FR2548846A1 - Resonator circuit which can be tuned discretely to a plurality of tuning frequencies and filter including at least one such circuit - Google Patents

Abstract

This resonator circuit which can be tuned discretely to a plurality of tuning frequencies includes at least one port 8 or 9 for connection to a transmission line transmitting signals to be filtered, a main line 1 plugged into at least one variable reactive circuit consisting of a voltage-controlled switching element 31, 32, 33, 34; this circuit is notable in that each variable reactive circuit consists of a secondary line 51, 52, 53, 54 connected to the main line 1 by the said switching element. Application: system using frequency-avoidance modulation.

Description

TUNING CIRCUIT TUNABLE IN A DISCRETE WAY ON A

  MULTIPLE TUNING FREQUENCIES AND FILTER COMPRISING AT LEAST

SUCH A CIRCUIT

  The invention relates to a resonator circuit tunable in a disorete manner on a plurality of tuning frequencies comprising at least one hearth oven access connected to a transmission line transmitting signals to be filtered, a main line to which is connected at least a variable reactive circuit constitutes

  from a voltage controlled corriutation element.

  The invention also relates to a filter comprising at least one such circuit.

  Such a filter can find important applications, in particular in transmission-reception systems using frequency evasion modulation (FREQUE or CY HIOPPING). The filter connected at the output of the transmitter or at the input of the receivers must follow the 'rapid change in frequency changes To follow such a rhythm, it is possible to use PI N diodes as switching elements. A Dremier circuit-resonator of this kind is described in the patent of the United States of America. Am 4 érique issued under the number 3 417 351 In this resonator the variable reactive circuit is simply constituted by a PIN diode considered, at the working frequency (3 G Hz), as a serial resonant element in the 'state open and as an inductive element in the closed state The tuning frequencies of this tuning circuit are dependent on the characteristics of the diodes used and the design of such a circuit first of all involves measuring the PIN diodes that the 'we go use. 25 The main line of this resonator circuit is connected directly to the supply line which carries the signals to be filtered. This results in a very low overvoltage coefficient

for the intended application.

  A second resonator clrcuit 30 of this type is also known, described in French patent application No. 2,495,844.

  In this known circuit, produced from a coaxial line, the reactive elements are obtained by structural modifications

of the soul of the coaxial line.

  The present invention provides a circuit of the kind mentioned in the preamble which, on the one hand, is less dependent on the characteristics of the switching elements and which has a better overvoltage coefficient than the known circuit-resonator pranier and which, on the other hand share, is of a structure much easier to

  realize that the second known resonator circuit.

  For this, a resonator circuit tunable in a discrete manner over a plurality of tuning frequencies is remarkable in that each variable reactive circuit is constituted by

  a secondary line connected to the main line by said switching element.

  The following description accompanied by the attached drawings, all given by way of non-limiting example, will do well

  understand how the invention can be realized.

  Figure 1 shows in exploded view a tunable resonator circuit according to the invention.

  Figures 2 to 8 show different diagrams

  electrical intended to explain the operation of the resonator circuit according to the invention.

  FIG. 9 represents two sectional views of the resonator circuit of FIG. 1.

  FIG. 10 represents a filter formed by several

  resonator circuits according to the invention.

  Figure 11 shows a loop coupling circuit suitable for a resonator circuit according to the invention.

  FIG. 1 represents a resonator circuit in accordance with the invention produced in triplate lines This resonator circuit is formed from a main line 1 whose length is practically less than a quarter of the wavelength corresponding to the frequency the highest on which the resonator circuit can be adjusted This line I is formed by a tape deposited 35 on an insulating plate of printed circuit 2 of the smallest possible thickness This plate is deposited in a metal shoemaker that one has, in FIG. 1, represented in two parts: a lower part 5 A which contains the plate 2 and an upper part 5 B normally coming into contact with part 5 A The walls of this shoemaker 5 A, 5 B constitute the plane of mass of line 1 The housing is filled with a plastic foam, like a honeycomb, whose permittivity is close to 1 and the dielectric losses, low so that the overvoltage coefficient is not reduced One end 6 of this line 1 is short-circuited: for this, it is brought into contact with a wall of the shoemaker 5 A, B The other end 7 is free An access 8 allows connection on a line, not shown, transmitting signals to be filtered, an access 9 provides the filtered signals with use; it is understood that the resonator circuit operates in the transmission mode. The absorption mode can also be envisaged. In the 15 locations identified by lines 11, 12, 13, 14, we have arranged

variable reactive circuits.

