GB1584223A

GB1584223A - Radar aerial feeds

Info

Publication number: GB1584223A
Application number: GB2257077A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1978-05-15
Filing date: 1978-05-15
Publication date: 1981-02-11

Description

(54) IMPROVEMENTS IN OR RELATING TO RADAR AERIAL FEEDS (71) We, THE PLESSEY COMPANY LI MITED, a British Company of Vicarage Lane, Ilford, Essex, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to radar aerials or aerial feeds.

It is known to provide an aerial feed which includes delay means distributed along its length whereby the launch angle of a radiated radar signal is rendered frequency dependent.

In practice the feed may comprise a length of waveguide having radiating slots formed in spaced apart relationship along its length and grooves formed within the waveguide on a surface facing the slots, the grooves being provided so as to increase the propagation time along the waveguide whereby phase changes experienced by signals launched into the waveguide are rendered frequency dependent whereby the launch angle is constrained also to be frequency dependent. Such aerial feeds are used in so-called 3D (three dimen sional) radar systems wherein the radar beam is scanned in elevation by changing the radar frequency.

It is also known to provide a variable polarisation aerial feed in which the polarisation of a radiated signal may be determined in accordance with signals fed to the feed.

A variable polarisation feed might comprise a pair of overmoded waveguides defined by two waveguides positioned side-by-side each having formed therein at spaced apart locations, slots aligned with the longitudinal axis of the guides and wherein overmoding is produced by providing in addition, transverse slots, at spaced apart locations which cut across both waveguides of the pair, the wall between the waveguides being relieved in the region of the transverse slots so that in these regions the waveguides are in mutual communication. With this arrange ment the waveguides of the pair are fed with a pair of similar signals one to each wave guide, the polarisation of the signal radiated from the feed being determined in depen dence upon the phase relationship between the signals of the pair.

It is an object of the present invention to provide an aerial feed in which the launch angle is variable in dependence upon two parameters appertaining to signals fed to the aerial feed whereby limits appertaining to one parameter between which that parameter must be changed to produce a predetermined change of launch angle are dependent upon the other parameter.

According to the present invention an aerial feed comprises a pair of waveguides arranged side-by-side and having formed therein along its length in spaced apart relationship slots at least some of which link the waveguides of the pair and phase modifying means responsive to signals fed from the slots for providing an output signal having an angle of launch relative to the feed which is determined in dependence upon the relative phase of signals fed to the waveguides of the pair.

Thus an aerial feed is provided in which the frequency change required to produce a predetermined change of launch angle is determined by the relative phase of the signals fed to the waveguides of the pair.

The launch angle is thus determined in dependence upon two parameters, the frequency of the signals fed to the waveguides of the pair and the relative phase of the signals.

The phase modifying means may comprise a plurality of open ended waveguide sections each operatively associated with a set of the slots and disposed orthogonally with respect to the longitudinal axis of the waveguides of the pair, the open ended waveguide sections each affording a phase delay determined in dependence upon the polarisation of the signal fed to it from the set of slots with which it is operatively associated.

Each set of slots may include a trans verse slot which links the two waveguides of the pair. The slots of each set may comprise one transverse slot and two vertical slots one in each waveguide of the pair whereby each set consists of three slots.

The open ended waveguide sections may be rectangular and the length of the wave guide open ended sections in the direction of radiation from the slot sets may be progressively increased from set to set along the feed to define a step configuration.

Each length or at least some lengths of open ended waveguide sections may be linked to the slot set with which it is operatively associated in the waveguide of a pair via a matching interface waveguide which may be of square cross section. The total length of the combination of each open ended waveguide plus its associated matching interface waveguide may be the same.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a perspective view of an aerial feed.

Referring now to the drawing, an aerial feed comprises a pair of waveguides 1 and 2 arranged side-by-side and separated by a dividing wall 3. Signals are introduced into the feed at one end of the waveguides 1 and 2 which are fed in parallel with signals via a phase adjusting arrangement (not shown) so that the phase relationship between the signals fed to the waveguides 1 and 2 can be controlled. In order to increase propagation delay along the waveguides 1 and 2 castellations or ridges 4 and 5 are provided along the length of the waveguide so as to form a plurality of grooves therein.

