Title of Invention

A MICROSTRIP ANTENNA ARRAY

Abstract This invention relates to a microstrip antenna array comprising of 512 square patch elements (11) distributed in a element planer array rectangular grid structure, the said square patch elements (11) provided on one side of a single layer microwave dielectric substrate (95) by photoetching, the other side of the said substrate (95) grounded with conductor cladding (96) and adhered to an antenna back up plate (122), the said square patch elements (11) fed through a corporate feed network (97 to 120), the said corporate feed network (97 to 120) realized by protecting, the said microstrip antenna, wherein a directive radiated beam with low sidelobes, low cross-polarisation and linear polarization over a wide bandwidth is transmitted from and/or received into the said Antenna Array in response to the RF excitation from the said coaxial connector (121), the circuit layout is realized by fine line photolithography and printing with use of one single large size photo tool in only one layer.
Full Text FIELD OF INVENTION :
The invention relates to antenna / antenna arrays particularly, to microstrip antenna arrays in X-Band frequency and more particularly to microstrip antenna arrays which are employed in nonportable battlefield surveillance radars.
BACKGROUND OF THE INVENTION :
Battlefield Surveillance Radars for Short Range Detection of 10 to 15 kms range are being extensively employed worldwide for front line of control and defence during times of war as well as peace. Such radars generally deployed in numbers, are nonportable and are capable of being carried easily on the shoulders of soldiers and hence, demand radar antennas of light weight, easy reproducibility / productionisability, at the same time offering electrical performances of high gain, low sidelobe radiation patterns over a large frequency band of operation. This increased demand of battlefield surveillance radar antennas has typically been met by Reflector Antennas and Slotted Waveguide Antenna Arrays, which are well known in the art.
However, the reflector antenna, known in the art, suffers from following disadvantages.
Primary disadvantage of reflector antenna, known in the prior art, is that this antenna is quite bulky and becomes highly expensive for meeting low sidelobe requirements.
Another disadvantage of reflector antenna, known in the prior art, is that this antenna inherently suffers from low aperture efficiency in view of feed spill over and aperture blockage problems.
The Slotted Waveguide Antenna Arrays, known in the prior art, are relatively lighter. However, these antenna arrays also suffer from the disadvantages.
Primary disadvantage of waveguide antenna arrays, known in the prior art, is that these antenna arrays are difficult to manufacture.
Another disadvantage of waveguide antenna arrays, known in the prior art, is that antenna arrays present narrow frequency bandwidths for realising low sidelobe radiation patterns.
Microstrip Antenna Array is another antenna array, which overcomes many of the disadvantages associated with Reflector Antennas as well as Slotted Waveguide Antenna Arrays. Microstrip Antenna Arrays employ an arrangement of planar Microstrip Antenna Elements connected through the planar transmission line feed networks to produce desired radiation pattern characteristics. Microstrip Antennas and Microstrip Antenna Arrays present distinct advantages in terms of their low profile with less space and weight, conformability, low fabrication cost i.e., easier manufacturability through photolithography by use of printed circuit technology, mechanical robustness and compatibility / easy integration with microstrip circuits (passive networks as well as active circuits). These microstrip antenna arrays are also known in the art.
However, the microstrip antenna arrays, known in the art, suffer from the following disadvantages.
Primary disadvantage of microstrip antenna arrays, known in the prior art, is that these antenna arrays do not provide high quality radiation pattern with low sidelobe levels over a wide frequency bandwidth.
Another disadvantage of microstrip antenna arrays, known in the prior art, is that these antenna arrays can not be realized in a single microwave substrate.
Yet another disadvantage of these microstrip antenna arrays, known in the prior art, is that these antenna arrays are difficult to be manufactured.
Still another disadvantage of these microstrip antenna arrays, known in the prior art, is that these are not very compact.
The present invention provides a low cost, light weight, easily manufacturable, compact (low profile) and large size (512 Element Aperture) microstrip antenna array in X-Band frequency, having a high gain, wide frequency bandwidth and low sidelobe pattern characteristics, with direct application to manportable battlefield surveillance radars.
OBJECTS OF THE INVENTION :
Primary object of the invention is to provide a microstrip antenna array preferably for manportable battlefield surveillance radar applications.
Another object of the invention is to provide a microstrip antenna array, which is realised through a printed array architecture on a single layer microwave dielectric substrate
Yet another object of the present invention is to provide a microstrip antenna array which is realised through low lass planar microstrip corporate feed networks, optimised for wide frequency bandwidth and at the same time, providing the requisite inphase taper amplitude excitations required for generation of low sidelobe radiation patterns.
Still another object of the present invention is to provide a microstrip antenna array whose circuit layout is only in one layer and is realised by photolithographic exposure and printing with use of one single large size photo tool.
Still further object of the present invention is to provide a microstrip antenna array, which is highly reliable with its high repeatable performance over a wide bandwidth in X-Band.
According to this invention there is provided a microstrip antenna array comprising of 512 square patch elements distributed in a element planer array rectangular grid structure, the said square patch elements provided on one side of a single layer microwave dielectric substrate by photoetching, the other side of the said substrate grounded with conductor cladding and adhered to an antenna back up plate, the said square patch elements fed through a corporate feed network, the said corporate feed network realized by protecting, the said microstrip antenna, wherein a directive radiated beam with low sidelobes, low cross-polarisation and linear polarization over a wide bandwidth is transmitted from and/or received into the said Antenna Array in response to the RF excitation from the said coaxial connector, the circuit layout is realized by fine line photolithography and printing with use of one single large size photo tool in only one layer.

