DK180061B1

DK180061B1 - A radar system comprising two back-to-back positioned radar antenna modules

Info

Publication number: DK180061B1
Application number: DKPA201870259A
Authority: DK
Inventors: van der Meer Rob; Hamminga Siete
Original assignee: Robin Radar Facilities Bv
Priority date: 2018-05-01
Filing date: 2018-05-01
Publication date: 2020-02-27
Also published as: DK201870259A1

Abstract

A radar system comprising a first and a second antenna module is provided, where each of the antenna modules comprises a first planar slotted waveguide antenna array configured for radiating electromagnetic waves, and a second planar slotted waveguide antenna array configured for receiving electromagnetic waves. For each of the antenna modules, each of the planar slotted waveguide antenna arrays comprises several longitudinal extending waveguide columns disposed in a parallel and adjacent position with respect to one another, wherein the waveguide columns have a front side and a rear side with a plurality of cavity slots on the front side. For each of the antenna modules, the first and second antenna arrays are arranged with the longitudinal direction of the waveguide columns extending in a single, horizontal direction, and with the waveguide columns of the first antenna array disposed below and in a parallel position to the waveguide columns of the second antenna array. The radar system further comprises a rotation system configured for supporting and rotating the first and second antenna modules around a vertical axis, with the first and second antenna modules arranged in a back-to-back position on opposite sides of a plane intersecting the vertical axis of rotation, and with the rear side of the waveguide columns of the antenna arrays of the first antenna module facing the rear side of the waveguide columns of the antenna arrays of the second antenna module. The radar system may further comprise a protective housing in the form of a radome covering the first and second antenna modules.

Description

A RADAR SYSTEM COMPRISING TWO BACK-TO-BACK POSITIONED RADAR ANTENNA MODULES

TECHNICAL FIELD

The disclosure relates generally to a radar system comprising two back-to-back positioned radar antenna modules. In particular, the disclosure relates to back-to-back positioned radar antenna modules holding cavity slotted-waveguide antenna arrays for radiating and receiving radar wave signals.

BACKGROUND

In the prior art, slotted-waveguide antennas, SWA, are well-known, where the waveguides may be arranged in an array of waveguides, such as a planar array of parallel waveguides. As the name suggests, slotted-waveguide antennas consist of lengths of waveguides with a multiple number of slots formed in the conducting walls of the waveguides. These slots introduce discontinuities in the conductor and interrupt the flow of current along the waveguide. Instead, the current must flow around the edges of the slots, causing them to act as dipole antennas.

The two basic types of SWAs are standing wave and traveling wave antennas. In a traveling wave SWA, the waveguide is built with matched loads or absorbers at the end, while in a standing wave SWA, the end of the waveguide is short-circuited.

Depending on the desired electric field polarization, the slots can be placed on either the narrow or broad wall of the waveguide. At the fundamental TE10 mode, longitudinal slots on the broad wall will produce a field with vertical polarization, while transverse slots on the narrow wall result in a horizontal field polarization.

For antenna systems used to detect small targets, such as birds or Unmanned Aerial Vehicles, UAV's, in a clutter rich environment, a horizontal polarization is preferred, which can be obtained by using an array of waveguides with transverse slots on the narrow wall.

Multi-beam radar systems with Frequency Modulated Continuous Wave, FMCW, waveforms is known in the art, and by using an antenna holding cavity slotted-waveguide arrays for transmitting and receiving electromagnetic waves, it is possible to obtain a multibeam FMCW antenna system, which is very compact in size, and which is suitable for detecting small targets, such as birds or UAV,s.

When detecting small objects or targets, it is required to have a high signal to noise ratio. A higher signal to noise ratio may be obtained by having an increased radar signal exposure time on the object or target.

It would be advantageous to have an improved cavity slotted-waveguide antenna system, which allows a high radar signal exposure time on an object or target, thereby increasing the possibility of a correct classification of detected objects or targets.

SUMMARY

It is an object of the invention to provide a cavity slotted-waveguide antenna array system, which allows a high radar signal exposure time on an object or target.

According to a first aspect there is provided a radar system comprising a first and a second antenna module, each said antenna module comprising:

a first planar slotted waveguide antenna array configured for radiating electromagnetic waves; and a second planar slotted waveguide antenna array configured for receiving electromagnetic waves;

wherein for each of the antenna modules, each planar slotted waveguide antenna array comprises several longitudinal extending waveguide columns disposed in a parallel and adjacent position with respect to one another, said waveguide columns having a front side and a rear side with a plurality of cavity slots on the front side, and said waveguide columns further having first and second column ends; and wherein for each of the antenna modules, the first and second antenna arrays are arranged with the longitudinal direction of the waveguide columns extending in a single, horizontal direction, and with the waveguide columns of the first antenna array disposed below and in a parallel position to the waveguide columns of the second antenna array;

said radar system further comprising a rotation system configured for supporting and rotating the first and second antenna modules around a vertical axis, with the first and second antenna modules arranged in a back-to-back position on opposite sides of a plane intersecting the vertical axis of rotation, and with the rear side of the waveguide columns of the antenna arrays of the first antenna module facing the rear side of the waveguide columns of the antenna arrays of the second antenna module.

Thus, the front side of the waveguide columns of the antenna arrays of the first antenna module faces away from the front side of the waveguide columns of the antenna arrays of the second antenna module. This allows the first and second antenna modules to transmit electromagnetic waves in different directions. By having a rotating radar system with two back-to-back positioned antenna modules, it is possible to decrease the speed of rotation to half the speed of a rotating radar system, which comprises only a single radar module, while still having the same speed of update of radar tracks obtained from received signals being reflected from detected objects or targets. By lowering the speed of rotation, a higher signal exposure time on target is obtained, resulting in a higher signal to noise ratio, which again results in more information of any detected target or object.

In a possible implementation form of the first aspect, the system further comprises a protective housing in the form of a radome covering said first and second antenna modules.

In a possible implementation form of the first aspect, the radome is arranged in a fixed position without following the rotation of the rotation system and the antenna modules. It is also within an alternative embodiment that the radome is connected to the rotational system for being rotated by the rotation of the rotational system.

In a possible implementation form of the first aspect, the waveguide columns within the first and second antenna arrays of both the first and second antenna modules have equal dimensions or equal mechanical dimensions. By having equal dimensioned waveguide columns for both antenna modules, it is possible to operate within the same frequency band for both antenna modules.

In a possible implementation form of the first aspect, then for one or both of the antenna modules, the front side of the columns holding the cavity slots of both the first and second antenna arrays are positioned substantially in the same plane. By having the radiating and receiving arrays in the same plane, a simplified manufacture of the antenna module may be obtained.

In a possible implementation form of the first aspect, then for one or both of the antenna modules, the cavity slots on the front side of the columns of the first array are arranged in a first plane, and the cavity slots on the front side of the columns of the second array are arranged in a second plane, and the first and second arrays are positioned with an angle between said first plane and said second plane. This angle should be a blunt or abuse angle, which may be closer to 180° than to 90°. By having the radiating and receiving arrays in angled planes, a higher scanning coverage may be obtained.

In a possible implementation form of the first aspect, the cavity slots on the front side of the columns of the second antenna array of the first antenna module are arranged in a partially upwards facing plane having a first acute angle to the vertical direction, and the cavity slots on the front side of the columns of the first antenna array of the second module are arranged in a partially upwards facing plane having a second acute angle to the vertical direction. In a possible implementation form of the first aspect, the first acute angle is substantial equal to the second acute angle.

In a possible implementation form of the first aspect, the first and second acute angles are in the range of 10-30°, such as about 20°.

In a possible implementation form of the first aspect, the first and second antenna module are arranged in a mirrored position relative to said plane intersecting the vertical axis of rotation.

In a possible implementation form of the first aspect, the radome has a dome shaped upper part. The dome shape gives an increased mechanical strength.

In a possible implementation form of the first aspect, the radome is made of a material having a high electromagnetic transparency, such as a plastic material, such as a polyethylene (PE) or polypropylene (PP) based material, such as a polyethylene (PE) or polypropylene (PP) based ultra heigh molecular weight plastic material.

In a possible implementation form of the first aspect, the radome is made of a material having a thickness in the range of 1-3mm, such as in the range of 1-2mm or such as in the range of 1-1,5 mm.

When having two back-to-back simultaneously operating antenna modules, it is important to minimize reflection of signals transmitted or radiated from the radiating array of one module to the receiving array of the other module. By reducing the material thickness of the radome, the electromagnetic transparency of the radome is increased, thereby minimizing the internal reflection from the radome. By using a PE or PP based material, such as a PE or PP based ultra heigh molecular weight plastic material, the electromagnetic transparency of the radome is increased even further.

