Title of Invention

A MICROSTRIP RADIO FREQUENCY LENS

Abstract

This invention relates to a micro strip radio frequency lens conjunction with line array antenna comprising of micro strip radio frequency lens assembly (6) characterized by having a plurality of beam ports (8), plurality of array ports (5), a printed circuit board (11) and a micro strip radio frequency lens (10), the said micro strip radio frequency lens (10) having a plurality of lens ports (16), each one of the said lens ports (16) coupled to a corresponding one micro strip exponentially tapered transmission line (18), each of the said micro strip exponentially tapered transmission line (18) coupled to a corresponding one variable length bootlace transmission line (19), each of the said variable length bootlace transmission line (19) coupled to a corresponding one array port (5), and each of the said array port (5) coupled to a corresponding one antenna elements (4), each one of the second opposing lens ports (15) of the said micro strip radio frequency lens (10) coupled to a corresponding beam ports (8) through a corresponding micro strip exponentially tapered transmission line (17); wherein, each of the said antenna element (4) is coupled to a corresponding one array port (5) through a corresponding one equal line length coaxial transmission line (7); wherein, each of the said beam port (8) is coupled to a EW/ Radar system (2) through a corresponding one coaxial transmission line (9); wherein, the said array ports (5) of the said lens assembly (6) are tilted with respect to the normal to array port (5) contour to achieve the symmetric amplitude distribution across array elements (4); wherein, the said lens assembly (6) is housed in a cavity with top plate edge (33) made of semi circular slots for coupling coaxial connector to provide input at the said beam ports (8) and coaxial output at the said array ports (5).