STATEMENT OF THE INVENTION :
'.n accordance with this invention theTlicrostrip antenna array
for nonportable battlefield surveillance radar applications, is configured
employing single layer microstrip antenna elements fed through planar microstrip corporate feed networks with output amplitude excitations of inphase and taper amplitude distribution, and is distributed over a large size rectangular antenna aperture. The microstrip antenna array comprises of a total of 512 square patch elements (11) inset fed with their coplanar feed networks (97 to 120) and is distributed in a (32 x 16) element planar array rectangular grid structure, and is realised by photoetching on one side of a single layer microwave dielectric laminate / substrate (95) which is grounded on the other side with conductor cladding (96) as well as mounted on Aluminium antenna back-up plate (122), the RF excitation (In / Out) for the microstrip antenna array having been provided through a coaxial SMA probe / connector (121) at the input end of the (1 : 512) way planar corporate feed network (97 to 120), the architecture and design of patch elements (11) and the corporate feed network (97 to 120) being such that in response to the RF excitation from the coaxial feed (121) at the input of the corporate feed network, a directive radiated beam with low sidelobes, low cross-polarisation and linear polarisation over a wide bandwidth is transmitted from and / or received into the antenna array.
In accordance with the present invention, the microstrip antenna array operating in X-Band is realised through planar array configuration of inset fed square patch elements (11) driven through wideband equiphase taper amplitude planar microstrip corporate feed network (97 to 120). The use of inset fed square patch elements (11) as the array radiating elements helped in wideband matching and practical readability of the corporate feed network, while the wideband equiphase taper amplitude design of the microstrip corporate feed network (97 to 120) provides the directive radiated beam of low sidelobes over a wide bandwidth. The microstrip antenna array of the present invention, realised through the improved printed array architecture on a single layer large size microwave dielectric laminate, provides wideband, high gain, low sidelobe radiation patterns, with easily reproducible, flat profile, light weight solution with high performance features. The microstrip antenna array back-up plate is also designed as a light weight structure in Aluminium, with easy mounting and interfaceability with the other electronic subsystems of the manportable battlefield surveillance radar.
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 the following drawings wherein.
BRIEF DESCRIPTION OF THE DRAWINGS :
Fig. 1 is the configuration of the basic Microstrip Antenna Array Element of the present embodiment, illustrative of the Square Patch Element with inset feed.
Fig. 2 (a) is a diagram illustrative of the Microstrip Antenna Array built up with basic Subarray Blocks of 4-elements (2 x 2).
Fig. 2 (b) is a diagram illustrative of the Microstrip Antenna Array built up with basic Subarray Blocks of 16-elements (4 x 4).
Fig. 2 (c) is a diagram illustrative of the Microstrip Antenna Array built up with basic Subarray Blocks of 64-elements (8 x 8).
Fig. 3 is a detailed layout of the Second Quadrant of the Microstrip Antenna Array of the present invention, with Subarray Block of 128 (16 x 8) elements.
Fig. 4 is a detailed layout and diagram illustrative of the 512-element (32 x 16) Microstrip Antenna Array of the present embodiment
Fig. 5 is the assembled view of the Microstrip Antenna Array on the Antenna Back-up Plate.
Fig. 6 is the rear view of the Antenna Back-up structure, illustrative of the RF excitation port (coaxial) and the ribbed structure for planarity, light weight and mounting / interface arrangements with the other radar electronics.
Fig. 7 is a plot depicting the Return Loss Characteristics of the Microstrip Antenna Array.
Fig. 8 is the record of the Measured Radiation Pattern Plots in Azimuth (H-) Plane, typically at fc : center frequency, illustrative of the low sidelobe pattern characteristics of the Microstrip Antenna Array.
Fig. 9 is the record of the Measured Radiation Pattern Plots in Elevation (E-) Plane, typically at fc : center of frequency, illustrative of the low sidelobe pattern characteristics of the Microstrip Antenna Array.
DESCRIPTION OF THE INVENTION:
Referring to Fig. 1, the basic configuration of the microstrip antenna array element, illustrative of the square patch element 01, comprises of a square conductor radiating patch 01 with dimensions L 06 and W 05, photo etched on the microwave dielectric substrate of height h 03, dielectric constant r,r 04 and with a conductor ground 02 on the other side of the dielectric substrate. The length L 06 and width W 05 of the square patch element 01 are chosen approximately equal to half wave length in the dielectric (1.12, X being the guided wavelength in the dielectric preferably at the centre frequency of operation), for acting as a resonant radiating array element at the centre frequency of operation and also over a band of frequency around The RF excitation of the square patch element is done through a planar microstrip feed line of width Wfeed 09 at 10, terminated as the inset feed at the patch input end with inset opening 07 and inset width 08 optimally chosen for a higher input impedance in the range of 200 ohms to 245 ohms. The design optimisation has been realised by employing EM (Electromagnetic) Simulation package, for obtaining the width of inset feed 09, its width 08 and opening 07 at the patch input, to offer much lower feed radiation and feed to patch coupling.
The array architecture employed for the microstrip antenna array of the present invention, is the constrained feed type with each of the array elements directly connected with transmission lines, with array interelement spacings decided by requirements of its directive radiation pattern. Specifically, for broadband and readability of lower sidelobe radiation patterns, the architecture of centre fed corporate feed structure is employed with square patch elements 01 as the basic array antenna elements.
