Claims:We Claim (s):
1. A fractal microstrip antenna based on Fibonacci series with Koch snowflake first iteration, wherein formation of one quadrant of the four-fold centro-symmetric structure requires four individual steps as follows:
-in step-1, a resultant pattern 60 is obtained by subtracting the two square boxes 53 and 54 from 52 wherein the outcome of the subtraction in step-1 is marked by 55, which is a part of 60, and the process repeated up-to step-4 in order to obtain first quadrant of the required geometry, wherein the subtrahend squares for step-2 to 4 are: 62, 63, 72, 73, 82 and 83, whereas minuend squares for same steps are: 61, 71 and 81;
-subtrahend squares for all the steps are obtained from Koch snowflake first iteration, which are merely scaling of one-third of their corresponding minuend squares;
-minuend squares are obtained through Fibonacci sequences in the reverse chronological order considering up to the seventh term of the series wherein before performing the subtraction, these derived subtrahend squares are flipped orthogonally in their consecutive steps;
- in step-2 to 4, the resultant patterns in the respective steps are: 70, 80 and 90 in which the subtraction in the corresponding steps are reflected by 64, 74 and 84 wherein the required geometrical shape of the antenna is obtained by making quadrantal symmetry of 90 about the axes and the resultant four-fold centro-symmetric fractal geometry is obtained as 100.
2. The micro-strip fractal patch antenna as claimed in claim 1, wherein micro-strip antenna structure for DSRC band using PCB laminate materials Roger 5880 comprises of:
-a radiating patch 100 in the top conducting layer of the substrate material which is designed based on the fractal geometry, wherein the length and width of the radiating patch is 26.18 mm and 16.21 mm, in which thickness of the conducting copper layer of Roger 5880 is 0.017 mm, wherein the value of C1 = 0.6245 mm;
-a middle dielectric layer 140 of Roger 5880 with relative dielectric constant ?r = 2.2 and thickness 0.787 mm;
-a lower conducting layer 150 of copper with length and width of 40 mm and 32 mm respectively, wherein the thickness of the lower layer is 0.017 mm.
-a down shift of the radiating patch with respect to its ground plane by an amount of 1.2 mm to improve the gain of the antenna;
-a copper feed line 110 in the top conducting layer with thickness 0.017 mm, width 2.29 mm and length 6.6425 mm connected with the radiating patch of 100;
-a 50 ? SMA connector 120 soldered at the feed end.
3. The microstrip fractal patch antenna as claimed in claim 1 and 2, wherein the dimensions of the four-fold centro-symmetric structure are dependent upon the choice of the numeric value of C1.
4. The microstrip fractal patch antenna as claimed in claim 1 to 3, wherein the geometric structure provides a single controlling parameter C1 for a design of a microstrip patch antenna in order to operate the resultant structure in a particular band.
5. The microstrip fractal patch antenna as claimed in claim 1 to 4, wherein the four-fold centro-symmetry structure provides a balance between the etched and un-etched portion in the radiating surface of the patch to achieve high gain at the designed resonating frequency.
6. The microstrip fractal patch antenna as claimed in claim 1 to 4, wherein the design and fabrication of a phased array antenna can be accomplished, in which elements of the array are derived from the fractal.
7. The microstrip fractal patch antenna as claimed in claim 1 to 4, wherein the design and fabrication of linear or planar array can be accomplished, in which elements of the array are derived from the fractal.
8. The microstrip fractal patch antenna design and fabrication as claimed in claim 1 to 4, wherein, the design and fabrication of a phased array RADAR can be accomplished, in which radiating element(elements) is(are) derived from the fractal.
9. The microstrip fractal patch antenna design and fabrication as claimed in claim 1 to 4, comprises of a conducting radiating patch, a middle dielectric layer, a lower conducting layer, a conducting stripline feed in the top layer of the structure which connects the radiating patch to the port, and an exciting port.
, Description:FIELD OF INVENTION:
[001] The present invention relates a fractal microstrip patch antenna which is derived from Fibonacci series with Koch snowflake first iteration for operating at Dedicated Short Range Communication (DSRC) band. The proposed antenna satisfies gain, directivity, symmetric radiation pattern, and bandwidth requirements in order to operate at DSRC band.
BACKGROUND OF THE INVENTION:
[002] Antenna is used to send/receive electromagnetic signals and its performance is mainly determined based on gain, bandwidth, directivity, and efficiency. Another important parameter in antenna design is the return loss, which is a measure of the fraction of the input power is being reflected by the antenna. The primary objective of using microstrip antennas are their compactness, less weight, low cost for fabrication, relatively less complicated matching network and easy interface with microwave devices. However, the major drawback of conventional patch antennas is their narrow operating bandwidth caused by a high-quality factor (Q), low gain and directivity. Existing methods to overcome the addressed drawbacks are either increase the size of the antenna or introduces difficulties in the fabrication. Several existing methods which incorporate known fractal geometries for the design of a microstrip patch antennas are: Koch snowflake fractal, Cantor square fractal, Sierpinski fractal, Minkowski Island fractal etc. In some cases, more than one fractal geometries are combined together to design a single microstrip patch antenna for obtaining the required resonating frequency. Most of these microstrip antennas are often suffers from poor gain. In order to improve the gain, sometimes, multilayer structures are incorporated in the antenna design which makes the antenna a bulky one and increases the fabrication cost and complexity. Thus there is a need for a compact microstrip antenna, which can give good gain, directivity, stable and symmetric radiation pattern with satisfactory return loss for a designated resonating frequency.
OBJECTIVES OF THE INVENTION:
[003] It is the primary object of the invention to provide a fractal based microstrip patch antenna, which has been derived from Fibonacci series with the incorporation of Koch snowflake first iteration, for getting a very good gain, directivity, symmetric radiation pattern, required bandwidth and satisfactory return loss, in order to operate at DSRC band.
[004] It is another object of the present invention to provide the layout of the proposed microstrip fractal patch antenna for any other desired frequency, by changing a single controlling parameter and thereby changing the dimension in the design.
SUMMARY OF THE INVENTION:
[005] A new fractal geometry is proposed to design of a microstrip patch antenna which has been derived from Fibonacci series with the incorporation of Koch snowflake first iteration, for operating at DSRC band. The overall dimension of the proposed fractal geometry is interrelated with the area of the smallest square box inside the geometry. Therefore, the resonating frequency of a microstrip antenna, based on the proposed design, can be determined by choosing the length of the smallest square box (in mm) inside the fractal geometry. Moreover, the proposed geometry provides a balance between the etched and un-etched portion in the radiating surface of the patch, and thereby capable of providing satisfactory gain at the designed resonating frequency.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
[006] The present invention will be described in more detail hereinafter with the aid of the description which relates to preferred embodiments of the invention explained with reference to the accompanying schematic drawings, in which:
Referring Fig. 1 is the conventional rectangular microstrip patch antenna.
Referring Fig. 2 is the stepwise formation of one quadrant of the proposed geometry.
Referring Fig. 3 is the complete proposed geometry with four-fold symmetry.
Referring Fig. 4 is the complete novel fractal antenna with stripline feed.
Referring Fig. 5 is the side view of the antenna.
Referring Fig. 6 is the prototype antenna for DSRC (5.9 GHz) band, based on the present invention.
Referring Fig. 7 shows the simulated and measured reflection coefficient of the proposed patch antenna.
Referring Fig. 8 shows the simulated and measured E-plane co and cross polarization of the proposed patch antenna.
Referring Fig. 9 shows the simulated and measured H-plane co and cross polarization of the proposed patch antenna.
Referring Fig. 10 shows the simulated 3D gain of the proposed patch antenna.

DETAILED DESCRIPTION OF THE INVENTION:
[007] The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques, and approaches are overcome by the present invention as described below in the preferred embodiments.
[008] In one embodiment of the present invention is to provide a geometric structure which can be used to design of a microstrip patch antenna with satisfactory gain and bandwidth. The proposed geometry has four-fold centro-symmetry about the origin. The symmetric is obtained by implementing Fibonacci square box followed by etching of Koch snowflake (first iteration) in all the four quadrants of the structure. A conventional microstrip patch antenna of length L and width W with stripline feed is shown in Fig. 1, where 10 is the radiating portion of the patch antenna. The stripline feed and port are indicated by 20 and 30 respectively. The top view of the patch antenna of Fig. 1 is indicated by 40. The detail step-by-step formation of the novel geometric structure of the proposed fractal patch antenna of Fig. 2 is as follows:
[009] In another embodiment of the present invention it can be seen from Fig. 2 (a), that right-hand side pattern of 60 is obtained by subtracting the two square boxes of 53 and 54 from the highlighted square of 52 in the left-hand side of the figure of 51. The outcome of step 1 is represented by the highlighted square represented by 55 which is a part of 60. The subtrahend squares: 53, 54, 62, 63, 72, 73, 82 and 83, for all the steps are obtained from Koch snowflake first iteration, which is merely scaling of one-third of the minuend squares of: 52, 61, 71, and 81 respectively. These subtrahend squares are flipped orthogonally in the consecutive steps before performing the subtraction as shown in Fig. 2. The minuend squares are obtained through Fibonacci sequences in the reverse chronological order considering up to the seventh term of the series. The process is continued up to step 4 as shown in Fig. 2 (a), (b), (c) and (d) respectively. The outcome of steps 2 to 4, as shown in Fig. 2 (b), (c) and (d) are: 70, 80 and 90 and their corresponding subtraction are reflected in the highlighted squares of 64, 74 and 84. The right-hand side of Fig. 2 (d) produces one of the quadrants of the required geometry of 90 as shown in Fig. 2 (e). The resultant geometrical shape represented by 100 in Fig. 3, is obtained by making quadrantal symmetry of Fig. 2 about the axes as shown by 90, 91, 92 and 93 respectively.
[010] In another embodiment of the present invention is in order to establish the superiority of the proposed geometric structure of Fig. 3, as an effective microstrip patch antenna, it has been implemented on the top layer of a number of most commonly used substrate materials like: Roger 5880, Neltec and FR-4 to design of a microstrip patch antenna which can operate in DSRC band. Therefore, it is required to achieve a resonating frequency of 5.9 GHz and bandwidth of 75 MHz with more than 5.5 dB gain, regardless of the type of the substrate material.
[011] In another embodiment of the present invention the derived antenna from the geometric structure of Fig. 3 is shown in Fig. 4, where, 100 represents the radiating patch, 110 represents the stripline feed, 120 represents the exciting port and the overall structure is represented by 130. The side view of the structure is shown in Fig. 5, where 100 represents the radiating patch, 110 represents the stripline feed, 120 represents the exciting port, 140 represents the substrate material and a ground conductor layer is represented by 150. In Fig. 5, ht and hs are denoting the thickness of the copper layer and middle substrate layers respectively.
[012] In another embodiment of the present invention in the proposed design, the value of C1 for Roger 5880, Neltec and FR-4 have been kept as 0.6245 mm, 0.52 mm and 0.51 mm respectively to operate the antenna at 5.9 GHz.
[013] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description only, though these are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously modifications remain possible, in particular from the point of view of the design of the various elements or by substitution of equivalent methods, without thus departing from the scope of protection of the invention.
EXPERIMENTAL RESULTS:
Experiment 1: In order to prove that the proposed geometric structure has a single controlling parameter to design an antenna with the desired resonating frequency the following experiments have been performed. The value of C1 has been changed from 1.55 mm to 0.18 mm for the substrate material Roger 5880. It has been observed that the antenna can be designed to operate on different frequency band by changing the value of C1 and thereby changing its corresponding dimension. The corresponding results are listed in Table 1.

Table 1: Parametric simulated result for different commercial frequency band
Commercial Band
[Frequency] Resonant Frequency
[GHz] Value of C1 [mm] Return Loss [dB] Bandwidth [MHz] Gain [dB] Efficiency [%] Size of Patch [mm2]
S
[2 - 4 GHz] 2.40 1.55 -24.30 24.50 6.67 70.00
DSRC 5.90 0.6245 -19.16 136.21 7.70 88.45
C
[4 - 8 GHz] 7.59 0.48 -37.63 241.54 7.16 84.17
X
[8 - 12 GHz] 10.29 0.35 -22.54 349.63 7.41 80.73
Ku
[12-18 GHz] 12.84 0.28 -32.66 507.58 7.09 76.08
K
[18-27 GHz] 19.62 0.18 -60.06 922.84 7.15 75.18
Experiment 2: The next experiment proves that the propose geometric structure can be used to design of a microstrip patch antenna for a particular band using different substrate material, provided that it retains a reasonable gain and required bandwidth, regardless of the type of the material. In this case, three different materials of Roger 5880, Neltec and FR-4 have been considered to design antennas for DSRC band. The results, listed in Table 2, shows that all the three antennas for three different substrate materials satisfy the gain and bandwidth requirements for the DSRC band.
Table 2: Parametric simulated result of the proposed antenna using different substrate material in order to operate at DSRC band
Material Name Roger 5880 Neltec (NX9320) FR-4
Loss tangent 0.0009 0.0024 0.025
Dielectric constant (?r) 2.2 3.2 4.3
Resonant Frequency (GHz) 5.9 5.9 5.905
C1 value (mm) 0.6245 0.52 0.51
Embodiment Size (mm2)
Return Loss (dB) -19.16 -13.75 -39.02
Gain (dB) 7.70 6.90 5.58
Directivity (dBi) 8.24 7.42 6.66
Bandwidth (MHz) 136.21 120.29 288.65
Efficiency (%) 88.45 84.96 77.96
FABRICATED PROTOTYPE ANTENNA USING THE PROPOSED GEOMETRIC STRUCTURE:
Prototypes of the proposed single element, operating in the DSRC band, have been fabricated using Roger 5880. It has been observed that gain of the antenna, designed to operate for DSRC band using Roger 5880, slightly improves by downshifting the radiating patch with respect to its ground plane by 1.2 mm, as pointed in Fig. 4 by DS. The dimension details are shown in Fig. 4, and their corresponding numeric values are listed in Table 3. The fabricated single element is shown in Fig. 6 and the corresponding simulated and measured return losses are shown in Fig. 7. The highlighted portion of Fig. 7 shows a resonant frequency of 5.894 GHz from the fabricated single element is compared with its simulated value of 5.9 GHz. The measured return loss of the single element at resonating frequency is recorded as -17.58 dB while the corresponding simulated value is -19.16 dB. The measured bandwidth of the single element is obtained as 128 MHz in compared with its simulated counterpart of 136.21 MHz. The simulated and measured E-plane co- and cross-polarization radiation patterns of the proposed single element are shown in Fig. 8, and the corresponding H-plane radiation patterns are shown in Fig. 9. Both the figures ensure a very good agreement between the simulated and measured results. The three-dimensional simulated radiation pattern of the antenna is shown in Fig. 10.
Table 3: Dimension of the proposed prototype of Fig. 6
Symbols WS LS Wp Lp ht
Values [mm] 40 32 26.229 16.237 0.017
Symbols C1 C2 C3 C4 hs
Values [mm] 0.6245 1.040 1.6653 2.70 0.787
Symbols DS Lb W50 --- ---
Values [mm] 1.2 6.6815 2.29 --- ---

The efficiency (?) of the fabricated structure at 5.9 GHz has been measured using Wheeler-cap method. The measured efficiency (?) of the antenna at 5.9 GHz is obtained as 85.11% which closely matches with its simulated version of 88.45%. The directivity of the fabricated single element is computed as 7.89 dBi from the measured half-power beam-width (HPBW) of E and H-plane radiation pattern of Fig. 8 and Fig. 9 as 101.350 and 78.120. The computed gain of the fabricated prototype is obtained as 7.54 dB. The measured results from the fabricated antenna of Fig. 6, are listed in Table 4, which proves the prototype as a very good antenna for the DSRC band.
Table 4: Measured results for the fabricated prototype of Fig.6
Parameters Value
Resonant Frequency 5.894 GHz
Return Loss -17.58 dB
Bandwidth 128.00 MHz
Gain 7.54 dB
Directivity 7.89 dBi
Efficiency 85.11 %