Full Text

FIELD Of INVENTION This invention relates to multi beam antennas adapted to operate over a relatively wideband of frequencies and more particularly to a radio frequency lens also known as Rotman lens. BACKGROUND OF THE INVENTION It is well known in the art that a radio frequency lens, in conjugation with linear array antenna, produces a plurality of simultaneously existing beams of radio frequency energy. The radio frequency lenses, also known as Rotman lenses, are used in wide variety of applications. One of the such application is to form a plurality of simultaneous existing beams of radio frequency energy whose position in space is invariant with frequency of such energy. These parallel plate radio frequency lenses could be realised in waveguide, stripline, or micro-strip geometries. A radio frequency lens formed using air as dielectric (waveguide configuration), though satisfies for many purposes, is generally large in size and its utility is limited to operation over a narrow band of frequencies. Further, the realisation of broadband transitions from parallel plate to 50 ohm poses a serious problem and it does not lend itself for mass production.. Parallel plate lens realized in strip line does not has access to printed lens to implement the side wall and internal multiple reflection reduction techniques. The Rotman Lens realized in Microstrip configuration has the accessibility to printed cards where the sidewalls and multiple internal reflection techniques can be easily implemented The parallel plate lens has a plurality of array ports which are coupled to an array of antenna elements and a plurality of beam ports, each one of which is associated with corresponding beam of radio frequency energy. The beam ports and array ports are disposed about the periphery of the lens. In most of the cases the shape of the lens may be substantially elliptical, in which case the beam and array ports are disposed about opposite or facing portions of the periphery of the lens. The radio frequency lenses are Rotman lenses are well known in the art. One of the Rotman lens, known in the art, has been described in US Patent No. 4490723. The stripline Rotman lens, described in this US Patent, has beam and array ports convent ally arranged normal to the beam and array port contours and were made as power dividers/combiners.. Isolation resistors were introduced between the branch lines of power divider/combiner at three points. The dielectric substrate of the upper printed card was removed to form pockets for the physical accommodation 'of resistors. However, this Rotman lens, known in the prior art, suffers from several disadvantages. The main disadvantage of this Rotman lens, known in the prior art, is that this type of port is difficult to implement and it needs a very high level of precision in the fabrication of the pockets. Another disadvantage of this Rotman lens, known in the prior art, is that it is costlier to realize. Still another disadvantage of this Rotman fens, known in the prior art, is that the air-gaps between the printed cards lead to multiple resonance which distort the amplitude and phase across array ports. With conventional arrangement of array ports normal to array port contour, efficient illumination is obtained with the central beam ports and the end beam ports may not provide adequate illumination of the array ports which are adjacent to the excited beam ports. This introduces severe asymmetric amplitude distribution across array ports and reduces the overall effectiveness of the lens. One technique adapted to improve the illumination effectiveness of the end beam ports was to tie pairs of end beam ports through a power divider. However, this method increases the insertion loss of the lens. Yet another type of Rotman lens has been described in US patent No. 4,22,254. In the Rotman lens, described in this US Patent , the beam and array ports of the printed lens are formed with dielectric wedges disposed between the second and third dielectric material, the dielectric constant of the wedge being different from the dielectric constant of the second and third dielectric materials. However, this type of Rotman lens also suffers from several disadvantages. Main disadvantage of this Rotman lens, known in the prior art, is that the fabrication of the lens is quite complicated and the lens is not suitable for mass production.. The radio frequency lens or Rotman lens of the present invention has improved and symmetric illumination across array ports of the lens by tilting the array ports by an angle half of the amount equal to when array ports are normal to the contour. Further, the radio frequency lens of the present invention utilises an optimized side wall shape and techniques implemented to suppress sidewall and multiple reflections. OBJECTS OF THE INVENTION Primary object of the invention is to provide a micro strip radio frequency lens, which in conjunction with linear array antenna produces a number of simultaneously existing beams incorporating a dielectric material having a dielectric constant greater than that of air. Another object of the invention is to provide a micro strip radio frequency lens which utilises printed circuit technique and shape the sidewall to avoid sidewall and multiple reflections and permit coupling of the resulting radio frequency energy in a most efficient manner to the array ports. Still another object of this invention is to provide a micro strip radio frequency lens in which the array ports are connected to array elements with equal length of transmission lines thereby improving the maintainability of the device. A further object of this invention is to provide micro strip radio frequency lens which realizes the symmetric amplitude distribution across array ports to avoid the problem of asymmetric beam shapes of multiple beam radiation patterns. Yet another object of this invention is to provide micro strip radio frequency lens which is capable of wide angle scanning. Still another object of this invention is to provide micro strip radio frequency lens which is simpler and cost effective to realize. Yet another object of this invention is to provide micro strip radio frequency lens which uses conventional tab type coaxial connectors for coupling the radio frequency lens to external circuitry. Still further object of this invention is to provide a multi beam antenna incorporating a micro strip radio frequency lens of the present invention coupled to a EW/Radar system for producing a plurality of simultaneously existing beams of radio frequency energy. These objects of this itivention have been attained by using printed circuit techniques to form the radio frequency lens along with the bootlace cables on a common substrate having dielectric constant greater than that of air. The radio frequency lens and transmission lines printed on the common substrate focus radio frequency energy at predetermined beam ports along a focal arc of the lens, and the lens and transmission lines are being printed in such a way so as to form constrained paths for RF energy. DESCRIPTION OF INVENTION According to this invention there is provided a micro strip