Claims:
1. A high gain cavity-enclosed slotted ridge waveguide antenna system, said system comprising:

a plurality of rows stacked vertically wherein said plurality of rows comprising a plurality of single ridge waveguides;

each row of said plurality of rows comprising said plurality of single ridge waveguides arranged linearly forming an array, wherein a predetermined number of said single ridge waveguides in said each row grouped to form atleast two sub-arrays;

atleast one calibration slot for each sub-array for enabling calibration of said single ridge waveguides;

said single ridge waveguide comprising:

a plurality of walls for defining said single ridge waveguide

atleast one slot disposed on atleast a wall of said single ridge waveguide for providing a desired radiation pattern; and

a ridge projected inward from a wall opposing said wall comprising said atleast one slot of said single ridge waveguide for providing grating lobe free elevation scanning; and

a cavity enclosing said atleast one slot on said wall of each of said single ridge waveguide for reducing mutual coupling between said single ridge waveguides.

2. The high gain ridge waveguide cavity enclosed slotted antenna system of claim 1, wherein said plurality of rows of said plurality of single ridge waveguides are stacked one upon another in elevation plane direction for forming a scalable planar array.

3. The high gain ridge waveguide cavity enclosed slotted antenna system of claim 1, further comprising a plurality of feeds for said each row of said plurality of single ridge waveguides.

4. The high gain ridge waveguide cavity enclosed slotted antenna system of claim 3, further comprising a back folded waveguide feed for reducing interference between said plurality of feeds and said plurality of single ridge waveguides.

5. The high gain ridge waveguide cavity enclosed slotted antenna system of claim 1, wherein said cavity provides mechanical stability and better electrical performance to said antenna system.

6. The high gain ridge waveguide cavity enclosed slotted antenna system of claim 1, wherein each row of said plurality of waveguides comprises atleast one calibration guide corresponding to said atleast one calibration slot and an isolation device is placed between a left calibration guide and a right calibration guide for improving calibration purity.

, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)

“HIGH GAIN CAVITY-ENCLOSED SLOTTED RIDGE WAVEGUIDE ANTENNA SYSTEM”
By
BHARAT ELECTRONICS LIMITED
Nationality: Indian
Address: OUTER RING ROAD, NAGAVARA, BANGALORE - 560045,
KARNATAKA, INDIA

The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
[0001] The present disclosure relates generally to an array of antennas and more particularly to a ridge waveguide cavity enclosed slotted antenna.

BACKGROUND
[0002] Antenna is a key component in design of any radar system. The radar or satellite communication systems require compact, broadband, low side lobe and low loss antennas with both elevation and azimuth plane scanning capabilities. The antennas currently in use are of different types such as printed PCB antennas, wire antennas and waveguide antennas. A waveguide is an electromagnetic wave conducting device made up of metal (Aluminium, Copper etc.,) with any kind of cross section such as rectangular, circular, elliptical etc. The openings machined in the conducting walls of waveguide, called slots are used for designing antennas and these types of antennas are called waveguide slotted antennas. A rectangular waveguide slotted antenna may have slots machined in either in a broad wall or a narrow wall according to design requirements. The waveguide slotted antennas are widely used at frequencies above 4GHz where high gain, high efficiency are the essential parameters. The waveguide slotted antennas are the most preferred for development of long range radars as they offer high efficiency compared to other two types of above mentioned antennas.

[0003] Though a simple rectangular waveguide antenna with slots in the broadwall has higher efficiencies, it can be used for only limited scanning in a planar array configuration due to the large broad wall dimension. Wide angle scanning requires half wavelength spacing between array elements. A ridge waveguide is a modified rectangular waveguide with inward projections called ridges. The ridge is used to reduce the cross-section of the waveguide. The ridge waveguide can be used to alleviate the above limitation of scanning. With the use of the ridge waveguide above spacing requirement can be used. But the dimensions of the ridge waveguide becomes compact that various hybrid modes along with the required dominant modestarts to propagate which need to be taken into account in the design of the antenna.

[0004] The prior art US 3189908A titled “Ridged waveguide Slot Antenna” discloses a slotted waveguide antenna in a ridge waveguide. However this does not have a provision for calibration channel and also does not have a provision for reducing mutual coupling between radiating slots in the antenna.The prior art US 4499474titled “Slot Antenna with Face Mounted Baffle" discloses a baffle interposed between two halves of antenna to reduce mutual coupling between antenna quadrants in a mono pulse array. However this also does not have provision to reduce mutual coupling between the radiating slots in the antenna, there by limiting the performance of the invention.

SUMMARY
[0005] The present invention discloses a cavity-enclosed slotted ridge waveguide antenna system with high gain. The cavity-enclosed slotted ridge waveguide antenna system comprises wide scanning capabilities and has reduced mutual coupling between radiating slots in the cavity-enclosed slotted ridge waveguide antenna system. The disclosed cavity-enclosed slotted ridge waveguide antenna system has improved performance with respect to wide frequency of operation with good matching, wide elevation scanning and an embedded calibration mechanism an essential feature for use of this antenna with active phased array.

