Description:FORM – 2

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

COMPLETE SPECIFICATION
(SEE SECTION 10, RULE 13)

YAGI ANTENNA WITH FOLDED REFLECTOR OFFSET DIRECTOR GEOMETRY

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 toradio wave communication systems. The invention, particularly, relates to Yagi antenna for use in wide band radar and communication antenna, more specifically, the present invention relates to a Yagi antenna with FROD geometry (Folded Reflector Offset Director) that leads to wide bandwidth.
BACKGROUND
[0002] The Yagi antenna which was initially used for broadcasting applications later also found wide applications in radars systems and communications equipment installed on-board vehicles. The conventional Yagi antenna consists of driven element, and two parasitic elements i.e. reflector and director element. These elements are placed along the length of boom. It is well known that the driven element is a folded dipole, reflector element which is located behind the driven element is linear dipole and director element/elements which is/are in front of the driven element is/are also linear dipole.
[0003] In general, the limitation of conventional Yagi configuration is that it leads to narrow bandwidth, (typically of around 10% with respect to centre frequency). This configuration makes them unsuitable for wide band & ultra-wide radar and communication applications where the need can be of more than 25-30% bandwidth.

[0004] Yagi antennas are most commonly fed with coaxial cable. This coaxial cable may radiate energy from the outer conductor (the shield) that can deteriorate the radiation pattern of the antenna. So, to minimize such radiation, usually the balun (“balanced to unbalanced”) is connected which feeds equal and opposite currents into the antenna.

[0005] Balun is basically a transformer, and it may introduce losses, thereby reducing antenna gain and therefore its efficiency. So, it is necessary to ensure that coaxial cable and balun used to feed the yagi antenna does not affect its radiation pattern, VSWR as it leads to deterioration of performance which ultimately impacts the bandwidth of Yagi antenna.

[0006] The wide bandwidth of Yagi antenna may be achieved by numerous methods. US patent 10,116,063 describes two different Internally fed directional folded Yagi antenna assemblies for two different frequency bands. It features internal matching to assure broad bandwidth. It ensures that coaxial cable used to feed the antenna does not affect the antenna performance, but band width achieved in this method is 8.65% in the frequency band (440 MHz- 490 MHz) and 10% in the band (880-960 MHz).

[0007] A compact Yagi Uda Antenna with Enhanced Bandwidth “IEEE antennas and wireless propagation letters, vol. 10, 2011” proposes a three-element compact yagiuda antenna to increase the bandwidth. The reflector and director elements are bowtie designs. However, the bandwidth achieved is again around 10% (300-330 MHz).

[0008] Patent application CN106450774 describes Ultra-wideband high-gain yagi antenna which comprises a wideband folded dipole exciting unit, 2-way micro-strip power divider, a first directing unit and a reflecting plate; the wideband folded dipole exciting unit is of a rectangular frame structure. The first directing unit is a half-wave dipole, is arranged on one side of the wideband folded dipole exciting unit in the height direction and is parallel to the wideband folded dipole exciting unit; the reflecting plate is arranged on the other side of the wideband folded dipole exciting unit in the height direction and is parallel to the wideband folded dipole exciting unit. The bandwidth achieved is 27% in the frequency range 1.70-2.243 GHz. The method involves micro strip power divider which may lead to mechanical challenges with respect to size and additional mounting arrangement and alignment etc.
[0009] WO 2020/251481 A1 discloses broadband quasi-Yagi antenna with ceramic substrate. Although broad bandwidth is achieved but at the expense of efficiency as Gain achieved is less (4-5dBi) for a single element.

SUMMARY
[0010] This summary is provided to introduce concepts of the invention related to a Yagi with FROD geometry (Folded Reflector Offset Director) for use inwide band radar and communication antenna. This summary is neither intended to identify essential features of the invention as per the present invention nor is it intended for use in determining or limiting the scope of the invention as per the present invention.
[0011] In accordance with an exemplary implementation of the present invention there is provided, a Yagi Antenna with FROD geometry for use in wide band radar and communication antenna. The Yagi antenna further comprises a folded dipoleas driven element; a folded dipole as parasitic reflector element; and director elements divided into sub director elements wherein the combination of folded dipole as reflector element and sub director elements are placed at offset from each other leads to wide bandwidth. Furthermore, in one of the implementations the constituent material of Yagi antenna is aluminium.

[0012] In accordance with another embodiment of the present invention, the Yagi antenna further comprises N numbers of director elements which are divided into 2N number of sub director elements. Furthermore, in other embodiments the corresponding sub director elements of every Nth director elements are placed at an offset distance of 0.05 lambda (?) from each other wherein lambda (?) refers to the wavelength of the electromagnetic radiation at the operating frequency of the antenna. In another implementation, for the Yagi antenna maintaining the length of corresponding each sub director elements are unbinding in nature.

