US3018454A

US3018454A - Microwave attenuator switch

Info

Publication number: US3018454A
Application number: US508711A
Authority: US
Inventors: Peter J Sferrazza
Original assignee: Sperry Rand Corp
Current assignee: Sperry Corp
Priority date: 1955-05-16
Filing date: 1955-05-16
Publication date: 1962-01-23
Anticipated expiration: 1979-01-23

Description

Jan. 23, 1962 P. J. sFERRAzzA 3,018,454

MICROWAVE ATTENUATOR SWITCH Filed May 16, 1955 nil l N VE TO R Pf TER d. JFf/QRA ZZA United States Patent() 3,018,454 MICROWAVE ATTENUATOR SWITCH Peter J. Sferrazza, Wantagh, N.Y., assignor to Sperry Rand Corporation, a corporation of Delaware Filed May 16, 1955, Ser. No. 508,711 3 Claims. (Cl. S33- 98) This invention relates generally to microwave transmission apparatus, and more particularly, is concerned with apparatus for attenuating, modulating, or switching microwave energy.

1t is well known that certain commercially available substances known as ferrites, when utilized in the propagation of microwaves, exhibit the phenomenon known as Faraday effect. Thus, when a piece of ferrite is placed in a wave guide propagating microwaves, and the ferrite is subjected to a strong magnetic field in the direction of propagation of the microwaves, the rotation of the plane of polarization of the incident wave results. The amount of rotation is linearly related to the length of the ferrite and the strength of the magnetic field. This phenomenon exhibited by the ferrites and other ferromagnetic materials has been utilized to provide microwave switches, modulators, or attenuators by utilizing means in a circular wave guide which is selectively responsive to energy propagated in only one polarization plane. an attenuator card extending across a circularwave guide attenuates energy propagated in a mode in which the electric field is parallel to the attenuator card, while energy having its electric vector perpendicular to the attenuator card is substantially unaffected. Thus, by varying the plane of polarization of the incident energy by changing the magnetic field applied to the ferrite, variable attenuation of the incident energy can be achieved. However, such known prior art devices utilizing the Faraday effect of ferrite on microwave energy have been confined to the circular wave guide type of transmission line, because the symmetry of circular wave guide permits energy to be propagated in an infinite number of planes. Since most microwave transmission line systems employ rectangular wave guides, such known devices require the use of rectangular-to-circular transition elements at either end of the ferrite device. Such transition devices add materiall1y to the length of the ferrite unit, its complexity and cost,

and adversely affect performance.

It is the general object of this invention to avoid the foregoing limitations in and objections to the prior art practice by the provision of a microwave attenuator switch utilizing ferrite rotation which is more compact in design, simpler in construction, and less expensive to build.

Another object of this invention is the provision of apparatus that can be utilized as an attenuator, a modulator, or a switch.

Another object of this invention is to provide apparatus using ferrite rotation which can be used in a rectangular wave guide transmission line system and requires no rectangular-to-circular wave guide transition sections.

These and other objects of the invention which will become apparent as the description proceeds are achieved by apparatus comprising a section of rectangular wave guide in which is centrally mounted a ferrite member. A magnetizing coil surrounds the wave guide in the region of the ferrite member for applying a magnetic field extending in a direction parallel to the longitudinal axis of the wave guide. By varying the magnetizing current through the coil, the degree of Faraday rotation of the incident energy in the wave guide can be controlled. Since the rectangular wave guide propagates energy in the dominant or TEN mode in which the electric vector is perpendicula-r to the broad walls of the wave guide, and acts as a cut-off wave guide to any mode of propagation in which the electric vector extends parallel to the broad For example,

3,018,454 Patented Jan. 23, 1962 ice walls of the rectangular wave guide, the rotational effect of the ferrite reduces the amount of energy propagated down to wave guide in the dominant TEN, mode.

For a better understanding of the invention, reference should be had to the accompanying drawing, wherein:

FIG. l is an elevational View in section of a structure incorporating the principles of the present invention;

FIG. 2 is an end view of the embodiment shown in FIG. l;

FIG. 3 is an elevational View in section of a modified version of the present invention; and

FIG. 4 is an end view of the embodiment shown in FIG. 3.

Referring to FIGS. l and 2, the numeral 10 indicates generally a section of rectangular wave guide which may be part of a rectangular wave guide transmission line coupling a source of microwave energy to a suitable utilization device or load. Positioned within the section of the rectangular wave guide is a rod 12 of ferrite, or other material exhibiting the Faraday effect as to microwave energy. The ferrite compounds are well-known in the art and are commercially available. They are composed of a magnetic oxide of iron plus other metallic oxides. The rod 12 is positioned centrally within the waveguide and supported by suitable dielectric support members, as indicated at 14 and 16.

An axially extending magnetic field is applied to the ferrite rod 12 by means of a wire coil 18 connected across an exciting current source 20. A rheostat 22 in series with the source 20 is provided for varying the strength of the magnetizing current in the coil. The coil 18 is wound around the outside of rectangular wave guide section 10.

