Performance of Spring Antennas in Different Frequency Bands

　　In the field of wireless communication, spring antennas, with their unique structural design, exhibit differentiated performance characteristics in different frequency bands, adapting to various application scenarios.

　　The low-frequency band (315MHz-915MHz) is a dominant area for spring antennas. In Sub-1GHz bands such as 433MHz and 868MHz, they are known for high stability, with a standing wave ratio typically controlled within 1.5 and a gain of up to 2-3dBi. Some copper models can even achieve a low standing wave ratio of 1.25 and a gain of 3.9dBi, and their omnidirectional radiation characteristics ensure more uniform signal coverage. This is due to the precise ratio of coil radius, pitch, and wire diameter. For example, the 433-453MHz model achieves 10MHz bandwidth coverage through the design of OD5.5mm coil and N19.75 pitch. Its low cost and strong vibration resistance make it an ideal choice for LoRa IoT devices and wireless remote controls, with a price only one-third of that of ceramic antennas, suitable for long-distance outdoor transmission. In the 470-490MHz VHF band, its performance with a standing wave ratio ≤1.5 and a gain of 2.15dBi plays a stable role in broadcast television and emergency communications. The fiberglass shell design enables it to maintain performance in environments ranging from -30℃ to 65℃.

　　The medium and high-frequency band (700MHz-2.5GHz) has witnessed structural innovations in spring antennas. The spring fiberglass antenna in the 700-1000MHz band achieves wide frequency coverage through a spiral radiator, with a standing wave ratio ≤1.92 and a gain of 5-9dBi. Its uniform horizontal radiation increases coverage by 30% compared to traditional dipole antennas. The low-wind-resistance spiral structure can withstand extreme weather and support polarization switching, making it a capable assistant for mobile communication base stations. In the 2.4GHz WiFi/Bluetooth band, although the spring antenna maintains a gain of 2-5dBi and a standing wave ratio ≤1.92, its bandwidth is narrow (about 50MHz). It needs to optimize impedance through a π-type matching network, reducing the standing wave ratio from 8.6 to below 2.0 to meet the built-in requirements of smart homes and industrial IoT.

　　Entering the high-frequency band (5GHz and above), spring antennas face new challenges and opportunities. The 5GHz band models (such as 1.35-5GHz) have a gain of about 4dBi, support vertical polarization, and cover the ISM band and federal S/C bands. However, they are sensitive to metal interference and need to maintain a distance of ≥5mm. Additionally, axial mode radiation is required to enhance coverage in urban environments. In the millimeter wave band above 24GHz, the skin effect leads to increased losses, and integration with PCB designs is usually necessary. For example, RFID tags with fractal spring structures can adapt to high-frequency stretching, but their gain is generally below 1dBi.

　　From the stability and reliability in the low frequency to technological breakthroughs in the high frequency, spring antennas continue to release value in various frequency bands through the optimization of design parameters - adjustment of coil geometry, material upgrading (copper is suitable for low frequencies, gold-plated coatings reduce high-frequency losses), debugging of matching networks, and precise control of environmental interference, making them a flexible and efficient choice in wireless communication.