Title of Invention

"AN ELLIPTICAL SLOTTED WAVEGUIDE ONE PLANE MONOPULSE ARRAY ANTENNA"

Abstract

The resonant planar array comprises of parallel rectangular waveguides into which longitudinal-offset slots have been cut as a basic radiating element. The radiating slots in each waveguide are spaced one half guide wavelength apart and are alternatively offset on opposite side of the waveguide centre line in order to have equiphase excitations. It requires coupling slots between radiating and feeding waveguide as feeding elements in addition to radiating slots. A centered-inclined slot located in the common broad wall of radiating and orthogonally placed feeding waveguide is the widely used coupling element because of its better off resonance behaviour. To get the required performance over a desired frequency band of operation, the entire aperture has been divided into number of sub arrays and each sub array is then connected to two layer unequal (unequal in amplitude but equal in phase) waveguide power divider network via inclined coupling slots. A monopulse compartor network forms a critical part of this antenna. This network extracts power from the two halves of the antenna to give a sum pattern and a difference pattern.

Full Text

FIELD OF INVENTION : This invention relates to mechanically scanned slotted waveguide array antennas and more specifically to multilayer elliptical resonant slotted waveguide one plane monopulse array antennas. PRIOR ART: High gain and efficient antennas form an integral part of any Radar utilised for ground as well as airborne applications. For airborne radar applications, the requirement for high gain, efficient and compact antennas is all the more high. These antennas could be of active as well as passive type. Active antennas employ active elements and have in-built transmit/receive modules for each of the radiating elements. Passive antennas do not employ active elements. These passive antennas can be categorised into reflector based antennas and planner phased arrays antennas. Planner phased antennas can be further categorised into electronically scanned arrays and mechanically scanned arrays. Among the mechanically scanned array antennas, waveguide slotted arrays have been attractive candidate for high efficiency planar array antennas as waveguide provides exceptionally low path loss. These arrays are known for their ruggedness, low loss and high power handling capability. This type of array generally use longitudinal off-set slot located on the broad wall of a rectangular waveguide as a radiating element, centered-inclined slot located in the common broadwall of two rectangular waveguides kept orthogonal to each other as coupling element, multilayer feeding structure comprising of a network of inclined coupling slots and corporate waveguide unequal power divider network along with monopulse comparator network.. The major function of a monopulse slotted array antenna is to produce a pencil/fan shaped radiated beam of the desired polarisation, beam width, copolar side lobe levels, cross polar levels and gain at the sum port of the antenna over a desired band of operation. The difference port of the antenna gives a difference pattern of the specified beam width in a specified plane with a null at bore sight. Performance of a slotted array antenna with a low side lobe level depends on the accuracy with which individual radiating and coupling slots are characterised. The mechanical parameters for the radiating and coupling slots are determined after analysing the complex boundary value electromagnetic problems. Accurate theoretical and numerical analysis are required to achieve a high degree of accuracy in determining these parameters. A design methodology, based on extensive electromagnetic modelling using Method of Moments and Finite Element Techniques is used to meet the stringent electrical and mechanical requirements Computer aided design tools followed by computer controlled slot machining and suitable fabrication methodologies and joining processes are the key features for developing this kind of antenna. The weight, size and profile (compactness) of the antenna depends on the individual modules of the array like radiating and feeding waveguide dimensions, feeder network profile and monopulse comparator network. The mass production as well as production yield is an important issue related to the development of this class of antennas for designers/inventors all over the world. The complicated three dimensional structure with large number of modules arranged in multi layers, require a very high level of mechanical precision. It requires high accuracy of alignment in assembling different parts of antenna spread over different layers and perfects electrical contact at all the joins. At present, dip brazing and vacuum brazing technologies are used for manufacturing these