US3621477A

US3621477A - Three-port circulator comprising only two crossing coils

Info

Publication number: US3621477A
Application number: US49392A
Authority: US
Inventors: Hendrik Bosma
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1969-07-02
Filing date: 1970-06-24
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: FR2050446B3; FR2050446A7; NL6910116A

Abstract

Three-port circulator comprising only two windings crossing each other at right angles so that the number of stray capacitances as compared with existing circulators is reduced and the bandwidth is less restricted.

Description

United States Patent [72] Inventor Hendrik Bosnia Emmasingel, Elndhoven, Netherlands [2|] Appl. No. 49,392 [22] Filed June 24, 1970 [45] Patented Nov. 16, 1971 [73] Assignee U. S. Phlllps Corporation New York, NY. [32] Priority July 2, 1969 3 3 Netherlands 3 l 1 69101 16 [54] THREE-PORT CIRCULATOR COMPRISING ONLY TWO CROSSING COILS 1 Claim, 3 Drawing Figs.

[52] U.S.Cl

[51] Int. Cl HOlp 1/32, H0 l p 5/ l 2 [50] FieldolSearch 333/l.l, 24.2

[56] References Cited UNITED STATES PATENTS 2,944,229 7/1960 De Vries 333/242 3,5l9,957 7/l970 Omori 333/l.l

Primary Examiner Herman Karl Saalbach Axsisran! Examiner--Paul L. Gensler Attorney-F rank R. Trifari ABSTRACT: Three-port circulator comprising only two windings crossing each other at right angles so that the number of stray capacitances as compared with existing circulators is reduced and the bandwidth is less restricted.

PATENTEDuuv 16 19?: 3,621,477

INVIENTOR. HENDRIK BOSMA THREE-PORT CIRCULATOR COMPRISING ONLY TWO CROSSING COILS The invention relates to a three-port circulator comprising at least one disc-shaped, ferromagnetic body prepolarized by a static magnetic field at right angles to the parallel major surfaces and comprising two windings located in intersecting planes parallel to the static magnetic field, said windings being coupled with the electromagnetic field in the disc and being connected to each other at one end and to connecting terminals at the other end.

Such a nonreciprocal device is connected by the connecting terminals to transmission lines. For matching the impedances of the windings to those of the transmission lines reactive networks are provided, which provide on the one hand a real input impedance by tuning the inductances of the windings at the working frequency and on the other hand adapt these impedances to the desired level in the frequency range of maximum width. When one of the transmission lines supplies energy to the circulator, this energy is passed totally, apart from losses in the circulator, to the next-following transmission line, energy supplied by the latter to the circulator is transmitted to the next-following transmission line and the energy supplied by the latter to the circulator is again passed to the first transmission line.

Owing to this circulator property the known devices have a threefold rotation-symmetrical structure. Such a circulator is known, for example, from German Pat. application (D.A.S.). 1,259,421; said circulator comprises three windings whose winding planes intersect each other at angles of 120. These windings cross each other approximately at the center of the disc. At the area of the crossings on either side of the disc stray capacitances occur between the windings. This construction comprising three crossing windings has the disadvantage that the number and the magnitude of these stray capacitances involve a restriction of the bandwidth of the circulator. The circulator according to the invention mitigates this disadvantage because only one stray capacitance occurs, which can be readily kept at a low level because structural possibilities are less restricted.

The invention is characterized in that only two windings are provided, which cross each other at right angles approximately at the center of the disc, said windings being connected to each other at one end through a conductor along the edge of the disc, a third connecting terminal being provided approximately midway said conductor.

It would be noted that a nonreciprocal, electric coupling device having two orthogonally crossing windings is known, which windings are coupled by means of a magnetically prepolarised ferrite body, there being, however, a purely imaginary impedance coupled with the windings. Moreover, this device is driven at the ferromagnetic resonance of the ferrite. The purpose is to utilize the resonance of the electron spins in the ferrite and no use is made of circuit resonance (resonance of the reactive network with the inductance of the winding). This device requires energy dissipation in the ferrite. Moreover, it comprises only one input terminal and one output terminal, so that it does not constitute a circulator but a unidirectional insulator.

The invention will be described more fully with reference to the embodiments shown in the FIGS., corresponding parts of the FIGS. are designated by the same references.

F 16. 1 shows schematically a known circulator.

FIGS. 2 and 3 show circulators according to the invention in a schematic view.

