EP2294652B1 - Stripe line having plated through holes - Google Patents

Description

The present invention relates to a strip line for high-frequency signals having a signal conductor and at least one ground conductor, both of which are arranged on a substrate of an electrically insulating material, wherein in the substrate at least one bore is formed, which is at least partially filled with an electrically conductive material, wherein an electrically conductive connection of at least one ground conductor is formed to the electrically conductive material, according to the preamble of claim 1. The invention further relates to an attenuator according to the preamble of claim 8. The invention further relates to a terminating resistor according to the preamble of claim. 9

For high precision attenuators and termination resistors, for example for calibrating vector network analyzers, stripline, in particular so-called "suspended" striplines, are used. Here, in the dimensioning of the strip line, counteracting parameters are to be optimized. On the one hand, the stripline and the substrate on which the stripline is formed, geometrically small as possible, since at frequencies whose wavelength of the geometric dimensions of the structure, in particular the substrate, or smaller, waveguide modes are excited, which are undesirable electrical Properties in terms of impedance matching. On the other hand, a maximum thermal load that can accommodate the stripline and substrate structure is due to the geometric dimensions of the substrate accordingly limited, so that only a limited electrical power can be transmitted via the attenuator and the terminator. At higher powers, the entire structure would be thermally damaged or destroyed. For higher powers, a larger geometric dimension, for example, of the substrate would be desirable, but this immediately leads to a lowering of the cutoff frequency, to which the structure with the desired electrical properties can be operated.

From the essay George E. Ponchak et al: "The Use of Metal Filled Via Holes for Improving Isolation in LTCC RF and Wireless Multichip Packages," IEEE Transactions on Advanced Packaging, IEEE Service Center, Piscataway, NJ, US, Vol. 23, No. 1 , February 1, 2000 (2000-02-01), pages 88 to 99, XP011002223, ISSN: 152-3323 a microstrip line is known in which a signal conductor is arranged on a dielectric substrate on one side and a full-area metallization on the opposite side as a ground plane. On both sides of the signal conductor through holes are formed, which are filled with an electrically conductive material, wherein the through holes are electrically connected to each other on one side of the signal conductor via a respective metal strip on the substrate. This is intended to compensate for the fact that, although the through holes should be spaced as closely as possible from each other, but this is not as far as desired possible for manufacturing reasons.

From the US 2004/0227232 A1 For example, a microwave device for mitigating or deriving power is known. This has a signal conductor and a grounding zone on a substrate. A resistance layer is connected on the one hand to the signal conductor and on the other hand to the grounding zone. The resistive layer is at least partially covered by a ground plane, the ground plane being connected to the grounding zone and isolated from the resistive layer by means of an insulating layer.

The essay by George E. Ponchak et al .: "Experimental Verification of the Use of Metal Filled Via Hole Fences for Crosstalk Control of Microstrip Lines in LTCC Packages", IEEE Transactions on Advanced Packaging, IEEE Service Center, Piscataway, NJ, US, Vol. 24, No. 1, February 1, 2001 (2001-02-01), pages 76 to 80, XP011002322, ISSN: 1521-3323 relates to the problem of coupling between microstrip lines in dense high-frequency packed arrangements which affects the performance of electrical circuits. Metal filled through holes between two adjacent microstrip lines increase the coupling between them. However, this coupling is reduced when tops of the through holes are connected to each other via a metal strip.

From the GB 2 322 237 A For example, a coplanar waveguide having two ground conductors is known on both sides of a signal conductor on a dielectric substrate. At the bottom of the substrate, another ground conductor is provided, which is connected via through holes in the substrate to the ground conductors on the top of the substrate.

From the US 4 521 755 A a stripline of circular cross-section is known. On opposite sides of each grooves for receiving a substrate are formed, wherein on the substrate, a center conductor is arranged. The center conductor comprises two metal strips arranged on opposite sides of the substrate, which are electrically connected to one another via through-holes through the substrate.

From the essay Xilang Zhou et al., "Quasistatic analysis or a new CCPW with cylindrical shielding", Microwave and Optical Technology Letters, Vol. 34, No. 3, 5 August 2002 (2002-08-05), pages 213 to 215, XP055055726, ISSN: 0895-2477 , DOI: 10.1002 / mop.10420 is a novel, coplanar coupled waveguide with cylindrical shielding known.

From the essay by Wolfgang Menzel et al .: "Miniaturized Suspended Stripline Filters for Integration into Extended Circuits", Microwave Conference, 2006. 36TH European, IEEE, PI, September 1, 2006 (2006-09-01), pages 909 to 912, XP031005718, ISBN: 978-2-9600551-6-0 Suspended Stripline (SSL) strip lines are known which have a shield to prevent radiation. The strip lines are constructed like microstrip strip lines, ie a signal line is arranged on one side of a substrate and a ground plane is arranged on an opposite side. The entire assembly is surrounded by a shield.

From the essay by E. Yamashita et al .: "Effects of side-wall grooves on transmission characteristics of suspended striplines", IEEE Transactions in Microwaves Theory and Techniques, Vol. 33, No. 12, December 1985 (1985-12), pages 1323 to 1328 , XP001370096 Suspended Stripline (SSL) strip lines are known, which have a signal conductor on a substrate, which are surrounded by a ground plane. In this case, if necessary, two or more signal conductors are arranged within the ground plane.

From the essay by Maloratsky LG: "Reviewing the Basics of Suspended Striplines", Microwave Journal, Horizon House Publications, Norwood, MA, US, Vol. 45, No. 10, Oct. 1, 2002 (2002-10-01), pp. 82, 84 , 86, 88, 91/92, 94 96, 98, XP001132173, ISSN: 0192-6225 For example, a suspended stripline stripline is known on a substrate enclosed by two housing halves, with ground metallization attached to the housing. Vias through the substrate connect the two housing halves together. The two housing halves form two ground plans, between which the stripline is arranged.

The invention has for its object to improve a stripline, an attenuator or a terminating resistor of the type mentioned above to the effect that at high cutoff frequency, a high electrical power can be transmitted simultaneously.

This object is achieved by a stripline o.g. Art having the features characterized in claim 1, by an attenuator of o.g. Art having the features characterized in claim 8 and by a terminating resistor of the o.g. Art solved with the features characterized in claim 9. Advantageous embodiments of the invention are described in the further claims.

For a stripline of the o.g. It is inventively provided that the strip line is formed as a coplanar strip line having a signal conductor which is arranged between two ground conductors, wherein along both ground conductors over the entire length of spaced bores are formed, wherein the substrate provided with the coplanar strip line in a tubular outer conductor part of an electrically conductive material is arranged such that the ground lines are electrically connected to the outer conductor part and the signal conductor is arranged at least approximately coaxial with the tubular outer conductor part.

This has the advantage that waveguide modes of the entire, the strip line forming structure are shifted to higher frequencies, so that geometrically large substrates can be used for the transmission of high RF power, even at such frequencies good electrical properties in terms of Have impedance matching or reflection factors or attenuation, where the wavelength is equal to or significantly smaller than the geometric dimensions of the substrate. According to the invention, power attenuation elements or terminating resistors for high power losses can be made available, which at the same time have a high upper cutoff frequency with respect to a predetermined attenuation of the transmitted RF signals, so that spurious modes are suppressed even at high frequencies.

A particularly good electrical efficiency with respect to the displacement of waveguide modes to higher frequencies is achieved by the fact that the bore is completely filled with the electrically conductive material.

Preferably, the bore is formed as a through hole guided through the substrate through hole.

Conveniently, two or more holes are formed parallel to each other.

In a preferred embodiment, three or more bores are formed uniformly spaced along at least one ground line.

Advantageously, for holding the substrate within the outer conductor part on an inner wall of the outer conductor part opposite radial grooves are formed, in which engages the substrate.

Conveniently, a plurality of bores are arranged in at least two spaced-apart planes, wherein on both sides of the signal conductor in each case at least one plane intersects the substrate spaced from the signal conductor. The electrically effective width of the substrate is limited to a region between the two planes, whereas the entire substrate remains effective for dissipating thermal energy.

The invention will be explained in more detail below with reference to the drawing. This shows in the only Fig. A preferred embodiment of a strip line according to the invention in a sectional view.

The sole FIGURE shows a preferred embodiment of a stripline according to the invention in the form of a "suspended" stripline (suspended strip) in the form of a coplanar line, in which a signal conductor 10 is arranged between two ground lines 12. Signal conductor 10 and ground lines 12 are on the first side 16 of the substrate 14 and thus arranged in a common, spanned by the first side 16 plane. The two planes 24 and 26 with the holes 20 are arranged on both sides of the signal conductor 10 and each extending parallel to a longitudinal axis of the ground conductor and the center of the ground conductor 12 and perpendicular to the plane spanned by the first side 16 level. The suspended strip has a cylindrical outer conductor part 30, wherein the substrate 14 is held in inner, radial recesses 32 of the outer conductor part 30 such that the signal conductor 10 extends approximately coaxially with the outer conductor part 30. The outer conductor part 30 is made of an electrically conductive material and is electrically connected to the ground conductors 12. The arranged with respect to the signal conductor 10 on both sides in the planes 24, 26 rows of filled holes 20 form a kind of grid, which limits the electrically effective expansion of the substrate 14 in the lateral direction 28. However, the portions of the substrate 14 which project beyond the planes 24, 26 in the lateral direction 28 remain thermally effective, so that high electrical powers via this strip line according to FIG. 3 also reach their cutoff frequency, such as, for example, 15 GHz to 30 GHz, in particular 18 GHz or 26.5 GHz, can be transmitted.

In the embodiment described above, the excitation of waveguide modes over the entire cross-section of the substrate 14 is avoided by the lattice-forming holes 20 in the planes 24, 26. The filled holes 20 are located in the region of the ground lines 12. The filled holes 20 are arranged in the longitudinal direction 34 along the ground conductor 12 from each other evenly spaced.

Claims (7)

1. Coplanar stripline for high frequency signals, comprising a signal conductor (10) which is arranged between two earth conductors (12) which are disposed on a first side (16) of a substrate (14) made of an electrically insulating material, wherein bores (20) are formed in two planes (24, 26) along both earth conductors (12) over the entire length thereof, wherein the two planes (24, 26) are arranged on either side of the signal conductor (10) and parallel to a longitudinal axis of the earth conductors (12) and centrally to the earth conductors (12) as well as perpendicular to a plane extending from the first side (16) of the substrate (14), wherein the bores (20) are at least partially filled with an electrically conductive material (22) and an electrically conductive connection is formed from each earth conductor (12) to the electrically conductive material (22), characterised in that the coplanar stripline has a tubular external conductor part (30), wherein the substrate (14) provided with the coplanar stripline is arranged in the tubular external conductor part (30) made of an electrically conductive material such that the earth conductors (12) are in direct electrical contact with the external conductor part (30) and the signal conductor (10) is arranged at least approximately coaxial with the tubular external conductor part (30), wherein mutually opposing radial grooves (32) are formed at an inner wall of the external conductor part (30), in which grooves the substrate (14) engages, wherein the rows of filled bores (20) are configured and arranged, relative to the signal conductor (10), on both sides in said planes (24, 26) such that said rows of filled bores constitute a type of grid which delimits the electrically effective extent of the substrate (14) in the lateral direction (28), wherein at the same time, the sections of the substrate (14) projecting in the lateral direction (28) beyond said planes (24, 26) remain thermally effective so that high electrical power levels can be transmitted via the stripline, even to almost the limit frequency thereof.
2. Stripline according to at least one of the preceding claims, characterised in that the bores (20) are entirely filled with the electrically conductive material (22).
3. Stripline according to at least one of the preceding claims, characterised in that the bores (20) are formed as through bores extending completely through the substrate (14).
4. Stripline according to at least one of the preceding claims, characterised in that two or more bores (20) are arranged parallel to one another.
5. Stripline according to at least one of the preceding claims, characterised in that, along at least one earth conductor (12), three of more bores (20) are provided equally spaced apart from one another.
6. Power attenuation member for an HF signal line, characterised in that the power attenuation member comprises a stripline which is configured according to one of the claims 1 to 5.
7. Terminating resistor for an HF signal line, characterised in that the terminating resistor comprises a stripline which is configured according to one of the claims 1 to 5.

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