In a possible implementation form of the first aspect, then for one or both antenna modules, an electromagnetic shield or shield plate is arranged substantially parallel to the waveguide columns and between the first lower radiating antenna array and the second upper receiving antenna array, said shield or shield plate extending outwards from the front side of the antenna module.

In a possible implementation form of the first aspect, the electromagnetic shield or shield plate is an electromagnetic absorbing shield or shield plate, or the shield or shield plate is fully or at least partly covered by an electromagnetic absorbing material.

In a possible implementation form of the first aspect, then for one or both antenna modules, a lower electromagnetic absorber shield or shield plate, which is fully or at least partly covered by an electromagnetic absorbing material, is arranged substantially parallel to the waveguide columns and below the lowermost waveguide column of the first lower radiating antenna array, said lower absorber shield or absorbing covered shield plate extending outwards from the front side of the antenna module.

In a possible implementation form of the first aspect, then for one or both antenna modules, an upper electromagnetic absorber shield or shield plate, which is fully or at least partly covered by an electromagnetic absorbing material, is arranged substantially parallel to the waveguide columns and above the uppermost waveguide column of the second upper receiving antenna array, said upper absorber shield or absorbing covered shield plate extending outwards from the front side of the antenna module.

In a possible implementation form of the first aspect, the electromagnetic absorber shield or electromagnetic absorbing material comprises a carbon loaded foam material, such as a carbon loaded foam tape.

In a possible implementation form of the first aspect, the electromagnetic absorber shield or electromagnetic absorbing material has a thickness in the range of 4-12mm, such as in the range of 5-10 mm, such as in the range of 5-8 mm, such as about 6 mm.

In a possible implementation form of the first aspect, then for one or both antenna modules, the first antenna array holds a number of parallel plate blinds secured to the front side of the first antenna array besides or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns of the first antenna array.

In a possible implementation form of the first aspect, then for one or both antenna modules, the second antenna array holds a number of parallel plate blinds secured to the front side of the second antenna array besides or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns of the second antenna array.

The plate blinds are vertical blinds or baffles for reducing electromagnetic power radiated in the cross-polarization, that is blinds or baffles for cross-polarization suppression. The plate blinds may be substantially U-shaped with two parallel side plates and a bottom plate.

By having the electromagnetic absorbing shield between the radiating array and the receiving array, and by having the lower and upper electromagnetic absorbing shields, the internal reflection of electromagnetic signals between and alongside the vertical plate blinds is reduced.

In a possible implementation form of the first aspect, each or at least part of the plate blinds is secured to the front side of the corresponding antenna array by one or more sliding dovetail joints.

The tail of a dovetail joint may be formed at a bottom part of the plate blind and the socket of the dovetail joint may be formed in at least the outermost positioned waveguide columns of the antenna array. The waveguide columns with no dovetail socket may hold a cut-out corresponding to the width of the bottom of the plate blinds. The use of dovetail joints and cut-outs serves to increase the mechanical stabilization of the arrays, and to keep the waveguide columns in alignment.

In a possible implementation form of the first aspect, then for one or both antenna modules, the waveguide columns of the first and second antenna arrays are of equal length.

In a possible implementation form of the first aspect, then for one or both antenna modules, the first ends of the waveguide columns of both the first and second antenna arrays are aligned in a direction perpendicular to the longitudinal direction of the waveguide columns, and the second ends of the waveguide columns of both the first and second antenna arrays are also aligned in a direction perpendicular to the longitudinal direction of the waveguide columns.

In a possible implementation form of the first aspect, then for one or both antenna modules, the waveguide columns of both the first and second antenna arrays hold an absorbing load within the second column end.

By having aligned waveguide columns with absorbing loads, the antenna arrays may function in the travelling wave mode.

In a possible implementation form of the first aspect, then for one or both antenna modules, the number of waveguide columns in the second receiving array is larger than the number of waveguide columns in the first radiating array.

In a possible implementation form of the first aspect, then for one or both antenna modules, the number of waveguide columns in the second receiving array is twice the number of waveguide columns in the first radiating array.

In a possible implementation form of the first aspect, then for one or both antenna modules, the first radiating array comprises four waveguide columns, and the second receiving array comprises eight waveguide columns.

In a possible implementation form of the first aspect, then for one or both antenna modules, a radiating signal probe is operably disposed in each column of the first antenna array, and a receiving signal probe is operably disposed in each column of the second antenna array.

In a possible implementation form of the first aspect, then for each waveguide column holding a signal probe, the signal probe is disposed proximal to the first end of the waveguide column. The signal probes may be loop probes with a loop or an open-ended loop for emitting and/or receiving the electromagnetic signal.

In a possible implementation form of the first aspect, the system further comprises a signal generating system holding a single signal generator, and the first antenna module holds first electronic transmit circuitry configured for feeding the first radiating array of the first antenna module to radiate first electromagnetic signals, and the second antenna module holds second electronic transmit circuitry configured for feeding the first radiating array of the second antenna module to radiate second electromagnetic signals, said first and second electromagnetic signals being fully synchronized electromagnetic signals based at least partly on signals provided by said single signal generator.

In a possible implementation form of the first aspect, the first antenna module holds first electronic receive circuitry configured for processing signals received by the second receiving array of the first antenna module, and the second antenna module holds second electronic receive circuitry configured for processing signals received by the second receiving array of the second antenna module, said first and second electronic receive circuitry being configured for processing the received signals in synchronization with the radiated electromagnetic signals, said synchronization being based on signals provided by the single signal generator.

In a possible implementation form of the first aspect, the system further comprises:

first processing circuitry for processing signals received by the first antenna module, said first processing circuitry being configured to provide first type radar plots of detected objects presented by said signals received by the first antenna module; and second processing circuitry for processing signals received by the second antenna module, said second processing circuitry being configured to provide second type radar plots of detected objects presented by said signals received by the second antenna module.

radar track processing circuitry, said radar track processing circuitry being configured to provide a radar track for a detected object based on both the first and the second type radar plots.

According to a second aspect there is provided a radar antenna module comprising:

a first planar slotted waveguide antenna array configured for radiating electromagnetic waves; and a second slotted waveguide antenna array configured for receiving electromagnetic waves;

wherein each planar slotted waveguide antenna array comprises several longitudinal extending waveguide columns disposed in a parallel and adjacent position with respect to one another, said waveguide columns having a front side and a rear side with a plurality of cavity slots on the front side, and said waveguide columns further having first and second column ends; and wherein the first and second antenna arrays are arranged with the waveguide columns of the first antenna array disposed in a parallel position to the waveguide columns of the second antenna array.

In a possible implementation form of the second aspect, the front side of the columns holding the cavity slots of both the first and second planar arrays are positioned substantially in the same plane. By having the radiating and receiving arrays in the same plane, a simplified manufacture of the antenna module may be obtained.

In a possible implementation form of the second aspect, the cavity slots on the front side of the columns of the first array are arranged in a first plane, and the cavity slots on the front side of the columns of the second array are arranged in a second plane, and the first and second arrays are positioned with an angle between said first plane and said second plane. This angle should be a blunt or abuse angle, which may be closer to 180° than to 90°. By having the radiating and receiving arrays in angled planes, a higher scanning coverage may be obtained.

In a possible implementation form of the second aspect, the first planar antenna array is a narrow sided slotted waveguide antenna array configured for radiating horizontal polarized electromagnetic waves, and the second planar antenna array is a narrow sided slotted waveguide antenna array configured for receiving horizontal polarized electromagnetic waves.

In a possible implementation form of the second aspect, the waveguide columns of the first and second antenna arrays are of equal length.

In a possible implementation form of the second aspect, an electromagnetic shield or shield plate is arranged substantially parallel to the waveguide columns and between the first radiating antenna array and the second receiving antenna array, said shield or shield plate extending outwards from the front side of the antenna module.

In a possible implementation form of the second aspect, the electromagnetic shield or shield plate is an electromagnetic absorbing shield or shield plate, or the shield or shield plate is fully or at least partly covered by an electromagnetic absorbing material.

In a possible implementation form of the second aspect, the first planar slotted waveguide antenna array is positioned as a lower radiating antenna array, and the second slotted waveguide antenna array is positioned above the first array as an upper receiving antenna array.

