Design of High-Performance Millimeter Wave and Sub-Millimeter Wave Quasi-Optical Isolators and Circulators

Faraday rotators using permanently magnetized ferrite materials are used to make quasi-optical isolators and circulators at millimeter wave and sub-millimeter wave frequencies that have far higher performance than their waveguide equivalents. This paper demonstrates state-of-the-art performance for four-port quasi-optical circulators with 60-dB isolation, 0.2-dB insertion loss, and better than 80-dB return loss for devices centered at 94 GHz. A method is presented for the accurate characterization of the complex permeability and permittivity of permanently magnetized ferrites via a series of frequency and polarization dependent transmission and reflection measurements. The dielectric and magnetic parameters for the sample are determined by fitting theoretical curves to the measured data. These fitted parameters are then used in a model for a complete quasi-optical Faraday rotator, including matching layers, allowing the accurate design and fabrication of these devices for any specific operational frequency band in the millimeter wave and sub-millimeter wave regime. Examples are given showing typical results and demonstrating how temperature cycling can significantly improve the temperature stability of these devices, while allowing fine tuning of the center frequency. We also indicate the performance possible at higher frequencies to above 1 THz and outline performance of truly planar isolators where lossy polarizer material is built into the Faraday rotator matching structure     

Quasi-optical techniques

The basic theory of quasi-optical Gaussian beam propagation and beam transformation by simple optical elements is summarized, and coupling to and between Gaussian beams is briefly discussed. Guidelines for Gaussian optics system design are reviewed, the most important being beam truncation and matching. Passive components in the terahertz frequency range based on quasi-optical propagation, including polarization processors, filters, diplexers, and ferrite devices, are examined. Some active quasi-optical devices, including multielement oscillators, frequency multipliers, and phase shifters, are described. Some specific applications of quasi-optical systems are briefly described     

Quasi-optical antenna duplexers

The development of antenna duplexers for transceiving quasi-optical systems of millimeter and submillimeter wavelengths are considered for two groups of devices — passive and active action. Duplexers, using properties of quasi-optical hybrids, belong to the first group, and duplexers on the base of semiconductor or ferrite devices are included to the second group. Results of developments and investigations of considered devices in the millimeter wave range are presented.     

Design of the Collective Thomson Scattering Diagnostics for Large Helical Device Using a Quasi-Optical Frequency Tunable Gyrotron as a Radiation Source

Collective Thomson scattering technique based on high power laser has already proved its ability in measuring the ion (bulk and fast) temperature (T _i) in fusion plasma devices like tokamaks and stellarators. This paper present first trial to implement collective Thomson scattering diagnostic based on quasi-optical gyrotron as a source of radiation. It was found utilization of this wavelength band gives more flexibility in diagnostic port arrangement.     

Quasioptical measurement of ferrite material parameters at terahertz frequencies by a new method: Faraday angle resonance

A new method for measuring the dielectric constant? _r and the saturation magnetizationM _S of ferrites in the terahertz frequency region is introduced in theory and experiment. The method, which bases on a resonance effect of the Faraday angle, gives an estimation of the loss factor tan δ, too. The derivation of the effect is based on a simple 4-port model of the ferrite disc which is axially premagnetized. Using the scattering matrix from the 4-port model the resonance effect is described and the extraction of the material parameters of some special data from the measurement record is explained. The measurement setup at 290 GHz is described and records of the ferrite Trans Tech TT 1–105 are evaluated, including an error calculation. Data for the hard ferrite Philips Ferroxdure FXD 330 are given, too. Using error minimizing algorithms which fit the material parameters to the measurement data a further increase in accuracy can be achieved.     

