Claims:CLAIMS
We Claim :
1. An improved microstrip antenna array for sidelobe suppression in radiation pattern, comprising:
a. a periodically arranged split ring resonator superstrate structure, placed at 0.5?0 height above the microstrip antenna array;
b. wherein, the split ring resonator superstrate acts as converging lens for the radiation beam to enhance the peak gain.
2. A system for sidelobe suppression of Microstrip array antenna, comprising:
placing a periodically arranged split ring resonator superstrate structure, at 0.5?0 height above the microstrip antenna array;
said superstrate configured to act as converging lens for the radiation beam and enhancing the peak gain along with simultaneous suppression of sidelobes.
3. The system for sidelobe suppression of Microstrip array antenna, as claimed in claim 2, wherein the antenna is a rectangular microstrip antenna array of 8-elements including a corporate power divider and hybrid power divider at 9.1GHz.
4. The system for sidelobe suppression of Microstrip array antenna, as claimed in claim 3, wherein the peak gain frequency shifts to 8.7GHz and the peak sidelobe level is -22.23dB.

Dated this 24th October 2020.
Senthil Kumar B
(Agent for the applicants)
IN/PA-1549
, Description:
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003
Complete Specification
(See section 10 and rule 13)
1.Title of the Invention :

DESIGN OF SPLIT RING RESONATOR SUPERSTRATE FOR SIDELOBE SUPPRESSION OF MICROSTRIP ARRAY ANTENNA

2. Applicants
Name Nationality Address
Dr. VANTAKU NAGENDRA LAKSHMANA KUMAR

Dr. M. SATYANARAYANA

Dr. SOHANPAL SINGH Indian

Indian

Indian

Department of Electronics and Communication Engineering, Maharaj Vijayaram Gajapathi Raj College of Engineering (Autonomous), Vizianagaram, Andhra Pradesh, India.

Department of Electronics and Communication Engineering, Maharaj Vijayaram Gajapathi Raj College of Engineering (Autonomous), Vizianagaram, Andhra Pradesh, India

Department of Electronics and Communication Engineering, Mahatma Gandhi Institute of Technology, Hyderabad, Telangana, India.

3. Preamble to the Description :

The following specification particularly describes the invention and the manner in which it is to be performed.

4. DESCRIPTION
Field of the Invention
The present invention is related to the field of electronic devices.
Background of the invention
Nowadays, the design of microstrip array antenna having peak SLL lower than -20dB is a challenging task. Although people like Taylor and Chebyshev had offered techniques for the generation of ultra sidelobes, still they fail in implementing printed antennas especially microstrip antenna arrays. Obtaining very low SLL requires unequal amplitude distribution, which in turn demands to implement the feed network with very thin microstrip lines. Implementing very thin lines is a limitation in printed circuit technology [1]. Designing an array antenna with low SLL is very much needed for suppressing EMI problems which exist in a multi-antenna system. It is also essential in Radar, to elude the wrong detection of targets [2]. David Pozar had analysed several factors, which should be taken into consideration for the design of low sidelobe microstrip antenna array [3]. In the paper [4], a peak SLL of -15dB was achieved for four-element linear microstrip array antenna using Wilkinson power divider with Chebyshev distribution. Implementing Chebyshev distribution using Wilkinson power divider is not practical for large size linear array. Due to the Wilkinson power divider, the feed network complexity increases in the large size array [5]. In paper [6], the concept of compact electromagnetic bandgap structures is proposed for SLL reduction. But it is very difficult to implement an EBG grid structure amid the superstrate slab at various heights above the antenna array.
The idea of CSRR structures on either end of the antenna array is given in [7]. By that 4.31dB reduction of peak SLL was achieved. In paper [8], the author has introduced the idea of CSRR (complementary split ring resonator) loaded amplitude tapering to suppress the peak SLL. The techniques mentioned in [7], [8] are more or less trail based. The technique of SIW and microstrip transition was used to reduce SLL for linear microstrip antenna array in [9]. In the paper [10], the technique of power split -T junctions for non-uniform excitation is proposed for suppressing SLL, for linear microstrip array antenna. The techniques stated in [9], [10] have limitations for implementing them to planar arrays. In the paper [11], the author had presented non-uniform positioning and proximity couple feed method for microstrip array antenna with eight elements and achieved peak SLL of -15.98dB. But it was implemented using discrete excitation rather than common feed. Cosine-square distribution over a pedestal amplitude distribution was used to suppress SLL for the planar array in [12]. This technique is complex to implement because it is required to use non-identical size antennas. Moreover, it is applicable for an array antenna with odd number of elements.
Summary of the invention
The technique of split ring resonator superstrate for suppression of sidelobes of microstrip array antenna is proposed in this invention. When a periodically arranged split ring resonator superstrate is placed over the microstrip array antenna at 0.5?0 height, it acts as converging lens for the radiation beam and enhances the peak gain with simultaneous suppression of sidelobes. A rectangular microstrip antenna array of 8-elements is designed with two different power dividers namely corporate power divider and hybrid power divider, at 9.1GHz. When split ring resonator superstrate is fixed at a height of 0.5?0 over these arrays, the peak gain frequency shifts to 8.7GHz and significant reduction of peak sidelobe levels are observed at 8.7GHz. Using this technique, peak sidelobe level of -22.23dB is achieved in case of array with hybrid power divider. Improvement of peak gain is also observed by this technique. The parametric study of split gap variations of the basic split ring resonator is also presented for peak gain frequency variations. The simulations are done using high frequency structure simulator software. The measured results are compared with simulation results.
Detailed Description of the invention
This invention is related to the technique of SRR (split ring resonator) based superstrate structure for SLL reduction. The performance of eight elements linear microstrip array antenna is studied, by fixing SRR.
When the SRR superstrate is kept at a height of ?0/2, the frequency of peak gain moves to 8.7GHz from 9.1GHz and peak SLL reduces significantly along with improved peak gain at 8.7GHz. The array performance is observed with 2 feed divider networks. One is corporate power divider and the other one is with hybrid power divider which is a modification of corporate power divider. Section 2 describes the design of rectangular patch array antenna of 8-elements with corporate power divider and with hybrid power divider. In Section 3, the design aspects of basic SRR cell and analysis of the superstrate structure for sidelobe suppression are explained. Section 4 demonstrates the results. The parametric study of split gap alterations for frequency change is also discussed. Section 5 presents the conclusion.
2 |DESIGN OF RECTANGULAR MICROSTRIP PATCH ARRAY ANTENNA OF 8-ELEMENTS
Initially, a single edge fed patch antenna of rectangular shape is designed for X-band frequency 9.1GHz on the FR4 substrate, having er value 4.4, loss tangent 0.02, and height 1.58mm. The length and width dimensions of the patch are evaluated by the equations mentioned in [13], [14]. The calculated values are obtained as width W=9.71mm and length L=7.18mm. The antenna is in turn optimized for best return loss, by changing length value. For L=6.81mm, S11 of -35.9dB is obtained. Thus optimized width and length of the patch antenna are given by W=9.71mm and L=6.81mm. These optimized values of single patch antenna (both W and L) are taken as reference in realizing eight elements linear patch array antenna. With the help of the corporate power divider technique, the array is designed as shown in Figure 1. Using 100 ? lines, the power gets distributed equally from the 50 ? mainline. Quarter wave transformer of 70.71 ? line is used to connect 50 ? and 100 ? lines. The impedance of the single patch antenna is 251 ?. Quarter wave transformer of 158 ? is used in the last stage to connect the 100 ? lines with patch antennas in the array. The dimensions of different lines are given in Table 1. The size of this antenna array is 1.20?0 X 4.22 ?0 X 0.048 ?0.
A spacing of 0.5?0 is maintained between the individual patch antennas in the array. The first stage in the corporate power divider of eight elements antenna array is modified by Wilkinson power divider to improve the isolation between the left and right side arms of the feed network. The second stage and third stage of the feed network are unchanged. The Wilkinson power divider contains the main transmission line, which further splits into two quarter-wavelength lines, where each line has an impedance of 1.414 times the characteristic impedance of the mainline [15]. An internal resistor having twice the characteristic impedance value is connected between the two quarter wave lines. A 1:1 Wilkinson power divider architecture is depicted in Figure 2. The array with corporate cum Wilkinson divider (hybrid power divider) is depicted in Figure 3. The size of this antenna array with hybrid power divider is 1.48?0 X 4.22 ?0 X 0.048 ?0. The principle of SRR superstrate will be investigated over these two arrays.

3 | DESIGN OF BASIC SRR CELL AND ANALYSIS OF SUPERSTRATE STRUCTURE FOR SIDELOBE SUPPRESSION
A. DESIGN OF SRR BASIC CELL
The split ring resonator structure is the elementary building block for constructing a superstrate structure. It has two concentric rings in a rectangular shape, each of strip width “c”, separated by a distance “d”. They have split gaps “s” existing on opposite sides. This structure exhibits the property of negative permeability [16] and acts as LC parallel resonator [17]. The overall capacitance arises due to the split capacitances (CS) from split gaps and the mutual capacitance (CMut) that exists between concentric strips. This is shown in Figure 4. The two concentric conducting strips also contribute to inductances L1 and L2 [18]. If the split gap “s” is increased, then it leads to decrease of CS, which results in the increase of resonant frequency [19], [20]
Radkovskaya and Sauviac had illustrated the equation for the resonant frequency in their base papers [21], [22]. It was given as
(1)
Where “p” was given as
(2)
and (3)
(4)
(5)
Here CS2, CS1 are the capacitances due to split gaps and CMut represents mutual capacitance, “M” denotes mutual inductance between the rings. The inductance calculations are discussed in [23].
The length and width of the outer loop are chosen as 9.71mm and 6.81mm respectively, which are same as the patch dimensions taken in section 2. The outer ring strip width is chosen as c2=0.25mm and c1=0.5mm respectively as shown in Figure 5. The strip width of the inner loop ring is selected as 0.5mm. The outer and inner rings are maintained with gap distances of d2=0.404mm and d1=0.605mm as shown in Figure 5. The split gap “s” for both the rings is taken as 0.5mm. The dimensions of c2, c1 d2, d1, and s are chosen as optimum values which give the desired peak gain frequency with low SLL, unlike the case where c2=c1 and d2=d1.
A. ANALYSIS OF SRR SUPERSTRATE STRUCTURE FOR SIDELOBE SUPPRESSION
The basic SRR cell is repeated 8 times and is patterned in a straight line on the FR4 dielectric substrate with a periodic gap of 0.5?o. This forms the superstrate structure as shown in Figure 6(a). The superstrate substrate should be one side coated i.e. it is having no copper coating on the bottom. Here its thickness is taken as 1.58mm. The dimensions of the superstrate substrate should be chosen the same as the dimensions of the microstrip array antenna substrate. The ?o corresponds to 9.1GHz frequency. The position of SRR cells from one edge of the superstrate is chosen similar to the position of individual patch antennas from one edge of the array substrate. The material properties like permeability and permittivity of superstrate structure can be found using the Nicolson-Ross-Weir method [24], [25].
Figure 7 depicts the refractive index versus frequency plot for the superstrate structure. Except at some frequencies, the real part of the refractive index is negative across the C band and X band range. For those frequencies, the property of refractive index being negative can be used for particular applications.
Figure 8(a) shows the nature of the electromagnetic wave when it enters from a positive refractive index medium to a negative indexed medium and positive indexed medium to a positive indexed medium. The positive indexed medium to a negative indexed medium case is equivalent to a left handed (LH) converging lens and the second case is equivalent to right handed (RH) diverging lens. It is depicted in Figure 8(b). This SRR negative indexed superstrate can be assumed to be acting like a converging lens. When this superstrate is placed over the array antenna at 0.5?o height as shown in Figure 6(b), it converges the radiation beam coming from the array antenna. Due to this convergence, the main lobe enhances further and sidelobes will be suppressed. Because of the main lobe enhancement, the peak gain also increases.
4 | RESULTS AND DISCUSSIONS
The 8-elements patch array antenna performance is observed by placing SRR superstrate at different heights of wavelength.
A. SRR SUPERSTRATE PLACED OVER THE 8-ELEMENTS ARRAY ANTENNA WITH CORPORATE POWER DIVIDER
When the SRR superstrate is positioned at a height of 0.5?o over the microstrip array antenna of 8-elements with corporate power divider as presented in Figure 9(a), the peak gain frequency moves to 8.7GHz from 9.1GHz. It is depicted in Figure 9(c). Without placing the superstrate, S11 of -15.59dB is observed at 9.1GHz, and with superstrate -16.86dB is observed at 8.7GHz.
Without SRR superstrate, the peak value of gain is 12.04dBi at frequency 9.1GHz and it is 11.12dBi at 8.7GHz. With the superstrate structure, the peak value of gain obtained is 13.34dBi at 8.7GHz. So, 8.7GHz is taken for the height variation of the superstrate.
TABLE 2 Performance comparison of 8-elements array with superstrate at various heights, at 8.7GHz
S.no. Parameters ?o 3?o/4 ?o/2 ?o/4
1 S11 in(dB) -13.726 -9.275 -16.869 -8.066
2 Peak gain in(dBi) 11.096 11.017 13.345 9.514
3 Peak SLL in(dB) -14.508 -13.463 -19.184 -10.975
4 % Radiation-efficiency 57.226 57.591 57.923 51.729
5 Front/back-ratio in(dB) 15.789 14.637 21.104 14.095

Table 2 gives the performance comparison of the array with superstrate at various heights. When the height is varied to 0.5?o, the peak SLL decreases significantly to -19.184dB and peak gain increases to 13.345dBi. The front/back ratio of 21.104dB is also obtained. Figure 10 depicts the gain (normalized) comparison graph of the array antenna with superstrate placed at various heights, at 8.7GHz. The peak SLL for array antenna without superstrate is -13.262dB at 9.1GHz and it is -13.651dB at 8.7GHz. The peak SLL has decreased by 5.53dB at 8.7GHz. At 8.7GHz, the radiation efficiency of the array antenna without superstrate is 60.71% and it has slightly diminished to 57.92% with the placement of superstrate.
B. SRR SUPERSTRATE PLACED OVER THE 8-ELEMENTS ARRAY ANTENNA WITH HYBRID POWER DIVIDER
The superstrate structure discussed in section 3B is placed over the array with hybrid power divider, at a height of 0.5?o. It is depicted in Figure 6(b). There is a small difference between the superstrate structure used in section 4A and in this section 4B. The difference is in terms of location of basic SRR cells from one edge and the size of the superstrate structure.
Figure 11(a) depicts the S11 plot comparison for the antenna array with hybrid power divider for two cases (without and with superstrate). Without superstrate, S11 of -16.21dB is obtained at 9.1GHz and with superstrate the peak gain frequency shifts to 8.7GHz with S11 of -20.92dB. Even though, it appears that the return loss at 8.4GHz is high, it has poor gain at that frequency. With superstrate, the peak value of gain is observed at 8.7GHz. Hence the performance of the array with superstrate is studied at 8.7GHz for various heights. From Table 3, it can be observed that the peak SLL of -22.23dB is obtained with 13.001dBi peak gain, for 0.5?o height. The limitation of this technique is that the radiation-efficiency decreases when compared to the efficiency without superstrate. Without superstrate, the radiation-efficiency of the array antenna with hybrid power divider is 54.47% at 8.7GHz.
TABLE 3 Performance comparison of the array with hybrid power divider, with superstrate height variations, at 8.7GHz
S.no. Parameters ?o 3?o/4 ?o/2 ?o/4
1 S11 in(dB) -12.556 -9.805 -20.922 -8.743
2 Peak gain in(dBi) 10.293 6.752 13.001 4.486
3 Peak SLL in(dB) -17.524 -10.016 -22.230 -12.355
4 % Radiation-efficiency 50.066 50.107 48.299 42.281
5 Front/back-ratio in(dB) 10.118 9.926 21.552 9.645

EXPERIMENTAL VERIFICATION
Figure 12(a) depicts the experimental setup for return loss measurement for the array antenna with hybrid power divider along with SRR superstrate placed at height of 0.5?o. From Figure 12(b), it is noted that at 8.7GHz the measured value of S11 is -16.62dB. Whereas -20.92dB simulation value is observed at 8.7GHz from Figure 11(a). A deviation of 4.3dB is observed at 8.7GHz.
Figures 13(a) and 13(b) depict the setup for the measurement of Co-polarization and Cross-polarization patterns in the anechoic chamber. Figures 14(a) and 14(b) depicts the H-plane Co- polarization and Cross- polarization comparison plots. Figures 15(a) and 15(b) depicts the E-plane Co-polarization and Cross-polarization comparison plots. It is perceived from Figure 14(a) that the simulated value of peak SLL is -22.230dB and the measured value of peak SLL is -19.52dB. A deviation of 2.71dB is observed between measured and simulated values. The deviation between measured and simulated values is because of using polystyrene pillars for supporting the SRR superstrate. Figures 16(a) and 16(b) depict the current density distributions in the bottom and top substrates of the antenna array with split ring resonator superstrate respectively. Figure 16(c) shows the electric field distribution of the antenna array with superstrate slab at 8.7GHz frequency. Figure 17 shows the axial ratio versus frequency plot for the antenna array with hybrid power divider, in two cases. The axial ratio bandwidth without superstrate is 1.92% and it has improved to 4.05% by placing SRR superstrate.
C. FREQUENCY CHANGES BY SPLIT GAP ALTERATIONS
In section 3A, the architecture of the basic SRR cell is explained. There C2=0.25mm, C1=0.50mm, d2=0.404mm, d1=0.605mm, and S=0.50mm are selected. When this unit cell is slightly changed by changing split-gap “s” and placing the superstrate at 0.5?o height above the array with corporate power divider, the peak gain frequency has changed. Figure 18 depicts the structure of the new unit cell. Here C2=C1=0.50mm and inner ring strip width=0.50mm are selected. The outer ring dimensions are chosen as 9.71mm and 6.81mm. Both outer and inner ring split gaps are maintained the same value “s”. This parameter “s” is varied and the performance comparison for the array is given in Table 4.
When “s” is changed from 0.20mm to 1.50mm, the peak gain frequency increases from 8.60GHz to 8.85GHz. The peak SLL also changes from -19.136dB to -17.539dB. Front/back-ratio values above 20dB are observed. The peak gains are also improved. As per the requirement proper value of “s” can be selected in the unit cell.
Table 5 shows the comparison of current method in contrast with existing methods in literature. Although the techniques mentioned in references [7] and [8] are promising low sidelobe level, they are more or less trail based. The technique mentioned in reference [10] is good enough for linear microstrip antenna array, but it has limitation in extending to planar array. The current method can even be extended to planar array. This technique can also be applied by considering the circular split ring resonator basic unit cell in the superstrate structure.
TABLE 4 Performance comparison for 8-elements antenna array with corporate power divider by Split- gap “s” variation
S.no. Parameters S=1.50mm S=1.00mm S=0.50mm S=0.20mm
1 Peak gain frequency (GHz) 8.85 8.80 8.70 8.60
2 S11 in(dB) -11.624 -10.075 -13.748 -12.566
3 Peak gain in(dBi) 13.413 13.335 13.265 13.272
4 Peak SLL in(dB) -17.539 -18.048 -19.155 -19.136
5 % Radiation-efficiency 55.575 57.593 57.697 55.651
6 Front/back-ratio in(dB) 21.698 20.734 21.956 22.340

TABLE 5 Current method in contrast with existing methods in the literature
Year,[Ref.] Method used Peak SLL (dB) Size of the array Peak Gain(dBi) Frequency(GHz) Spacing
2010,[6] Electromagnetic bandgap structures between the elements of the antenna array -18.10 1x4-linear Not Reported 5.60-6.00 ?o/2
2012,[4] Chebyshev distribution using Wilkinson power divider -15.20 1x4-linear 12.00 6.00 ?o/2
2015,[7] CSRRs on either end of the array -21.50 4x8-planar 20.96 9.90 ?o/2
2016,[9] DRA with SIW technology and microstrip transition -19.17 1x8-linear 13.00 28.0-38.0 ?o/2
2016,[11] Proximity couple feed & Non uniform spacing -15.99 1x8-linear 15.40 28.00 0.5?o to 0.7?o
2017,[10] Non uniform excitation by power split- T junction -22.12 1x12-linear Not Reported 5.75-5.85 Non uniform -spacing
2018,[8] Amplitude tapering through CSRR -22.00 2x6-planar 16.10 10.90 0.71?o
2019,[12] amplitude distribution by cosine square distribution over a pedestal -17.50 13 elements- planar Not Reported 10.00 ?o/2
Current method Placing SRR- superstrate at a height of 0.5?o above the array antenna -22.23 1x8-linear 13.00 8.70 ?o/2
CONCLUSION
The design of microstrip array antenna for suppression of peak sidelobe level is investigated using the SRR superstrate structure. When the SRR superstrate slab is fixed at a height of 0.5?0 over the array antenna, it acts as a converging lens and focuses the beam. Due to this, the main lobe enhances and simultaneously suppress the sidelobes. At 8.70 GHz, the peak gain has increased to 13.34dBi and peak sidelobe level has decreased to -19.18dB, when the superstrate structure is placed above the array with corporate power divider. A 5.53dB reduction of peak SLL is observed in this case. The peak gain also improves by 2.25dB at that frequency.
This technique is also applied for the array with hybrid power divider and its performance is verified. Peak SLL has suppressed to -22.23dB and peak gain has improved by 1.90dB, at 8.7GHz. The only limitation of this technique is that the radiation efficiency is less compared to the radiation efficiency of the array without superstrate. The effect of split-gap variation on peak gain frequency is also observed. The proposed technique can also be applied for planar microstrip antenna arrays for sidelobe suppression.
Description of Drawings
FIGURE 1: 8-elements microstrip patch array with corporate power divider
FIGURE 2: Wilkinson power divider
FIGURE 3: 8-elements patch array with hybrid power divider
FIGURE 4: Split ring resonator cell with split and mutual capacitances
FIGURE 5: Architecture for basic split ring resonator cell
FIGURE 6 (a): Structure of SRR Superstrate
FIGURE 6 (b): SRR superstrate placed over the array with hybrid power divider
FIGURE 7: Refractive index graph for split ring resonator superstrate
FIGURE 8 (a): Refraction in Negative index and Normal mediums
FIGURE 8 (b): Converging Nature of SRR Superstrate
FIGURE 9 (a): 8-elements array antenna with superstrate structure
FIGURE 9 (b): S11 comparison plot of 8-elements array for the two cases
FIGURE 9 (c): Gain Vs frequency comparison plot for 8-elements antenna array
FIGURE 10: Gain plot comparison for 8-elements array at various heights of superstrate slab
FIGURE 11 (a): S11 plot comparison for the array with hybrid power divider
FIGURE 11 (b) Gain plot comparison for 8-elements array with hybrid power divider at various heights of superstrate slab
FIGURE 11 (c) 8-elements array with hybrid power divider and superstrate slab
FIGURE 12(a) Setup for S11 measurement
FIGURE 12(b) S11 measured plot
FIGURE 13 (a) Antenna Setup for Co-polarization measurement
FIGURE 13(b) Antenna Setup for Cross-polarization measurement
FIGURE 14 (a) Comparison of H-plane Co-pol. patterns
FIGURE 14 (b) Comparison of H-plane Cross-pol. patterns
FIGURE 15 (a) Comparison of E-plane Co-pol. patterns
FIGURE 15 (b) Comparison of E-plane Cross-pol. patterns
FIGURE 16 (a) Current density distribution of bottom substrate of the antenna array with SRR superstrate
FIGURE 16 (b) Current density distribution of top substrate of the antenna array with SRR superstrate
FIGURE 16 (c) Electric filed distribution of the antenna array with SRR superstrate
FIGURE 17 Axial ratio versus frequency plot for the antenna array with hybrid power divider in two cases
FIGURE 18 Schematic of new unit SRR cell

REFERENCES

1. Koziel S, Ogurtsov S. On systematic design of corporate feeds for Chebyshev microstrip linear arrays. IEEE Antennas Propag Int. Sympos. July, 2017;1-2.
2. Sudheer kumar T, Raju GRLVNS, Raju GSN. Array pattern synthesis using flower pollination algorithm. Proc(INCEMIC). Dec, 2016;1-4. DOI: 10.1109/INCEMIC.2016.7921465.
3. Pozar DM, Kaufman B. Design considerations for low sidelobe microstrip arrays. IEEE Trans Antenna Propag. Aug, 1990;38(8):1176-1185.
4. Kasi B, Chakrabarty CK. Ultra-Wideband Antenna Array Design for Target Detection. Prog In Electromag Research. 2012;25:67–79.
5. Shamaileh KA, Nihad D, Abushamleh S. A Dual-Band 1:10 Wilkinson Power Divider Based on Multi-T-Section Characterization of High-Impedance Transmission Lines. IEEE Microw Wireless Compon Lett. Oct, 2017;27(10):897-899.
6. Coulombe M, Koodiani SF, Caloz C. Compact Elongated Mushroom (EM)-EBG Structure for Enhancement of Patch Antenna Array Performances. IEEE Trans Antennas Propag. April, 2010;58(4):1076-1086.
7. Wahid A, Sreenivasan M, Rao PH. CSRR Loaded Microstrip Array Antenna With Low Sidelobe Level. IEEE Antennas Wireless PropagLett. 2015;14:1169-1171.
8. Manikandan R, Jawahar PK, Rao PH. Low sidelobe level csrr loaded weighted array antenna. IEEE Trans Antennas Propag. Dec, 2018;66(12):6893 – 6905.
9. Gupta SH, et al. Low-Side Lobe Level Aperture Coupled Dielectric Resonator Antenna Array Fed by SIW. 10th European Confer Antennas Propag(EuCAP). June, 2016;1-4.
10. Ogurtsov S, Koziel S. Systematic approach to sidelobe reduction in linear antenna arrays through corporate-feed controlled excitation. IET Microwave Antennas Propag. June, 2017;11(6):779-786.
11. Zainal NA, et al. Sidelobe Reduction of Unequally Spaced Arrays for 5G Applications. 2016 European Confer Antennas Propag(EuCAP). June, 2016;1-4.
12. Singh B, Sarwade N, Ray KP. Compact Planar Antenna Array With Tapering in Both Planes for Desired First Sidelobe Reduction. IEEE Antennas Wireless PropagLett. 2019;18(3):531-535.
13. Balanis CA. Antenna Theory Analysis and Design. 3rd edition, Hoboken (New Jersey): John Wiley & Sons, 2005. ISBN 0-471-66782-X
14. Stutzman WL, Thiele GA. Antenna Theory and Design. 3rd edition, Hoboken (New Jersey): John Wiley &Sons, 2013. ISBN 978-0-470-57664-9
15. Li JL, Wang BZ. Novel Design of Wilkinson Power Dividers with Arbitrary Power Division Ratios. IEEE Trans Industrial Elec. June, 2011;58(6):2541-2546.DOI: 10.1109/TIE.2010.2066536
16. Pendry JB, Holden, et al. Magnetism from conductors and enhanced nonlinear phenomena. IEEE Trans Microwav Theory Tech. Nov, 1999;47(11):2075–2084. DOI: 10.1109/22.798002
17. Baena JD, Bonache J, et al. Equivalent Circuit models for SRRs and CSRRs coupled to planar transmission lines. IEEE Trans Microwav Theory Tech. April, 2005;53(4):1451-1461. DOI: 10.1109/TMTT.2005.845211
18. Marques R, Mesa F, et al. Comparative analysis of edge- and broadside-coupled split ring resonators for metamaterial design-theory and experiments. IEEE Trans Antennas Propag. Oct, 2003;51(10):2572–2581. DOI: 10.1109/TAP.2003.817562
19. Aydin K, Bulu I, et al. Investigation of magnetic resonances for different split-ring resonator parameters and designs. New jour Physics. 2005;7:1-16. DOI:10.1088/1367-2630/7/1/168
20. Reddy AN, Raghavan S. Split Ring Resonator and its Evolved Structures over the Past Decade. In Proc IEEE(ICECCN). 2013:625-629. DOI: 10.1109/ICE-CCN.2013.6528575
21. Radkovskaya A, et al. Resonant frequencies of a combination of split rings: Experimental, analytical and numerical study. Microwav Optical Techn Lett. May, 2005;46(5):473-476. DOI: 10.1002/mop.21021
22. Sauviac B, Simovski CR, et al. Double Split-Ring Resonators: Analytical Modelling and Numerical Simulations. Electromagnetics. May, 2004;24(5):317-338. DOI: 10.1080/02726340490457890
23. Paul CR. Inductance: Loop and Partial. Hoboken (New Jersey): John Wiley &Sons. 2010. ISBN 978-0-470-46188-4
24. Ziolkowski RW. Design, Fabrication and Testing of Double Negative Metamaterials. IEEE Trans Antennas Propag. July, 2003;51(7):1516-1529. DOI: 10.1109/TAP.2003.813622
25. Rothwell EJ, et al. Analysis of the Nicolson-Ross-Weir Method for Characterizing the Electromagnetic Properties of Engineered Materials. Prog In Electromag Research. 2016; 157:31–47. DOI:10.2528/PIER16071706

Senthil Kumar B
(Agent for the applicants)
IN/PA-1549