Description:FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(SEE SECTION 10, RULE 13)

ULTRA WIDEBAND SEGMENTED ANTENNA RADOME FOR AN ANTENNA ASSEMBLY

BHARAT ELECTRONICS LIMITED
WITH 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 invention in general relates to radio wave communication systems. The invention, particularly, relates to a Radome, more specifically, the present invention relates to a Radome which provides very low transmission and reflection losses over the ultra-wide band frequency covering multiple communication bands.
BACKGROUND
[0002] Radome is an electromechanical structure that acts as a weatherproof enclosure to protect the antenna. It protects delicate antenna radiators and other electronic/electrical equipment from surroundings. General fields of radome application are in ground-based, shipboard and airborne etc. Application wise, Radome is typically used in RADAR (Radio Detection And Ranging), satellite communication etc. In satellite communication, microwave dish antennas are used for transmission and reception of electromagnetic-radiation signals that are typically outfitted with a Radome for outdoor operation.
[0003] Radome design is based on the material selection & its unique construction is needed to provide optimum electrical performance with sufficient safety margins within acceptable size and weight.
[0004] Ideally, a Radome should be completely transparent to the signals transmitted or received by its corresponding antenna. In practice, Radomes are designed to minimize interference with that transmission and/or receipt of signals by the antenna. Consequently, Radomes are typically made from non-conductive materials. Radomes are generally composed of low-loss dielectrics using composites with thickness comparable to the wavelength of operation.
[0005] Known prior art U.S. 7,420,523, B1 discloses a basic 3-layer B –sandwich Radome structure. The fourth layer is added by this art to increases the transmission efficiency of the multi-layer design from 60 percent to about 75 percent for the worst cases, however it also increase weight as disclosed U.S. patent application Ser. No. 13/135,263 Weight reduction by 20-30% of multi-layer Radome has been disclosed in prior art US 9,099,782 B2 which proposes multilayer A and C type Radome for dual band (K-Ka frequency bands) in which “ A-sandwich” comprises of 4 layers and “C-sandwich” has 7 layers.
[0006] A known prior art US patent 20180145403 discloses multi-piece Radome structure with a plurality of Radome segments. Each of the pieces of this Radome has a structural core layer and an overlying outer layer. Each piece has two radial faces and a perimeter section. Radial faces are so arranged that they fit with each other like puzzle (like tongue and groove arrangement) to assemble the segmented Radome. Total perimetric segments are four and there is one central dome segment.
[0007] Another prior art US 11,621,484 B1 discloses 5 layered wideband Radome for Ku to Ka band using woven fiber clothes like E glass, S glass, polyethylene; central and internal cores comprised of syntactic foams. Dielectric constants of different layers keep on increasing from central layer towards outer layers in conventional manner.
[0008] Prior arts mentioned above typically used only for dual Radio Frequency (RF) band operations and do not clearly discuss mechanical/environment considerations like parameters such as withstanding the wind load, stress, weather proof, etc. which is the primary function of Radome. Further, a Radome shall provide low transmission loss at for operational frequency bands.

