CA1212731A - Matching and isolating device comprising a ferrite circulator - Google Patents
Matching and isolating device comprising a ferrite circulatorInfo
- Publication number
- CA1212731A CA1212731A CA000433144A CA433144A CA1212731A CA 1212731 A CA1212731 A CA 1212731A CA 000433144 A CA000433144 A CA 000433144A CA 433144 A CA433144 A CA 433144A CA 1212731 A CA1212731 A CA 1212731A
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- Prior art keywords
- circuit
- matched
- circulator
- matching
- impedance
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/32—Non-reciprocal transmission devices
- H01P1/38—Circulators
- H01P1/383—Junction circulators, e.g. Y-circulators
- H01P1/387—Strip line circulators
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- Non-Reversible Transmitting Devices (AREA)
- Control Of Motors That Do Not Use Commutators (AREA)
- Microwave Amplifiers (AREA)
Abstract
A MATCHING AND ISOLATING DEVICE
COMPRISING A FERRITE CIRCULATOR
ABSTRACT
A ferrite circulator is placed between a circuit to be matched and a connection point for performing the function of a directional isolator. In order to achieve matching of the circuit to be matched without any need to add a matching circuit of the parallel resonant type, advantage is taken of the fact that the access impedances of a ferrite circulator are comparable with those of parallel resonant circuits. The choice of the circulator is accordingly governed by the need to ensure that the impedance of its access which is coupled to the circuit to be matched corresponds as nearly as possible to the conjugate impedance of the circuit to be matched. If necessary, an impedance transformer such as a quarter-wave transformer which is not provided with a parallel resonant element can be inserted between the circuit to be matched and the circulator.
COMPRISING A FERRITE CIRCULATOR
ABSTRACT
A ferrite circulator is placed between a circuit to be matched and a connection point for performing the function of a directional isolator. In order to achieve matching of the circuit to be matched without any need to add a matching circuit of the parallel resonant type, advantage is taken of the fact that the access impedances of a ferrite circulator are comparable with those of parallel resonant circuits. The choice of the circulator is accordingly governed by the need to ensure that the impedance of its access which is coupled to the circuit to be matched corresponds as nearly as possible to the conjugate impedance of the circuit to be matched. If necessary, an impedance transformer such as a quarter-wave transformer which is not provided with a parallel resonant element can be inserted between the circuit to be matched and the circulator.
Description
~2~73~
A MATCHING AN~ ISOLATING DEVICE
COMPRISING A FERRIT~ CIRCUhATOR
BACRGROUND OF THE INVENTION
The present invention relates to a matching and iæolating device comprising a ferrite circulator for coupling a circuit to be matched to a connecting point, the circuit to be matched being comparable from an impedance standpoint with a series xesonant circuit.
Broad-band matching devices for microwave circuits are based on th~ use of resonators which, in the event that the circuit to be matched is not comparable with a parallal resonant circuit, make it possible to provide an impedance corresponding to that of the circuit to be matched in order to obtain a wide band of operating frequencies. Furthermore, it is already known to make use of a circulator between the micro~ave circuit with its matching and access device under consideration with a view to providing isolation or to improving the standing-wave ratio (SW~). The connection between the circulator and the microwave circuit to be ma~ched ls effected in the con-ventional manner by means of a passage at a standardized characteristic impedance (50 ohms, for example). This entails the need for two ma~ching devices, namely one for ~he circulator and one for the circuit to be matched, and consequently for a reduction of the passband.
73iL
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to over-come these disadvantages which arise from the use of two matching devices.
This object is attained by producing the circuit-matching device by means of the ferrite circulator.
According to the invention ~here ~s provided a matching and isolating device for coupling a circuit to be matched to a connection point, the circuit to be~matched being comparable from an impedance standpoint with a series resonant circuit. The device comprises a matching ~ircuit of the parallel resonant circuit type which is coupled to the circuit to be matched and a ferrite cir-culator having a first access coupled to the connection point and a second access coupled to the circuit to be matched. In this device, the circulator comprises a switching circuit with accesses and said accesses have impedances which are comparable with those of parallel resonant circuits so tha~ the circulator itself constitutes the matching circuit.
In a related field, it should be noted that an isolator is known in which provision is made for a circu-lator. In this circulator, in order to ensure optimum matching of one of the three inputs of the circulator pro-per (corresponding to the switching function) with which a 121Z73iL
dissipative load is coupled, the coupling element chosen is a series oscillating circuit whose impedance added to that of the dissipative load is as clos~ as possible to the conjugate impedance of the circulator ; thls series oscillating circuit replace~ the type ~4 impedance trans-former which is usually employed for the matching operation and normally forms part of the circulator. This arrange-ment bears only a remote comparison with the invention which does not involve replacement of a typs A/4 impedance transformer (forming part of the cir~ulator) by a series oscillating circuit (added to the circulator) but dis-penses with the need for a ma~ching circuit of the parallel resonant circuit type usually employed for coupling a circuit to be matched and a circulator. The circuit to be matched is thus coupled directly to the cir-culator without using any element as a substitute for the matching circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features of the invent~on will be more apparent upon consideration of the followtng desaription and accompanying drawings, wherein :
- Figs. 1 and 4 show representative impedances of circuits ;
- Figs. 2 and 3 show circuit assemblies relating respectively to the prior art and to the invention ;
- Figs. S and 6 are views showing a ferrite ~2~Z~3~
circulator employed ln the circuit assembly of Fig. 3.
In ~he different figures, corresponding elements are designated by the same references.
