europe. The four-element array is planar with a small clearance of only 4 mm, which is suitable for most of the current mobile phones. Each reconfigurable array element is fed by one shielded stripline and has three switchable radiation patterns: two broadside directions and one endfire direction. The beam switching is realized by applying two reconfigurable directors on both sides of the dipole, which also reduces the antenna profile. The directors are activated when the p-i-n diodes are at OFF mode, which minimizes the energy loss on the p-i-n diodes. The parasitic influence of the p-i-n diodes, the soldering process, and mobile environment are discussed in detail. The measured results show good agreement with the simulations. [ABSTRACT FROM AUTHOR]

In this report, a Ku-band, compact, polarization-reconfigurable, multilayered, wideband antenna is proposed. Two orthogonal linear polarizations can be realized by switching the ON-OFF state of four p-i-n diodes that are embedded into the polarization-reconfigurable coupling slots. The p-i-n diode switches and capacitors are installed in the middle layer of the microwave multilayer board to reduce their impact from the external environment, which improves the reliability and consistency of the antenna. Structure miniaturization of the antenna can be achieved by using a set of orthogonal cross gaps. The bandwidth and broadside gain characteristic of the proposed antenna can be significantly enhanced by employing a hollow-cavity substrate and stacked patches. A prototype of the proposed reconfigurable antenna has been fabricated and tested. The measured fractional impedance bandwidth is larger than 22.4% with the reference of |S11| &le; -10 dB. In addition, the polarization purity is better than 20 dB in both E- and H-planes. The measured gain versus frequency is stable and higher than 4 dBi within the operating frequency band. [ABSTRACT FROM AUTHOR]