Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/203—Strip line filters
  • H01P1/2039—Galvanic coupling between Input/Output

Definitions

• the invention relates to the field of microwave band cut filtering.
• Tunable microwave cut-off filtering devices are already known.
• At least one filtering cell comprising a microstrip segment coupled to the main transmission line arranged parallel to and at a distance therefrom, and a tunable LC resonant circuit.
• a signal applied to one end of the transmission line is filtered, and the central frequency of the filtering device obtained is variable thanks to a control of the voltage applied to the tunable resonant circuit LC.
• the microstrip segment has a first end in open circuit and a second end connected to the potential of to ground through the tunable LC resonant circuit notably comprising a varactor.
• the tunable LC resonant circuit notably comprising a varactor.
• connection of the second end of the microstrip segment to the ground potential through the resonant circuit is carried out using a metallized hole which generates a residual inductance of typical value of 0.2 at 0.3 nanohenrys.
• this has the effect of limiting the application of the filtering device in the high frequency ranges (typically above 12 GHz).
• the losses associated with this metallized hole reduce the overall performance of the filter and in particular the overvoltage coefficient of the resonant circuit.
• the filtering cell supplying the varactor diode in the aforementioned patent is very difficult to achieve for operations in a very large band of use and / or with a high tuning speed.
• One of the aims of the invention is to remedy these drawbacks.
• the invention proposes a new structure making it possible to modify the connection of the tunable LC resonant circuit.
• the tunable resonant circuit LC is interposed between one of the ends of the coupled line segment and the main microwave transmission line.
• This structure according to the invention which derives from the fixed frequency structure called by a person skilled in the art "SPURLINE", has the following advantages:
• the tunable LC resonant circuit comprises an inductor connected in series with an adjustable capacitance, the other of the ends of the coupled line segment being in open circuit.
• the adjustable capacity advantageously consists of a varactor, one of the electrodes of which is connected to one of the ends of the coupled line segment and the other of which is connected on the one hand to one of the inductance terminals and secondly to a control circuit.
• the tunable LC resonant circuit comprises an inductor connected in parallel with an adjustable capacitance, the other of the ends of the coupled line segment being connected to ground.
• the varactor is controlled by a control circuit comprising a source of potential decoupled from microwave by a self induc ⁇ tance or by a diplexer.
• the Applicant has posed the problem of controlling the varacitor in a simpler manner and at low cost while improving the performance of the filter at low frequency, that is to say for frequencies below 2 GHz.
• the solution to this problem consists, according to the invention, in using a control circuit comprising a resistance with a high ohmic value which does not or only slightly disturb the microwave wave regime.
• the operating principle of a varactor being that of a reverse bias diode, the current delivered by such a control circuit according to the invention is negligible and the control voltage is fully transmitted to the varactor.
• the filtering device according to the invention is used in cut or strip rejection in which it cuts a small filter strip and positions this last in the wide band from 2 to 18 GHz.
• the resonance conditions of a filter according to the invention at variable frequency are different from those at fixed frequency. More precisely, the conditions of resonance in variable frequency sound such that the parasitic rejections no longer appear three times at the reference frequency but rather sensibly for the two times; the reference frequency being the frequency at which the elementary structure corresponds to a quarter wavelength.
• Another object of the invention is precisely to provide a filtering device j_ * oupe-band tunable microwave capable of effectively ejecting at lower frequency while keeping a useful band greater than or equal to that of 2 to 18 GHz.
• the invention uses a filtering device of the type mentioned above.
• the main microwave transmission line is subdivided into two adjacent sections, the line segment being coupled to the first section of electrical length chosen L1, the second section being free and of electrical length chosen L2, and the sum of the lengths L1 and L2 corresponding substantially to a quarter of the wavelength at the central frequency of rejection of the filter.