DETAILEn DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description will be concerned with a circuit to be matched and more especially a microwave circuit such as an amplifier, fllter, mlxer, and so on.
There is shown diagrammatically in Fig. 1 the impedance of a circuit to be matched in the most~general . 10 case, that is, in the case in which said impedance is comparable with that of a series resonant circuit Rl-L-Cl.
If the mid-band operating frequency F0 of the circuit to be matched is different from its resonance frequency, an impedance is added in series with the circuit to be matched in order to make these two irequencies equal. In the case of Fig~ 1, this impedance is obtained by means of an inductance ~'1. It will be considered in the following description and in the appended claims that thls additional impedance forms part of the circuit to be matched and this latter will be considered as a series resonant circuit ~ormed by the elements Rl-Ll-Cl with L1 = ~ + L'l ; and the angular frequency ~0 corresponding to the mid-band operating frequency is such that : Ll.Cl.~o = 1.
The impedance, at the angular frequency w, of the circuit to ~e matched as shown in Fig. 1 is :
Zl = Rl ~ ~(Ll.~ ~ Cl ~) (1) os and its Q factor is :
Ll.~
Ql Rl (2, When a circuit to be matched of the type con-sidered in the foregoing has to be coupled tG a connection point via an isolation circult, it is a known practice to employ for this purpose a ferrite circulator in a circui~
arrangement which i5 shown diagrammatically in Fig. 2.
Flg. 2 shows a circuit 1 to be matched which is coupled to a connection point A by means of a matching circuit 10 followed by a circulator 20 to 23. The match-ing circuit 10 is constructed in the conventional manner by means of one or a number of parallel resonant circuits.
The elements of said circuit 10 are chosen so as to present a purely ohmic input impedance having a given value Zc ~hroughout the operating frequency band when its ou~put is connected to the input of the circuit to be matched.
Although consisting of a single Plement, the circulator is represented by four blocks in order to distinguish between its different functions : a block 20 de~ignated as a switching circult and relating to the "circulator"
function proper, and three blocks 21 to 23 designated as impedance ~ransform~rs and connected to each of the three accesses of the switching circuit 20 in order to restore the impedances of ~he three~circulator accesses to the value Zc mentioned earlier. The "circulator" function 7~ 1 represented by the block 20 serves to isolate the circuit 1 to be ma~ched from another circuit to be matched and connected downstream with respect to the point A in order ~o improve the standing-wave ratio at the point A. In the same manner as the matching circuit 10, the lmpedance transformers 21 to 23 have an impedance matching func~ion but, in contrast to the circuit 10, do not call or the use of resonators in order to perform this function by reason of the fact that, as will be indicated hereinafter, a circulator is provided at its accesses with impedances of the same type as those of the parallel resonant circuit~.
The impedance transformers 21 to 23 consist of quarter-wave transformers in the majority of instances. The impedance transformer 21 is connected to the point A, the impedance 1~ transformer 22 is connected to the first end of a resistor R, the second end of which is connected to ground. In regard to the impedance transformer 23, this latter is coupled to the circuit 1 to be matched via the matching circuit 10.
Fig. 3 shows how the circuit arrangement shown in Fig. 2 is modified in accordance with the invention.
The arrangement shown in Fig, 3 is distinguished from the arrangement of Fig. 2 by the fact that the impedance transformer 23 and the matching circuit 10 have been dis-pen~ed with and replaced, according to requirements, either by a direct connection or by a simple impedance transformer 73~
3 which is not provided with a parallel resonant element.
This alternativ~ is represented in the figure by the block 3 in dashed outline~ By eliminating the impedance trans-former 23 and the matching circuit 10 and therefore lts resonator, a circuit arrangement of this ~ype has a pass-band of greater wid~h than the arrangement shown in Fig. 2.
Moreover, by reason of the reduction in number of elements, the circuit of Fig. 3 is less subject to losses than the circuit of Fig. 2~
The reason why the arrangement shown in Fig. 3 is possible will be sho~n in the following description.
In the case of a ferrite circulator, it is known that the impedances of the accesses are comparable with those of parallel resonant circuits as can be vexified by means of measurements. Reference may be made in this connection to the article entitled "Operation of the ferrite junction circulator" which appeared in the January 1965 issue of IEEE transactions on microwave theory and techniques, pages 15 to 27.
Fig. 4 illustrates a parallel resonant circuit formed by a resistor R2 ln parallel with an inductance ~2 and a capacitor C2. This figure is the schematic repre-sentation of the impedance of an access of a ferrite cir~
culator whose impedance at the angular frequency ~ is :
Z2 = 1 1 (3) R2 ~ i (C2.~ ~ L2 ~-) 73~
The Q factor of the resonant cireuit according to Fig. 4 is :
Q2 = R2.C2.~o (4) where ~O is the resonant angular frequency of the S circulator and ls such that L2.C20~2 = 1.
When a circulator is employed in a cir~uit assembly as an isolation device for a microwave circuit, its resonance ~requency is chosen for reasons of bandwidth of operating frequencles so as to be equal to or at least as near as possible to the mid-band operating frequency and therefore the resonance frequency of the microwave circuit. It is for this reason that, in the form ~l.Cl.~o = 1 relating to the circuit to be matched of Fig. 1 and in the formula L2.C2.~o = 1, the resonant angular frequency is represented by ~ in both instances.
