FR2531272A1 - ADAPTATION AND ISOLATION DEVICE COMPRISING A FERRITES CIRCULATOR - Google Patents

Abstract

DEVICE INTENDED TO CONNECT A MICROWAVE CIRCUIT TO A CONNECTION POINT, WHEN THE IMPEDANCE OF THE CIRCUIT IS LIKELY TO A SERIAL RESONANT CIRCUIT. TO CONNECT A CIRCUIT TO BE ADAPTED 1 TO A CONNECTION POINT, A FERRITE CIRCULATOR 20-21-22 IS USED TO ENSURE THE ISOLATION. TO ENSURE THE ADAPTATION OF THE CIRCUIT BY AVOIDING ADDING AN ADAPTATION CIRCUIT OF THE SERIAL RESONANT TYPE, TAKE ADVANTAGE OF THE FACT THAT THE ACCESS IMPEDANCES OF A FERRITE CIRCULATOR ARE SIMILAR TO THOSE OF PARALLEL RESONANT CIRCUITS; TO THIS END THE CIRCULATOR IS CHOSEN SO THAT THE IMPEDANCE OF ITS COUPLED ACCESS TO THE CIRCUIT TO BE ADAPTED 1 CORRESPONDS, AS NEAR AS POSSIBLE, TO THE CONJUGATE IMPEDANCE OF THE CIRCUIT TO BE ADAPTED. POSSIBLY AN IMPEDANCE TRANSFORMER, FOR EXAMPLE, OF THE QUARTER WAVE TRANSFORMER TYPE, NOT INCLUDING A PARALLEL RESONANT ELEMENT, CAN BE INSERTED BETWEEN THE CIRCUIT AND THE CIRCULATOR. APPLICATION TO MICROWAVE CIRCUITS.

Description

ADAPTATION AND ISOLATION DEVICE

  COMPRISING A FERRITES CIRCULATOR

  The present invention relates to an adaptation and isolation device, comprising a ferrite circulator, for coupling a circuit

  to adapt to a connection point, the circuit to be adapted being assimilated

  lable, from the point of view of its impedance, to a series resonant circuit.

  Broadband adaptation devices for micro-circuits

  waves are based on the use of resonators which, in the case where the circuit to be adapted is not comparable to a parallel resonant circuit, make it possible to achieve the impedance conjugated with that of the circuit to be adapted in order to obtain a wide band Moreover, it is known to use a circulator between the microwave circuit with its adaptation device and the access considered, for the purpose of achieving isolation or improving the standing wave ratio. (ROS) The connection between the circulator and the microwave circuit to be adapted is conventionally made by a transition to a standardized characteristic impedance (50 ohms for example) this entails the need for two adaptation devices, one for the circulator and one for the circuit to

  adapt, and therefore a reduction in bandwidth.

  The present invention aims to avoid these disadvantages due to

  the use of both adaptation devices.

  2 R O This is achieved by realizing the circuit adaptation device to

  adapt from the ferrite circulator.

  According to the invention, an adaptation and isolation device for coupling a circuit to be adapted to a connection point, comprising a matching circuit of the circuit to be adapted, of the parallel resonant circuit type, coupled to the circuit to be adapted, and a circulator ferrites having a first port coupled to the branch point and a second port coupled to the circuit to be adapted, is characterized in that the matching circuit

  comprises, as parallel resonant circuit, the circulator.

2531-272

  The present invention will be better understood and other characteristics

  ticks will appear using the following description and figures

  which represent: FIGS. 1 and 4 representative circuit impedances, FIGS. 2 and 3 respectively relating to the prior art and to the invention, FIGS. 5 and 6 are views showing a ferrite circulator.

  used in the assembly according to Figure 3.

  In the different figures, the corresponding elements bear the

same landmarks.

  In what follows it will be question of a circuit to adapt; he

  This will be a microwave circuit of the amplifier, filter, melange

  geur- etc. In FIG. 1 is schematically the impedance of a 1 circuit to be adapted in the most general case, that is to say in the case where this impedance is similar to a series resonant circuit. RI-L-Cl If the tuning frequency F0 of the circuit to be matched is different from its resonance frequency, an impedance is connected in series with the circuit to be adapted to make these two frequencies equal in the case of Figure 1 this impedance is obtained by an inductor

  The Io In what follows and in the claims this impedance, to be added

  possibly, will be considered part of the circuit to be

  ter and it will be considered as a resonant circuit series form

  elements R 1-LI-Cl with LI = L + I; and the pulse W O, corres-

  laying at the working percent frequency, is such that: LI CI 2 = 1 The impedance, at the pulsation, of the circuit to be adapted of FIG. 1 is: ZI = RI + j (L 1 W -CW) 61) and its overvoltage coefficient Ll W 2

IQ = RI 2)

  When a circuit to be adapted, of the type referred to above, must be coupled to a connection point through an isolation circuit, it is known to use a ferrite circulator for this purpose.

  a mounting shown schematically in FIG.