[0013] In an embodiment, the Yagi antenna, further comprises: a feeder cable assembly; a balun cable assembly; and a protective cover covering both the feeder cable assembly and the balun cable assembly wherein the feeder cable assembly is routed inside the boom and extends towards the end of the boom behind the reflector element for connecting to the driven element.

[0014] In another embodiment, the protective cover covering both the feeder cable assembly and the balun cable assembly of the Yagi antenna is Teflon rods.

[0015] In accordance with another embodiment of the present invention, the feeder cable assembly and the balun cable assembly are both coaxial cable of impedance 50 ohms.

[0016] In accordance with another embodiment of the present invention the wide return loss band width ranges from 30.4% - 31.3%. In one of the implementations the wide return loss band width for three element configurations is 31.3% and the wide return loss band width for four element configurations is 30.4%.

[0017] In accordance with another embodiment of the present invention the cross-polarization compliance is provided over a complete bandwidth.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0018] 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 features and modules.
[0019] FIG. 1 illustrates block diagram depicting the conventional Yagi antenna as part of the prior art.
[0020] FIG. 2a illustrates simulation model depicting the three element Yagi antenna with FROD geometry along with Feeder and Balun cable assembly according to an exemplary implementation of the present invention.
[0021] FIG. 2b illustrates simulation model depicting the four element Yagi antenna with FROD geometry along with Feeder and Balun cable assembly according to an exemplary implementation of the present invention.
[0022] FIG. 3a illustrates simulation model depicting 3D view of the three element Yagi antenna with FROD geometry according to an exemplary implementation of the present invention.
[0023] FIG. 3b illustrates simulation model depicting 3D view of the four element Yagi antenna with FROD geometry according to an exemplary implementation of the present invention.
[0024] FIG. 4 illustrates a simulation model depicting the portion of coaxial cable covered with a protective layer according to an exemplary implementation of the present invention.
[0025] FIG. 5 illustrates a simulation model depicting the connection of coaxial cables with driven element according to an exemplary implementation of the present invention.
[0026] FIG.6a illustrates a plot depicting the return loss over the frequency range for three element Yagi antenna with FROD geometry according to an exemplary working example of the present invention.
[0027] FIG.6b illustrates a plot depicting the return loss over the frequency range for four element Yagi antenna with FROD geometry according to an exemplary working example of the present invention.
[0028] FIG.7a illustrates a plot of radiation pattern (elevation and azimuth) at centre frequency for three element Yagi antenna with FROD geometry according to an exemplary working example of the present invention.
[0029] FIG.7b illustrates a plot of radiation pattern (elevation and azimuth) at centre frequency for four element Yagi antenna with FROD geometry according to an exemplary working example of the present invention.
[0030] FIG. 8a illustrates a plot of elevation and azimuth plane co-polarized and cross-polarized radiation pattern at center frequency for three element Yagi antenna with FROD geometry according to an exemplary working example of the present invention.
[0031] FIG. 8b illustrates a plot of elevation and azimuth plane co-polarized and cross polarized radiation pattern at center frequency for four element Yagi antenna with FROD geometry according to an exemplary working example of the present invention.
[0032] 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
[0033] The various embodiments of the present invention describe wide band Yagi antenna with FROD geometry for use in radars and communication antennas.
[0034] The conventional Yagi antenna designs suffer from narrow bandwidth, typically around 10% with respect to the central frequency, which is insufficient for wide band radar and communication applications wherein it requires more than 25-30% bandwidth. Additionally, the use of coaxial cables and baluns to feed the antenna can introduce losses, reducing antenna gain and efficiency, further limiting its performance. Conventional Yagi antennas are unbinding in nature so that an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only.
[0035] The present invention as disclosed herein introduces a Yagi antenna with Folded Reflector Offset Director (FROD) geometry to address the bandwidth limitation. The Yagi antenna with FROD geometry as disclosed herein helps for bandwidth enhancement. The Yagi antenna with FROD geometry consists of driven element as folded dipole. The reflector element which is larger in length as compared to driven element is also a folded dipole. The director element/elements which is/are shorter in length as compared to driven element is divided into two sub elements. These two sub elements are placed offset from each other. The driven element is fed by coaxial cable assembly of 50 Ohms. Along with feeder cable, one more coaxial cable assembly of 50 Ohms is used which acts as a Balun. This FROD geometry of Yagi antenna, which includes two folded dipoles and director elements divided into two elements and placed at offset from each other leads to wide bandwidth, nominal efficiency and is mechanically easy to fabricate. This makes it suitable for wide band radar and communication systems applications. Furthermore, the unbinding nature of the Yagi antenna helps to concentrate its signal in a particular direction.
[0036] 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.
[0037] However, the systems and methodsare 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.
[0038] 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.
[0039] The present embodiment discloses a wide band Yagi antenna with FROD geometry for use in radars and communication antennas.
[0040] FIG. 1 illustrates block diagram depicting the conventional Yagi antenna as part of the prior art.
[0041] Referring to Fig 1, conventional Yagi antenna 100 consists of folded dipole as driven element 120, whereas the parasitic elements i.e. reflector element 130 and director element 110 are linear dipoles. These three elements are placed on boom 140.
[0042] FIG. 2a illustrates simulation model depicting the three element Yagi antenna with FROD geometry according to an implementation of the present invention, along with Feeder and Balun cable assembly.
