# Flexible Phased Antenna Arrays: A Review
## 5 Performance Comparison  
Following the analysis of the main challenges in FPA design, a comparative study was carried out based on key performance parameters. The results are summarized in Table 3, which provides a compact overview of the surveyed works on FPAs. The table includes multiple parameters essential for evaluating FPA performance: operating frequency (freq), array size, bandwidth (BW), gain (in dB), maximum beam steering angle, insertion loss, beam width, flexibility characteristics, bending radius or curvature (flex curve), bending performance, polarization type (pol), and thermal performance (thermal perf). A multi-dimensional evaluation is necessary due to the variability introduced by different application scenarios. Among the most critical parameters, bandwidth reflects frequency agility, while the maximum steering angle quantifies beam reconfigurability. Insertion loss is analyzed to assess signal power loss and system efficiency. Beam width is relevant for resolution and directionality. Flexibility-related information is divided into how flexibility is achieved (e.g., flexible substrates, additive manufacturing, rigid-flex integration), the achieved bending radius, and the impact of bending on performance. Lastly, the table reports the polarization (e.g., linear or circular) and thermal behavior, including maximum operating temperature, cooling strategies, and any observed performance degradation under thermal stress. It is possible to extract some information regarding the performance, design choice, and practical implications of FPA based on the comparative analysis across multiple works. FPAs are being designed over a range of frequencies highlighting the diversity in applications such as UHF communications, SATCOM, 5G/6G communications, and radar systems. The size of the arrays also varies from small and compact \(1\times 4\) arrays to large \(16\times 16\) configurations depending on the type of application. This reflects the trade-off between size of the array, gain of the array, and beam control. Moreover, the gain of the array varies from small values of 1 dB or 6 dB for smaller arrays to higher values as high as 60.5 dB (EIRP) for higher frequencies and large scale designs. Moreover, beam scanning is a major factor in PA, with a substantial number of works with a steering angle range up to \(\pm\)70\({}^{\circ}\). This indicates strong reconfigurability. The wide scanning range comes with an increase in the value of insertion loss and a degradation in the gain, especially at extreme angles. Based on the type of applications, bandwidth also varies, with some designs supporting UWB operation while others are optimized for narrowband applications. This suggests a trade-off between bandwidth and parameters such as structural complexity and fabrication methodologies. Furthermore, the major focus of this comparative analysis was flexibility. Flexibility in FPA is primarily achieved with the utilization of flexible substrates such as polymide and LCP, sometimes using AM like IP to define the conductive traces on the flexible substrates. Another approach for obtaining flexibility was introduced in the form of hybrid rigid-flex design. Performance under bending is also analyzed for the analysis with bending radii ranging from 3 cm to 50 cm, with most studies having stability in performance under mechanical deformation. Moreover, in some circumstances, phase compensation techniques are implemented to mitigate performance degradation. Ultimately, thermal performance is discussed, particularly for high-power and space applications. Several arrays demonstrate good thermal stability up to 400 \({}^{\circ}\)C or are labeled as compatible for space applications, highlighting robustness under extreme conditions. The key trade-offs are between the flexibility and performance parameters such as bandwidth, gain, and beam steering. In cases of high flexibility, gain or bandwidth can be compromised to a certain extent.