In a possible implementation form of the second aspect, a first or lower electromagnetic absorber shield or shield plate, which is fully or at least partly covered by an electromagnetic absorbing material, is arranged substantially parallel to the waveguide columns and below the lowermost waveguide column of the first lower radiating antenna array, said lower absorber shield or absorbing covered shield plate extending outwards from the front side of the antenna module.

In a possible implementation form of the second aspect, a second or upper electromagnetic absorber shield or shield plate, which is fully or at least partly covered by an electromagnetic absorbing material, is arranged substantially parallel to the waveguide columns and above the uppermost waveguide column of the second upper receiving antenna array, said upper absorber shield or absorbing covered shield plate extending outwards from the front side of the antenna module.

In a possible implementation form of the second aspect, the electromagnetic absorber shield or electromagnetic absorbing material comprises a carbon loaded foam material, such as a carbon loaded foam tape.

In a possible implementation form of the second aspect, the electromagnetic absorber shield or electromagnetic absorbing material has a thickness in the range of 4-12mm, such as in the range of 5-10 mm, such as in the range of 5-8 mm, such as about 6 mm.

In a possible implementation form of the second aspect, the first antenna array holds a number of parallel plate blinds secured to the front side of the first antenna array besides or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns of the first antenna array.

In a possible implementation form of the second aspect, the second antenna array holds a number of parallel plate blinds secured to the front side of the second antenna array besides or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns of the second antenna array. The plate blinds are vertical blinds or baffles for reducing electromagnetic power radiated in the crosspolarization, that is blinds or baffles for cross-polarization suppression. The plate blinds may be substantially U-shaped with two parallel side plates and a bottom plate.

In a possible implementation form of the second aspect, each or at least part of the plate blinds is secured to the front side of the corresponding antenna array by one or more sliding dovetail joints. The tail of a dovetail joint may be formed at a bottom part of the plate blind and the socket of the dovetail joint may be formed in at least the outermost positioned waveguide columns of the antenna array. The waveguide columns with no dovetail socket may hold a cut-out corresponding to the width of the bottom of the plate blinds. The use of dovetail joints and cut-outs serves to increase the mechanical stabilization of the arrays, and to keep the waveguide columns in alignment.

In a possible implementation form of the second aspect, the first ends of the waveguide columns of both the first and second antenna arrays are aligned in a direction perpendicular to the longitudinal direction of the waveguide columns, and the second ends of the waveguide columns of both the first and second antenna arrays are also aligned in a direction perpendicular to the longitudinal direction of the waveguide columns.

In a possible implementation form of the second aspect, the waveguide columns of both the first and second antenna arrays hold an absorbing load within the second column end. By having aligned waveguide columns with absorbing loads, the antenna arrays may function in the travelling wave mode.

In a possible implementation form of the second aspect, the number of waveguide columns in the second receiving array is larger than the number of waveguide columns in the first radiating array. In a possible implementation form of the second aspect, the number of waveguide columns in the second receiving array is twice the number of waveguide columns in the first radiating array. In a possible implementation form of the second aspect, the for one or both antenna modules, the first radiating array comprises four waveguide columns, and the second receiving array comprises eight waveguide columns.

In a possible implementation form of the second aspect, a radiating signal probe is operably disposed in each column of the first antenna array, and a receiving signal probe is operably disposed in each column of the second antenna array. In a possible implementation form of the second aspect, then for each waveguide column holding a signal probe, the signal probe is disposed proximal to the first end of the waveguide column. The signal probes may be loop probes with a loop or an open-ended loop for emitting and/or receiving the electromagnetic signal.

A back-to-back radar antenna system may be provided by using two radar antenna modules, where each antenna module is selected from the possible implementation forms of the antenna module according to the second aspect.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. These and other aspects of the invention will be apparent from the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

Fig. 1 is a schematic block diagram illustrating the basic structure of a scanning radar system according to an example embodiment;

Figs. 2a and 2b are schematic cross-sectional views illustrating a back-to-back to arrangement of antenna modules for the radar system of Fig. 1 according to an example embodiment;

Figs. 3a, b, c illustrates manufacturing of an array of slotted cavity columns for use in a planar cavity slotted-waveguide antenna array according to an example embodiment, with

Fig. 3a illustrating manufacturing of a first one-piece metal element, and Figs. 3b and 3c illustrating manufacturing of a second one-piece metal;

Fig. 4 is a bottom view illustrating further manufacturing steps of a cavity slottedwaveguide antenna array according to an example embodiment;

Fig. 5 shows a cavity slotted-waveguide antenna array holding plate blinds according to an example embodiment;

Figs. 6a and 6b show a cut through end view and an enlarged cut out view of a cavity slotted-waveguide antenna array with signal probes inserted according to an example embodiment;

Figs. 7a and 7b are perspective and side views, respectively, of a cavity slotted waveguide antenna array holding both a radiating array and a receiving array with absorber shields according to an example embodiment;

Fig. 8 is a side view illustrating a back-to-back arrangement of two antenna modules each holding an antenna array as illustrated in in Fig. 7a and 7b, according to an example embodiment;

Figs. 9a-9c illustrate scanning of a fixed object using a radar system holding two back-toback antenna modules according to an example embodiment;

Figs. 10a-10i illustrate scanning of four moving object using a radar system holding two back-to-back antenna modules according to an example embodiment;

Fig. 11 is a table giving an overview of the scanning illustrated in Figs. 10a-10i; and

Fig. 12 illustrates simultaneous radar image capture for two opposed radar image lines using a radar system holding two back-to-back antenna modules according to an example embodiment.

DETAILED DESCRIPTION

Fig. 1 is a schematic block diagram illustrating the basic structure of a scanning radar system according to an example embodiment. The system comprises a rotating scanning radar system 101, which is configured to operate as a Frequency Modulated Continuous Wave, FMCW, radar system. The scanning radar system 101 is electronically connected to a computer system 102. Generated output data may be communicated to an external command and control system 103, where the data may be communicated by live data streaming, where for example Extensible Markup Language, XML, may be used for streaming.

The scanning radar system 101 holds two back-to-back positioned antenna modules, a first antenna module 110a and a second antenna module 110b, where each antenna module 110a, 110b comprises a first planar slotted waveguide antenna array 111a, 111b configured for radiating electromagnetic waves 113a, 113b, and a second planar slotted waveguide antenna array 112a, 112b configured for receiving electromagnetic waves 114b. The antennas modules 110a, 110b are mounted to a rotation system 116 configured for rotating 117 the antenna modules 110a, 110b around a vertical axis 115 at a rotational speed. By having the two simultaneously operating antenna modules 110a, 110b, which are both operating as a FMCW radar antenna module, a full 360 degree radar image can be obtained for every half rotation of the radar system 101. The rotational speed may be of 30 rounds per minute, rpm, whereby a full 360 degree radar image can be obtained every second.

The targets or objects being exposed to the radar signals may include one or more Unmanned Aerial Vehicles, UAVs, 105 and one or more birds 106.

The antenna modules 110a, 110b are enclosed by a protecting radome 118 having a high electromagnetic transparency in order to minimize reflection of signals transmitted or radiated from the radiating arrays 111a, 111b to the receiving arrays 112b, 112a. In order to obtain a high electromagnetic transparency, the radome should be relatively thin and may be made of a material having a thickness in the range of 1-3mm, such as in the range of 1-2mm or such as in the range of 1-1,5 mm. Also in order to obtain a high electromagnetic transparency, the radome may be made of a polyethylene (PE) or polypropylene (PP) based ultra heigh molecular weight plastic material. When using a relatively thin wall thickness of below 3 mm, such a in the range of 1-1,5 mm, it is preferred that the radome 118 has a dome shaped upper part in order to increase the mechanical strength of the radome 118. The radome 118 is arranged in a fixed position without following the rotation of the rotation system 116 and the antenna modules 110a, 110b. However, it is also within an embodiment that the radome 118 is connected to the rotation system 116 for being rotated together with the antenna modules 110a, 110b.

Figs. 2a and 2b are schematic cross-sectional views illustrating a back-to-back arrangement of the two antenna modules 110a, 110b for the radar system 101 of Fig. 1 according to an example embodiment. The radar system 101 holds on-board circuitry, which includes a signal generating system 125 holding a single signal generator. For the illustrated embodiment of Figs. 2a and 2b, the signal generating system 125 is positioned at the back of the second antenna module 110b.