Referring to Fig. 2 (a), 2(b) & 2(c), the array elements are connected in parallel with pairs of antenna elements connected with reactive microstrip transmission line power splitters. The connected pairs are, in turn, connected with another power splitter, extending to the array center feed. Thus, there are layers (levels) of power splitters required for larger arrays and are designed for unequal amplitude, equiphase power splitting ratios.
The Subarray Blocks of 4-elements (2 x 2), 16-elements (4 x 4) and 64-
elements (8 x 8) are the basic Subarray Blocks employed in building the complete
Microstrip Antenna Array of the present embodiment, with interelement spacings of dx,
dy in X- and Y- axes respectively. Each of the Subarray Blocks contains Square Patch
Array Elements 01 with their array feed networks realised (photo etched ) on one side
of the dielectric substrate 12 with grounded conductive plane 13 on the other side.
There are two levels of power splitters viz., (14, 15) and (16), used for building
corporate feed of the 4-element (2x2) Subarray, as in Fig. 2(a). Similarly, there are 15
power splitters used in four layers (levels) viz., 1st Layer: (17, 18), (20, 21), (23, 24),
(26, 27), 2nd Layer : 19, 22, 25, 28,
3rd Layer: (29, 30) and 4th Layer: (31), for building the Subarray of 16-elements (4 x 4). The 64-element (8 x 8) Subarray Block with a center fed Planar Microstrip Corporate Feed Network consisting of 63 power splitters, realised in six Layers (levels), viz., 1st Layer: (32, 33, 35, 36, 38, 39, 41, 42), (47, 48, 50, 51, 53, 54, 56, 57), (62, 63, 65, 66, 68, 69, 71, 72), (77, 78, 80, 81, 83, 84, 86, 87), 2nd Layer: (34, 37, 40, 43, 49, 52, 55, 58, 64, 67, 70, 73, 79, 82, 85, 88), 3rd Layer: (44, 45, 59, 60, 74, 75, 89, 90), 4th Layer: (46, 61, 76, 91), 5th Layer: (92, 93) and 6th Layer : (94). Each of the power splitters are designed for unequal amplitude, equiphase power output ratios over a broad frequency bandwidth as required to achieve the amplitude excitation of the respective Antenna Elements
Referring to Fig. 4, the Microstrip Antenna Array of the present invention, is configured employing single layer Microstrip Square Patch Elements 11 fed through Planar Microstrip Corporate Feed Network center fed at 121. The Microstrip Antenna Array is distributed over a rectangular aperture of length a = 600 mm and width b = 400 mm. A total of 512 Patch Elements 11 are photo etched on a Microwave Laminate / Substrate 95 with its ground plane 96 mounted on an Aluminium Antenna Back-up Plate 122 of Fig. 6. The 512 Elements are distributed in a (32 x 16) planar array rectangular grid of interelement spacings dx = 0.644 X,0, dy = 0.858 X0 (A,0: free space wavelength at the center frequency of operation in X-Band). The complete Array is built up with basic Subarray Blocks of 4-elements (2 x 2), 16-elements (4 x 4) and 64-elements (8x8), which are driven through the Structure of Planar Microstrip Corporate Feed Network
The complete Antenna Array is divided into Four Quadrants, each one containing 128 Array Elements fed through the Microstrip Corporate Feed Network designed for a Taper Amplitude Distribution, with a low insertion loss and the desired low sidelobe level pattern performances. The (1:4) way Quadrant Level Power distribution is realised through two level (layer) power splitters, viz., 1st Level: (120) and 2nd Level : (119). The (1:4) way Quadrant Level Distribution Network is centre fed orthogonally at 121 with a coaxial probe passing through the ground plane 96 of the Array, the coaxial connector at 121 having been mounted on the Antenna Back-up Plate (Refer Fig. 5).
Referring to Fig. 3, a Planar Microstrip Corporate Feed Network is employed with (1:128) way power division (for a (16 x 8) element Subarray) which is realised using 7 level (layer) power splitters, viz., 1st Level : (111), 2nd Level : (118), 3rd Level : (109,
110), 4th Level : (116, 117), 5th Level . (105, 106, 107, 108), 6th Level : (112, 113, 114, 115), and 7th Level : (97, 98, 99, 100, 101, 102, 103, 104). The Four Quadrant Level (1:128) way Microstrip Feed Networks have a mirror image symmetry around X- and Y- axes, as shown in Fig. 4. The power splitters at each of the layers (levels) of the Quadrant Level Feed Networks are design optimised using multi-quarter wavelength sections of microstrip transmission lines, for obtaining a low insertion loss, broadband performance and a low feed radiation (by choice of impedances employed in realising the multi-quarter wavelength sections of the two way power splitters). The EM Simulation package as well as Linear Circuit Simulators have been employed for the design optimisation of all the power splitters used in the Quadrant Level Planar Corporate Feed Networks.
For low sidelobe radiation pattern realisation with proper Beamwidth and Gain, type of Amplitude Distribution chosen for the Microstrip Antenna Array is Taylor's Distribution with ) = 4, sidelobe level SLL= -33 dB which is found to be the optimum for obtaining a pattern sidelobe level (SLL) of the order of -25 dB or better. The end element tapers for this Distribution are of the order of -15 dB to -16 dB (along the X-axis and Y-axis) with respect to the central elements as against higher taper values of other Distributions viz., Chebyshev and Cosine2 on a Pedestal. Also, it provides lower far off sidelobes as compared to Chebyshev Distribution. Hence, according to the Taylor's Amplitude Distribution with ) = 4, SLL = -33 dB, chosen as an optimum Distribution, the Amplitude Excitations in dB have been worked out for each element of the 512-element ( 32 x 16 ) Microstrip Antenna Array and the various level (layer) unequal power split ratios to be realised in dB (with equiphase output response) in each of the Four Quadrant Level Microstrip Corporate Feed Network are as below :

