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Ferrite isolators used to protect magnetrons in indusrial microwave equipment may be simpler in design than those for communication applications since reverse attenuation and bandwidth requirements are moderate. On the other hand, high average power and large load reflection call for careful design of cooling parameters.A method is given which yields a constant surface temperature along the ferrite body by means of special tapering of ferrite slab height. This results in minimum isolator length. By proper choice of ferrite material (e.g. yttrium-iron garnet) and careful construction, average power handling of 25 kW at 915 MHz is possible.

The introduction of ferrite microwave circuit elements has allowed considerable simplification in the realization of many system functions. However, to date practical low loss ferrite devices have not been built to operate at frequencies below 3,000 mc. Many problems arise when one attempts to build devices to operate below this frequency. Some of these problems arise from the fact that mechanisms of loss occur in the ferrites at lower frequencies which are negligible at the higher microwave frequencies. In addition, at frequencies below 1,000 mc, one can seldom neglect the existence of internal anisotropy fields in the ferrite materials. The most fundamental limitation to the operation of ferrite devices at very low microwave frequencies, however, is that one is approaching the relaxation frequency for ferromagnetic resonance, and as a result the performance of all ferrite microwave devices must deteriorate at sufficiently low frequencies, regardless of whether one assumes a ferrite whose other properties are ideal. All these problems are discussed and quantitative expressions are obtained for the ultimate low-frequency limitation of ferrite isolators, circulators, and microwave gyrators.

The wave propagation in a dielectric rod is used to explain the behaviour of ferrite rods in 45° Faraday-rotation isolators. The influence of the diameter of the rod and of variations in wavelength upon the Faraday rotation are considered.

The paper reviews some of the research and development projects which led to the designs for a ferrite directional coupler, a ferrite microwave switch and ferrite-loaded cavity filters. Directional coupling is accomplished at microwave frequencies by extending a ferrite cylinder through the common wall of two rectangular waveguides joined at the broad face. Experimental data for coupling and directivity are given for two ferrite materials as a function of frequency, biasing field and diameter of the Ferrite post. A microwave circulator utilizing ferrite elements can be converted into a fast-acting microwave switch by placing the ferrite in a pulsed magnetic field. The design of a switch based on the Faraday rotation phenomenon and techniques for the reduction of the short-circuited-turn effect of the waveguide are discussed. Large ferrite samples are placed in microwave cavities with the object of achieving tunable microwave filters. Experimental data at X-band frequencies on variation of cavity resonant frequency, bandwidth, loss, cavity and window coupling are given as a function of applied magnetic field. Of particular interest are the results obtained with a circularly polarized cavity designed to produce a reflectionless filter which couples nearly 100% of the energy from the main waveguide at the cavity resonant frequency.

A technique is described for high-speed electronic tuning of an inductive device capable of handling VHF powers in excess of 100 watts CW. Electronic tuning is accomplished by means of a controlled dc bias applied to an inductor with a ferrite core. The orthogonal relationship of the applied dc magnetic bias and the absorption and dispersion of the ferrite is fundamental to circumventing problems that hitherto have limited the use of ferrite in magnetically tuned circuit,,; handling RF power. As opposed to conventional magnetic-bias tuning, the ferrite core is operated above saturation. In this mode, it is seen that the ferrite cores can be operated with high RF fields with no detectahle degradation of Q and negligible distortion products. Specific examples are presented of file application of this new capability in medium-power amplifiers operating over the frequency range of 70-300 MHz.

This paper is intended as a review of developments which allow ferrite materials in a planar geometry to be used in the realization of magnetic devices which are compatible in form with other microwave integrated circuits. These devices include phase shifters (reciprocal and nonreciprocal), latching circulators, isolators, and phase and amplitude modulators. The application of some of these devices is demonstrated in the form of electronically steerable array antennas.