  These reactive circuits include a switching element 31, 32, 33, 34; this switching element is preferably a diode P I N The conduction or non-conduction state of these elements 31 to 34 is determined by the position of the switches 41, 42, 43 and 44; depending on the open or closed position of these switches, a control voltage V from a source of

  voltage 50 is applied or not to elements 31, 32, 33 and 34.

  So by operating these switches it is possible to tune

  the resonator circuit on different frequencies.

  According to the invention, each variable reactive circuit is constituted by a secondary line 51, 52, 53 and 54 respectively connected to the main line 1 by the respective switching elements 31, 32, 33 and 34.

  Secondary lines whose electrical length is, in practice, less than 90 may have their end opposite to the main line, free or short-circuited. Thus, lines 52, 53 and 54 have their ends open while line 51 constitutes a triplate line short-circuited for the high frequency by means of a plate 59 To apply the control voltages to the diodes 31, 32, 33 and 34 it is advisable to envisage certain measures Thus for the diode 31, the plate 59 is connected to bottoms of parts 5 A and 5 B of the housing, by means of a capacitor: thus in FIG. 1, the capacitor is represented

  which is pressed against the bottom of part 5 A An electrical connection 61 then connects the plate 59 to one end of the switch 41.

  To bias the diodes 32, 33 and 3411, localized coils 62, 63 and 64 are provided, which are still effective at the frequencies envisaged (% 300 M Hz). One end of these coils is connected to the free ends of the secondary lines 52, 53 and 54 and the other end to switches 42, 43 and 44 by means of passage capacitors 72, 73 and 74 fixed to the walls of parts 5 A and 5 B The coupling between acecs 8 and 9 and the resonator circuit is provided 15 by small antennas 75 and 76 located towards the free end of

main line 1.

  In FIG. 2, an equivalent diagram of the resonator circuit of FIG. 1 has been represented. In this FIG. 2, the references B 1, B 2, B 3 and B 4 correspond to the susceptances reduced to the 20 levels of the lines 11, 12, 13 and 14 by lines 51, 52, 53 and 54.

  The susceptance brought back is negative for line 51 and positive

for lines 52, 53 and 54.

  Bl = j Y 1 cotg (e ú 1) B 2 = + j Y 2 tg (e 2) B 3 = + j Y 3 tg (f ú 3) B 4 = + j Y 4 tg (f ú 4) Y 1, Y 2, Y 3, Y 4 are the respective characteristic admittances of lines 51, 52, 53 and 54, ú 1, ú 2, ú 3 and ú 4 are their geometric lengths. is the wavenumber: = 2 r o A is the wavelength, w is the pulsation of the wave, ú the permittivity of the medium filling the triple line, we take

r l.

  Note that in practice lines 51, 52, 53 35 and 54 are short in front of X so that: Bl = -j Y 1 B 2 = j Y 2 92 B 3 = j Y 3 9 3 B 4 = j Y 4 (4 these lines then have a purely inductive or purely capacitive behavior. To simplify the explanations, consider one of these susceptances for example B 3, which is represented in FIGS. 3 to 8 The susceptance B 3 is therefore connected to line 1 through the middle of diode PIN 53 (figure 3) When a diode PI N. leads, it is equivalent to a low resistance Rds in series with B 3 (figure 4) If the susceptance B 3 is, for example, a capacity C 3, the diagram of FIG. 5 is equivalent to that of FIG. 4 with R = 1 / Rds (C 3,) 2 (1) provided that Rd C 3 W << 1 which is always checked When the PIN diode is blocked, it is equivalent to a large resistance Rdp shunted by a parasitic capacitance Cp 3, all arranged in series with B 3 (figure 6) If the susceptance B 3 corresponds to a capacitance d agreement C 3, the diagram of FIG. 6 is equivalent to that of FIG. 7 o:

C 3 C C

C = C and RI = Rd _ Pa (2)

  provided that Rd C <w "1 which is always verified.

  Comm C "C 3, we have Ct and C R and R R the To ,, P, P 3, t radio diagram corresponding to the blocked diode is that

of figure 8.

