Search

Theory and simulations predict the metamaterial-enhanced resistive wall amplifier (MERWA) may offer improvements to megawatt-level high-power microwave (HPM) amplifiers in terms of combined bandwidth and gain rates. A low-power proof-of-concept test prototype has been designed using a metamaterial (MTM) consisting of a linear array of periodically spaced thin lossy meandered wires. Direct simulations of these arrays of thin meandering wires using typical 3-D particle-in-cell (PIC) solvers are inaccurate, creating significant challenges for obtaining trustworthy hot test simulations of the prototype device. This work enables predictive PIC simulations of the experimental MERWA prototype by replacing the thin lossy wire structure with an equivalent effective-medium model. We find that a finite-width rod having an anisotropic Drude–Lorentz permittivity is a suitable model to replace the lossy wire MTM structure. We detail our modeling process and assumptions, fitting procedures, and model fitting results. The model is validated by comparing PIC simulations to experimental results.

We present the design and proof-of-concept demonstration of a dual-band reflectarray antenna capable of generating two beams at $X$ - and $Ku$ -bands, whose directions of maximum radiation can be set independently of each other. The reflectarray uses dual-band polarization-rotating (PR) unit cells with 1 bit phase quantization. The proposed unit cell provides independent phase shifts at two frequency bands by controlling a cluster of two orthogonal dipoles to operate as either +90° or −90° reflective polarization rotators. Two dipole clusters are interleaved in a unit cell and used to achieve dual-band operation. Simulation results of a unit cell designed to operate at $X$ - and $Ku$ -bands demonstrate independently controlled, dual-band PR operation over 16.1% and 20% bandwidths for the lower and higher bands, respectively. The dual-band unit cells were used to construct three different static reflectarray prototypes demonstrating the different ways where such independent phase control at the two bands of a dual-band reflectarray antenna may be advantageous. The three static reflectarray prototypes were simulated, fabricated, and experimentally characterized. Simulation and measurement results of these prototypes agree well and demonstrate independent phase shift control at the $X$ - and $Ku$ -bands over a relatively wide field of view without exciting grating lobes.

LaB6 has been used as a commercial electron emitter for decades. Despite the large number of studies on the work function of LaB6, there is no comprehensive understanding of work function trends in the hexaboride materials family. In this study, we use Density Functional Theory (DFT) calculations to calculated trends of rare earth hexaboride work function and rationalize these trends based on the electronegativity of the metal element. We predict that alloying LaB6 with Ba can further lower the work function by ~0.2 eV. Interestingly, we find that alloyed (La, Ba)B6 can have lower work functions than either LaB6 or BaB6, benefitting from an enhanced surface dipole due to metal element size mismatch. In addition to hexaborides we also investigate work function trends of similar materials families, namely tetraborides and transition metal nitrides, which, like hexaborides, are electrically conductive and refractory and thus may also be promising materials for electron emission applications. We find that tetraborides consistently have higher work functions than their hexaboride analogues as the tetraborides having less ionic bonding and smaller positive surface dipoles. Finally, we find that HfN has a low work function of about 2.2 eV, making HfN a potentially promising new electron emitter material.

We present a cylindrical, multibeam, modified Luneburg lens antenna. The proposed antenna features low-profile, good impedance match, high gain, and wide angle scanning capability. We tapered the thickness of a dielectric disk along its radius to achieve the required refractive index profile of the lens in a nondispersive fashion. Seventeen dielectric-filled waveguide feeds, arranged circumferentially around the focal arc of the lens, provide almost invariant azimuthal scanning in the range of ±60° from broadside direction. The lens and the interior of the waveguide feeds are made of the same dielectric material, offering a smooth impedance transition from the feed antenna to the lens. A prototype of the antenna was fabricated and characterized. Measured reflection coefficient is better than −10 dB from 14 to 16 GHz. The isolations between feeds remain higher than 24 dB over the entire operational frequency range. We measured a maximum antenna gain of 20.5 dB with only 1.5 dB gain loss near the maximum 60° scanning angle. The proposed high-gain, multibeam antenna design can be used in a wide range of applications including automotive and surveillance radars.