This paper discusses the design problems of microwave Faraday modulators for use with signal frequencies at the lower end of the megacycle spectrum. The frequency limitation caused by skin effects in the guide wall is overcome by using the waveguide as a modulating helix. It is shown that the other important factor is ferromagnetic resonance phenomenon in the ferrite at the signal frequencies. Means are suggested for avoiding this limitation by using ferrite compositions which give reasonable performance at both the carrier and signal frequencies. Details of the modulation conversion efficiency of two experimental modulators are given, and these show that a first order sideband output 15-20db down on the input power of an X-band carrier can be realized.

This paper describes the use of ferrite materials as cores for inductors and develops methods for taking maximum advantage of their properties in the design of inductors for communication circuits.

This report describes a design concept and its implementation for an all-channel transistorized TV tuner with common RF amplifier, mixer and local oscillator for both VHF and UHF TV bands. The VHF and UHF tuned circuits of each stage are mounted on a common wafer of the channel selector. Interaction between the VHF and UHF tuned circuits is eliminated by the novel use of ferrite beads and shielding. The result obtained by this design concept is a low cost, compact and simple all-channel TV tuner with single knob tuning capability. This work was done at Hazeltine Corporation, Hazeltine Research Division (Plainview, N.Y.), under a contract with Hazeltine Research, Inc.

The dispersion relations (/spl omega/-/spl beta/diagrams) for propagation of the quasi-TEM mode and higher-order symmetric modes in longitudinally magnetized ferrite-filled coaxial waveguide are presented. The dispersion relations for ferrite-filled coaxial cavity resonators are analyzed and presented graphically. The performance and operation of an X-band tunable ferrite filter is evaluated in light of the /spl omega/-/spl beta/diagrams

Loading a ferrite resonance isolator or differential phase shifter with a dielectric or biasing the ferrite with an inhomogeneous dc magnetic field are very useful ways of improving the performance of these ferrite devices. Whereas these methods are very commonly used in transverse-field ferrite devices, no extensive analytical treatment of the subject has appeared in the literature. It is the purpose of this paper to present a theoretical analysis of the problem, chiefly by means of combined boundary-value and perturbation-theory approach. It will be shown that dielectric-loading and tapered-field techniques increase the bandwidth of isolators and phase shifters, the isolation-to-insertion loss ratio of the former, and the phase shift of the latter.

The ferrite isolator and the ferrite circulator have been applied separately to improve the accuracy of measuring small microwave noise powers or small power differences. Either the isolator or the circulator effectively isolated the input circuit of a microwave receiver from the impedance of the source. As a result, the measurement errors introduced by mismatched source impedances were reduced by as much as 98 per cent. The added input circuit losses of the ferrite components reduced the receiver sensitivity by only about 10 per cent. Since the accuracy of measuring small noise power differences was limited principally by impedance errors, the addition of ferrite isolation to the receiver input circuit increased the sensitivity of measurement to near the theoretical limit. The ferrite isolator was used as a passive transmission element in these experiments. The ferrite circulator, however, was used as an electrically-operated, microwave switch. This switch was used to replace the mechanical chopper in a Dicke-type radiometer. In addition to impedance isolation, the ferrite switch makes possible rapid comparison measurements of the microwave noise powers from any two sources, or of the noise powers from the same source in two different polarizations.

Several ferrite devices recently developed for systems applications are described. The behaviour and characteristics of extremely compact u.h.f. isolators based on new microwave techniques are reported. Faraday rotation and Y-circulators operating over wide temperature ranges and with broad frequency bandwidths are described. Also included are switches based on Faraday rotation, turnstile-junction and stripline-junction circulators. Strip and rectangular coaxial transmission-line phase shifters particularly suitable for antenna scanning applications are discussed. A discussion in terms of the intrinsic properties of ferrite materials is given that defines the frequency regions of operation for these phase shifters.