SUMMARY
[0009] This summary is provided to introduce concepts of the invention related to a Radome which provides very low transmission and reflection losses over the ultra-wide band frequency and covering multiple communication bands, as disclosed herein. This summary is neither intended to identify essential features of the invention as per the present invention nor it is intended for use in determining or limiting the scope of the invention as per the present invention.
[0010] In accordance with an exemplary implementation of the present invention a Radome for an antenna assembly is disclosed, the Radome structure further comprises a hemispherical structure configured to enclose a passive antenna; wherein the hemispherical structure is coated with a thin multilayer structure making the hemispherical structure transparent to an ultra-wide band frequency range. In another embodiment the hemispherical structure is mounted on a base plate.
[0011] In one of the implementations the hemispherical structure of Radome comprises a plurality of segments joined with each other by panel joining flanges.
[0012] In another embodiment, the Radome is coated with a thin multilayer structure comprising two solid laminate layers; a foam layer, wherein the foam layer is sandwiched between the two solid laminate layers; and a gel coat layer as an outermost protective layer. In one of the implementations the foam layer is a honeycomb layer. In another implementation, the solid laminate layers are made of E glass prepreg and having a thickness of about 0.3mm, wherein the gel coat layer has a thickness of about 0.5mm.
[0013] In accordance with an exemplary implementation of the present invention there is provided the Radome, wherein the thin multi-layer structure provides low loss of about 0.4 dB to radio frequency signals.
[0014] In accordance with an exemplary implementation of the present invention there is provided the Radome, wherein the ultra-wide band frequency ranges from 3.635GHz to 14.5GHz covering S, C, X and Ku band and in another exemplary implementation of the present invention there is provided the Radome wherein deterioration in the Side Lobe Level (SLL) in both azimuth and elevation plane of Ku band antenna is within 0.3 dB.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0015] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and modules.
[0016] Figure 1 illustrates the isometric view of the multiband segmented Radome according to an exemplary implementation of the present invention.
[0017] Figure 2(a) illustrates multiband segmented Radome with maintenance hatch door according to an exemplary implementation of the present invention.
[0018] Figure 2(b) illustrates the exploded view of maintenance hatch door according to an exemplary implementation of the present invention.
[0019] Figure 3 illustrates the octagonal base ring according to an exemplary implementation of the present invention.
[0020] Figure 4 illustrates four-layer configuration of Multiband Segmented Radome body: These layers are: (i) Gelcoat, (ii) E glass Prepreg, (iii) Honeycomb, (iv) E glass prepreg according to an exemplary implementation of the present invention.
[0021] Figure 5(a) illustrates a plot measuring azimuth patterns of a satellite communication Antenna without 501 and with Radome 502 at Ku Band frequency according to an exemplary implementation of the present invention.
[0022] Figure 5(b) illustrates a plot showing the elevation patterns of a satellite communication Antenna without 503 and with Radome 504 at Ku Band frequency according to an exemplary implementation of the present invention.
[0023] Figure 6 (a) illustrates the plot showing the estimated transmission losses of Radome from 3.625 GHz to 14.5 GHz ultra-wideband of operation according to an exemplary implementation of the present invention.
[0024] Figure 6(b) illustrates a plot showing the reflection losses of Radome from 3.625 GHz to 14.5 GHz ultra-wideband of operation according to an exemplary implementation of the present invention.
[0025] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present invention. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether such computer or processor is explicitly shown.