[0043] The antenna as shown in fig 2a is a modified Yagi antenna with FROD geometry 200 in which driven element 230 is a folded dipole, first parasitic element i.e. reflector element 240 is also a folded dipole and the second parasitic element i.e. director element is divided into two sub elements 210, 220. Theelements (210,220) are placed on boom 250.
[0044] In one of the embodiments the number of directors (with offset sub director elements) in Yagi antenna with FROD geometry can be increased as per the Gain requirement.
[0045] FIG. 2b illustrates simulation model depicting the four element Yagi antenna with FROD geometry along with Feeder and Balun cable assembly according to an exemplary implementation of the present invention wherein two directors with offset director elements (210, 220, 280, 290) are placed on boom 250.
[0046] In one of the implementations of the present invention numbers of director elements are divided into 2N number of sub director elements wherein corresponding sub director elements of all Nth director elements are placed at an offset distance of 0.05 lambda (?) from each other wherein lambda (?) refers to the wavelength of the electromagnetic radiation at the operating frequency of the antenna.
[0047] In another implementations the boom is rectangular in shape.
[0048] In one of the embodiments the Yagi antenna with FROD geometry includes two coaxial cable assemblies: feeder cable assembly 260 and balun cable assembly 270.
[0049] According to the present invention, in one of the implementations the driven element 230, which is a folded dipole, is designed for 200 ohms impedance.
[0050] In another embodiment, the driven element 230 is fed with feeder cable assembly 260 which is coaxial cable of 50 Ohm impedance. The feeder cable assembly 260 is routed inside boom 250 and it extends towards the end of boom where reflector element 240 is located.
[0051] In another embodiment, along with feeder cable assembly 260, there is one more coaxial cable of 50 Ohms which acts as a balun cable assembly 270.
[0052] In another embodiment, the balun cable assembly 270 is also routed inside the boom 250 and is of U shape. The length of the balun coaxial cable assembly 270 is nearly ?/4 at the central frequency.
[0053] According to the present invention, the folded dipole as reflector element 240 improves the impedance matching and thereby enhances the bandwidth at lower frequencies. The length of the reflector element 240 is around 0.55 ? with respect to the centre frequency. The director element dipole is divided into two sub elements 210,220 for three element Yagi antenna. The dimensions of these two elements are similar and these two elements are placed at some offset from each other along the boom as shown in fig 2(a) and fig 2(b). The division of director element into two sub elements 210,220 and placing them at offset leads to bandwidth enhancement at higher frequencies. The spacing between the driven element 230, reflector element 240 and director elements 210, 220 is selected and optimized to obtain the maximum bandwidthwherein maintaining the length of corresponding each sub director elements are unbinding in nature.
[0054] In one of the embodiments the material of the driven element, reflector element and director elements used is aluminium and diameter of all the elements may be kept identical for the ease of manufacturing.
[0055] FIG. 3a illustrates a simulation model depicting 3D view of the three element Yagi antenna with FROD geometry according to an exemplary implementation of the present invention.
[0056] FIG. 3b illustrates simulation model depicting 3D view of the four element Yagi antenna with FROD geometry according to an exemplary implementation of the present invention.
[0057] The antenna as shown in Fig 3a is a modified three element Yagi antenna with FROD geometry 3D view 300 in which driven element 330 is a folded dipole, first parasitic element i.e. reflector element 340 is also a folded dipole and the second parasitic element i.e. director element is divided into two sub elements 310, 320. The elements (310, 320) are placed on boom 350.
[0058] FIG. 3b illustrates simulation model depicting the four element Yagi antenna with FROD geometry 3D view along with Feeder and Balun cable assembly according to an exemplary implementation of the present invention wherein two directors with offset director elements (310, 320, 380, 390) are placed on boom 350.
[0059] FIG. 4 illustrates a simulation model depicting the portion of coaxial cable covered with a protective layer according to an exemplary implementation of the present invention.
[0060] Referring to Figure 4, showing the portion of balun cable assembly 270 and feeder cable assembly 260 is covered with a protective layer. In one of the embodiments the protective layer may be Teflon rods 410, 420. It ensures that the radiation from the outer conductor of balun cable assembly 270 and feeder cable assembly 260 does not affect the performance of the antenna.
[0061] FIG. 5 illustrates a simulation model depicting the connection of coaxial cables with driven element according to an exemplary implementation of the present invention.
[0062] Figure 5 illustrates the connection of feeder cable assembly 260 and balun cable assembly 270 with driven element 230. The central conductor 501 of two ends of balun cable assembly 270 is connected to two ends of driven element 230. The center conductor 510 of feeder cable assembly 260 is connected to one end of the central conductor 501 of the balun cable assembly 270. The outer conductor 520 of feeder cable assembly 260 is connected to outer conductor 502 of balun coaxial cable assembly 270.
WORKING EXAMPLE:
[0063] Figure 6a is a plot of return loss 610 over the frequency range. The return loss achieved is better than -10 dB over the frequency band (185MHz- 255MHz) for three element Yagi antenna with FROD geometry.
[0064] Figure 6b is a plot of return loss 620 over the frequency range. The return loss is better than -10 dB over the frequency band (185 MHz- 252MHz) for four element Yagi antenna with FROD geometry.
[0065] Figure 7a is a plot of azimuth 710 and elevation pattern 720 at centre frequency for three element Yagi antenna with FROD geometry.
[0066] Figure 7b is a plot of azimuth 710 and elevation pattern 720 at centre frequency for four element Yagi antenna with FROD geometry.
[0067] FIG. 8a illustrates a plot of Co polarization (710, 720) vs Cross polarisation ( 810,820) azimuth and elevation pattern at central frequency for three element Yagi antenna with FROD geometry.
[0068] FIG. 8billustrates a plot of Co polarization ( 730,740) vs Cross polarisation ( 830,840) azimuth and elevation pattern at central frequency for four element Yagi antenna with FROD geometry.
[0069] The objective of the present invention was to design a wide band Yagi antenna with Gain remaining unaffected. The simulation results of the same over the whole frequency band are summarized below in table 2.