We present a new method for achieving 2-bit phase quantization for beam-steerable reflectarrays by exploiting four distinct reflection modes of a unit cell. Two of the four modes perform polarization-rotation (PR) operation while the other two are non-PR modes when the unit cell is illuminated by an $x$ - or $y$ -polarized incident wave. With a specific phase relation between the four reflection modes, the unit cell acts as a 2-bit phase shifter under illumination with an incident wave polarized along a diagonal direction of the square-shaped unit cell. The proposed operating principle was demonstrated with an illustrative unit cell consisting of three metallic layers and using four single-junction connections that can be replaced with single-pole single-throw (SPST) switches for reconfiguration. Simulation results predict an operating bandwidth of about 20% for the unit cell and a good beam scanning performance over a scan range of ±45° for a beam-steerable reflectarray constructed using this unit cell. Two static prototypes of the beam-steerable reflectarray antenna providing beam collimation at two different directions at 10 GHz were fabricated and experimentally characterized. Measurement results show good agreement with the simulation results, validating the proposed design approach for 2-bit reflective unit cells.

This study presents a beam-steerable antenna system that uses two mechanically-rotatable, phase-shifting surfaces (PSSs) functioning like a pair of Risley prisms for beam scanning operation at X-band. One of the PSSs also acts as a lens, performing beam collimation in addition to providing a phase shift gradient. Unit cells constituting the two PSSs were co-designed to determine the distance between the two surfaces that results in high transmission coefficients and small phase errors under different beam-scanning conditions. Both simulation and measurement results have verified that the distance of 2 mm provides the best performance regarding to peak gain. Prototypes of the PSSs having circular apertures with diameters of 11.5 λ 0 at 10 GHz were fabricated and illuminated by a feed antenna to characterise the beam scanning performance. The measurement results of the proposed antenna system demonstrate the capability to steer the main beam within a ± 60 ° scanning range with a maximum gain variation of less than 3.6 dB by rotating the two PSSs with respect to each other. The fabricated prototype provides side lobe levels less than − 13.1 dB , polarisation purity higher than 20 dB, and small beam pointing errors of no more than 1 ° in all examined beam scan scenarios.

We present a new low-profile, wideband, transmitarray design based on polarization-rotating (PR), miniaturized-element, frequency-selective surfaces (MEFSSs). These MEFSS unit cells rotate the polarization of the transmitted wave by 90° either in the counterclockwise or in the clockwise direction. Each PR element consists of three metal layers separated by two dielectric substrates. The constituent metallic layers comprise metallic strips with specific alignments to twist the polarization of the transmitted electromagnetic wave by ±90°. We used the two rotation directions to achieve a 0°/180° phase difference in the transmission mode to achieve a 1 bit phase shifter. We also show that variations in the unit cell dimensions can be combined with polarization rotation to create an additional 90° phase shifts, which can be combined with the PR phase shift mechanism to achieve a 2 bit phase shifter. We designed, fabricated, and experimentally characterized two illustrative transmitarray prototypes with 1 and 2 bit phase-correction patterns. The measured results agree well with the simulation predictions and demonstrate wideband operation for both arrays. The measured 3 dB gain bandwidth and maximum gain are 33.4% and 24.5 dBi, respectively, for the 1 bit prototype, and 24.1% and 27.2 dBi, respectively, for the 2 bit prototype.

With the focus on increasing instantaneous bandwidth capabilities of high-power microwave (HPM) devices, the Metamaterial Enhanced Resistive Wall Amplifier (MERWA) is being investigated for potential use as an HPM amplifier 1 , 2 , 3 . Rather than growth of a circuit wave, the MERWA operates via growth of the beam’s slow space charge wave. MERWA theory uses a 2D impedance matching technique at the boundary of the beam to show that growing wave solutions exist if a nearby metamaterial wall presents a resistive-inductive admittance to the beam 1 . Although the theory never expects or requires that an axially propagating cold circuit wave would exist, a low power experimental prototype was found to support a lossy backward wave in the vicinity of growth 2 , 3 . Using a two-wave coupling theory, we show that the space charge wave growth (of this specific prototype) can alternatively be explained in terms of coupling between the beam’s slow space charge wave and the lossy backward circuit wave. In contrast to the coupling with a lossless backward wave, which is known to produce a pair of non-growing waves, the interaction with the lossy backward wave produces a region of stable exponential space charge wave growth below an oscillation threshold. This two-wave coupling perspective provides insight into performance capabilities, limitations, and tradeoffs. Among these insights, we discuss how the amount of cold circuit loss affects the maximum stable growth rate, oscillation threshold, and gain-bandwidth product. We will compare analytical predictions against simulation results for validation.

