Test probe for high-frequency measurementTechnical Field
The invention relates to a test probe (test rod) for high-frequency measurements, having a contact-side end for electrical contact with a planar structure and a cable-side end for connection to a cable, in particular a coaxial cable-side end, wherein a coplanar conductor structure having at least two conductors, in particular three conductors, is arranged between the contact-side end and the cable-side end, a dielectric for supporting the coplanar conductor structure being arranged in the coplanar conductor structure, the dielectric being arranged on one or both sides in a predetermined interval between the cable-side end and the contact-side end, wherein the test probe is designed such that: the conductors of the coplanar conductor structure are arranged freely in space and suspended with respect to the dielectric for support, between the dielectric and the contact-side end.
Background
Such test probes are known, for example, from DE 19945178 a 1. It is advantageous that a test probe with impedance control is possible, which can be economically manufactured even in mass production, and has high accuracy, thereby minimizing reflection (reflection) generated in a process of contacting a planar structure for measurement purposes. The arrangement according to the invention is characterized by an operating frequency of up to 40-60Hz or more, wherein the impedance is substantially dispersion-free (i.e. independent of the operating frequency) throughout the coplanar conductor structure due to the design according to the invention. The freely suspended arrangement of the conductors in the coplanar conductor structure between the dielectric and the side ends of the coaxial cable means that a high contact quality between all the conductors of the coplanar conductor structure and the corresponding contact points of the device to be measured is ensured, wherein the contact quality is insensitive in the case of a test probe placed at an angle on the contact points of the planar structure.
From US 5565788 a shielded microwave test probe is known having a coaxial cable end connected to probe fingers forming a coplanar conductor, the probe fingers including ground and signal probe fingers. The ground probe fingers are connected to each other via the shielding element. The shield element is spaced a distance from the signal probe finger and is disposed between the signal probe finger and the device under test to prevent the generation of external signals or parasitic coupling from the device under test that could impair measurement accuracy.
Disclosure of Invention
The invention is based on the problem of further improving the test probe of the aforementioned type with respect to electrical properties.
According to the invention, this problem is solved by a test probe of the aforementioned type having the following features.
A test probe for high-frequency measurements, having a contact-side end for electrical contact with a planar structure and a cable-side end for connection to a cable, in particular a coaxial cable-side end, wherein a coplanar conductor structure having at least two conductors, in particular three conductors, is arranged between the contact-side end and the cable-side end, wherein a dielectric for supporting the coplanar conductor structure is arranged in the coplanar conductor structure, which dielectric is arranged in a predetermined interval between the cable-side end and the contact-side end on one or both sides, wherein the test probe is designed to: between the dielectric and the contact-side end, the conductors of the coplanar conductor structure are arranged in a spatially free and suspended manner with respect to the dielectric for supporting, wherein the side of the test probe facing the planar structure when in contact therewith is provided with a shielding element which is designed in such a way that it extends between the dielectric and the contact-side end into the region of the coplanar conductor structure arranged in a spatially free and suspended manner with respect to the dielectric for supporting.
In a test probe of the above-mentioned type, according to the invention, a shielding element is arranged and designed on one side of the test probe, which shielding element faces the planar structure when the test probe is in contact with the planar structure, so that the shielding element extends between the dielectric and the contact-side end into the region of a coplanar conductor structure which is suspended freely in space and elastically with respect to the supporting dielectric, wherein the test probe has a housing made of an electrically conductive material, with which the shielding element is electrically connected.
It is advantageous that the coplanar conductor structures suspended in a manner free in space and resilient with respect to the supporting dielectric are electrically shielded from the planar structure, so that undesired crosstalk of electrical signals from the planar structure to the freely suspended portions of the coplanar conductor structures is effectively prevented, while undesired electrical effects, in particular in terms of calibration (calibration), caused by the proximity between the coplanar conductor structures and the planar structure are avoided or at least significantly reduced.
Advantageous embodiments of the invention are described in the following schemes.
The particularly good electrical shielding of the planar structure in combination with the small thickness of the shielding element of the coplanar conductor structure is achieved in that the shielding element is made of an electrically conductive material.
In a preferred embodiment, the shielding element is electrically connected to at least one conductor in a coplanar conductor structure which is freely suspended in space and which is arranged in a resilient manner with respect to the supporting dielectric.
Advantageously, the shielding element is electrically connected at one end facing the contact-side end of the test probe to at least one conductor of a coplanar conductor structure which is freely suspended in space and which is arranged in a resilient manner with respect to the supporting dielectric.
A particularly simple construction of the electrical contact between the shielding element and the conductors of the coplanar conductor structure is achieved by mechanically connecting the shielding element also with the at least one conductor in the coplanar conductor structure which is freely suspended in space and which is configured in a resilient manner with respect to the supporting dielectric.
In a preferred embodiment, the conductor of the coplanar conductor structure to which the shielding element is electrically or mechanically connected is a ground conductor.
In a preferred embodiment, the coplanar conductor structure has three conductors, with the center conductor being a signal conductor and the other two conductors being ground conductors.
In order to further improve the shielding, an additional shielding element is arranged on the side of the test probe opposite to the side, which additional shielding element is designed such that it extends between the dielectric and the contact-side end into the region of the coplanar conductor structure arranged in a freely suspended and resilient manner in the space with respect to the supporting dielectric.
Drawings
The invention is described in more detail below with reference to the attached drawing figures, wherein:
figure 1 shows a preferred embodiment of a test probe according to the invention seen from below on the side facing the planar conductor structure,
figure 2 shows a side view of the test probe according to figure 1,
figure 3 shows an enlarged detail view of region a of figure 2,
fig. 4 shows a front view of the test probe according to fig. 1, which shows the contact-side end of the test probe in the direction of the arrow B in fig. 3.
Detailed Description
The preferred embodiment of the test probe according to the present invention shown in fig. 1 to 4 includes: a housing 10; a coaxial cable side end 12 having a coaxial plug connector 14 for connection with a coaxial cable (not shown); a contact-side end 16 for contacting the planar structure 38; and a coplanar conductor structure having a middle signal conductor 18 and two ground conductors 20 and disposed between the coaxial cable side end 12 and the contact side end 16. A gap 22 is formed between the signal conductor 18 and the adjacent ground conductor 20 of the coplanar conductor structure. The gap 22 is formed over the entire length of the coplanar conductor structures 18, 20 so that a constant predetermined characteristic impedance is obtained.
In the central region between the coaxial-cable-side end 12 and the contact-side end 16, the coplanar conductor structures 18, 20 are held by a dielectric 24 (fig. 4), for example in the form of a quartz block, wherein the dielectric 24 is arranged on one or both sides of the coplanar conductor structures 18, 20, so that each side of the coplanar conductor structures 18, 20 is held by the dielectric 24. The dielectric 24 and coplanar conductor structures 18, 20 are placed together in a sandwich-like configuration. A dielectric 24 is fixedly connected to the coplanar conductor structures 18, 20, which dielectric carries a metallization (metallization) on the side facing the coplanar conductor structures 18, 20, which metallization corresponds substantially to the shape of the coplanar conductor structures 18, 20 in the region of the dielectric 24. In this way, a particularly strong and tight connection is achieved between the dielectric 24 and the conductors 18, 20 of the coplanar conductor structure. Due to the electromagnetic relationship with the dielectric 24, the gap 22 widens in the region of the dielectric 24, so that a generally constant characteristic impedance is obtained over the entire length of the coplanar conductor structures 18, 20 from the coaxial-cable-side end 12 to the contact-side end 16. The dielectric 24 is embedded in the housing 10 in such a way that the dielectric 24 is flush with the end 40 of the housing 10 facing the contact-side end 16.
The conductors 18, 20 are freely arranged in the space of the region 26 between the dielectric 24 and the contact-side end 16, so that the respective conductor 18, 20 is elastic with respect to its mounting in the dielectric 24. If the contact-side end 16 of the test probe is mechanically pressed against a corresponding contact point on the planar structure 38, e.g. a circuit to be tested, the possibility that each individual conductor 18, 20 of the coplanar conductor structure is free to spring back (resilient) means that each individual conductor 18, 20 has an electrical contact optimized for the contact point assigned to it. Any tilting of the test probe when mechanically pressed against the contact point, and any tolerances in the conductors 18, 20 themselves and in the surface of the contact point of the planar structure 38, are compensated by the elasticity of the individual conductors 18, 20. As a result, always the same (always-identified) and defined contact is established each time the conductors 18, 20 are mechanically applied to the corresponding contact points, so that optimum measurements can be obtained with the test probe according to the invention.
The representation of a test probe with three conductors 18, 20 arranged in a ground-signal-ground or g-s-g (g ═ ground, s ═ signal) manner is intended as an example only. Of course, a coplanar conductor configuration with only two conductors 18, 20 or more than three conductors 18, 20 is also possible, with signal and ground conductors being divided into the following forms: g-s-g-s-g-s-g. In this manner, a circuit under test having several coplanar signal conductors with contact points on a planar structure can be contacted using a single test probe.
Optionally, the entire surface of the dielectric 24 on the side away from the coplanar conductor structures 18, 20 is metallized (not shown). This metallization results on the one hand in the suppression of undesired high-order modes outside the desired operating frequency, while forming a closed system over the entire predetermined area of the coplanar conductor structures 18, 20.
At the contact-side end 16, the conductors 18, 20 of the coplanar conductor structure are reduced to the end points (point)28 of the signal conductors 18 and the end points 30 of the ground conductors 20, thereby forming an arrangement of the conductors 18, 20 corresponding to the arrangement of the planar structure 38 to be contacted, in particular the contact points of the circuit to be tested.
A particularly prominent property of the test probe according to the present invention shown in fig. 1-4 is that the impedance established by means of the gap 22 throughout the coplanar conductor structures 18, 20 is substantially free-dispersing, i.e. the impedance and phase velocity are substantially independent of the operating frequency.
According to the invention, a shielding element 34 is also arranged on the side 32 of the test probe, said side 32 being the side facing the planar structure 38 when the test probe is brought into contact with the contact point of the planar structure 38 (see fig. 2, 3). Fig. 1 shows a view of the side 32 of the test probe. The shield element 34 extends between the coaxial-cable-side end 12 and the contact-side end 16 into the region 26 in which the conductors 18, 20 are freely suspended in space.
When a test probe is brought into contact with a contact point on the planar structure 38, the shielding element 34 is thus spatially disposed between the planar structure 38 and the coplanar conductor structures 18, 20, as shown in fig. 2 and 3, thereby electrically and electromagnetically shielding the coplanar conductor structures 18, 20 from the planar structure 38 or the circuit under test. This effectively prevents or at least significantly reduces the undesirable effects of the planar structure 38 on the test probe or coplanar conductor structure 18, 20. These undesirable effects include, for example: the intrusion or crosstalk (crosstalk) of electrical signals originating from the planar structure 38 into the coplanar conductor structures 18, 20, or the variation of the coplanar conductor structures 18, 20, for example, with respect to calibrated electrical characteristics. All of this can result in undesirable variations in the measurement results when the planar structure 38 is tested using a test probe.
The shielding element 34 is connected in an electrically conductive manner, indicated with 35 in fig. 1, to the housing 10. The housing 10, which is preferably made of an electrically conductive material, is electrically connected to the ground contact by means of corresponding electrical connections, so that the housing 10 forms a defined ground level, and the shielding element 34 thus also forms a defined ground level. Preferably, the shielding element 34 is also made of an electrically conductive material, so that shielding can be achieved with a small thickness of the shielding element 34.
In order to further increase the shielding function of the shielding element 34, the shielding element 34 is electrically connected to the two ground conductors 20 via contact points 36 at the end of the shielding element facing the contact-side end 16 of the test probe. By means of a corresponding movable or flexible design of the shielding element 34, the movability of the measuring conductor 20 in the region 26 is influenced only to a negligible extent.