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

Definitions

• the present invention relates to a bandpass filter with coupled resonators. It finds an application in electronics, in particular in the production of bandpass filters whose working frequency is located in the FM band, that is to say substantially from 70 to 120 MHz.
• the filter of the invention is of the type with coupled resonators.
• French application FR-A-2-626-716 (or the corresponding European application EP-A-0 326 498) describes a filter with coupled resonators which is illustrated in FIG. 1.
• this filter comprises five resonators C1 to C5 deposited on the same substrate 10.
• Each resonator comprises a line with a conductive microstrip 14 (made of copper for example) forming a loop with an opening 16. Connected through this opening is an adjustable capacitor 18, or adjusted once and for all. The entire line and the capacitor form an LC resonant circuit.
• the length of the microstrip is of the order of ⁇ / 8 if ⁇ is the wavelength associated with the resonance frequency of the circuit.
• the substrate 10 is made of dielectric material (for example epoxy glass, Teflon, etc.). On the underside of this substrate is a conductive layer (not shown in copper for example) forming a ground plane.
• the different resonators are coupled to each other by parallel and adjacent sides.
• the filter is completed by an input microstrip E and an output microstrip S.
• Such filters work in the frequency band ranging appreciably from 950 to 1750 MHz, in particular in stations for receiving television signals. broadcast by satellites.
• this filter requires input and output matching circuits.
• Such a filter causes losses due to the coupling between resonators and it is very difficult to simulate, because no software is capable of simulating such numerous couplings and, for some, so distant. As soon as the number of resonators is changed, for example to vary the bandwidth, the couplings change and the entire simulation must be repeated.
• the object of the present invention is precisely to remedy these drawbacks. To this end, it offers a filter whose dimensions are reduced
• the filter of the invention has very low losses, of the order of 2 dB. Its bandwidth can be adjusted between a narrow band (2%) and a wide band (40%).
• the resonators of a cell are each constituted by a microstrip line playing, at the working frequency, essentially the role of an inductor and by a tuning capacitor. It is therefore still an LC type resonator. But, according to a first characteristic of the resonator, the line is not in the form of a loop with opening. The tuning capacitor is therefore not inserted into an opening but connected to one of the ends of the line and it has an armature to the electrical ground.
• the line comprises a straight portion (or bran ⁇ che) used to couple together the two resonators of the same cell and, to do this, the two straight branches specific to the two resonators are juxtaposed.
• the length of these branches, as well as their width, makes it easy to adjust the coupling to the appropriate value.
• the filter comprises several elementary cells, connected directly to each other consecutively, the access specific to the second resonator of a cell being connected to the access specific to the first resonator of the cell which follows .
• the losses due to the cascading are thus reduced to their minimum compared to the filter of the FREQUENZ document already cited where the cascading of the resonators was carried out by coupling.
• the filter of the invention has lower losses and its simulation is greatly simplified.
• the present invention therefore relates to a bandpass filter with coupled resonators, characterized in that it comprises at least one elementary filtering cell, each elementary cell being formed of resonators exclusive of two, ci -after designated first and second resonator, each resonator of a cell comprising:
• this line comprising a first rectilinear part representing at least one part of the microstrip, this first part having one end connected to an electrical ground, both first parts specific to two resonators of the same cell being juxtaposed and ensuring coupling between the resonators, the line further comprising a second part if the first does not constitute the whole of the line, this second part having one end,
• tuning capacitor having an armature connected to the end of the second part and another armature connected to the electrical ground
• the filter of the invention can comprise several cells of this kind, in which case two consecutive cells are connected directly to each other, the access specific to the second resonator of a cell being connected to the access specific to the first resonator of the next cell.
• the rest of the microstrip line if the first part does not constitute the entire line), i.e. -to say the second branch, can have any shape and arrangement: inclined, at right angles, in continuation of the first, etc.
• the microstrip line can therefore have various shapes in L, T, etc.
• the widths of the branches of the microstrip are not necessarily identical. They can be different from each other. They can even vary gradually, or by jumps, along the same branch.
• FIG. 3 illustrates an embodiment with a fully rectilinear microstrip
• FIG. 5 illustrates an embodiment with a microstrip having a coupling branch of variable width
• FIG. 6 illustrates an embodiment with microstrip with second branch of variable width
• FIG. 7 shows a mask for the realization of a two-cell filter
• FIG. 8 is an electrical diagram of a two-cell filter
• FIG. 10 shows the attenuation of the filter as a function of frequency, in a range from 1 to 200 MHz;
• FIG. 12 shows the standing wave rate in a frequency range from 1 to 200 MHz.
• each microstrip comprises a first straight part (or branch) L1 (respectively L2) and a second part (or branch) The I (L'2) which, in the illustrated variant, forms, with the part L1 (L2), a T.
• the end el (e2) of the branch L1 (L2) is connected to the ground plane 22 by a stud and a conductive passage 24/1, (24/2).
• the end e'I (e'2) of the branch I (L'2) is connected to one of the armatures of a capacitor Cl (C2), the other armature of the capacitor being connected to the ground plane 22 by a pad and a conductive passage 26/1 (26/2).
• a single conductive pad and a single conductive passage can be used to join the ends el, e2 to the ground plane.
• the lines are therefore well short-circuited at one of their ends.
• the cell entry E takes place between Cl and L'I and the exit S between C2 and L'2.
• the device is symmetrical and one can enter S and exit at E.
• FIG. 3 first of all, the branches Ll
• the branches I (L'2) not used for coupling are inclined by a certain angle ( ⁇ ) on the branches L1 (L2) used for coupling.
• the branches I, L'2 thus form, between them, an angle double (2 ⁇ ).
• the coupling branch L1 sees its width increase from one end (in this case that which is grounded) to the other, the reverse being also possible.
• FIGS. 7 and 8 illustrate a particular embodiment of a filter according to the invention in the case where this filter comprises two cells.
• FIG. 7 firstly shows the mask used to constitute the printed circuit on the upper face of the substrate.
• This mask is shown on a scale of 3, which makes it possible to appreciate the reduced dimensions of the filter of the invention.
• This mask comprises two parts which are symmetrical with respect to a point O. Each part comprises an entry access strip ME and exit MS, and two juxtaposed T strips forming a set Ml, 2 (M3,4) which will correspond to both cells.
• Figure 8 shows the electrical diagram corresponding to Figure 7, once the capacitors C1, C2, C3, C4 have been reported.
• the coupled branches are respectively L1, L2 for the first cell and L3, L4 for the second.
• connection ribbon is referenced 30. There is therefore no longer any coupling, as in the prior art, but a simple serialization.
• the two cells are arranged in such a way that they are as far apart as possible from one another to avoid any coupling between them.
• the second cell C3-4 is not available in the extension of the first Cl-2, but placed symmetrically with respect to the element 30.
• the filter included more than two cells, this would always be the case, with alternating cells oriented sometimes in one direction sometimes in the other to form a cascade of cells in staggered rows.
• FIGs 9 to 12 illustrate the performance of the filter in Figures 7 and 8.
• Figure 9 first of all, shows the attenuation of the filter in the band from 78 to 118 MHz. We see that the attenuation in the center of the passband is very low (around 2 dB).
• Figure 10 gives the same attenuation but over a wider frequency range, from 1 MHz to 200 MHz.
• Figure 11 shows the attenuation towards high frequencies, up to 2000 MHz.
• Figure 12 shows the standing wave rate (TOS) as a function of frequency. In bandwidth, this rate drops to around -22 dB.
• TOS standing wave rate

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

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• 1993
  • 1993-05-04 FR FR9305287A patent/FR2704983B1/fr not_active Expired - Fee Related
• 1994
  • 1994-05-03 EP EP94915581A patent/EP0649571B1/de not_active Expired - Lifetime
  • 1994-05-03 DE DE69420924T patent/DE69420924T2/de not_active Expired - Fee Related
  • 1994-05-03 WO PCT/FR1994/000511 patent/WO1994025996A1/fr active IP Right Grant
• 1995
  • 1995-01-03 FI FI950033A patent/FI115332B/fi active IP Right Grant

Non-Patent Citations (1)

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