array antennas. These array antennas and the methods for manufacturing the same are already known to the prior art. However, these array antennas and the methods for manufacturing the same suffer from following disadvantages. Main disadvantage of these array antennas, already known in the prior art is that these are not very compact, as these antennas utilise conventional three magic tees. Another disadvantage of these array antennas, known in the prior art is that manufacturing of these array antennas require very large infrastructure investment as these are manufactured by utilising costly dip brazing and vacuum brazing technologies. Still another disadvantage of these array antennas, known in the prior art is that these manufacturing of these antennas require highly skilled operations. Yet another disadvantage of these array antennas, known in the prior art is that Manufacturing of these antennas suffer from high rejection rate. Still another disadvantage these array antennas, known in the prior art is that these antennas suffer from high loss and low efficiency due to the accumulation of flux in the waveguide structures during the brazing operation. OBJECTS OF THE INVENTION: The primary object of this invention is to provide an elliptical slotted waveguide one plane monopuse array antenna and a process for manufacturing the same. Another object of the invention is to provide an elliptical slotted waveguide one plane monopulse array antenna which can be utilised for several applications including maritime patrol air borne radar applications. Yet another object of the invention is to provide an elliptical slotted waveguide one plane monopulse array antenna which is very compact as it employs an improved feeder network incorporating waveguide with nonstandard dimensions 'having reduced height and one plane monopulse comparator network incorporating waveguide planar magic tee. DESCRIPTION OF THE TN VENTION; According to this invention there is provided an elliptical slotted waveguide one plane monopulse array antenaa comprising: i) radiating cavity plate (1) forming the first layer of * said antennacomprises a plurality of rectangular waveguides (7) stacked side by side making a planar aperture, a portion of narrow wall of each of the said rectangular waveguide (7) sitting in the corresponding grooves (15) made in the said aperture cover plate (2) to mechanically join the said radiating cavity plate (1) to the said aperture cover plate (2); i i ) said aperture cover plate (2) forming the second layer of the said antenna and having a plurality of grooves(15) corresponding to the sealing height of the said narrow walls of the said rectangular waveguides (7), a portion of the said narrow walls of the said rectangular waveguides (7) sitting in the said grooves (15) of the said aperture cover plate (2), the said aperture cover plate (2) having suitable means to mechanically join the said aperture cover plate (2) with the said combined shield cover (3) 111 ' said combined shield cover plate (3) forming the third layer of the said antenna and havingplurality of grooves (23) with lugs on the ore side of the plate as joining means for mechanically joining the said combined shield cover plate (3) with the said cover plate (2) and plurality of grooves (29) with lugs on the other side of the plate as joining means to mechanically join the said combined shield cover plate (3) with the said power divider network (4), the said magic tee network (5) and the said folded shorts (6) ; iv) said power division network (4) having two 1:8 unequal waveguide corporate power divider networks (32,33), the said two corporate power divider networks (32,33) separately comprising 1:4 unequal power divider networks (34,35) and (36,37) respectively which are connected through a 1:2 equal power divider networks (38,39); v) said planar magic tee network (5) has a two layer structure comprising H-plane waveguide: tee junction (69), the said H-plane waveguide junction (69) connected to another waveguide (71) lying above and parallel to the main arm (72) of the said H-plane waveguide tee junction through slot (70); DESCRIPTION OF INVENTION In accordance with the present invention, there is provided an elliptical slotted waveguide one plane monopulse array antenna which can be utilised for ground based as well as airborne Radar applications. The elliptical slotted waveguide one plane monopulse array antenna of the present invention is highly compact, efficient and is easy to manufacture. The antenna of the present invention does not require costly dip brazing techniques for manufacturing purposes. The profile of the antenna of the present invention has been devised based upon an improved feeder network design using non-standard, reduced heigh wavegined dimensions and new one plane monopulse comparator network design based on waveguide planar magic