This paper and the one following describe the application of ferrite circulators at VHF frequencies. A brief description of the non-reciprocal properties of ferrites is given along with a summary of the theoretical operation of a junction circulator. Several applications are briefly described in this paper in addition to the detailed description of a multiplexer in R. Klein's paper. A detailed bibliography on ferrite devices is included for those who wish to pursue the subject in greater depth.

Resonance isolators operating at X -band frequencies have been constructed in conventional 50-ohm microstripline by positioning ferrite strips on the surface of the alumina substrate adjacent to the stripline conductor. A transverse external magnetic field is applied in the plane of the surface to obtain the necessary Kittel resonance condition. It is shown that by suitable choice of ferrite dimensions the performance may be optimized to give a forward loss of 0.5 dB together with a reverse loss in excess of 30 dB at resonance. The influence of saturation magnetization of the ferrite as well as relative permittivity of the substrate material has also been examined. Nonreciprocal phase shift may be obtained by using this geometry; but high external field is required to saturate the ferrite. A modification employing an all-ferrite substrate, which may be used to design a phase shifter operated at remanence, is described.

In recent experiments the compositions and methods of preparation of various ferrites were varied with the aim of achieving optimum magnetic, magnetomechanical and mechanical performance. Essential improvements of the temperature dependence of the permeability, the piezomagnetic coupling coefficient and the mechanical resonant frequencies have been obtained. These were achieved by small cobalt substitutions in nickel and lithium ferrite and in mixed nickel-zinc and lithium-zinc ferrites.The total variations of the mechanical resonant and anti-resonant frequencies of ferrite filter elements in the temperature range 20–50°C are normally 0·10–0·25% in existing commercial nickel and nickel-zinc ferrites, but have been reduced to 0·03% or less. The coupling coefficient at remanence of such a stable ferrite may be well above 0·20 with a suitably modified sintering treatment. Since the mechanical Q-factors are usually much better than 2000, such ferrite vibrators can be profitably applied to the construction of electrical and electromechanical band-pass filters. The cobalt substitutions, apart from leading to a very low temperature coefficient of the real part of the permeability, also decrease the imaginary part, so that these cobalt-substituted ferrites have a high figure of merit.

The paper deals with an application of ferrite inductors where their high Q-factors are of prime importance. The design and performance of two pairs of complementary low- and high-pass filters using ferrite inductors is discussed. The filters provide a discrimination of 40 dB between pass and stop bands. In the first version, the pass band of the low-pass filter ends at 59·4 kc/s and the stop band begins at 60·6 kc/s In the improved version, the transition range has been reduced to 59·7?60·3 kc/s. The use of these filters as group-separating filters in a 24-circuit carrier-on-cable telephone system is considered.

The paper describes certain properties of manganese-zinc ferrite cores used in inductor coils. In particular, the stability characteristics which appear to be substantially different from those of iron or alloy dust cores are examined. It is pointed out that the permeability variations are due to several external causes. Only the principal features of these phenomena may be given because of the large quality dispersion of ferrites.Owing to its very reduced losses the manganese-zinc ferrite is the best material for low-induction coils used in the zero to some hundred kilocycles per second frequency range. However, its use requires very accurate knowledge of the different aspects of the stability phenomenon.Some measurement results illustrate the typical behaviour of essential ferrite characteristics.

The factors affecting the production of frequency modulation are considered when the modulator is either a reactance valve or a variable inductance employing magnetic variation of the core permeability. It is shown that whilst the effectiveness of the reactance valve is reduced at high oscillator frequencies or with large fractional frequency deviations, the inductance modulator is not affected to the same extent. The losses inherent in the magnetic core of the inductance modulator are considerably reduced by using magnetic ferrites; such a ferrite modulator is described. The effects of magnetic hysteresis, in producing oscillator frequency instability, are minimized by applying a specific level of polarization from a permanent magnet. A figure of merit is developed by which the frequency instability can be calculated from a knowledge of the prevailing magnetic conditions. The ferrite frequency modulator is particularly suitable for use with variable frequency oscillators where the equipment is to be portable and free from spurious sub-harmonic outputs. Results are given which serve to indicate the performance of this modulator.

