Electric power transmission system for hyperfrequencies having a gyromagnetic effect

An electric power transmission system for hyperfrequencies having a gyromagnetic effect. The system includes a gyrator device having at least one disc-shaped wafer of gyromagnetic material such as ferrite, one side of which is set to a reference potential, and at least two tuning networks each comprising an inductance arranged on the other side of the wafer and one end of which is connected to the ground of the gyrator device whereas the other end is connected to an input terminal of the transmission system. The gyrator device is subjected to a homogeneous magnetostatic field for energizing the gyrator device and a layer of electrically insulating material of low permittivity is provided between the inductances and the wafer of gyromagnetic material. The device is usable for circulators, isolators or filters.

BACKGROUND OF THE INVENTION 
The invention relates to an electric power transmission system for 
hyperfrequencies with a gyromagnetic effect, such as a circulator, an 
isolator or a filter, of the type comprising a gyrator device which 
comprises at least one advantageously disc-shaped wafer made from a 
gyromagnetic material such as ferrite material, one side of which is set 
at a reference potential such as a metal plane which may either be or not 
be connected to the ground of the system, and at least two tuning 
networks, each comprising an inductance arranged on the other side of the 
wafer and one end of which is connected to the ground of the gyrator 
device whereas the other end is connected at an input terminal of the 
transmission system, the gyrator device being subjected to a homogeneous 
magnetostatic field for energizing the gyrator. 
The utilization limits of transmission systems of this type which are known 
are imposed by the natural resonance frequency of the gyrator, i.e. by the 
frequency determined by parasitic capacitances inherent in the 
configuration of the component elements and of the structure of the whole. 
A second limit appears when it is desired to have the power transmitted 
through the system. In a general manner the transmitted power is 
proportional to the diameter of the gyromagnetic wafer used and inversely 
proportional to the transmission losses. The increase in the size of the 
gyrator device increases the parasitic capacitance and is thus attended by 
a reduction in the natural resonance frequency. It is moreover known that 
the transmission losses may be minimized by a suitable selection of the 
magnetic parameters as well as of an optimum coupling coefficient, i.e. 
close to 1. Such a coupling coefficient is obtained by increasing the 
number of conducting leads which form the inductance. The increase in the 
number of leads results again in an increase of the parasitic capacitance 
and therefore in a reduction of the natural reasonance frequency. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a transmission system of 
the kind referred to hereinabove which allows at least substantially 
decreasing this parasitic capacitance so as to increase the natural 
frequency. 
Another object of the invention is to allow the selection of the other 
parameters of the system such as the geometric dimensions of the gyrator 
device, the number of conducting leads of the inductances and the coupling 
coefficient in an advantageous fashion without this being detrimental to 
the natural resonance frequency. 
For achieving this goal a transmission system according to the invention is 
provided with a layer made from an electrically insulating material and 
with a small permittivity disposed between the inductances and the wafer 
of gyromagnetic material. 
According to an advantageous embodiment of the invention, the insulating 
layer comprises the superposition of several chips made from an insulating 
material of small permittivity which are interposed between the aforesaid 
inductances while electrically insulating the inductances from each other. 
According to another advantageous embodiment of the invention, the 
aforesaid inductance is made as a number of conducting leads connected 
with one end to the ground of the gyrator device and mounted in 
parallel-connecting relationship, such a number ranging from 2 to 10.

DETAILED DESCRIPTION 
Referring to FIGS. 1 and 2 there is shown an electric power transmission 
system for hyper-frequencies with a gyromagnetic effect essentially 
comprising a gyrator device 1 adapted to be mounted onto a printed circuit 
chip 2 arranged between upper and lower plates 3 and 4, respectively, made 
from metal or from a non magnetic alloy, such as, for instance, aluminum, 
each plate being formed with a central opening 5 adapted to receive a 
polar piece 7 made, for instance, from steel and a magnet 8. An upper 
magnetic closing plate 10 and a lower magnetic closing plate 11 are 
disposed on the free outer surfaces of the upper and lower magnets 8, 
respectively. The whole is surrounded by a belt 12 consisting of several 
elements 13, 14, 15 and magnetically connecting the upper and lower 
closing plates 10 and 11 for making the magnetic circuit. The belt 
comprises three connectors 16 which are secured to three sides of the 
plates 3 and 4 in the assembled state of the system. 
