Air-brush (spray printing) printing technique is used to randomly place inks with a wide viscosity range on the surface [10, 11]. The basic schematic of the production technique is given in Figure 4-a. The proposed antenna is fabricated using a Magic Brushmark airbrush and silver ink (Figure 4-b). The antenna prototypes fabricated on Kapton is given in Figure 4-c-d.
3.1) Radiation performance analysis
The produced antenna's performance parameters(reflection coefficient, radiation pattern, total efficiency, and gain) were measured in a chamber environment using the N9928A model network analyzer. VNA calibration was performed. The simulated and measured reflection coefficient of the proposed UWB antenna is shown in Figure 5. The comparative analysis of the simulation and measured results of the proposed flexible dual notch band UWB antenna is given in Table 3. The design results and the measurement results are in harmony and provide an ultra-wide operating frequency band with dual-band rejection characteristics. A horn antenna with high gain and efficiency value operating in a wide frequency range in the 2-18 GHz range has been used in this study. The measurement environment is shown in Figure 6. Antenna gain was calculated using the 3-point method. The efficiency and gain results of the dual notched antenna are plotted in Figure 7. There is more than 90% agreement between antenna gain measurement and simulation results. The notch band frequencies ranges have less than −3 dB gain performance, which provides it to reject the interference of other systems. The efficiency value measure and simulation results are harmonious.
Table.3 The proposed flexible UWB antenna results
|
Peak Gain (dBi)
|
Efficiency (%)
|
-10 dB Bandwitdh (GHz)
|
UWB
(simulated)
|
12.72
|
73-94
|
2.05-14
|
UWB
(measured)
|
12.57
|
71-85.2
|
2.05-14
|
UWB dual notched
(simulated)
|
12.73
|
70.8-2.95
|
2.05-14
|
UWB dual notched
(measured)
|
11.63
|
67.1-85.4
|
2.05-14
|
The E field and H field patterns of free space measurements both without notched and with dual notched are made in an anechoic environment. The simulation and measurement results of the antenna's E field and H field radiation patterns at 3-6-12 GHz are shown in Figure 8. It has been observed that the produced antenna shows a dipole-shaped radiation pattern in the E field and an omnidirectional radiation pattern in the H field for the frequencies examined in the UWB frequency range (3,6,12 GHz). According to radiation analysis is understood that the proposed antenna can be used for various wearable biomedical devices with its high-performance features, flexible and compact structure. The proposed antenna may be an excellent candidate to meet UWB requirements, and its compact configuration makes it suitable for all RF applications.
3.2 Bending Test:
The proposed UWB flexible antenna with dual notch bands needs to be evaluated in different configurations for potential use in devices. The antenna's flexibility is investigated experimentally by placing it on foam cylinders with different radii of curvature. The antenna in the bent form in different configurations is shown in Table 4 . Performance characteristics such as S11, gain, and radiation pattern was measured experimentally to validate the simulation results, considering all configurations. Simulation and measurement results are presented in Table 4. According to Table 4, the effects of bending on the performance characteristics are reasonable, not affecting the overall performance. Both the double notch band and the UWB feature are preserved. The radiation pattern of the proposed UWB flexible antenna with dual notch bands is measured for bending radius R=20 mm in the vertical and horizontal positions, the results are shown in Figure 9. From the simulation and measurement bending results, it is seen that the proposed antenna structure is suitable for flexible applications for the bending radius of 10mm and 20 mm. In general, the vertical and horizontal bending configurations maintain wider impedance bandwidth with dual notch bands. In addition to bending, the foam cylinder material (εr=1.03 [26] may have had a minimal effect on antenna performance. No significant deterioration in basic operating parameters was observed after testing the antenna under different bending conditions. The proposed design, structural strength, and continuity of performance characterize its usability in wearable biomedical devices.
Table.4 The proposed UWB flexible antenna with dual notch bands bending results