In operation, energy propagates in the rectangular wave guide in the TEm mode in which the electric vector is normal to the broad walls. When the energy encounters the ferrite to which an axially extending magnetic field has been applied, rotation of the electric vector is effected by yan amount `depending upon the strength of the magnetic field for a given length of ferrite rod. Rotation results in a component of the incident energy which extends parallel to the broad walls of the rectangular wave guide. However, the component of energy having the electric vector extending parallel to the broad walls, corresponding to the TEM mode, cannot propagate along the wave guide, -since the wave guide is below cut-off for this mode. Thus, by varying the strength of the magnetic field applied to the rotator, the division of energy between the TEN, and the TEM mode can be varied. By rotation, the component of energy having the electric vector normal to the broad walls is reduced, with the result that the energy propagated down the wave guide is substantially attenuated. By increasing the magnetizing current to a value where the incident energy is rotated through substantially no energy is propagated beyond the ferrite. Thus, the deviceV of FIGS. l and 2 can be utilized as a variable attenuator or a switch.

In the embodiment of the invention above described in connection with FIGS. l and 2, the component of energy having the electric vector extending parallel lto the broad walls of the wave guide is subjected to continuous internal reflection and attenuation by the ferrite rod and the walls of the wave guide. In the embodiment of FIGS. 3 and 4, an attenuator card, indicated generally at 24, is provided extending between the narrow walls of the wave guide section 10. To permit room for the attenuator card, the ferrite rod is positioned adjacent to a broad wall of the wave guide 10 and secured thereto. By introducing the attenuator card as shown in the modification of FIGS. 3 and 4, the component of energy extending parallel to the broad walls, as produced by the rotation introduced by the ferrite member 24, is substantially attenuated. This reduces reflections and improves the matching of this device to the line.

Instead of a variable D.C. magnetizing current, as provided by the battery 20 and rheostat 22, an A.C. signal may be applied to the magnetic coil 18 to modulate the microwave energy propagated along the rectangular wave guide at the frequency of the A.C. signal applied to the coil 18.

From the above description of the invention, it will be seen that the various objects have been achieved by a ferrite rotator employing a rectangular wave guide. The property of the rectangular wave guide of propagating only the dominant mode in which the electric vector is normal to the broad walls of the wave guide is utilized to achieve attenuation or modulation of the microwave energy propagated along the line. This structure obviates the need for rectangular-to-circular transition sections heretofore required in known prior art ferrite rotators. While the invention has been described as utilizing coils for applying an axially extending magnetic field through the ferrite rod, it will be understood that other suitable means, such as permanent magnets, may be utilized for establishing the magnetic field.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus comprising a section of rectangular wave guide for propagating microwave energy in the dominant TEM) mode only, a ferrite member positioned within the wave guide, an attenuator card extending parallel to the broad walls of the Wave guide, the card being positioned in the region of the ferrite member, a wire coil surrounding the wave guide in the region of the ferrite member, means connected to the wire coil for passing a magnetizing current therethrough to establish a magnetic field directed axially Within said waveguide in the region occupied by said ferrite member, said magnetic field having a strength to magnetize said ferrite member to a condition that causes rotation of the plane of p-olarization of microwave energy propagating through said waveguide, whereby at least a component of the microwave energy has its electric vector rotated parallel' to a broad wall ofsaid waveguide and is reflected thereby, said attenuator card serving to attenuate said retiected energy, and means for varying the current through the wire coil to control the rotation of the microwave energy by the ferrite member.

2. Apparatus comprising a section of rectangular wave guide for propagating microwave energy in the dominant TEM, mode only, a ferrite member positioned within the wave guide, attenuator means comprising a body of dissipative material within said wave guide for attenuating energy components having the electric vector extending parallel to the broad walls of the wave guide, and means for producing a magnetic field which is directed along the longitudinal axis of the wave guide in the region of the ferrite member, said magnetic field having a strength to magnetize said ferrite member to a condition that causes rotation of the plane of polarization of microwave energy propagating through said waveguide.

3. Apparatus comprising a section of wave guide having unequal cross-sectional dimensions whereby the wave guide is above cut-off for energy polarized in one plane and below cut-ofi for energy polarized in another plane, a plane of polarization rotator disposed within said wave guide section for rotating the plane of polarization of the electric vector of the microwave energy propagating in theV wage guide, and attenuator means comprising a body of dissipative material within said wave guide for atteinuating the resulting component of energy having the electric vector parallel to the broad walls of the wave guide.

References'Cited in the file of this patent UNITED STATES PATENTS 2,542,185 Fox Feb. 20, 1951 2,628,278 zaleski Feb. 10, 1953 2,650,350 Heath Aug. 25, 1953 2,719,274 Luhrs sept. 27, 1955 2,729,794 Cohn Jan. 3, 1956 2,745,069 Hewitt May 8, 1956 2,748,353 Hogan May 29, 1956 2,802,183 Read Aug. 6, 1957 2,820,200 Du Pre Jan. 14, 1958 OTHER REFERENCES Article, Behavior and Applications of Ferrites in the Microwave Region, by Fox et al pub. in Bell System Technical Journal, vol. 34, No. 1, Jan. 1955, pages 5-103, page 74 relied on,