Thus, the design optimisation of all the above power splitters and their appropriate layout within the array rectangular grid structure of interelement spadngs dx and dy has lead to realisation of the complete Microstrip Antenna Array Configuration. The choice of linewidths (ie , the choice of respective impedances) of the multi-quarter wavelength sections of microstrip transmission lines used in realising the above power splitters, have been limited within 125 |im to 1400 urn, so that proper Feed Network Layout is realised containing spurious feed radiations, as well as realisable linewidths (of 125^m) with fine line photolithography.
Referring to Fig. 5, the assembled view of Iho Mir.rostrip Antenna Array on the Antenna Back-up Plate 122, indicates the 512 (32 x 16) Square Patch Elements 11 fed through the centre fed Microstrip Corporate Feed Network and distributed over the rectangular aperture. The complete Antenna Array is fabricated on a single Microwave Substrate / Laminate 95 which is glued with silver epoxy on to the Antenna Back-up Plate 122.
Referring to Fig. 6, the Antenna Back-up Plate is the main Structural Framework of the Array Antenna, which is fabricated out of light Aluminium Alloy. This is realised as a ribbed structure 123 for proper structural reinforcement to obtain the planarity, light weight and mounting / interface arrangements as required for other radar electronics of nonportable battlefield survellance radar. The orthogonal coaxial SMA In/Out connector at Port 121 is mounted on to the Antenna Back up Plate and gets connected to the input of the Planar Corporate Feed Network of the Microstrip Antenna Array, through a reactively matched broadband microstrip network at power splitter 120.
Referring to Fig. 7, the Design Architecture and careful Design Simulation as well as precision photolithography (with line widths of the order of 125 urn) and precision fabrication / assembly have resulted in realising the Microstrip Antenna Array with a High Gain >30 dB, Sharp Beamwidths : 3.5° x 4.5" and an input Return Loss Referring to Fig.8 & 9, it has also resulted in low sidelobe ( 4%) in X-Band centered around 10.3 GHz.
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. A microstrip antenna array comprising of 512 square patch
elements (11) distributed in a element planer array rectangular
grid structure, the said square patch elements (11) provided on one
side of a single layer microwave dielectric substrate (95) by
photoetching, the other side of the said substrate (95) grounded
with conductor cladding (96) and adhered to an antenna back up
plate (122), the said square patch elements (11) fed through a
corporate feed network (97 to 120), the said corporate feed network
(97 to 120) realized by protecting, the said microstrip antenna,
wherein a directive radiated beam with low sidelobes, low cross-
polarisation and linear polarization over a wide bandwidth is
transmitted from and/or received into the said Antenna Array in
response to the RF excitation from the said coaxial connector
(121), the circuit layout is realized by fine line photolithography
and printing with use of one single large size photo tool in only one
layer.
2. A microstrip antenna array as claimed in claim 1 wherein said
pitch elements (11) are distributed on a 32 x 16 element planer
array.
3. A microstrip antenna array as claimed in claim 1, wherein the said
Antenna Array Elements are configured employing single layer
optimized Square Patch Elements (11) easily integrable with planer
microstrip feed networks, for a low feed radiation and feed to patch
coupling.