This paper discusses different components of a high-power test setup for replicating multipactor in a laboratory environment. We developed a broadband test cell for parallel-plate multipactor discharges that can operate from DC to 1.2 GHz. The proposed test cell design features a multi-step transition from a coaxial line to a microstripline with negligible insertion loss suitable for high-power breakdown experiments. The multipactor section is adjustable and replaceable, offering flexibility in conducting various multipactor tests, such as different gap distances and local surface treatments. We incorporated two local multipactor detection methods, an electron multiplier tube and a biased standalone probe to rapidly and reliably detect the growth of secondary electrons in the multipactor vicinity. The driving circuits of these detection methods have been designed to filter out RF coupling while preserving the detection signal due to multipactor current. To demonstrate the accuracy of the proposed test setup, we validated the multipactor thresholds determined in simulation using the 3D particle-in-cell module of CST Microwave Studio. We obtained very good agreement between simulation and experimental results over the broadband frequency range. The topics discussed in this paper further inform how to address the design obstacles encountered in developing a bench-top multipactor test setup.

Analysis of temperature-limited flow, space-charge-limited flow, and the transition between them using a simple planar diode with a thermionic cathode, in which the cathode surface has spatially nonuniform emission properties, is presented. Our theoretical results, which are derived from a model based on solutions to the Vlasov and Poisson equations, compare well with the results of particle-in-cell simulations. We find that the location and the shape of the knee in the anode current versus temperature characteristic (Miram or “rollover” curve) are significantly affected by non-uniformities in the space-charge density in the A–K gap, but are relatively unaffected by the electron motion parallel to the electrode surfaces. In particular, emission from an actively emitting region is strongly affected by the forces (or lack thereof) exerted by the space-charge of the electrons emitted by their neighbors. Perhaps, most remarkably, we find that the limiting current reaching the anode is approximately given by the classical 1-D Child–Langmuir law, even if a significant fraction of the cathode surface is non-emitting.

SrVO3 thin films with a high figure of merit for applications as transparent conductors were crystallized from amorphous layers using solid phase epitaxy (SPE). Epitaxial SrVO3 films crystallized on SrTiO3 using SPE exhibit a room temperature resistivity of 2.5 x 10-5 Ohms cm, a residual resistivity ratio of 3.8, and visible light transmission above 0.5 for a 60 nm-thick film. SrVO3 layers were deposited at room temperature using radio-frequency sputtering in an amorphous form and subsequently crystallized by heating in controlled gas environment. The lattice parameters and mosaic angular width of x-ray reflections from the crystallized films are consistent with partial relaxation of the strain resulting from the epitaxial mismatch between SrVO3 and SrTiO3. A reflection high-energy electron diffraction study of the kinetics of SPE indicates that crystallization occurs via the thermally activated propagation of the crystalline/amorphous interface, similar to SPE phenomena in other perovskite oxides. Thermodynamic calculations based on density functional theory predict the temperature and oxygen partial pressure conditions required to produce the SrVO3 phase and are consistent with the experiments. The separate control of deposition and crystallization conditions in SPE presents new possibilities for the crystallization of transparent conductors in complex geometries and over large areas., Comment: Keywords: epitaxial transparent conducting oxides, solid-phase epitaxy, strontium vanadate, phase selection in oxide synthesis

First-principles calculations based on Density Functional Theory (DFT) previously revealed that perovskite SrVO 3 is a promising candidate for thermionic emission applications. In this work, polycrystalline bulk and epitaxial thin film SrVO3 samples have been experimentally examined. Both bulk and epitaxial SrVO 3 can exhibit low work function, consistent with DFT calculations and corresponding promising thermionic emission behavior. SrVO 3 is a potentially good thermionic emitter material and points more broadly to perovskite materials as a family of compounds which may further the development of next-generation thermionic electron emitters.

The work function is a crucial parameter for electron emitters used in vacuum electronic devices as lower function allows higher current density and/or lower operating temperature. Perovskite oxides are a novel class of materials for potential use in electron emission applications due to their tunable work functions, robust stability, and good electronic conductivity. In this work, we performed a high-throughput screening based on Density Functional Theory (DFT) simulations and predicted BaMoO 3 to be promising emitter materials with low work function, good stability and high electronic conductivity. Our work also provides a general materials design principle governing the work function of perovskites, which is that perovskites with nearly empty electronic d-bands have the lowest work functions.