radio frequency lens conjunction with line array antenna comprising of micro strip radio frequency lens assembly characterized by having a plurality of beam ports, plurality of array ports, a printed circuit board and a micro strip radio frequency lens, the said micro strip radio frequency lens having a plurality of lens^ ports, each one of the said lens ports coupled to a corresponding one mibro strip exponentially tapered transmission line, each of the said micro strip exponentially tapered transmission line coupled to a corresponding one variable length bootlace transmission line, each of the said variable length bootlace transmission line coupled to a corresponding one array port, and each of the said array port coupled to a corresponding one antenna elements, each one of the second opposing lens ports of the said micro strip radio frequency lens coupled to a corresponding beam ports through a corresponding micro strip exponentially tapered transmission line; wherein, each of the said antenna element is coupled to a corresponding one array port through a corresponding one equal line length coaxial transmission line;-wherein, each of the said beam port is coupled to a EW/Radar system through a corresponding one coaxial transmission line; wherein, the said array ports of the said lens assembly are tilted with respect to the normal to array port contour to achieve the symmetric amplitude distribution across array elements; wherein, the said lens assembly is housed in a cavity with top plate edge made of semi circular slots for coupling coaxial connector to provide input at the said beam ports and coaxial output at the said array ports. The array ports of the lens of the present invention are titled optimally with respect to normal to array port contour to achieve the symmetric amplitude distribution across array elements thereby avoiding the problem of asymmetric beam shape of the multiple beam radiation patterns. The side walls of the lens are optimally shaped and are provided with edge ports to trap the uncoupled radio frequency energy reaching the said walls thereby reducing the unwanted side wall reflections. The unwanted side wall and multiple reflections from the beam and array port contours are further suppressed by using optimally contoured microwave absorbers covering the parallel plate region and side walls The optimally contoured absorbers helped in achieving the dual purpose of suppressing the internal multiple reflections and achieving the uniform amplitude distribution across array ports. The portions of beam and array ports are designed with exponential tapered transitions to provide efficient coupling of radio frequency between parallel plate and 50 ohm coaxial input or output.. The lens of the present invention is fabricated using printed circuit-techniques and the bootlace variable length transmission lines being printed along with the array ports of the lens on the same substrate to enable the interconnection of Rotman lens and linear array using equal length transmission line and thereby improving the repeatability and matntainability of the lens system. The printed micro strip lens of the present invention is housed in a cavity with top plate edge made of semi circular slots to have easy and effective method of attaching the 50 ohm coaxial connector to provide input and output connections. The micro strip lens of the present invention is simpler and hence cost effective to realize physically. Further, the lens can be adapted having any number of beam as well as array ports. The present invention also provides a multi beam antenna, incorporating a micro strip radio frequency lens of the present invention, coupled to a EW/Radar system for producing a plurality of simultaneously existing beams of radio frequency energy. DESCRIPTION WITH REFERENCE TO ACCOMPANYING DRAWINGS • FIG.1 is an isometric view of micro strip radio frequency lens assembly of the present invention coupled to an array of antenna elements to provide an array antenna for a EW system coup;ed through the lens assembly. FIG.2 is a diagram of the plan view of central conductor formed on the upper surface of the dielectric substrate with tilted array ports along with bootlace transmission lines printed on dielectric substrate of the lens assembly and optimized side wall shape of FIG. 1. FIG.3 is a diagram showing the optimally shaped thin microwave absorber covering the entire parallel plate region and partially covering the beam and array port transitions to suppress the internal multiple and sidewall reflections to achieve the symmetric and uniform amplitude distribution across array ports. FIG. 4 is a diagram showing the contoured non-absorbing materials used towards the beam and array ports. FIG. 5 is a diagram showing the thick microwave absorber used to fill the cavity of micro strip lens. FIG. 6 is a diagram showing the achieved symmetric amplitude distribution across array ports compared to conventional method. Referring now to FIG.1, a multi-beam linear array antenna (1) is shown coupled to an EW system (2) in a conventional manner. The multi beam antenna (1) includes an array (3) of antenna elements (4), each one of such antenna elements being coupled to a corresponding port of a plurality of array ports (5) of a micro strip radio frequency lens assembly (6) through a plurality of equal line length coaxial transmission lines (7) respectively. The EW system (2) is coupled to a plurality of beam ports (8) of the radio frequency lens assembly (6) through coaxial transmission lines (9). The array antenna system (1) is adapted to produce a plurality of simultaneous multiple existing beams of radio frequency energy, each of such beams being produced by the common array (3) of antenna elements (4), each one of such beams having the gain and bandwidth of the entire aperture, each one of such beams being associated with a corresponding one of the beam ports. Thus, here the lens fed array antenna (1) is adapted to produce 15 beams of radio frequency energy, each one of such beams being associated with a corresponding one of the beam ports (8) being produced from the array (3) of antenna elements (4). The radio frequency lens assembly (6) here includes a micro strip radio frequency lens (10) and a printed circuit board (11), having a conductive layer to provide a ground plane conductor (12) disposed on the bottom surface of the printed board (11). Formed on the upper surface of the dielectric substrate board (11), the center conductor circuitry (13) for the micro strip transmission line lens assembly (6),. such center conductor circuitry (13) being formed using conventional photolithographic -chemical etching processes. Referring to FIG.2, the micro strip radio frequency lens assembly (6) has center conductor circuitry (13) formed on the upper surface of the dielectric substrate (11). The center conductor circuitry (13) includes a central region (1),4 which provides the center conductor circuitry for the micro strip radio frequency lens (10). The micro strip radio frequency lens (10) in turn comprises a plurality of lens ports (15) on beam port (8) side and plurality of lens ports (16) on array port (5) side