Radiating apertures or slots 6, 7 and 8 are defined in one wall of the wave guides, the slot 6 being transverse and linking the waveguides 1 and 2 and the slots 7 and 8 being vertical and aligned with the longitudinal axes of the guides. The slot 7 is formed in waveguide 2 and the slot 8 is formed in waveguide 1. The slot 6 which extends between the waveguides 1 and 2 produces in operation a phenomena described as overmoding. Beneath the slot 6 the wall 3 is relieved so that there is a communicating aperture in the wall between the waveguide 1 and the waveguide 2 whereby overmoding is facilitated. When the waveguides 1 and 2 are fed in parallel, a signal will be radiated from the slots 6, 7 and 8 into an open ended waveguide section 9 which is linked to the slots via a matching interface waveguide 10 of square cross section. The polarisation of the signal which is fed to the open ended waveguide 9 will be determined by the relative phase of the signals fed to the waveguides 1 and 2. In order to simplify the drawing only the slots 6, 7 and 8 associated with the interface waveguide 10 are shown.

These slots 6, 7, 8 which are normally covered by the interface waveguide 10, are therefore shown in broken lines. It will be appreciated that similar slots are provided (although not shown) communicating with open ended waveguide sections 11 and 12 via associated square matching interface waveguides 14 and 15, open ended waveguide section 13 being arranged directly to couple with its associated set of slots (not shown).

Due to the delay produced along the waveguides 1 and 2 by the grooves formed on an internal surface facing the slots, the phase angle of signals produced at the open ended waveguides 9, 11, 12 and 13 will be dependent upon the frequency fed to the waveguides. Thus it will be apparent that the launch angle of signals from the feed relative to its vertical axis say may be determined in accordance with the fre quency fed to the guides 1 and 2. How ever since the polarisation of the signals fed to the open ended waveguides 9, 11, 12 and 13 is determined in accordance with the relative phase relationship between the signals fed to the waveguides 1 and 2 and since the delay contributed by the open ended waveguides 9, I I, 12 and 13 is deter mined in accordance with the polarisation of the signals fed thereto, it will be apprecia ted that the relative phase of the signals apparent at guides 9, 11, 12 and 13 and thus the launch angle may be varied in accordance with the relative phase angle between the signals fed to the guides 1 and 2.

It will therefore be appreciated that a launch angle of 0 may be produced when the radar frequency is Fa say for a given phase angle between the signals fed to the waveguides, whereas the same launch angle may be produced at a different radar fre quency if the phase angle as aforesaid is changed.

WHAT WE CLAIM IS: 1. An aerial feed comprising a pair of waveguides arranged side by side and having formed therein along its length in spaced apart relationship slots, at least some of which link the waveguides of the pair and phase modifying means responsive to signals fed from the slots for providing an output signal having an angle of launch relative to the feed which is determined in dependence upon the relative phase of signals fed to the waveguides of the pair.

2. An aerial feed as claimed in claim 1, wherein the phase modifying means com prises a plurality of open-ended waveguide sections each operatively associated with a set of the slots and disposed orthogonally with respect to the longitudinal axis of the waveguides of the pair, the open-ended waveguide sections each affording a phase delay determined in dependence upon the polarisation of the signal fed to it from the set of slots with which it is operatively associated.

3. An aerial feed as claimed in claim 2, wherein each set of slots includes a transverse slot which links the two waveguides of the pair.

4. An aerial feed as claimed in claim 3, wherein the slots of each set comprise one transverse slot and two axial slots, one in

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Claims

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progressively increased from set to set along the feed to define a step configuration.

Each length or at least some lengths of open ended waveguide sections may be linked to the slot set with which it is operatively associated in the waveguide of a pair via a matching interface waveguide which may be of square cross section. The total length of the combination of each open ended waveguide plus its associated matching interface waveguide may be the same.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a perspective view of an aerial feed.

Referring now to the drawing, an aerial feed comprises a pair of waveguides 1 and 2 arranged side-by-side and separated by a dividing wall 3. Signals are introduced into the feed at one end of the waveguides 1 and 2 which are fed in parallel with signals via a phase adjusting arrangement (not shown) so that the phase relationship between the signals fed to the waveguides 1 and 2 can be controlled. In order to increase propagation delay along the waveguides 1 and 2 castellations or ridges 4 and 5 are provided along the length of the waveguide so as to form a plurality of grooves therein.

