# Flexible Antennas: A Review
## 10 Flexible Antenna for Future Wireless Solutions  
Flexible antennas for future wireless solutions are expected to work in a broad range of frequencies due to the increased demand for wireless applications such as the Internet of Things (IoT), body area network (BAN), and biomedical devices. There are different antenna methodologies, single-band antenna, multiband antenna, and reconfigurable antenna. Multiband design is often necessary, for example, devices in wireless LAN should operate in both 2.4 and 5 GHz range. In addition, the design should ensure that the antenna's characteristics stay consistent under bending conditions. A low-cost inkjet-printed multiband antenna was developed in an earlier article [236]. A novel triangular iterative design with coplanar waveguide (CPW) feed printed on Kapton polyimide-based flexible substrate was used to achieve multiband operation with wide bandwidth. The antenna covers the GSM 900, GPS, UMTS, WLAN, ISM, Bluetooth, LTE 2300/2500, and WiMAX standards. Concave and convex bending was used to evaluate the antenna. Convex bending shows no significant resonance frequency shift, while during concave bending, there is a maximum 3% shift. A planar inverted-F antenna (PIFA) made of a flexible printed circuit (FPC) with multi-band operation available for Bluetooth and IEEE 802.11a/b/g standards were developed earlier [268]. The antenna's characteristics stay consistent while the angle of folding is less than 90 degrees. Flexible and wearable antennas were designed in [269] for wireless and satellite-based Internet of Things (IoT) and wireless body area network (WBAN) applications. The antenna operates in the C-band (4-8 GHz) for satellite communication to avoid congestion in lower frequency satellite bands. There are different types of reconfigurable antennas, including polarization, frequency, and reconfigurable pattern antenna. The significant benefit of a reconfigurable antenna is its capability to switch bands based on the end-user's application requirements. In a previous work [270], a flexible, spiral-shaped frequency reconfigurable antenna is developed that covers aeronautical radio navigation, fixed satellite communication, WLAN, and WiMAX standards. Frequency reconfiguration is achieved by the incorporation of a lumped element in the strip so that the antenna can switch between different resonances. A flexible, reconfigurable antenna using polarization was proposed in earlier work [271] (Figure 22b). The intended use for the antenna is in biomedical applications as a remote patient monitoring system operating in WBAN and WiMAX standards. In another article [272], a wearable pattern-reconfigurable antenna was proposed. The inductor loaded patch antenna can change its resonance between zero-order resonance and the +1 resonance, yielding two different radiation patterns. The antenna was designed to operate in the 2.4 GHz band. Ultrawideband (UWB) technology allows for efficient bandwidth utilization using spectrum overlay (often referred to as shared unlicensed) with transmission power control. By restricting the transmission power, devices can operate in 3.1-10.6 GHz without causing interference. Therefore, UWB technology is attractive for wireless indoor and wearable applications. In a prior article [273], a wearable band notched UWB antenna is proposed. The band notch is included to avoid interference from WLAN applications, as is recommended for wearable and indoor UWB applications in the IEEE 802.11a standard. Antenna properties have negligible variations when bent at different angles and can withstand extreme conditions. A flexible and transparent UWB antenna was proposed in another study [49]. The antenna consisted of a transparent conductive tissue integrated with polydimethylsiloxane (PDMS). The antenna operates between 2.2 and 25 GHz. No significant performance degradation is measured under folding.