US 3860893 A
An active circuit one octave circulator made of three identical arms interconnected at the three-ports, each arm consisting of a gyrator comprising voltage and current single stage transistorized amplifiers, the impedance at each port being matched with the standard impedance of microwave circuits, and capacitive interconnecting means are provided at each end of the arms and between the two amplifiers. The circulators are designed as microwave integrated circuits.
Description (OCR text may contain errors)
United States Patent [191 Ropars et al.
[ Jan. 14, 1975  Filed: Jan. 2, 1974  Appl. No.: 429,741
 Foreign Application Priority Data Jan. 2, 1973 France 73.0013
 U.S. Cl. 333/80 R, 333/1.l, 333/80 T  Int. Cl. H03h 7/44  Field of Search 333/l.1, 80 R, 80 T  References Cited UNITED STATES PATENTS 3,513.40] 5/1970 Tokunaga 333/l.l X
3,582,803 6/1971 Greenaway et al 333/l.l X 3,700,832 10/1972 Beurrier 333/l.l UX 3,716,729 2/l973 Rollett 333/l.l X
Primary ExaminerPaul L. Gensler Attorney, Agent, or Firm-Kemon, Palmer & Estabrook [57} ABSTRACT An active circuit one octave circulator made of three identical arms interconnected at the three-ports, each arm consisting of a gyrator comprising voltage and current single stage transistorized amplifiers, the impedance at each port being matched with the standard impedance of microwave circuits, and capacitive interconnecting means are provided at each end of the arms and between the two amplifiers. The circulators are designed as microwave integrated circuits.
4 Claims, 12 Drawing Figures PATENTEUJANMISYS SHEET 10F 5 fig.2
PATENTEDJAN 1 4|975 SHEET 3 OF 5 as M fig. 7a
= fig. 7b
WIDE BAND ACTIVE CIRCUIT THREE-PORT CIRCULATOR FOR ULTRA-HIGH FREQUENCIES AND MICROWAVES BACKGROUND OF THE INVENTION This invention relates to a wideband circulator for use in the frequency range from 100 megahertz to several gigahertz. The word circulator often relates to an apparatus for microwave operations. It is here used in the following meaning. In an n port circulator, with the said ports connected to their matched impedance and numbered successively from 1 to n, the application of a signal to any port ranked k results in a response only at the port (k 1), when k is lower than n, and at the port 1 when k n.
FIG. 1 illustrates a three-port circulator in which, by way of example, the forward direction of propagation 1 2 3 is counter-clockwise. Circulators are generally based on the microwave properties of ferrimagnetic materials. The present invention relates to a circulator which utilises active four-terminal networks which are better adapted to operation in the lower part of the microwave range, i.e., between 0.1 GHZ and several GI-Iz. In an article published with the Applicants consent in No. 1 of the magazine Cables et Transmission, 1957, pages 66 to 73, under the title Gyrateurs et systmesja. sens unique, Maria Prudhon gives the general relation between the impedances of a nonactive and non-dissipative fourterminal network, and then shows that in the particular case of a non-active and non-dissipative linear four-terminal network, called a gyrator, this relation becomes Z =-Z S, S being a real impedance. The gyrator is described as ideal when the input and output circuits impedances are zero and the equations of the voltages as a function of the currents are reduced to U -SI and U: S1,. The author thereafter shows that a four-terminal network comprising only ideal gyrators and passive elements can have different attenuations in the two transmission directions provided that the elements other than the gyrators are not all pure reactances, i.e., some of them have a resistive impedance.
