First-Order Nonlinear Theory in Hexagonal Ferrites with Planar Anisotropy under Perpendicular Pumping

The first-order spinwave instability under perpendicular pumping at large signal power in an hexagonal ferrite ellipsoid with planar anisotropy biased in the easy plane is studied. The nonlinear coupling coefficient is obtained in terms of the physical variables of the unstable spinwaves and the uniform mode magnetization such as the orientation and ellipticity of the unstable spinwaves, the coordinates of the spinwave propagation vector k, and the uniform mode ellipticity. Results obtained using a computer in the case of a sphere are included. Also included are experimental results on the coincidence region with the dc field in the easy plane and with the dc field out of the easy plane. This latter arrangement leads to a new tunable coincidence limiter.     

Design of Composite Magnetic Circuits for Temperature Stabilization of Microwave Ferrite Devices

The magnetic flux density of unsaturated microwave ferrites can be made almost constant although microwave ferrite saturation magnetization, coercive force, and hysteresis loop shapes change substantially. Temperature stabilization of flux is achieved by a composite series magnetic circuit consisting of microwave, driver, and flux-limiter ferrites, and a control coil. The flux limiter constrains the circuit flux to an almost constant level throughout the operating temperature range, despite large changes in the size and shape of the microwave ferrite hysteresis loop. The driver ferrite supplies the MMF necessary to sustain the flux. Current impulses in the control coil energize and switch the circuit flux. Estimates of the required lengths and cross-sectional areas of the circuit elements, and of the required switching field and energy for a waveguide remanence phase shifter are given, along with the effects of leakage and fringing fluxes. Composite circuit techniques have been applied to an experimental remanence phase shifter. Unstabilized, a 16 percent loss of phase shift was incurred as a result of an 80/spl deg/C rise in temperature. By applying composite circuit techniques, this value was reduced to less than 2 1/2 percent for the same temperature range.     

A Strain‐Mediated Magnetoelectric‐Spin‐Torque Hybrid Structure

Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching.     

A rigorous method for computation of ferrite toroidal phaseshifters

Coupled-wave theory is used to calculate the performance of twin-toroidal phase shifters. Computation results show that this method is effective, rather simple, and easy to handle. In comparison with the single-toroid phase shifter, the twin-toroidal model's phase shift is considerably larger and its production is simpler. The wires carrying magnetizing currents are located in the weak microwave electric field area. Hence, their influence on the performance of the phase shifter is negligible; this also facilitates production. The loss factors of these two kinds of toroid phase shifters are about the same. Experimental results are in good agreement with theoretical analysis. On this basis, it is concluded that coupled-wave theory is a powerful method for treating electromagnetic problems of waveguides loaded with magnetized ferrites     

铁氧体双模器件的广义理论

铁氧体双模器件包括双模移相器,圆极化移相器,旋转场移相器.双模变极化器等等.其种类繁多,每种器件由若干基本双模段级联而成.每个基本单元上,外加磁场形式各不相同,有四磁极磁化场,纵向磁化场,双磁极磁化场及其混合磁化场.本文拟用统一的理论对其进行处理及分析并引入具体实例使用CAD技术进行计算,从而进一步确认理论的正确性.     

Low-cost nonplanar microstrip-line ferrite phase shifter utilizing circular polarization

A low-cost microwave ferrite phase shifter is proposed in this paper. The phase shifter is comprised of three parallel nonplanar microstrip lines separated from a ground plane by a substrate containing a ferrite rod/slab. The amount of phase shift between the input and output ports is determined by the strength of the magnetic bias field applied to the ferrite. A three-way power divider was designed to feed the microstrip lines with different magnitudes and phases. By combining the effects of the nonplanar geometry and the phase offsets introduced by the feed network, circularly polarized waves can be produced in the ferrite. These waves strongly interact with the biased ferrite resulting in a large phase shift over a short distance-90/spl deg//cm based on current simulation results. This device will be best suited for use in high-gain phased-array radar systems.     

Advances in Scanning Reflectarray Antennas Based on Ferroelectric Thin-Film Phase Shifters for Deep-Space Communications

Though there are a few examples of scanning phased array antennas that have flown successfully in space, the quest for ldquolow costrdquo high-efficiency large-aperture microwave phased arrays continues. Fixed and mobile applications that may be part of a heterogeneous exploration communication architecture will benefit from the agile (rapid) beam steering and graceful degradation afforded by phased array antennas. The reflectarray promises greater efficiency and economy compared to directly radiating varieties. Implementing a practical scanning version has proven elusive. The ferroelectric reflectarray, under development and described herein, involves phase shifters based on coupled microstrip patterned on films that were laser ablated onto substrates. These devices outperform their semiconductor counterparts from X- through and K-band frequencies. There are special issues associated with the implementation of a scanning reflectarray antenna, especially one realized with thin-film ferroelectric phase shifters. This paper will discuss these issues, which include relevance of phase shifter loss; modulo 2 effects and phase shifter transient effects on bit error rate; scattering from the ground plane; presentation of a novel hybrid ferroelectric-semiconductor phase shifter; and the effect of mild radiation exposure on phase shifter performance.     