Each of the FMCW radar antenna modules 110a, 110b holds electronic on-board circuitry, which includes first electronic transmit circuitry 123a configured for feeding the first radiating array 111a of the first antenna module 110a to radiate first FMCW electromagnetic signals 113a and positioned at the back of the first antenna module 110a, and which includes second electronic transmit circuitry 123b configured for feeding the first radiating array 111b of the second antenna module 110b to radiate second FMCW electromagnetic signals 113b and positioned at the back of the second antenna module 110b. The first and second transmit circuitries 123a, 123b are both being fed with signals from the signal generating system 125 in order to control the first and second electromagnetic signals 113a, 113b to be fully synchronized electromagnetic signals based at least partly on signals provided by the single signal generator of the signal generating system 125.

As part of the electronic on-board circuitry, the first antenna module 110a holds first electronic receive circuitry 124a configured for processing signals received by the second receiving array 112a of the first antenna module 110a, and the second antenna module 110b holds second electronic receive circuitry 124b configured for processing signals received by the second receiving array 112b of the second antenna module 110b. The first electronic receive circuitry 124a is positioned at the back of the first antenna module 110a, and the second electronic receive circuitry 124b is positioned at the back of the second antenna module 110b. The first and second electronic receive circuitry 124a, 124b are configured for processing the received signals in synchronization with the radiated electromagnetic signals 113a, 113b, which synchronization is based on signals provided by the single signal generator of the signal generating system 125.

The on-board circuitry of the radar system 101 also includes a motor controller 119 for controlling the rotation system 116. An azimuth encoder may be provided at the rotation system 116, which encoder is configured for encoding and communicating the degree of rotation, and thereby the azimuth angle of the antenna modules 110a, 110b, at a very high precision. The on-board circuitry also includes signal processing circuitry 126 for performing first on-board processing of signals received from the first receive circuitry 124a, and for performing second on-board processing of signals received from the second receive circuitry 124b, to thereby obtain first digital scan data representing the electromagnetic signals received by the first antenna module 110a, and to obtain second digital scan data representing the electromagnetic signals 114b received by the second antenna module 110b. The signal processing circuitry 126 also provides a control signal to the signal generator system 125.

For the illustrated embodiment of Figs. 2a and 2b, the signal processing circuitry 126 is positioned at the back of the first antenna module 110a.

The different circuitries of the on-board circuitry, the signal generator system 125, the first and second transmit circuitry123a, 123b, the first and second receive circuitry 124a, 124b and the signal processing circuitry 126 may be enclosed by an aluminium shield, which shields for electronic noise signals. The on-board signal processing circuitry 126 may be electronically connected to back end circuitry being part of the azimuth encoder for communicating the azimuth angle. The on-board signal processing circuitry 126 and the back end circuitry are electronically connected to the computer system 102, for forwarding the first and second digital scan data together with data for the azimuth angle to the computer system 102. The electronic signals are transferred via a glass fibre cable from the signal processing circuitry 126 to a rotary joint at the rotation system 116, which is further connected to the computer system 102 by cables.

The computer system 102 may hold first processing circuitry for processing the received first digital scan data and azimuth data to provide first type radar plots of detected objects presented by the signals received by the first antenna module, and further hold second processing circuitry for processing the received second digital scan data and azimuth data to provide second type radar plots of detected objects presented by the signals received by the second antenna module. The computer system 102 may also hold radar track processing circuitry configured to provide a radar track for a detected object based on both first and second type radar plots. The computer system 102 may also hold classifying circuitry for classifying the objects of the tracks.

The current scanning radar system 101 is based on two antenna modules 110a, 110b, where each antenna module comprises a first planar slotted waveguide antenna array 111a, 111b configured for radiating electromagnetic waves 113a, 113b, and a second planar slotted waveguide antenna array 112a, 112b configured for receiving electromagnetic waves 114b.

Figs. 3a, b, c illustrates manufacturing of an array of slotted cavity columns for use in a planar cavity slotted-waveguide antenna array according to an example embodiment, with Fig. 3a illustrating manufacturing of a first one-piece metal element, and Figs. 3b and 3c illustrating manufacturing of a second one-piece metal.

Fig. 4 is a bottom view illustrating further manufacturing steps of a cavity slottedwaveguide antenna array according to an example embodiment.

Fig.3a illustrates manufacturing of a first one-piece metal element 201, which is a first single flat piece of metal, where a plurality of longitudinally extending parallel and equidistantly arranged open rear column portions 203a of equal dimensions are formed in the first flat piece of metal 201. In order to save weight of the final array, grooves 204 may be formed in the metal material left between the rear column portions 203a.

Figs. 3b and 3c illustrate manufacturing of a second one-piece metal element 202, which is a second single flat piece of metal, where a plurality of longitudinally extending parallel and equidistantly arranged open front column portions 203b of equal dimensions are formed in the second flat piece of metal 202. The front column portions 203b have a width and a length equal to the width and length of the rear column portions 203a, and the front column portions 203b are arranged with a spacing equal to the spacing of the rear column portions 203a. After formation of the front column portions 203b, a plurality of longitudinally extending parallel front recesses 205 are formed in the second metal element 202. These front recesses 205 extend into the second metal element 202 from the front surface of the element 202, and the front recesses 205 define first and second sidewalls 206, 207 of a front part of the front column portions 203b. After the formation of the front recesses 205, a plurality of slots 208 are formed in the front column portions 203b. Each slot 208 extends from the bottom of the corresponding front column portion 203b to a front surface 209 of the second metal element 202.

A signal probe hole 210 is formed at the bottom of the rear column portions 203a, where each probe hole extends from the bottom of the corresponding rear column portion 203a to a rear surface 211 of the first metal element 201. When the slots 208 and probe holes 210 have been formed, the first and the second metal elements 201 and 202 are connected together with the openings of the rear column portions 203a facing the openings of the front column portions 203b. The connection of the first and second metal elements 201 and 202 forms a housing, which comprises a number of parallel slottedwaveguide columns 203 having a rectangular cross-section, see Fig. 5, where the parallel slotted-waveguide columns 203 are formed by the rear and front column portions 203a, 203b. The arrangement of the probe holes 210 at the rear surface 211 of the first metal element 201 is illustrated in Fig. 4, which also shows the first and second metal elements 201 and 202 being connected together. The diameter of the probe hole 210 may equal the internal width of the columns 203 or rear column portions 203a. In Fig. 4 is also shown screw holes 220, which are provided at the rear surface 211 of the first metal element 201 in between the rear column portions 203a. The screw holes 220 may hold screws connecting the first and second metal elements 201 and 202.

The material used for the metal elements 201 and 202 may be anodized aluminum. Is it preferred that the formation of the rear column portions 203a and grooves 204 in the first metal element 201, the formation of the front column portions 203b, the front recesses 205, and the slots 208 in the second metal element 202 are performed by use of milling. The probe holes 210 may also be formed in the first metal element 201 by drilling.

Fig. 5 shows part of a cavity slotted-waveguide antenna array 200, which has been manufactured and assembled as described above in connection with Figs. 3a,b,c and Fig.

4. According to an example embodiment, the array 200 is further provided with a number of conductive parallel plate blinds 212, which are conductively secured to the front side or surface 209 of the housing holding the waveguide columns 203b, 203, where the front side or surface 209 holds the cavity slots 208. The plate blinds 212 are arranged substantially perpendicular to the longitudinal direction of the waveguide columns 203. The plate blinds 212 have two parallel outer surfaces being first and second parallel outer surfaces, and the blinds 212 are substantially U-shaped with two parallel side plates and a bottom plate. The plate blinds 212 are secured to the front side or surface 209 of the housing holding the waveguide columns 203b, 203 by a sliding dovetail joint 213. The tail of a dovetail joint is formed at a bottom part of a U-shaped plate blind 212 and the socket of the dovetail joint is formed in the front side or surface 209 of the housing holding the outermost positioned waveguide columns 203b, 203. The waveguide columns 203 with no dovetail socket in the front surface 209 may hold a cut-out corresponding to the width of the bottom of the plate blinds. The use of dovetail joints and cut-outs serves to increase the mechanical stabilization of the arrays, and to keep the waveguide columns in alignment. The use of plate blinds 212 is optional.

In order for the slotted-waveguide columns 203 to emit or receive an electromagnetic signal, a signal probe may be inserted in the probe hole 210. This is illustrated in Figs. 6a and 6b, which show a cut through end view and an enlarged cut out view of a cavity slottedwaveguide antenna array 200 with signal probes 214 inserted in each waveguide column 203, according to an example embodiment.

The array 200 has eight waveguide columns 203 disposed in a predetermined adjacent position with respect to one another, where each column may be formed by a rear column portion 203a formed in a first one-piece metal element 201 and by a front column portion 203b formed in a second one-piece metal element 202. Each column 203 has a number of slots 208 formed in the front column portion 203b, see Fig. 3c, and each column 203 has an upper and a lower end. The waveguide columns 203 have a rectangular crosssection, and the waveguide columns 203 are defined by two wide inner surfaces being first and second wide inner surfaces, a narrow inner back surface, and narrow inner front surface. The narrow inner front surface and the front side 209 of the housing define a narrow front wall holding the cavity slots 208. The slots 208 are narrow walled slots or transverse narrow walled slots 208, which reach from the first inner wide surface to the second wide inner surface.

A signal probe 214 is operably disposed in each column 203 for emitting and/or receiving an electromagnetic signal. The electromagnetic signal may have a free-space wavelength of Ä0, and the signal propagates within the column 203 holding the signal probe 214 as electromagnetic waves with a corresponding guided signal wavelength Ag. For the embodiment illustrated in Fig. 6, the signal probes 214 are open ended loop probes with an open ended loop disposed at the narrow inner back surface opposite and facing the narrow inner front surface of the waveguide column 203 holding the loop probe 214.

The open ended loop of the loop probe 214 is arranged in a direction perpendicular to the longitudinal direction of the waveguide column 203, and the open ended loop probe 214 may be disposed proximal to the lower end of the column 203 holding the probe 214. According to an embodiment, each column 203 has an absorbing load at its upper end while the lower end of the waveguide column may be terminated with a short circuiting end geometry (blind end) or an absorbing load, to enable the column 203 to function in a travelling wave mode.

The signal probes 214 are formed of an electrically conductive material, such as copper or silver-plated copper, and are electrically non-conductively secured to the columns 203. The open ended loop of a loop probe 214 forms part of a loop circle, which may have a circumference in the range of 1/3 to 2/3, such as about 1/2 of the guided signal wavelength Ag.

The housing holding the waveguide columns 203 has a rear side surface, and a waveguide bottom wall is defined by the narrow inner back surface of a waveguide column 203 and the rear side surface of the housing, whereby an outer back surface of the waveguide bottom wall is defined by the rear side of the housing. The open ended loop probes 214 have a probe connection part 215 opposite the open ended loop, where the probe connection part 215 extends through probe holes 210 provided at the waveguide bottom wall. An enclosure part 218 is disposed between a printed circuit board, PCB, 217 and the outer back surface of the waveguide bottom wall, and the loop probe connection part 215 extends through a surrounding part 219 formed by the enclosure part 218 to reach the printed circuit board 217. An end part of the connection part 215 of each of the loop probes 214, which may reach through the PCB 217 by a so-called via, is electrically connected to a corresponding electrical conductive signal trace provided at the front surface of the printed circuit board 217. The surrounding parts 219 of the enclosure part 218 may be formed to fit or fill out the probe holes 210, and the probe holes 210 may have a diameter equal to the internal width of the column 203. An electrically non-conductive material 216 surrounds the probe connection part 215 extending through the enclosure part 218. The electrical non-conductive material may comprise or is made of Polyether Ether Ketone, PEEK, plastic. The enclosure part 218 holds sidewalls 222, and a lid 223 is secured to the sidewalls to close off the enclosure part 218.

The enclosure part 218 is made of an electrical conductive material, such as aluminium. Before securing the enclosure part 218 to the rear side of the array housing holding the waveguide columns, the probes 214 and the PCB 217 may be connected to the enclosure part 218. First, each loop probe 214 is connected to the enclosure part 218 by having the connection part 215 surrounded by the non-conductive material 216 and arranged within the surrounding part 219 of the enclosure part 218. The printed circuit board, PCB, 217 can then be secured to the enclosure part 218 by screws 221 with the end part of the probe connection part 215 reaching through the PCB 217 by the so-called via. The end part of the probe connection part 215 can now be soldered or electrical connected to a corresponding electrical conductive signal trace provided at the front surface of the printed circuit board 217. The PCB 217 has a bottom surface facing the enclosure part 218, where the PCB bottom surface holds electrical conductive ground traces or parts to provide an electrical ground connection to the enclosure part 218. In an embodiment, the enclosure part 218 is silver plated for maintaining an electrical connection between the enclosure part 218 and the PCB bottom ground traces. Each PCB signal trace corresponding to a loop probe 214 may have a first trace end soldered to the end part 215 of the loop probe 214, and each of these PCB signal traces is a copper trace, which preferably is formed to obtain a characteristic impedance of 50 Ohm. The PCB signal traces having one end electrically corresponding to a loop probe 214, may in the other end be electrically connected to radio frequency transmit circuitry, when the array is a transmitting array, or connected to receive circuitry, when the array is a receiving array, where the transmit or receive circuitry may be arranged at the front surface of the PCB 217. The radio frequency transmit circuitry may comprise a radio frequency amplifier, and the receive circuitry may comprise a pseudomorphic high electron mobility transistor, PHEMT.

Figs. 7a and 7b are perspective and side views, respectively, showing a cavity slotted waveguide antenna array 300 holding both a first radiating array 300a and a second receiving array 300b according to an example embodiment. The radiating array 300a and the receiving array 300b may be manufactured and assembled as described above in connection with Figs. 3 to 6. Each of the antenna modules 110a and 110b may hold an antenna array equal to the array 300 of Figs. 7a and 7b.

For the array 300 of Figs. 7a and 7b, the waveguide columns within the first radiating array 300a and second receiving array have equal dimensions. The first radiating array 300a comprises four waveguide columns 303a, and the second receiving array 300b comprises eight waveguide columns 303b. Thus, both antenna modules 110a and 110b may have equal dimensioned waveguide columns 303a, 303b, whereby it is possible to operate within the same frequency band for both antenna modules.

For the array 300, the front side of the columns 303a, 303b holding the cavity slots 208, see Fig. 3c, of both the first and second antenna arrays 300a, 300b are positioned substantially in the same plane. By having the radiating and receiving arrays in the same plane, a simplified manufacture of the antenna module may be obtained. The waveguide columns 303a, 303b of the first and second antenna arrays 300a, 300b are of equal length, and first ends of the waveguide columns 303a, 303b of both the first and second antenna arrays 300a, 300b are aligned in a direction perpendicular to the longitudinal direction of the waveguide columns 303a, 303b, and opposite second ends of the waveguide columns 303a, 303b of both the first and second antenna arrays 300a, 300b are also aligned in a direction perpendicular to the longitudinal direction of the waveguide columns 303a, 303b.

The first radiating antenna array 300a holds a number of parallel plate blinds 312a secured to the front side of the first antenna array 300a besides or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns 303a of the first antenna array, and the second receiving antenna array 300b holds a number of parallel plate blinds 312b secured to the front side of the second antenna array 300b besides or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns 303b of the second antenna array. The plate blinds 312a, 312b are vertical blinds or baffles for reducing electromagnetic power radiated in the cross-polarization, that is blinds or baffles for cross-polarization suppression. The plate blinds 312a, 312b may be substantially U-shaped with two parallel side plates and a bottom plate.

A radiating signal probe, not shown in Fig. 7a and 7b, see the probe 214 of Figs.6a and 6b, is operably disposed proximal to a first end in each column 303a of the first antenna array 300a, and a receiving signal probe 214 is operably disposed proximal to a first end in each column 303b of the second antenna array 300b. The waveguide columns 303a, 303b of both the first and second antenna arrays 300a, 300b hold an absorbing load within the second column end. By having aligned waveguide columns of equal length provided with absorbing loads, the antenna arrays may function in the travelling wave mode.

For the array 300, an electromagnetic shield or shield plate 320 is arranged substantially parallel to the waveguide columns 303a, 303b and between the first lower radiating antenna array 300a and the second upper receiving antenna array 300b, where the shield or shield plate 320 extends outwards from the front side of the antenna array 300. The electromagnetic shield or shield plate 320 is an electromagnetic absorbing shield or shield plate, or the shield or shield plate 320, which is fully or at least partly covered by an electromagnetic absorbing material. The array 300 also holds a lower electromagnetic absorber shield or shield plate 321, which is fully or at least partly covered by an electromagnetic absorbing material, and which is arranged substantially parallel to the waveguide columns 303a and below the lowermost waveguide column 303a of the first lower radiating antenna array 300a. The lower absorber shield or absorbing covered shield plate 321 extends outwards from the front side of the antenna array 300. The array 300 further holds an upper electromagnetic absorber shield or shield plate 322, which is fully or at least partly covered by an electromagnetic absorbing material, and which is arranged substantially parallel to the waveguide columns 303b and above the uppermost waveguide column 303b of the second upper receiving antenna array 300b. The upper absorber shield or absorbing covered shield plate 322 extends outwards from the front side of the antenna array 300. The height of the upper and lower absorbers shields 322 and 321 should be at least equal to the height of the plate blinds 312a, 321b. The height of the shield pate or absorber shield 320 between the first lower radiating antenna array 300a and the second upper receiving antenna array 300b should also be at least equal to the height of the plate blinds 312a, 321b, and preferably the height of the shield 320 is higher than the height of the upper and lower absorbers shields 322 and 321.

The electromagnetic absorber shield or electromagnetic absorbing material may comprise a carbon loaded foam material, such as a carbon loaded foam tape. The electromagnetic absorber shield or electromagnetic absorbing material may have a thickness in the range of 4-12mm, such as in the range of 5-10 mm, such as in the range of 5-8 mm, such as about 6 mm.

By having the electromagnetic absorbing shield 320 between the radiating array 300a and the receiving array 300b, and by having the lower and upper electromagnetic absorbing shields 321 and 322, the internal reflection of electromagnetic signals between and alongside the vertical plate blinds 312a, 312b is reduced.

In an embodiment, part of the dimensions of the array 300 are as follows: the total length of the array 300 and the columns 303a, 303b is 420 mm; the total width of the array 300 is 282 mm; the length of the plate blinds 312a covering the four columns 303a of the radiating array 300a is 73 mm; the length of the plate blinds 312b covering the eight columns 303b of the receiving array 300b is 153 mm; distance between closest side walls of neighboring plate blinds 412 is 14,5 mm; height of the electromagnetic shield or shield plate 320 when measured from the top or front side of the array 300 is 50 mm; height of the lower electromagnetic absorber shield or shield plate 321 when measured from the top or front side of the array 300a is 20 mm; height of the upper electromagnetic absorber shield or shield plate 322 when measured from the top or front side of the array 300b is 20 mm.

Fig. 8 is a side view illustrating a back-to-back to arrangement 400 of two antenna modules 410a and 410b each holding an antenna array similar to the array 300 as illustrated in in Fig. 7a and 7b, according to an example embodiment. The first antenna module 410a holds a first and lower radiating array 400aa with four waveguide columns 403aa and a second higher receiving array 400ba with eight waveguide columns 403ba. Both the first and second arrays 400aa and 400ba holds plate blinds 412aa and 412ba, respectively, arranged perpendicular to the longitudinal direction of the waveguide columns 403aa, 403ba.

An electromagnetic shield or shield plate 420a is arranged substantially parallel to the waveguide columns 403aa, 403ba and between the first lower radiating antenna array 400aa and the second upper receiving antenna array 400ba. A lower electromagnetic absorber shield or shield plate 421a is arranged substantially parallel to the waveguide columns 403aa and below the lowermost waveguide column 403aa of the first lower radiating antenna array 400aa. An upper electromagnetic absorber shield or shield plate 422a is arranged substantially parallel to the waveguide columns 403ba and above the uppermost waveguide column 403ba of the second upper receiving antenna array 400ba.

Similar to the first antenna module 410a, the second antenna module 410b holds a first and lower radiating array 400ab with four waveguide columns 403ab and a second higher receiving array 400bb with eight waveguide columns 403bb. Both the first and second arrays 400ab and 400bb holds plate blinds 412ab and 412bb, respectively, arranged perpendicular to the longitudinal direction of the waveguide columns 403ab, 403bb.

An electromagnetic shield or shield plate 420b is arranged substantially parallel to the waveguide columns 403ab, 403bb and between the first lower radiating antenna array 400ab and the second upper receiving antenna array 400bb. A lower electromagnetic absorber shield or shield plate 421b is arranged substantially parallel to the waveguide columns 403ab and below the lowermost waveguide column 403ab of the first lower radiating antenna array 400ab. An upper electromagnetic absorber shield or shield plate 422b is arranged substantially parallel to the waveguide columns 403bb and above the uppermost waveguide column 403bb of the second upper receiving antenna array 400bb.

The first antenna module 410a also holds on-board circuitry including signal processing circuitry 426a and electronic transmit circuitry 423a, not shown in Fig. 8, and electronic receive circuitry 424a, not shown in Fig. 8. The second antenna module 410b also holds on-board circuitry including signal generating system 425, not shown in Fig. 8, and electronic transmit circuitry 423b, and electronic receive circuitry 424b. The arrangement 400 is supported by a rotation system 416 and holds a motor controller 419 for controlling the rotation system 416.

For the arrangement 400 of Fig. 8, the first and second antenna modules 410a and 410b are arranged in a mirrored position relative to a plane intersecting the vertical axis of rotation, see axis 115 of Fig. 1. The cavity slots on the front side of the columns 403aa and 403ba of the first and second antenna arrays 400aa and 400ba of the first antenna module 410a are arranged in a partially upwards facing plane having a first acute angle to the vertical direction. Also the cavity slots on the front side of the columns 403ab and 403bb of the first and second antenna arrays 400ab and 400bb of the second antenna module 401b are arranged in a partially upwards facing plane having a second acute angle to the vertical direction. When the antenna modules 410a and 410b are in the mirrored position, the first acute angle is substantial equal to the second acute angle. It is preferred that the first and second acute angles are in the range of 10-30°, such as about 20°.

Figs. 9a-9c illustrate scanning of a fixed object A, 105a, using the radar system 101 holding two back-to-back antenna modules 110a, 110b according to an example embodiment. The difference in azimuth angles between the two modules 110a and 110b is 180°. In Fig. 9a, the azimuth angle is 0°, 180° and the object A is scanned by radiated waves 113a of the first antenna module 110a, while no object is scanned by the waves 113b of the second module 110b. In Fig. 9b, the azimuth angle is 90°, 270° and no object is scanned. In Fig. 9c, the azimuth angle is 180°, 0° and the object A is scanned by radiated waves 113b of the second antenna module 110b, while no object is scanned by the waves 113a of the first module 110a.

Figs. 10a-10i illustrate scanning of four moving objects A,B,C,D , 105a,b,c,d, using a radar system 101 holding two back-to-back antenna modules 110a, 110b according to an example embodiment. In Fig. 10a, the azimuth angle is 0°, 180° and no objects are scanned. In Fig. 10b, the azimuth angle is 45°, 225° and object A is scanned by radiated waves 113a of the first antenna module 110a, while no object is scanned by the waves 113b of the second module 110b. In Fig. 10c, the azimuth angle is 90°, 270° and object C is scanned by radiated waves 113b of the second antenna module 110b, while no object is scanned by the waves 113a of the first module 110a. In Fig. 10d, the azimuth angle is 135°, 305° and object B is scanned by radiated waves 113a of the first antenna module 110a, and object D is scanned by radiated waves 113b of the second antenna module 110b. In Fig. 10e, the azimuth angle is 180°, 0° and no objects are scanned. In Fig. 10f, the azimuth angle is 225°, 45° and object C is scanned by radiated waves 113a of the first antenna module 110a, while no object is scanned by the waves 113b of the second module 110b. In Fig. 10g, the azimuth angle is 270°, 90° and object D is scanned by radiated waves 113a of the first antenna module 110a, and object A is scanned by radiated waves 113b of the second antenna module 110b. In Fig. 10h, the azimuth angle is 315°, 135° and object B is scanned by radiated waves 113b of the second antenna module 110b, while no object is scanned by the waves 113a of the first module 110a. In Fig. 10i, the azimuth angle is 360°, 0° and object C is scanned by radiated waves 113b of the second antenna module 110b, while no object is scanned by the waves 113a of the first module 110a.

Fig. 11 is a table, Table I, giving an overview of the scanning results illustrated in Figs. 10a-10i. Table I shows which objects are being hit or scanned with progress in time of rotation of the radar system 101, which of the antenna modules 110a or 110 b hits or scans the object and at which azimuth angle. Table I also indicates a change in range of the moving objects from one scan to a following scan, where a first range is indicated by Y, a second range is Y+δ, and a third range is Y+Ö2.

Fig. 12 illustrates simultaneous radar image capture for two opposed radar image lines using a radar system 101 holding two back-to-back antenna modules 110a and 110b according to an example embodiment. A full circular radar has 80 image lines to cover a full 360° radar image, whereby each image line covers 4,5°. By having the two back-toback arranged antenna modules 110a and 110b, two opposite radar image lines are scanned at the same time. Thus, when the radar system 101 rotates with 30 rounds per minute, RPM, one full radar image can be obtained for half a rotation and for every second. The radar modules 110a and 110b may be configured to have an azimuth beam width of 6° in order to obtain a satisfying radar signal exposure time for each image line of 4,5°. Each image line may be divided inn 1587 range cells, and each radar antenna module 110a and 110b may be configured to transmit 100 FMCW sweeps per image line, to thereby obtain the necessary data for generating radar plots.

In the following a further discussion of the dimensions and operation of the cavity slottedwaveguide antennas 200 and 300 of Figs. 5, 6 and 7 is provided.

The antenna arrays 200, 300 of Figs. 5, 6 and 7 holds several waveguide columns 203, 303 disposed in a predetermined adjacent position with respect to one another. For the array 200 shown in Figs. 5 and 6, the number of waveguide columns 203 is eight. The waveguide columns 203, 303 are vertically disposed in a housing, have a rectangular cross-section, and are defined by two wide inner surfaces being first and second wide inner surfaces, a narrow inner back surface, and narrow inner front surface. The narrow inner front surface and the front side 209 of the housing define a narrow front wall holding the cavity slots 208. Each column 203 has a first, upper end and an opposite second, lower end, and each column 203 holds the same number of narrow walled slots 208 disposed in the narrow front wall.

Each waveguide column 203, 303 in the array 200 or 300 forms an antenna, which is dimensioned for radiating and/or receiving electromagnetic waves at a free-space wavelength, A0. Wave front propagating in waveguides is slower than in air, as the wave front takes a crisscross path inside the waveguide. Thus, the wavelength, Ag, inside the waveguide column 203, 303 is slightly larger than the free-space wavelength, Ä0. In order for the waveguide column 203 to radiate waves in the correct phase, the dimensions of the waveguide 203 must be selected according to the guided wavelength, Ag, while the dimensions of the slots 208 must be selected to radiate waves at the free-space wavelength, A0. At the fundamental TE10 mode, the guided wavelength, Ag, may be found from the equation:

Ag = A0/(<(1- (A0/2a)²) (1).

In equation (1), “a” is the length of the wide inner surfaces of the rectangular waveguides 203, where the cut-off wavelength, Ac, of the waveguide 203 is set equal to 2a.

In an embodiment, each column 203 has an absorbing load provided at the second end opposite the first end holding signal loops in order to enable the columns 203 to guide the electromagnetic waves in the travelling wave mode, while the first end of each column 203 may be terminated with a short circuiting end geometry (blind end). For a waveguide column 203 designed to host a travelling wave, the slots 208 may be spaced at half the guided wavelength, Ag, and the column 203 should be terminated at the second end with an absorbing load spaced at three quarters of the guided wavelength, Ag, from the centre of the last slot 208. The signal probe 214 may be inserted into the column 203 with a spacing of three quarters of guided wavelength, Ag, from the centre of the first slot 208, while the column 203 should be terminated at the first end with a short circuiting end geometry spaced at one quarter of the guided wavelength, Ag, from the coupling probe 214.

The slots 208, which are formed in the narrow front wall, need to be relatively narrow with a width, which is small compared to the length of the slot 208. The length of the slots should be approximately half the free-space wavelength, A0.

In order to achieve a resonant length of half the free-space wavelength, A0, for the narrow walled slots 208, the slots 208 must penetrate into the sidewalls of the columns 203, which sidewalls form the two wide inner waveguide surfaces. This type of slots 208 are known as edge-slots. The slots 208 may be arranged in pairs, where each cavity slot pair includes an upper slot and a lower slot, and where each slot 208 has an associated angular displacement to the longitudinal direction of the waveguide columns 203. The angular displacements of the upper and lower slots 208 are substantially equivalent to one another, but in an opposite orientation.

By tilting the direction of the slots 208, a fraction of the current flow along the waveguide column 203 is interrupted, causing the slots 208 to radiate. By having opposite inclinations of adjacent slots 208, the vertical components from these slots 208 may be partly cancelled out in space.

Ideally, the vertical polarized components from the narrow walled slots 208 should be fully cancelled out, leaving only the horizontal polarized components. The remaining vertical polarized components, also named the cross-polarization radiation pattern, can be reduced by use of conductive plate blinds 212, 212 arranged between each pair of slots 208. Thus, the antenna array 200, 300 may be provided with several conductive parallel plate blinds 212, 312 being conductively secured to the front side or surface 209 of the housing holding the waveguide columns 203. Each plate blind 212, 312 comprises two parallel outer surfaces, a first and a second outer surface. The plate blinds 212, 312 are secured to front the side 209 of the housing holding the waveguide columns 203 with the parallel outer surfaces of the plate blinds 212, 312 being substantially perpendicular to the longitudinal direction of the waveguide columns 203, 303 and substantial perpendicular to the front side of the housing holding the waveguide columns 203, 303. The plate blinds 212, 312 are arranged so that two adjacent plate blinds 212, 312 are disposed with a single waveguide slot 208 in between. Thus, a plate blind 212, 312 is provided between the two slots 208 of each cavity slot pair. Also a plate blind 212, 312 is provided near the first column end before the first column slot 208, and a plate blind 212, 312 is provided near the second column end after the last column slot 208.

For the waveguide columns 203 of the antenna arrays 200, 300 the centres of the slots 208 of each column 203 are separated by half of the guided wavelength, Ag. The plate blinds 212, 312 are arranged with a spacing equal to the spacing of the slots 208, and the spacing between the centres of adjacent plate blinds is therefore substantially equal to half the guided signal wavelength, Ag.

An effective reduction of the cross-polarization radiation may be obtained when the spacing between the plate blinds 212, 312 is less than half the free-space signal wave length A0, which again is smaller than the guided signal wave length, Ag. Thus, in order to reduce the distance between the plate blinds 212, 312 below half the free space signal wave length A0, the width of the plate blinds 212, 312 is increased by keeping a distance between the first and second outer surfaces, where the distance between the first and second outer surfaces of the plate blinds 312 may be in the range of one third to one half of the free-space signal wave length, A0.

The height of the plate blinds 212, 312 also has an influence on the cross-polarization suppression, and for the arrays 200, 300 of Figs. 5 and 7, the height of the parallel outer surfaces of the plate blinds above the outer front surface of the columns 203, 303 is selected to be in the range of 20-60% of the free-space signal wave length, and it is preferred that the height is substantial equal to 1/2 of the free-space signal wave length.

In order to save material and weight and also for ease of manufacturing, the plate blinds 212, 312 are designed to be substantially U-shaped with two parallel side plates and a bottom plate.

The distance between the centres of adjacent positioned waveguides columns 203, 303 should be set to be equal to or above half the free-space wavelength Ä0. For the array 200, the distance between the centres of adjacent positioned waveguides columns 203 is set about 2/3 or in the range of 0,5 to 0,75 of the free-space wavelength Ä0.

The following describes construction details for an example embodiment of an antenna array 200 or 300 designed to operate in a wideband frequency range of 9550 to 9750MHz, corresponding to a free-space wavelength Ä0 in the range of 30,77-31,4mm, or to operate with a free-space wavelength Ä0 about 30mm.

In order to operate in the above mentioned frequency range, the waveguide columns 203, 303 are dimensioned with a height “a” of the wide inner surfaces to be about 2/3 A0,such as 20mm and a width “b” of the narrow inner back and front surfaces to be about 1/3 Å0,such as 10mm. The waveguide columns 203 are produced by use of milling from the first and second metal elements 201, 202 being of anodized aluminium having a plate thickness of 12 mm, and the thickness of the walls 106, 107 defining the upper parts of the wide inner surfaces of the waveguide columns 103b, 103 is about 2mm, and the thickness of the narrow front wall is also 2mm.

From equation (1) the guided wavelength, Ag, can be calculated by inserting the values of λ0 and “a”, where A0 set to 30,77mm gives a value of Ag, which is equal to 48mm, and where A0 set to 31,4mm gives a value of Ag, which is equal to 50,64mm.

From the above values of A0 and Ag, the average values are found as A0,av equal to 31mm and Agav equal to 49,3mm, which gives a value for half the free-space wavelength, A0, to be about 15,5mm, and a value for half the guided wavelength, Ag, to be about

24,66mm.