In order to ensure that the parallel resonant circuit in accordance with Fig. 4 can constitute a matching circuit for the series resonant circuit in accordance with Fig~ 1 or, in other words, in order to ensure that the diagram of Fig. 2 can be replaced by ~he diagram of Fig. 3 with a coupling between the circuits 20 and 1 without an lmpedance transformer, the impedance Z2 of the parallel resonant circuit must be equal to the conjugate of the impedance Zl. In other words, it must be ensured that 12 ~ j(C2.~ ~ ~ = Rl ~ j(Ll.~ ~ Cl ~) ~2~%73~
Cl and L2 being replaced in this eguation by their valuec derived from the formulae Ll.CL ~o = 1 and L2~C2.~o = 1 then it follows that by establishing equality between the real parts and the imaginary parts + Ll.C2.~ ( 2 o)2 = 1 (5) Ll.~ ~ _ ~2 (Rl.C2.~ ~ R2 ) ~ 2 ~ = ~ (6) when ~ = ~0, it follows from relation (5) that :
Rl = R2 when ~ is different from ~0, it follows from relation (6 that .
Rl.c2.~ = R2 which produces, by multiplying by ~
Rl.c2-~o = R2 This may be written, taking into account formulae (2) and (4), Ql = Q2 When the values of Rl and of Ql at the resonant angular frequency ~0 of A circuit to be match~d are known, it is always possible to construct a circulator in which the resonant angular frequency, the Q factor and ~he resonance impedance are respectively e~ual or at least close in value to l~o~ Ql and Rl. Thus it is possi~le to ~2~73~
achleve optim~n matchlng in a broad band between the circular and the microwave circuit.
It ~hould be noted that, if the resistance value of the circulator resistor R2 is distinctly different from S the value of the resistor Rl o.~ the circult to be matched, it is possible to carry out matching by means of an impedance transformer without any parallel resonant element and mounted in the s~me manner as the imp~dance transformer 3 of Fig~ 3. The assembly constituted by the impedance transformer 3 associated with the circuit 1 to be matched always has the same resonant angular frequency as the circuit 1 to be matched and its resistance is so determined as to be equal to R2, Moreover, its Q factor at the angular frequency ~0 is no longer equal to Q1 but is modified by ~he impedance transformer 3. ~he circulator must therefore have been chosen ~o as to ensure that its resonance quality factor Q2 ls as close as possible to the Q factor of the assembly consisting of circuit 1 and transformer 3.
One example of construction of a circulator which is intended for an assembly in accordance with Fig. 3 with direct coupling without the transformer 3 between the circuit 1 to be matched and the switching circuit 20 will .hereinafter be described with reference to Figs. 5 and 6.
The circuit to be matched made use of a gallium-arsenide field-effect transistor which operated within the fre~uency 3~. ~
range of 3.6 - 4.2 GHz and had the following character-istics :
- resonance frequency : FO ~ 3.9 GHz - ~uality factor : Ql = 3.15 - resonance impedance : Rl = 15 ohms.
The general aim of matching of this circuit was to obtain a field-effect transistor having a minim~n noise factor.
The completed circulator (as shown ln Figs. 5 and 6) has the following characteristics :
- resonance frequency : FO = 3.9 ~Hz - quality factor : Q2 - 2.12 - resonance impedance : R2 = 15 ohms.
It may be conceded ~hat the circulator shown :in Figs. 5 and 6 do~s not wholly satisfy the condition Q2 = Ql.
However, measuxements have demonstrated the fact that, within the range of operating frequencies (3.6 - 4.2 GHz), ~h~ difference between the optimum impedance which makes it possiblP to obtain the minimum noise factor and the ~0 impedance produced by the circulator remains of small value and the noise factor thus obtained is practically at a minimum.
Fig. 5 shows in dashed lines the periphery C of the assembly constltuted by the casing of the circulator and the casing of the circuit to be matched, sald casings being placed in juxtaposed relation. There are shown in ~%'73~
Fig. 5 only a component 4 locat~d at the center o~the circulator, two resonator connection plugs 31, 32 and the field-effect transistor 11 of the circuit 1 to be matchPd and shown in Fig. 3.
The component 4 constitutes the lnternal conducting strip in a structure of the three-plate wave~
guide type or in other words a structure formed by two parallel ground planes and by a strip placed between the two ground planes in parallel relation to these latter.
Said two ground planes are shown in Fig. 6 and designated by the reference numerals 61 and 62. The component 4 i5 constituted by a metal plate of silver-plated brass 1.2 mm in thickness and comprising a resonator disk 40 having a diameter of 14 n~l and pierced by a centering hole 44. Around said disk are arranged three branches 41, 42, 43 relatively spaced at angulax intervals of 120, The branches 41 and 42 are of distinctly greater length than the branch 43 and are soldered to the internal conductor of the coaxial connecting plugs 31, 32. Said plugs have a characteristic impedance equal to 50 ohms and permit connection to the point A and to the resistor R (shown in Fig. 3). The outer conductor is not shown in Fig. 5 but is connected to the circulator casing. ~he branch 43, which is shown only by way of indication for connecting purposes, is soldered to the end of the gate connection G of the field-effect transistor 11 of the circuit to be matched.