PRIOR ART The Applicants filed in 1958, under Pat. No. 1,196,139, a French patent application entitled Appareil electrique non reciproque," in which there is described a fourterminal network which can be used as an isolator in the frequency band from 2.5 to 5 megahertz, the said apparatus having an isolation higher than 40 decibels and an insertion loss between 9 and l5 decibels, depending upon the frequency. Thereafter, the use of active circuits as gyrators has been described several times in the literature, as well as the interconnection of a number of gyrators to build up a circulator. D. Rombold describes, in the March 1971 issue of the Nachrichtenteehnische Zeitschrift pages 121 to 176, a circulator having six transistors and three Zener diodes, which has, however, the following limitations:
the highest frequency of the bandwidth remains limited to 30 MHz;
the maximum input power at the ports tolerated without reduction of bandwidth is in the tenth of milliwatt range;
stray oscillations tend to build up in the circuit owing to the high gain of the voltage amplifiers and makes it impossible to operate the device in microwave the band;
two stabilised supply sources are necessary;
the balancing for obtaining the best performances and a zero unidirectional voltage at the ports at zero input signal is critical.
BRIEF DISCLOSURE OF THE INVENTION The object of the present invention is to provide a circulator which can be used above MHz and which is capable of transmitting a power of the order of a milliwatt with a very low insertion loss and an isolation of at least 20 decibels within a one-octave band width.
The three-port circulator is obtained by interconnecting three gyrators made of identical active circuits, each of which consists of transistorized voltage and current amplifiers, said gyrators being designed as microwave integrated circuits on a single substrate, in which each comprises an input connecting a capacitor, matched with the impedance of one of the ports of the circulator, capacitive means connecting said voltage and said current amplifiers and capacitive connecting means between the input of said voltage amplifier and the output of the current amplifier of the preceding gyrator.
The advantages of the circulators according to the invention are as follows:
Since their dimensions are smaller than those of ferrite circulators operating in the same frequency band, their use with microwave integrated circuit is easier and provides reduction in the bulkiness of the design. For example, a circulator having a bandwidth from 0.55 to l GI-Iz can be designed with dimensions, in mm, of 35 X 35 X 14 or 28 X 39 X 14. If miniature coaxial connectors are used, the aforesaid dimensions are re duced to 35 X 35 X 6 millimeters and the circulator weighs a few grammes. A ferrite circulator marketed by the Assignee under the reference number R 2947 B, having the same bandwidth, and comparable isolation and insertion loss values, weighs 1.3 Kg and occupies the volume of a cylinder of a diameter of millimeters and a height of 40 millimeters, which makes it impossible to introduce it in an integrated microwave design.
With equal overall dimensions, the bandwidth of active-circuit circulators is very much higher than that of ferrite circulators. As an example, reference is made to types F 58100 A and F 58101 A circulators marketed by the Assignee. The overall dimensions are those of a cylinder of a diameter of 50 millimeters and a height of 20 millimeters. The first covers the bandwidth between 70 and 360 MHZ and the second the bandwidth between 200 and 500 MHz. In order to scan each of these two bands with ferrite circulators, it is necessary to use four different devices, each having a volume equivalent to that of the unique active-circuit circulator.
The circulator according to the invention requires a single supply, of which one output is earthed, and consequently there is no problem of balancing the voltages.
The circulator according to the invention may be operated in the very high-frequency and microwave ranges. As higher cut-off frequency transistors become commercially available, it will be possible to introduce them into the circulator according to the invention without modifying the circuit design and the maximum operating frequency of the circulator will be raised accordingly.
DETAILED DESCRIPTION OF THE INVENTION Further features and advantages of the invention will become apparent in the course of the description illustrated by FIGS. 1 to 10, which are given purely by way of illustration and have no limiting character, and in which:
FIG. 1 shows a three-part circulator,
FIG. 2 is the block diagram of the circulator according to the invention,
FIG. 3 is the electric circuit diagram of one of the gyrator arms of the circulator,
FIG. 4 illustrates, the design of the circulator,
FIG. 5 illustrates the input standing wave ratio of a circulator of a first type, as seen from the outside,
FIG. 6 illustrates a variant of the matching circuit of the ports of the circulator,
FIG. 7a illustrates the insertion loss of a circulator of the first type and FIG. 7b that of a circulator of the second type,
FIG. 8a illustrates the isolation of a circulator of the first type and FIG. 8b that of a circulator of the second type,
FIG. 9 illustrates the figure of merit of a circulator of the first type, and
FIG. 10 illustrates an example of the variation of the insertion loss and of the isolation of a circulator as a function of the amplitude of the input signal.
In FIG. 2, in which the ports of the circulator are denoted by l, 2 and 3, voltage amplifiers 30 are connected to current amplifiers 31 by capacitors 32; capacitors 33 connect the output of the amplifiers 31 to the following amplifier 30. The ports of the circulator are connected to the input of the voltage amplifiers by means of capacitors 34. The supply of the amplifiers is not shown.
In FIG. 3, which partially shows the electric circuit diagram of the circulator, the interrupted-line contour 4 surrounds one of the three identical gyrators. Each of them comprises two transistors, i.e., the transistor 5 connected as a voltage amplifier corresponding to the reference 30 in FIG. 2, and the transistor 6 connected as a current amplifier corresponding to the reference 31 in FIG. 2. The transistor 5 is connected through a capacitor 7 to the port which precedes it, and which is denoted by way of example by the numeral 2 in FIG. 3, and through a capacitor 8 to the current amplifier which precedes it. Resistors 9 and 10 form a bridge between earth and the general supply voltage available at the end of a resistor 21 connected to a capacitor 22. The base of the transistor 5 is connected to the intermediate point of this bridge. In addition, it is connected by means of a capacitor 7 in series with a low-value inductor 14 to the port 2 and by means of a resistor 12 adjusted to an optimum value in the neighbourhood of 50 ohms in accordance with the operating frequency band in series with a capacitor 8 to the emitter of the output transistor of the preceding gyrator. A 50-ohm resistor 13 connects the emitter of the said transistor to the emitter of the transistor 5. A SO-ohm resistor denoted by ll connects the emitter of the transistor 5 to earth. The capacitors 7 and 8 have the same capacitance value, for example 4,700 picofarads.
A capacitor 15 connects buffer resistor 16 of the transistor 5 to the base of the transistor 6. The base of the latter transistor is in addition connected to the resistors 17 and 18. A resistor 19 of low value is connected between the collector of the transistor 6 and that end of the resistor 21 which is connected to the decoupling capacitor 22. A high frequency capacitor 23 of low value is connected in parallel with the capacitor 22. A resistor 20 of a value of ohms provided between the emitter of the transistor 6 and earth constitutes the output of the current amplifier.
FIG. 4 illustrates the design of a circulator according to the invention according to microwave integrated circuit technology. The standardized 50-ohm microwave outputs 41, 42, 43 serving as ports are fixed to the casing 45. The amplifiers 30 of FIG. 2 are formed by the transistors 40, while the current amplifiers 3l consist of the transistors 44. Transistors 35 821E marketed by the company Hewlett-Packard, transistors MS 175 marketed by Texas Instruments, transistors BS-Tl4 manufactured and marketed by the Assignee have been successfully used in such design. The main technical data for this transistor, are as follows: maximum operating frequency 6 to 7 GHz, cut-off frequency 4.5 GHz, noise factor at l GHz 2 dB, maximum power 100 milliwatts. The supply means for the circulator, which is separated from the closed metal casing 45, is connected by a coaxial line 46 having its sheathing connected to the earth of the casing.