The subsidiary resonance observed in ferrite at high microwave magnetic field intensities is suitable for limiting purposes. The limiter threshold power is related to the units of magnetic field intensity produced in the ferrite per unit of power input. The circumferential field about a wire is directly proportional to the current and inversely proportional to the wire diameter. Thus a fine wire embedded in ferrite will produce intense microwave fields at low microwave power levels provided that the wire is properly matched to the microwave structure. The response of a ferrite limiter to a microwave pulse characteristically exhibits a leakage spike and a plateau whose power level is proportional to ΔHK2. Thus, low threshold power levels normally can be achieved with narrow-linewidth materials. This paper analyzes the fine-wire technique for limiter applications and shows that threshold power levels less than a watt can be achieved in ferrite with wide linewidths. Particular structures were designed, built...

This investigation describes analytical and experimental results obtained on a broadband ferrite limiter at K u band which utilizes a synchronously tuned waveguide bandpass structure. This device is aimed at providing protection for communications and electronic warfare systems over a bandwidth from 12 to 30 percent at K u -band frequencies. The circuit consists of a series of three cavities in a waveguide transmission line, the coupling being accomplished via the irises or symmetrical inductive slits between cavities. Because of this cavity structure, the observed threshold power levels have been reduced by an order of magnitude. By utilizing a combination of single crystal YIG and lithium ferrite rods, the threshold power for limiting varies from 0.75 W at 16.0 GHz to 2.0 W at 17.0 GHz with an insertion loss of 0.9 dB.

We made a stripline-type ferrite tuner with polycrystalline CaV garnet at UHF band. The properties of the ferrite disk were first evaluated in a bandstop filter configuration. The effective line width was measured as a function of both frequency and t/D over the band 100-4000 MHz, and we discussed the necessary conditions for making a narrow filter with small insertion loss at low frequency. The coupling theory of the ferrite tuner together with the theoretical equation of the external Q are presented. The experimental values of the external Q almost coincides with the theoretical ones. Tests of this tuner resulted in an insertion loss is 1.9-2.5 dB, a bandwidth of 20-30 MHz, and an attenuation at the image frequency of more than 30 dB. The performance of higher modes is also discussed.

This paper will describe a new type of ferrite switch that was invented by the author. Generally, a microwave ferrite switch has unstable characteristics because of the unstable characteristics with temperature of the ferrite material used. A stable ferrite switch can be made using two hybrids and two new wave guide elements with ferrites, and making the best of balancing characteristics obtained by combining the wave guides.

An edge-guided mode of propagation is found in wide microstrip and stripline transmission devices using ferrite dielectric slabs magnetized perpendicular to the ground plane. The theory of propagation is reviewed, and applications of the principles are described for devices such as isolators, multiport circulators, and phase shifters.

Presented is design of VLF ferrite loaded antennas and a general review of the properties of short electrical radiators, of a general theoretical analysis of the performance of ferrite loaded antennas, of the presentation and discussion of extensive experimental verifications of the theory, and, finally, of a preliminary design of an Omega type antenna system. The latter would operate at 10.2 Kc/s with a radiated power up to 20 Kw, and with an efficiency of the order of 10%. While this design is tentative, it constitutes a sound reference basis for the development of a final ferrite loaded antenna system. The work discussed indicates that the use of ferrite loading provides considerable wavelength reduction along the axis of the radiator and results in structures which have radiation resistance larger than that of metal air antennas having the same height. The over all design may be achieved with satisfactory characteristics of efficiency, reliability, bandwidth and cost. The maximum radiated power is limited by the distortion which occurs when the magnetic materials becomes saturated; how ever, in practice satisfactory levels of out put power may be obtained for medium power applications.

