# 5G-Enabled E-Textiles Based on a Low-Profile Millimeter-Wave Textile Antenna +
## 3 mmWave E-Textile Antenna Characterization  
The fabricated prototype was characterized experimentally to evaluate its bandwidth and radiation properties. A key requirement of a mmWave antenna is the maintenance of a broad bandwidth [4]. To explain, a key advantage of operating at mmWave frequen  
Figure 1: Fabrication process of e-textile mmWave antennas for 5G+ applications based on etched polyimide copper laminates: (**a**) 25 \(\upmu\)m-thick copper-clad Kapton; (**b**) photoresist deposition; (**c**) UV exposure through a film mask; (**d**) antenna traces following etching; (**e**) antenna traces adhered to fabric.  
Figure 2: The Kapton-on-woven polyester mmWave antenna (**a**) layout and dimensions (in mm); (**b**) the fabricated device; (**c**) applied to a surface with approximate bend radius of 5 mm.  
cies is the wider spectrum availability compared to sub-6 GHz bands [2]. For example, mmWave 5G uses the 26 and 28 GHz bands, with a combined bandwidth of over 4 GHz. To measure the antenna's response, a solder-terminated 1.85 mm connector was added to the microstrip feed. The antenna's reflection coefficient was measured using an Agilent E8361A PNA Vector Network Analyzer (VNA), calibrated using a standard electronic calibration kit. Figure 3 shows the measured reflection coefficient of the antenna as well as the simulated response, obtained through full-wave numerical electromagnetic simulation in CST Microwave Studio Suite.  
As observed in Figure 3, the antenna fulfills the bandwidth requirement of a 5G wearable antenna, where both the measured and simulated S11 responses indicate that over 90% of the power will be accepted by the antenna, demonstrating its suitability for integration in mmWave 24.2-30 GHz transceiver RF chains including amplifiers.  
To evaluate the antenna's far-field properties and subsequent performance in real-world, on-body mmWave links, the antenna's radiation patterns were experimentally measured. The polarized radiation pattern measurements were performed relative to a standard 20 dBi gain waveguide horn antenna in an anechoic chamber. The total efficiency of the textile antenna (inclusive of impedance mismatch losses) was calculated relative to the horn antenna [4]. Figure 4a shows the measured 3D radiation patterns of the antenna, where it can be seen that the antenna maintains two main lobes, in line with a standard second-order mode microstrip patch antenna.  
Figure 4: The far-field performance of the e-textile mmWave antenna: (**a**) measured 3D spherical radiation patterns; (**b**) measured channel gain between symmetric antennas on-body, with and without main beam alignment at a 60 cm distance.  
Figure 3: Simulated (no marker) and measured (solid with markers) reflection coefficient (S11) of the antenna, showing an S11 \(<-\)10 dB bandwidth from 24.2 to 31.1 GHz.  
The total efficiency of the antenna, with respect to the reference horn, was found to be around 60% (\(\pm\)5%). The antenna was experimentally characterized through channel gain measurements to show its suitability for on-body mmWave communications. In Figure 4b, it can be seen that over \(-\)55 dB forward transmission can be maintained between two symmetric textile antennas along the body with and without main beam alignment. Such a link budget would enable this e-textile antenna to integrate with recently reported, short-range, high-data-rate mmWave transceivers, such as low-power, high-speed backscattering modulators printed on flexible substrates [7].