DETAILED DESCRIPTION
[0026] The various embodiments of the present invention relate to a Radome which provides very low transmission and reflection losses over the ultra-wide band frequency covering multiple communication bands.
[0027] In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0028] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
[0029] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0030] According to the present invention, the Radome is a protective cover for an antenna, shaped like a half-sphere, and it's made transparent to allow signals to pass through. It has layers that include a sturdy outer coating, foam for strength, and a gel layer for protection. The Radome can handle a wide range of frequencies from 3.635GHz to 14.5GHz, which covers various bands like S, C, X, and Ku. It has minimum signal loss and ensures that the antenna's performance, particularly in terms of side lobe levels, remains stable within acceptable limits. The Radome as disclosed herein also designed with segments joined together for easy assembly, making it a reliable and efficient component for antenna systems.
[0031] In general, the Radome as part of the prior arts typically used only for dual Radio Frequency (RF) band operations and do not clearly discuss mechanical/environment considerations like parameters such as withstanding the wind load, stress, weatherproof, etc. which is the primary function of Radome. Further, a Radome shall provide low transmission loss at for operational frequency bands.
[0032] Therefore, there is a further requirement in arts for a mechanically robust Radome with low transmission loss for enclosing satellite communication antenna operating in multiple frequency bands (C, X and Ku bands) for ground/ship-based applications.
[0033] According to the present invention, a novel Radome design which provides very low transmission and reflection losses over the ultra-wideband frequency operation from 3.625 GHz to 14.5 GHz, covering multiple communication bands: S, C, Ext C, X and Ku frequency bands. The present invention has 10.875 GHz bandwidth [120% fractional bandwidth] and also provides a strong structural cover suitable for outdoor antenna.
[0034] Embodiments of the present invention are not limited to Radomes used only for ground satellite terminals. These Radomes can be used for ship and even for low-speed vehicles. Radomes in accordance with embodiments of the present invention can be used for other types of antennas too such as in Doppler weather radar antenna, Troposphere communication antenna etc.
[0035] Figure 1 illustrates the isometric view of the multiband Radome (100). In another embodiment of the present invention a hemispherical structure (110) or a dome shape of the Radome (100) is depicted in figure 1.
[0036] Figure 2(a) illustrates multiband segmented Radome with maintenance hatch door (202) according to an exemplary implementation of the present invention.
[0037] Referring initially to Fig. 2 (a), a dome shaped Radome 100 for a satellite reflector antenna is illustrated enclosing a passive antenna with all other outdoor subparts. This Radome 100 has a curved shaped body (201) which resembles a dome mount on cylindrical structure (206, 203) that is configured to withstand wide variety of harsh environmental conditions like wind, rain, mechanical stresses, etc.
[0038] Radome is shaped in this particular design to have minimum boresight error in all antenna positions.
[0039] According to one implementation of the present invention, the present embodiment describes a hemispherical structure (110) consisting of plurality of segments (201, 203, 206) assembled.
[0040] Figure 2(b) illustrates the exploded view of maintenance hatch door (202) according to an exemplary implementation of the present invention wherein the maintenance hatch door is attached with the segmented Radome with panel joining flanges (208). Panel joining flanges are considered for ensuring strong joint, manufacturing ease and good aesthetics.
[0041] According to the present invention all segments of the Radome body 100 are constructed such that it is transparent to ultra-wideband microwave energy emitted or received by the passive reflector antenna enclosed inside. As such, the electromagnetic wave incident angles can be changed upto several degrees in accordance with the setting satellite look angles.
[0042] However, the shape of Radome ensures that incident angles are not changed drastically which may result into high losses to signals. The above-mentioned multi-band electromagnetic energy from the passive antenna contacts mostly the hemispherical upper segments of Radome body at small incident angles while communicating with the satellite.
[0043] Furthermore, as illustrated in Figure 3 the entire segmented Radome structure is placed on a base plate (300) according to an exemplary implementation of the present invention.
[0044] In one of the embodiments this base plate (300) can be octagonal in shape. In other embodiments this base plate (300) can be a ring or any other similar shape.
[0045] The base plate (300) provides a mechanical support to the entire Radome structure.
[0046] Generally, antenna Radome are usually a sandwich construction utilizing the electrical properties of the layers to maximize transmission in the desired frequency band(s). Permittivity and dielectric loss tangent are important parameters to characterize when working with Radome design and characterization. The permittivity and loss tangent of the materials used, together with the thickness of the materials, decide the transmission and reflection coefficients of the Radome wall.
[0047] Also, the Radome layers are chosen in such a way that it is transparent to all the frequency bands of microwave energy mentioned above emitted or received by the satellite communication antenna. This antenna is generally a passive reflector and is fitted with azimuth, elevation and polarization rotation provisions. Therefore, present invention caters to free movement of enclosed antenna along with all its peripheral parts.
[0048] The embodiment presented here is a thin multilayer structure as illustrated in figure 4. According to an implementation of the present invention the thin multilayer structure (400) comprises two solid laminate layers (402); a foam layer (403), wherein the foam layer (403) is sandwiched between the two solid laminate layers (402); and a gel coat layer (401) as an outermost protective layer.
[0049] In one of the implementations the outermost layer 401 is gelcoat to protect inner layers of Radome from environmental damages.
[0050] In another embodiment of the present invention gel coat layer (401) has a thickness of about 0.5mm.
[0051] In another implementation the second layer 402 from outside is made up of E glass prepreg which is a ready-to-use kind of E glass fiber mixed with appropriate amount and quality of epoxy. However, in another embodiment any equivalent material like resin (with different processing parameters eg. Pot time, gel time etc.), glass cloth (wooven patern, gsm etc), adhesive, etc. may be used.
[0052] In another embodiment of the present invention the third layer 403 is made from honeycomb (like Nomex) to have minimum dielectric constant but not compromising too much on material strength, as honeycomb’s normal compressive strength is quite high.
[0053] In another implementation the last layer or innermost layer is again a replica of second layer E glass material.
[0054] In another embodiment of the present invention 0.3mm is the general thickness of E glass prepreg available commercially.
[0055] In case of different glass cloth (GSM, etc.), number of prepreg layers is designed in such that the electrical properties (like dielectric constant and tangent loss) and mechanical properties like thickness be maintained as per original specifications mentioned in this invention. Rotation of fiber orientation for each layer of glass cloth is implemented to achieve properties as homogenous as possible, in plane of fiber cloth.
[0056] As illustrated in in figure 2 the panel joining flanges are considered for ensuring strong joint, manufacturing ease and good aesthetics. In another implementations all gaps are filled with minimum amount of resin required. Hydrophobic gelcoat used on outside makes the Radome smooth and with improved aesthetic. However, the important function of gelcoat is to provide perforation free rain proof outer Radome surface.
[0057] In another embodiment of the present invention the outside edges and corner are not left sharp for safety of users and to maintain maximum electromagnetic homogeneity possible.
[0058] In one of the implementations of the present invention all segmented panels of the Radome are maintained with lowest minimum surface rms values with respect to design, which is achieved by applying extra epoxy coating followed by buffing.
[0059] In another embodiment the outer of the Radome may be painted to provide a particular finish. So, any other appropriate colour scheme according to application requirement is not outside the scope of this invention.
ADVANTAGES
[0060] Since the passive microwave satellite communication antenna is positioned inside the invention near the centre of hemispherical and cylindrical parts of the Radome, it ensures that performance of the antenna does not downgrade to an obvious level. Antenna signals will generally have a low incident angle at Radome surface (about =30°). Low transmission loss of present embodiment ensures that sensitivity and link margin of the enclosed antenna do not deteriorate over wide band of frequencies as mentioned herein above.
[0061] Antenna with large beamwidths is more prone for deteriorated performance due to large changes of path lengths and amplitude while crossing a relatively large portion of the Radome. However, satellite communication antenna generally has narrow beams and present invention keeps deterioration in side lobe levels almost negligible. Radome passed relevant mechanical /environmental tests like thermal (high and low temperature), stress- strain, physical dimension checks, and rain and dust erosion. The thin Radome meets the operational wind speed requirement upto 180 kmph and survival wind speed upto 240kmph.