The known circulator shown in FIG. 1 comprises a discshaped, ferromagnetic body 4, which is prepolarised by a static magnetic field H. The connecting

terminals

1,2 and 3 are connected for example, via capacitor C to the windings W,, W and W which are represented in the F16. bythreequarter turns. These windings intersect each other at angles of 120", are interconnected at point p and cross each other approximately at the center of the disc. The stray capacitance between the windings W, and W is designated by C that between W, and W by C and that between W and W by C13.

lt is supposed that the winding W is located between the windings W, and W so that: C =C --2C-. Because three windings are provided, three stray capacitances occur, the values of which are, moreover, difierent. Owing to the highly restricted structural possibilities because of the necessity of an optimum magnetic coupling of the windings in order to avoid leakage fluxes, it is difiicult to minimize these capacitances. The bandwidth of the circulator is strongly restricted by these capacitances. v

The circulator shown in FIG. 2 in accordance with the invention comprises two windings w, and W each formed by half a turn crossing each other at right angles approximately at the center of the disc and connected at one end through capacitors C to the connecting

terminals

1 and 2 and at the other end to a conductor G, which follows the edge of the ferrite disc. A third connecting terminal 3 is provided approximately midway the conductor G. From the FIG. it will be apparent that only one stray capacitance 0,, can occur between the windings. It can, in addition, be readily minimized because there are only two windings.

It may be provided by the law of energy continuity that a loss-free, nonreciprocal, matched tripole is a circulator (see, for example, H. J. Carlin, Polytechn. Inst. Brooklyn, Microwave Research Inst. Symposia Series Vol. 4, page 191, 1954). On this basis the operation of the circulator may be accounted for as follows:

The relationship between the magnetic inductance and the magnetic field intensity in directions at right angles to the direction of magnetic prepolarization of the disc is given by:

In the construction according to the invention two orthogonal windings are used, which are coupled via the ferrite body. The mutual inductance is thus determined solely by those proportionality factors which indicate the relation between the magnetic inductance in one direction and the magnetic field strength in the direction at right angles thereto. It will be apparent that the factor determining the relation between one winding and the other has an opposite sign to that determining the relation between the other winding and the first winding (which qualifies the nonreciprocal behavior) and that these factors differs a factor j= *1 from those of any reciprocal mutual inductances. This means that the induced voltages are in phase or in phase opposition to the voltage applied through the windings.

For matching the device to real transmission lines capacitors are used the value of which is such that at the working frequency the series combination of a capacitor and the inductance is obtained. Instead of using a single series-connected capacitor more complicated circuits of reactive network elements may be employed for having the device matching the transmission lines in a wide frequency range. In correct operation the connecting terminals are closed by a real resistance value, for example, the characteristic impedance of the coaxial cable. The value of this resistance and the magnitude of the nonreciprocal mutual coupling, determined by the number of turns of each winding, the nature of the ferrite, the strength of the prepolarized magnetic field and the work frequency, are chosen to be equal.

The operation will be further explained with reference to FIG. 2.

When connecting a voltage source to terminal I and when using the correct resistance value for closing the connecting terminal 3 and an arbitrary value for closing terminal 2, the voltage induced by a current through winding 1 in the winding 2 the static magnetic field having the direction shown, will be equal to and in phase opposition to the voltage across the resistor connected to terminal 3 so that the voltage at terminal 2 is zero. All energy then passes from connecting terminal 1 to connecting terminal 3.

When the voltage source is connected to terminal 3 and when the terminal 2 is correctly closed and the terminal 1 is closed arbitrarily, the current through the winding 2 induces in winding 1 a voltage equal and in phase opposition to the voltage of the source. Terminal 1 is then isolated and the energy passes from the connecting tenninal 3 to terminal 2.

When the voltage source is connected to terminal 2 and when the terminal 1 is correctly closed and the terminal 3 is closed arbitrarily, the voltage induced in winding 2 by the current through the winding 1 is in phase opposition to the voltage source connected to said terminal so that the voltage at terminal 3 becomes zero, whereas the current through winding 2 induces in winding 1 a voltage producing a terminal volt age at terminal 1, so that the energy passes from 2 to 1. By inverting the direction of the static magnetic field, the direction of circulation is inverted.

In order to obtain an optimum value of the nonreciprocal coupling, the work frequency is chosen to be offset with respect to the ferromagnetic spin resonance. It is thus ensured at the same time that the pass attenuation can be kept low.

FlG. 3 shows a circulator according to the invention in a schematic view; the number of turns is an even-numbered multiple of half turns per winding. This has the advantage that the three connecting terminals are located on one side of the disc.

What is claimed is:

l. A three-port circulator comprising at least one discshaped, ferromagnetic body prepolarized at right angles to the parallel major faces by a static magnetic field and comprising two windings located in intersecting planes parallel to the static magnetic field and coupled with the electromagnetic field in the disc and connected to each other at one via a conductor following the edge of the disc end and coupled at the other end to connecting terminals said windings crossing each other at right angles approximately at the center of the disc, a third connecting terminal being provided approximately midway of said conductor.

Claims

1. A three-port circulator comprising at least one disc-shaped, ferromagnetic body prepolarized at right angles to the parallel major faces by a static magnetic field and comprising two windings located in intersecting planes parallel to the static magnetic field and coupled with the electromagnetic field in the disc and connected to each other at one via a conductor following the edge of the disc end and coupled at the other end to connecting terminals said windings crossing each other at right angles approximately at the center of the disc, a third connecting terminal being provided approximately midway of said conductor.