US3882428A

US3882428A - Non-reciprocal field displacement isolator

Info

Publication number: US3882428A
Application number: US442471A
Authority: US
Inventors: Johannes Petrus Leenders; Peter Caspar Stephanus Rutjes
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1973-03-22
Filing date: 1974-02-14
Publication date: 1975-05-06
Anticipated expiration: 1992-05-06
Also published as: DE2412414A1; NL7304001A; FR2231122A1; GB1467973A; JPS49123756A; JPS5610802B2; FR2231122B3; IT1009365B

Abstract

A rectangular ferrite bar is asymmetrically arranged in a rectangular waveguide and is prepolarised in the direction of the smallest dimension of the waveguide by a static magnetic field. Electrically conductive strips the longitudinal dimension of which coincides with the direction of the magnetic field, are provided on the ferrite bar.

Description

Leenders et al.

May 6, 1975 NON-RECIPROCAL FIELD DISPLACEMENT ISOLATOR Inventors: Johannes Petrus Leenders; Peter Caspar Stephanus Rutjes, both of Emmasingel, Eindhoven,

Netherlands Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: Feb. 14, 1974 Appl. No.: 442,471

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 3,00L154 9/l96l Reggia 333/73 W 3.082383 3/l963 Stern r. 333/17 Primary ExaminerPaul L. Gensler Attorney, Agent, or FirmFrank R. Trifari; George B. Berka [57] ABSTRACT A rectangular ferrite bar is asymmetrically arranged in a rectangular waveguide and is prepolarised in the direction of the smallest dimension of the waveguide by [973 Netherlands "730400[ a static magnetic field. Electrically conductive strips the longitudinal dimension of which coincides with the LS. Cl- M direction of the magnetic field. are provided on the int. Cl. HOlp 1/32 ferrite bar Field of Search 333/].1, 24.1, 24.2, 24.3,

333/73 w 3 Claims, 4 Drawing Figures PERMANENT MAGNET 6 3 -4 fm 5 FERRITE I I conoucnvs 7 STRIPS PERMANENT MAGNET NON-RECIPROCAL FIELD DISPLACEMENT ISOLATOR The invention relates to a non-reciprocal field displacement isolator. comprising a rectangular waveguide and a rectangular bar of gyromagnetic material which is arranged in the waveguide at a small distance from one of the side walls. the side faces ofthe said bar extending parallel to the waveguide walls. the bar of gy romagnetic material being prepolarised in the direction of the smallest dimension of the waveguide by a static magnetic field.

A non-reciprocal isolator is generally used in the microwave field as an isolating member between a source and a load. the part ofthe energy applied by the source to the load which is reflected by the load being attenu ated by the non-reciprocal isolator so as to prevent the reflected energy from influencing the source.

A non-reciprocal field displacement isolator as herein described in which a homogeneously distributed resistance layer is provided on the surface of the bar which faces the centre of the waveguide is inter alia known from the article The field displacement isolator" by S. Weisbaum and H. Seidel published in "Bell System Technical Journal No. 35 in I956. pages 877-898.

The operation of this field displacement isolator is based on the property that a wave of the type H which propagates in the waveguide contains an electric field component at the area of the resistance layer whose strength is dependent of the direction of propagation. If the bar is suitably proportioned and suitably arranged in the waveguide and if the static magnetic field has a given size. the strength is maximum for one of the propagation directions and is minimum (substantially null) for the other propagation direction. As a result. the re sistance layer attenuates the wave which has a maximum electric field strength at this area. and allows sub stantially unattenuated passage of the wave which has a minimum electric field strength at this area.

This known non-reciprocal field displacement isolator has the drawback that it has a rather small isolation per unit of length of the isolator. which necessitates a comparatively long and hence heavy and unpractical isolator configuration if an isolator having a high isolation is required.

Furthermore. the heat is dissipated in the very thin resistance layer. after which it is depleted to the bar which is made. for example. of ferrite. This implies that the heat developed per unit oftime and hence the maxim um permissible power for which the isolator can still be used is determined by the very thin resistance layer.

These drawbacks are alleviated according to the invention which has for its object to realize a nonreciprocal field displacement isolator which has a comparatively high isolation per unit of length of the isolator.

The non-reciprocal field displacement isolator according to the invention is characterized in that electrically properly conductive strips which are insulated from each other by intermediate spaces are provided on the surface of the bar of gyromagnetic material which faces the centre of the waveguide. the longitudinal dimensions of the said strips coinciding with the direction of the static magnetic field.

The invention and its advantages will be described in detail hereinafter with reference to the embodiment shown in the drawing. corresponding parts being denoted by the same references in the various Figures.

FIG. I is a front view of the non-reciprocal isolator according to the invention.

FIG. 2 is a sectional view taken according to the line A-A of the non-reciprocal isolator shown in FIG. 1.

FIG. 3 is a sectional view taken according to the line BB of the non-reciprocal isolator shown in FIG. 1, and

FIG. 4 shows graphs of the insertion loss and isolation as functions of the frequency of the non-reciprocal isolator shown in FIG. I.

The non-reciprocal isolator shown in the FIGS. I. 2 and 3 comprises a rectangular waveguide l which is provided with

connection flanges

2 and 3 and a rectangular bar 5 of ferromagnetic material such as ferrite which is mounted in the waveguide by way of a dielectric holder 4. This ferrite bar 5 is arranged in the waveguide such that its side faces extend parallel to the walls of the waveguide and that it is situated at a small dis tance from one of the side walls. Also provided are per manent magnets 6 and 7 which are interconnected by a magnetic yoke which is situated outside the wave guide and which is not shown in the Figures. By means of these magnets. the ferrite bar 5 has been prepolarised to a point far below the gyromagnetic resonance by an internal static magnetic field H which extends parallel to the side walls of the waveguide. For a given proportioning of the ferrite bar 5. a given loca tion in the width ofthe waveguide and a given direction and strength of the static magnetic field H... it is achieved in known manner that in a wave of the type Ho! which propagates from flange 2 in the direction of flange 3. to be referred to hereinafter as the positive direction. a minimum strength of the electric field component occurs at the area of the surface of the ferrite bar 5 which faces the centre of the waveguide. to be referred to hereinafter as the active surface. Similarly. for a wave of the type H which propagates in the negative direction it is achieved that at the area of the active surface a maximum strength of the electric field component occurs.

In known non-reciprocal field displacement isolators a thin layer of graphite emulsion or a very thin homogeneous metal layer is deposited at the area of the active surface by spraying. spreading. or vapour deposition. with or without the assistance of a dielectric foil which is used as a carrier. In this layer power is dissipated by a wave whose maximum electric field component oc curs at the area of the active surface. with the result that this wave is attenuated. and a wave of the type H which propagates in the opposite direction is allowed to pass substantially unattenuated. For an attenuation layer having a layer resistance of to Ohms/- square. an attenuation of maximum 5 dB per cm of length of the non-reciprocal isolator is obtained at 10 GHz.

So as to achieve a substantial increase of the isolation per length unit of the isolator. according to the invention electrically properly conductive strips 8 which are insulated from each other by intermediate spaces and whose longitudinal dimensions coincide with the direction of the static magnetic field H,, are provided at the area of the active surface of the ferrite bar 5.

The operation of the non-reciprocal isolator is as follows.

As already stated. a wave of the type H which propagates in the negative direction has an electric field component of maximum strength at the area of the ac tive surface of the ferrite bar 5. the direction of this component coinciding with the longitudinal direction of the strips. Under the influence thereof. large cur' rents flow in the properly conductive strips 8. These large currents are accompanied by strong magnetic fields which are situated in planes perpendicular to the direction of these currents. Half of the lines of force of these fields extend outside the ferrite bar 5 and the other half extends inside the ferrite bar 5. the lines being closed via the intermediate spaces of adequate dimensions which are provided between the strips. with the result that very strong fields arise. In the ferrite bar these fields extend perpendicular to the inner static magnetic field H... The circularly polarised component of this field. whose rotary direction corresponds to the rotary direction of the spins in the ferrite bar which is determined by the direction of the static magnetic field H will transfer its energy to the spins in known manner. As a result. the wave propagating in the negative direction will be substantially attenuated.

The isolation of such a non-reciprocal isolator amounts to at least dB per cm of length of this isola tor. so that a short and hence light nonreciprocal isola tor has been realized fora given required isolation. The injection loss of a wave of the type H propagating in the positive direction amounts to only a few tenths of dB. P16. 4 shows the isolation 01 and the injection loss a of such a non-reciprocal isolator. comprising a ferrite bar having a length of 0.9 cm. as a function of the frequency.

In this type of non-reciprocal isolator the heat is developed directly in the ferrite body. with the result that. moreover. this isolator is better suitable for use with higher powers than the known nonweciprocal isolator comprising a resistance layer.

In order to achieve an optimum effect. the strips 8 must contact the ferrite bar 5 without intermediate layer such as an adhesive layer. To this end. a foil 9 of. for example. Mylar is used on which the strips are glued or vapour-deposited. after which the side ofthe foil on which the strips are provided is arranged against the active ferrite surface and is secured such that the strips are in direct contact with the ferrite.

So as to achieve an optimum effect it is also neces sary that the strips 8 are as long as possible. However, they may not be substantially longer than one half of the wavelength of the HF oscillation which occurs in the ferrite at the operating frequency. whilst the distance between the strips amounts to approximately one quarter of this wavelength. However. it is to be noted that the strips need not be uniform. nor need the spacing be equal. even though this results in an optimum effect for one given frequency.

The finite thickness of the strips and the section of the ferrite bar locally cause impedance variations which cause reflections. So as to counteract this phenomenon as much as possible. a U-shaped matching element ll is provided as shown in the FIGS. 1 and 2. This element 11 and the foil 9 are omitted in FIG. 2 so as to allow a clear view of the arrangement of the conductive strips 8. The matching element ll is made. for example. of Alundum. and is arranged with its back against the foil 9. the legs of the U being perpendicular to the active ferrite surface. A reflection coefficient of less than 1.24 is thus realized over the entire band from 9.1 to 9.6 GHZ.

Due to the use of the ferrite bar 5 and the matching element ll. undesired modes can locally propagate. So as to counteract the appearance of these modes. an inductive element 12 is provided halfway the ferrite bar 5, the said element being formed by a partition 12 which extends from the wave guide side wall opposite to the active surface of the ferrite bar 5 over the entire waveguide height almost as far as the centre of the waveguide. The impedance of this inductive element 12 has been taken into account in the proportioning of the matching element 11.

What is claimed is'.

l. A non-reciprocal field displacement isolator, comprising a rectangular waveguide and a rectangular bar of gyromagnetic material which is arranged in the waveguide at a small distance from one of the side walls. the side faces of the said bar extending parallel to the waveguide walls. the bar of gyromagnetic material being prepolarised in the direction of the smallest dimension of the waveguide by a static magnetic field, characterized in that electrically properly conductive strips which are insulated from each other by intermediate spaces are provided on the surface of the bar of gyromagnetic material which faces the centre of the waveguide. the longitudinal dimensions of the said strips coinciding with the direction of the static mag netic field.

2. A non-reciprocal field displacement isolator as claimed in claim 1, characterized in that the strips are in direct contact with the bar of gyromagnetic material.

3. A non-reciprocal field displacement isolator as claimed in claim 1, characterized in that. so as to suppress undesired modes. an inductive element is pro vided between the surface of the bar of gyromagnetic material which faces the centre of the waveguide and the oppositely situated part of the waveguide side wall. l= i i i

Claims

1. A non-reciprocal field displacement isolator, comprising a rectangular waveguide and a rectangular bar of gyromagnetic material which is arranged in the waveguide at a small distance from one of the side walls, the side faces of the said bar extending parallel to the waveguide walls, the bar of gyromagnetic material being prepolarised in the direction of the smallest dimension of the waveguide by a static magnetic field, characterized in that electrically properly conductive strips which are insulated from each other by intermediate spaces are provided on the surface of the bar of gyromagnetic material which faces the centre of the waveguide, the longitudinal dimensions of the said strips coinciding with the direction of the static magnetic field.

3. A non-reciprocal field displacement isolator as claimed in claim 1, characterized in that, so as to suppress undesired modes, an inductive element is provided between the surface of the bar of gyromagnetic material which faces the centre of the waveguide and the oppositely situated part of the waveguide side wall.