WO2013092356A1

WO2013092356A1 - Test card for printed circuit card in the field of wireless systems

Info

Publication number: WO2013092356A1
Application number: PCT/EP2012/075290
Authority: WO
Inventors: Dominique Lo Hine Tong; Philippe Minard; Ali Louzir
Original assignee: Thomson Licensing
Priority date: 2011-12-22
Filing date: 2012-12-12
Publication date: 2013-06-27
Also published as: CN104115328A; CN104115328B; FR2976146A1; HK1203245A1; BR112014014915A2

Abstract

The present invention relates to a test card for printed circuit card comprising a radiofrequency circuit linked by a transmission line (18) to an antenna (3), characterized in that the test card consists of a substrate comprising at least one dielectric substrate layer (10), said substrate being furnished on one face with a first conducting zone receiving the test connector, said first conducting zone being linked to a second conducting zone on the opposite face of the substrate, the test card comprising at least one power supply line (15) linked to the first conducting zone and forming at least one means making it possible to create at the level of the antenna an electromagnetic coupling of line/slot type and a means (16) for returning a quasi-zero impedance at the level of the coupling.

Description

TEST CARD FOR CIRCUIT BOARD PRINTED IN THE FIELD OF WIRELESS SYSTEMS

The present invention relates to a test card for a printed circuit board used in the field of wireless systems. The present invention also relates to a printed circuit board allowing the use of said test card.

STATE OF THE ART

PCBs, known as PCBs

(for Printed Circuit Board in English) used in wireless systems, generally comprise two major parts, namely a transmitter / receiver part and an "antenna" part. During the mass production of such a system, it is difficult to correctly check the performance of the transceiver circuit through the antenna. As a result, a switchable test connector soldered to the circuit surface between the transmitter / receiver part and the antenna part is used. The test connectors currently used are surface mount components of the CMS type. The connector is mechanically switchable and operates such that in operational mode, the connector is short-circuited and the signal arriving at the transceiver is directly connected to the antenna at insertion losses near the connector and, in test mode, a test probe is inserted into the connector of the card, which has the effect of disconnecting the antenna path of the transmitter / receiver path and recovering the transmitter / receiver signal.

Test connectors of this type are widely used in all types of wireless systems such as mobile phones, gateways or gateways, set-top boxes and other WiFi systems. Current technology allows testing up to 6 GHz.

FIGS. 1a and 1b show the position of a conventional test connector in the case of a printed circuit board comprising an antenna 3 of the Vivaldi type made on the substrate 1 of the card also called motherboard. More specifically, on the substrate 1 of the printed circuit board, a metal layer 2 has been deposited forming a ground plane into which the slot antenna 3 has been etched, which, in the embodiment shown, is a Vivaldi-type antenna. . On the face of the substrate opposite to the face receiving the ground plane 2, the feed line 4 of the antenna for supplying the antenna by electromagnetic coupling between the line 4 and the slot 3 has been made, this line extending to the transmitter / receiver portion made on the printed circuit board or motherboard. As shown in FIGS. 1a and 1b, on this line 5 has been mounted a switchable test connector 5.

However, this well-known solution of the prior art has two main disadvantages. Firstly, this type of connector has a high cost, but wireless systems are increasingly oriented MIMO (for Multiple Input Multiple Output in English), therefore the number of antennas connected to the transmitter / receiver part in a WiFi system increases significantly, resulting in the use of a large number of switchable test connectors and, as a result, the cost of connectors currently accounts for about 20% of the cost of the printed circuit board or motherboard . There is therefore a demand from the manufacturers to find a solution to limit the use of these switchable test connectors.

Second, these switchable test connectors have an impact on system performance. Indeed, these connectors being placed at the output of the transmitter / receiver part, insertion losses have a direct impact on the sensitivity of the receiver and on the output power transmitted. Thus, typically towards the 5 GHz frequency band, the insertion loss due to the test connectors is of the order of 0.3 - 0.4 dB.

To overcome these drawbacks, new solutions have been proposed for testing printed circuit boards. Thus, in US Patent 7746062 in the name of Hon Hai Precision Indus., It has been proposed a radio frequency test card which comprises two pellets, one connected to the output of the transceiver part while the other pellet is connected to the antenna part at a distance from the first pellet equal to λ / 4 where λ is the operating wavelength. The second wafer is electrically grounded so that an open circuit is formed at the first wafer and, therefore, the sender / receiver signal is directed only to the test probe on the wafer 1. This solution can only work with a limited frequency bandwidth and can not be applied to WiFi systems operating in the 5 GHz band or, even more so, in two different frequency bands, namely bands 2.4 and 5. GHz.

SUMMARY OF THE INVENTION

The present invention aims to overcome the problems mentioned above by providing a test card operating in a wide frequency band and having the lowest possible cost.

The subject of the present invention is therefore a test card for a printed circuit board comprising a radio-frequency circuit connected by a transmission line to an antenna, characterized in that the test card consists of a substrate comprising at least one dielectric substrate layer, said substrate being provided on one side with a first conductive zone receiving the test connector, said conductive zone being connected to a second conductive zone on the opposite face of the substrate, the test card comprising at least one supply line connected to the first conductive area and forming at least one means for creating at the antenna an electromagnetic coupling line / slot, and means for returning an impedance at the line / slot coupling point almost zero.

On the other hand, according to a first embodiment, the means for returning a quasi-zero impedance at the line / slot coupling point is constituted by an insulated line positioned parallel to the supply line. According to another embodiment, the means for returning to the level of the line / slot coupling point a quasi-zero impedance is constituted by two ground line sections positioned on the motherboard on each side of the excitation line of the antenna.

The isolated line which serves to short-circuit the fields at the opening of the antenna is a printed line whose two ends are in open circuit. When the antenna is a slot-type antenna, the supply line is a microstrip line, one end of which is connected to the first conductive zone and the other end of which is in an open circuit. In this case, the supply line may be made either on the face of the substrate opposite the face of the test connector, or on the face receiving the test connector or, in the case of a multilayer substrate, on one of the intermediate faces.

To allow short-circuiting of the fields at the antenna opening, the isolated line is, in this embodiment, positioned at a distance k / 4 from the feed line where k is an integer and λ is the length wave in the transmission line at the center frequency of the operating band of the system.

According to another embodiment, when the antenna is a printed antenna connected to the radio frequency circuit by a microstrip line or a monopole type antenna connected to the radio frequency circuit by a coplanar line or microstrip, the substrate is a multilayer substrate and the line feed is constituted by a slit line made in an intermediate conductive layer. In this case, the supply line is connected to the first conductive zone by a second line / slot transition and the isolated line is positioned at a distance k / 2 from the supply line where k is an integer and λ is the length wave in the transmission line at the center frequency of the operating band of the system.

The present invention also relates to a printed circuit board comprising a radio frequency circuit connected by a transmission line to an antenna, characterized in that it comprises, next to the transmission line and the antenna, at least one conducting zone. forming mass. Preferably, the card comprises, next to the antenna, at least one pattern made on the printed circuit.

The printed circuit board allows the implementation of a test card as described above.

Thus, the present invention relates to a printed circuit board comprising a radio frequency circuit connected by a transmission line to an antenna allowing the implementation of a test card, characterized in that it comprises next to the transmission line. and the antenna, at least one conductive area forming mass to be brought into contact with the second conductive area of the test card.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will appear on reading the detailed description given below with reference to the accompanying drawings, in which:

FIGS. 1a and 1b, already described, respectively represent a top plan view and a schematic perspective view of the antenna portion of a printed circuit board or motherboard provided with a switchable test connector according to FIG. prior art.

Figures 2a and 2b schematically show a view from below (Figure 2a) and a top view (Figure 2b) of a test card according to the present invention.

Figure 3 is a schematic sectional view of the test card of Figures 2a and 2b and a printed circuit board for receiving the test card.

Figures 4a and 4b are a schematic representation in plan respectively of the printed circuit board or motherboard (Figure 4a) and the motherboard provided with the test card shown in Figures 2 (Figure 4b).

FIG. 5 represents the transmission and reflection diagrams of the signal transmitted between the transmitter / receiver part and the test probe of a simulated test card according to FIGS. 2a and 2b. Figure 6 is a schematic sectional view of another embodiment of a test card according to the present invention and the motherboard receiving this test card.

Fig. 7 is a schematic sectional view of a further embodiment of a test card according to the present invention and the associated motherboard.

FIGS. 8a and 8b are respectively, for FIG. 8a, a plan view of another additional embodiment of a test card according to the present invention positioned on a motherboard and, for FIG. 8b, a view of schematic section of the test card and the associated motherboard.

FIGS. 9a and 9b are respectively, for FIG. 9a, a plan view from above of a further embodiment of a test card according to the present invention positioned on a motherboard and, for FIG. 9b, a schematic sectional view of the test card and the motherboard with which it is used.

Figures 10a and 10b are respectively, for Figure 10a, a schematic top plan view of yet another embodiment of a test card according to the present invention and the associated motherboard and, for the figure 10b, a schematic sectional view of the test card and the associated motherboard shown in FIG. 10a.

DETAILED DESCRIPTION OF THE INVENTION

It will be recalled first of all that the present invention implements, for the operation of the test card, the electromagnetic coupling of a line / slot with a printed line known as the Knorr coupling. In this case, a microstrip line printed on one side of a multilayer substrate crosses a line-slot made in the opposite face of the substrate. The microstrip line has an open-circuit end positioned at a distance λ / 4 from the crossing point (λ being the wavelength in the line at the working frequency), which means that the microstrip line brings back a short plane - circuit at this point. The line-slot has a short circuit at a distance λ '/ 4 of the crossing point (λ' being the wavelength in the slot), which means that the line-slot brings an open circuit plane to the level of the crossover point, which effectively transmit a microwave signal microstrip mode to the slot mode or vice versa.

This being recalled, a first embodiment of a test card according to the present invention will first be described with reference to FIGS. 2 to 5.

As shown in FIGS. 2a and 2b, on a substrate 1 0 which is, in the embodiment shown, a simple printed double-sided dielectric substrate, a conductive zone 13 and a power supply line have been formed on the underside. Forming at its free end 1 5a an open circuit and the other end 1 5b is connected by a metallized hole 14 to a zone 12 on the upper face of the test card 1 0 intended to receive the test probe.

On the other hand, on the upper face of the test card 1 0 is formed a conductive zone 1 1 which is electrically connected by metallized holes for example, to the zone 1 3, this zone 1 1 being intended to form the zone mass of a conventional test connector. This is actually the solder areas of the connector for the ground, while the area 12 is soldered to the signal area of the connector.

As shown in FIG. 2a, a printed insulated line 16 is made on the underside of the test card. This line 1 6 is made parallel to the supply line 15 receiving the test signal at a distance Wk / 4 of the line 1 5 with k an integer and λ the wavelength of the transmission line.

As shown diagrammatically with reference to FIGS. 3 and 4a and 4b, when it is desired to carry out a test, the test card 10 is brought into contact with the motherboard 1.

In the embodiment shown in FIG. 4a, on the upper face of the substrate receiving the transmission line 1 8 feeding the Vivaldi antenna 3, a mass zone 17 having a shape substantially identical to the zone 13 made on the card 10 has been made. This zone 17 is connected by metallized holes to the ground plane 2 formed on the lower face of the substrate 1 constituting the motherboard. Thus, as shown in FIG. 3 and in FIG. 4b, the test card is applied to the Vivaldi antenna 3 so that the zone 13 is in contact with the zone 17 to connect the motherboard mass to that of the motherboard. test card. The isolated line 16 having circuits open at each end is placed perpendicular to the slot of the Vivaldi type antenna 3 and symmetrically with respect to the axis of symmetry of said antenna. Therefore, the power supply line 15 is placed perpendicular to the slot of the Vivaldi type antenna forming a line-slot type electromagnetic coupling operating as recalled above. The precise positioning of the test card with respect to the motherboard can be achieved by using printed patterns on the motherboard, this operation being done automatically in the mass production phase, thanks to optical control equipment.

When the test card is positioned as shown in Figure 4b, the test can be performed in a conventional manner through a test connector 19 welded to the areas 1 1 and 12 of the motherboard. Due to its position relative to the line 15 operating according to the Knorr principle, the isolated line 16 has the role of short-circuiting the slot of the Vivaldi-type slot antenna 3 in the operating frequency band, because it makes it possible to reduce a quasi-zero impedance to the level of the plane of the supply line 15 in order to limit as much as possible the radiation of the slot. The length of this line 16 is determined to be able to create the short circuit and it corresponds to approximately λ / 2 where λ is the wavelength in the line in microstrip mode. The isolated line 16 thus reduces a quasi-zero impedance corresponding to a short circuit at the supply line 15 of the test signal, thereby enabling the maximum power transfer from the excitation line 18 of the antenna Vivaldi to line 15 of the test card. The concept described above was simulated using a Vivaldi-type slot antenna printed on a dielectric substrate known as RO4003 with a thickness of 0.81 mm and a permittivity of 3.38, the Vivaldi type antenna operating in the 5 MHz band. GHz. To validate the concept, electromagnetic simulations using the IE3D software were performed on a structure conforming to that shown in Figure 4a. The results of the simulations relating to the quality of transmission of the signal from the transmitter / receiver part to the test probe are shown in FIG. 5 which gives, for the curve dB [S (2.1)], the transmission response. and for the curve dB [S (1, 1)] the reflection response. These curves give the following performances: low insertion losses of the order of 0.8 to 1 .6 dB, 4.9 to 6 GHz and good adaptation greater than 18 dB in a very wide band largely covering the operating band.

Two other embodiments of a test card according to the present invention and operating with a motherboard having, in the antenna part, a slot-type antenna will now be described with reference to FIGS. 6 and 7. As shown in FIGS. 6 and 7, in this case the antenna-slot is made on the upper part of the substrate 1, namely in the conductive layer 2a, and this antenna-slot is electromagnetically coupled between the slot and the slot. feed line 18a made on the underside of the substrate 1. Two different embodiments of a test card can then be used.

According to a first embodiment shown in FIG. 6, the test card 10 comprises on its upper face the conductive zone 1 1 connected to the conductive zone 13 by metallized holes to form a ground zone on which the connector of FIG. test 19. The supply line 15a is formed on the upper part of the substrate 10 of the test card, so as to form a line-slot coupling with the slot not shown and made in the metal layer 2a of the motherboard. As in the case of the first embodiment, the insulated line 16 which short-circuits the slot is made on the underside of the substrate 10. The mass transfer, between the zones 1 1, 13 and the zone 17 of the motherboard, is carried out identically to the previous embodiment.

According to one variant, the test card represented in FIG. 7 was made using, for the test card, a multilayer substrate, namely a substrate comprising a first substrate 10a and a second substrate 10b. In this case, the supply line 15c, which is used for the electromagnetic coupling with the slot antenna of the motherboard, is made in the conductive layer between the two substrates 10a and 10b. This supply line 15c is connected by a metallized hole to an end of the supply line 15b connected to the test connector 19.

In this embodiment, the two substrates 10a and 10b may have identical or different characteristics in particular in terms of thickness and permittivity, the supply line of the test signal 15c being printed on the intermediate conductive layer. The first substrate, namely the lower substrate 10b, has the role of enabling the required coupling between the supply line 15c and the slot of the slot antenna and the second substrate, namely the upper substrate 10a, has the purpose to ensure the mechanical rigidity of the assembly and to conform to the usual design rules of muticouche circuits. .

With reference to FIGS. 8 to 10, reference will now be made to other embodiments of the test card that is applicable, in particular with printed antennas such as "patch" type antennas or monopole antennas.

FIG. 8a shows a view from above of a test card positioned on a motherboard comprising a patch antenna 20 connected to an excitation line 21, made by a microstrip line printed on the upper face of the substrate 22 forming the motherboard provided with a conductive layer 23 forming a ground plane.

In this embodiment and as shown in FIG. 8b, the test card is made using a multilayer substrate comprising, in the present case, two dielectric layers 24a and 24b and three conductive layers referenced C1, C2, C3. To be able to couple the excitation line 21 of the patch antenna 20 with the supply line 30 of the test connector 29 using an electromagnetic line-slot coupling, a slot 25 is formed in the intermediate conductive layer C2.

As shown in FIG. 8a, the line-slot 25 terminates in a short circuit 25a which is at a length substantially equal to λ / 4 (λ wavelength in the slot) of the intersection point A between the excitation line 21 and the feed slot 25.

On the other hand, as shown in FIG. 8b, the test card also comprises a conductive ground zone 26 formed in the conductive layer C1 and connected by metallized holes passing through the two substrates to a conducting mass zone 27 made in the conductive layer C3. The zone 26 forms the grounding zone of the test connector 29. Likewise, as in the previous embodiments, an insulated line 28 is made in the lower conductive layer C3. The isolated line 28 is used to reduce a short-circuit or quasi-zero impedance in the plane of intersection between the excitation line 21 and the power slot line 25, namely the plane passing through the point d In this case, the isolated line 23 is positioned at a distance of the order Ι <λ / 2 where k is an integer and λ is the wavelength in the excitation line 21.

In the embodiment shown in FIG. 8a, to recover the test signal from the slot line 25 at the test connector 29, a second line-to-slot transition is made between the slot 25 and the microwave power supply line. ribbon 30 made in the conductive layer C1. One end of the micro-ribbon line 30 is connected to the point 30a forming the signal welding zone of the test connector 29, the other end 30b of the micro-ribbon line 30 forming an open circuit and being positioned at a distance λ ' / 4 of the intersection point of the plane B (λ 'being the wavelength in the micro-ribbon line) while the line / slot 25 ends with a short-circuit 25b at a distance λ / 4 from the point of intersection B (λ being the wavelength in the line-slot). We will now describe with reference to FIGS. 9a and 9b, another variant embodiment which applies to the case where an antenna 40 such as a monopole type antenna is excited by a coplanar line 41.

In the embodiment shown in FIG. 9b, the test card is a card made on a multilayer substrate comprising two dielectric layers 42a, 42b and three conductive layers C1, C2, C3. In this case, the test card is similar to that of Figure 8b. In the intermediate conductive layer C2, a line-slot 43 has been formed forming the supply line for the test signal. On the underside of the test card, were made in the conductive layer C3, the mass transfer zone 44 and the isolated line 45. In the conductive layer C1 of the upper face of the test card, were carried out the mass transfer zone 46 connected by metallized holes to the mass transfer zone 44 and the power supply line 47 of the test connector 48.

As shown in FIG. 9a, the test card is positioned above the coplanar line, as in the embodiment of FIG. 8a, namely the excitation line 41 forms with the slot 43 a line-to-line transition. slot for transmitting the test signal by electromagnetic coupling at the point A. On the other hand, a second line-slot transition for transmitting the test signal of the slot line 43 to the connection point 47a with the connector of test 48 is performed at point B. The sizing of the various elements 47, 43 and 45 are made as in the embodiment of Figures 8a and 8b.

A variant embodiment of a test card operating with an antenna 50 of monopole or "patch" type made on the underside of the motherboard, as shown in FIG. 1, will now be described with reference to FIGS. 10a and 10b. 10b. In this case, the excitation line 51 is a coplanar line.

In this embodiment, the test card is made on a substrate with a single dielectric layer 53 with two conductive layers C1 and C2. To achieve the electromagnetic coupling between the excitation line 51 of the antenna and the power supply line 57 of the connector of test 55, a slot line 54 has been etched in the conductive layer C2 with dimensions in accordance with those mentioned above. On the other hand, on the upper conductive layer C1 receiving the test connector 55, a conducting zone 56 connected by metallized holes to the lower conductive layer C2 has been produced to obtain a mass transfer and the test connector 55 is connected. by a second line-slot transition to the line-slot 54 by a line 57 made in the conductive layer C1.

In this embodiment, the two line-slot transitions take place, as shown in FIG. 10a, respectively at the points A and B, the different lines and slots being dimensioned to satisfy the Knorr principle, as recalled above.

In this case, the means for bringing a short-circuit plane to the point of intersection A is constituted by two line elements 52a, 52b made on the upper face of the motherboard substrate on each side. the excitation line of the antenna 51 at a distance from the intersection point A calculated to impose the short-circuit plane when the test card is brought into contact with the circuit to be tested.

Claims

1 - Test card for a printed circuit board comprising a radio frequency circuit connected by a transmission line (18, 18a, 21, 41, 51) to an antenna (3, 20, 40, 50), characterized in that the card test consists of a substrate comprising at least one dielectric substrate layer (10; 10a; 10b; 24a; 24b; 42a; 42b; 53), said substrate being provided on one face with a first conductive zone (1 1, 2646, 56) receiving the test connector (19, 29, 48, 55), said first conductive area being connected to a second conductive area (13, 27, 44) on the opposite side of the substrate, the test comprising at least one supply line (15, 25, 43, 54) connected to the first conductive zone and forming at least one means for creating at the antenna an electromagnetic coupling of line / slot type and a means (16,28,45,52a, 52b) to reduce at the coupling level a quasi-zero impedance.

2- test card according to claim 1, characterized in that the means for returning at the coupling a quasi-zero impedance is constituted by an isolated line (16,28,45) positioned parallel to the supply line.

3- test card according to claim 2, characterized in that the isolated line is a printed line whose two ends are in open circuit.

4- test card according to one of claims 1 to 3, characterized in that, when the antenna is a slot-type antenna, the supply line is a micro-ribbon line (15), one end of which is connected to the first conductive zone and the other end is in open circuit. 5- test card according to claim 4, characterized in that the supply line is formed on the face of the substrate opposite to the face receiving the test connector, on the face receiving the test connector or, in the case of a multilayer substrate, on one of the intermediate faces.

6- test card according to one of claims 4 or 5, characterized in that the isolated line is positioned at a distance k / 4 of the supply line where k is an integer and λ the wavelength in the transmission line.

7- Test card according to one of claims 1 to 2, characterized in that, when the antenna is a printed antenna connected to the radio frequency circuit by a micro-ribbon line or a monopole type antenna connected to the radio frequency circuit by a coplanar line or micro ribbon, the substrate is a multi-layer substrate and the feed line is constituted by a slot line (25,43,54) made in an intermediate conductive layer.

8- Test card according to claim 7, characterized in that the supply line is connected to the first conductive zone by a second line / slot transition.

9- Test card according to one of claims 7 or 8, characterized in that the isolated line (28,45) is positioned at a distance k / 2 of the supply line where k is an integer and λ the length wave of the transmission line.

10- Printed circuit board comprising a radio frequency circuit connected by a transmission line to an antenna, characterized in that it comprises next to the transmission line and the antenna, at least one conductive area forming mass. 1 1 - printed circuit board according to claim 10, characterized in that it comprises, next to the antenna, at least one pattern made on the printed circuit. 12- Printed circuit board according to one of the claims

10 and 1 1, characterized in that it allows the implementation of a test card according to one of claims 1 to 9.

13- printed circuit board comprising a radio frequency circuit connected by a transmission line to an antenna allowing the implementation of a test card according to one of claims 1 to 9, characterized in that it comprises of the transmission line and the antenna, at least one conductive area forming a mass intended to be brought into contact with the second conductive zone of the test card.