Switching characteristics of latching ferrite devices are discussed and it is shown that the switching time may be defined in several ways, depending on the application of the device, The interdependence of the switching time specification with several other pertinent variables, such as driver cost, switching energy, and bandwidth, is discussed.

The Arc Plasma Spray process (APS) makes possible the fabrication of complex ferrite/dielectric composite structures suitable for use as substrates for microwave integrated circuits. A typical two layered microstrip geometry is shown in the insert of Fig. 2. The usual microstrip design problems are now complicated because of the choice possible in the selection of the ferrite and dielectric material constants (dielectric constant and permeability) and the relative heights of the two materials. As an example of the structures possible, a substrate for a non-reciprocal latching meanderline phase shifter is shown in Fig. 1. TT1-390 ferrite material was deposited in a preformed cavity of a 0.035" substrate with /spl epsiv//sub d/ = 13. A metallization is made and the meanderline structure is formed. Circulators, filters, etc., can be fabricated in the same fashion. Some of the advantages of this approach are: a) the design of previously unavailable circuits is now feasible, b) ferrite materials can be deposited only where they are required in a given circuit, c) the ferrite microwave properties are maintained or enhanced through the APS process, d) high power handling capability is now possible in planar MIC's and e) potential cost savings .

In many microwave systems there is need for a fast-acting switch which has negligible insertion loss in its "On" condition and substantial attenuation in its "Off" condition. Ferrite switches can in general be made fast-acting by thinning waveguide walls to a few skin depths, using low inductance coils and applying pulse circuitry techniques. Switches in rectangular or circular waveguide have been either of the Faraday rotation or the waveguide-beyond-cutoff variety. Some coaxial or stripline structures have been described which show interesting properties. Early work at Bell Telephone Laboratories on ferrite loaded coaxial lines indicated that large amounts of attenuation could be obtained with axial magnetic fields. The high attenuation is the result of a cutoff condition in the ferrite loaded line, and/or ferromagnetic resonance in the ferrite. The applied field may be switched to bring the line into a propagating and low loss condition.

A description is given of the ferrite biasing system for the four tuned radio frequency cavities of the synchrotron. Each ferrite loaded double cavity has a single turn bias winding which is driven to a peak current of 13,500 amperes by a push-pull transformer arrangement. There is automatic tap changing of the transformer to accommodate the variable impedance load (for power considerations). The programming and frequency response of the system have to be such that each cavity can operate as the reso nant circuit of a self tracking radio frequency amplifier over the frequency range 6.5 to 30 Mc at the 20 cps repetition rate of the synchrotron. Between acceleration cycles it is necessary to program the ferrite to a given magnetic state, near that of maximum radio frequency permeability. (auth)

An elevated substrate ferrite film circulator has been designed. The ferrite film and the rf conductor are deposited completely above the substrate. The ferrite disc has its thermal expansion coefficient adjusted to match the sapphire substrate. Circulator insertion loss and isolation are 0.6 dB and 20 dB over a 5% bandwidth (f/sub o/ = 12.3 GHz), respectively.

Diaphragms made of ferrite slabs or metal diaphragms with ferrite screens have nonlinear susceptibility dependent on the applied transverse direct magnetic field. Such diaphragms, employing D type ferrite material, have been used at frequencies of 9 and 10GHz for coupling to a cavity, and measurements of v.s.w.r., Qfactor and impedance have confirmed theoretical predictions that by altering the magnetic field it is possible to tune the cavity. Similar elements can be used in variable directional couplers etc.

A new type of ferrite antenna with fairly high sensitivity has been studied and experimental results are presented. Although ferrite antennas have long been used as one of the typical antennas of small size, it seems that the remarkable increase of the sensitivity of the ferrite antennas depends upon dimensions and performance of ferrite material, and improvement of those factors is not expected so easily at the present state of the art. One solution for this problem may be the application of the integration technique, that is combining an antenna and active devices in a unified structure with an inseparable form. To form an active device within an antenna, parametric excitation is incorporated into a ferrite antenna structure, and the principle of power transfer between signals, which follows Manley-Rowe's relation, is applied to it for obtaining an active gain within the antenna itself. The permeability variation of the ferrite material is effectively utilized to produce an active function from a passive antenna system. Results show about 5 to 10 dB gain depending upon the pumping power interims of S/N over the conventional passive ferrite antenna having the same size as that of the active antenna.

In recent experiments the compositions and methods of preparation of various ferrites were varied with the aim of achieving optimum mechanical and piezomagnetic performance. Essential improvements could be obtained by small, highly effective variations in the chemical composition and by suitable modifications of the mechanical and thermal treatments. In CW operation, ferrites can excite radiation intensities up to about 10 w/cm2, with an electroacoustic efficiency of more than 75% up to 50 kc/sec. So they are highly promising for underwater transmission and processing, in spite of their brittle nature (ultimate tensile strength about 6 kg/mm2). Wide‐band hydrophones with linear frequency response and high pressure‐sensitivity can also be built from such ferrites having magnetomechanical coupling coefficients at remanence up to almost 0.25, like Permendur. The total variation of the mechanical resonant and antiresonant frequencies of ferrite filter elements in the temperature range from +20 to +50°C, being 0.1 to 0.25% for existing commercial ferrites, could be lowered to 0.03% and less. Since the mechanical quality factors are usually much better than 2000, such ferrites can be profitably applied to the construction of electrical and electromechanical band filters.

The letter investigates the distribution of power as a function of frequency in a cavity containing a resonant ferrite sample. Formulas and a Figure are presented for the maximum power that can be incident on the system without deterioration of the resonance linewidth of the sample.

Microwave power division employing the field-controllable microwave permeability of ferrites has been used as the basis of current-controlled variable attenuators and switches. Three such devices are described:(a) A 4-port device in waveguide, with ferrite phase shift controlling power division between two ports of exit. Its operating range is 2.7-3.3 Gc/s. (b) A 3-port device, in waveguide or stripline, with a similar basis of control. However, its most suitable application is with a fixed field, as a circulator. (c) A cross-polarization waveguide device using a ferrite to control the rotation of polarization, thereby forming a reflective switch. It is simple and has a good bandwidth, but frequency control is difficult. The construction, mode of operation, and performance are given in each case.

The paper discusses possible configurations of ferrite elements for application to an 8 mm isolator operating in the circular TE01 mode. It is concluded that, when using this wave mode at such a frequency, there is one configuration that offers particular advantages—namely that of an eccentrically mounted rod of a highly anisotropic ferrite transversely magnetised to give gyromagnetic resonance at the frequency of operation. The application of perturbation theory to this arrangement shows that there are two alternative positions of the ferrite rod, at different radii, for which the reverse/forward loss ratio is a maximum, and it indicates that the position nearer to the axis of the waveguide should provide the better performance. As the TE01 mode is not dominant in a circular waveguide, the isolator must inevitably operate under conditions capable of providing for the support of a number of other modes at the same time. In the reverse direction of the isolator, the ferrite introduces strong coupling between the TE01 mode and some of these other propagating modes, so that a mode filter forms an essential part of the isolator. Results are given of an experimental investigation showing that a worthwhile degree of isolation can be obtained with a device of this kind.

An essential feature of Bosnia's theory of the three-port stripline junction circulator is the smallness of the splitting of a degenerate pair of normal modes. This results in only a small asymmetric distortion of the isotropic field configuration in the disks. A new junction geometry is described which makes use of a garnet ring around a ceramic disk instead of the conventional garnet disk shape. When the degenerate modes of the two isotropic configurations are identical, the circulation adjustment for each geometry is nearly the same. This new circulator geometry is characterized by a low insertion loss and a large thermal capacity.

The theoretical behaviour of some microwave ferrite structures has been experimentally verified by detecting the thermal rise produced by the dissipated r.f. power in certain characteristic regions.