  FIG. 2 shows a circuit to be adapted, 1, which is connected to a connection point, A, by an adaptation circuit, 10, followed by a circulator, 20 to 23. The matching circuit, 10, consists of conventionally using one or more parallel resonant circuits; the elements of this circuit 10 are chosen such that it has a purely ohmic input impedance and a given value Zc throughout the working frequency band, when its output is connected to the input of the circuit to be adapted. circulator, although consisting of a single element, has been represented by four blocks so as to distinguish between its different functions: a block, 20, called switching circuit which relates to the "circulator" function itself and three blocks, 21 to 23, called impedance transformers, connected to each of the three ports of the switching circuit 20 to bring back to the value Zc, mentioned above, -the impedances of the three accesses of the circulator The "1 circulator" function represented by the block 20, isolates the circuit to be adapted 1 of another circuit to adapt connected downstream of the point A, so as to improve the standing wave ratio at point A impedance transformers, 2 1 to 23, have, like the adaptation circuit 10, a role

  impedance matching but, unlike circuit 10, they do not require

  There are no resonators for this role since, as will be indicated below, a circulator has at its access impedances of the type of those of parallel resonant circuits; the impedance transformers 21 to 23 are, generally, constituted by quarter-wave transformers. The impedance transformer 21 is connected to the point A, the impedance transformer 22 is connected to the first end of a transformer. resistance R whose second end is grounded; as for the impedance transformer 23 it is coupled to the circuit to be adapted

1 by the matching circuit 10.

  FIG. 3 shows how, in the context of the invention, the assembly according to FIG. 2 is modified. The arrangement according to FIG. 3 differs from the assembly according to FIG. 2 in that the impedance transformer 23 and the circuit of FIG. adaptation 10 have been removed and replaced, depending on the case, either by a direct connection or by a simple impedance transformer 3 having no parallel resonant element; this alternative is represented by a drawing of the periphery of the block

  3 in broken lines Such an assembly, by the suppression of the transformation

  impedance transmitter 23 and the matching circuit 10 and therefore its resonator, has a bandwidth wider than the assembly according to Figure 2; moreover, because of the reduction in the number of elements, the assembly according to FIG. 3 presents less losses than the assembly according to FIG. 2.

  In the following description it will be shown why the

  mounting according to Figure 3 is possible.

  For a circulator errites it is known (see in particular the article: Operation of the ferrite junction circulator, published in IEEE Transactions on microwave theory and techniques, from January 1965, pages to 27), and measurements allow to verify it, that the impedances

  access are comparable to those of parallel resonant circuits.

  FIG. 4 represents a parallel resonant circuit formed of a

  resistance R 2 in parallel on an inductance L 2 and a capacitor C 2.

  This figure is the schematic representation of the impedance of an access of a ferrite circulator whose impedance, at the pulse W is

Z 2 = (3)

R 2- + j (C 2 W L 2.

  The overvoltage coefficient of the resonant circuit according to FIG. 4 is:

Q 2 = R 2 C 2W (4)

  o W is the resonant pulsation of the circulator and is such that

L 2.C 2 2 = 1

  When a circulator is used in an assembly, as

  tif isolation for a microwave circuit, its resonant frequency is

  chosen for reasons of operational bandwidth

  equal or at least as close as possible to the frequency

  center of work and therefore of the resonance frequency of the micro-

  waves; this is why in the form LI CI W 2 = 1 relative to the circuit to be adapted of FIG. 1 and in the formula L 2 C 2 2 O, the resonance pulse is, in both cases, represented by WO. parallel resonant circuit according to Figure 4 may constitute an adaptation circuit for the series resonant circuit according to Figure 1, that is to say that the diagram of Figure 2 can be

  replaced by the diagram of Figure 3 with a connection without

  Since the impedance Z 2 of the parallel resonant circuit is impedance between circuits 20 and 1, it must equal the conjugate of the impedance Z 1, that is, -t -1 1 - = R I j (LI aw Y l S + j (C 2 RI -j (LI CI R 2 + Lj (C 2 -L 2 W) by replacing, in this equation, CI and L 2 by their values derived from formulas L 1.Cl W 2 = 1 and L 2 C 20 W 2 = 1 where it comes, making equality between the real parts on the one hand and the imaginary parts on the other hand

2 22

  RI 2W wom R '"2 + L Io C 2 o Ww (e S = 1 (5)

2 2

  (R Io C 2W L- R m _) = O (6) R 2) 'u 2} for W = W the relation (5) implies: o Rl = R 2 for W different from W the relation (6) implies o RI. C 2 u lR w o which gives by multiplying by LI w

RI.C 2 W =

  R 2

  what can be written, given formulas (2) and (4)

QI 1 = Q 2

  Knowing the values of RI and IQ, at the wo resonance pulse, of a circuit to be adapted, it is always possible to produce a circulator whose resonance pulse, the overvoltage coefficient and the resonance impedance are respectively equal, or at least close, of W o, QI and RI Thus it is possible to realize the adaptation

  optimal broadband between the circulator and the microwave circuit.

  It should be noted that if the resistance R 2 of the circulator is clearly different from the resistor RI of the circuit to be adapted, it is possible to carry out an adaptation by an impedance transformer, without parallel resonant element, mounted as the transformer of impedance 3 of FIG. 3 The assembly constituted by the impedance transformer 3 associated with the circuit to be adapted, 1, always has the same resonance pulse w as the circuit to be adapted 1 and its resistance is determined to be equal to R 2 ; moreover, its overvoltage coefficient at the pulsation W o is no longer equal to QI but is modified by the impedance transformer, 3, it is therefore necessary that the circulator has been chosen so that its overvoltage coefficient at 1, resonance, Q 2, be as close as possible

  the overvoltage coefficient of the set "circuit 1 and transformer 3.

  An exemplary embodiment of a crulator for an assembly according to FIG. 3, with direct connection, without the transformer 3, between the circuit to be adapted 1 and the switching circuit 20, will be described hereinafter using Figures 5 and 6 The circuit to be adapted was a circuit using a field effect transistor X gallium arsdnkure, working in the

  range of frequencies 3.6 4.2 Hz e having the characteristics

  after: resonance frequency: FO = 3.9 G Hz overvoltage coefficient QI = 3.15 resonance impedance Ri = 15 ohms The purpose of the adaptation of this circuit was to obtain the minimum

  noise factor of the field effect transistor.

  The circulator produced (FIGS. 5 and 6) has the following characteristics: resonance frequency: F O 3.9 G Hz overvoltage coefficient Q 2 = 2.12

  impedance at resonance: R 2 = 15 ohms.

  It should be noted that the circulator according to FIGS. 5 and 6 does not perfectly satisfy the condition Q 2 = Qi; however, measurements have shown that in the range of working frequencies (3.6 4.2 GHz), the difference between the optimum impedance that achieves the minimum noise factor and the impedance achieved by the circulator, remains weak and

  that the noise factor obtained is practically minimum.

  FIG. 5 shows, in phantom, the periphery C of the assembly constituted by the housing of the circulator and the housing of the circuit to be fitted which are contiguous. In FIG. 5 only one part 4 located in the middle of the circulator, two resonator connection plugs, 31, 32, and the field effect transistor, 11, of the

Adapt 1 of Figure 3.

  The piece 4 constitutes the inner conductive part or ribbon (strip in the Anglo-Saxon literature) of a structure of the triplaque waveguide type, that is to say of a structure formed of two parallel mass planes and a ribbon disposed parallel to the two ground planes and between them These two ground planes appear in Figure 6 o they carry the marks 61 and 62 The piece 4 consists of a metal plate made of silver brass 1.2 mm thickness having a resonator disk 40, 14 mm in diameter, pierced with a centering hole, 44; around this disc are arranged three branches, 41, 42, 43, 120 from each other The branches 41 and 42, of length much greater than the branch 43, are welded to the inner conductor of the coaxial plugs,

  31, 32 These plugs, characteristic impedance equal to 50 ohms, allow-

  attempt the connection to point A and resistor R (Figure 3); their outer conductor connected to the casing of the circulator, has not been shown in Figure 5 The branch 43, which is actually there only for repertoire for the connection, is welded to the end of the connection of gate, G, of the field effect transistor, 11, of the circuit to be adapted; the length of the gate connection of the transistor 11, i.e. the length of the connection between the transistor housing and the disk 40, determines

  the inductance L'1 discussed in the description of Figure 1;

  for the sake of simplification and because it would bring nothing to the understanding of the invention, the elements connected to the drain, D, of transistor II have not been represented; as to the source of transistor 11, it has two output connections, 51 and 52, which are all

  two welded on the housing of the circuit to be adapted.

  It should be noted that, in the embodiment described, the polarization of the gate of transistor II is via the circulator; indeed, the resistor R which, for the sake of simplification, is connected in FIG. 3 directly between the circulator and the ground is, in fact, connected by its first end to the circulator (transformer 22 comprising the branch 42) and by its second end to a decoupling circuit; this decoupling circuit behaves like a short circuit at the working frequencies of the circuit to be adapted and as an infinite impedance for the DC bias voltage; this bias voltage is applied to the second end of the resistor R. The decoupling circuit can be conventionally produced by open quarter-wave lines

  which bring back a short circuit and / or a capacitor.