• the choice of the length L1 of the first section makes it possible to move the parasitic bandstop tape more than twice the value Vg / 4.L1 where Vg is the group speed in the transmission medium for operation of the device. rejection filter centered at Vg / 4 (L1 + L2).
• the length L1 is of the order of 3.3 mm
• the length L2 is of the order of 1.7 mm
• the central rejection frequency of the filter is 6 GHz.
• FIG. 1 schematically shows a tunable microwave filtering device according to the prior art
• FIG. 2 shows a filter attenuation curve described with reference to Figure 1;
• FIG. 3 is a schematic view of an LC resonant circuit filter cell mounted in series between the main transmission line and the coupled line segment according to the invention
• FIG. 4 is a schematic view of a filter cell with an LC resonant circuit mounted in parallel between the main transmission line and the coupled line segment according to the invention
• FIG. 5 is a schematic view of the varactor control circuit associated with the device described with reference to Figure 3;
• FIG. 6 is a schematic view of a mask of a device with three filter cells of Figures 3 and 5 according to the invention.
• FIG. 7 is a schematic view of the varactor control circuit associated with the device of Figure 1 according to the invention.
• FIG. 8 is a schematic view of a mask of a device with three filter cells of Figures 1 and 7 according to the invention
• - Figure 9 is a schematic view of the subdivision of the main transmission line associated with three filter cells of Figure 8 according to the invention.
• FIG. 10 is a schematic view of the subdivision of the main transmission line associated with three filter cells of Figure 9 according to the invention.
• FIG. 1 the structure claimed in French patent No 88 03187 is shown, relating to a band-cut filter of the type known as coupled lines produced in microstrip technology.
• Such a filter comprises a transmission line 1 in the form of a microstrip or microstrip connecting a generator 2 of microwave signals to a load impedance 3.
• At least one filtering cell formed by a microstrip segment 4 arranged parallel to the transmission line, having an electrical length corresponding substantially to a quarter wavelength at the central rejection frequency which it is desired to give. to the filter.
• the segment 4 has one of its ends in open circuit and the other of its ends connected to ground through a tunable LC resonant circuit formed by an inductor 5 in series with an adjustable capacity 6, this circuit therefore constituting a load for the coupled line.
• the adjustable capacity 6 consists of a varactor, the cathode of which is connected to ground and the anode of which is connected on the one hand to one of the terminals of the inductor 5 and on the other hand to a source of negative continuous potential -V.
• the filtering device can for example comprise 5 filter cells each formed by a segment 4. It should be noted that by increasing the number of cells, the shape of the response of the filter is adjusted.
• the attenuation provided by such a filter is illustrated in FIG. 2, where it can be seen that the central frequency FO can move between a minimum value FOmin and a maximum value FOmax according to the potential applied to the cathode of the varactor, the minimum frequency being obtained by the maximum capacity of the varactor, itself corresponding to the lowest control potential.
• the central frequency FO is determined by the length of each segment 4 and the rejection bandwidth depends on the number of cells and the impedance of the coupled line of each of them.
• the connection of the tunable resonant circuit LC is modified.
• the tunable LC resonant circuit is now interposed between one of the ends of the micro-band segment 4 and the microwave transmission line 1.
• the adjustable capacitor 6 consists of a varactor, the cathode of which is connected to one end of the transmission line 1 and the anode of which is connected on the one hand to one of the terminals of 1 ' inductance 5 and on the other hand to a source of negative continuous potential -V.
• the tuning frequency of the resonant circuit LC varies with the control voltage of the varactor.
• the operation of the filter is then modified and its frequency tuning essentially depends on the DC voltage applied to the varactor.
• the structure shown in FIG. 3 has the advantage of being able to be produced in microru ⁇ ban technology and also in technology with suspended substrate thanks to the absence of metallized hole.
• the tunable resonant circuit LC interposed between one of the ends of the microstrip segment and the microwave transmission line, comprises an inductor 5 mounted in parallel with an adjustable capacitance 6.
• microstrip segment 4 is connected to the potential of the mass.
