[Special Analysis] Research on the Recognition Capabilities of Three Mainstream Band Radars Including S, C and X Bands in Anti-UAV Systems

  The extensive deployment of unmanned aerial vehicles (UAVs) is reshaping the offense-defense landscape in low-altitude security defense and modern battlefield confrontations. Ranging from small-scale tactical reconnaissance and kamikaze strikes to swarm assaults and long-range strikes at the strategic level, UAVs have become a pivotal factor altering battlefield dynamics. As the "first line of defense" in anti-UAV systems, radars’ band selection directly determines the identification efficiency of UAV targets and the response speed of defense chains. Featuring distinct electromagnetic properties respectively, the three mainstream radar bands—S, C and X—cover differentiated application scenarios and capability thresholds for UAV detection. Whether dealing with large integrated reconnaissance-strike UAVs or miniature consumer-grade drones, operating in complex electromagnetic countermeasure environments or extreme meteorological conditions, the technical adaptability, tactical merits and practical operational drawbacks of radars in different bands exert profound impacts on the construction logic and resource allocation strategies of anti-UAV defense systems.

1.Characteristics and Differences of S, C and X Band Radars

  The identification of unmanned aerial vehicles (UAVs) by radars is essentially a process that involves transmitting electromagnetic waves of specific frequency bands, receiving echo signals reflected by targets, extracting core characteristic parameters such as target range, velocity, attitude and radar cross section (RCS) through signal processing, and thereby completing target detection, trajectory tracking and attribute discrimination. The classification of S, C and X bands stems from differences in the frequency ranges of the electromagnetic spectrum. Such differences directly shape their performance in core indicators including propagation characteristics, beamwidth, resolution and anti-interference capability, and ultimately define the limit of their ability to identify various types of UAVs. Based on the core logic of the radar range equation, detection range is positively correlated with transmit power and antenna gain, negatively correlated with the minimum detectable signal, and proportional to the one-fourth power of the target RCS. The electromagnetic properties of different frequency bands exert impacts on these critical parameters, resulting in a tiered differentiation of target identification capabilities.

  Specifically, the S-band covers a frequency range of 2–4 GHz with wavelengths of 10–15 centimeters, falling within the medium-wave band. Its core advantage lies in the low propagation loss of electromagnetic waves in the atmosphere, with an attenuation coefficient of only 0.01–0.03 dB/km, delivering strong penetration capability. The C-band operates at frequencies of 4–8 GHz with wavelengths of 3.75–7.5 centimeters, sitting in the transition zone between medium and short waves, striking a balance between propagation loss (0.05–0.1 dB/km) and resolution. The X-band spans frequencies of 8–12 GHz with wavelengths of 2.5–3.75 centimeters, classified as the short-wave band. It features a narrow beamwidth and range resolution better than 1 meter, yet suffers markedly higher atmospheric propagation loss (0.1–0.3 dB/km) and is far more susceptible to weather conditions such as rain, snow and fog. These distinct band characteristics directly correspond to the core requirements of drone detection: the S-band is optimal for long-range early warning, the C-band focuses on balanced medium-range identification, and the X-band specializes in high-precision short-range tracking. Together, the three bands form a naturally complementary capability system.

  It is worth noting that there is a critical interactive relationship between the RCS characteristics of unmanned aerial vehicles (UAVs) and waveband selection. Public data shows that the RCS of micro-UAVs can be as low as 0.001 to 0.005 square meters, the RCS of small UAVs is approximately 0.01 to 0.02 square meters, and the RCS of large reconnaissance-strike integrated UAVs stands at around 0.1 square meters. Derived from the radar range equation, when the target's RCS drops from 0.1 square meters to 0.01 square meters, the detection range of the same radar will be reduced by more than 40%; if the RCS further falls to 0.001 square meters, the detection range will shrink by over 60%. This rule directly determines that the high resolution of the X-band is more suitable for identifying low-RCS micro-UAVs, while the long-range detection advantage of the S-band makes it better suited for locking onto large UAV targets.

2.Advantages, Disadvantages and Applicable Scenarios of Three Major Waveband Radars

(I) S-band Radar: The "Low-Altitude Watchman" for Wide-Area Early Warning

  The core strengths of S-band radar lie in its dual features of long-distance detection and strong environmental adaptability. Benefiting from low atmospheric propagation loss, it can detect unmanned aerial vehicles (UAVs) with an RCS of 0.1 square meters at a range of 15 to 25 kilometers, and its detection range for large UAVs with an RCS of 1 square meter can even exceed 30 kilometers. It can effectively cover wide-area protection zones such as border lines, the peripheries of military bases, nuclear power plants and large industrial parks, providing the defense system with an early warning window of 3 to 8 minutes, which is sufficient to support the deployment and response of interception weapons. Meanwhile, S-band electromagnetic waves boast far stronger penetration through adverse weather conditions including rain, snow and haze compared with X-band waves. Under rainfall of 20 millimeters per hour, its detection range only attenuates by 10% to 15%, enabling continuous all-weather and all-time operation without significant interference from light and meteorological variations. In terms of multi-target identification, thanks to ample power margin and signal processing bandwidth, S-band radar can track dozens or even hundreds of aerial targets simultaneously, granting it the fundamental capability to counter small-scale swarming UAV attacks.

  However, its drawbacks are equally prominent and irreplaceable. First, the resolution is relatively low. Due to its long wavelength, its beam width generally ranges from 1 to 2 degrees, making it hard to accurately capture the detailed features of small unmanned aerial vehicles (UAVs). It faces extreme difficulty identifying micro-UAVs with a radar cross-section (RCS) less than 0.1 square meters and is prone to confusing them with low-altitude targets such as birds and balloons. Second, low-altitude clutter interference is severe. In complex terrains including urban building clusters and mountainous areas, clutter signals reflected from the ground share similar frequency characteristics with UAV echo signals, pushing up the false alarm rate. Even advanced algorithms such as Moving Target Indication (MTI) and Pulse Doppler (PD) cannot completely filter out clutter interference. Third, the equipment features large size and high power consumption. The antenna of a typical S-band phased array radar usually covers an area of 2 to 5 square meters and weighs several tons. Its mobile deployment requires dedicated vehicles or fixed positions, failing to meet the demands of frontline tactical mobile defense. Therefore, S-band radars are more suitable for wide-area early warning at fixed strategic and operational positions, serving as the "long-range eyes" of anti-UAV defense systems.

(II) C-band Radar: A Versatile All-Rounder with Balanced Performance
  Featuring balanced performance as its core attribute, C-band radar strikes an optimal balance between detection range and identification accuracy, making it the mainstream option for small and medium-sized anti-UAV defense systems. It can detect UAVs with an RCS of 0.1 square meters from 8 to 15 kilometers away and micro-UAVs with an RCS of 0.01 square meters at a distance of approximately 4 to 6 kilometers, a performance level between S-band and X-band radars. It can fulfill protection requirements for medium-sized areas such as industrial parks, logistics parks and large event venues, and also act as a medium-short range gap-filling component in large-scale defense systems. Compared with S-band radar, C-band radar has a shorter wavelength and its beam width can be narrowed down to 0.5 to 1 degree, delivering markedly improved resolution. It can track the flight attitude and trajectory of UAVs with higher precision, achieving an identification accuracy of over 85% for small and medium-sized UAVs. Compared with X-band radar, it suffers less atmospheric propagation attenuation. Under rainfall of 20 millimeters per hour, its detection range only decreases by 20% to 25%, granting it stronger adaptability to weather and more stable identification performance amid harsh weather conditions.

  The limitations of the C-band are mainly reflected in two aspects. First, there remains pressure in filtering low-altitude clutter. Although it outperforms the S-band, clutter signals can still impair identification accuracy in complex environments such as dense building clusters and heavily wooded areas. Multi-sensor fusion technologies like radar-electro-optical integration and radar-acoustic integration are required to reduce the false alarm rate. Second, its anti-electromagnetic interference capability is moderate. As the C-band is a common frequency band for civil aviation and satellite communications, it is susceptible to interference from civil electromagnetic signals. In intense electromagnetic countermeasure environments, its signals are vulnerable to suppression or deception, undermining stable identification of drone targets. In addition, C-band radars feature a size and power consumption level between those of S-band and X-band radars, enabling vehicle-mounted mobile deployment. Nevertheless, they lack sufficient mobility and flexibility compared with portable X-band radars. Overall, the balanced performance of C-band radars delivers the broadest adaptability; they can independently build small and medium anti-drone defense systems, and can also be integrated into large defense networks to achieve coordinated complementarity.

(III) X-band Radars: "Short-Range Hunters" for Precision Identification

  Leveraging short-wavelength characteristics, X-band radars serve as the core solution for precise drone identification and short-range interception guidance, with their core strengths lying in dual breakthroughs of high resolution and robust anti-clutter performance. Thanks to their extremely short wavelengths, their beamwidth can be narrowed to 0.1–0.5 degrees, and their range resolution can reach within 0.5 meters. They can clearly distinguish detailed features of small drones such as shape profiles and rotor counts, and even accurately identify micro-drones with an RCS of merely 0.01 square meters at a distance of 3 kilometers. They exhibit exceptional identification efficiency against low, slow, small targets including FPV suicide drones and loitering munitions. More importantly, X-band radars can extract micro-Doppler frequency signatures generated by rotating drone rotors to accurately distinguish hovering drones from interfering objects such as ground clutter and birds. For instance, Denmark’s XENTA-C radar achieves an identification accuracy of over 95% for hovering drones by detecting rotor micro-Doppler signals, effectively addressing the core pain point of identifying small low-altitude targets.

  Its biggest weakness lies in its short detection range, which is significantly affected by atmospheric propagation loss and meteorological conditions: its detection range for UAVs with an RCS of 0.1 square meters is only 6 to 10 kilometers, while the detection range for micro-UAVs with an RCS of 0.01 square meters is less than 3 kilometers, making it only suitable for short-range protection scenarios such as airport clear zones, core areas of critical facilities, and venues of large-scale events. Under severe weather conditions, the performance degradation of X-band radar is more prominent. When rainfall reaches 20 mm per hour, the detection range can decrease by 40% to 50%, and it may even shrink by more than 60% in hazy weather. Meanwhile, it is susceptible to electromagnetic interference, and its operational stability in complex electromagnetic environments relies on anti-interference technologies such as frequency hopping and spread spectrum. Nevertheless, X-band radars boast remarkable advantages in volume and power consumption. The antenna size of miniaturized X-band radars can be reduced to less than 0.5 square meters with a weight below 100 kilograms, and they can even be deployed portably to meet tactical-level defense demands for frontline squads and vehicle-mounted mobile applications. Accordingly, X-band radars are more applicable to tactical short-range precise identification and interception guidance, serving as the "last line of defense" in anti-UAV defense systems.