The printed circuit chip 2 exhibits in its center a recess 17 adapted to 
accommodate the gyrator device 1. The plate 2 carries on its top side a 
pattern of electrically conducting strips and zones, namely three 
substantially radial strips 19 which extend from the edge of the recess 17 
to the edge of the plate and are adapted to be each electrically connected 
to the conductor 18 (FIG. 2) of one of the connectors 16, and three zones 
20 which are electrically insulated at 21 from the strips 19 and are 
adapted to be in electric contact with the upper plate 3 which bears upon 
each zone 20 with a pin 22 and constitutes a ground electrode. 
It should be pointed out that each strip 19 is generally connected to the 
corresponding conductor 18 through the medium of a matching network not 
shown and comprises LC-type cells as known per se. 
Referring to FIGS. 3 to 5, three embodiments of a gyrator device 1 
according to the present invention will be described hereinafter. 
According to a first embodiment shown in FIG. 3, the gyrator device 1 
comprises a configuration of three inductances 23, 24, 25 each comprising 
two conducting portions or leads 27, 28 arranged in the same plane and 
which are parallel and connected at their ends designated at 29 and 30. 
These ends are made as electric connecting lugs one of which, for 
instance, the lug 29 is connected to one of the ground zones 20 of the 
printed circuit on the plate 2 and of the gyrator device whereas the other 
lug designated by the reference numeral 30 will be electrically connected 
to one of the conducting strips 19 of the printed circuit. These 
inductances 23 to 25 may be made from any suitable conducting metal and 
exhibit a self-supporting structure. The inductances are electrically 
insulated from one another by the interposition of a suitable insulating 
material. The inductances are arranged so as to be angularly spaced by 
120.degree.. 
Both discs 32, 33 of circular shape in the example shown and made from an 
electrically insulating material with a small permittivity are arranged on 
either side of the configuration of the three inductances 23 to 25. These 
discs could be discs made from Teflon or from a dielectric material such 
as ceramic. On each disc 32, 33 is provided a disc 34, 35, respectively, 
made from a gyromagnetic material such as ferrite material. The outer face 
of each gyromagnetic disc therefore is in the assembled condition of the 
system in contact with a metal plane (the faces of poll pieces 7) which 
may either be or not be connected to the ground of the system. As it 
appears from FIG. 1, the various connecting lugs 29, 30 are radially 
projecting from the whole consisting of the stack of discs 32 to 35 on the 
central configuration of the inductances 23, 24, 25 so that they may be 
electrically connected to the printed circuit of the chip 2. 
FIG. 4 shows an embodiment of the gyrator device 1 wherein the insulating 
layer of small permittivity is formed of four discs or plates of smaller 
thicknesses 37 to 40 which are stacked between the upper and lower 
gyromagnetic discs 34, 35. The three inductances 23 to 25 are each 
arranged between two neighboring insulating discs while being angularly 
spaced by 120.degree. as shown on FIG. 3. In this embodiment each 
inductance comprises ten parallel leads. Each inductance may be made so as 
to exhibit a self-supporting structure or be deposited as a printed 
circuit onto one surface of one of the discs 37 to 40 while of course 
providing a support for the connecting lugs 29, 30. In this embodiment, 
the discs 37 to 40 are advantageously made from a dielectric material such 
as ceramic. 
In the embodiment according to FIG. 5, the insulating layer with a small 
permittivity is formed of seven discs 42 to 48 which are stacked between 
the gyromagnetic discs 34, 35 with the inductances arranged therebetween 
in sandwich-like fashion. In this embodiment, each inductance is divided 
into two halves which within the whole gyrator assembly are juxtaposed and 
electrically connected in parallel relationship. For instance, the 
inductance 23 of FIGS. 3 and 4 is now formed of both half-inductances 23a 
and 23b interposed between the discs 43, 44 and 46, 47, respectively, i.e. 
between two different pairs of discs. Likewise, the inductances 24 and 25 
are formed of the half-inductances 24a, 24b and 25a, 25b, respectively, 
and arranged between two different pairs of discs as shown on FIG. 5. 
The operation of the system according to the present invention which has 
just been described will be described hereinafter with reference to the 
Figures. 
The general structure of such a transmission system is known per se and 
therefore needs not be described in more detail. The discs made from a 
gyromagnetic material 34, 35 are disposed in the static magnetic field 
generated by the magnets 8 as clearly shown in FIGS. 1 and 2. The magnetic 
circuit is closed through the upper and lower closure plates 10 and 11 and 
the belt 12. Through the connectors 16, a perpendicular hyperfrequency 
field is applied to the gyromagnetic material, the wavelength of this 
field being very great with respect to the lengths of the axes of the 
gyromagnetic discs so that the field is uniform within the volumes 
thereof. 