all disposed about the central region (14). Each one of the lens port (15) are coupled to a corresponding beam port (8) through a corresponding micro strip exponentially tapered transmission line (17). Each one of a second opposing portion of the lens portions (16) are coupled to a corresponding micro strip' exponentially tapered transmission line (18). The tapered exponential micro strip transmission lines (18) are in turn coupled to corresponding one of the variable line length bootlace transmission lines (19). The variable length transmission lines (19) are coupled to corresponding one of the array ports (5). Each one of the array ports constituted by lens portions (16), exponentially tapered transitions (18) and bootlace line lengths (19) are tilted at an angle equal to the half angle which when the ports are maintained normal (20) to the array contour (21). The edge ports (22) are used as dummy ports to provide the same environment to end ports (15) on beam port side. Similarly edge ports (23) are used as dummy ports to provide the same environment to end ports (16) on array port side. The sidewall of the center conductor circuitry (13) is made in the shape of triangle (24) on lower side micro strip radio frequency lens (10) with edge ports (25) and triangle (24) on lower side micro strip lens (10) with edge ports (25). The sidewalls (24) are covered with microwave absorber to suppress the sidewall reflections FIG.3 shows the thin microwave absorber (26) with special contours (27) on beam ports (8) side and (28) on the array port (5) side covering completely the central circuitry of the radio frequency lens and partially the beam and array ports. The covering gradually varies little at edge ports to maximum at the central ports of the beam and array ports. FIG. 4a shows a non-absorbing material (29) whose contours (30) and (31) match with the inner contour (32) of the top plate cavity (33) and the thin absorber contour (27) on beam port (8) side respectively. FIG. 4b shows, on the opposite side, a non-absorbing material (34) whose contours (35) and (36) match with the inner contour (37) of the top plate cavity (33) and the thin absorber contour (28) on the array port side (5). FIG. 5 shows another absorber (38) of substantial thickness having a shape and size equal to the over all size of the printed circuit substrate board (11) and to the inner dimensions of the top metallic plate (33) which is placed over the absorbers (26), (29) and (34). The overall thickness obtained with the combination of absorbers (26), (29), (34) and (38) is equal to the depth of the cavity (33). The edges of the top plate (33) were made of semicircular slots (39) to have transitions from micro strip to 50-ohm coaxial input at beam ports (8) and coaxial output at array ports (5). The conventional coaxial connectors (40) have its center conductor electrically and mechanically connected to the micro strip transmission line and outer conductor electrically connected to the outer edge of the bottom plate (41) and top plate (33) using screws (42). The top plate (33) and bottom plate (41) are fastened together by using screws (43). Referring to FIG.6, curve (44) shows the amplitude distribution across array ports of a radio frequency lens with array ports printed normal to contour according to the prior art and curve (45) shows amplitude distribution across array ports of the micro strip radio frequency lens of the present invention. It shows that a substantial improvement in symmetric amplitude distribution has been achieved in the micro strip radio frequency . lens of the present invention. 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 claim I CLAIM; 1. A micro strip radio frequency lens conjunction with line array antenna comprising of micro strip radio frequency lens assembly (6) characterized by having a plurality of beam ports (8), plurality of array ports (5), a printed circuit board (11) and a micro strip radio frequency lens (10), the said micro strip radio frequency lens (10) having a plurality of lens ports (16), each one of the said lens ports (16) coupled to a corresponding one micro strip exponentially tapered transmission line (18), each of the said micro strip exponentially tapered transmission line (18) coupled to a corresponding one variable length bootlace transmission line (19), each of the said variable length bootlace transmission line (19) coupled to a corresponding one array port (5), and each of the said array port (5) coupled to a corresponding one antenna elements (4), each one of the second opposing lens ports (15) of the said micro strip radio frequency lens (10) coupled to a corresponding beam ports (8) through a corresponding micro strip exponentially tapered transmission line (17); wherein, each of the said antenna element (4) is coupled to a corresponding one array port (5) through a corresponding one equal line length coaxial transmission line (7); wherein, each of the said beam port (8) is coupled to a EW/Radar system (2) through a corresponding one coaxial transmission line (9); wherein, the said array ports (5) of the said lens assembly (6) are tilted with respect to the normal to array port (5) contour to achieve the symmetric amplitude distribution across array elements (4); wherein, the said lens assembly (6) is housed in a cavity with top plate edge (33) made of semi circular slots for coupling coaxial connector to provide input at the said beam ports (8) and coaxial output at the said array ports (5). 2. A micro strip radio frequency lens assembly (6), as claimed in preceding claims, wherein the said walls of the said micro strip micro strip radio frequency lens (10) are optimally shaped and are provided with edge ports to trap the uncoupled radio frequency energy reaching the said side walls. 3. A micro strip radio frequency lens assembly (6), as claimed in preceding claims (1), wherein unwanted side wall and multiple reflections from the said beam ports (8) and the said array ports (5) are suppressed by covering the said side walls of the said beam ports (8) and array ports (5) with optimally controlled microwave absorbers. 4. A micro strip radio frequency lens assembly (6), as claimed in preceding claims (1), wherein the said micro strip radio frequency lens (10) is fabricated using printed circuits technique, the bootlac variable length transmission lines (19) being printed along with the array ports (5) of the said micro strip radio frequency lens (10) on the same substrate. 5. A micro strip radio frequency lens assembly (6), substantially as described and illustrated herein.

Documents:

503-DEL-2004-Abstract-(26-08-2009).pdf

503-del-2004-abstract.pdf

503-DEL-2004-Claims-(26-08-2009).pdf

503-del-2004-claims.pdf

503-del-2004-Correspondence-Others-(01-09-2009).pdf

503-DEL-2004-Correspondence-Others-(26-08-2009).pdf

503-del-2004-correspondence.pdf

503-DEL-2004-Description (Complete)-(26-08-2009).pdf

503-del-2004-description.pdf

503-DEL-2004-Drawings-(26-08-2009).pdf

503-del-2004-drawings.pdf

503-DEL-2004-Form-1-(26-08-2009).pdf

503-DEL-2004-Form-2-(26-08-2009).pdf

503-del-2004-form1.pdf

503-del-2004-form2.pdf

503-del-2004-GPA--(01-09-2009).pdf