Wireless Body Area Networks: UWB Wearable Textile Antenna for Telemedicine and Mobile Health Systems

A compact textile ultra-wideband (UWB) antenna with an electrical dimension of 0.24λo × 0.24λo × 0.009λo with microstrip line feed at lower edge and a frequency of operation of 2.96 GHz is proposed for UWB application. The analytical investigation using circuit theory concepts and the cavity model of the antenna is presented to validate the design. The main contribution of this paper is to propose a wearable antenna with wide impedance bandwidth of 118.68 % (2.96–11.6 GHz) applicable for UWB range of 3.1 to 10.6 GHz. The results present a maximum gain of 5.47 dBi at 7.3 GHz frequency. Moreover, this antenna exhibits Omni and quasi-Omni radiation patterns at various frequencies (4 GHz, 7 GHz and 10 GHz) for short-distance communication. The cutting notch and slot on the patch, and its effect on the antenna impedance to increase performance through current distribution is also presented. The time-domain characteristic of the proposed antenna is also discussed for the analysis of the pulse distortion phenomena. A constant group delay less than 1 ns is obtained over the entire operating impedance bandwidth (2.96–11.6 GHz) of the textile antenna in both situations, i.e., side by side and front to front. Linear phase consideration is also presented for both situations, as well as configurations of reception and transmission. An assessment of the effects of bending and humidity has been demonstrated by placing the antenna on the human body. The specific absorption rate (SAR) value was tested to show the radiation effect on the human body, and it was found that its impact on the human body SAR value is 1.68 W/kg, which indicates the safer limit to avoid radiation effects. Therefore, the proposed method is promising for telemedicine and mobile health systems.


Introduction
The communications and telemedicine industry have been continuously evolving over the years. Wearable compact antennas constitute a significant part of every wearable communication for telemedicine systems. The wideband characteristic of wearable antennas is critical for telemedicine and mobile healthcare systems. In healthcare scenarios, the integration of antennas with a human body is essential to promote continuous monitoring. However, these processes arise due to deformation on The entire paper is organized in five different sections with an introduction to cover in section one. The UWB antenna configuration is presented in section two, whereas parametric analysis is in section three. The results and discussion are presented in section four. Finally, the conclusion is given in section five.

Materials and Methods
This section presents the textile antenna design and theoretical analysis. The textile material has low dielectric constant, which reduces the surface wave losses occur in the antenna. The wearable antennas' application should be incorporated with the human body. However, due to the human body's shape and electrical properties of biological tissues, the antenna's functioning is affected. The rigid materials with high dielectric constant fail these criteria, and low-dielectric-constant materials came into the picture to fulfil all these requirements. The low-dielectric materials also play a critical role for bandwidth enhancement and antennas flexibility. Therefore, the optimization process is proposed to justify the UWB antenna design. Furthermore, the mathematical circuit theory analysis is also performed to verify the function of the UWB textile antenna. As a result, the following subsections describe the material and designing methods. Figure 1a,b shows the rectangular patch and design of the proposed textile antenna in the UWB range. The antenna is made of a copper patch sandwiched with jeans fabric, where the upper patch is the radiating element and the lower patch is the ground plane and the jeans' fabric is the substrate. The jeans' fabric has low dielectric constant (εr = 1. 7), and that reduces the surface wave losses by improving the impedance of the textile antenna. Therefore, it is used as a substrate in the antenna design. Furthermore, a 3.5 × 10 × 1 mm 3 microstrip line is used to provide excellent impedance matching of 50 Ω in the designed antenna. The proposed antenna design came out from the optimization process in HFSS (High Frequency Structure Simulator) simulator. Table 1 describes the optimized geometrical parameters of the textile antenna.  The proposed antenna design came out from the optimization process in HFSS (High Frequency Structure Simulator) simulator. Table 1 describes the optimized geometrical parameters of the textile antenna. Moreover, Figure 2 visualizes the side view layout of textile antenna used in this manuscript.

Textile Antenna Design
Micromachines 2020, 11 Moreover, Figure  The basic structure of the textile antenna includes a radiating patch with asymmetric microstrip line feed and a partial ground plane. The final structure is obtained through the evolution process, in which various activities of optimization process (patch length-width variation, slot, notch and ground variation) have been performed by HFSS simulator under parametric study. The use of slotting has been verified by reducing the shape and size of the radiating element and ground plane, while the full ground plane of the antenna has an effect on its impedance characteristic. The impedance matching has been improved by cutting a slot (W2 × L2), two notches (W4 × L3) and Wsub − (W1 + W6 + W4) × (L4 + L2 + 1). The best impedance matching is achieved by adjusting feed position (Wf) and ground plane (G) and, therefore, the antenna's performance is improved.
On the one hand, by applying the iteration process to the primary antenna, the final design was obtained in which good impedance matching was achieved compared to the primary antenna. On the other hand, it can be observed that with a variation in a different slot, notch, patch and justified partial ground plane, the antenna reveals broad impedance bandwidth from 2.96 to 11.6 GHz (118.68%) with maximum resonance at 7.3 GHz frequency. As a result, the proposed antenna contains the complete 3.1-10.6 GHz range (UWB range) designated by FCC. Furthermore, the finalized textile antenna has been fabricated on jeans textile substrate including copper as a perfect electric conductor with loss tangent (tan (δ) = 0.025), thickness of 0.035 mm, εr = 1.7 and h = 1 mm. A 50 Ω SMA connector is joined via microstrip line feed to energize the antenna as illustrated in Figure 3.  The basic structure of the textile antenna includes a radiating patch with asymmetric microstrip line feed and a partial ground plane. The final structure is obtained through the evolution process, in which various activities of optimization process (patch length-width variation, slot, notch and ground variation) have been performed by HFSS simulator under parametric study. The use of slotting has been verified by reducing the shape and size of the radiating element and ground plane, while the full ground plane of the antenna has an effect on its impedance characteristic. The impedance matching has been improved by cutting a slot (W 2 × L 2 ), two notches (W 4 × L 3 ) and W sub − (W 1 + W 6 + W 4 ) × (L 4 + L 2 + 1). The best impedance matching is achieved by adjusting feed position (W f ) and ground plane (G) and, therefore, the antenna's performance is improved.

Theoretical Analysis of Textile Antenna
On the one hand, by applying the iteration process to the primary antenna, the final design was obtained in which good impedance matching was achieved compared to the primary antenna. On the other hand, it can be observed that with a variation in a different slot, notch, patch and justified partial ground plane, the antenna reveals broad impedance bandwidth from 2.96 to 11.6 GHz (118.68%) with maximum resonance at 7.3 GHz frequency. As a result, the proposed antenna contains the complete 3.1-10.6 GHz range (UWB range) designated by FCC. Furthermore, the finalized textile antenna has been fabricated on jeans textile substrate including copper as a perfect electric conductor with loss tangent (tan (δ) = 0.025), thickness of 0.035 mm, ε r = 1.7 and h = 1 mm. A 50 Ω SMA connector is joined via microstrip line feed to energize the antenna as illustrated in Figure 3.  1  Wsub  25  9  W2  8  2  Lsub  25  10  W3  6  3  L1  15  11  W4  6  4  L2  9  12  W5  15.5  5  L3  13  13  W6  4  6  L4  2  14  Wf  3.5  7  Lf  10  15  G  9  8  W1  11  16  h  1 Moreover, Figure 2 visualizes the side view layout of textile antenna used in this manuscript. The basic structure of the textile antenna includes a radiating patch with asymmetric microstrip line feed and a partial ground plane. The final structure is obtained through the evolution process, in which various activities of optimization process (patch length-width variation, slot, notch and ground variation) have been performed by HFSS simulator under parametric study. The use of slotting has been verified by reducing the shape and size of the radiating element and ground plane, while the full ground plane of the antenna has an effect on its impedance characteristic. The impedance matching has been improved by cutting a slot (W2 × L2), two notches (W4 × L3) and Wsub − (W1 + W6 + W4) × (L4 + L2 + 1). The best impedance matching is achieved by adjusting feed position (Wf) and ground plane (G) and, therefore, the antenna's performance is improved.

Patch
On the one hand, by applying the iteration process to the primary antenna, the final design was obtained in which good impedance matching was achieved compared to the primary antenna. On the other hand, it can be observed that with a variation in a different slot, notch, patch and justified partial ground plane, the antenna reveals broad impedance bandwidth from 2.96 to 11.6 GHz (118.68%) with maximum resonance at 7.3 GHz frequency. As a result, the proposed antenna contains the complete 3.1-10.6 GHz range (UWB range) designated by FCC. Furthermore, the finalized textile antenna has been fabricated on jeans textile substrate including copper as a perfect electric conductor with loss tangent (tan (δ) = 0.025), thickness of 0.035 mm, εr = 1.7 and h = 1 mm. A 50 Ω SMA connector is joined via microstrip line feed to energize the antenna as illustrated in Figure 3.

Theoretical Analysis of Textile Antenna
The electrical equivalent circuit of a simple rectangular patch antenna is the parallel combination of resistance (R 1 ), inductance (L 1 ) and capacitance (C 1 ) and their parameter values are given by [27].
where ε r = relative permittivity and ε e = effective permittivity, h = height of substrate.
where Q r = quality factor, f = resonating frequency and c = speed of light. The impedance of a simple patch can be calculated as the following manner, which is presenting in Equation (6).
This antenna is excited by a 50-ohm microstrip line feed, and its parameter values are evaluated by Equations (7) and (8) [28].
In the optimized design, a slot was removed from the patch, and it makes a series combination of resistance of slot and reactance of slot, which are given in Equations (9)-(11) [29].
x dx L sl = length of slot, C = 0.5772 (Euler's constant) and k = propagation constant. Cutting a slit on the edges of a patch is considered as a notch, which includes a parallel combination of R 2 , L 2 and C 2 whereas L 2 is the series inductance value of L 1 , ∆L 1 and ∆L 2 . Similarly, C 2 is also the series capacitance value of C 1 , ∆C 1 and ∆C 2 [30]. The additional inductance and capacitance values are evaluated by Equations (12)- (15). The total impedance due to two notches is calculated by using Equation (16).
When a patch is included with a notch, coupling capacitance is introduced in the equivalent circuit of the proposed antenna, which is given in Equations (17) and (18), and gives its impedance value [31].
where k c = coupling coefficient The total impedance between notch and slot is evaluated by parallel combination in it and when coupling impedance is considered. Therefore, a combination series of Z and Z C is obtained for total impedance. Finally, the input impedance is calculated by the parallel combination of Z patch and (Z c + Z). The reflection coefficient, voltage standing wave ratio (VSWR) and return loss values are evaluated by using Equations (21)-(23), respectively.
Return Loss dB = 20 log|Γ| (24) Figure 4 represents the equivalent circuit of the proposed antenna. Furthermore, this design is also verified by circuit theory analysis through advanced design system (ADS), a key sight circuit simulator, and electrical parameters are evaluated.

Parametric Study of Textile UWB Antenna
The parametric analysis has been done to provide complete information about the design of the antenna. The variation in the radiating patch, cut slot, substrate, feed width and ground of any antenna causes variations in its dimensions as well as electrical parameters. Therefore, the performance parameters of the antenna are also changed. Different parametric studies have been used to analyze the antenna performance.
The primary antenna was passed through different iterations in patch and ground to find out the proposed design, which produces various wideband performances. Multiple slots and notches have removed from the radiating patch and presented a justified ground plane by a partial ground modification to provide a reliable impedance matching. The feed width of 3.5 mm provides the best impedance matching with stable radiation properties.
The impedance matching is also affected by the variation in substrate material property, and it changes to the shifting of the characteristic impedance of the microstrip feed from 50 Ώ. The proposed antenna performance is analyzed with three substrates with the same dimensions, as shown in Figure  5. In the case of 2.2 and 4.4 return loss (S11) and bandwidth are substantially affected. However, jeans substrate offers more bandwidth (2.96-12 GHz) among all three substrates because low-dielectricconstant material reduces the surface wave loss to improve impedance bandwidth. The best impedance matching is obtained at dielectric constant of 1.7.

Parametric Study of Textile UWB Antenna
The parametric analysis has been done to provide complete information about the design of the antenna. The variation in the radiating patch, cut slot, substrate, feed width and ground of any antenna causes variations in its dimensions as well as electrical parameters. Therefore, the performance parameters of the antenna are also changed. Different parametric studies have been used to analyze the antenna performance.
The primary antenna was passed through different iterations in patch and ground to find out the proposed design, which produces various wideband performances. Multiple slots and notches have removed from the radiating patch and presented a justified ground plane by a partial ground modification to provide a reliable impedance matching. The feed width of 3.5 mm provides the best impedance matching with stable radiation properties.
The impedance matching is also affected by the variation in substrate material property, and it changes to the shifting of the characteristic impedance of the microstrip feed from 50 Ω. The proposed antenna performance is analyzed with three substrates with the same dimensions, as shown in Figure 5. In the case of 2.2 and 4.4 return loss (S 11 ) and bandwidth are substantially affected. However, jeans substrate offers more bandwidth (2.96-12 GHz) among all three substrates because low-dielectric-constant material reduces the surface wave loss to improve impedance bandwidth. The best impedance matching is obtained at dielectric constant of 1.7.

Parametric Study of Textile UWB Antenna
The parametric analysis has been done to provide complete information about the design of the antenna. The variation in the radiating patch, cut slot, substrate, feed width and ground of any antenna causes variations in its dimensions as well as electrical parameters. Therefore, the performance parameters of the antenna are also changed. Different parametric studies have been used to analyze the antenna performance.
The primary antenna was passed through different iterations in patch and ground to find out the proposed design, which produces various wideband performances. Multiple slots and notches have removed from the radiating patch and presented a justified ground plane by a partial ground modification to provide a reliable impedance matching. The feed width of 3.5 mm provides the best impedance matching with stable radiation properties.
The impedance matching is also affected by the variation in substrate material property, and it changes to the shifting of the characteristic impedance of the microstrip feed from 50 Ώ. The proposed antenna performance is analyzed with three substrates with the same dimensions, as shown in Figure  5. In the case of 2.2 and 4.4 return loss (S11) and bandwidth are substantially affected. However, jeans substrate offers more bandwidth (2.96-12 GHz) among all three substrates because low-dielectricconstant material reduces the surface wave loss to improve impedance bandwidth. The best impedance matching is obtained at dielectric constant of 1.7.  A significant variation in the ground plane is effected on antenna impedance matching at higher frequencies than at lower frequencies. By changing the ground plane from 8 mm to 10 mm with a step of 1 mm, proper matching is achieved at a partial ground plane value of 9 mm, which is shown in Figure 6. For ground plane (G) values of 8 and 10 mm, the resonance frequency is shifted from higher to lower value and return loss of the antenna is increased. Moreover, the bandwidth of the antenna is reduced. In both cases (8 and 9 mm), the return loss of the antenna is increased, which, in turn, can degrade the antenna performance. Therefore, a ground size of 9 mm is selected as the optimum size for a bandwidth of 120.85% (2.96-12 GHz).
Micromachines 2020, 11, x 8 of 22 A significant variation in the ground plane is effected on antenna impedance matching at higher frequencies than at lower frequencies. By changing the ground plane from 8 mm to 10 mm with a step of 1 mm, proper matching is achieved at a partial ground plane value of 9 mm, which is shown in Figure 6. For ground plane (G) values of 8 and 10 mm, the resonance frequency is shifted from higher to lower value and return loss of the antenna is increased. Moreover, the bandwidth of the antenna is reduced. In both cases (8 and 9 mm), the return loss of the antenna is increased, which, in turn, can degrade the antenna performance. Therefore, a ground size of 9 mm is selected as the optimum size for a bandwidth of 120.85% (2.96-12 GHz). The coupling capacitor plays a critical role in controlling the resonance frequency and return loss (S11) as shown in Figure 7. With the increase of notch width, the effect of the coupling capacitor (CC) is analyzed. From 5 to 7 mm the return loss gradually increased and less effect on bandwidth. Finally, for 8 mm, the minimum return loss of −50 dB is obtained, which means the maximum possible impedance.  The coupling capacitor plays a critical role in controlling the resonance frequency and return loss (S 11 ) as shown in Figure 7. With the increase of notch width, the effect of the coupling capacitor (C C ) is analyzed. From 5 to 7 mm the return loss gradually increased and less effect on bandwidth. Finally, for 8 mm, the minimum return loss of −50 dB is obtained, which means the maximum possible impedance.
Micromachines 2020, 11, x 8 of 22 A significant variation in the ground plane is effected on antenna impedance matching at higher frequencies than at lower frequencies. By changing the ground plane from 8 mm to 10 mm with a step of 1 mm, proper matching is achieved at a partial ground plane value of 9 mm, which is shown in Figure 6. For ground plane (G) values of 8 and 10 mm, the resonance frequency is shifted from higher to lower value and return loss of the antenna is increased. Moreover, the bandwidth of the antenna is reduced. In both cases (8 and 9 mm), the return loss of the antenna is increased, which, in turn, can degrade the antenna performance. Therefore, a ground size of 9 mm is selected as the optimum size for a bandwidth of 120.85% (2.96-12 GHz). The coupling capacitor plays a critical role in controlling the resonance frequency and return loss (S11) as shown in Figure 7. With the increase of notch width, the effect of the coupling capacitor (CC) is analyzed. From 5 to 7 mm the return loss gradually increased and less effect on bandwidth. Finally, for 8 mm, the minimum return loss of −50 dB is obtained, which means the maximum possible impedance.   If the values of (W f ) are increased from 2.5 mm to 4.5 mm, the resonance frequency is shifted towards the lower band. Furthermore, at the 3.5 mm optimum value of (W f ), the return loss debases at some resonance frequency 7.3 GHz and improves impedance bandwidth. Consequently, an optimum value of 3.5 mm was considered in the proposed prototype.
Micromachines 2020, 11, x 9 of 22 Figure 8 shows the effect of varying the feed width (Wf) of microstrip-line-fed on the return loss characteristics. If the values of (Wf) are increased from 2.5 mm to 4.5 mm, the resonance frequency is shifted towards the lower band. Furthermore, at the 3.5 mm optimum value of (Wf), the return loss debases at some resonance frequency 7.3 GHz and improves impedance bandwidth. Consequently, an optimum value of 3.5 mm was considered in the proposed prototype.

Results and Discussion
The presented textile UWB antenna is simulated on HFSS software by using the finite element method (FEM) of simulation.

Results and Discussion
The presented textile UWB antenna is simulated on HFSS software by using the finite element method (FEM) of simulation. Figures 9 and 10 demonstrate the measurement of the proposed textile antenna through the Vector Network Analyzer (VNA Anritsu MS2038C).
Micromachines 2020, 11, x 9 of 22 Figure 8 shows the effect of varying the feed width (Wf) of microstrip-line-fed on the return loss characteristics. If the values of (Wf) are increased from 2.5 mm to 4.5 mm, the resonance frequency is shifted towards the lower band. Furthermore, at the 3.5 mm optimum value of (Wf), the return loss debases at some resonance frequency 7.3 GHz and improves impedance bandwidth. Consequently, an optimum value of 3.5 mm was considered in the proposed prototype.

Results and Discussion
The presented textile UWB antenna is simulated on HFSS software by using the finite element method (FEM) of simulation. Figures 9 and 10     Furthermore, the comparison of the simulated, measured and theoretical results of return loss (S11) is represented in Figure 11. In this figure, it is also evident that the antenna provides an IBW (impedance bandwidth) of 120.85% (2.96-12 GHz) in simulation and approximately 118.68% (2.96-11.6 GHz) in measurement. A significant difference of 2.17% between simulated and measured results was verified. Moreover, theoretical IBW (impedance bandwidth) is 123.88%, which, when compared with measured values, means there is also a significant difference of 5.2%. In the simulation, we have a 100% (ideal) environment, whereas, in practical cases, there are some limitations regarding the fabrication method, material and insertion loss. Due to these limitations, low variations are observed in return loss (S11) results of simulation, measurement and theoretical findings.  Furthermore, the comparison of the simulated, measured and theoretical results of return loss (S 11 ) is represented in Figure 11. In this figure, it is also evident that the antenna provides an IBW (impedance bandwidth) of 120.85% (2.96-12 GHz) in simulation and approximately 118.68% (2.96-11.6 GHz) in measurement. A significant difference of 2.17% between simulated and measured results was verified. Moreover, theoretical IBW (impedance bandwidth) is 123.88%, which, when compared with measured values, means there is also a significant difference of 5.2%. In the simulation, we have a 100% (ideal) environment, whereas, in practical cases, there are some limitations regarding the fabrication method, material and insertion loss. Due to these limitations, low variations are observed in return loss (S 11 ) results of simulation, measurement and theoretical findings. Furthermore, the comparison of the simulated, measured and theoretical results of return loss (S11) is represented in Figure 11. In this figure, it is also evident that the antenna provides an IBW (impedance bandwidth) of 120.85% (2.96-12 GHz) in simulation and approximately 118.68% (2.96-11.6 GHz) in measurement. A significant difference of 2.17% between simulated and measured results was verified. Moreover, theoretical IBW (impedance bandwidth) is 123.88%, which, when compared with measured values, means there is also a significant difference of 5.2%. In the simulation, we have a 100% (ideal) environment, whereas, in practical cases, there are some limitations regarding the fabrication method, material and insertion loss. Due to these limitations, low variations are observed in return loss (S11) results of simulation, measurement and theoretical findings.

Gain
The gain of the antenna is 0 dBi, which means it offers an omnidirectional radiation pattern. On the one hand, when the gain is increasing in positive values, the shape of pattern is changed to directional. On the other hand, when the gain is less than 0 dBi or represents negative values, this means there is a change of shape in radiation pattern due to back lobe variation. Figure 13 depicts the gain of the antenna versus frequency plot, and it also reveals that the highest gain value of 5.47 dBi is observed at 7.3 GHz frequency in broadside direction. It can be noticed that at, specific frequencies, the gain dropped down below 0 dBi, which confirms that the antenna does not radiate energy in the desired direction due to back lobe radiation, whereas gain is almost matched in the other part of the frequencies.

Radiation Pattern
Three radiation pattern plots of the resonating frequencies (4 GHz, 7 GHz and 10 GHz) are illustrated in Figure 14. The H-plane (x-z plane) and E-plane (y-z plane) are selected to explain the antenna radiation patterns. Figure 14 shows the antenna E-field and H-field patterns at 4 GHz, which signifies that an omnidirectional pattern in the H-field and slight variation in E-field pattern has been observed, respectively. Moving towards upper frequencies, at 7 GHz, a quasi-omnidirectional pattern, and, at 10 GHz, omnidirectional patterns in H-planes and E-planes are found, which signifies

Gain
The gain of the antenna is 0 dBi, which means it offers an omnidirectional radiation pattern. On the one hand, when the gain is increasing in positive values, the shape of pattern is changed to directional. On the other hand, when the gain is less than 0 dBi or represents negative values, this means there is a change of shape in radiation pattern due to back lobe variation. Figure 13 depicts the gain of the antenna versus frequency plot, and it also reveals that the highest gain value of 5.47 dBi is observed at 7.3 GHz frequency in broadside direction. It can be noticed that at, specific frequencies, the gain dropped down below 0 dBi, which confirms that the antenna does not radiate energy in the desired direction due to back lobe radiation, whereas gain is almost matched in the other part of the frequencies.
Micromachines 2020, 11, x 11 of 22 Furthermore, justifications between both results were also observed. Because of the fabrication challenges of the textile antenna through artwork development and joining the SMA connector, minor variations between both the results (measured and simulated) were obtained.

Gain
The gain of the antenna is 0 dBi, which means it offers an omnidirectional radiation pattern. On the one hand, when the gain is increasing in positive values, the shape of pattern is changed to directional. On the other hand, when the gain is less than 0 dBi or represents negative values, this means there is a change of shape in radiation pattern due to back lobe variation. Figure 13 depicts the gain of the antenna versus frequency plot, and it also reveals that the highest gain value of 5.47 dBi is observed at 7.3 GHz frequency in broadside direction. It can be noticed that at, specific frequencies, the gain dropped down below 0 dBi, which confirms that the antenna does not radiate energy in the desired direction due to back lobe radiation, whereas gain is almost matched in the other part of the frequencies.

4.2.Radiation Pattern
Three radiation pattern plots of the resonating frequencies (4 GHz, 7 GHz and 10 GHz) are illustrated in Figure 14. The H-plane (x-z plane) and E-plane (y-z plane) are selected to explain the antenna radiation patterns. Figure 14 shows the antenna E-field and H-field patterns at 4 GHz, which signifies that an omnidirectional pattern in the H-field and slight variation in E-field pattern has been observed, respectively. Moving towards upper frequencies, at 7 GHz, a quasi-omnidirectional pattern, and, at 10 GHz, omnidirectional patterns in H-planes and E-planes are found, which signifies

Radiation Pattern
Three radiation pattern plots of the resonating frequencies (4 GHz, 7 GHz and 10 GHz) are illustrated in Figure 14. The H-plane (x-z plane) and E-plane (y-z plane) are selected to explain the antenna radiation patterns. Figure 14 shows the antenna E-field and H-field patterns at 4 GHz, which signifies that an omnidirectional pattern in the H-field and slight variation in E-field pattern has been observed, respectively. Moving towards upper frequencies, at 7 GHz, a quasi-omnidirectional pattern, and, at 10 GHz, omnidirectional patterns in H-planes and E-planes are found, which signifies that the proposed antenna can receive signals from all directions. On the other hand, on-body performance of the antenna is also affected by the lossy component of biological human body tissues, which absorbs the energy from electromagnetic radiation.

Current Distribution
The current distribution effect of the antenna without notch and with notch configuration is explained in Figure 15. Figure 15a shows the effect of current in the primary antenna structure, and it is observed that most of the current has focused around the microstrip line feeding point and left corner of the ground plane.
Moreover, the distribution of current on the radiator (without a notch) and right corner of the ground are very poor at frequency 7 GHz, which has a significant effect on antenna impedance matching. It can be seen from Figure 15b-d, the current distribution performance has improved by cutting a notch on the edges of a patch from the lower edge of frequency up to the higher edge of frequency of 4 GHz, 7 GHz and 10 GHz, which results in proper impedance matching.

Current Distribution
The current distribution effect of the antenna without notch and with notch configuration is explained in Figure 15. Figure 15a shows the effect of current in the primary antenna structure, and it is observed that most of the current has focused around the microstrip line feeding point and left corner of the ground plane.
Moreover, the distribution of current on the radiator (without a notch) and right corner of the ground are very poor at frequency 7 GHz, which has a significant effect on antenna impedance matching. It can be seen from Figure 15b-d, the current distribution performance has improved by cutting a notch on the edges of a patch from the lower edge of frequency up to the higher edge of frequency of 4 GHz, 7 GHz and 10 GHz, which results in proper impedance matching.

Time Domain Characteristics
The phase response of S21, isolation factor and group delay performance were also investigated in transient analysis. The transient analysis was carried out in HFSS simulator by placing two similar antennas, one as a transmitter and other works as a receiver, at a distance of 100 m in side-by-side and front-to-front situations, as shown in Figures 16 and 17.

Time Domain Characteristics
The phase response of S 21 , isolation factor and group delay performance were also investigated in transient analysis. The transient analysis was carried out in HFSS simulator by placing two similar antennas, one as a transmitter and other works as a receiver, at a distance of 100 m in side-by-side and front-to-front situations, as shown in Figures 16 and 17.

Time Domain Characteristics
The phase response of S21, isolation factor and group delay performance were also investigated in transient analysis. The transient analysis was carried out in HFSS simulator by placing two similar antennas, one as a transmitter and other works as a receiver, at a distance of 100 m in side-by-side and front-to-front situations, as shown in Figures 16 and 17.   From Figure 18, it is clear that, approximately constant group delay (i.e., group delay <1 ns) is analyzed for the textile antenna in both side-by-side and front-to-front configurations. Small variations are observed around 3.2 GHz and 7.1 GHz due to small distortions in signal transmission. By continuing the second property, the phase response of transmission coefficient S21 of the proposed textile UWB antenna is shown in Figures 19 and 20. A linear phase is required to present a good phase characteristic, which reduces the distortion between transmitting and receiving antenna. From Figures 19 and 20, the proposed structure reveals that approximately linear phase response occurred in both front-to-front and side-by-side configurations.  From Figure 18, it is clear that, approximately constant group delay (i.e., group delay <1 ns) is analyzed for the textile antenna in both side-by-side and front-to-front configurations. Small variations are observed around 3.2 GHz and 7.1 GHz due to small distortions in signal transmission. By continuing the second property, the phase response of transmission coefficient S21 of the proposed textile UWB antenna is shown in Figures 19 and 20. A linear phase is required to present a good phase characteristic, which reduces the distortion between transmitting and receiving antenna. From Figures 19 and 20, the proposed structure reveals that approximately linear phase response occurred in both front-to-front and side-by-side configurations.  By continuing the second property, the phase response of transmission coefficient S 21 of the proposed textile UWB antenna is shown in Figures 19 and 20. A linear phase is required to present a good phase characteristic, which reduces the distortion between transmitting and receiving antenna. From Figures 19 and 20, the proposed structure reveals that approximately linear phase response occurred in both front-to-front and side-by-side configurations. From Figure 18, it is clear that, approximately constant group delay (i.e., group delay <1 ns) is analyzed for the textile antenna in both side-by-side and front-to-front configurations. Small variations are observed around 3.2 GHz and 7.1 GHz due to small distortions in signal transmission. By continuing the second property, the phase response of transmission coefficient S21 of the proposed textile UWB antenna is shown in Figures 19 and 20. A linear phase is required to present a good phase characteristic, which reduces the distortion between transmitting and receiving antenna. From Figures 19 and 20, the proposed structure reveals that approximately linear phase response occurred in both front-to-front and side-by-side configurations.   The isolation characteristic, i.e., S21, of the proposed design is also studied and explained in Figure 21. As it can be seen from the plot, the antenna gives proper isolation, i.e., S21 < −25 dB, for front-to-front and side-by-side configurations.

Specific Absorption Rate (SAR) Effect on Human Body
For radiation effect assessment on the human body, the antenna is attached with a customized model of the human body in the HFSS environment and the simulations have been performed. The following mathematical formula was used to evaluate SAR value.
where σ is the conductivity (s/m), E is the electric field (V/m), and ρ is the mass density of biological tissue in Kg/m 3 . The biological properties of human body tissues are given in Table 2 [32][33][34]. The isolation characteristic, i.e., S 21 , of the proposed design is also studied and explained in Figure 21. As it can be seen from the plot, the antenna gives proper isolation, i.e., S 21 < −25 dB, for front-to-front and side-by-side configurations. The isolation characteristic, i.e., S21, of the proposed design is also studied and explained in Figure 21. As it can be seen from the plot, the antenna gives proper isolation, i.e., S21 < −25 dB, for front-to-front and side-by-side configurations.

Specific Absorption Rate (SAR) Effect on Human Body
For radiation effect assessment on the human body, the antenna is attached with a customized model of the human body in the HFSS environment and the simulations have been performed. The following mathematical formula was used to evaluate SAR value.
where σ is the conductivity (s/m), E is the electric field (V/m), and ρ is the mass density of biological tissue in Kg/m 3 . The biological properties of human body tissues are given in Table 2 [32][33][34].

Specific Absorption Rate (SAR) Effect on Human Body
For radiation effect assessment on the human body, the antenna is attached with a customized model of the human body in the HFSS environment and the simulations have been performed. The following mathematical formula was used to evaluate SAR value.
where σ is the conductivity (s/m), E is the electric field (V/m), and ρ is the mass density of biological tissue in Kg/m 3 . The biological properties of human body tissues are given in Table 2 [32][33][34]. A cross-sectional view of the three-layer human body model is presented in Figure 22. This includes a skin layer, fat layer and muscle layer. A cross-sectional view of the three-layer human body model is presented in Figure 22. This includes a skin layer, fat layer and muscle layer.   By increasing the source power from 25 mW to 150 mW, the SAR value has increased. As per European standard guidelines, the maximum SAR value should not exceed 2 W/Kg of an average mass of 10 gm tissue. The simulated SAR values for different source power inputs are mentioned in Table 3.

Frequency (GHz)
Source Power (mW) Figure 22. Three-layer human body biological model. Figure 23 illustrates the SAR simulation at 7 GHz frequency under HFSS environment. From Figure 23 it can be seen that the peak value of a 10 gm averaged and SAR is 1.6018 W/Kg. A cross-sectional view of the three-layer human body model is presented in Figure 22. This includes a skin layer, fat layer and muscle layer.   By increasing the source power from 25 mW to 150 mW, the SAR value has increased. As per European standard guidelines, the maximum SAR value should not exceed 2 W/Kg of an average mass of 10 gm tissue. The simulated SAR values for different source power inputs are mentioned in Table 3.
By increasing the source power from 25 mW to 150 mW, the SAR value has increased. As per European standard guidelines, the maximum SAR value should not exceed 2 W/Kg of an average mass of 10 gm tissue. The simulated SAR values for different source power inputs are mentioned in Table 3.

Performance Analysis on Human Body
When the antenna is placed on a human body, it is required to work in all situations. However, most of the conventional or rigid antennas have limitations regarding the change of body deformity and dielectric properties of human biological tissues. Textile antennas have a low-profile antenna, i.e., low dielectric constant (ε r = 1.7), and provide reliable impedance matching by reducing surface wave losses. Therefore, textile-based antennas depend on all environmental and other conditions, whereas conventional or rigid antennas do not achieve these requirements [35][36][37]. Figure 24 shows that return loss (S 11 ) performance is obtained under the UWB range in free space and on the lower part of the left arm of the human body during measurements. The human body acts as a lossy element due to its biological tissue properties, and it absorbs some amount of the energy from the radiation. Therefore, the return loss obtained during on body measurement is slightly different from the measurement during free space, which is shown in Figure 24. From Figure 25, the antenna is investigated under three different conditions during measurement. The return loss characteristic is varying due to change of subject movement and antenna under wet environmental conditions. After immersing the antenna in water, it was taken out and tested on the VNA. This results in detuning or frequency shift in return loss measurements. The bending of the proposed antenna gives the variation in return loss (S 11 ) performance. To show this effect, the antenna was placed on the lower part of the left arm with an angular bending of 10 0 . Measured results are compared with the free-space value and a significant variation of return loss (S 11 ) results due to the bending effect is observed.

Performance Analysis on Human Body
When the antenna is placed on a human body, it is required to work in all situations. However, most of the conventional or rigid antennas have limitations regarding the change of body deformity and dielectric properties of human biological tissues. Textile antennas have a low-profile antenna, i.e., low dielectric constant (εr = 1.7), and provide reliable impedance matching by reducing surface wave losses. Therefore, textile-based antennas depend on all environmental and other conditions, whereas conventional or rigid antennas do not achieve these requirements [35][36][37]. Figure 24 shows that return loss (S11) performance is obtained under the UWB range in free space and on the lower part of the left arm of the human body during measurements. The human body acts as a lossy element due to its biological tissue properties, and it absorbs some amount of the energy from the radiation. Therefore, the return loss obtained during on body measurement is slightly different from the measurement during free space, which is shown in Figure 24. From Figure 25, the antenna is investigated under three different conditions during measurement. The return loss characteristic is varying due to change of subject movement and antenna under wet environmental conditions. After immersing the antenna in water, it was taken out and tested on the VNA. This results in detuning or frequency shift in return loss measurements. The bending of the proposed antenna gives the variation in return loss (S11) performance. To show this effect, the antenna was placed on the lower part of the left arm with an angular bending of 10 0 . Measured results are compared with the free-space value and a significant variation of return loss (S11) results due to the bending effect is observed.    Table 4. Considering the results presented by the authors of [38][39][40][41], the proposed method provides better electrical dimension. Referring to the gain properties and safer SAR limit, the proposed antenna offers better performance than [38][39][40][41]. In summary, the outcomes of this antenna, in comparison with other antennas, are described as follows: 1. The proposed study presents a fabric-substrate-based antenna, which can be integrated with the human body. 2. This textile antenna has low power required to excite the antenna, and low radiation effect. 3. The proposed textile antenna is applicable for high-speed data transfer for short distance coverage. 4. This UWB textile antenna incorporates a compact novel design, which gives novelty of the structure. 5. The electrical equivalent circuit model of the given textile antenna is also presented to calculate the electrical parameters. The comparisons of different UWB antennas are listed in Table 4. Considering the results presented by the authors of [38][39][40][41], the proposed method provides better electrical dimension. Referring to the gain properties and safer SAR limit, the proposed antenna offers better performance than [38][39][40][41]. In summary, the outcomes of this antenna, in comparison with other antennas, are described as follows: 1.
The proposed study presents a fabric-substrate-based antenna, which can be integrated with the human body.

2.
This textile antenna has low power required to excite the antenna, and low radiation effect.

3.
The proposed textile antenna is applicable for high-speed data transfer for short distance coverage.

4.
This UWB textile antenna incorporates a compact novel design, which gives novelty of the structure. 5.
The electrical equivalent circuit model of the given textile antenna is also presented to calculate the electrical parameters. 6.
Excellent time-domain characteristics are achieved to validate the antenna for UWB application. The SAR has also been calculated to avoid the effect of electromagnetic radiation on the human body. In sum, the authors can use various techniques to promote a low SAR limit.

Conclusions
In this manuscript, the development of compact textile antenna has been designed, which is applicable for the UWB application. The mathematical analysis was completed through circuit theory using the cavity model of antenna, which validates the proposed design. Different slots and notches were removed from the radiating patch, presenting a justified ground plane, and impedance-matching performance through current distribution was presented.
The proposed antenna has a significant impedance bandwidth of 118.68% (2.96-11.6 GHz), which covers the complete UWB range (3.1-10.6 GHz) designated by the FCC, and has a maximum gain of 5.47 dBi at 7.3 GHz frequency. The time-domain characteristic was also presented to state the pulse distortion phenomena of the developed antenna. The phase of the designed antenna was found to be linear and constant group delay less than 1 ns was achieved. The SAR value of the antenna was tested to show the radiation effect on the human body, and it was found that the SAR value of the antenna is 1.6018 W/Kg, which is less than 2 W/Kg according to the International Electrotechnical Commission (IEC) standard. This point explains the outcomes of this antenna, which distinguishes itself from other antennas. With these results, we propose this wearable textile antenna for telemedicine and mobile health systems.
Author Contributions: All authors have designed the study, developed the methodology, performed the analysis, and written the manuscript. All authors have read and agreed to the published version of the manuscript.
Funding: This research was partially funded by the grants HAZITEK and IT-905-16 of Basque Country Government.