The interposition of an insulating layer having a small permittivity 
between the configuration of the inductances and each disc of gyromagnetic 
material permits substantially reducing the parasitic capacitance due to 
the sizes of the conducting strips, of the inductances and of their 
numbers of leads and of the thickness of the gyromagnetic material. The 
great reduction of this parasitic capacitance allows increasing the 
natural resonance frequency of the gyrator system which is given by the 
equation: 
##EQU1## 
where L.sub.o is the value of an inductance for a permeability 
.mu..sub.eff =1 and C' being the sum of parasitic capacitances. 
It thus becomes apparent that it is possible to increase the natural 
frequency, i.e. the operating frequency of the gyrator device 1 while 
decreasing the parasitic capacitance C'. This operating frequency 
constitutes the limit frequency of the system. As a matter of fact, the 
frequency to which the system will be tuned is determined by the mounting 
in parallel connecting relationship on each input or access of the gyrator 
device 1 of a capacitor (not shown) and the relative pass-band as well as 
the resistance may be changed by means of LC-type cells inserted at the 
input of the gyrator device. 
By arranging the insulating layer having a small permittivity as one or 
several discs between both gyromagnetic discs 34, 35 of the device 1 a 
capacitance C" is inserted which may be written as follows: 
##EQU2## 
where .SIGMA..sub.o, .SIGMA..sub.r, e and S designate the permittivity of 
the vacuum, the relative permittivity of the insulating material, the 
thickness and the surface area of the insulating layer, respectively. 
This capacitance C" may be assumed to be connected in series with the 
parasitic capacitance C' and by selecting the smallest possible 
.SIGMA..sub.r and the greatest possible thickness, the inserted 
capacitance C" takes such a small value that the total capacitance is 
substantially decreased. By way of example, Teflon exhibits an 
.SIGMA..sub.r =2. As to the thickness of the insulating layer in the 
embodiment according to FIG. 5, each Teflon disc could have a thickness of 
0.1 mm which gives a total thickness of the insulation of 0.7 mm. In a 
general manner the maximum thickness is a function of the thicknesses of 
the gyromagnetic discs and is roughly determined by the term 
##EQU3## 
where H is the thickness of the gyromagnetic disc. 
It has been proved that the limit frequency F of a gyrator according to the 
invention is multiplied by .sqroot.K with respect to a conventional 
gyrator if K is the coefficient by which the parasitic capacitance has 
been decreased by providing insulating layers of small permittivities as 
just described. 
The addition of the insulation of small permittivity and of relatively 
great thickness of from 1 to several tenths of a millimeter also permits 
increasing the size of the discs of gyromagnetic material and the number 
of leads constituting the inductances and thus to improve the coupling 
coefficient. The admissible power may be multiplied by two or three taking 
into account the smaller thermal resistance, the larger heat exchange 
surfaces and improved energy distribution inside of the gyromagnetic 
material. Owing to the measures just stated, it is possible to decrease 
the losses and to increase the relative frequency band. 
FIGS. 6 and 7 which show the limit frequency F (in MHz) and the admissible 
power Pa (in Watts), respectively, versus the diameter D of the disc of 
gyromagnetic material such as ferrite material (in cm), confirm what has 
just been specified. In each Figure the curve A gives the values of a 
typical system using the conventional structure whereas the curve B gives 
the values which have been measured under the same conditions as for the 
curve A, of a system according to the invention, i.e. comprising an 
insulation of small permittivity and of great thickness between the 
configuration of inductances and the discs of gyromagnetic ferrite. 
It has, moreover, been discovered that the relative frequency passbands of 
a system according to the invention may have a width which is twice as 
large as that of a known system in the low frequency range of 30 MHz. 
The improvements just mentioned may be applied to various types of systems, 
in particular, to all those which require either a reciprocal or non 
reciprocal coupling such as circulators, isolators and filters. 
The invention such as described with reference to the Figures may be 
modified in various ways without departing from the scope of the 
invention. The techniques for practicing the invention may be of various 
kinds. The layer added to reduce the parasitic capacitance may be an 
insulation of the adhesive or adhesive type, a dielectric such as ceramic 
with a small permittivity or the like. The printed circuits may be with a 
single or double face or of the multilayer kind. The shapes of the wafers 
of gyromagnetic material may have any suitable known shape. The same holds 
true for the insulating layer and the inductances. The number of wafers 
and of insulating layers may vary. The invention is also applicable to a 
system structure using one single gyromagnetic wafer only onto which will 
be laid the configuration of inductances with the interposition of at 
least one insulating layer of small permittivity. The number of access 
connections may, of course, be different and vary from two to a higher 
number.