Empirical model generation techniques for planar microwave components using electromagnetic linear regression models

Accurate and efficient empirical model generation techniques of microwave devices, for a large range of geometric and material parameters opportunely chosen, are presented. The empirical models are based on multiple linear regression approach, which compensates the error between an initial inaccurate empirical model and an electromagnetic (EM) full-wave solver (or measurement data). The aim of these techniques is to generate accurate empirical models, which are computationally very efficient with respect to any EM technique. These simple models could be integrated in a toolbox of any commercially available computed-aided design tools for RF/microwave circuits. Comparisons with artificial neural networks and linear-regression-based models are listed and discussed for the dispersion of a microstrip transmission line propagating the quasi-TEM mode and a microwave tunable phase shifter propagating the even mode.     

铁氧体非互易移相器的高功率容量分析

通过计算铁氧体波导移相器的微波磁场和功率分布,给出了一种分析该类器件峰值功率容量的有效方法,取得了与工程试验相一致的结果,从而使得铁氧体非互易移相器的峰值功率容量大小能够在设计阶段得以较准确计算。     

Magnetic Anisotropy of Cr7Ni Spin Clusters on Surfaces

The problem of the experimental and theoretical determination of magnetic anisotropy in isolated molecular spin clusters is addressed here. To this end, the case of molecular Cr₇Ni rings sublimated in ultrahigh vacuum conditions and assembled in an ordered fashion on Au(111) surface is addressed and investigated using X‐ray magnetic dichroism (XMCD) and theoretical calculations. Fixing the experimental conditions at a temperature T = 8 K and a magnetic field of 5 T, the angular‐dependence of the dichroic signal reveals an easy‐axis anisotropy for the Ni magnetization along the direction perpendicular to the ring while the magnetization of the whole Cr₇Ni molecule is preferentially aligned within the ring plane. These features are well reproduced by spin Hamiltonian simulations, which reflect the character of the S = 3/2 first excited multiplet, dominating at T = 8 K and 5 T. Density functional theory (DFT) calculations show that local spin orbit interactions determine an easy axis anisotropy at the Ni site while the Cr magnetic moment turns out to be more isotropic. This is the first direct observation of the interplay between the single ion and the overall magnetic anisotropy in complex (polynuclear) molecular systems.     

Magnetic Anisotropy Switch: Easy Axis to Easy Plane Conversion and Vice Versa

The rational design of the magnetic anisotropy of molecular materials constitutes a goal of primary importance in molecular magnetism. Indeed, the applications of molecular nanomagnets, such as single‐molecule magnets and molecular magnetic refrigerants, depend on the full control over this property. Axially anisotropic magnetic systems are frequently classified as easy axis or easy plane, depending on whether the lowest energy is obtained by application of a magnetic field parallelly or perpendicularly to the unique axis. Here, the magnetic anisotropy of three lanthanide complexes is studied as a function of magnetic field and temperature. It is found that for two of these the type of magnetic anisotropy switches as a function of these parameters. Thus, this paper experimentally demonstrates that the magnetic anisotropy is not uniquely defined by the intrinsic electronic structure of the systems in question but can also be reversibly switched using external stimuli: temperature and magnetic field.     

MEMS移相器及其在微型通信系统中的应用

从传统移相器的构造和原理出发，进一步分析了MEMS移相器的结构、特性。结果表明，MEMS移相器具有传统移相器所无法比拟的体积小、损耗小、成本低、频带宽、易于集成等突出优点。随着高阻硅衬底在微波领域应用的扩展，MEMS移相器介质损耗大幅度降低，将能与信号处理电路一同集成于硅衬底上，便于相控阵雷达等通信系统实现微小型化。     

Microwave phase shifter using optical waveguide structure

A microwave phase shifter with an integrated optics structure with high efficiency is discussed. The structure and the performance of the device are discussed. Microwave phase shifting was carried out using the fabricated phase shifter of titanium diffused LiNbO₃ optical waveguides. The measured voltage to obtain halfwave phase shift for a 800 MHz microwave signal was 7.0 V. The input microwave power was 21 dBm, and the detected output microwave power was -24 dBm, so the microwave insertion loss was calculated to be approximately -45 dB. The optical insertion loss of the device was -12 dB     

Parallel Pumping in Hexagonal Ferrites with the Dc Field Off the Easy Plane

This paper gives the theory of spinwave instability under parallel pumping in hexagonal Zn/sub 2/Y ferrites with planar anisotropy in the case of a sphere. The configuration considered in this paper is the one in which the dc field makes an angle /spl beta/ with the easy plane and the resultant magnetization lies at an angle /spl alpha/ to it. To obtain parallel pumping with this arrangement it is necessfly to align the RF field along the magnetization. This leads to a new spinwave spectrometer which allows the dependence of the spinwave linewidth upon the angle /spl alpha/ which the unstable spinwave makes with the c axis of the crystal to be determined. The experimental results obtained on two Mn-Zn/sub 2/Y single-crystal ferrite spheres show that the spinwave linewidth increases with the angle /spl alpha/.     