  In summary, in the case where the tuning element is a positive susceptance (capacitance C 3), FIG. 5 shows that with the diode leading, the capacitance C 3 shunted is effectively brought back in parallel on the main line of the resonator by a large resistance In the case where the diode is blocked (figure 8), one returns in parallel on the line two very weak susceptances in front of Yo (characteristic admittance of line 1) namely CW and 1 / RO which have Pu

1 / Rd which have a weak influence.

p

2548846 '

  We can, by comparing the expressions (1) and (2) and choosing R = R 'Rd either get sensiú d Rds get sensiblenent for the two operations of the PIN diode (driving or blocked) the same coefficient of overvoltage So with R = 2,104 ohms and Rd = 0.15 ohms, we deduce for f = 3,108 Hz: Ci = 9.7 p F It is an average value of the capacities required

  to tune the cavity It should be noted that, in the parametric evaluation of the resonator, it is necessary to take account of the parasitic capacity Cp 3 or better of the very close capacity Ct.

  To fix the ideas, we specify in the following, different c 3 tes of the resonator circuit shown in Figure 1 The secondary lines are represented, for the clarity of the drawing by small blocks referenced by the capacity or self induction that they provide, the secondary lines being very short of 15 before the wavelength A Table I gives the values of L 1, C 2, C 3 and C 4 brought by the lines 51, 52, 53 and 54 and the distances dl , d 2, d 3, d 4 of their location, counted from

  the open end of line 1.

TABLE I

  dl = 115 mm d 2 = 159 md 3 = 170 mm d 4 = 184 mm L 1 = 5.87 n HC 2 = 28.8 p CF 3 = 17.13 p CF 4 = 11.76 p F the length d T of main line 1 has the value:

  d T = 245.85 mm, its width W = 132 mm, the height b of the resonator circuit: b = 22, its total width úT = 190 its total length LT = 320 mm.

  The following table II gives the values of the tuning frequencies of the resonator circuit according to the positions

  O or F of switches 41, 42, 43 and 44.

TABLE II

POSITION OF 41 42

SWITCHES

43 44

  15 o O O O o o F F F F F F F F F F F F F o F F F F o o F F F F o o F F o F F O F F F F o F F F F O

229.98 236.97

  244>, 45 252.38 262.45 272.48 283.12 294.35 306.58 317.05

  327.94 339.44 355.53 370.80 385.70 400.31

  TUNING FREQUENCIES M Hz i The filter shown in FIG. 10 is made up of five resonator circuits in accordance with the invention. These circuits bear the references 100, 101, 102, 103 and 104, these circuits are placed side by side on their largest face. so that circuits 100 and 101, 101 and 102, 102 and 103 and finally 103 and 104 have a common wall 25 Accesses 110 and 111 are provided respectively on the external walls of resonator circuits 100 and 104 for a connection of use The couplings are carried out both for the accesses and for the resonator circuits between them by small antennas

, 116, 117, 118 and 120.

  The coupling instead of being carried out by small

  antennas can be by loops 200 and 201 arranged in the vicinity of the end 6 as shown in FIG. 11.

  This loop coupling can be used both for use connections and for coupling the resonator circuits together.

2548846 '

Claims (10)

CLAIMS:   1 Resonator circuit tunable in a discrete manner on a plurality of tuning frequencies comprising at least one access to be connected to a transmission line transmitting signals to be filtered, a main line on which is branehée at least one variable reactive circuit consisting of a voltage-controlled switching element, characterized in that each variable active circuit r is constituted by a secondary line connected to the main line by said switching element. 2 resonator circuit according to claim 1, characterized in that the main line has a length of the order of a quarter of the wavelength corresponding to the average frequency of   the plurality of tuning frequencies and has a short circuit end.   3 resonator circuit according to claim 1 or 2,   characterized in that said lines are triplate lines.   4 Cireuit-resonator according to one of claims   1 to 3, characterized in that the switching elements are P 1 N diodes.   Cireuit-resonator according to one of claims   3 and 4, characterized in that the core of the three-ply lines is supported by a very thin dileeometric support so as to form a printed circuit supporting the switching elements and the biasing means for bringing the control voltage to the switching elements.   6 resonator circuit according to one of claims   3 to 5, characterized in that the space copied between the core of the triplate line and the ground walls are filled with a honeycomb foam to form a dielectric behaving like air.   7 resonator circuit according to one of claims   I to 6, characterized in that a coupling circuit is provided   to connect the circuit to the access.   8 resonator circuit according to claim 6, characterized in that the coupling circuit consists of a   small antenna placed on the open side of the main line.   9 resonator circuit according to claim 6, characterized in that the coupling circuit consists of a loop disposed near the short-circuited end of the main line. Filter comprising at least one resonator circuit   according to one of claims 1 to 7, provided with coupling circuits according to claim 8 or 9.