iL2~ ~73~
The length of the ga~e connectl~n of the ~ransis~or 11, or in other words the length of the connection between the transistor casing and the disk 40, determi~es the inductance L'l mentioned earlier in the description of Fig. 1. For the sake of simplification, and because it would not be conducive to easier understanding of the invention, the elements connected to the drain D of the transistor 11 axe not shown in the drawings. In regard to the source of the transistor 11, said source comprises two output connections Sl and S2, which are both soldered to the casing of the circuit to be matched~
A point worthy of note is the fact that, in the embodiment described, the gate of the transis~or 11 is biased by the circulator. In order to s~mplify the drawings, the resistor R as shown in Fig~ 3 is connected directly between the circulator and ground. In actual practice, however, the first end of said resistor is connected to the circulator (transformer 22 associated with the branch 42) and the second end is connected to a decoupling circuit. Said decoupling circuit behaves as a short-circuit at the operating frequencies of the circuit to be matched and as an infinite ~mpedance at the direct~
current bias voltage. Said bias voltage is applied to the second end of the resistor R. ~he decoupling circuit can be formed in the conventional manner by open quartex-wave lines which bring back a short-circuit and/or by a capacitor, In Fig. 3, consideration was glven to the impedance transformers 21 and 22 and ~he switching circuit 20 which con~tituted the circulator. In Fig. 4, ~he resonator disk 40 and the branches 41 and 42 correspond re~pectlvely to the switching circuit 20 and to the impedance transformers 21 and 22, Said lmpedance trans-formers are of the quarter-wave type. In other words, the length of the branches is substant1ally equal to one-quarter of the wavelength, within the circulator, at themean frequency of 3.9 GHz. In more precise terms, the blocks 20, 21 and 22 of Fig. 3 are to be identified with the association of the elements 40, 41, 42 and of the elements between which said blocks are inserted in the circulator and which will be described with reference to Fig~ 6.
Fig. 6 is a sectional view of the circulator, taken along the axis X-X of Fig. 5. This view shows two structures arranged symmetrically with respect to the strip 4 on each side of this latterO Starting from the strip, said structures comprise :
- a ferrite disk 51, 52 having a diameter which is sub~
stantially equal to the diameter of the resona~or disk 40 (shown in Fig. 5) and a silica component 53, 54 which covers practically the entire portion of the strip 4 which is located outside the disk 40 (shown in Fig. 5) ;
73~L
the compo~ents 51 to 54 have a thickness of 2.1 mm ; the ferrite disk 51, 52 is pierced with a central hole ;
- an aluminum plate 61, 62 constituting one of the afore-mentioned ground planes and pro~ided in ~he face remot~
5 from the strip ~ with a recess having the shape of a circular cup and located opposite to the ferrite disks 51, 52 ;
- within the cup-shaped recess : an air layer 71, 72, a mild steel washer 81, 82 having a thickness of 0.5 mm, and a permanent magnet 91, 92 having a thickness of 1.5 mm ; the magnetic circuit formed by the two magnets 91, 92 produces a field of 400 gauss ;
- a U-section member 609 the two opposite flanges of which cover respectively the two magnets ~1, 92 in order to close their field lines ; said U-section member is fabricated from a mild steel strip having a thickness of 1 mm and a width of 17 mm.
A cylindrical insula~ing rod 45 made of nylon (registered trademark) passes through the holes pierced in the strip 4 (hole 44) and through the ferrite disks 51, 52 in order to effect positioning of these components with respect to each other.
~ very thin silver foil (not shown in Fig. 6) is placed between the disk 51 and on the one hand the silica component 53 and on the o~her hand the plate 61 in order to ensure a good electrical contact between these ~lZ~7~
element~. Another foil (not shown) ~nsures a good contact between the disk 52 and on the one hand ~he silica component 54 and on the other hand the pla~e 62.
The circulator casing ls provided between the plates 61 and 62 and the U-section member 60 with a connector 31 which is fixed on the plates 61 and 62 by means of screws (not shown in the figure).
Sald ferxite circulator has been fabricated as a function of the characteristics to be obtained in order to achieve matching of the circuit which has been considered in the foregoing and is intended to be ma~ched. To this end, preference was initially given to a circulator of a current type having charactexistics which were fairly close to those contemplated. ThPn~ after successive tests, the circulator described with reference to Figs. 5 and 6 was finally adopted.
It should be noted that the invention is no~
limited to the example hereinbefore described. From this it follows in particular that, in the circuit arrangement of Fig. 3, it would be poss~ble to dispense with the impedance transformer 22, that is to say in practlce, to eliminate the branch 42 of the strip 4 (shown in Fig. 5~.
In such a case, it would only be necessary to give the resistor R the value of resistance existing at the corre-sponding output of the resonator in the resonant state.
Another noteworthy point is that the cixculator can be employed as a matching element for a circuit to be matched, not only at the input of the circuit as ln the example described but also at the output of the circuit.
Thus the same circulator can serve as a matching element for two circuits to be matched : the ou~put of a first circuit to be matched is coupled to one of the accesses of the circulator and the input of a second circuit to be matched is coupl0d to another access of the circula~or.
A MATCHING AN~ ISOLATING DEVICE
COMPRISING A FERRIT~ CIRCUhATOR
BACRGROUND OF THE INVENTION
The present invention relates to a matching and iæolating device comprising a ferrite circulator for coupling a circuit to be matched to a connecting point, the circuit to be matched being comparable from an impedance standpoint with a series xesonant circuit.
Broad-band matching devices for microwave circuits are based on th~ use of resonators which, in the event that the circuit to be matched is not comparable with a parallal resonant circuit, make it possible to provide an impedance corresponding to that of the circuit to be matched in order to obtain a wide band of operating frequencies. Furthermore, it is already known to make use of a circulator between the micro~ave circuit with its matching and access device under consideration with a view to providing isolation or to improving the standing-wave ratio (SW~). The connection between the circulator and the microwave circuit to be ma~ched ls effected in the con-ventional manner by means of a passage at a standardized characteristic impedance (50 ohms, for example). This entails the need for two ma~ching devices, namely one for ~he circulator and one for the circuit to be matched, and consequently for a reduction of the passband.