4. A microstrip antenna array as claimed in claim 1 wherein the said corporate feed network (97 to 120) is optimized for wide frequency bandwidth providing the in-phase unequal output taper amplitude excitations required for generation of low side lobe radiation patterns.
5. A microstrip antenna array as claimed in claim (1), wherein the said antenna back-up plate (122) is a structurally made light weight back-up plate with planarity and mounting/interface arrangements.
6. A microstrip antenna array substantially as described and illustrated herein.

Documents:

1377-DEL-2003-Abstract-(17-04-2008).pdf

1377-del-2003-abstract.pdf

1377-DEL-2003-Claims-(17-04-2008).pdf

1377-del-2003-claims.pdf

1377-DEL-2003-Correspondence-Others-(17-04-2008).pdf

1377-del-2003-correspondence-others.pdf

1377-del-2003-correspondence-po.pdf

1377-DEL-2003-Description (Complete)-(17-04-2008).pdf

1377-del-2003-description (complete).pdf

1377-DEL-2003-Drawings-(17-04-2008).pdf

1377-del-2003-drawings.pdf

1377-del-2003-form-1.pdf

1377-del-2003-form-18.pdf

1377-DEL-2003-Form-2-(17-04-2008).pdf

1377-del-2003-form-2.pdf

1377-del-2003-gpa.pdf


Patent Number 246841
Indian Patent Application Number 1377/DEL/2003
PG Journal Number 11/2011
Publication Date 18-Mar-2011
Grant Date 16-Mar-2011
Date of Filing 10-Nov-2003
Name of Patentee DIRECTOR GENERAL, Defence Research & Development Organisation, Ministry of Defence, Govt. of India
Applicant Address DEFENCE RESEARCH & DEVELOPMENT ORGANISATION, MINISTRY OF DEFENCE, GOVT. OF INDIA, DTE OF ER & IPR/IPR GROUP, WEST BLOCK 8, WING, R K PURAM, NEW DELHI-110011.
Inventors:
# Inventor's Name Inventor's Address
1 UDAYSHANKAR KASHINATHRAO REVANKAR ELECTRONICS AND RADAR DEVELOPMENT ESTABLISHMENT(LRDE) DRDO COMPLEX, C V RAMAN NAGAR, BANGALORE-560093, INDIA
2 KARUKUNNEL SREEDHARAN BEENAMOLE ELECTRONICS AND RADAR DEVELOPMENT ESTABLISHMENT(LRDE) DRDO COMPLEX, C V NAGAR, BANGALORE-560093, INDIA
PCT International Classification Number H01Q 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA