US 3745487 A
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[ July 10, 1973  MICROWAVE PHASE-SHIFT DEVICES 0F 3,423,699 V1969 Hines 333m R THE TYPE 2,429,652 I0/l947 Termun 333/32 X  Inventors: Roland Milard; Charles Hubert, OTHER PUBLICATIONS both of Pans eme) France Van Valkenburg, Network Analysis, PrenticeHall,  Assignee: Thomson-CS1", Paris, France N.J., 1955, Title Page and Page 3144 relied on.
 Filed: Oct. 18, 1971 Primary Exammer-Paul L. Gensler PP NOJ 190,133 Att0rneyEdwin E. Greigg  Foreign Application Priority Data 57 ABSTRACT Oct. 23, I970 France 7038330 A O 7T microwave phase shift devicfi for operation in 52 US. Cl. 333/31 R, 333/33, 333/73 c, a frfiquency band 333/73 3 The device, connected to one end of a two-wire 51 Int. Cl. H01p l/l8 microwave Propagation line, comprises a filter m  Field of Search 333/29 R, 31 R, 70 s, followed y a semimnducwr diode The filter is a 333/73 C, 73 S, 32, 33 series m-derived half-section low-pass filter derived from the half-section low-pass filter circuit equivalent 5 References Cited to the diode end its output connections, the diode being UNITED STATES PATENTS 2,956,160 10/1960 Sharpless 333/32 X 4 Claims, 4 Drawing Figures i 1 a ul/lill 1 I I 7 l I J. I 5 1 l 6/ I l l I 7 Ill I v/////////// l i MICROWAVE PHASE-SHIFT DEVICES OF THE O-rr TYPE The present invention relates to improvements in microwave phase-shift devices of the kind commonly known as O 1r phase-shift devices. These devices or reflecting phase-shifters operate at reflection and are designed to produce a phase-shift angle of 11' in a microwave upon application of an electric control signal thereto. The invention relates to such phase-shift devices which are designed as solid-state devices of the microcircuit type, and suitable for operation within a very wide frequency range.
These phase-shift devices are currently manufactured on a microstrip structure, or, in the form of a coaxial-output sealed capsule, the latter being a more widely used form. The term microstrip defines a stripline network, made up of a dielectric substrate supporting respectively on two opposites faces, a strip conductor and a ground plane.
The principle of operation of the O 'rr phase-shift device is based upon a phase-shift angle of rr of a reflected microwave in the propagation line, this being produced by inverting the state and consequently the impedance of a semiconductor arranged at an end of the propagation line. The microwave is transmitted to the phase-shift device and then recovered after reflection by an associated microwave device such as a circulator, a 3 dB coupler, ahybrid junction etc. inserted in the microwave transmission line. The semiconductor is generally constituted by a diode which may present either of two states, depending upon whether it is reverse-biased (blocked) or forwardbiased (conductive). The control of the state is effected by an auxiliary control circuit generating a corresponding bias signal. The forward-biased diode is equivalent to a short circuit and the reverse-biased to a capacitive reactancesThe output connections of the diode are designed to produce a small inductive reactance the value of which being predetermined as a function, in particular, of the reverse capacitance of the diode. Theperformance, from the point of view of useful bandwidth, is determined in practice by that of a half (or L) section low-pass filter which is electrically equivalent to the reverse-biased diode and its output connections.
A known improvement is achieved by connecting the semiconductor to i the microwave propagation line through another half-section low-pass filter. The circuit thus constituted does not enable a peak value frequency better than 0.6 F F being the cut-off frequency of the resultant low-pass filter, with an accuracy at the most equal to 4 percent,
An object of the present invention is to produce a O 7r phase-shift device which will operate in a wider frequency range with a better accuracy. By way of indication, the microwave range can extend to a peak value of 0.9 F, with an accuracy better than 2 percent compared with the optimum performance achieved in known circuits and considering the same cut-off frequency.
According to the present invention there is provided a microwave phase-shift device of the O- 1r type, comprising a semiconductor diode connected to one end of a two-conductor microwave propagation line through a series m-derived half-section low-pass filter which is derived from the half-section low-pass filter defined by the inductive reactance of the diode output connections and by the reverse capacitance of the diode.
The present invention will be described further by way of example, with reference to various embodiments, as illustrated to the accompanying drawings in which FIG. 1 is an equivalent electric diagram of a relevant known phase-shift device;
FIG. 2 is an equivalent electric diagram of a phase shift device in accordance with the invention;
FIG. 3 is a microstrip embodiment of a phase-shift device in accordance with the invention;
FIG. 4 is a coaxial-output sealed capsule embodiment of a phase-shift device in accordance with the invention.
Referring now to FIG. 1, part a thereof shows an equivalent circuit diagram of a semiconductor diode. The contact breaker I symbolises the state change control. In reverse-biased condition, the diode behaves as a very small capacitance C, for example of some few tenths of a picofarad, shunted across a very high resistance R. In forward-biased condition, the equivalent diagram is a very low resistance R practically a shortcircuit. The output connections are designed to produce an inductive reactance L of given value, arranged in the output lead of the diode, this being connected to the end (not shown) of the centralconductor of a microwave coaxial-line, or the strip conductor of a microstrip line. The second output lead is connected either to the external coaxial conductor or to the ground plane, as the case may be, and is thus at the earth reference potential. The active terms R and R in view of their respective values, can be neglected. The reverseoperated condition thus involves the elements L and C and constitutes a half-section, or L section, low-pass filter. A known improvement consists in connecting the semiconductor to the propagation line through another half-section low-pass filter which incorporates the elements L and C and is shown in part b, FIG. 1.
In order to produce a phase-shift angle of 11 when the diode is operated through a given operating frequency range, it is necessary for the product of the reactances respectively presented at the input terminals of the circuit in each of the two states, to remain constant and to be equal to the square of the characteristic impedance of the microwave propagation line. However, considering each of the two circuits thus far dealt with, this product contains terms which vary with frequency and thus to a greater or lesser extent restricts the effective bandwidth towards the high-frequency range, depending upon the circuit type.
Better matching of the circuit is achieved by using an impedance transformer which matches the impedance throughout a wide band and is constituted by a series m-derived half-section, low-pass filter derived from the half-section low-pass filter defined previously by the elements L and C. F IG. 2 illustrates an equivalent electric circuit diagram of such a O 1r phase-shift device. The series m-derived half-section low-pass filter F,, is connected by its output terminals directly to the semi conductor and by its input terminals to the microwave propagation line (not shown). At the input side it comprises in, the shunt arm, a capacitive reactance of mC value (C being the reverse capacitance of the semiconductor and m the selected derivation factor) in series with an inductive reactance of [(l m)L]/m value (L being the inductance previously defined for the semiconductor circuit). A second inductive reactance of mL value constitutes the series arm of the filter F and is connected in series to the inductance L of the semiconductor.
It will be noticed that permutations of elements are possible without modifying the characteristics of the circuit. Thus for example,the respective locations of the elements mC and (lm )/m L can be interchanged with one another in the shunt arm of the filter Fm.
A first embodiment of a phase-shift device is shown in FIG. 3 and relates to a circuit connected to a microstrip microwave propagation line. Thin-film techniques make it possible to produce a capacitance or a junction diode in the form of parallelepiped pills of very small dimensions. The element mC and the assembly D, of FIG. 2, are produced in this form and welded by one face to the end of the strip conductor 1 of the line. The capacitive element marked 4 can in particular consists of a ceramic material metallised on two opposite plane faces. The connection to the ground plane 2 which constitutes the second line conductor, is realized in the form of a metal stud 6 and connecting leads 7 and 8. The stud 6 is in the form of a cylindrical body located in a hole formed transversely in the dielectric substrate 3, for example a ceramic, and the ground plane 2; this body is terminated in a larger-diameter base rendered integral with the ground plane 2 by welding. The lead 7 between the capacitor 4 and the visible top part of the stud 6, correspnds to the inductance [(1m L]/m of FIG. 2. Similarly, the lead 8 between the junction diode 5 and said stud 6 corresponds to the assembly mL and L of FIG. 2 and has an inductance of value (m l) L. The leads 7 and 8 are welded to the corresponding elements at each end.
This embodiment is in no way lirnitative of the invention and, in particular, the stud 6 could be dispensed with and the leads 7 and 8 welded to the lateral face 9 of the substrate 3 after the deposition of a metallised layer with its underside in contact with the ground plane 2.
FIG. 4 relates to another embodiment of a phase-shift device in the form of a coaxialoutput sealed capsule designed for connection to a coaxial propagation line. The coaxial structure comprises a central conductor 10, and outer conductor 11 and a dielectric 12 to provide insulation and mechanically secure said conductors. The internal part, located within a fitted housing 13, comprises two pills 4 and 5 corresponding to those marked by the same references in the preceding figure, and welded by one face to the ring of the external conductor 11. The connection of the pills to the central conductor is effected by lead wires 14 and 15 having respective impedances of [(l-m )L]/m and (m l)L value. The dimensions of the capsule thus produced may quite easily be as little as 4 mm in external diameter and 4 mm in height.
A such embodiment comprising a diode with a reverse capacitance of 0.2 pF and a series m-derived halfsection low-pass filter, where m 0.6 and L 0,1nH, enables the microwave frequency range to be covered with an accuracy substantially of 2 percent, up to 14 GI-Iz, the cut-off frequency being between 15 and 16 GI-Iz.
The auxiliary control circuits which produce and transmit a bias signal to the semiconductor, are produced by conventional techniques which are not detailed in the present invention.
Of course, the invention is not limited to the embodiments described and shown which were given solely by way of example.
What is claimed, is
l. A microwave phase-shift device of the O-rr type, for connection to one end of a two-conductor microwave propagation line, comprising two terminals respectively connected to said conductors at said one end a series m-derived half-section low-pass filter comprising a shunt arm and a series arm, said shunt arm being connected across said terminals and said series arm being connected to one of said terminals a half-section low-pass filter, comprising a series arm connected in series with said first mentioned series arm and a shunt arm connected between said second mentioned series arm and the other of said terminals, the capacity of said second mentioned shunt arm being that of a reversely biased diode and control means for selectively switching said diode from reverse to direct state and conversely.
2. A microwave phase-shift device as claimed in .claim 1, wherein said diode and the capacity in the shunt arm of said m-derived low-pass filter are in the form of respective pills having two opposite metallized faces each of said pills being connected by a firstmetallized face directly to a first one of said conductors and a lead, connecting the second metallized face to the second conductor of said propagation line.
3. A microwave phase-shift device as claimed in claim 2, wherein said propagation line is an element of the microstrip line type, said first conductor corresponding to the strip and said second conductor to the ground plane, and wherein a cylindrical conductor stud, located in an opening formed transversely through said microstrip line, connects said leads to said ground plane.
4. A microwave phase-shift device as claimed in claim 2, wherein said microwave propagation line is an element of the coaxial line type, said first conductor corresponding to the external coaxial conductor and said second conductor to the central coaxial conductor and wherein a removable sealed-capsule housing accommodates said coaxial line element and said pills and leads.