73iL
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to over-come these disadvantages which arise from the use of two matching devices.
This object is attained by producing the circuit-matching device by means of the ferrite circulator.
According to the invention ~here ~s provided a matching and isolating device for coupling a circuit to be matched to a connection point, the circuit to be~matched being comparable from an impedance standpoint with a series resonant circuit. The device comprises a matching ~ircuit of the parallel resonant circuit type which is coupled to the circuit to be matched and a ferrite cir-culator having a first access coupled to the connection point and a second access coupled to the circuit to be matched. In this device, the circulator comprises a switching circuit with accesses and said accesses have impedances which are comparable with those of parallel resonant circuits so tha~ the circulator itself constitutes the matching circuit.
In a related field, it should be noted that an isolator is known in which provision is made for a circu-lator. In this circulator, in order to ensure optimum matching of one of the three inputs of the circulator pro-per (corresponding to the switching function) with which a 121Z73iL
dissipative load is coupled, the coupling element chosen is a series oscillating circuit whose impedance added to that of the dissipative load is as clos~ as possible to the conjugate impedance of the circulator ; thls series oscillating circuit replace~ the type ~4 impedance trans-former which is usually employed for the matching operation and normally forms part of the circulator. This arrange-ment bears only a remote comparison with the invention which does not involve replacement of a typs A/4 impedance transformer (forming part of the cir~ulator) by a series oscillating circuit (added to the circulator) but dis-penses with the need for a ma~ching circuit of the parallel resonant circuit type usually employed for coupling a circuit to be matched and a circulator. The circuit to be matched is thus coupled directly to the cir-culator without using any element as a substitute for the matching circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features of the invent~on will be more apparent upon consideration of the followtng desaription and accompanying drawings, wherein :
- Figs. 1 and 4 show representative impedances of circuits ;
- Figs. 2 and 3 show circuit assemblies relating respectively to the prior art and to the invention ;
- Figs. S and 6 are views showing a ferrite ~2~Z~3~
circulator employed ln the circuit assembly of Fig. 3.
In ~he different figures, corresponding elements are designated by the same references.
DETAILEn DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description will be concerned with a circuit to be matched and more especially a microwave circuit such as an amplifier, fllter, mlxer, and so on.
There is shown diagrammatically in Fig. 1 the impedance of a circuit to be matched in the most~general . 10 case, that is, in the case in which said impedance is comparable with that of a series resonant circuit Rl-L-Cl.
If the mid-band operating frequency F0 of the circuit to be matched is different from its resonance frequency, an impedance is added in series with the circuit to be matched in order to make these two irequencies equal. In the case of Fig~ 1, this impedance is obtained by means of an inductance ~'1. It will be considered in the following description and in the appended claims that thls additional impedance forms part of the circuit to be matched and this latter will be considered as a series resonant circuit ~ormed by the elements Rl-Ll-Cl with L1 = ~ + L'l ; and the angular frequency ~0 corresponding to the mid-band operating frequency is such that : Ll.Cl.~o = 1.
The impedance, at the angular frequency w, of the circuit to ~e matched as shown in Fig. 1 is :
Zl = Rl ~ ~(Ll.~ ~ Cl ~) (1) os and its Q factor is :
Ll.~
Ql Rl (2, When a circuit to be matched of the type con-sidered in the foregoing has to be coupled tG a connection point via an isolation circult, it is a known practice to employ for this purpose a ferrite circulator in a circui~
arrangement which i5 shown diagrammatically in Fig. 2.
Flg. 2 shows a circuit 1 to be matched which is coupled to a connection point A by means of a matching circuit 10 followed by a circulator 20 to 23. The match-ing circuit 10 is constructed in the conventional manner by means of one or a number of parallel resonant circuits.
The elements of said circuit 10 are chosen so as to present a purely ohmic input impedance having a given value Zc ~hroughout the operating frequency band when its ou~put is connected to the input of the circuit to be matched.
Although consisting of a single Plement, the circulator is represented by four blocks in order to distinguish between its different functions : a block 20 de~ignated as a switching circult and relating to the "circulator"
function proper, and three blocks 21 to 23 designated as impedance ~ransform~rs and connected to each of the three accesses of the switching circuit 20 in order to restore the impedances of ~he three~circulator accesses to the value Zc mentioned earlier. The "circulator" function 7~ 1 represented by the block 20 serves to isolate the circuit 1 to be ma~ched from another circuit to be matched and connected downstream with respect to the point A in order ~o improve the standing-wave ratio at the point A. In the same manner as the matching circuit 10, the lmpedance transformers 21 to 23 have an impedance matching func~ion but, in contrast to the circuit 10, do not call or the use of resonators in order to perform this function by reason of the fact that, as will be indicated hereinafter, a circulator is provided at its accesses with impedances of the same type as those of the parallel resonant circuit~.
The impedance transformers 21 to 23 consist of quarter-wave transformers in the majority of instances. The impedance transformer 21 is connected to the point A, the impedance 1~ transformer 22 is connected to the first end of a resistor R, the second end of which is connected to ground. In regard to the impedance transformer 23, this latter is coupled to the circuit 1 to be matched via the matching circuit 10.
Fig. 3 shows how the circuit arrangement shown in Fig. 2 is modified in accordance with the invention.
The arrangement shown in Fig, 3 is distinguished from the arrangement of Fig. 2 by the fact that the impedance transformer 23 and the matching circuit 10 have been dis-pen~ed with and replaced, according to requirements, either by a direct connection or by a simple impedance transformer 73~
3 which is not provided with a parallel resonant element.
This alternativ~ is represented in the figure by the block 3 in dashed outline~ By eliminating the impedance trans-former 23 and the matching circuit 10 and therefore lts resonator, a circuit arrangement of this ~ype has a pass-band of greater wid~h than the arrangement shown in Fig. 2.
Moreover, by reason of the reduction in number of elements, the circuit of Fig. 3 is less subject to losses than the circuit of Fig. 2~
The reason why the arrangement shown in Fig. 3 is possible will be sho~n in the following description.
In the case of a ferrite circulator, it is known that the impedances of the accesses are comparable with those of parallel resonant circuits as can be vexified by means of measurements. Reference may be made in this connection to the article entitled "Operation of the ferrite junction circulator" which appeared in the January 1965 issue of IEEE transactions on microwave theory and techniques, pages 15 to 27.
Fig. 4 illustrates a parallel resonant circuit formed by a resistor R2 ln parallel with an inductance ~2 and a capacitor C2. This figure is the schematic repre-sentation of the impedance of an access of a ferrite cir~
culator whose impedance at the angular frequency ~ is :
Z2 = 1 1 (3) R2 ~ i (C2.~ ~ L2 ~-) 73~
The Q factor of the resonant cireuit according to Fig. 4 is :
Q2 = R2.C2.~o (4) where ~O is the resonant angular frequency of the S circulator and ls such that L2.C20~2 = 1.
When a circulator is employed in a cir~uit assembly as an isolation device for a microwave circuit, its resonance ~requency is chosen for reasons of bandwidth of operating frequencles so as to be equal to or at least as near as possible to the mid-band operating frequency and therefore the resonance frequency of the microwave circuit. It is for this reason that, in the form ~l.Cl.~o = 1 relating to the circuit to be matched of Fig. 1 and in the formula L2.C2.~o = 1, the resonant angular frequency is represented by ~ in both instances.
In order to ensure that the parallel resonant circuit in accordance with Fig. 4 can constitute a matching circuit for the series resonant circuit in accordance with Fig~ 1 or, in other words, in order to ensure that the diagram of Fig. 2 can be replaced by ~he diagram of Fig. 3 with a coupling between the circuits 20 and 1 without an lmpedance transformer, the impedance Z2 of the parallel resonant circuit must be equal to the conjugate of the impedance Zl. In other words, it must be ensured that 12 ~ j(C2.~ ~ ~ = Rl ~ j(Ll.~ ~ Cl ~) ~2~%73~
Cl and L2 being replaced in this eguation by their valuec derived from the formulae Ll.CL ~o = 1 and L2~C2.~o = 1 then it follows that by establishing equality between the real parts and the imaginary parts + Ll.C2.~ ( 2 o)2 = 1 (5) Ll.~ ~ _ ~2 (Rl.C2.~ ~ R2 ) ~ 2 ~ = ~ (6) when ~ = ~0, it follows from relation (5) that :
Rl = R2 when ~ is different from ~0, it follows from relation (6 that .
Rl.c2.~ = R2 which produces, by multiplying by ~
Rl.c2-~o = R2 This may be written, taking into account formulae (2) and (4), Ql = Q2 When the values of Rl and of Ql at the resonant angular frequency ~0 of A circuit to be match~d are known, it is always possible to construct a circulator in which the resonant angular frequency, the Q factor and ~he resonance impedance are respectively e~ual or at least close in value to l~o~ Ql and Rl. Thus it is possi~le to ~2~73~
achleve optim~n matchlng in a broad band between the circular and the microwave circuit.
It ~hould be noted that, if the resistance value of the circulator resistor R2 is distinctly different from S the value of the resistor Rl o.~ the circult to be matched, it is possible to carry out matching by means of an impedance transformer without any parallel resonant element and mounted in the s~me manner as the imp~dance transformer 3 of Fig~ 3. The assembly constituted by the impedance transformer 3 associated with the circuit 1 to be matched always has the same resonant angular frequency as the circuit 1 to be matched and its resistance is so determined as to be equal to R2, Moreover, its Q factor at the angular frequency ~0 is no longer equal to Q1 but is modified by ~he impedance transformer 3. ~he circulator must therefore have been chosen ~o as to ensure that its resonance quality factor Q2 ls as close as possible to the Q factor of the assembly consisting of circuit 1 and transformer 3.
One example of construction of a circulator which is intended for an assembly in accordance with Fig. 3 with direct coupling without the transformer 3 between the circuit 1 to be matched and the switching circuit 20 will .hereinafter be described with reference to Figs. 5 and 6.
The circuit to be matched made use of a gallium-arsenide field-effect transistor which operated within the fre~uency 3~. ~
range of 3.6 - 4.2 GHz and had the following character-istics :
- resonance frequency : FO ~ 3.9 GHz - ~uality factor : Ql = 3.15 - resonance impedance : Rl = 15 ohms.
The general aim of matching of this circuit was to obtain a field-effect transistor having a minim~n noise factor.
The completed circulator (as shown ln Figs. 5 and 6) has the following characteristics :
- resonance frequency : FO = 3.9 ~Hz - quality factor : Q2 - 2.12 - resonance impedance : R2 = 15 ohms.
It may be conceded ~hat the circulator shown :in Figs. 5 and 6 do~s not wholly satisfy the condition Q2 = Ql.