[0006] The disclosed antenna of the present invention is a high gain cavity enclosed slotted waveguide antenna system comprises multiple vertically stacked single ridge waveguides. Each of the single ridge waveguide antenna has a slot machined in a broadwall of the single ridge waveguide for enabling radiation. A number of such single ridge waveguides are adjacently placed in horizontal direction to form a linear array and a predetermined number of the single ridge waveguides are grouped to form atleast two sub-array. A metallic plate may be placed between consecutive sub-arrays to improve the isolation between the sub-arrays. The linear sub-arrays are stacked upon one another in vertical direction, that is elevation direction for forming a planar array.

[0007] A single ridge waveguide is a hollow structure formed by four metallic walls, with an inward cuboid shaped projection called ridge from a broadwall. Atleast one slot which serves as a radiating element is disposed on the broadwall opposite to the ridge of a ridge waveguide. This slot is surrounded by a cavity formed by four side metallic walls. The cavity reduces mutual coupling between the radiating elements i.e. the slots. The cavity also provides mechanical stability to the high gain cavity-enclosed slotted ridge waveguide antenna system.

[0008] Each of the single ridge waveguide in the antenna sub array system further comprises one calibration slot electromagnetically coupled to a calibration guide of the subarray. A device known as magic tee is used to combine sub-array calibration guides with a high degree of isolation between them. Each sub-array is fed independently with a back side folded waveguide having a coaxial connector.

[0009] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention

BRIEF DESCRIPTION OF DRAWINGS
[0010] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0011] FIGS. 1A-1B exemplarily illustrate an architecture of a high gain ridge waveguide cavity enclosed slotted antenna system.

[0012] FIG. 2 exemplarily illustrates a single ridge waveguide with the radiating element of a linear sub array.

[0013] FIG. 3 exemplarily illustrates the linear array comprising multiple radiating structures.

[0014] FIG. 4 exemplarily illustrates a feed input with a back side folded waveguide for a linear sub-array of the linear array.

[0015] FIG. 5 exemplarily illustrates the magic tee junction, the guard antenna, the feed input, a calibration slot, and a calibration guide integrated with multiple rows of the linear sub-arrays.

[0016] FIGS. 6A-6B illustrates measured radiation pattern of the high gain cavity enclosed slotted waveguide antenna system in the azimuth plane and the elevation plane respectively.

[0017] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF DRAWINGS
[0018] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0019] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0020] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.

[0021] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic is intended to provide.

[0022] FIGS. 1A through 6B, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communications system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.

[0023] FIGS. 1A-1B exemplarily illustrate an architecture of a high gain cavity-enclosed slotted ridge waveguide antenna system 100, henceforth referred to as waveguide antenna system 100. FIG. 1A exemplarily illustrates a top view of the high gain cavity enclosed slotted waveguide antenna system 100. The antenna system 100comprises multiple rows of single ridge waveguides 102 stacked vertically to form a scalable planar array. Each row of single ridge waveguides 102 comprises multiple waveguides and each row as a whole is called as a linear array 102. FIG. 1B exemplarily illustrates a bottom view of the antenna system 100. The antenna system 100 further comprises a magic tee 103, and a guard antenna 104.The linear arrays 102 may be stacked one upon another to form a planar array in a vertical direction (in elevation).The antenna system 100 may be used for all the frequency bands, for example, X-band. The antenna system 100 may be fabricated either by a Computer Numerical Control (CNC) machine or 3D Printing methods.

[0024] .FIG. 2 exemplarily illustrates a single ridge waveguide 101of a linear array102. The single ridge waveguide 101 comprises multiple walls, such as, a pair of broad walls and a pair of narrow walls for defining the single ridge waveguide 101 comprises a radiating slot 201, herein after referred to as antenna element 201 that is cut on the broad wall of single ridge waveguide 101. The position of the antenna elements 201 in the broad wall of single ridge waveguide 101 is based on a desired radiation pattern characteristics for the antenna system 100. The antenna element 201 is cut in a predetermined fashion on the broad wall of the single ridge waveguide 101. A single side open-ended rectangular cavity 202 encloses the antenna element 201 for reducing mutual coupling between the single ridge waveguides 101. The cavity 202 provides better electrical performance along with ease of mechanical fabrication and mechanical stability to the antenna system 100. Embedding the antenna element 201 in the single side open-ended rectangular cavity 202 resulted in an improvement in the frequency bandwidth of the antenna. In an embodiment, the cavity 202 is a metallic cavity. The single ridge waveguide 101 further comprises a ridge 203 projected inward from a wall opposing the wall comprising the antenna element 201.