[0070] 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.
[0071] ADVANTAGES: The Yagi antenna with FROD geometry disclosed herein above invoke innovation in design of Yagi antenna geometry for bandwidth enhancement. The return loss better than -10 dB achieved is (31.3% bandwidth) in the frequency range (185 MHz- 254 MHz) for three element Yagi antenna and (30.4% bandwidth) in the frequency range (185 MHz- 252 MHz) for four element Yagi antenna.
[0072] 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:
1. A Yagi Antenna with FROD geometry (200), the Yagi antenna comprising:
-a folded dipole (230) as driven element;
-a folded dipole (240) as parasitic reflector element; and
-director elements divided into sub director elements (210,220) wherein the combination of the folded dipole (240) as reflector element and sub director elements (210, 220) are placed at offset from each other leads to wide bandwidth.

2. The Yagi antenna as claimed in claim 1, wherein N numbers of director elements are divided into 2N number of sub director elements.

3. The Yagi antenna as claimed in claim 1, further comprises:
-a feeder cable assembly (260);
-a balun cable assembly (270); and
-a protective cover covering both the feeder cable assembly and the balun cable assembly;
wherein the feeder cable assembly (260) is routed inside the boom (250) and extends towards the end of the boom (250) behind the reflector element (240) for connecting to the driven element (230).

4. The Yagi antenna as claimed in claim 3, wherein the protective cover covering both the feeder cable assembly and the balun cable assembly is Teflon rods (410, 420).

5. The Yagi antenna as claimed in claim 3, wherein the feeder cable assembly (260) is a coaxial cable of impedance 50 ohms.

6. The Yagi antenna as claimed in claim 3, wherein the balun cable assembly (270) is a coaxial cable of impedance 50 ohms.

7. The Yagi antenna as claimed in claim 2, wherein corresponding sub director elements of every Nth director elements are placed at an offset distance of 0.05 lambda (?) from each other wherein lambda (?) refers to the wavelength of the electromagnetic radiation at the operating frequency of the antenna.

8. The Yagi antenna as claimed in claim 2, wherein maintaining the length of corresponding each sub director elements are unbinding in nature.
9. The Yagi antenna as claimed in claim 1, wherein wide return loss band width is 31.3% (610) for three element configuration.
10. The Yagi antenna as claimed in claim 1, wherein wide return loss band width is 30.4% (620) for four element configuration.

11. The Yagi antenna as claimed in claim 1, wherein cross polarization compliance (810,820) is provided over a complete bandwidth.

12. The Yagi antenna as claimed in claim 1, wherein aluminium is used as constituent material.