However, measuxements have demonstrated the fact that, within the range of operating frequencies (3.6 - 4.2 GHz), ~h~ difference between the optimum impedance which makes it possiblP to obtain the minimum noise factor and the ~0 impedance produced by the circulator remains of small value and the noise factor thus obtained is practically at a minimum.
Fig. 5 shows in dashed lines the periphery C of the assembly constltuted by the casing of the circulator and the casing of the circuit to be matched, sald casings being placed in juxtaposed relation. There are shown in ~%'73~
Fig. 5 only a component 4 locat~d at the center o~the circulator, two resonator connection plugs 31, 32 and the field-effect transistor 11 of the circuit 1 to be matchPd and shown in Fig. 3.
The component 4 constitutes the lnternal conducting strip in a structure of the three-plate wave~
guide type or in other words a structure formed by two parallel ground planes and by a strip placed between the two ground planes in parallel relation to these latter.
Said two ground planes are shown in Fig. 6 and designated by the reference numerals 61 and 62. The component 4 i5 constituted by a metal plate of silver-plated brass 1.2 mm in thickness and comprising a resonator disk 40 having a diameter of 14 n~l and pierced by a centering hole 44. Around said disk are arranged three branches 41, 42, 43 relatively spaced at angulax intervals of 120, The branches 41 and 42 are of distinctly greater length than the branch 43 and are soldered to the internal conductor of the coaxial connecting plugs 31, 32. Said plugs have a characteristic impedance equal to 50 ohms and permit connection to the point A and to the resistor R (shown in Fig. 3). The outer conductor is not shown in Fig. 5 but is connected to the circulator casing. ~he branch 43, which is shown only by way of indication for connecting purposes, is soldered to the end of the gate connection G of the field-effect transistor 11 of the circuit to be matched.
iL2~ ~73~
The length of the ga~e connectl~n of the ~ransis~or 11, or in other words the length of the connection between the transistor casing and the disk 40, determi~es the inductance L'l mentioned earlier in the description of Fig. 1. For the sake of simplification, and because it would not be conducive to easier understanding of the invention, the elements connected to the drain D of the transistor 11 axe not shown in the drawings. In regard to the source of the transistor 11, said source comprises two output connections Sl and S2, which are both soldered to the casing of the circuit to be matched~
A point worthy of note is the fact that, in the embodiment described, the gate of the transis~or 11 is biased by the circulator. In order to s~mplify the drawings, the resistor R as shown in Fig~ 3 is connected directly between the circulator and ground. In actual practice, however, the first end of said resistor is connected to the circulator (transformer 22 associated with the branch 42) and the second end is connected to a decoupling circuit. Said decoupling circuit behaves as a short-circuit at the operating frequencies of the circuit to be matched and as an infinite ~mpedance at the direct~
current bias voltage. Said bias voltage is applied to the second end of the resistor R. ~he decoupling circuit can be formed in the conventional manner by open quartex-wave lines which bring back a short-circuit and/or by a capacitor, In Fig. 3, consideration was glven to the impedance transformers 21 and 22 and ~he switching circuit 20 which con~tituted the circulator. In Fig. 4, ~he resonator disk 40 and the branches 41 and 42 correspond re~pectlvely to the switching circuit 20 and to the impedance transformers 21 and 22, Said lmpedance trans-formers are of the quarter-wave type. In other words, the length of the branches is substant1ally equal to one-quarter of the wavelength, within the circulator, at themean frequency of 3.9 GHz. In more precise terms, the blocks 20, 21 and 22 of Fig. 3 are to be identified with the association of the elements 40, 41, 42 and of the elements between which said blocks are inserted in the circulator and which will be described with reference to Fig~ 6.
Fig. 6 is a sectional view of the circulator, taken along the axis X-X of Fig. 5. This view shows two structures arranged symmetrically with respect to the strip 4 on each side of this latterO Starting from the strip, said structures comprise :
- a ferrite disk 51, 52 having a diameter which is sub~
stantially equal to the diameter of the resona~or disk 40 (shown in Fig. 5) and a silica component 53, 54 which covers practically the entire portion of the strip 4 which is located outside the disk 40 (shown in Fig. 5) ;
73~L
the compo~ents 51 to 54 have a thickness of 2.1 mm ; the ferrite disk 51, 52 is pierced with a central hole ;
- an aluminum plate 61, 62 constituting one of the afore-mentioned ground planes and pro~ided in ~he face remot~
5 from the strip ~ with a recess having the shape of a circular cup and located opposite to the ferrite disks 51, 52 ;
- within the cup-shaped recess : an air layer 71, 72, a mild steel washer 81, 82 having a thickness of 0.5 mm, and a permanent magnet 91, 92 having a thickness of 1.5 mm ; the magnetic circuit formed by the two magnets 91, 92 produces a field of 400 gauss ;
- a U-section member 609 the two opposite flanges of which cover respectively the two magnets ~1, 92 in order to close their field lines ; said U-section member is fabricated from a mild steel strip having a thickness of 1 mm and a width of 17 mm.
A cylindrical insula~ing rod 45 made of nylon (registered trademark) passes through the holes pierced in the strip 4 (hole 44) and through the ferrite disks 51, 52 in order to effect positioning of these components with respect to each other.
~ very thin silver foil (not shown in Fig. 6) is placed between the disk 51 and on the one hand the silica component 53 and on the o~her hand the plate 61 in order to ensure a good electrical contact between these ~lZ~7~
element~. Another foil (not shown) ~nsures a good contact between the disk 52 and on the one hand ~he silica component 54 and on the other hand the pla~e 62.