Previously, we constructed a first-principles statistical model to predict the non-uniform emission from polycrystalline tungsten cathodes, which incorporated microstructure characterization results, crystallographic-orientation-specific work function values via density functional theory (DFT), and temperature-limited (TL) emission physics. This previous model could only predict the TL region of the Miram curve and not the transition between TL and full-space-charge-limited (FSCL) regions. In this work, we have expanded our model to predict emission along the entire Miram curve, including the transition from TL to FSCL regions, without any empirical assumptions on work function distribution or empirical emission equations. This more advanced model provides a pathway to understanding the complex physics of emission from heterogeneous cathode surfaces, which is a key issue for the commercial production and use of thermionic cathodes in vacuum electronic devices.

Experimental observations have long-established that there exists a smooth roll-off or knee transition between the temperature-limited (TL) and full-space-charge-limited (FSCL) emission regions of the emission current density-temperature J-T (Miram) curve, or the emission current density-voltage J-V curve for a thermionic emission cathode. In this paper, we demonstrate that this experimentally observed smooth transition does not require frequently used a priori assumptions of a continuous distribution of work functions on the cathode surface. Instead, we find the smooth transition arises as a natural consequence of the physics of nonuniform thermionic emission from a spatially heterogeneous cathode surface. We obtain this smooth transition for both J-T and J-V curves using a predictive nonuniform thermionic emission model that includes 3-D space charge, patch fields (electrostatic potential nonuniformity on the cathode surface based on local work function values), and Schottky barrier lowering physics and illustrate that a smooth knee can arise from a thermionic cathode surface with as few as two discrete work function values. Importantly, we find that the inclusion of patch field effects is crucial for obtaining accurate J-T and J-V curves, and the further inclusion of Schottky barrier lowering is needed for accurate J-V curves. This finding, and the emission model provided in this paper have important implications for modeling electron emission from realistic, heterogeneous surfaces. Such modeling is important for improved understanding of the interplay of emission physics, cathode materials engineering, and design of numerous devices employing electron emission cathodes., IEEE Transactions on Electron Devices (2021)

Reconfigurable reflectarrays (RAs) have attracted significant interest as affordable and relatively low-complexity beam scanning antennas for radar and satellite communication applications. We present a dual-band, beam-steerable RA capable of independent beam control at X and Ku bands based on a 1-bit polarization-rotating unit cell (PRUC). Two static versions of the RAs with different beam scanning scenarios are simulated, fabricated and measured. Good beam steering performance with independent beam control at each band is achieved.

We present a new technique for designing wideband, single-layer reflectarray antennas. The proposed reflectarray exploits a wideband, polarization rotating unit cell that rotates the polarization of the reflected wave with respect to that of the incident wave by 90°. This unit cell and its mirror image were used as 1 bit spatial phase shifters capable of providing a 0°/180° phase shift over a wide bandwidth of 5.4–12.7 GHz. Using this, a reflectarray antenna with 1 bit phase quantization was designed to operate at ${X}$ -band with aperture dimensions of $28.8\,\,\text {cm}\times 28.8$ cm and a focal length of 30 cm. A prototype of the proposed reflectarray was fabricated and characterized using a spherical near-field measurement system. We determined the antenna’s 3 dB gain bandwidth to be approximately 37.4% with a maximum realized gain of 24.2 dBi. Over its entire band of operation, the polarization purity of the antenna remains better than 13 dB and sidelobe levels of better than 12 dB were achieved.

We describe the results of a wideband, reconfigurable reflectarray concept based on polarization-rotating unit cells (PRUCs) with a minimum-switch topology design. To enhance the simplicity and decrease the cost, the approach focuses exclusively on a one-bit phase shifting architecture. We investigated PRUCs having four conducting, single-headed arrow structures on their top surfaces and crossed, conducting strips acting as hard-wired switches on their bottom surfaces. The top-surface arrows and the bottom-surface strips are connected with four vertical vias. The switch states of the bottom conducting strips determine the two operating states of the unit cell for rotating the polarization of the reflected waves by +90° and -90° with respect to that of the incident, linearly polarized waves. The PRUC provides a co-polarization reflection coefficient of better than -1 dB over the wide frequency range of 8-12 GHz, as demonstrated by the simulation results. The PRUCs were incorporated into an illustrative reflectarray operating in the X-band. The full-wave simulation results show good beam scanning performance over the range of ±45° with a maximum scan loss of 3 dB. Two static realizations of the reflectarray for beam collimation at θ = 0° and θ = 45° in the xz plane were fabricated and experimentally characterized. The measurement results show good agreement with the simulation results and demonstrate the beam steering operation of the proposed reflectarray.