WORKING EXAMPLES:

[0062] Referring to Fig. 5(a), 501 is the azimuth cut radiation pattern of the satellite communication antenna without Radome while 502 is with Radome. Fig 5 (b) refers to the elevation cut of the same antenna with and without Radome. As it can be seen from Fig5, losses due to Radome is lesser than 0.4 dB, highlighting RF transparency of the Radome(100).
[0063] Referring to the list below 1st Side lobe level (SLL) of Ku band satellite communication antenna without Radome and with Radome is shown. The 1st SLL deterioration due to Radome is less than 0.3dB.

SN. Parameter Measured Data
Without Radome With Radome
1. Gain 41.77 41.4
2. Side Lobe Level Azimuth
Plane 26.37 26.2
Elevation
Plane 17 16.7

Gain and Side Lobe Level of with and without Radome in tabular format

[0064] Now, referring to Fig. 6(a), it shows transmission losses 600 for the Radome embodiment described in this art. Losses at ultra-wide band frequencies upto Ku-band are below 0.4 dB. Now, referring to Fig. 6(b), it shows return losses 700 for the Radome embodiment described in this art. Return loss at ultra-wideband frequencies over 10 GHz bandwidth are below -13 dB.
[0065] The Radome losses are estimated over ultra-wide band using the BEL copyrighted Radome design and analysis software Radworld© (copyright registration no SW- 14627/2021). The same is validated in field with Ku-band satellite.
[0066] The description of the invention given here is illustrative and should not be considered as limited to this description. Although only some exemplary embodiments of this invention are described here, those who are skilled in the art will see that many minor modifications are possible in the present embodiments. Therefore, all such modifications should be considered included within the scope of this invention as defined in the claims.
[0067] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.

, Claims:WE CLAIM:
1. A Radome (100) for an antenna assembly, the Radome (100) comprising:
a hemispherical structure (110) configured to enclose a passive antenna;
wherein the hemispherical structure (110) is coated with a thin multilayer structure (400) making the hemispherical structure (110) transparent to an ultra-wide band frequency range.

2. The Radome (100) as claimed in claim 1, wherein the thin multilayer structure (400) comprises:
-two solid laminate layers (402);
-a foam layer (403), wherein the foam layer (403) is sandwiched between the two solid laminate layers (402); and
- a gel coat layer (401) as an outermost protective layer.

3. The Radome (100) as claimed in claim 3, wherein the foam layer is a honeycomb layer.

4. The Radome (100) as claimed in claim 3, wherein the solid laminate layers (402) are made of E glass prepreg.

5. The Radome as claimed in claim 3, wherein each of the solid laminate layers (402) have thickness of about 0.3mm.

6. The Radome as claimed in claim 3, wherein the gel coat layer (401) has a thickness of about 0.5mm.

7. The Radome (100) as claimed in claim 1, wherein the hemispherical structure comprises a plurality of segments (201, 203, 206) joined with each other by panel joining flanges (208).

8. The Radome (100) as claimed in claim 1, wherein the ultra-wide band frequency ranges from 3.635GHz to 14.5GHz covering S, C, X and Ku band.

9. The Radome (100) of Claim 3, wherein the thin multi-layer structure (400) provides low loss of about 0.4 dB to radio frequency signals.

10. The Radome (100) of Claim 9, wherein deterioration in the Side Lobe Level (SLL) in both azimuth and elevation plane of Ku band antenna is within 0.3 dB.

Dated this 28th day of March, 2024
For BHARAT ELECTRONICS LIMITED
(By their Agent)

D. MANOJ KUMAR (IN/PA-2110)
KRISHNA & SAURASTRI ASSOCIATES LLP.