tee. An improved magic tee utilised in the antenna of the present invention has helped in reducing its overall size and weight to a great extent and thereby making it most suitable for airborne Radar applications. The antenna of the present invention is easier and cheaper to make and its manufacturing process doesnot suffer from high rejection rates. DESCRIPTION OF THE DRAWINGS: Any further characteristics, advantages and applications of the invention will become evident from the detailed description of the preferred embodiment which has been described and illustrated with the help of following drawings wherein, Fig. 1 shows an exploded view of the antenna of the present invention Fig. 2 shows the radiating cavity plate Fig. 3 shows the aperture cover plate Fig. 4 shows the combined shield cover plate Fig. 5 shows the power division network Fig. 6 shows the magic tee network Fig. 7 shows the folded short Fig. 8 shows longitudinal offset slot in a rectangular waveguide Fig. 9 shows coupling between two waveguides through a centred-inclined slot Fig. 10 shows cross-sectional view of a typical H-plane waveguide tee joint Fig. 11 shows magic tee junction with a transverse slot coupled difference arm DESCRIPTION OF THE INVENTION The multi layer slotted array antenna of the present invention comprises of about 50 radiating waveguides of dimensions 22.43 x 5.08 mm, stacked side by side to make an elliptical planar array of the radiating aperture size 1200 mm x 250 mm (max.). The non-standard radiating and feeding waveguide dimensions have been chosen in such a way that inter element spacing in both the waveguides (i.e. radiating waveguide and feeding waveguide) remains same. The entire aperture of the planar array is divided into 16 subarrays to get the required 400 MHz bandwidth. The radiating waveguides of each subarray are short circuited at both ends and an additional waveguide called feed guide passes perpendicular to and underneath radiating waveguides is used to feed the radiating waveguide via coupling slots (called first layer coupling slots or radiating guide feed slots). The coupling slots, one for each radiating waveguide are situated in the common broad wall of the two waveguides. These slots are spaced half a guide wavelength apart in the feeding waveguide and are alternatively inclined in opposite directions to achieve equiphase excitation from coupling slots to the radiating waveguides. These feed lines in turn are connected to the unequal power divider network through another layer waveguide containing second layer coupling slots which in turn connected to monopulse comparator network Referring to Fig (1), the antenna of the present invention comprises main sub-assemblies: radiating cavity plate (1), aperture cover plate (2), combined shield cover plate (3), power Ouision network (4), magic tee network (5) and folded short (6). Referring to Fig (2), the radiating cavity plate (1) contains 100 number of rectangular channels (7) (forming rectangular waveguides with one of their broad walls removed) of the dimensions (22.43 mm X 5.58 mm) sharing a common narrow wall (8) of thickness 1 mrn with each other. Out of 5.58 mm height, 0.5 mm height (9) is used for the sealing purposes with the next assembly (2) giving actual internal waveguide dimensions of 22.43 mm X 5.08 mm after assembly. The broad walls (of thickness 1 mm) of 100 waveguides have 452 round corner rectangular slots (10) of the above dimensions and locations machined on it. Number of different types of taped holes (11, 12 & 13) are provided at the cross over of rectangular channel narrow walls. This looks like as if number of rectangular waveguides are stacked side by side to make a planar aperture with one of the broad walls of these waveguides removed. A minimum of four miniature screw threads (14) provided for each waveguide channel to fix with the aperture cover plate (2). This forms the top (first) layer of the antenna. Referring to Fig (3), the aperture cover plate comprises a number of grooves (15) on one side of the plate with 100 number of round cornered centred-inclined slots (16) on a 1 mm wall. These grooves are to accommodate the sealing height (9) of the radiating cavity plate. The other side of the plate have 16 number of rectangular channels (17) made in such a way that these rectangular channels are perpendicular to the grooves of the other side of the plate. Number of different types of holes (through holes and counter bore) 23) are provided to match with cavity and hinge brackets, threaded mounting pads (24-27) for integration with combined shield cover (3). This forms the second layer of the antenna. The radiating cavity plate (1) and aperture (2) cover plate are kept in such a way that a portion (9) of the narrow wall of the rectangular waveguide channel (8) of radiating cavity plate (1) sits in the groove (15) of the aperture cover plate (2) such that a common wall exists between two plates. In this arrangement, the rectangular waveguide channels of (1) and (2) are perpendicular to each other with a common broad wall where round cornered centred- inclined rectangular slots are located. Referring to Fig. (4) the combined shield cover plate (3) which is 1 mm thick sheet, is provided with about 1 mm wide and 0.3 mm .deep grooves (28) with suitable lugs (24-27) on one side of the plate to seal the rectangular channel (17) of aperture cover plate (2). The other face of the plate have sealing grooves (29) with number of suitable lugs with holes (24-27) to seal the power divider network (4), magic tee network (5) and folded shorts (6). The plate have a number of round cornered rectangular slots (30) as per location, orientation and dimension and folded short apertures (31) on the 1 mm wall. Referring to Fig. (5) Powei 'i.vision network comprises of two 1:8 unequal waveguide corporate power divo«r networks (32, 33). These power divider networks separately comprise tw 1:4 unequal power divider networks( 34, 35) and (36, 37) respectively connected through a 1:2 equal power divider networks 38 and 39 of waveguide dimensions 22.43 x 5.38 mm. 0.3 mm height out of 5.38 mm is utilizing in sealing with the surface groove 28 of the combined shield cover (3). This 1:2 equal waveguide power divider (38 & 39) is septum based biplane tee junction. Septum 40 has been utilized to divide the incoming power into two equal parts. The length of the tee arm is kept in such a way that input of the 1:4 power divider network (34 & 35) receives same power both in amplitude and phase. The incoming signal in power divider (34) is divided unequally into two parts using septum (41) of dimensions 11.5 x 1.2 x 5.38 mm at said location. Two irises (42) are utilized to improve the input match along with two optimized Eplane bends (43, 44). The unequally divided signals using septum (41) is further divided into four unequal parts using septums (45) and (46). Number of irises (47, 48, 49, 50,51,52, 53 & 54) are used to improve the overall input match of the power divider. As output locations (55, 56, 57 & 58) of the power divider network (34 (typical) is fixed and has to match with the shielded cover inclined slot locations, number of E-plane bends (59, 60, 61, 62, 63 & 64) are used. Different type of mounting lugs (65, 66 & 67), distributed suitably to match with the corresponding lugs/holes of the shield cover (3) are provided to make the sealing with combined shield cover effective. Referring to Fig. (6), the planar magic tee network (5) is a two layer structure to provide monopulse capability for the array antenna. This two layer structure (68) consists of a H-plane waveguide tee junction (69) through a slot (70) to another waveguide (71) lying above and parallel to the main arm (72) of the biplane tee junction. The slot is located in the common broad wall of the two waveguides as per said dimensions and locations given. The upper waveguide (71) is fed from one end (73) and short-circuited to the other end at appropriate point (74). This waveguide will correspond to the difference arm of the magic tee. The other three magic tee ports (75, 76 & 77) are located in the bottom side as shown. A septum (78) of the said dimension and location is used to divide the incoming power from the port (77) without affecting the coupling from the waveguide (71) to the waveguide (69) through slot (70). Two irises (79) and (80) are used to improve the input match of sum and difference ports. This two layer structure has to match suitably with power dividers (38) and (39). Different type of lugs/holes. (81,82) are provided for proper fixing and sealing with the power divider network. Referring to Fig. (7), when two first layer feed waveguides (17) meet end to end, there is not enough space for each waveguide to continue to a short circuit half a guide wavelength beyond tn« last slot. It is therefore necessary to fold the waveguide as shown in Fig (1) md create a short circuit at an appropriate distance equivalent to a half guide wavelength short circuit in a straight waveguide. The end folded short (83) and combined folded short (84) shown in Fig (7) are placed at appropriate places (85, 86) as shown in Fig (1). Referring to Fig. (8), The resonant planar array consists of parallel rectangular waveguides into which longitudinal - offset slots have been cut as a basic radiating element. The radiating slots (10) in each waveguide are spaced one half guide wavelength apart and are alternatively offset on opposite side of the waveguide centre line in order to have equiphase excitations. It requires coupling slots between radiating and feeding waveguide as feeding elements in addition to radiating slots. Referring to Fig. (9), a centered-inclined slot (16) located in the common broad wall of radiating and orthogonally placed feeding waveguide is the widely used coupling element because of its better off resonance behaviour. To get the required performance over a desired frequency band of operation, the entire aperture has been divided into number of sub arrays and each sub array is then connected to two layer unequal (unequal in amplitude but equal in phase) waveguide power divider network via inclined coupling slots. A monopulse compartor network forms a critical part of this antenna. This network extracts power from the two halves of the antenna to give a sum pattern and a difference pattern. Referring to Fig. (10), the coupling waveguides are connected together through a waveguide unequal power divider network, which takes care of distribution and matching. The unequal power divider network is based on Hplane tee junction with two irises, first to split the incoming power to two output ports and the second to match the input port. A number of such H-plane tee junctions in conjunction with different types of bends and matching irises are used to improve the design of two layered 1:n unequal power divider network within the space available. Referring to Fig. (11), A novel technique based on Method of Moments and FEM have been invented to design a compact, non-standard, reduced height waveguide planar magic tee junction. It is a two layer structure consisting of Hplane waveguide tee junction coupled through a slot to another waveguide lying underneath and parallel to the main arm of the H-plane tee junction. The distinguishing feature of this component is the placement of difference port on a layer separated from other three ports by a common waveguide broad wall. The two parts of the component are coupled through ^ slot located in the common broad wall of twor T-he lower waveguide (shown in dotted line) is fed from one end (port # 4) and short circuited at other end at appropriate point. This waveguide will correspond to the difference arm of the magic tee. The other three magic tee ports are located in the bottom side as shown by solid lines. Referring to Fig. (1), during transmit/receive mode of operation, a RF signal of unit amplitude is applied to the sum/difference port of the antenna manifold. The sum port / difference port Junetions split the RF signal into first half signal that corresponds to the outgoing/incoming RF signal as transmitted/received by one half of the antenna and a Second half signal that corresponds to the outgoing/incoming RF signal as transmitted/received by another half of the antenna through a waveguide unequal power divider network. The sum port junction which is a septum based H-plane tee junction, splits the signal into two halves both in amplitude and phase and thus giving a sum pattern. The difference port, which is achieved through a co-linear waveguide to waveguide coupling through a transverse slot, splits the signal into two halves equal in amplitude but opposite in phase, thus producing a difference pattern. The first half/ second half signa[ is further divided equally by the tee junction (38) and "(39")'Half slgViaTarrlvihg~af junctidn~"(38)"6f the'"waveguide power divider network gets splitted further into two parts equally (both in amplitude and phase) by septum (40). Afterwards, first quarter signal flows in quadrant (34) and the second quarter signal flows in quadrant (35) of the antenna. For the sake of simplicity, the RF signal flow in only one quadrant (34) of the antenna is described here. The signal flow in all other quadrants are similar. First quarter signal flowing in quadrant (34) power divider network get divided unequally in amplitude but equally in phase at junctions (41, 45 & 46) to get the required amplitude distribution at the waveguide out put ports (input of the sub array ports). This amplitude weighting (distribution) is used to get the required side lobe pattern of the antenna during transmit and receive modes of operation. RF signal reaching waveguide power divider network output ports (55, 55, 57 and 58) are coupled to the first layer feed guide rectangular channels (17) through second layer round cornered centered inclined slots (30). The orientation and dimensions of the slots are designed in such a way that the signal flowing to the power divider network output ports get coupled fully to the first layer feeder guide. The signal flowing in feed guide rectangular channels (17) are coupled to the radiating waveguide rectangular channel (7) through first layer inclined slots (10) located in the common broad wall of radiating waveguide rectangular channels (7) and first layer feed guide rectangular channel (17). The dimensions and orientation/tilt of the inclined slots are designed to get the required amplitude distribution across the first layer rectangular channels. First layer inclined slots (17), one for each rectangular channel (7), are used to excite radiating slots (10) to get the required amplitude and phase excitation across the radiating slots for a specified radiation pattern. The present embodiment of the invention, which has been set forth above, was for the purpose of illustration and is not intended to limit the scope of the invention. It is to be understood that various changes, adaptations and modifications can be made in the invention described above by those skilled in the art without departing from the scope of the invention which has been defined by following claims. WE CLAIM: 1. An elliptical slotted waveguide one plane monopulse array antenna comprising i) radiating cavity plate (1) forming the first layer of said antenna /comprises a plurality of rectangular waveguides (7) stacked side by side making a planar aperture, a portion of narrow wall of each of the said rectangular waveguide (7) sitting in the corresponding grooves (15) made in the said aperture cover plate (2) to mechanically join the said radiating cavity plate (1) to the said aperture cover plate (2); ii) said aperture cover plate (2) forming the second layer of the said antenna and having a plurality of grooves(15) corresponding to the sealing height of the said narrow walls of the said rectangular waveguides (7), a portion of the said narrow walls of the said rectangular waveguides (7) sitting in the said grooves (15) of the said aperture coyer plate (2), the said aperture cover plate (2) having suitable means to mechanically join the said aperture cover plate (2) with the said combined shield cover (3) said combined shield cover plate (3) forming the third layer of the said antenna and having plurality of grooves (28) with lugs on the one side of the plate as joining means for mechanically joining the said combined shield cover plate (3) with the said cover plate (2) and plurality of grooves (29) with lugs on the other side of the plate as joining means to mechanically join the said combined shield cover plate (3) with the said power divider network (4), the said magic tee network (5) and the said folded shorts (6); iv) said power division network (4) having two 1:8 unequal waveguide corporate power divider networks (32,33), the said two corporate power divider networks (32,33) separately comprising 1:4 unequal power divider networks (34,35) and (36,37) respectively which are connected through a 1:2 equal power divider networks (38,39); v) said planar magic tee network (5) has a two layer structure comprising H-plane waveguide; tee junction (69), the said H-plane waveguide junction (69) connected to another waveguide (71) lying above and parallel to the main arm (72) of the said H-plane waveguide tee junction through slot (70); 2. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said V2 equal power divider (38, 39) of said power division network (4) is a septun based H-plane tee junction. 3. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said power division network (4) comprises a plurality of septums to divide the incoming power and a plurality of irises to improve the input match. 4. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said power division network (4) has comprises means to mechanically join the said power division network (4) with the said combined shield cover (3). 5. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said planar magic tee network (5) is a two layer structure comprising a H-plane waveguide tee junction (69) coupled to another waveguide (71) through a suitable slot. 6. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said magic tee network (5) comprises a plurality of septums to suitably divide the incoming power and a plurality of irises to suitably improve the input match. 7. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said magic tee network (5) has suitable means to mechanically join the said magic tee network (5) with the said power division network (4). 8 An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1) wherein, the said plurality of rectangular waveguides have longitudinal offset slots cut therein. 9. An elliptical slotted waveguide one plane monopulse array antenna as claimed in claim (1), wherein the said magic tee (5) is of non-standard type having reduced height and size. 10. An elliptical slotted waveguide one plane monopulse array antenna substantially as described and illustrated herein.

Documents:

686-del-2002-Abstract-(26-12-2013).pdf

686-del-2002-abstract.pdf

686-del-2002-Claims-(26-12-2013).pdf

686-del-2002-claims.pdf

686-del-2002-Correspondence Others-(26-12-2013).pdf

686-del-2002-Correspondence-others (10-08-2009).pdf

686-del-2002-correspondence-others.pdf

686-del-2002-correspondence-po.pdf

686-del-2002-description (complete).pdf

686-del-2002-drawings.pdf

686-del-2002-form-1.pdf

686-del-2002-form-18.pdf

686-del-2002-form-3.pdf

686-del-2002-gpa.pdf