回旋管准光辐射器研究与设计

准光辐射器是高功率回旋管准光模式变换器的重要组成部分.本文首先采用几何光学理论分析圆波导准光辐射器,然后根据高斯波束(TEM00模)在辐射器切口处形成的原因,采用耦合波理论设计波纹波导准光辐射器.通过编写程序并进行数值优化完成140GHz,TE28,8模式回旋管波纹波导准光辐射器的设计,结果表明波纹波导辐射器的总长度仅为205.2mm,切口长度为47.2mm,在辐射器螺旋切口Brillouin区内高斯模式标量相关系数大于98%.本文所用的方法也可用于其它频率和模式的回旋管准光辐射器设计.     

Design of a Quasi-Optical System Converting the TE06 Output Mode of a Gyrotron into a Gaussian-Like Beam

Gaussian optics can be used to design a quasi-optical system converting the TE₀₆ mode output (f=388 GHz) of a submillimeter wave gyrotron into a well-collimated, linearly-polarized free-space beam with a circular cross-section. A quasi-optical antenna produces a main beam with an elliptical cross-section, which is then converted by two mirrors into a well-collimated beam with a circular cross-section.     

New concedpts for high frequency and high power frequency multipliers and their impact on quasi-optical monolithic array design

Varactors have been extensively employed for harmonic generation, where high cut-off frequency is dependent upon small C _min , which is typically achieved using small device active area. However, small area limits the output power. Furthermore, the power and frequency dependences of the series resistance in the epitaxial region degrade the efficiency and cut-off frequency as well. As a result, currently utilized varactors are only officient for relatively low power generation and limited output frequency. Herein, we describe our new approach where by epitaxially stacking single quantum barrier structures, more than an order of magnitude improvement in cut-off frequency and power handling ability may be possible. Alternatively, by combining a Schottky barrier with stacked single quantum barriers, superior performance can also be achieved. These concepts can be readily employed for quasi-optical frequency multiplier arrays, and appear to result in simplified fabrication compared to other devices. The design of high performance quasi optical arrays requires optimization of the passive (metalization) grid as well as the embedded semiconductor devices. Recent work has resulted in an improved impedance model for the standard diode-loaded strip array, including a quantitative estimate of the shunt capacitance introduced across the diode by the discontinuity of the metal strip at the diode site (“gap”). The value of this capacitance exceeds the predictedC _min for these new devices. We discuss two grid design approaches that can suppress this capacitance.     

Self and mutual admittance of slot antennas on a dielectric half-space

In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ _r =3.80), crystal quartz (∈ _r =4.53), silicon (∈ _r =11.9) and GaAs (∈ _r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies.     

Observation of and noise reduction by vortex lattice matching in YBa2Cu3O7 thin films and rf SQUIDs with regular arrays of antidots

We report on the detection of matching effects between antidot and Abrikosov vortex lattices for fields far below the matching field B_m using rf SQUIDs and demonstrate, that antidots can strongly reduce the low-frequency l/f noise in active devices in unshielded environment. Square lattices of submicron holes (antidots) with diameters of 250–450 nm and lattice parameters ranging from 0.5–5 μm are patterned into optimized sputtered YBa₂Cu₃O₇ thin films on CeO₂-buffered sapphire substrates without deterioration of superconducting properties. A special experimental set-up consisting of an antidot lattice in flip-chip configuration with a bicrystal rf-SQUID has been used for the measurements. Thus, two different matching conditions are exposed upon the vortex lattice defined by the vortex–antidot interaction and the vortex–grain boundary interaction at the grain boundary in the washer. Vortices within the vicinity of the grain boundary of the washer can either be trapped (reduction of l/f noise) or exposed to a kind of double potential (increase of l/f noise) depending upon the magnitude of the applied magnetic induction and the geometrical arrangement between antidot array and grain boundary in the washer. Matching effects between vortex and antidot lattice could be observed in the form of minima in the noise spectrum for magnetic inductions much smaller then the matching field, e.g. for B^*=(1/18)²B_m. The maxima in the low-frequency noise are a result of the existence of two matching conditions, i.e. caused by the presence of the grain boundary in the SQUID washer. The experiments demonstrate that thermally activated hopping of vortices can strongly be reduced by antidots in the superconducting layer. The resulting reduction of the low frequency excess noise bears a great potential for applications of active high-T_c superconducting devices if other matching conditions are avoided, e.g. by using step-edge type rf-SQUIDs.     