Radiating apertures or slots 6, 7 and 8 are defined in one wall of the wave guides, the slot 6 being transverse and linking the waveguides 1 and 2 and the slots 7 and 8 being vertical and aligned with the longitudinal axes of the guides. The slot 7 is formed in waveguide 2 and the slot 8 is formed in waveguide 1. The slot 6 which extends between the waveguides 1 and 2 produces in operation a phenomena described as overmoding. Beneath the slot 6 the wall 3 is relieved so that there is a communicating aperture in the wall between the waveguide 1 and the waveguide 2 whereby overmoding is facilitated. When the waveguides 1 and 2 are fed in parallel, a signal will be radiated from the slots 6, 7 and 8 into an open ended waveguide section 9 which is linked to the slots via a matching interface waveguide 10 of square cross section. The polarisation of the signal which is fed to the open ended waveguide 9 will be determined by the relative phase of the signals fed to the waveguides 1 and 2. In order to simplify the drawing only the slots 6, 7 and 8 associated with the interface waveguide 10 are shown.

These slots 6, 7, 8 which are normally covered by the interface waveguide 10, are therefore shown in broken lines. It will be appreciated that similar slots are provided (although not shown) communicating with open ended waveguide sections 11 and 12 via associated square matching interface waveguides 14 and 15, open ended waveguide section 13 being arranged directly to couple with its associated set of slots (not shown).

Due to the delay produced along the waveguides 1 and 2 by the grooves formed on an internal surface facing the slots, the phase angle of signals produced at the open ended waveguides 9, 11, 12 and 13 will be dependent upon the frequency fed to the waveguides. Thus it will be apparent that the launch angle of signals from the feed relative to its vertical axis say may be determined in accordance with the fre quency fed to the guides 1 and 2. How ever since the polarisation of the signals fed to the open ended waveguides 9, 11,

12 and 13 is determined in accordance with the relative phase relationship between the signals fed to the waveguides 1 and 2 and since the delay contributed by the open ended waveguides 9, I I, 12 and 13 is deter mined in accordance with the polarisation of the signals fed thereto, it will be apprecia ted that the relative phase of the signals apparent at guides 9, 11, 12 and 13 and thus the launch angle may be varied in accordance with the relative phase angle between the signals fed to the guides 1 and 2.

It will therefore be appreciated that a launch angle of 0 may be produced when the radar frequency is Fa say for a given phase angle between the signals fed to the waveguides, whereas the same launch angle may be produced at a different radar fre quency if the phase angle as aforesaid is changed.

WHAT WE CLAIM IS: 1. An aerial feed comprising a pair of waveguides arranged side by side and having formed therein along its length in spaced apart relationship slots, at least some of which link the waveguides of the pair and phase modifying means responsive to signals fed from the slots for providing an output signal having an angle of launch relative to the feed which is determined in dependence upon the relative phase of signals fed to the waveguides of the pair.
2. An aerial feed as claimed in claim 1, wherein the phase modifying means com prises a plurality of open-ended waveguide sections each operatively associated with a set of the slots and disposed orthogonally with respect to the longitudinal axis of the waveguides of the pair, the open-ended waveguide sections each affording a phase delay determined in dependence upon the polarisation of the signal fed to it from the set of slots with which it is operatively associated.
3. An aerial feed as claimed in claim 2, wherein each set of slots includes a transverse slot which links the two waveguides of the pair.
4. An aerial feed as claimed in claim 3, wherein the slots of each set comprise one transverse slot and two axial slots, one in

each waveguide of the pair whereby each set consists of three slots.
5. An aerial feed as claimed in any of claims 2 to 4, wherein the length of the waveguide open-ended sections in the direction of radiation from the slot sets is progressively increased from set to set along the feed to define a step configuration.
6. An aerial feed as claimed in any preceding claim, wherein each length or at least some lengths of open-ended waveguide section are linked to the slots with which it is operatively associated in the waveguides of the pair, via a matching interface waveguide.
7. An aerial feed as claimed in claim 6, wherein the open ended waveguide sections are rectangular.
8. An aerial feed as claimed in claim 5 or claim 6, wherein the matching interface waveguide are of the square cross-section.
9. An aerial feed as claimed in claim 6, claim 7 or claim 8, wherein the total length of the combination of each open-ended waveguide plus its associated matching interface waveguide is the same.
10. An aerial feed as claimed in any preceding claim, wherein grooves or corrugations or the like are provided on an inside surface of the waveguides opposite the slots, the grooves being effective to delay the propagation along the waveguides of signals launched into the waveguides.
11. An aerial feed substantially as hereinbefore described with reference to the accompanying drawing.
12. An aerial feed as claimed in any preceding claim in combination with a cylindrical parabolic reflector.
13. A radar system including an aerial feed as claimed in claim 12.