Thus, the distance between the centres of neighbouring slots 208 of a waveguide column 203, 303 is set to about 24,66mm or 25mm, and the total length of the edge-slots 208 including the penetrations into the sidewalls 206, 207 is set to about 15,5mm or 15mm. The width of the edge-slots 208 is set to 3,6 mmm, and the slots 208 are arranged with an angular displacement of about 35 degrees to the longitudinal direction to the waveguide column 103, where neighbouring slots 108 are arranged with equal, but opposite angular displacement.

The waveguide columns 303 of Figs. 7a and 7b have a total outer length of 420mm.

For the travelling waveguide columns 203, 303 the absorbing load at the second end is arranged with a spacing of three quarters of the guided wavelength, Ag, which is equal to 37mm, to the centre of the last slot 208. The signal probe 214 is inserted into the column 203 with a spacing of three quarters of a guided wavelength, Ag, which is about 42mm, to the centre of the first slot 208, while the short circuiting end geometry at the first end is arranged with a spacing of one quarter of the guided wavelength, Ag, which is at least about 12-13mm, such as 12,4mm, to the centre of the coupling probe 214.

The distance between the centres of adjacent positioned waveguides columns 203, 303 is set to be about 20mm, which is about two third of the free-space wavelength A0. This distance leaves a free space of about 6mm between the sidewalls of neighbouring columns 203, 303.

The spacing between the centres of adjacent plate blinds 212, 312 is set equal to the distance between the centres of neighbouring slots 208, which is 24,66mm or 25mm, to be about half the guided signal wavelength, Ag, and the distance between the first and second outer surfaces of the plate blinds 212, 312 may be set to 9,86-12mm, which is in between one third and half of the free-space signal wave length, A0. The spacing left between opposite outer surfaces of neighbouring plate blinds 212 is then about 12,6614,8mm, which is below half the free-space signal wave length of 15,5mm, in order to effectively reduce the cross-polarization radiation. The height of the parallel outer surfaces of the plate blinds 212, 312 above the outer front surface of the columns 203, 303 may be set to be 15,5mm, which is substantial equal to 1/2 of the free-space signal wave length, to thereby further reduce the cross-polarization radiation. The U-shaped plate blinds 212, 313 are made in aluminum with a sidewall thickness of 1,8 mm. The bottom part of the Ushaped plate blinds 212, 312 has a wall thickness of 1,7 mm, and holds the tail of the dovetail joint to fit with the socket of the dovetail joint formed in part of the waveguide columns 203, 303.

The invention has been described in conjunction with various embodiments herein.

However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not 5 exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

Any method described herein and in the claims may be supplemented by any features of the apparatuses and systems described herein and in the claims in terms of method 10 features.

Claims

A radar system comprising a first and a second antenna module, each antenna module comprising:

a first planar slotted waveguide antenna structure configured to radiate electromagnetic waves; and a second planar slotted waveguide antenna structure configured to receive electromagnetic waves;

wherein, for each of the antenna modules, each planar slotted waveguide antenna structure comprises a plurality of longitudinal waveguide columns arranged in a parallel and adjacent position relative to each other, the waveguide columns having a front and a backside with a plurality of cavity slots on the front, and the waveguide columns further having first and second column ends;

wherein, for each of the antenna modules, the first and second antenna structures are arranged with the longitudinal direction of the waveguide columns extending in one horizontal direction, and wherein the waveguide columns of the first antenna structure are arranged below and in a parallel position to the waveguide columns of the second antenna structure; and wherein for each antenna module an electromagnetic shield or shield plate is disposed substantially parallel to the waveguide columns and between the first lower radiating antenna structure and the second upper receiving antenna structure, the shield or shield plate extending outwardly from the front of the antenna module;

which radar system further comprises a rotation system configured to support and rotate the first and second antenna modules about a vertical axis with the first and second antenna modules arranged in a back-to-back position on opposite sides of a plane intersecting the vertical axis of rotation, and wherein the back of the waveguide columns of the antenna structures of the first antenna module faces the back of the waveguide columns of the antenna structures of the second antenna module.

A radar system according to claim 1, which system further comprises a protective housing in the form of a radome covering the first and the second antenna module.

A radar system according to claim 1 or 2, wherein the waveguide columns in the first and second antenna structures of both the first and second antenna modules have the same dimensions; and wherein the front of the columns holding the cavity slots for both the first and second antenna structures is located substantially in the same plane for each of the antenna modules.

A radar system according to any one of claims 1 to 3, wherein the cavity slots on the front of the columns of the second antenna structure of the first antenna module are arranged in a partially upward plane with a first acute angle to the vertical direction, and wherein the cavity slots on the front of the columns of the first antenna structure of the second antenna module is arranged in a partially upward plane with a second acute angle to the vertical direction.

A radar system according to claim 4, wherein the first acute angle is substantially equal to the second acute angle, and wherein the first and second acute angles are preferably in the range of 10-30 °, such as approx. 20 °.

A radar system according to any one of claims 1 to 5, wherein the first and second antenna modules are arranged in a mirrored position relative to the plane intersecting the vertical axis of rotation.

A radar system according to any one of claims 2 to 6, wherein the radome is made of a material with high electromagnetic transparency, such as made of a polyethylene (PE) or polypropylene (PP) -based ultra-high molecular weight plastic material; and wherein the radome is preferably made of a material with a thickness in the range 1-3 mm, such as in the range 1-2 mm or as in the range 1-1.5 mm.

A radar system according to any one of claims 1 to 7, wherein the electromagnetic shield or shield plate is an electromagnetic absorbing shield or shield plate which is wholly or partly covered by an electromagnetic absorbing material.

A radar system according to any one of claims 1 to 8, wherein for each antenna module there is a lower electromagnetic absorber shield or shield plate which is wholly or partly covered by an electromagnetic absorbing material and which is arranged substantially parallel to the waveguide columns. and below the lower waveguide column of the first lower radiating antenna structure, the lower absorber shield or absorber-covered shield plate extending outwardly from the front of the antenna module.

A radar system according to any one of claims 1 to 9, wherein for each antenna module there is an upper electromagnetic absorber shield or shield plate which is wholly or partly covered by an electromagnetic absorbing material and which is arranged substantially parallel to the waveguide columns. and over the upper waveguide column of the second upper receiving antenna structure, the upper absorber shield or absorber-covered shield plate extending outwardly from the front of the antenna module.

A radar system according to any one of claims 8 to 10, wherein the electromagnetic absorber shield or electromagnetic absorbent material comprises a foam material containing carbon, such as a carbon foam tape.

A radar system according to any one of claims 1 to 11, wherein, for each antenna module, the first antenna structure holds a plurality of parallel shield plates attached to the front of the first antenna structure adjacent to or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns in the first antenna structure, and wherein the second antenna structure holds a plurality of parallel shield plates attached to the front of the second antenna structure adjacent to or between the cavity slots and substantially perpendicular to the longitudinal direction of the waveguide columns in the second antenna structure.

A radar system according to any one of claims 1 to 12, wherein, for each antenna module, the number of waveguide columns in the second reception structure is greater than the number of waveguide columns in the first radiation structure; and wherein, for each antenna module, the number of waveguide columns in the second receiving structure is preferably twice the number of waveguide columns in the first radiation structure.

A radar system according to any one of claims 1 to 13, wherein the system further comprises a signal generation system comprising a single signal generator, and wherein the first antenna module comprises a first electronic transmission circuit configured to feed the first radiation structure of the first antenna module for radiating. first electromagnetic signals, and the second antenna module comprises a second electronic transmission circuit configured to feed the first radiation structure of the second antenna module to radiate other electromagnetic signals, the first and second electromagnetic signals being fully synchronized electromagnetic signals based at least in part on signals provided of the individual signal generator.

A radar system according to claim 14, wherein the first antenna module comprises a first electronic receiving circuit configured to process signals received by the second receiving structure of the first antenna module, and the second antenna module comprises a second electronic receiving circuit configured to process signals received by the second antenna module. receiving structure, wherein the first and second electronic receiving circuits are configured to process the received signals synchronously with the radiated electromagnetic signals, the synchronization being based on signals provided by the individual signal generator.

A radar system according to any one of claims 1 to 15, wherein the system further comprises:

a first processing circuit for processing signals received by the first antenna module, the first processing circuit being configured to provide the first type of radar plots of detected objects represented by the signals received by the first antenna module; and a second processing circuit for processing signals received by the second antenna module, the second processing circuit being configured to provide second type of radar plots of detected objects represented by the signals received by the second antenna module.

A radar system according to claim 16, wherein the system further comprises:

a third processing circuit, which is a radar track processing circuit, the radar track processing circuit configured to provide a radar track for a detected object based on both the first and second types of radar plots.