The circulator operates as follows: the transistor 5 of FIG. 3 is located on the diagonal of a Wheatstone bridge consisting of the resistors 11, 12, 13 and the purely ohmic impedance of the load as seen through the port 2, which is balanced if the load is appropriate, because the capacitances 7 and 8 balance one another. Any signal coming from the resistor 20 situated on one of the diagonals of the bridge gives a zero resultant in the other diagonal, in which the transistor 5 is situated. The signal coming from the port 1 therefore cannot be transmitted to the port 3. On the other hand, in the arm at which the port 2 is connected, a signal appears which is transmitted through the latter to the output owing to the fact that its coefficient of reflection in this direction is zero. It is necessary for this condition to be satisfied throughout the operating frequency band. This involves forming the ports by means of coaxial standard 50-ohm outputs to which are connected coaxial connectors and coaxial cables of the same standard. As seen from the outside through each port, the circulator is also matched. This result is obtained in a satisfactory bandwidth by means of an inductor made of two turns of wire having a diameter of 1.6 mm, coiled on a diameter of 20 mm, which are denoted by 14 in FIG. 3. However, when the frequency band of the circulator reaches the microwave range, the bias of each transistor 5 is experimentally adjusted in such manner that its cut-off frequency is maximum. The matching of each port of the circulator in a large bandwidth is then obtained by means of a more elaborate network of impedances.
FIG. 5 illustrates the standing wave ratio of a first type of circulator as seen from the outside through any one of its three ports. This figure shows that the frequency band in which this type of circulator can be operated extends from to 500 megahertz. As an illustration of what has been stated in the foregoing, FIG. 6 shows in the interrupted-line square a circuit for matching the ports of a second type of circulator designed with transistors BST 14 in the frequency band from 300 to 1,000 MHZ. This circuit comprises a series inductor 62 whose characteristics are substantially the same as those of the inductance 14, a capacitor 63 (12 picofarads, for example), in series with a resistor 64, (for example of 220 ohms). The latter two elements are connected between earth and the common point of the This bandwidth can be modified by changing the operating frequency of the Wheatstone bridge at the input of each gyrator. This is obtained in practice by slightly changing the bias of the transistors 5. By way of example, the following results are obtained with the same circulator:
inductance 62 and the capacitor 7.
FIG. 7a illustrates the insertion loss, in decibels, of a circulator of the first type with respect to frequency. As this curve shows, at frequencies below 350 MHZ the circulator amplifies any wave entering through any one of its ports and leaving by the following one in the direct circulating direction of the circulator, and at frequencies above 350 MHZ it attenuates a wave propagating in the same circulating direction.
FIG. 7b illustrates the insertion loss of a circulator of the second type.
FIG. 8a illustrates the isolation in decibels of a circulator of the first type.
FIG. Sbillustrates the isolation of a circulator of the second type.
FIG. 9, which is derived from FIGS. 7a and 8a, is a curve illustrating the figure of merit of a circulator of the first type as a function of frequency; it shows the ratio of the power of the forward wave to that of the backward wave in decibels.
In PK). 10, the curve denoted by 101 shows the insertion loss and the curve denoted by I02 shows the isolation of a circulator of the first type. measured at 200 MHZ, as a function of the amplitude of the voltage of the input ultra-high-frequency signal.
Measurements of the bandwidth of the circulator of the first type as a function of the input power have given the following results with an insertion loss of 1 dB and an isolation of 16 dB:
with an input power of0.5 mW the band spans I50 500 MHz do lmW do 200 500 MHz do 2 mW do 220 350 MHz do 5 mW do Noise measurements were made with rdriffeL nt designs of the circulator. As a typical result in a circulator, with transistors 35821 E the value of the noise factor is 8.5 dB at 60 MHZ and II dB at 250 MHZ.
I. A wide band active circuit circulator made of three identical gyrators serially interconnected comprising each a current amplifier and a voltage amplifier serially connected and three ports respectively at the interconnections between two gyrators which comprises first capacitive coupling means between each port and the input of the connected gyrator, second capacitive coupling means between each port and the output of the connected gyrator, third capacitive coupling means be tween said current and voltage amplifiers of the same gyrator, and a single supply means for said amplifiers one output of which is earthed.
2. A wide band active circuit circulator according to claim 1 in which said first and second capacitive coupling means contain capacitors of the same value.
3. A wide band active circuit circulator according to claim 1 in which said first capacitive coupling means is serially connected with an impedance matching section.
4. A wide band active circuit circulator according to claim 3 in which said impedance matching section consists of a series capacitorinductor circuit.
several MHz around 220 MHz.