Waveguide circulator

Abstract

A waveguide circular which includes at least three waveguide H plane ports, said ports so arranged that at their junction a ferrimagnetic post is provided, one or two matching conductor or dielectric members which are provided in relation to said ferrimagnetic post, and a magnetic device which magnetizes statically said ferrimagnetic post. The characteristic features of the present invention are that the cross section of said ferrimagnetic post is inscribed with a circle the diameter of which is nearly equal to the value calculated from the dielectric resonator mode TM.sub.ml (m .gtoreq. 2), one end of said ferrimagnetic post is directly or indirectly fixed to the center of the matching members the total thickness of which is selected to be nearly equal to the height of said ferrimagnetic post and an air gap is provided between the other end of said ferrimagnetic post and the H plane of said waveguide or another matching member, and the electrical length of said air gap is adjusted so as to obtain the wide band characteristics of said waveguide circulator.

Description

The present invention relates to a circulator and especially, relates to the circulator which provides wide band characteristics without insertion loss characteristics.

The conventional wide band waveguide circulator is composed of waveguide H plane ports, a ferrimagnetic post which is provided at the junction of said ports, one or two matching conductor or dielectric members which are provided in relation to said ferrite pillar, and a magnetic device which magnetizes statically said ferrimagnetic post.

However, the design theory with respect to the waveguide circulator does not develop like the strip line circulator. Therefore, concerning the waveguide circulator, only the qualitative explanation is given and the design of said waveguide circulator has been carried out experimentally.

Further, it is very difficult to produce, with precision, the ferrimagnetic post, and the dielectric and conductor members, and to precisely position the abovementioned elements. Also, a suitable adhesive material for assembling these elements cannot be obtained. These factors cause incongruities of the characteristics of the circulator and result in the high cost of the circulator. Further, an inconvenience is created because the use of a casted waveguide port having insufficient accuracy is difficult. Above all, one of the main drawbacks of the conventional waveguide Y circulator is the fact that the elements to be assembled are numerous.

An object of the present invention is to provide a waveguide circulator which can overcome the above-mentioned drawbacks.

Another object of the present invention is to provide a waveguide circulator which is simply constructed and is composed of a minimum number of components.

A further object of the present invention is to provide a waveguide circulator which is manufactured in less time and at lower cost than the conventional waveguide circulator.

According to the present invention, a waveguide circulator includes at least three waveguide H plane ports, said ports so arranged that at their junction a ferrimagnetic post is provided one or two matching conductor or dielectric members which are provided in relation to said ferrimagnetic post, and a magnetic device which magnetizes statically said ferrimagnetic post. Characteristic features of the present invention are that (a) the cross section of said ferrimagnetic post is inscribed with a circle the diameter of which is nearly equal to the value calculated from the dielectric resonator mode TM.sub.ml (m.gtoreq.2), (b) one end of said ferrite pillar is directly or indirectly fixed to the center of the matching member, an air gap is provided between the other end of said ferrimagnetic post and the H plane of said waveguide or another matching member, and the electrical length of said air gap is adjusted so as to obtain the wide band characteristics of said waveguide circulator.

Further features and advantages of the present invention will be apparent from the ensuing description with reference to the accompanying drawings to which, however, the scope of the invention is in no way limited.

FIGS. 1A and 1B show one embodiment of a conventional waveguide circulator; FIG. 1A is a perspective view of said circulator and FIG. 1B is a cross section viewed from the direction 0 indicated by the arrow in FIG. 1A;

FIGS. 2A through 2C are diagrams showing the distribution of the microwave electromagnetic field in the ferrimagnetic post; FIG. 2A concerns the TM.sub.11 mode, FIG. 2B concerns the TM.sub.21 mode and FIG. 2C shows the coordinate system;

FIGS. 3A through 3C show embodiments of the waveguide circulator according to the present invention; FIG. 3A is a side view of the waveguide circulator, FIG. 3B is the plan view of the waveguide circulator shown in FIG. 3A; FIG. 3C is another embodiment of the present invention;

FIGS. 4A and 4B are graphs of the experimental data of the embodiments according to the present invention; and

FIG. 5 is a graph of the experimental data of another embodiment of the present invention.

One example of the construction of a conventional wide band waveguide Y circulator is shown in FIGS. 1A and 1B. FIG. 1A shows a perspective view of the conventional waveguide Y circulator and FIG. 1B is a cross section viewed from the direction 0. Referring to FIGS. 1A and 1B, 1 is a waveguide Y port, 1a, 1b, and 1c are conductor screws for adjusting the attenuation in the reverse direction of the waveguide circulator, 2 is a ferrimagnetic material, 3-1 and 3-2 are permanent magnets, 4-1a and 4-2a are triangular member conductors, which are used for impedance matching, 5-1 and 5-2 are triangular dielectric plates for impedance matching. In FIG. 1A, permanent magnets 3-1 and 3-2 are not shown: 1A, 1B and 1C are the opening portions of the waveguide Y junctions.

It is conventionally well known that, when the ferrimagnetic material is in the form of a cylinder as shown in FIG. 1A, it is difficult for the waveguide to provide wide band characteristics, but when the ferrimagnetic material is formed as a triangular member, adequate wide band characteristics can be obtained.

However, in the conventional construction as shown in FIG. 1A, (a) it is very difficult to produce, with precision, the ferrimagnetic post, the triangular dielectric plates 5-1, 5-2, and the triangular member conductors, (b) it is very difficult to assemble with precise positioning the above-mentioned elements and (c) suitable adhesive material for assembling these elements cannot be obtained.

Now, we will explain the waveguide circulator according to the present invention, with respect to the most simple embodiment, shown in FIGS. 3A through 3C.

The present invention is composed of the following three conditions.

1. The form of the ferrimagnetic post is selected to be cylindrical and the value of the diameter of the ferrimagnetic cylinder is selected on the basis of TM.sub.210, that is, one of the higher order modes, or near said value.

2. Mode matching between the ferrite cylinder and the external waveguide is carried out with the most simple construction. For example, on one triangular member, the ferrimagnetic post is fixed directly with the adhesive material.

3. Impedance matching between the ferrimagnetic cylinder and the external waveguide is carried out by precisely selecting the distance between a free end of the ferrimagnetic cylinder (that is, the end which is not fixed to the triangular plate) and an inner waveguide H plane facing said free end or other triangular member placed on said inner plane of the waveguide.

These three conditions will now be explained in more detail.

(Condition 1)

FIG. 2A shows the distribution of the microwave magnetic field TM.sub.11 in the ferrimagnetic cylinder 2a when said distribution is observed from the direction P indicated in FIG. 1B which shows the conventional waveguide Y circulator. Referring to FIG. 2A, the curved lines 9 in the ferrite cylinder 2a indicate vectors of the magnetic fields and arrows viewed from the head or tail 10 indicate the vectors of electrical fields. Arrows 1 , 2 and 3 on the exterior of the ferrite pillar 2a show the direction of the opening portions 1A, 1B and 1C of the waveguide Y junction.

When the direct magnetic field H.sub.DC is applied as represented by the arrow viewed from the tail, in FIG. 2A, the input applied from arrow 1 appears at the direction 2 but not at the direction 3 .

The distribution shown in FIG. 2A is a basic mode of the circulator, that is, TM.sub.110. Herein, TM shows a magnetic transverse wave and the numbers 110 represent the number of the standing waves in coordinates .phi., r, z respectively, corresponding to the coordinate system as shown in FIG. 2C. Generally, the mode is expressed only with respect to the number of standing waves in the direction of .phi. and r, and when we calculate the electromagnetic energy or load Q; Q.sub.L, the number of standing waves in the direction z must be expressed in accordance with the resonance mode. However, the number of waves in the direction z has no relation to the present invention, therefore we have omitted it for purposes of simplifying the explanation.

According to C. E. FAY and R. L. COMSTOCK, Operation of the Ferrite Junction Circulator, IEEE Transactions on Microwave Theory and Techniques, January 1965, page 20, the following result is obtained with respect to the TM.sub.110 mode. ##EQU1## wherein, Q.sub.L is a load of the circulator, .omega. is an angular frequency, R and d are respectively the radius and the height of the ferrite cylinder, .epsilon. is the specific inductive capacity of the ferrimagnetic cylinder, .epsilon..sub.o is the dielectric constant in vacuum condition and G.sub.R is the conductance as viewed from the exterior of the ferrimagnetic post.

On page 20 of the above-mentioned reference, it is described that although the circulator can function with respect to mode TM.sub.21 or modes higher than TM.sub.21, the conclusion is that no advantage exists with respect to mode TM.sub.21 or modes higher than TM.sub.21. However, the present inventors are of the opinion that this conclusion has room for doubt.

Therefore, the inventors calculated the Q.sub.L of the circulator with respect to TM.sub.210.

FIG. 2B shows the distribution of the microwave electromagnetic field of the TM.sub.210 mode. As is well known, the following equation is obtained. ##EQU2## wherein U is an energy which is stored in the ferrimagnetic cylinder and Pout is an electric power which is radiated to the exterior from the ferrimagnetic cylinder. It is known that U in equation (2) may be calculated as shown in following equation. ##EQU3## wherein J.sub.2 (kr) is the first kind and the second order of Bessel function, k is a constant, r and .phi. are variables, and E.sub.m is the maximum electric field at the periphery of the ferrite cylinder.

When we calculate the equation (3) using the value of the constant k = 3.054 in the TM.sub.21 mode, the following equation can be obtained.

when G.sub.R shows the admittance viewed from the interior to the exterior of the ferrimagnetic post, the electrical power Pout is calculated by the following equation.

From equations (2), (4) and (5), ##EQU4## therefore, the following equation can be obtained. ##EQU5##

In the above calculations, we assume that G.sub.R is the admittance viewed from the periphery of the ferrimagnetic cylinder to either the exterior or interior of the ferrimagnetic cylinder. In the strip-line circulator, G.sub.R is the characteristic admittance corresponding to the TEM mode of strip-line which exists on the outside of the ferrimagnetic post and is independent of the frequency. Whereas, in the waveguide circulator, G.sub.R is the admittance of the waveguide which exists outside of the ferrimagnetic cylinder and has frequency characteristics. However, the triangular member conductors 4-1a and 4-2a shown in FIG. 1B have the function of converting the waveguide mode from the TE.sub.11 mode into a quasi TEM mode for the reason given in condition 2. Since, in the waveguide circulator, G.sub.R is a characteristic admittance with respect to the TEM mode viewed from the inferior to the exterior of the ferrimagnetic cylinder, and is considered to be the same as in the strip-line circulator, the above-mentioned equation (7) can be applied to the strip-line circulator as well as the waveguide circulator.

Next, according to H. J. Butterweck, Der Y Zirkulator, AEU, Vol. 17, April 1963, pp 163 through 176 which is referred to in the above-mentioned C. E. Fay and R. L. Comstock, if we assume that the resonant frequencies of the resonators correspond to positive and negative circular polarized waves in the TM.sub.110 mode circulator that a center frequency of the circulator is represented by .omega., and that .delta.' is expressed as ##EQU6## the following equation (9) may be obtained because .omega..sup.+ and .omega..sup.- have a phase difference of .+-.30.degree. with respect to .omega.. ##EQU7## Now, the following equation can be obtained with respect to the TM.sub.21 mode. ##EQU8##

Further, according to the reference H. Bosma, On Stripline Y circulation at UHF; IEEE trans on MTT Jan. 1964, page 64, FIG. 4, the values of splits 2.delta.' of the positive and negative circular polarized waves with respect to the same value of K/.mu. (wherein K and .mu. are Polder tensor components) are the same in the TM.sub.11 mode and the TM.sub.21 mode. That is, when we assume that the value of K/.mu. determined by a saturation magnetization of the ferrite cylinder and that the internal direct field remain constant, in equations (9) and (8), 2.delta.'.sub.1 .apprxeq.2.delta.'.sub.2, therefore, the following equation (11) can be obtained. ##EQU9##

Equation (11) gives nearly the same result as equation (7). That is, the circulator which uses the TM.sub.21 mode can obtain a wide band twice as large as the circulator which uses the TM.sub.11 mode, and the value of the center frequency which is calculated with the TM.sub.210 mode corresponds to the experimental result.

The above explanation was given with respect to the TM.sub.21 mode only of the ferrimagnetic post having a circular cross section. However, in the waveguide circulators which are calculated with a higher mode TM.sub.ml (m.gtoreq.2), the center frequency of the circulator corresponds with the experimental results and it is supposed that an optimum higher mode which has wide band characteristics will exist.

Next, we will explain the relation between the diameter of the ferrite cylinder and the mode TM.sub.mnp. As is well known, the following equation exists only in approximate terms. ##EQU10## wherein the resonance mode is TM.sub.mnp, l is the length of the resonator, x.sub.mn is an eigen value corresponding to mode TM.sub.mn, .epsilon. is the relative dielectric constant of the ferrite body, .mu..sub.r is the relative permeability of the ferrite body, .lambda..sub.o is the wavelength of the center frequency in free space and f.sub.o = C/.mu..sub.o (wherein C is the light velocity). And, p is the number of the standing waves appearing along the ferrimagnetic post in its longitudinal direction. The value of p is between 0 and 1, and in most cases said value is near 0.

(Conditions 2 and 3)

Condition 1 is essential for the present invention, however, condition 2 and 3 mentioned hereinafter are secondary conditions.

When we connect the ferrite cylinder having wide band characteristics to the external waveguide, the mode conversion and the characteristic impedance matching must be considered. With respect to the impedance matching, the reactance component can be matched with the conductor screws 1a, 1b and 1c which is provided on the waveguide H plane.

In the simplest embodiment of the present invention, as described hereinafter, the object of the invention is achieved by fixing one end of the ferrimagnetic cylinder with a diameter determined by the mode TM.sub.m10 (m.gtoreq.2) of the dielectric resonator, directly or indirectly to the center portion of one matching triangular conductor member, and adjusting precisely the distance between the other end of the ferrimagnetic cylinder and the inner surface of the waveguide H plane.

FIG. 3A shows a side view of the portion of the embodiment according to the present invention, FIG. 3B is a cross section along A--A of FIG. 3A and FIG. 3C is another embodiment of the present invention wherein the matching triangular conductor member 6 shown in FIG. 3A is divided into two portions, that is, 6-1b and 6-2b and these divided portions are fixed on upper and lower H planes at the center of the junction of the waveguide ports.

Referring to FIGS. 3A through 3C, 1 is the waveguide port, and 3-1 and 3-2 are permanent magnets, similar to FIGS. 1A and 1B. And 5 and 5b indicate the ferrimagnetic cylinder, 6, 6-1b and 6-2b represent matching triangular conductor members. The diameter of the ferrimagnetic cylinders and the dimensions of the triangular conductor members are determined in accordance with the above-mentioned conditions 1, 2 and 3.

The experiments confirmed that when the sides of the matching triangular conductor members 6, 6-1b and 6-2b are equal in length and the thickness of the member 6 is equal to the sum of the thicknesses of members 6-1b and 6-2b the wide band characteristics of the embodiments shown in FIG. 3A and FIG. 3C are the same. The total thickness of the matching member or members is selected to be nearly equal to the height of the ferrimagnetic post.

Further, according to the experiment, it was confirmed that the gap between one end of the ferrite cylinder and the H plane has an optimum value and the thicknesses of the members 6, 6-1b and 6-2b and the air gap are the same.

FIGS. 4A and 4B show experimental results of the characteristics of the waveguide circulator according to the present invention. FIG. 4A is the characteristic data showing the relation between the frequency GHz and the attenuation in the reverse direction dB of the waveguide circulator which is adjusted to the Tschebysheff form by using the conductor screws which are respectively provided on the H planes of the opening portions 1A, 1B and 1C of the waveguide Y junction and FIG. 4B represents the case of the waveguide circulator being adjusted to the maximally flat form. In FIG. 4A and 4B, the curves shown by o--o, x--x and .DELTA.--.DELTA. show the characteristic of each portion of the three opening portions 1A, 1B and 1C.

This explanation was given with regard to the case where matching triangular conductor members are used, however, when matching circular conductor members are used, a result the same as shown in FIG. 5 can be obtained the curves shown by o--o, x--x and .DELTA.--.DELTA. are respectively the same as those shown in FIGS. 4A and 4B--.

As mentioned above, the waveguide circulator, which is composed of the ferrimagnetic post calculated by the dielectric resonator mode TM.sub.210 and one or a pair of matching members and conductor screws, provides the same characteristics as the conventional waveguide circulator having a complex construction. Therefore, the waveguide circulator according to the present invention can be manufactured inexpensively and with simple construction and the time required to manufacture the waveguide circulator can be considerably reduced.

Further, the above explanation was given with respect to the case where the ferrimagnetic post is a cylinder, however, it should be understood that the same effect can be obtained by triangular or other forms of the ferrimagnetic post, the cross section of which is inscribed with a circle the diameter of which is calculated according to the abovementioned condition 1.

Claims

What is claimed is:

1. A waveguide circulator including at least three waveguide H plane ports, said ports so arranged that a ferrimagnetic post is provided at their junction, at least one matching conductor which is provided in relation to said ferrimagnetic post, and a magnetic device for statically magnetizing said ferrimagnetic post, characterized in that the cross section of said ferrimagnetic post is circumscribed within a circle having a diameter equal to the value calculated from the equation ##EQU11## wherein the resonance mode is TM.sub.mn (m.gtoreq.2, n=1), D is the diameter, l is the length of the resonator, X.sub.mn is an eigen value corresponding to mode TM.sub.mn (m.gtoreq.2, n=1), .epsilon. is the relative dielectric constant of the ferrimagnetic post, .mu..sub.r is the relative permeability of the ferrimagnetic post, .lambda..sub.o is the wavelength of the center frequency in free space, and p is the number of the standing waves appearing along the ferrimagnetic post in its longitudinal direction.

2. A waveguide circulator according to claim 1, wherein a conductor member is arranged on H planes at the center of the junction of waveguide ports, the thickness of said member is selected to be approximately equal to the height of said ferrimagnetic post, one end of said ferrimagnetic post is fixed to the center of said conductor member and an air gap is provided between the other end of said ferrimagnetic post and said H plane, and the electrical length of said air gap is adjusted so as to obtain the wide band characteristics of said waveguide circulator.

3. A waveguide circulator according to claim 1, wherein a first and second conductor member are arranged respectively on upper and lower H planes at the center of the junction of waveguide ports, the total thickness of said first and second conductor member is selected to be approximately equal to the height of said ferrimagnetic post, one end of said ferrimagnetic post is fixed to the center of said first conductor member and an air gap is provided between the other end of said ferrimagnetic post and said second conductor member, and the electrical length of said air gap is adjusted so as to obtain the wide band characteristics of said waveguide circulator.