Moldable Polymer/Ferrite Composite and Application to an Integrated CPW Tunable Phase Shifter

A moldable polymer/ferrite composite (MPFC), easily moldable into arbitrary volumetric shapes is presented. The composite material is produced at room temperature and does not require any postprocessing treatment. The utility of the MPFC is demonstrated in a meandrous coplanar waveguide line phase shifter tuned by an applied magnetic dc field. Due to its low cost and high flexibility, the proposed MPFC may find applications in various tunable and non-reciprocal microwave components.     

Magnetic structure and magnetoresistance of patterned epitaxial iron thin films: The influence of shape and magnetocrystalline anisotropy

A magnetic-force-microscopy investigation is conducted into the influence of the shape and magnetic anisotropy on the magnetic structure and the mode of magnetization reorientation in epitaxial iron thin films patterned by subtractive techniques. Magnetic anisotropy is found to have a strong influence on the magnetic structure. With an applied field directed along a specimen, the latter is in a single-domain state when oriented parallel to the easy axis of magnetization, and is in a multidomain state when oriented perpendicular to the easy axis, the domain magnetic moments being parallel to the easy axis in both cases. The magnetic structure appears as a streaky pattern. Magnetization reorientation proceeds by domain-wall motion in both cases. The tanks do not change the mechanism of magnetization reorientation in the rectangular part, yet they ensure a single-domain state at lower magnetic flux densities. The results should offer some scope for using epitaxial iron thin films of suitable shape and crystallographic orientation in spin-valve injectors or detectors.     

A Ku‐Band 5‐Bit Phase Shifter Using Compensation Resistors for Reducing the Insertion Loss Variation

This paper describes the performance of a Ku‐band 5‐bit monolithic phase shifter with metal semiconductor field effect transistor (MESFET) switches and the implementation of a ceramic packaged phase shifter for phase array antennas. Using compensation resistors reduced the insertion loss variation of the phase shifter. Measurement of the 5‐bit phase shifter with a monolithic microwave integrated circuit demonstrated a phase error of less than 7.5° root‐mean‐square (RMS) and an insertion loss variation of less than 0.9 dB RMS for 13 to 15 GHz. For all 32 states of the developed 5‐bit phase shifter, the insertion losses were 8.2 ± 1.4 dB, the input return losses were higher than 7.7 dB, and the output return losses were higher than 6.8 dB for 13 to 15 GHz. The chip size of the 5‐bit monolithic phase shifter with a digital circuit for controlling all five bits was 2.35 mm × 1.65 mm. The packaged phase shifter demonstrated a phase error of less than 11.3° RMS, measured insertion losses of 12.2 ± 2.2 dB, and an insertion loss variation of 1.0 dB RMS for 13 to 15 GHz. For all 32 states, the input return losses were higher than 5.0 dB and the output return losses were higher than 6.2 dB for 13 to 15 GHz. The size of the packaged phase shifter was 7.20 mm × 6.20 mm.     

BSTO电光材料及其制备

用ＢＳＴＯ电光材料制作的电光移相器与铁氧体移相器相比,具有非常好的性能,它以高的功率、高的相移速度、低的插入损耗、低的驱动功率、充分宽的工作温度范围以及低的成本,受到相控阵天线技术的关注。文章介绍了ＢＳＴＯ材料及其制备方法,简要概述了这种材料研究的进展,讨论了ＢＳＴＯ电光材料化学组成、工艺制备技术和非铁电相对ＢＳＴＯ电光材料性能的影响,最后提出了发展该材料的方向。     

Forced nonlinear precession of the magnetization vector under the conditions of an orientation transition

Forced nonlinear precession of the magnetization vector in a normally magnetized magnetic plate under the conditions of an orientation transition is considered. It is shown that, in the field lower than the form demagnetization field, the variable circularly polarized field causes precession of the equilibrium position of the magnetization vector. It is demonstrated based on a vector model in which the precession period of the equilibrium position is inversely proportional to the squared amplitude of the variable field and the sine of the angle of deviation of the equilibrium position of magnetization from the constant field. It is shown that the critical parameters necessary for excitation of precession of the equilibrium position are the amplitude and frequency of the variable field. Diagrams determining domains of existence of precession of the equilibrium position for different saturation magnetization of a magnetic plate are constructed in terms of the coordinates variable field amplitude-frequency. The role of dissipation of magnetization oscillations in the determination of the critical parameters is elucidated. The features of precession in the presence of asymmetric excitation and in the presence of anisotropy in the plane of the plate are noted.