Metamaterials (MTMs) are structured materials with subwavelength features that can be engineered to have some unique properties not found in nature, such as negative refractive index, reversed Doppler effect, and reversed Cherenkov radiation. Based on these novel MTMs, several important research groups have made great attempts to develop novel MTM-inspired vacuum electron devices (VEDs) and accelerators. Just as solid-state power devices are innovated by incessant emerging of new semiconductor materials, VEDs can also be inspired by MTMs to have very remarkable advantages, such as smaller size, higher power, higher efficiency, and/or larger gain relative to conventional VEDs, such as traveling-wave tubes, backward-wave oscillators, and klystrons. Similarly, relative to conventional accelerators, MTM-inspired accelerators have obvious advantages, such as smaller size and higher accelerating gradient. Furthermore, MTM-inspired devices have promising applications in areas such as radar, communication, electronic warfare, microwave heating, and imaging.

The high electron emission resulting from low-work-function scandate-added dispenser cathodes has generated a great deal of interest and research since the late 1970s. Despite the reported high current density at low temperatures, scandate cathodes have not yet seen wide-scale industrial adoption due to poor emission uniformity, inadequate reproducibility, and short lifetimes. This lack of industrial adoption stemming from the above issues is likely due to insufficient fundamental understanding of the role that scandium plays in the emission process. Recent work by five research teams under the U.S. Defense Advanced Research Projects Agency Innovative Vacuum Electronics Science and Technology Program aims at advancing this fundamental understanding and the cathode manufacturing processing. Emission microscopy of model surfaces of adsorbed Ba–Sc–O on single crystal tungsten and detailed characterization techniques, such as Wulff shape analysis, are being used to understand the morphology, composition and phase of each of the species that comprise the cathode emitting surfaces. The structure of tungsten grains at the cathode surface of activated and unactivated scandate cathodes and the resulting emission performance are observed. 3-D printing is being investigated as an advanced manufacturing method to meet the demanding requirements of modern vacuum electron devices. Finally, density functional theory is being employed to study the work function of perovskite oxides as a novel class of alternative materials to tungsten dispenser cathodes.

Previous studies have shown greater fluorophore uptake during electroporation on the anode-facing side of the cell than on the cathode-facing side. Based on these observations, we hypothesized that hyperpolarizing a cell before electroporation would decrease the requisite pulsed electric field intensity for electroporation outcomes, thereby yielding a higher probability of reversible electroporation at lower electric field strengths and a higher probability of irreversible electroporation (IRE) at higher electric field strengths. In this study, we tested this hypothesis by hyperpolarizing HL-60 cells using ionomycin before electroporation. These cells were then electroporated in a solution containing propidium iodide, a membrane integrity indicator. After 20 min, we added trypan blue to identify IRE cells. Our results showed that hyperpolarizing cells before electroporation alters the pulsed electric field intensity thresholds for reversible electroporation and IRE, allowing for greater control and selectivity of electroporation outcomes.

Metal-based epsilon negative metamaterials (MTMs) have been investigated for use as a waveguide liner to allow for an electromagnetic passband below the cutoff frequency of the empty waveguide. In this paper, we investigate both the theory and a practical implementation of an MTM lined waveguide. Specifically, we have investigated the use of inductive meander lines as the elements of a vacuum-electronics-compatible MTM structure to line one side of a rectangular waveguide. The MTM implementation creates an effective medium with a Drude–Lorentz dispersion response. The transmission of the waveguide and dispersion were both simulated and measured experimentally and demonstrate good agreement.

We have constructed a model capturing the statistical nature of non-uniform thermionic electron emission from polycrystalline W cathodes. This model incorporates the proportion of different crystallographic emitting surfaces from commercial cathode samples via electron backscatter diffraction (EBSD), the effects of surface roughness from optical interferometry measurements, and surface-specific work function values calculated using density functional theory (DFT). Using this model, we aim to calculate 2D emission maps and the corresponding Miram curves for real cathodes. This model provides a pathway to understanding the complex physics of emission from inhomogeneous cathode surfaces, which is a key issue for the commercial production and use of impregnated cathodes in vacuum electronic devices.

