Patent Description:
The current trend in microwave transmission for measurement as well as for communication is towards higher frequencies. In particular in comparison with existing radar level gauging systems, this increases the demand for available energy which in turn requires new strategies for fulfilling the requirements for Ex certification for explosive environments, and/or new solutions to allow high capacity energy storage.

One such strategy is to encapsulate the electronics of the microwave transmission arrangement (such as according to IEC <NUM>-<NUM>, clause <NUM>) to avoid spark-ignition requirements. This means that the amount of energy storage (capacitance) may be increased but difficulties remain since a signal line from the microwave transceiver circuitry of the microwave transmission arrangement needs to comply with all applicable Ex-related requirements, while still being able to radiate sufficient microwave energy.

<CIT> discloses one approach, in which a dielectric sealing element is arranged inside the hollow waveguide to provide a seal between a main region of the waveguide and a start region of the waveguide, forming a cavity in which a radiator element is arranged.

In the event of leakage at the interface between the dielectric sealing element and the hollow waveguide, inside the hollow waveguide, there is a risk that flammable gas can come into contact with the radiator element, and other unprotected parts of the microwave transceiver circuitry.

It would therefore be desirable to provide an improved microwave transmission arrangement, having an improved encapsulation solution.

<CIT> discloses a high-frequency module for level measurement and a radar level gauge using the high-frequency, where a nonconductive module cover is provided for sealing the radiating element.

In view of the above, a general object of the present invention is to provide an improved microwave transmission arrangement, in particular a microwave transmission arrangement having an improved encapsulation solution.

According to an aspect of the present invention, it is therefore provided a microwave transmission arrangement, comprising: a microwave circuit board including a dielectric carrier, and a first conductor pattern on a first side of the dielectric carrier, the first conductor pattern including a patch for radiating or receiving microwave signals, a patch line, and a first ground plane surrounding the patch and the patch feed line; microwave transceiver circuitry arranged on the microwave circuit board, the microwave transceiver circuitry having an output for providing microwave signals generated by the microwave transceiver circuitry and an input for receiving microwave signals, wherein the patch line is connected to at least one of the output and the input; an electrically conductive hollow waveguide extending from a first end to a second end and arranged to guide microwave signals radiated by the patch from the first end towards the second end, and/or guide received microwave signals from the second end towards the first end; and a separator sheet sandwiched between the microwave circuit board and the first end of the hollow waveguide, the separator sheet being configured to allow passage of microwaves between the patch and the hollow waveguide through the separator sheet, wherein the separator sheet is included in an encapsulation separating an encapsulated interior of the microwave transmission arrangement from an exterior outside the encapsulation, the patch, the patch line, and the microwave transceiver circuitry being in the encapsulated interior, and the hollow waveguide being in the exterior outside the encapsulation, wherein the separator sheet is in direct contact with the first side of the microwave circuit board and the first end of the hollow waveguide, so that there is no internal cavity between the microwave circuit board and the separator sheet.

The "microwave transceiver circuitry" may be implemented as one functional unit capable of transmitting and receiving microwave signals, or may be a system comprising separate transmitter and receiver units.

The present invention is based on the realization that the sensitivity to leaks at a sealing interface can be avoided by sandwiching a separator sheet between the microwave circuit board and the first end of the hollow waveguide. In this way, any leakage along a contact surface between the first end of the hollow waveguide and the separator sheet can be prevented from reaching the patch or the patch line. Through the sandwiching of the separator sheet between the microwave circuit board and the first end of the hollow waveguide, the separator sheet will be in direct contact with the microwave circuit board, so that there is no internal cavity between the microwave circuit board and the separator sheet. Advantageously, the hollow waveguide may be pressed towards the microwave circuit board, so that pressure is applied on the separator sheet.

Through such a configuration, with the separator sheet sandwiched between the microwave circuit board and the first end of the hollow waveguide, the only possible leakage path between the interior of the hollow waveguide and the patch or patch line on the microwave circuit board is through the material of the separator sheet, which is much more unlikely to occur than through a sealing between two parts, so that the sealing provided by the separator sheet can be considered to be infallible.

For efficient transmission of microwaves through the separator sheet, the separator sheet may advantageously comprise a dielectric portion arranged between the patch and the interior of the hollow waveguide. This dielectric portion then acts as a microwave transmission window. The dielectric portion may suitably extend through the entire thickness of the separator sheet between the interior of the hollow waveguide and the patch in the microwave circuit board. Moreover, the dielectric portion may advantageously extend across substantially the entire inner cross-sectional area of the hollow waveguide, at the first end of the hollow waveguide.

For leakage safety, and for avoiding transmission of energy through dielectric breakdown of the dielectric portion, the thickness of the separator sheet, in the dielectric portion, may be at least <NUM>.

According to various embodiments, furthermore, the separator sheet may comprise a dielectric substrate having a first side and a second side opposite the first side; a first conductive layer on the first side of the substrate; a second conductive layer on the second side of the substrate; and a plurality of conductive vias passing through the dielectric substrate and electrically conductively connecting the first conductive layer and the second conductive layer.

For efficient grounding of the electrically conductive hollow waveguide, the first conductive layer of the separator sheet may be electrically conductively connected to the first ground plane of the microwave circuit board; and the second conductive layer of the separator sheet may be electrically conductively connected to the first end of the hollow waveguide.

The respective electrical connections may advantageously be achieved by pressing the hollow waveguide towards the microwave circuit board, thereby pressing the first conductive layer of the separator sheet against the first ground plane of the microwave circuit board and the second conductive layer of the separator sheet against the first end of the hollow waveguide.

The microwave transmission arrangement according to various embodiments of the present invention may advantageously be included in a communication and/or measuring system, further comprising processing circuitry coupled to the microwave transceiver circuitry and configured to control the microwave transceiver circuitry to provide microwave signals and/or to perform signal processing on microwave signals received by the microwave transceiver circuitry.

According to one particular embodiment, this microwave transmission arrangement may advantageously be included in a radar level gauge system for determining the filling level of a product in a tank, the radar level gauge system further comprising an antenna coupled to the second end of the hollow waveguide of the microwave transmission arrangement for radiating an electromagnetic transmit signal from the microwave transmission arrangement towards a surface of the product and for returning an electromagnetic reflection signal resulting from reflection of the electromagnetic transmit signal at the surface back towards the microwave transmission arrangement; and processing circuitry coupled to the microwave transceiver circuitry comprised in the microwave transmission arrangement and configured to determine the filling level based on a timing relation between the transmit signal and the reflection signal.

For all embodiments, it should be noted that the processing circuitry may be provided as one device or several devices working together.

In summary, the present invention thus relates to a microwave transmission arrangement, comprising a microwave circuit board including a patch; microwave transceiver circuitry coupled to the patch; an electrically conductive hollow waveguide arranged to guide microwave signals between a first end and a second end; and a separator sheet sandwiched between the microwave circuit board and the first end of the hollow waveguide, the separator sheet being configured to allow passage of microwaves between the patch and the hollow waveguide through the separator sheet. The separator sheet is included in an encapsulation separating an encapsulated interior of the microwave transmission arrangement from an exterior outside the encapsulation, the patch, and the microwave transceiver circuitry being in the encapsulated interior, and the hollow waveguide being in the exterior outside the encapsulation.

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing a currently preferred embodiment of the invention, wherein:.

In the present detailed description, various embodiments of the microwave transmission arrangement according to the present invention are mainly discussed with reference to a radar level gauge system.

It should be noted that this by no means limits the scope of the present invention, which equally well includes, for example, microwave transmission arrangements used for other applications, such as communication systems, for example microwave links as may, for example, be used in <NUM> communication systems.

<FIG> schematically shows an industry site <NUM>, such as a process industry, for example a refinery or similar. As is schematically shown in <FIG>, the industry site <NUM> includes tanks <NUM> and various process equipment <NUM>. Depending on the type of industry, there may be hazardous environments on the industry site <NUM>, requiring equipment used on the site <NUM> to be certified according to applicable standards. Suitably, at least some of the equipment used on the site <NUM> may fulfill relevant requirements for intrinsic safety, meaning that the equipment is certified as not being capable of causing ignition in a hazardous environment. Examples of applicable standards for intrinsic safety are IEC610079-<NUM> and IEC610079-<NUM>.

Examples of equipment on the industry site <NUM> that may advantageously be configured to fulfill requirements for intrinsic safety may include the microwave link <NUM> and the radar level gauge system <NUM> schematically indicated in <FIG>. Common to such systems according to embodiments of the present invention is that they each include a microwave transmission arrangement for transmission of microwave signals between transceiver circuitry and an antenna. As is well known to those skilled in the relevant art, various specifications may be different for equipment used in a microwave link <NUM> and a radar level gauge system <NUM>, respectively. For instance, the antenna configuration may be specifically adapted to the environment where the antenna is arranged. However, the microwave transmission arrangement used in the various applications may have substantially the same configuration.

<FIG> is a schematic side view of one example application of the microwave transmission arrangement according to embodiments of the present invention, in the form of an exemplary radar level gauge system <NUM>.

As is conceptually indicated in <FIG>, the radar level gauge system <NUM> comprises microwave transceiver circuitry <NUM>, a microwave transmission arrangement <NUM> including a hollow waveguide <NUM>, an antenna <NUM>, processing circuitry <NUM>, communication circuitry <NUM>, and a process connection, here in the form of a flange <NUM>.

The microwave transceiver circuitry <NUM> has an output <NUM> - here shown as a combined microwave output and input port - for providing microwave signals generated by the microwave transceiver circuitry <NUM>, and an input <NUM> for receiving microwave signals. As is schematically indicated in <FIG>, the microwave transceiver circuitry <NUM> also has a measurement data interface <NUM> coupled to a corresponding measurement data interface <NUM> of the processing circuitry <NUM>. The processing circuitry <NUM> additionally has a communication interface <NUM> that is coupled to a corresponding communication interface <NUM> of the communication circuitry <NUM>.

In operation of the radar level gauge system <NUM>, the processing circuitry <NUM> controls the microwave transceiver circuitry <NUM> to generate and transmit microwave transmit signals. The microwave transmit signals are provided by the microwave transceiver circuitry <NUM> to the microwave transmission arrangement <NUM>, which transitions the microwave transmit signals to the antenna <NUM>. Referring briefly to <FIG>, the antenna <NUM> radiates the microwave transmit signals ST towards a surface <NUM> of a product <NUM> in the tank <NUM>. The microwave transmit signals ST are at least partly reflected back towards the antenna <NUM> as microwave reflection signals SR. The microwave reflection signals SR hit the antenna <NUM>, and are guided by the hollow waveguide <NUM> and the microwave transmission arrangement <NUM> transitions the microwave reflection signals SR from signals guided by the hollow waveguide <NUM> to signals carried by a strip-line on a microwave circuit board (not shown in <FIG>) back to the microwave transceiver circuitry <NUM>. Based on a timing relation between the microwave transmit signals ST and the microwave reflection signals SR, the processing circuitry <NUM> determines the filling level of the product <NUM> in the tank <NUM> in a, per se, well-known manner. A communication signal indicative of the determined filling level is communicated to an external host by the communication circuitry <NUM>.

In the microwave link <NUM>, there may be no determination of a distance, but instead data may be encoded on a transmitted signal, and data may be retrieved by decoding a received signal, in ways well-known to those skilled in the relevant art.

<FIG> schematically illustrate a microwave transmission arrangement <NUM> according to example embodiments of the present invention. The microwave transmission arrangement <NUM> of the kind schematically shown in <FIG> may be used in various systems, such as the microwave link <NUM> and the radar level gauge system <NUM> in <FIG>.

Referring first to <FIG>, which is an exploded view of the microwave transmission arrangement <NUM>, the microwave transmission arrangement <NUM> comprises a microwave circuit board <NUM>, microwave transceiver circuitry <NUM>, here in the form of an MMIC (monolithic microwave integrated circuit), an electrically conductive hollow waveguide <NUM>, and a separator sheet <NUM>.

As is shown in <FIG>, but better visible in <FIG>, the microwave circuit board <NUM> includes a dielectric carrier <NUM> and a first conductor pattern on a first side (the top side in <FIG>) of the dielectric carrier <NUM>. The first conductor pattern includes a patch <NUM> for radiating or receiving microwave signals, a patch line <NUM>, and a first ground plane <NUM> surrounding the patch <NUM> and the patch line <NUM>. There is a gap <NUM> in the first conductor pattern separating the patch <NUM> and the first ground plane <NUM>. The patch <NUM> is here shown as being substantially rectangular, because the patch <NUM> is adapted to the hollow waveguide <NUM>. For other waveguide configurations, other patch configurations may be suitable, as will be understood to those skilled in the relevant art.

In the example configuration in <FIG> (best seen in <FIG>), the microwave circuit board <NUM> additionally has a second conductor pattern on a second side of the dielectric carrier <NUM>, opposite the first side. The second conductor pattern includes a second ground plane <NUM> arranged opposite the patch <NUM> and the first ground plane <NUM>. As is schematically shown in <FIG> the first ground plane <NUM> and the second ground plane <NUM> are interconnected by electrically conducting vias <NUM> extending through the dielectric carrier <NUM>.

As can be seen in <FIG>, the microwave transceiver circuitry <NUM> is arranged on the microwave circuit board <NUM>. Although not shown in the figures, the microwave transceiver circuitry <NUM> has an output for providing microwave signals generated by the microwave transceiver circuitry <NUM> and an input for receiving microwave signals. The output and the input may be separate from each other, but in the embodiments shown in <FIG>, the output and the input of the microwave transceiver circuitry are embodied by a common I/O, that is connected to the patch <NUM>, via the patch line <NUM>.

The electrically conductive hollow waveguide <NUM> extends from a first end <NUM> to a second end <NUM>, and is arranged to guide microwave signals radiated by the patch <NUM> from the first end <NUM> towards the second end <NUM> and to guide received microwave signals from the second end <NUM> towards the first end <NUM>.

The hollow waveguide <NUM> has a hollow interior that is defined by an electrically conductive waveguide body <NUM>. Accordingly, the first end <NUM> of the hollow waveguide <NUM> includes a first end surface of the electrically conductive waveguide body <NUM> and a waveguide opening facing the patch <NUM>.

The hollow waveguide <NUM> is configured to guide microwave signals in a predefined wavelength range, in a predefined propagation mode along a signal propagation path defined by the hollow waveguide <NUM>. The predefined wavelength range may, for example, be <NUM>-<NUM>, and the predefined propagation mode may, for example, be TE10, but other wavelength ranges and/or propagation modes are possible and may be beneficial depending on the application.

In the exemplary embodiment of <FIG>, a single patch <NUM> is provided for transmitting and receiving microwaves. It should be noted that the first conductor pattern may equally well include separate transmitter and receiver patches, respectively. Such separate transmitter and receiver patches may advantageously be combined with a hollow waveguide having separate hollow waveguide openings at the first end <NUM> of the hollow waveguide, one hollow waveguide opening for each patch in the first conductor pattern.

The separator sheet <NUM> is sandwiched between the microwave circuit board <NUM> and the first end <NUM> of the hollow waveguide <NUM>, and is configured to allow passage of microwaves between the patch <NUM> (or patches in embodiments with a plurality of patches) and the hollow waveguide <NUM> through the separator sheet <NUM>.

The separator sheet <NUM> is included in an encapsulation separating an encapsulated interior of the microwave transmission arrangement <NUM> from an exterior outside the encapsulation. The patch <NUM>, the patch line <NUM>, and the microwave transceiver circuitry <NUM> are in the encapsulated interior, and the hollow waveguide <NUM> (the interior of the hollow waveguide) is in the exterior outside the encapsulation.

As is perhaps best seen in <FIG>, the separator sheet <NUM> is sandwiched between a top surface of the microwave circuit board <NUM> and the first end <NUM> of the hollow waveguide (the first end surface of the electrically conductive waveguide body <NUM> as well as the waveguide opening facing the patch <NUM>). Hereby, a first side <NUM> of the separator sheet <NUM> is in contact with the top surface of the microwave circuit board <NUM> and a second side <NUM> of the separator sheet <NUM> is in contact with the first end <NUM> of the hollow waveguide <NUM>.

In addition to the separator sheet <NUM>, the above-mentioned encapsulation includes a potting compound <NUM> that at least partly fills a housing <NUM> of the microwave transmission arrangement <NUM>. The hollow waveguide <NUM> may be pressed against the microwave circuit board <NUM>, for instance using screws (not shown in <FIG>). Hereby, potting compound <NUM> can be kept out of the pressurized stack formed by the microwave circuit board <NUM>, the separator sheet <NUM>, and the hollow waveguide <NUM>. However, potting compound <NUM> will cover edge surfaces of the separator sheet <NUM>, so that the interfaces between the hollow waveguide <NUM> and the separator sheet <NUM>, and between the separator sheet <NUM> and the microwave circuit board <NUM> are covered by the potting compound <NUM>.

As is schematically shown in <FIG>, there may be a through-going hole <NUM> in the waveguide body <NUM>, configured to accommodate the MMIC <NUM>. Before providing the potting compound <NUM>, a barrier may be provided for preventing the potting compound <NUM> from entering a narrow space between the MMIC <NUM> and the microwave circuit board <NUM>. Such a barrier may, for example, be provided by dispensing, through the hole <NUM>, another potting compound with a higher viscosity, and/or by inserting a sealing body in the through-hole <NUM>.

Referring to <FIG>, the separator sheet <NUM> may comprise a dielectric portion <NUM> arranged between the patch <NUM> and an interior of the hollow waveguide <NUM>, at the first end <NUM> of the hollow waveguide <NUM> to allow microwave signals to propagate between the patch <NUM> and the interior of the hollow waveguide <NUM>, through the dielectric portion <NUM> of the separator sheet <NUM>. To provide for an explosion proof configuration, in compliance with the relevant standards, a thickness of the separator sheet <NUM>, in the dielectric portion <NUM>, may be at least <NUM>. The material of the dielectric portion may advantageously be robust and durable, and have a relatively high dielectric strength. Examples of suitable dielectric materials include low loss substrates suitable for high frequency microwave use. Examples of suitable materials may include ceramics, PTFE, and hybrid configurations including PTFE with various fillers.

To provide for a favorable combination of the sealing and electrical separation provided by the separator sheet <NUM>, and the microwave transmission performance of the microwave transmission arrangement <NUM>, the separator sheet <NUM> may advantageously be configured to additionally provide for grounding of the hollow waveguide <NUM>. Therefore, referring to <FIG> and <FIG>, the separator sheet <NUM> may comprise a dielectric substrate <NUM>, a first conductive layer <NUM> on a first side of the dielectric substrate <NUM>, a second conductive layer <NUM> on a second side of the dielectric substrate <NUM>, and a plurality of conductive vias <NUM> passing through the dielectric substrate <NUM> and electrically conductively connecting the first conductive layer <NUM> and the second conductive layer <NUM>. The vias <NUM> are filled, and not open.

In the example embodiment in <FIG>, the first conductive layer <NUM> of the separator sheet <NUM> is electrically conductively connected to the first ground plane <NUM> of the microwave circuit board, and the second conductive layer <NUM> of the separator sheet is electrically conductively connected to the first end <NUM> of the hollow waveguide (to the end surface of the hollow waveguide body <NUM>).

To provide the above-mentioned dielectric portion <NUM> of the separator sheet <NUM>, the first conductive layer <NUM> of the separator sheet <NUM> may have an open portion, and the second conductive layer <NUM> of the separator sheet <NUM> may have an open portion aligned with the open portion of the first conductive layer <NUM>. This example configuration is schematically illustrated in <FIG> and <FIG>.

Furthermore, the first conductive layer <NUM> defines an open channel <NUM> that is aligned with the patch line <NUM> of the microwave circuit board <NUM>, to further reduce any impact of the separator sheet <NUM> on the microwave transmission performance of the microwave transmission arrangement <NUM>.

Claim 1:
A microwave transmission arrangement (<NUM>), comprising:
a microwave circuit board (<NUM>) including a dielectric carrier (<NUM>), and a first conductor pattern on a first side of the dielectric carrier (<NUM>), the first conductor pattern including a patch (<NUM>) for radiating or receiving microwave signals, a patch line (<NUM>), and a first ground plane (<NUM>) surrounding the patch (<NUM>) and the patch feed line (<NUM>);
microwave transceiver circuitry (<NUM>) arranged on the microwave circuit board (<NUM>), the microwave transceiver circuitry (<NUM>) having an output for providing microwave signals generated by the microwave transceiver circuitry (<NUM>) and an input for receiving microwave signals, wherein the patch line (<NUM>) is connected to at least one of the output and the input;
an electrically conductive hollow waveguide (<NUM>) extending from a first end (<NUM>) to a second end and arranged to guide microwave signals radiated by the patch (<NUM>) from the first end towards the second end, and/or guide received microwave signals from the second end towards the first end (<NUM>); and
a separator sheet (<NUM>) sandwiched between the microwave circuit board (<NUM>) and the first end (<NUM>) of the hollow waveguide (<NUM>), the separator sheet (<NUM>) being configured to allow passage of microwaves between the patch (<NUM>) and the hollow waveguide (<NUM>) through the separator sheet (<NUM>),
wherein the separator sheet (<NUM>) is included in an encapsulation separating an encapsulated interior of the microwave transmission arrangement (<NUM>) from an exterior outside the encapsulation, the patch (<NUM>), the patch line (<NUM>), and the microwave transceiver circuitry (<NUM>) being in the encapsulated interior, and the hollow waveguide (<NUM>) being in the exterior outside the encapsulation, characterized in that the separator sheet (<NUM>) is in direct contact with the first side of the microwave circuit board (<NUM>) and the first end (<NUM>) of the hollow waveguide (<NUM>), so that there is no internal cavity between the microwave circuit board (<NUM>) and the separator sheet (<NUM>).