  In FIG. 3 reference is made to impedance transformers 21 and 22 and to the switching circuit 20 which constituted the circulator. In FIG. 4, the resonator disc 40 and the branches 41 and 42 correspond to each other.

  respectively to the switching circuit 20 and the

  dance 21 and 22; these impedance transformers are of the transfor-

  quarter-wave meters, that is to say that the length of the branches is substantially equal to a quarter of the length, in the circulator, of the wave at the average frequency of 3.9 G Hz In fact the blocks 20 , 21 and 22 of Figure 3 are more exactly to identify with the combination of elements, 41, 42 and elements between which they are inserted in the

  circulator and will be described using Figure 6.

  FIG. 6 is a sectional view along the axis XX (FIG. 5) of the circulator. This view shows that, on either side of the ribbon 4, there are two symmetrical structures with respect to the ribbon and which comprise, starting from ribbon: a ferrite disk 51, 52 whose diameter is substantially equal to the diameter of the resonator disk 40 (FIG. 5) and a silica part, 53, 54, which covers most of the portion of the ribbon 4 outside the disk 40 (FIG. Figure 5); parts 51 to 54 have a thickness of 2.1 mm; the ferrite disc 51, 52 is pierced with a hole in its center, an aluminum flange, 61, 62, constituting one of the ground planes mentioned above and which comprises, in its face opposite to the ribbon 4, a hollow in the form of a circular bowl arranged opposite the ferrite disks 51, 52 in the trough-shaped recess: an air knife 71, 72, a washer made of mild steel 0.5 mm thick, 81, 82 and a permanent magnet, 91, 92, 1.5 mm thick the magnetic circuit formed with the two magnets 91, 92 provides a field of 400 gauss, a bar of a U-shaped iron, 60; this iron U covers, respectively by its two bars opposite, the two magnets 91, 92 to close their field lines; this U-shaped iron is made with a

  mild steel strip 1 mm thick and 17 mm wide.

  A cylindrical insulating rod, 45, made of nylon (brand

  sée), through the holes drilled in the ribbon 4 (hole 44) and in the ferrite disks 51, 52, to ensure the positioning of these parts some

compared to others.

  A very thin silver sheet, not shown in FIG. 6, is disposed between the disk 51 and the silica part 53 on the one hand and the flange 61 on the other hand, to ensure good electrical contact between these elements. another sheet, not shown, provides good contact between the disc 52 and the silica part 54 on the one hand and the flange 62 on the other hand. The housing of the circulator comprises, between the flanges 61 and 62 and the U-shaped iron 60, a socket 31, fixed on the flanges 61 and 62, by means of

screws not shown.

  This ferrite circulator was manufactured according to the characteristics

  to obtain the adaptation of the circuit to be adapted, which has been mentioned above; for that, the choice was first made on an existing circulator having characteristics quite similar to those to be obtained then, after successive tests, the circulator described in

  the help of Figures 5 and 6 has been realized.

  It should be noted that the invention is not limited to the example described; it is thus, in particular, that it is possible, in the assembly according to FIG. 3, to eliminate the impedance transformer 22, that is to say, practically the branch 42 of the ribbon 4 (see FIG. 5) , then just

  give R the value presented, the resonance, by the corresponding output

the resonator.

  It should also be noted that the circulator can be used as a matching element of a circuit to be adapted, not only to the input of the circuit, as in the example described, but also to the output of the circuit; thus the same circulator can serve as an adaptation element for two circuits to be adapted: a first circuit to be adapted having its output coupled to one of the ports of the circulator and a second circuit

  to adapt having its input coupled to another access of the circulator.

the

Claims (4)

  1 adaptation and isolation device for coupling a circuit to be adapted (1) to a connection point (A), comprising an adaptation circuit (R 2 -L 2-C 2) of the circuit to be adapted, of the type resonant circuit   parallel, coupled to the circuit to be adapted and a ferrite circulator (2021-   22) having a first port coupled to the branch point and a second port coupled to the circuit to be adapted, characterized in that the circuit   The adapter comprises, as a parallel resonant circuit, the circulator.   2 Device according to claim 1, characterized in that the circuit to be adapted is directly connected to a circuit access 1 referral.   3 Device according to claim 2, characterized in that, the circuit to be adapted being comparable to a series resonant circuit (RI-LI-CI) having a resonance pulse W 0, an impedance RI at resonance and a QI overvoltage coefficient , the circulator is chosen such that, from the point of view of the access to which the circuit to be adapted is connected, it is comparable to a parallel resonant circuit of pulsation W 0, of impedance R 2 to resonance and of overvoltage coefficient Q 2 with R 2 and Q 2 substantially equal respectively to RI and IQ.