Microwave Ferrite Devices Research Articles

Ferrite thin films for microwave applications

Production of ferrite thin films is the key to integration of microwave ferrite devices (circulators for phased array antennas, for instance). The interesting materials are the usual microwave ferrites: garnets, lithium ferrites, barium hexaferrites. The required thicknesses are a few tens of micrometers, and it will be important to achieve high deposition rates. Different substrates can be used: silicon and alumina both with and without metallization. The films were deposited by rf sputtering from a single target. The as-deposited films are amorphous and therefore require careful annealing in oxygen atmosphere. The sputtered films are a few micrometers thick on 4 in. substrates. The optimum annealing temperature was found by trying to obtain the highest possible magnetization for each ferrite. The precision on the value of magnetization is limited by the precision on the thickness of the film. We obtain magnetization values slightly lower than the target’s. The ferromagnetic resonance linewidth was measured on toroids from 5 to 18 GHz.

A generation of microwave ferrite devices

The development of microwave ferrite materials and devices over the last thirty years is traced. The status of materials, devices, and theoretical understanding prevalent in the mid-1950s is first reviewed. Developments in materials engineering of garnets and lithium ferrites in the 1960s and 1970s are described, along with the evolution of circulators and phase shifters. Current levels of performance achievable in circulators and phase shifters are described, and future challenges and opportunities are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave Ferrite Devices: The First Ten Years

The first twenty years of microwave radar development was done entirely without the benefit of ferrite devices. The first experimental microwave ferrite device was demonstrated in 1949. Ten more years of research and development on the devices was required before significant performance was achieved and large scale commercial participation began. This is the story of those ten years.

The present status of microwave Ferrite materials and devices in China

The recent research, development, and production of the microwave ferrites and devices in some dozen of institutions in China are discussed. The improvement of microwave ferrites through the study of ionic substitution, ionic distribution, solid-state reaction, mechanisms of loss, as well as preparation technologies are given. Also presented in the paper are the theoretical and experimental studies which have resulted in the enhancement of the performance of microwave ferrite devices, such as lumped element circulators and isolators, low-temperature and low-loss circulators, yttrium iron garnet (YIG) tuned filters, etc. Magnetostatic wave delay lines now under investigation are discussed.

Annotated literature survey of microwave ferrite materials and devices

An annotated literature survey covering major development in the area of microwave ferrite materials and devices for the period 1968-1974 is presented.

Magnetism in Microwave Devices

The functions of ferrite components in advanced microwave systems are briefly outlined, and the principal requirements described. The successful development of these sophisticated devices is the cumulative result of contributions from many areas of basic research and technology. As an example of the dependence of device performance on diverse efforts, the status and evolution of ferromagnetic digital phasers are reviewed. In this instance, materials research, ceramic technology, methods of numerical analysis, and the understanding of basic damping mechanisms have all contributed to the realization of practical devices. The application of ferrite devices to microwave integrated circuits is also outlined and some recent experimental results given. Other new trends in the field of microwave ferrite devices are briefly mentioned, as are areas most in need of further research.

Permanent magnets for microwave devices

The magnetron, invented in 1939, created the need for a microwave tube magnet which evolved from the early horn magnet to the U magnet, the E magnet, and finally the bowl magnet. A more recent innovation, the self-shielded cylindrical magnet, is now used on many crossed-field amplifiers. The klystron and the traveling wave tube created the need for permanent magnets with gaps longer than their diameters. The field straightener and the periodic permanent magnet facilitated the use of permanent magnets in focusing these linear beam tubes. The operation of magnetrons, crossed field amplifiers, klystrons, traveling wave tubes, and microwave ferrite devices, and the permanent magnets which are used in conjunction with these devices are described. Magnetic circuit design criteria, design methods, and the magnetization and stabilization of permanent magnets are discussed. The requirements of microwave devices have provided much of the incentive for the great advances in permanent magnet materials made in the last decade. The recent development of rare-earth-cobalt powders which exhibit the highest magnetocrystalline anisotropy ever recorded are of great interest to the microwave device designer.

Microwave ferrite materials and devices

The crystal structure of ferrites including garnets and their methods of preparation are first reviewed. This is followed by an examination of microwave ferrite devices and their application to actual systems. Sufficient theoretical details as well as an extensive though not exhaustive list of references are included for ready reference. The most widely used microwave ferrite device is the isolator, a device which possesses nonreciprocal properties. The function of this device in various configurations is therefore studied in some detail. Then, ferrite-phase shifters, including the latching variety, circulators, modulators, power limiters, switches, amplifiers, delay lines, and filters are examined in turn. Microwave ferrite devices, in particular isolators and circulators, are commonly used in the laboratory. Other devices, such as modulators, limiters, and switches, are used respectively in microwave systems in carrier modulation, receiver protection, and antenna switching, etc. Much of the ferrite device research and development in recent years has been concerned with the Y -junction circulator and the coincidence power 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.