The circulator casing ls provided between the plates 61 and 62 and the U-section member 60 with a connector 31 which is fixed on the plates 61 and 62 by means of screws (not shown in the figure).
Sald ferxite circulator has been fabricated as a function of the characteristics to be obtained in order to achieve matching of the circuit which has been considered in the foregoing and is intended to be ma~ched. To this end, preference was initially given to a circulator of a current type having charactexistics which were fairly close to those contemplated. ThPn~ after successive tests, the circulator described with reference to Figs. 5 and 6 was finally adopted.
It should be noted that the invention is no~
limited to the example hereinbefore described. From this it follows in particular that, in the circuit arrangement of Fig. 3, it would be poss~ble to dispense with the impedance transformer 22, that is to say in practlce, to eliminate the branch 42 of the strip 4 (shown in Fig. 5~.
In such a case, it would only be necessary to give the resistor R the value of resistance existing at the corre-sponding output of the resonator in the resonant state.
Another noteworthy point is that the cixculator can be employed as a matching element for a circuit to be matched, not only at the input of the circuit as ln the example described but also at the output of the circuit.
Thus the same circulator can serve as a matching element for two circuits to be matched : the ou~put of a first circuit to be matched is coupled to one of the accesses of the circulator and the input of a second circuit to be matched is coupl0d to another access of the circula~or.
Claims (4)
1. A matching and isolating device for coupling a microwave circuit to be matched to a connection point, said device being constructed as a three-port strip-line ferrite circulator comprising:
- a central disk;
- a first quarter-wavelength arm connected to said connection point;
- a dissipative grounded termination network;
- a second quarter-wavelength arm connected to said dissipative grounded termination network; and a third insignificant stub arm connected to said microwave circuit to be matched for effectively connecting said microwave circuit to be matched directly to said central disk.
- a central disk;
- a first quarter-wavelength arm connected to said connection point;
- a dissipative grounded termination network;
- a second quarter-wavelength arm connected to said dissipative grounded termination network; and a third insignificant stub arm connected to said microwave circuit to be matched for effectively connecting said microwave circuit to be matched directly to said central disk.
2. A matching and isolating device for coupling a microwave circuit to be matched to a connection point, said device being construted as a three port strip-line ferrite circulator having:
- a central disk;
- a first arm constructed as an impedance transformer and connected to said connection point;
- a dissipative grounded termination network;
- a second arm constructed as an impedance transformer and connected to said dissipative grounded termination network; and - a third insignificant stub arm directly connecting to said microwave circuit to be matched to said central disk.
- a central disk;
- a first arm constructed as an impedance transformer and connected to said connection point;
- a dissipative grounded termination network;
- a second arm constructed as an impedance transformer and connected to said dissipative grounded termination network; and - a third insignificant stub arm directly connecting to said microwave circuit to be matched to said central disk.
3. A matching and isolating device according to claim 1 further comprising a microwave circuit to be matched which uses a transistor operating substantially within the frequency range of 3.6 - 4.2 GHz.
4. A matching and isolating device according to claim 2 further comprising a microwave circuit to be matched which uses a transistor operating substantially within the frequency range of 3.6 - 4.2 GHz.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8213105 | 1982-07-27 | ||
| FR8213105A FR2531272B1 (en) | 1982-07-27 | 1982-07-27 | ADAPTATION AND ISOLATION DEVICE COMPRISING A FERRITE CIRCULATOR |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1212731A true CA1212731A (en) | 1986-10-14 |
Family
ID=9276361
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000433144A Expired CA1212731A (en) | 1982-07-27 | 1983-07-25 | Matching and isolating device comprising a ferrite circulator |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0100274B1 (en) |
| JP (1) | JPS5941901A (en) |
| CA (1) | CA1212731A (en) |
| DE (1) | DE3379494D1 (en) |
| FR (1) | FR2531272B1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116259944B (en) * | 2023-02-22 | 2024-01-30 | 东南大学 | Circulator based on principle of space-time symmetry |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3651430A (en) * | 1964-10-06 | 1972-03-21 | Fujitsu Ltd | Strip-line circulator having movable compensating stub strip overlying central strip-line conductors |
| DE2253175A1 (en) * | 1972-10-30 | 1974-05-09 | Siemens Ag | CIRCULATOR WITH CONNECTING ARMS TRAINED IN MIC TECHNOLOGY |
| US3935548A (en) * | 1974-06-04 | 1976-01-27 | The Washington University | Wide-band microwave circulator |
| DE3034034C2 (en) * | 1980-09-10 | 1985-07-18 | Siemens AG, 1000 Berlin und 8000 München | Y-circulator in stripline construction |
-
1982
- 1982-07-27 FR FR8213105A patent/FR2531272B1/en not_active Expired
-
1983
- 1983-07-19 EP EP19830401483 patent/EP0100274B1/en not_active Expired
- 1983-07-19 DE DE8383401483T patent/DE3379494D1/en not_active Expired
- 1983-07-25 CA CA000433144A patent/CA1212731A/en not_active Expired
- 1983-07-27 JP JP13602283A patent/JPS5941901A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0100274B1 (en) | 1989-03-22 |
| DE3379494D1 (en) | 1989-04-27 |
| EP0100274A1 (en) | 1984-02-08 |
| FR2531272B1 (en) | 1985-09-13 |
| JPS5941901A (en) | 1984-03-08 |
| FR2531272A1 (en) | 1984-02-03 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |