The presented antenna is designed and fabricated using a commercial FR4 substrate with a permittivity and height, loss tangent of 4.4, and 1.6 mm and 0.02, respectively. The modeling and simulation of the antenna were conducted using HFSS (v13).
A. Proposed TVC-EBG Structure
EBG structures act as a band stop filter in a particular frequency range. Thus, EBG structures behave as high impedance surfaces at the resonant frequency. The TVC-EBG structure is made up of the copper patch surface, dielectric, ground surface, and via. The design formulations are given below in (1) and (2) as highlighted in [8], [17–20]
\(\begin{gathered} L={\mu _0}h \hfill \\ C=\frac{{w{\varepsilon _0}({\varepsilon _r}+1)}}{\pi }{\operatorname{Cos} ^{ - 1}}\left\{ {\frac{{2w+g}}{g}} \right\} \hfill \\ \end{gathered}\)
\({f_c}=\frac{1}{{2\pi \sqrt {LC} }}\)
Where, ɛ0, p, g, ɛr, and µ0 are the permittivity in free space, the width of the patch, relative permeability, and absolute permittivity respectively. To achieve compactness in the EBG unit cell, the equivalent values of the capacitor (C) and the inductor (L) are increased. To increase the value of L and C, a slot and via are inserted on the EBG unit structure. Figure 1(a) shows the proposed EBG unit cell.
Parameter
|
Ls
|
Ws
|
WF
|
Table 1
Parameters of the suggested antenna
Units(mm)
|
42.72
|
28
|
1.8
|
Parameter
|
W1
|
L1
|
Lf
|
Units(mm)
|
5.5
|
11
|
9
|
Parameter
|
d1
|
d2
|
d3
|
Units(mm)
|
1.7
|
2.7
|
6
|
Parameter
|
R
|
R1
|
R2
|
Units(mm)
|
6
|
10
|
2.5
|
Parameter
|
d5
|
d4
|
d3
|
Units(mm)
|
3
|
1
|
6
|
Ref.
|
IB (GHz)
|
ARBW
(GHz)
|
No. of element
|
Band notches
(GHz)
|
No. of band notches
|
Size
(mm2)
|
Isolation
(dB)
|
Table 2
Comparison with previous works
Proposed Antenna
|
3–11
|
3-10.4
|
2
|
3.5,5.5&8.2
|
3
|
42.72×55
|
-15
|
[9]
|
3.2–9.6
|
3.2–8.8
|
1
|
5.2and 5.8
|
2
|
65×65
|
NA
|
[27]
|
5.10–5.85
|
5.10–5.85
|
2
|
NA
|
NA
|
56×32
|
-20
|
[28]
|
5.772–5.864
|
5.49–6.024
|
2
|
NA
|
NA
|
97× 26.72
|
-33
|
[29]
|
5.8
|
5.6-6
|
2
|
NA
|
NA
|
110×58
|
NA
|
[30]
|
5.71–8.2
|
7.72–8.04
|
2
|
NA
|
NA
|
80 × 80
|
-15
|
[31]
|
4.56–8.5
|
4.75–8.45
|
1
|
NA
|
NA
|
40 × 40
|
NA
|
[32]
|
5.02–10.84
|
5.07–9.22
|
1
|
NA
|
NA
|
40 × 40
|
NA
|
[33]
|
2.08–3.75
|
2.28–3.76
|
1
|
NA
|
NA
|
46.6 × 70
|
NA
|
[34]
|
1.84–2.43
|
1.89–2.43
|
1
|
NA
|
NA
|
50 × 50
|
NA
|
$${f_{c1}}=\frac{1}{{2\pi \sqrt {{L_1}{C_1}} }}$$ ,
4
$${f_{c2}}=\frac{1}{{2\pi \sqrt {{L_2}{C_{2eq}}} }}$$ ,
5
$${f_{c3}}=\frac{1}{{2\pi \sqrt {{L_3}{C_{3eq}}} }}$$ , 6
B. Triple band rejected CP UWB Antenna
The final geometry of the CP UWB antenna with EBG unit cell is shown in Fig. 2. The design comprises an improved ring- shaped CP UWB antenna fed by a Microstrip feed line. To achieve the three rejected bands, the TVC-EBG cell is positioned close to the feedline of the UWB antenna. To attain wider ARBW, a slot and stub are inserted in the ground surface. The design parameter details of the CP UWB antenna with triple-band rejection are given in Table I. The step-wise evolution of the resonating antenna is shown in Fig. 3. Firstly, a modified ring monopole with a ground plane (Antenna-A) is simulated, as illustrated in Fig. 3(a). For antenna A, the axial ratio and VSWR range from 3–11 GHz with and ARBW between 4–5 GHz. In Fig. 3(b) the TVC-EBG structure is positioned near the feed line (Antenna-B) to achieve three notch bands. Figure 3(c) shows that by inserting stub and slots in the ground surface (Antenna-C) we can widen the ARBW.
C. Triple band rejected Circularly polarized UWB MIMO Antenna
Because of space restrictions in wireless communication devices and terminals, the antenna size must be as compact as possible [21]. A compact two port MIMO antenna is tough to design because of the port and field isolation issues among its radiating elements. The symmetrical arrangement of the suggested structure is introduced and Table 1 presents the specification of the structure. The geometry of the MIMO antenna is presented in Fig. 6. The complete size of the presented antenna is 42.7×55×1.6 mm3.
D. Generation of circular polarization
The suggested structure is fabricated with polarization diversity rather than working with the same CP mode. This type of structure results in both the RHCP and LHCP modes. To understand the CP of the presented antenna surface currents are used. Figure 7 shows the surface currents distribution at different stages 0˚, 90˚, 180˚, and 270˚. For 0°, the predominant vector is in -Y direction, though for 90° the vector direction is - X direction. The vector direction is inverse to 0° and 90° for 180° and 270°. In the Fig. 7 when observed from + Z direction it is seen that the surface current moves in the left to right direction. The suggested antenna with Port 1 is operating with LHCP. Correspondingly, when Port 2 is working, the current distribution moves in opposite way as the phase moves from 0˚ to 270˚, as specified in Figure. 8. This produces the RHCP in the CP UWB MIMO antenna. Thus, polarization diversity is achieved which will reduce the ECC values automatically