# Flexible Phased Antenna Arrays: A Review
## 3 Mostly Used Materials  
An analysis of various studies on material characterization for FPAs reveals consistent trends in the selection of materials for both conductive and dielectric layers. Copper evidently emerges as the most widely used conductive material, particularly in traditional PCB-based implementations, where its high electrical conductivity and excellent RF performance make it the preferred choice. Its effectiveness also extends to rigid-flex approaches, ensuring low-loss transmission and reliable integration. Although chromium is also reported as a conductive material in some cases, its use is significantly less common [50; 51; 54; 58; 59; 60; 61]. In contrast, SNP ink is gaining attention for its compatibility with AM techniques, especially in the advanced manufacturing of flexible electronics. Despite its lower conductivity compared to copper, SNP remains a viable alternative for RF applications due to its excellent processability and suitability for printed electronics [43; 44; 62]. Its compatibility with IP processes makes it particularly attractive for complex geometries and conformal surfaces [41; 42; 63]. In terms of dielectric materials, the analysis highlights two main categories: semi-rigid dielectric substrates and flexible polymers compatible with flexible applications. Among semi-rigid substrates, Rogers(r) holds a leading position due to a series of patents covering PTFE-based laminates composed of resin mixtures with various fillers, yet free of internal glass fabric. This composition allows controlled mechanical flexibility under specific bending conditions, making them suitable for semi-conformal implementations. In particular, Rogers(r) RT5880 is extensively used in high-frequency applications due to its low dielectric constant and minimal loss tangent, which are critical for preserving signal integrity and reducing RF losses [50; 51; 54; 59; 61]. Comparable performance is also offered by other PTFE-based laminates (with or without woven glass reinforcement) such as Rogers(r) 4003C, Rogers(r) 3003, and Taconic(r) FastFilmt, which combine suitable dielectric characteristics with moderate flexibility [44; 62; 64]. However, fully flexible substrates are required for highly flexible or deployable applications such as space-deployable arrays. Several polymers have been widely adopted in the reviewed studies. Kapton(r) HN, a polyimide, combines good dielectric properties with excellent mechanical flexibility and thermal stability. This allows it to conform to non-planar surfaces and endure high-temperature processes without significant degradation [62]. LCP is another commonly used substrate due to its low dielectric constant (\(\approx\)2.9-3.2) and low loss tangent (\(\approx\)0.002-0.005), together with its natural flexibility and high dimensional stability under bending [65; 66; 67]. An example of such a single antenna element fabricated using the LCP flexible substrate and the antenna array fabricated using the LCP substrate demonstrating the bending capability of such a design is presented in Figure 4. Polydimethylsiloxane (PDMS) and PEI fibers have also been explored for their conformability and thermal resistance, making them suitable for integration on cylindrical or deformable surfaces [57; 68]. An example of a flexible radiating element and an array configuration is shown in Figure 4. Other notable flexible solutions include DuPont Pyralux(r)-based laminates, which combine thin polyimide films with copper cladding, enabling multilayer flexible designs with good electrical and mechanical performance.