DESC:FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

Title: A RUGGEDIZED COMPACT MULTI OCTAVE SPIRAL ANTENNA

APPLICANT DETAILS:
(a) NAME: BHARAT ELECTRONICS LIMITED
(b) NATIONALITY: Indian
(c) ADDRESS: Outer Ring Road, Nagavara, Bangalore 560045, Karnataka, India

PREAMBLE TO THE DESCRIPTION:
The following specification (particularly) describes the nature of the invention (and the manner in which it is to be performed):

A RUGGEDIZED COMPACT MULTI OCTAVE SPIRAL ANTENNA

FIELD OF INVENTION:
The present disclosure relates to the radio wave communication systems. The disclosure, more particularly, relates to a wideband sinusoidal cavity backed spiral antenna with compact size.

BACKGROUND OF THE INVENTION:
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication expressly or implicitly
It is necessary for any Antenna to be compact in size and exhibit wideband characteristics in the present-day scenario. Spiral Antennas are quite popular because of their wideband characteristics with compact size. Some of the prior art in the field of spiral antenna are discussed below.
EP1026777A2 discloses a Sinusoidal spiral antenna which is operating from 1.43 GHz to 18 GHz. Within 50 mm Diameter by including sinusoidal modulation lower frequency of operation is reduced from 2 GHz to 1.43 GHz. Details of substrate material, Radome & fixtures used are not provided. Details about VSWR, Gain and polarisation of the antenna is not mentioned. The literature lacks the information on the performance of the antenna.
US patent US 8749451 B1 discloses a spiral antenna with a ground plane behind it for bleeding back lobe of signal away from spiral to ground. Antenna is operating in the frequency range of 2 – 18 GHz. Dimensions of antenna are given as 2.4? (60.96 mm) (D) * 0.4? (10.16 mm) (H). Details about VSWR, Gain and polarisation of the antenna is not mentioned. The literature lacks the information on the performance of the antenna with Radome and fixtures.
US patent US 2019/0207317 A1 discloses an Archimedean spiral antenna backed by a cavity having four conical perturbation elements. Antenna achieved (7-30 GHz) 124.3% of Impedance Band width and 107.2% of 3 dB Axial Ratio Band width. It achieved a peek gain of 10.7 dBic. Its 3 dB peak Gain Band width is 72 % within 7 – 15 GHz & 28.6 % within 19.7 – 26.5 GHz. Dimensions of antenna are 0.89 * ?L 2 (D*H). Details are not provided about the Radome and fixing of the antenna. The literature lacks the information on the performance of the antenna with radome.
US patent 10381719B2 discloses a comparative analysis between circular and polygonal spiral. Antenna is operating in the frequency range of 2 – 18 GHz with VSWR < 2.5 and Axial ratio < 3.5 dB. Antenna achieved a peak gain of 6.52 dBi at 8 GHz. Details of Dimensions of antenna and substrate material, Radome & fixtures used are not provided. The literature lacks the information on the performance of the antenna with Radome.

OBJECTIVES OF THE INVENTION:
The primary object of the present invention is to overcome the problem stated in the prior art.
Another object of the present invention is to provide a wideband sinusoidal cavity backed spiral antenna with compact size.

SUMMARY OF THE INVENTION:
The present invention provides a ruggedized compact multi octave spiral antenna comprising:
a) a multi octave wideband circularly polarized teflon loaded metallic cavity backed spiral antenna;
b) a sinusoidal modulated dual arm archimedean is etched on a double-sided copper laminated substrate; and
c) a wide band balun backed with an absorber filled cavity for unidirectional radiation with provision for placement of a mounting screws and a nuts for providing support and a thin wall wide band radome.

In an embodiment, the antenna operates in the frequency range of 1GHz – 18 GHz.
In an embodiment, the antenna exhibits improved impedance matching in lower range of frequencies through resistive loading.
In an embodiment, the antenna has a peak gain of >-10 dBiC from >1 GHz to 2GHz and , > 0 dBic from 2GHz to 18 GHz and 3dB Beam width = 55º from 1 to 18 GHz in a compact form factor.
In an embodiment, the stack up of absorbers for suppressing back reflections configured to improved FBR > 12 dB in the operating range of frequencies.
In an embodiment, the Antenna is CP polarized with boresight axial ratio of = 3 dB and at ± 45° axial ratio of = 6.5 dB is achieved in the entire frequency range of operation.
In an embodiment, the antenna is compact with dimensions of 71 mm (Diameter) and 80 mm with radome.
In an embodiment, the radome is configured to protect the antenna against all terrain and all-weather conditions.
In an embodiment, the gain of the antenna is controlled within the same dimensions by controlling the sinusoidal modulation on the arms.

DETAILED DESCRIPTION OF DRAWINGS:
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of their scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings in which:
Fig. 1: illustrates a simulation model of spiral antenna.
Fig. 2: illustrates fabricated model of spiral antenna.
Fig. 3: illustrates slow wave spiral techniques to reduce size of spiral antenna.
Fig. 4: illustrates VSWR (Voltage Standing Wave Ratio) of spiral antenna.
Fig. 5: illustrates plot of gain vs frequency of spiral antenna respectively.
Fig. 6: illustrates the plot of Axial Ratio vs frequency of spiral antenna.
Fig. 7: illustrates plot of beam width vs frequency of spiral antenna.
Fig. 8: illustrates plot of back lobe level (simulated FBR i.e front to back ratio) of antenna vs frequency.

DETAILED DESCRIPTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
According to the present disclosure the radiator is etched on a substrate material with a metallic cavity backed structure filled with lossy microwave absorbing material to obtain unidirectional pattern over Wide band of frequency.
In an embodiment, the present invention provides a ruggedized compact multi octave spiral antenna comprising:
a) a multi octave wideband circularly polarized teflon loaded metallic cavity backed spiral antenna;
b) a sinusoidal modulated dual arm archimedean is etched on a double-sided copper laminated substrate; and
c) a wide band balun backed with an absorber filled cavity for unidirectional radiation with provision for placement of a mounting screws and a nuts for providing support and a thin wall wide band radome.
In an embodiment, the antenna operates in the frequency range of 1GHz – 18 GHz.
In an embodiment, the antenna exhibits improved impedance matching in lower range of frequencies through resistive loading.
In an embodiment, the antenna has a peak gain of >-10 dBiC from >=1 GHz to GHz and , > 0 dBic from 2GHz to 18 GHz and 3dB Beam width = 55º from 1 to 18 GHz in a compact form factor.
In an embodiment, the stack up of absorbers for suppressing back reflections configured to improved FBR > 12 dB in the operating range of frequencies.
In an embodiment, the Antenna is CP polarized with boresight axial ratio of = 3 dB and at ± 45° axial ratio of = 6.5 dB is achieved in the entire frequency range of operation.
In an embodiment, the antenna is compact with dimensions of 71 mm (Diameter) and 80 mm (Height).
In an embodiment, the radome is configured to protect the antenna against all terrain and all-weather conditions.
In an embodiment, the gain of the antenna is controlled within the same dimensions by controlling the sinusoidal modulation on the arms.
The Antenna with stable radiation pattern and VSWR <2.2 throughout the frequency of operation can be achieved by using mechanical fitments like base plate, set of screws, fasteners, Radom etc. All weather rugged designs are to withstand all environmental conditions by using suitable Radom. Antenna with suppressed back radiation and stable radiation pattern by using a stack of microwave absorbing material within the metallic cavity. Antenna with higher gain through coherent space combining of radiated fields from dual arm spirals of one wavelength circumference with equal currents at diametrically opposite points. Enhanced frequency bandwidth in a compact size is achieved by restive loading to improve impedance matching at lower frequency ranges. Usage of Teflon loading for improving the radiation pattern at lower frequencies by creating a constructive interference of forward and reflected waves.
Figures 1 and 2 illustrates simulation and fabricated model of spiral antenna. The spiral antenna belongs to the class of frequency independent antenna which means its electrical characteristics like impedance, polarization and radiation pattern are unchanged over large impedance Bandwidth. Spiral antennas are travelling wave antennas, they provide stable radiation pattern. Generally Spiral Antenna exhibits bidirectional radiation pattern which is not suitable for many applications as half of the power getting radiated into unwanted region. A 104 can be used to redirect back radiation into front region. For the constructive interference of reflected waves with radiated waves in the front region the distance from the bottom of 104 and 102 should be order of quarter wavelength. When operating in broad frequency band it is difficult to maintain quarter wavelength cavity at every frequency and even it might affect the compactness of the antenna so a 108 in 104 can be used instead. It suppresses the back radiation by absorption instead of reflecting the radiated waves. It leads to decrement in gain as half of the radiated power is getting dissipated in the l08. Archimedean spiral antennas are widely used as a kind of broad-bandwidth antennas to achieve good frequency-independent characteristics like symmetric radiation pattern as their structure itself is symmetric.
Archimedean spiral is self-complementary that is two arms are 180? out of phase or mirror image to each other. Circular polarized antennas have gained significant attention in wireless communication due to their distinct advantages like reducing polarization mismatch and suppression of multipath interference. Spiral Antennas exhibit circular polarization when they are excited in balanced mode as they are already balanced structures.
Design of the Spiral antenna started with simulation and analysis of 105. 102 is basically a balanced structure. When a balanced structure like 102 is fed directly by 109, mainly two problems arise one is impedance mismatch, 109 will be of 50 ohms whereas input impedance of 102 will be in the order of 120-200 ohms and second problem of 109 is that it is an unbalanced structure. So, a wideband 105 is needed.
With properly designed 105 both impedance transformation and unbalanced to balanced transition can be achieved. 105 structure consists of a tapered strip printed on substrate and ground plane on other side of substrate. The line width at bottom end of tapered line is calculated to match with 50O input impedance and as it is tapered along its length the impedance increases and at top of 105-line width of tapered line is maintained in such a way that impedance should be in the order of 120 to 200 O to match with input impedance of 102. Figure 3 consists of a thin metal foil spiral etched on Substrate which is fed from centre. In this case it is Dual arm Archimedean spiral, each arm is fed with equal amplitude and 180° out of phase signal. So, when circumference of spiral is one wavelength, the currents at complementary or opposite points on each arm add in phase in far field. The radiation at any frequency is contributed from the region whose circumference is equal to or greater than one wavelength and this region is called Active Region. Hence, inner and outer radius of the spiral should satisfy the following equations.

Where Eeff is the dielectric constant of the substrate used.
So, Rin and Rout are chosen according to the required Frequency band of operation. Slow wave spiral techniques were introduced as shown in Figure 3 to reduce size of 100. A 102 is produced by adding sinusoidal type of high frequency profile, as shown in Figure 3 and increased the circumference of the 102. Slow wave techniques are employed to move the radiation zone closer to the centre of the 102 for a specific wavelength. As a result, this reduces the velocity of propagation along the length of 102, which operates at lower frequency for reduced size. By including sinusoidal meandering in the 102 gains at lower frequency is also improved as active region at lower frequencies are increased. 107 were added at the end of each of the spiral arms to overcome the above problem performance degradation at lower frequency.
It reduces the reflection from the end of each arm and improved the low frequency Voltage Standing Wave Ratio (VSWR) and axial ratio. Height and material of 103 has been chosen in such a way that quarter wavelength requirement has been fulfilled at lower frequency so that unsuppressed reflections will be added in phase with forward travelling waves. Lower frequency cut-off can be reduced by terminating the end of each arm of the spiral with 107. 102 is integrated with 105 and simulated in CST. During simulation mechanical housing like fixtures, screws are also taken care to obtain maximum matching between simulation and measured results. Measured results are illustrated in Figures 4 to Figure 8.
VSWR and gain of antenna are illustrated in figure 4, figure 5 respectively. Axial Ratio, beam width, back lobe level of antenna are shown in figure 6, figure 7, figure 8 respectively.
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 ruggedized compact multi octave spiral antenna comprising:
a) a multi octave wideband circularly polarized teflon loaded metallic cavity backed spiral antenna;
b) a sinusoidal modulated dual arm archimedean is etched on a double-sided copper laminated substrate; and
c) a wide band balun backed with an absorber filled cavity for unidirectional radiation with provision for placement of a mounting screws and a nuts for providing support and a thin wall wide band radome.
2. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein operates in the frequency range of 1GHz – 18 GHz.
3. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein exhibits improved impedance matching in lower range of frequencies through resistive loading.
4. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein the antenna has a peak gain of >-10 dBiC from 1 GHz to >2GHz and , > 0 dBic from 2 GHz to 18 GHz and 3dB Beam width = 55º from 1 to 18 GHz in a compact form factor.
5. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein a stack up of absorbers for suppressing back reflections configured to improved FBR > 12 dB in the operating range of frequencies.
6. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein the Antenna is CP polarized with boresight axial ratio of = 3 dB and at ± 45° axial ratio of = 6.5 dB is achieved in the entire frequency range of operation.
7. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein the antenna is compact with dimensions of 71 mm (Diameter) and 80 mm (Height) .
8. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein the radome is configured to protect the antenna against all terrain and all-weather conditions.
9. The ruggedized compact multi octave spiral antenna as claimed in claim 1, wherein the gain of the antenna is controlled within the same dimensions by controlling the sinusoidal modulation on the arms.