US 3286201 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Nov. 15, 1966 R. w. ROBERTS, JR 3,236,201
FERRITE CIRGULATOR HAVING THREE MUTUALLY COUPLED COILS COUPLED TO THE FERRITE MATERIAL 5 Sheets-Sheet 1 Filed April 29, 1966 INVENTOR. ROY W. ROBERTS JR.
W MM. ATTORNEYS Nov. 15, 1966 R ROBERTS, JR 3,286,201
FERRITE CIRCULATOR ING THREE MUTUALLY COUPLED COILS COUPLED TO THE FERRITE MATERIAL Filed April 29, 1966 5 Sheets-Sheet 2 INVENTOR. ROY W. ROBERTS JR.
ATTORNEYS Nov. 15, 1966 R. w. ROBERTS, JR
FERRITE CIRCULATOR HAVING THREE MUTUALLY COUPLED GOILS COUPLED TO THE FERRITE MATERIAL 5 Sheets-Sheet 5 Filed April 29, 1966 'INVENTOR. ROY w. \ROBERTS JR w WM ATTORNEYS United States Patent FERRITE CIRCULATOR HAVING THREE MUTU- This application is a continuation-impart of copending application Serial No. 326,850, filed November 29, 1963 now abandoned.
This invention relates generally to circulators, and more particularly to circulators for the UHF and lower frequency ranges.
A circulator, as used herein, is an N port device where N is greater than 2. It has the property that when'the ports are suitably numbered 1 through N, an applied input electrical signal at port 1 emerges from port 2 with a minimum of attenuation while neglible power emerges from the other ports. Likewise, a signal applied to port 2 emerges from port 3, etc.
Circulators have been made for several years for the microwave frequency range. These have taken the form of differential phase shift circulators and Faraday rotation circulators. Both types make use'of a ferrite element as a non-reciprocal perturbation. Because of this, the usable band width has been limited and the size of the circulator relatively large.
Ferrites, as discussed in this application, include all types of ferrimagnetic oxides such as substitution ferrites, spinels, perovskites, garnets, anti-ferromagnetics and hexagonal barium ferrites. These are discussed in Lax and Button, Microwave Fer-rites and F-errimagnetics, McGraw-Hill, 1962.
In recent years. considerable advances have been made in so-called junction ci'rculators. This class of circulator makes use of ferrite elements at the junction of three or more transmission lines. These devices have considerably reduced the size of such circulators partly because the ferrite interaction is dominant rather than a perturbation.
These latter junction circulators consisted of a disc of ferrite located at the junction of three strip transmission lines. The dimensions of the ferrite disc were such that the diameter was approximately equal to one-half wavelength at the operating frequency of the circulator. The ferrite acts as a resonant cavity in which electric energy is stored in the capacitance between the stri-pline center conductor and ground planes and magnetic energy is stored in the RF magnetic fields in the ferrite. A perpendicular D.-C. magnetic field causes the permeability of the ferrite t-o anisotropic, thus causing non-reciprocal coupling between the ports. The dimensions of the ferrite disc determine the resonant frequency of the cavity which, in turn, determines the operating frequency of the circulator. This results in a linear dependence betweencirculator diameter and wavelength.
The result of this linear relationship between the operating wavelength and the size of the ferrite disc is that the circulator becomes extremely large at low frequencies. For example, a circulator designed to operate at 150 MHZ. has a diameter of approximately eight inches. The large size of these distributed constant junction circulators makes them impractical for use in many UHF and lower frequency range applications. The large ferrite size also results in a high cost.
It is, therefore, a general object of the present invention to provide a circulator for use in ultra high frequency and lower frequency ranges of the electrical frequency spectrum.
It is another object of the present invention to provide a circulator which is compact and simple in construction.
3,286,201 Patented Nov. 15, 1966 It is still another object of the present invention to provide a circulator making use of a multiple turn circuitferrite interaction.
It is a further object of the present invention to provide a circulator in which the function of non-reciprocity and circuit tuning are separated.
It is a further object of the present invention to provide a circulator which is broad band and inexpensive.
The foregoing and other objects of the invention will be more clearly apparent from the following description taken in conjunction with the accompanying drawing.
Referring to the drawing:
FIGURE 1 is a plan view, partly broken away, to show the interior of a typical circulator in accordance with the invention;
FIGURE 2 is a side elevational view of the circulator of FIGURE 1, again partly broken away, to show the interior elements;
FIGURE 3 is a sectional view taken along the line 33 of FIGURE 2;
FIGURE 4 is a perspective view showing the multiple turn circuit ferrite interaction arrangement;
FIGURE 5 shows the equivalent electric circuit for one connect-ion of the lumped circuit elements;
FIGURE 6 shows an equivalent circuit diagram for another connection of the lumped circuit elements;
FIGURE 7 shows an equivalent circuit diagram for a double tuned connection of lumped circuit elements;
FIGURE 8 shows an equivalent circuit diagram for another double tuned connection of lumped circuit elements;
FIGURE 9 shows the equivalent electrical circuit for a delta connection of the lumped circuit elements; and
FIGURE 10 is a curve showing the circulators electn'cal properties as a function of frequency.
Generally, in accordance with the present invention, there is provided a circulator which includes a junction of at least three transmission lines which includes mutually coupled coils. A ferrite material is disposed in cooperative relationship with the mutually coupled coils. Means for magnetizing the ferrite are provided to impart non-reciprocity. Lumped capacitance is connected in each of the transmission lines. The coils, capacitors and ferrite provide separation of the functions of non-reciprocity and circuit tuning.
The lumped constant circulator of the present invention is made up of two basic portions; a magnetic energy storage element and an electrical energy storage element. These two elements interact together in such a way as to resonate at the frequency of interest. The magnetic energy storage element is responsible for the nonreciprocal properties of the resulting circulator. The magnetic energy storage element consists of a ferrite body on which is wound three or more coils connected together in a wye or delta configuration. A D.-C. magnetic field perpendicular to the axis of all three coils magnetizes the ferrite body to a low loss anisotropic state considerably above (or below) the field producing ferromagnetic resonance. The properties of the magnetic energy storage device are determined by the number of turns of wire on the windings and the D.-C. magnetic field applied to the ferrite body.
The electric energy storage element can consist of many different circuit connections. For example, a simple capacitor in series with each of the three windings gives excellent performance at narrow bandwidths. Here, the value of the capacitor is chosen such as to resonate with the inductance of the magnetic energy storage element at the desired frequency. Exact values of the capacitance are determined by the inductance of the magnetic energy storage device, the impedance of the input and output circuits and the desired operating frequency of the device.
It is important to note that the electric energy storage element does not have to be located within the circulator,
but can be located remotely from the magnetic energy storage element; and, in fact can consist of parasitic capacitances existing elsewhere in the circuit. Hence, two generalized configurations of the lumped constant circulator exist. In both cases, the non-reciprocal properties of the device are determined by the magnetic energy storage element. The two configurations comprise a magnetic energy storage element alone with the electric energy storage device being located remotely or as a part of a surrounding circuit and an integrated device in which the electric and magnetic energy storage elements are housed within a single structure.
FIGURE shows a typical plot of a lumped constant circulators electrical properties as a function of frequency. It is seen that the device has tuned circuit properties and over a reasonably wide band affords a very high ratio of forward to reverse attenuation. Varying the capacitive energy storage element would permit tuning of this device over a moderate frequency range and more complex electrical energy storage elements would give broader band performance.
Referring to FIGURES l3, a typical circulator for UHF includes spaced ground planes 12 and 13. Mounting plates14, 16 and 17 of the coaxial connectors 18, 19 and 21 are secured by screws to spaced ground planes.
The center conductors 31, 32 and 33 of each of the coaxial connectors are each connected to a conventional radio frequency capacitor 36, 37 and 38, respectively. Each of the capacitors have their other terminal connected to one end of a coil 41, 42 and 43, respectively. The capacitors illustrated include a plurality of interleaved plates. However, any conventional capacitor may be used. The coils are mutually coupled to one another. The coils may include a plurality of turns for tight coupling or may comprise a single elongated lead portion adjacent to the ferrite for less coupling. The amount of coupling, i.e., the number of turns, depends upon the circuit application and the impedance desired. The other ends of the coils or leads may be connected to one another to define a Y. It will be apparent to one skilled in the art that the mutually coupled coils may also be connected in a delta connection, as will be presently described. The coils 41, 42 and 43 shown are in the form of multiple turns wound about a ferrite wafer 46, which forms the nonreciprocal element, as will be presently described. FIG- URE 4 is an enlarged perspective view of this arrangement.
The combination of series capacitors and coils 36 41; 37, 42; and 38, 43 form a tuning means whereby the circulator can be matched to the associated transmission line.
The ground planes 12 and 13 may each include a recess or well 47 and 48, respectively, which accommodate permanent magnets 49 and 51, respectively. Cover plates 52 and 53 are disposed over the well and serve to retain the permanent magnet material 49 and 51 in the proper relationship with respect to the ferrite wafer whereby to provide a field through the ferrite material in such a direction as to give rise to the desired non-reciprocity in accordance with well known techniques. In certain instances, it may be desirable to employ magnetic material for the cover plates to offer a lower reluctance path for the magnetic fields of the permanent magnet. For further reduction of the reluctance, side plates 60 of magnetic material may be provided to bridge the space between the ground planes.
The complete assembly may be placed within a housing 56 which includes openings for receiving the associated coaxial connectors and which may have a removable cover plate 58 secured by spaced screws 59.
Referring to FIGURE 5, there is schematically illustrated an equivalent electrical circuit diagram for the circulator just described. The voltage generators defined by the source 61 and resistors 62 represent the signal of the circulator.
at each of the transmission lines. The arrow 63 represents the non-reciprocal characteristic of the ferrite material, while the capacitors and inductors correspond to those previously described and bear like reference numbers.
It is seen then that the tuning function is separated from the non-reciprocal characteristic of the ferrite. The coils are mutually coupled to one another and to the ferrite.
The capacitors may be connected in shunt with the input terminals rather than in series therewith. This is schematically illustrated in FIGURE 6 where like reference numerals refer to like parts.
In FIGURE 7, there is shown an input circuit which provides operation over a broader frequency band. This circuit, in addition to the elements previously described, includes a tuned circuit comprising a capacitor 66 and conventional inductor 67 connected in each of the arms The tuned circuit has one terminal grounded and the inductor connected by a tap to the capacitance and inductance previously described. The double tuning arrangement of FIGURE 7 provides what is known in the art as double tuning to increase the band of frequencies over which the device is operable.
Double tuning can be provided in conjunction with a shunt circuit by introducing a series tuned circuit. This is schematically illustrated in FIGURE 8 by the series capacitor 68 and inductor 69.
FIGURE 9 illustrates the delta connection for mutually coupled coils 41a, 42a and 43a. Capacitors 36, 37 and 38 are shown connected in series with the associated lines. It is to be understood that the capacitors can be connected in shunt. Further, double tuning, as previously described, may be employed.
The diameter of lumped constant junction circulators, unlike the distributed constant circulator, is independent of frequency. For example an approximately /2 inch diameter ferrite disc, as defined herein, can be made to .operate over the 50 to 350 me. range with only a change and inexpensive.
in the number of turns on the ferrite and an adjustment of the D.-C. field. For circulator action, of course, a proper electric energy storage element must be provided.
Thus, there is provided a circulator which is simple The function of tuning and reciprocity are separated so as to be independently controlled. This then provides a circulator which can easily be matched since only lumped elements need be adjusted.
I claim: 1
l.- A circulator device of the character described comprising a junction of at least three transmission lines. mutually coupledcoils intersecting at substantially equal angles electrically connected to said transmission lines at said junction, ferrite material coupled to said coils, and means for applying a magnetic field to said ferrite material.
2. A circulator as in claim 1 additionally comprising means including a capacitor for matching said device to an associated transmission line. i
3. A circulator comprising a junction of at least three transmission lines forming a common region, mutually coupled coils electrically connected to said transmission lines at said junction, .ferrite material disposed in said region in coupled relationship with said coils, means for applying a magnetic field to said ferrite material, and a capacitor connected in series with each of the transmission lines and said coils.
4. A circulator as in'claim 3 including additionally a tuned circuit connected to said capacitor.
5. A circulator comprising a junction of at least three transmission lines, mutually coupled coils electrically connected to said transmission lines at said junction, ferrite material disposed in coupled relationship to said coils, means for applying a magnetic field'to said ferrite material, a capacitor connected between ground and said coilS at each of said transmission lines, and means for connecting the transmission line between the capacitor and the coils.
6. A circulator as in claim 5 including additionally a tuned circuit connected to said capacitor.
7. A circulator comprising a junction of at least three transmission lines, spaced ground planes, ferrite material disposed and supported in spaced relationship with respect to said ground planes means for applying a magnetic field to said ferrite material, mutually coupled coils coupled to said ferrite and electrically connected to said transmission lines, and a capacitor electrically connected to each of said transmission lines and said coils.
8. A circulator as in claim 7 in which said coils each comprise a plurality of turns of conductive material wound about said ferrite material.
9. A circulator comprising spaced ground planes, permanent magnet means carried by said ground planes, a ferrite material disposed between said ground planes to receive the magnetic field from the permanent magnet, at least three transmission lines communicating with said ground planes, mutually coupled coils electrically connected to said transmission lines, said coils being coupled to said ferrite, and a capacitor electrically connected between each of said transmission lines and said coils.
10. A circulator as in claim 9 in which said coils each comprise a plurality of turns of conductive material Wound about said ferrite material.
11. A circulator as in claim 10 including additionally magnetic material extending between said ground planes.
12. A circulator device of the character described comprising at least three mutually coupled coils intersecting at substantially equal angles each adapted to be electrically connected to an associated line, ferrite material disposed so as to be coupled to said coils, and means for applying a magnetic field to said magnetic material and arranged to apply the magnetic field linearly across and substantially perpendicular to the axis of said coils.
13. A device as in claim 12 wherein said coils are electrically connected to a common point.
14. A device as in claim 12 comprising additionally means including a reactive network for matching said device to an associated line.
References Cited by the Examiner UNITED STATES PATENTS 6/1962 De Vries 33324.2 1/1965 Drumheller et al 333 1.1