Matching degradation of threshold voltage and gate voltage of NMOSFET after Hot Carrier Injection stress

Device degradation modelling is more and more important for reliable circuit design. On MOSFET, the threshold voltage drift in time can lead to circuit performance degradation. In this study, V_T shift due to Hot Carrier Injection stress is accelerated on small width devices. V_T matching is also degraded during stress as a function of V_T deterioration. This width dependence allows explaining gate voltage matching behavior in the sub-threshold area used in low power analog applications.     

Precise Design of Millimeter Wave Quasi-Optical Faraday Rotators

A method of designing high performance millimeter wave quasi-optical Faraday rotators (QOFR) is reported in this paper. First, the dielectric and magnetic parameters for the ferrite sample are determined by fitting theoretical curves to the measured data. These fitted parameters are then used in a precise numerical model to predict the rotation angle and insertion loss of the QOFR. Finally, the parameters of the QOFR are optimized according to the requirements of devices. Examples are given showing the performance of the QOFR with an isolation better than 20 dB and an insertion loss less than 0.6 dB from 75 GHz to 95 GHz.     

Improving the Magnetic Properties of Li-Zn-Ti Ferrite by Doping with H3BO3-Bi2O3-SiO2-ZnO Glass for LTCC Technology

Li-Zn-Ti ferrite doped with 0.5 wt.% to 16 wt.% H₃BO₃-Bi₂O₃-SiO₂-ZnO (BBSZ) glass was synthesized using a low-temperature ceramic sintering process. Selected parameters of saturation induction (B _S), coercivity (H _C), Curie temperature (T _C), and complex permeability spectra were measured as functions of doping content, and their relationships with ferrite density and microstructure are discussed. It was found that Li-Zn-Ti ferrite can be fired at low temperature (900°C) with BBSZ glass content varying from 0.5 wt.% to 2 wt.%. The real permeability increased from 80 to 190 in the frequency range from 1 MHz to 3 MHz, the saturation induction B _S increased from 105 mT to 150 mT at 1 kHz, whereas the coercivity H _C decreased from 165 A/m to 65 A/m at 1 kHz and the Curie temperature T _C slightly declined from 155°C to 143°C. These results confirm that this new ferrite material could be used in low-temperature cofired ceramic (LTCC) devices.     

Properties of NixZn(1−x)Fe2O4 thick films at microwave frequencies

The thick film Ni_xZn_(1−x)Fe₂O₄ on alumina substrate was prepared by screen printing of the ferrite powder synthesized by chemical co-precipitation method using nitrate precursors. These Ni_xZn_(1−x)Fe₂O₄ thick films of varying x were characterized by X-ray diffraction, FTIR spectroscopy and SEM (scanning electron microscopy). The permittivity and permeability were measured by overlay technique. Voltage standing wave ratio method was also used to measure the dielectric constant. The permittivity was found to increase with Ni content varying between 13 and 18. The permeability was ∼3.01. The overlay technique provides an easy method for measurement of permittivity and permeability of ferrite thick film.     

MnxZn1−xFe2−yRyO4 (R=Gd,Eu) ferrite nanocrystals for magnetocaloric applications

The use of a ferromagnetic fluid for cooling applications represents an encouraging alternative to traditional methods; the fact that the fluid can be pumped with no moving mechanical parts, using the magnetocaloric effect, can be a great advantage for many applications where high maintenance costs and power consumption are undesirable. The nanocrystalline material suitable for this specific application must exhibit certain specific properties, such as tunable Curie temperature (T_C) and high saturation magnetization (M_s). The present work is focused on the aqueous synthesis and characterization of Mn–Zn ferrite nanocrystals and their subsequent doping with rare-earth elements (Gd and Eu ions), as an attempt to modify the T_C. Magnetic characterization of ferrite nanocrystals showed that room temperature M_s and the corresponding T_C values were strongly dependent on the type and amount of the dopant species.     