Temperature Stabilization of Unsaturated Microwave Ferrite Devices

A technique utilizing a composite magnetic series circuit is described wherein the flux density of unsaturated microwave ferrite is maintained constant in spite of large changes in microwave ferrite saturation magnetization, coercive force, and hysteresis loop shape. The composite circuit consists of a driver, a flux limiter, and a microwave ferrite. The driver supplies the necessary mmf to maintain constant flux level in the circuit throughout the temperature range. The flux limiter, a particularly stable ferrite material, establishes the constant flux level. The driver and flux limiter may lie outside the microwave region and may in consequence possess indifferent microwave properties. A simple design procedure is described for determining the driver and flux limiter dimensions. Special attention is given to the effects of air gaps and leakage fluxes which tend to reduce the effectiveness of the technique. A remanence phase shifter is described which suffers a 16% loss of phase shift as a result of an 80°C rise of temperature. By the application of composite circuit techniques, the temperature sensitivity was reduced to less than 2½% over the same temperature range.

SCATTERING MATRIX AND EQUIVALENT CIRCUIT OF AN X-BAND RECTANGULAR WAVEGUIDE CONTAINING FERRITE POSTS

This paper is intended to describe the properties of nonreciprocal microwave ferrite devices from the four-terminal network analysis. First, the impedance and the scattering matrix of an X-band rectangular waveguide containing a transversely magnetized ferrite post are measured as a function of the (1) diameter of the post, (2) position of the post in the waveguide, and (3) applied d. c. magnetic field. Then, the T-equivalent circuits are obtained from the scattering matrix measurements. Results prove that when a thin ferrite post is placed near a side wall of the guide, it acts essentially as a shunting capacitance. The susceptance decreases with d. c. mangetic field. As far as the impedance is concerned, the post itself behaves like a tuning screw. Finally, the equivalent circuit of a waveguide containing two or more ferrite posts is studied. It is found that when the distance between the two nearest posts is greater then λ/2, the equivalent circuit is simply the "single post" circuits connected in cascade. A phase shift network is used to illustrate the application of the principle of the circuit analysis.

Temperature Effects in Microwave Ferrite Devices

With proper choice of shape, it is possible to minimize the frequency shift of ferromagnetic resonance in microwave ferrite components operating over a wide range of ambient temperatures. Calculations have been made for minimum resonance frequency shift change in saturation moment. Curves relating the resonance frequency shift as a function of saturation magnetization are plotted for several ferrite geometries. Design curves are presented for reducing dependence of resonance frequency on temperature.

Foreword (Jan. 1958 [T-MTT

With the tremendous advances being made in the microwave ferrite field and solid-state microwave devices, and with the success of the Harvard Symposium in April, 1956, it was felt that further symposia were desired on the subject especially at the radio engineers' level. Hence, it was proposed that the Long Island, New York, and Northern New Jersey Chapters of the PGMTT hold a jointly sponsored meeting on the subject during the 1956-1957 season.

Round Table Discussion on Design Limitations of Microwave Ferrite Devices

The 1957 Annual PGMTT Meeting concluded on May 10 with a round table discussion on Design Limitations of Microwave Ferrite Devices. This discussion was moderated by Professor C. L. Hogan of Harvard University, and the panel members were Drs. J. O. Artman, H, J. Carlin, D. L. Fresh, G. S. Heller, R. C. LeCraw, H. Seidel, and P. H. Vartanian. The topics considered appropriate for discussion were: 1) high-power effects (nonlinearity), 2) low-frequency limits, 3) high-frequency limits, 4) anomalous propagation in ferrite loaded waveguides, 5) below-saturation behavior of ferrites, 6) "fast" ferrite devices (depending on relaxation time), 7) bandwidth problems, 8) materials and losses, and 9) high-speed magnetic field problems. An edited version of the recorded discussion is published on the following pages.

Frequency and Loss Characteristics of Microwave Ferrite Devices

The four major microwave ferrite devices, ie., the Faraday rotator, the resonance isolator, the nonreciprocal phase shifter, and the field displacement devices are discussed in terms of their loss properties over a range of frequencies. By means of perturbation theory the figure of merit of these devices is derived in the idealized limits for various ferrite geometries. These limiting values are analyzed in terms of the experimental results of the resonance loss for polycrystalline and single crystal measurements and compared with existing data on practical devices. The analysis indicates a possible low-frequency limit of Faraday and nonreciprocal phase shift circulators at about 1000 mc. The low-frequency limit of the resonance isolator is estimated at about 200 mc with a reverse-to-forward ratio of about 10. The problem of broad banding is also discussed in terms of the perturbation results.

The Elements of Nonreciprocal Microwave Devices

This paper gives an elementary but nevertheless quite complete introduction to the basic theory of nonreciprocal microwave devices. The concept of reciprocity, itself, is introduced and some of the consequences which result when one violates reciprocity are pointed out. The basic theory of microwave ferrite devices is developed from a classical theory which gives one a strong intuitive feeling for extrapolating the theory to devices not discussed in the paper. The analysis is extended to include basic design criterion for the three general types of microwave ferrite devices which exist today. The operation of these devices are compared and advantages and disadvantages of the various devices are pointed out for the benefit of the component engineer.