The metamaterial-enhanced resistive wall amplifier (ME-RWA) has been shown to be capable of producing large gains over wide bandwidths. Previous theoretical investigation of the ME-RWA focused on an idealized case using a homogenous dielectric with Drude dispersion to provide the negative permittivity required to achieve high gains. This paper reports the results of investigating practical metamaterial implementations with approximate Drude-type responses that enable the realization of a ME-RWA. Using these metamaterials, an architecture for a ME-RWA using periodically spaced inductive meandered lines is proposed. Our theoretical analyses and particle in cell simulations of this device predict that the proposed technique provides a practical method of implementing ME-RWAs, capable of providing a large gain over a substantial bandwidth.

We present techniques for designing large-scale, mechanically tunable periodic structures (PSs). Overlapping combined with relative movement, stretching/compression, and flexure are the three mechanical tuning techniques studied in this paper. We demonstrate that all of these mechanical movements may be used to tune the capacitance and inductance of elementary periodic structures with capacitive and inductive surface impedances over wide ranges of values. Analytic formulas for calculating the variable inductance and capacitance of these tunable PSs are also provided. These elementary PSs are the building blocks of a wide range of other PSs with more complicated unit cells and response types. One such structure—a frequency selective surface (FSS) composed of series combination of these inductive and capacitive structures—is also examined to demonstrate the application of the proposed tuning and analysis concepts. The FSS is fabricated on an accordion-like substrate that can be contracted or stretched to change its frequency of operation. The response and tuning properties of this structure are experimentally characterized using a free-space measurement system. A very good agreement between theory and experiment is obtained. This demonstrates that the behavior of such complex mechanically tunable PSs can be analyzed by examining the behavior of their constitutive inductive and capacitive elements.

We propose a semi-analytic approach to investigate the multipactor in parallel plate structures with improved accuracy. The effects of emission velocity and transit time of electrons are studied and their corresponding susceptibility charts are calculated. As a result, the proposed model covers more dynamics of multipactor. In calculating the susceptibility chart, we propose a decision-making process taking into account impact velocity, required voltage, and trajectory of electrons. Therefore, we obtain a more accurate susceptibility chart that excludes non-physical scenarios. Our investigation reveals a different mechanism of multipactor, where the transit time of an electron across the gap can be either shorter or longer than the conventional half-cycle of the RF signal. The extent of this deviation depends on the maximum emission velocity of the secondaries. With this deviation, we demonstrate that the multipactor evolves over broader practical situations occurring not necessarily within a half-cycle of the RF signal. Finally, we study the higher-order multipactor resonances and also calculate their susceptibility charts. We demonstrate an overlap between the susceptibility charts of different orders depending on the emission velocity of primary electrons. The discussions herein provide an insight into the underlying dynamics of the multipactor, which can be used for practical multipactor suppression methods.

The work function is one of the most fundamental surface properties of a material, and understanding and controlling its value is of central importance for manipulating electron flow in applications ranging from high power vacuum electronics to oxide electronics and solar cells. Recent computational studies using Density Functional Theory (DFT) have demonstrated that DFT-calculated work function values for metals tend to agree well (within about 0.3 eV on average) with experimental values. However, a detailed validation of DFT-calculated work functions for oxide materials has not been conducted and is challenging due to the complex dipole structures that can occur on oxide surfaces. In this work, we have focused our investigation on the widely studied perovskite SrTiO3 as a case study example. We find that DFT can accurately predict the work function values of clean and reconstructed SrTiO3 surfaces vs experiment at about the same level of accuracy as metals when direct comparisons can be made. Furthermore, to aid in understanding the factors governing the work function of oxides, we have performed systematic studies on the influence of common surface features, including surface point defects, doping, adsorbates, reconstructions, and surface steps, on the work function. The relationships between the surface structure and work function for SrTiO3 identified here may be qualitatively applicable to other complex oxide materials.

We demonstrate the use of polarization rotating (PR) unit cells in designing wideband reflectarray (RA) and transmitarray (TA) antennas. A reflective/transmissive PR unit cell and its mirror image can provide 1-bit phase quantization over a very wide frequency range. The PR unit cells were used to design a RA and TA antennas, both with aperture dimensions of $30 \times 30$ cm$^{2}$ and focal lengths of 30 cm, for operation at X-band. The fabricated RA and TA antenna prototypes provided a maximum realized gain of 24.5 dBi, 3-dB gain bandwidths of up to 40%, and polarization purity and side lobe levels of better than 11.5 dB.