Hybridization-induced charge rebalancing at the weakly interactive C60/Fe3O4(001) spinterface

Spin injection in organic and molecular spintronic devices is largely defined by the electronic and magnetic structure of the constituting organic/ferromagnetic “spinterfaces”. Unlike most of the previous studies involving highly interactive organic/metallic interfaces, we present here the valence electronic structure of a weakly hybridized interface between C₆₀ and epitaxial Fe₃O₄(001), which is unraveled for the first time by means of synchrotron-based photoelectron spectroscopy. Using resonant excitation of Fe 2p core electrons into the unoccupied 3d states, we are able to extract the effect of C₆₀ adsorption on the different ionic sites of the mixed valence magnetic oxide. We elucidate, using a proposed model, that electron donation from C₆₀ leads to surface charge rebalancing in Fe₃O₄, which is accompanied by an enhancement of the conductivity, where the half-metallic nature of the ferrite is largely preserved. These observations, which have so far not been reported for existing organic/metallic systems, are expected to play a significant role in spin transport across this novel interface. Our work showcases the fascinating physical phenomena unique to organic/magnetic oxide spinterfaces, and offers a new pathway towards interface engineering for organic spintronic applications.     

Transformation of symmetric waves of a circular waveguides on a bianisotropically gyrotropic diaphragm

A method for solving the problem of transmission of symmetric Е- and Н-waves of a circular waveguide with perfectly conducting walls through an azimuthally symmetric diaphragm of a bianisotropically gyrotropic material is developed. Solving the problem is reduced to the numerical solution of a system of partial differential equations for the potentials. Conditions for the mutual transformation of the Н₀₁- and Е₀₁-waves passing through ferrite and plasma diaphragms in a longitudinal magnetic field are studied numerically.     

Nouvelle méthode de détermination des parties réelles des paramétres électriques et magnétiques des résonateurs à ferrites saturés et non saturés

Real parts of dielectric and magnetic material parameters of saturated and partially magnetised ferrites are determined in the frequency range : 2.5-4 GHz. Formulas of the tensor permeability elements are not used for the calculation of these parameters which are deduced from the degenerated resonant requencies of theTM ₀₂₀ andTM _?210 modes. These frequencies are measured in an appropriate metallic cavity where is centered a ferrite disk suitable for a 2 GHz circulator.     

Influence of Oxygen Pressure on the Properties of Ni-Mn-Zn Ferrite Films on Silicon Substrate

Ni-Mn-Zn ferrite films were prepared on silicon substrate with CeO₂/YSZ (YSZ: yttria-stabilized ZrO₂) as buffer layer by pulsed laser deposition. The influence of oxygen pressure on the microstructures and magnetic properties of films were studied. It was shown that the film crystallinity, microstructure and soft magnetic properties were sensitive to the oxygen pressure. High quality film with preferred (311) orientation, uniform surface structure, high purity and excellent soft magnetic properties can be obtained at the oxygen pressure of 1 Pa. The saturation magnetization (M _s) is higher than 230 emu/cm³ with a coercivity (H _c) smaller than 30Oe, which is suitable to be used in high-frequency devices.     

A spherical scatterer inside a circular hollow dielectric waveguide

A theoretical investigation is presented of scattering characteristics of a perfectly conducting spherical object placed inside a quasi-optical transmission line of the millimeter and submillimeter waves in the form of a circular hollow dielectric waveguide (HDW). From the analytical expressions obtained, backscattering and extinction cross sections of this object are derived via the excitation coefficient of the dominantHE ₁₁ mode of the circular HDW and the HDW geometrical parameters. The agreement of the results with the corresponding data for the scattering of a plane homogeneous wave is shown.