Horn antenna

A horn antenna for a radar measuring device, particularly a radar level gauge, with an antenna horn emitting at the front in a primary direction of emission, a rear feed device, and a filling, which at least partially fills the horn antenna and seals it at the front, with at least one seal being arranged between the filling and the antenna horn, with the seal being arranged in a radial direction perpendicular in reference to the primary direction of emission of the horn antenna at least partially outside the antenna horn or an extension of the antenna horn.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to European Patent Application 15 194470.9, filed on Nov. 13, 2015.

No federal government funds were used in researching or developing this invention.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

SEQUENCE LISTING INCLUDED AND INCORPORATED BY REFERENCE HEREIN

Not applicable.

BACKGROUND

1. Field of the Invention

The present invention relates to a horn antenna.

2. Background of the Invention

Radar measuring devices are known from prior art, particularly radar level gauges, which based on the principle of acoustical logging detect a fill level of a fill good located in a container, particularly liquids and bulk goods. Such radar level gauges are equipped with horn antennas, for example, by which a coupled HF-signal is emitted in the direction of the fill good and is reflected thereby. In a combined transceiver system of the radar level gauge the microwave pulses reflected by the fill good are detected and by way of measuring the elapsed time of said pulses a distance is determined from the fill level gauge to the fill good.

In general, horn antennas show a simple and robust design, very good effectivity, and they can be produced in a cost-effective fashion. However, as soon as the interior of the antenna horn becomes soiled, this has negative effects upon the performance of the horn antenna.

Therefore it is known from prior art to protect the antennas of such fill level gauges from soiling and/or corrosion caused by aggressive measuring environments. This is achieved for example by covering the antennas at the front with a blister or to fill the horn with a medium, e.g., synthetic material.

Although covering the horn antenna with a blister is able to keep soiling and aggressive media from the antenna horn, however such horn antennas are still not suitable for the use in pressurized environments or in a vacuum.

Accordingly, in prior art there are horn antennas in which the antenna horn is filled completely with a solid medium, e.g., a synthetic material. Here, a gap between the antenna horn and the filling must be sealed in a pressure-tight fashion in order to prevent any undesired media from penetrating in the feed direction and reaching the electronics. In prior art usually O-rings are used as seals between the antenna horn and the dielectric in the area of the antenna at the front in a primary direction of emission. However, inside the antenna these O-rings generate reflections of the electromagnetic waves fed therein, which reflect a portion of the inserted energy back to the source, for example a hollow conductor, resulting in worsened return loss and thus lower antenna yields. Accordingly the effectiveness of the antenna is reduced.

The reflected energy generates a so-called pseudo-echo in the radar device, which leads to increased antenna ringing.

It has been acknowledged that the reason for this type of reflections is caused primarily in the different dielectricity values between the O-ring and the filler of the antenna horn, and thus the material of the O-ring is directly of influence upon the characteristic of the antenna. If different seals and/or O-rings are used for various purposes of the antenna here the performance of the antenna changes. This is considered disadvantageous.

The objective of the present invention is to further develop an antenna known from prior art such that any antenna ringing is minimized to the extent possible and undesired reflections inside the antenna are eliminated. Further, any sensitivity shall be prevented of the antenna towards various materials of the seals.

This objective is attained in a horn antenna as described herein.

BRIEF SUMMARY OF THE INVENTION

In a preferred embodiment, a horn antenna (1) for a radar measuring device, particularly a radar level gauge, with an antenna horn (3) emitting at the front in a primary direction of emission, a feed device (5) at the rear, and a filling (7), which at least partially fills the horn antenna (1) and seals it at the front, with between the filling (7) and the antenna horn (3) at least one seal (9) being arranged, characterized in that the seal (9) is arranged in a radial direction (R) perpendicular in reference to the primary direction of emission (HA) of the horn antenna (1) at least partially outside the antenna horn (3) or an extension (V) of the antenna horn (3).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the seal (9) is embodied as an O-ring (91,92).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the seal (9) is arranged in a groove (71,72,31,32).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the antenna horn (3) comprises at least in the proximity of the seal (9) an attachment (11) pointing outwardly in the radial direction (R).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the attachment (11) is embodied as a step (11) projecting outwardly in the radial direction (R) comprising a circumferential collar (12) and/or a circumferential groove (31,32,33) extending in the primary direction of emission (HA).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the filling (7) comprises in the proximity of the seal (9) a groove (71,72) for at least partially accepting the seal (9).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that a circumferential centering ring (15) is arranged between the antenna horn (3) and the filling (7).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the centering ring (15) is embodied as an O-ring (91,92).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that the centering ring (15) is arranged in a circumferential third groove (33) of the antenna horn (3).

In another preferred embodiment, a horn antenna (1) as described herein, characterized in that at least two O-rings (91,92) are arranged in a frontal section in the primary direction of emission (HA) and one centering ring (15) in a rear section in a primary direction of emission (HA).

DETAILED DESCRIPTION OF THE INVENTION

A horn antenna according to the invention for a radar measuring device, particularly a radar level gauge, comprises an antenna horn, emitting radiation in a frontal direction, a rear feeding device, and a filling, which at least partially fills the horn antenna and seals it towards the front, with at least one seal being arranged between the filling and the antenna horn. A horn antenna according to the invention is characterized in that the seal is arranged in a radial direction perpendicular in reference to the primary direction of emission of the horn antenna, at least partially outside the antenna horn, or a virtual extension of the antenna horn. Due to the fact that the electromagnetic waves coupled in the horn antenna typically propagate inside the filling, which is usually made from a dielectric material, with the direction of propagation normally being predetermined by a conical design of the antenna horn, by an arrangement of the seals at least partially outside the antenna horn and/or outside an extension of the antenna horn here a more distinct function can be yielded of the reflections generated by the boundary between the material of the filling and the material of the seal.

Ideally the seals are arranged completely outside a contour of the antenna horn, so that such reflections can be completely avoided at a boundary between the filling and the seal.

Here it shall be mentioned that in the sense of the present application an arrangement of the seal at least partially outside the antenna horn or an extension of the antenna horn shall be understood such that the seal is arranged at least partially outside a linear extension or, in case of an interruption of the contour of the antenna horn, partially outside a linear extension of this contour.

In principle, any suitable material can be used as a gasket for sealing the gap between the antenna horn and the filling. However, a particularly simple embodiment can be achieved when the seal is embodied as an O-ring, because such O-rings are freely available in the market in a plurality of embodiments and materials.

An arrangement of the seal predetermined in reference to the antenna horn and the filling as well as a clever arrangement outside the antenna horn and/or an extension of the antenna horn can be yielded when the seals are arranged in a groove. Such a groove may be provided for example in the antenna horn and/or the filling.

For example, in the proximity of the seal the antenna horn may at least show an attachment pointing outwardly in a radial direction. Such an attachment can be embodied for example as a step projecting outwardly in the radial direction with a circumferential collar and/or a circumferential groove extending in the primary direction of emission. By such attachments, using simple means an accepting seat can be generated for one or more seals, which in the sense of the present invention is arranged outside the antenna horn and/or a virtual extension or continuation of the antenna horn.

By a step projecting outwardly further a mechanic support of the filling can be yielded and thus increased strength of the antenna overall can be insured to resist pressures.

Additionally or alternatively in the proximity of the seal the filling may show a groove for an at least partial acceptance of the seal. This may be advantageous, for example, when the antenna horn shows an attachment projecting outwardly in the area at the front in the primary direction of emission, which is also filled with the material of the filling, however is located outside a virtual extension of the antenna horn. A groove for accepting the seal may be arranged in such an area of the filling so that a sealing arrangement can be yielded in a simple fashion.

A circumferential centering ring may further be arranged between the antenna horn and the filling in order to ensure an arrangement of the filling inside the antenna horn as symmetrical and centered as possible. The centering ring may also be arranged in a groove of the antenna horn projecting outwardly, with the centering ring perhaps being embodied as an O-ring as well to ensure a simple design.

In order to ensure a centered coupling of the electromagnetic waves in the filling, here the centering ring can be arranged for example in an end section of the filling facing the feed. This way it is ensured that this filling is aligned in a centered fashion in reference to the feed.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1shows a perspective illustration of a horn antenna1in a longitudinal section in the primary direction of emission HA. An antenna horn3of the horn antenna1is essentially embodied as a conically designed metallic jacket, at which in the primary direction of emission HA at the front a step11, projecting outwardly, is arranged with a circumferential collar12extending in the primary direction of emission HA. By the step11projecting outwardly and the collar12here a cylindrical section is formed at the front of the antenna horn3, which in the present exemplary embodiment, similarly to the antenna horn3, is almost completely filled with a filling7. The filling7is embodied conically at the rear area seen in the primary direction of emission HA, with an apex extending in the direction of a feed device5, formed at the rear at the horn antenna1, at the front of a hollow conductor.

At the front in the primary direction of emission HA the filling7comprises a convexly shaped exposed surface19, which contributes by a lens-effect to the directional characteristic of the horn antenna1. The filling7is circumferentially sealed towards the circumferential collar12via a first O-ring91and a second O-ring92, which in the present exemplary embodiment are arranged in two circumferential grooves71,72arranged in the filling7. Both the two grooves71,72as well as the O-rings91,92arranged therein, as indicated in the illustration ofFIG. 1, are arranged at least partially outside a linear extension V of the antenna horn3. In the present exemplary embodiment the first O-ring91is arranged by approximately 50% outside said extension V and the second O-ring92is arranged completely outside the extension V, so that the reflections of electromagnetic waves are considerably reduced at a boundary between the filling7and the O-rings91,92.

By the step11it is further achieved that the filling7is provided in the rear direction with a circumferential reinforcement, allowing to yield increased pressure resistance of the horn antenna1.

In order to yield a centered alignment of the filling7in reference to the feed device5embodied as a hollow conductor, further a circumferential centering ring15is arranged between the antenna horn3and the filling7, which in the present exemplary embodiment is also embodied as an O-ring. In order to also reduce reflections at this centering ring15or to avoid it entirely, if possible, the centering ring15comprises a third groove33of the antenna horn3projecting radially outwardly, so that the centering ring15is also at least partially distanced from the area of propagation of the electromagnetic waves. In order to ensure a correct alignment of the filling7inside the antenna horn3, in the present exemplary embodiment a centering brace16, projecting circumferentially inwardly, is provided at the transition between the antenna horn3to the step11projecting radially outwardly, which adjusts a distance between the filling7and the antenna horn3in a frontal section of the horn antenna1.

FIG. 2shows an alternative embodiment of a frontal section of the horn antenna1ofFIG. 1.

The alternative embodiment ofFIG. 2shows the circumferential collar12with an increased wall thickness so that the first groove31and the second groove32may be provided circumferentially in the collar12to accept the first O-ring91and the second O-ring92.

This way the material of the filling7can be embodied at this point without any grooves, allowing a further reduction of potential boundary reflections. Contrary to the exemplary embodiment shown inFIG. 1, according toFIG. 2both O-rings91,92are arranged outside an extension V of the antenna horn3such that here a particularly effective reduction of interferences can be yielded.FIG. 2shows once more clearly the circumferential centering brace16which ensures an alignment of the filling7in reference to the antenna horn3in the frontal area.

FIG. 3shows an alternative embodiment of a rear section of the horn antenna1ofFIG. 1seen in the primary direction of emission HA.

The embodiment according toFIG. 3differs essentially such that any centering of the filling7in reference to the antenna horn3, particularly in reference to the feed device5embodied as a hollow conductor, is not achieved by an O-ring arranged in a groove projecting outwardly but by an attachment75provided circumferentially at the filling7. Such an attachment75can also yield a centered alignment of the filling7in reference to the feed device5, by which a defined air gap17can be adjusted over the entire length of the filling7between the filling7and the antenna horn3. Compared to a circumferential groove with an O-ring arranged therein, an appropriate attachment75leads to reduced production expenses, thus with lower costs a comparably good result can be yielded.

FIG. 4shows as an example the propagation of the electromagnetic waves inside a horn antenna1. The propagation shown inFIG. 4is illustrated using an example of a horn antenna1with a section at the front according toFIG. 1and a rear section according toFIG. 3. As discernible from the illustration ofFIG. 4, at the O-rings91,92as well as the attachment75only minor interferences of the propagation of the electromagnetic waves are discernible inside the horn antenna1, so that the effect according to the invention is very well achieved.

LIST OF REFERENCE NUMBERS:

1horn antenna3antenna horn5direction of feed7filling9seal11step12collar15centering ring16centering brace17air gap19exposed area31first groove of the antenna horn32second groove of the antenna horn33third groove of the antenna horn71first groove of the filling72second groove of the filling75attachment91first O-ring92second O-ringHA primary direction of emissionR radial directionV extension

The references recited herein are incorporated herein in their entirety, particularly as they relate to teaching the level of ordinary skill in this art and for any disclosure necessary for the commoner understanding of the subject matter of the claimed invention. It will be clear to a person of ordinary skill in the art that the above embodiments may be altered or that insubstantial changes may be made without departing from the scope of the invention. Accordingly, the scope of the invention is determined by the scope of the following claims and their equitable equivalents.