[0025] FIG. 3 exemplarily illustrates a sub-array comprising multiple single ridge waveguides 101. Each linear array comprises a predetermined number of single ridge waveguides 101 grouped to form atleast two sub-arrays. The two sub-arrays may be placed adjacent to each other horizontally forming the linear array 102 of multiple single ridge waveguides 101. .The two sub-arrays are left sub-array and right sub-array. A metallic wall 301 may be placed between the consecutive sub-arrays, that is the left sub-array and the right sub-array. The metallic wall 301 acts as an isolating plate between left sub-array and the right sub-arrays. Each sub-array comprises equal number of single ridge waveguides 101 and the antenna elements 201. The cavity 202 surrounding each antenna element 201 aids in reduction of mutual coupling between the antenna elements 201. A scalable planar array design may be accomplished by replicating and stacking the linear arrays 102 one over another in an elevation plane direction. Stacking of the linear arrays 102 of the single ridge waveguides 101 aids in achieving grating lobe free wide elevation scanning.

[0026] FIG. 4 exemplarily illustrates the mechanism of feeding each sub-array with a back folded waveguide 402. A feeding input 401 is a coaxial feed with a U shaped ridge structure 403. Each sub-array of the linear array 102 of the antenna system 100 is fed from ends with equal phase and amplitude through the feeding mechanism comprising 401, 402 and 403. Each linear array 102 is fed with multiple feeding inputs 401. Feeding each sub-array of the linear array 102 of the antenna system 100 from both ends with equal phase and amplitude ensures a broadband performance while maintaining high gain and beamwidth. Projection length of the centre conductor of the coaxial connector into the U shaped ridge structure 403 is optimized for broadband match. The projected centre conductor of the coaxial connector in the middle of the U shaped ridge structure 403 acts as an electric probe and excites dominate mode in the ridge guide which in turn excites the left sub-array and the right sub-array.

[0027] The feeding inputs 401 of the left sub-array and the right sub-array of the linear array 102 are brought to the bottom by a back folded waveguide 402 with a 180 ° bend. The signal to each left sub-array and right sub-array is fed through the back folded waveguide 402 along with the coaxial connector. The use of the back folded waveguide 402 feed mechanism reduces the interference of signal feeding structures, such as, the feeding inputs 401, with the antenna elements 201. The feeding mechanism with 401, 402, and 403 reduces the overall length of the antenna system 100 thereby making the antenna system 100 compact. The use of back folded waveguide 402 aids in designing an integrated dual (one for each end) compact, closely spaced transmit-receive modules providing the minimized loss of signal, imbalance in amplitude and phase between the left sub-array and the right subarray. The left sub-array and the right sub-array feeding by separate feeding input 401, enables realization of monopulse feature that may be used for tracking. .The antenna system 100 is scalable in vertical direction depending on gain requirement The capability of feeding the linear arrays 102 of the antenna system 100 using the back folded waveguide 402,enables the feed location to be reconfigurable to any position in backside of the antenna system 100 without disturbing radiating modules.

[0028] FIG. 5 exemplarily illustrates the magic tee junction 103, the guard antenna103, the feed input 401, a calibration slot 501, and a calibration guide 502 integrated with the stacked sub-arrays. The antenna system 100 comprises a calibration methodology for usage in an active phased linear array systems. The antenna system 100 comprises atleast one calibration slot 501 for each sub-array. A calibration guide 502 along with the calibration slot 501 is used to calibrate each of the electronics feeding the sub-arrays of linear array 102.The integrated magic tee 102 provides isolation between left and right calibration guides 502 corresponding to the left sub-array and right sub-array of the linear array 102. Integration of the magic tee 102 with the sub-arrays provide high degree of isolation between calibration guides 502. The magic tee 102 couples signals from right and left calibration guides 502 with high isolation and improves calibration purity. The guard antenna 103, integrated with the slotted waveguide antenna system 100 on the same face, cancels the side lobes on the same radiating plane as that of the sub-arrays.

[0029] FIGS. 6A-6B exemplarily illustrate measured radiation patterns of an antenna system 100 in the azimuth plane and the elevation plane respectively. The fabricated antenna system 100 comprises 31 stacked linear arrays 102. Each linear array 102 has two sub-arrays with each sub array having 16 elements. Dimensions of the ridge waveguide enabled the linear array to be used as an element in a planar array design with spacing of 0.5*?0.This in turn ensured a grating lobe free elevation scanning in the elevation plane and provides dimensions of a compact antenna. The measured gain is about 35dBi.and has an efficiency of 95%.

[0030] Those skilled in this technology can make various alterations and modifications without departing from the scope and spirit of the invention. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.

[0031] FIGS. 1A-6B are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. FIGS. 1A-6Billustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.

[0032] In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.

[0033] It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.