• the adjustable capacity consists of a varactor, the cathode of which is connected to one end of the microwave line and the anode of which is connected on the one hand to the microstrip line and on the other hand to the circuit of ordered.
• the varactor control circuit com ⁇ takes a source of potential 7 which supplies the varactor through a resistance of high ohmic value 8.
• the ohmic value of the resistor 8 is of the order of a few thousand ohms for correct operation of the varactor.
• FIG. 6 shows a mask in microstrip technology of a filtering device with three filter cells of the type described with reference to FIGS. 3 and 5.
• the main microwave transmission line 1 is found there, with which three filter cells are associated.
• a filter cell is composed of a line segment 4 coupled to a line section 9 and a tunable LC resonant circuit interposed between the section 9 and the segment 4.
• the LC resonant circuit consists of a varactor 6 and an inductor 5.
• the varactor 6 consists of a block affixed on the line segment 4 and the inductor 5 consists of a connecting wire placed between the varactor 6 and the line section 9.
• the resistor 8 of the varactor control circuit consists of a strip connected to one end of the line segment 4.
• the source of potential 7 supplies the resistor 8.
• the resistor 8 is applied as close as possible to the varactor, but the implementation constraints can lead to positioning it, for example at any point of the line segment.
• the adjacent sections 9 have an electrical length substantially equal to that of the line segments 4. This length corresponds substantially to a quarter of a wavelength at the central frequency of rejection of the filter. For example, for a central rejection frequency of 6 GHz, the length of the sections 9 and segments 4 is of the order of 5 mm.
• FIG. 7 the control circuit of the filtering device described with reference to FIG. 1 is shown.
• FIG. 8 shows a mask in microstrip technology of a filtering device with three filter cells of the type described with reference to FIGS. 1 and 7.
• the main microwave transmission line 1 is found there, with which three filter cells are associated.
• Each filter cell is composed of a line segment 4 coupled to a line section 9 and of a tunable LC resonant circuit interposed between ground and one of the ends of line segment 4.
• the mass is represented by a metallized hole 15 (in dashed lines in FIG. 8).
• the inductance 5 consists of a block 13 on which is affixed the block 6 forming a varactor. Connecting wires 14 connect the varactor 6 to the resistor 8 of the control circuit of said varactor according to the invention.
• the adjacent line sections 9 have an electrical length substantially equal to that of the line segments 4.
• This electrical length corresponds substantially to a quarter wavelength at the central frequency of rejection of the filter.
• FIG. 9 shows a mask of a filtering device having its microwave transmission line subdivided into several adjacent sections of different electrical lengths to move the parasitic rejections beyond the useful band 2-18 GHz.
• the filtering device is here associated with three filtering cells such as those described with reference to FIGS. 1 and 8.
• the microwave transmission line is subdivided into a plurality of pairs of adjacent sections 10 and 11.
• the line segment 4 of each filter cell is coupled to the first section 10 of electrical length L1.
• the second section 11, adjacent to the section 10, is free. It has an electrical length L2.
• the sum of the lengths L1 and L2 is chosen so that it is substantially equal to a quarter of a wavelength at the central frequency of rejection of the filter.
• FIG. 10 shows a mask of a filtering device with three filter cells of the type described with reference to FIGS. 3, 5 and 6.
• the main transmission line 1 is subdivided into a plurality of pairs of adjacent sections 10 and 11 to reject parasitic rejections beyond the useful band 2-18 GHz.
• the sections 10 and 11 are delimited by shoulders 17. It should be noted that generally the coupled line segments 4 have a width of value equal to that of the main transmission line 1.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9414411

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (8)

Citations (2)

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• 1991
  • 1991-06-27 FR FR9108003A patent/FR2678450B1/fr not_active Expired - Fee Related
• 1992
  • 1992-06-25 WO PCT/FR1992/000585 patent/WO1993000718A1/fr active Application Filing
  • 1992-06-25 US US07/980,794 patent/US5448210A/en not_active Expired - Fee Related
  • 1992-06-25 DE DE4291983T patent/DE4291983T1/de active Pending
  • 1992-06-25 DE DE4291983A patent/DE4291983C2/de not_active Expired - Fee Related
  • 1992-06-25 GB GB9303377A patent/GB2263583B/en not_active Expired - Fee Related

Patent Citations (2)

Non-Patent Citations (4)

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