The 868 mhz cavity filter is a coaxial resonant RF filtering device specially designed for medium and low-frequency ISM public frequency bands. Its core operating frequency range covers 863MHz to 870MHz, accurately targeting the core frequency point of 868MHz. It serves as an essential supporting hardware for medium and low-frequency IoT wireless networking, LoRa communication, UHF radio frequency identification, and low-altitude wireless sensing systems. In the RF spectrum system, frequency bands below 3GHz are classified as medium and low-frequency bands, which have the core advantages of low propagation loss, strong diffraction capability, long coverage distance, excellent penetration performance and low networking cost, making them the mainstream communication bands for civil wireless sensing, industrial Internet of Things, smart home, smart municipal and other scenarios. Different from high-frequency RF bands that suffer from severe signal attenuation and limited coverage, the 868MHz medium and low-frequency band is suitable for large-scale, long-distance and multi-occlusion civil and industrial wireless transmission scenarios. However, as a free public ISM band, it is faced with numerous industry pain points such as dense equipment distribution, mixed signals, severe adjacent frequency interference and complex harmonic crosstalk. From the perspective of medium and low-frequency bands, the 868 mhz cavity filter perfectly adapts to the spectral characteristics and transmission rules of medium and low-frequency bands relying on the high-Q physical characteristics of cavity resonance, and specifically solves the common problems of medium and low-frequency networking including disordered signals, insufficient filtering accuracy, poor loss control and weak working condition stability, acting as a core device to realize pure, stable and long-distance signal transmission for medium and low-frequency wireless communication systems.

　　From the perspective of spectral characteristic adaptation of medium and low-frequency bands, the resonant cavity structure of the 868 mhz cavity filter is highly consistent with the propagation laws of medium and low-frequency signals, realizing accurate frequency selection for dedicated frequency bands. Medium and low-frequency RF signals have longer wavelengths and more stable spatial transmission than high-frequency microwave signals, and have differentiated requirements for filter loss control, passband flatness and out-of-band rejection accuracy. Although traditional LC filters and ordinary ceramic filters adapt to medium and low-frequency bands, they have inherent defects such as low Q value, large passband fluctuation and slow out-of-band attenuation, failing to cope with dense clutter interference in the 868MHz band. Adopting a closed metal cavity resonant structure and multi-stage coupled coaxial resonant cavity design, the 868 mhz cavity filter achieves ultra-high resonance accuracy in medium and low-frequency bands with a much higher Q value than conventional medium and low-frequency filter devices. It can accurately lock the effective passband of 863–870MHz and strictly distinguish effective signals from out-of-band spurious signals. There are multiple interference frequency points such as 833MHz and 903MHz around the 868MHz band, with cross superposition of signals from various civil wireless equipment, remote control equipment and sensing equipment. Ordinary filters cannot achieve deep isolation, while the 868 mhz cavity filter realizes out-of-band rejection of more than 40dB, which can thoroughly filter all kinds of clutter interference in medium and low-frequency bands, perfectly adapting to the characteristics of dense spectrum and diverse interference in medium and low-frequency bands and ensuring the pure transmission of core 868MHz band signals.

　　In terms of transmission loss optimization for medium and low-frequency bands, the 868 mhz cavity filter gives full play to the core advantage of low loss of cavity devices, maximizing the long-distance transmission value of medium and low-frequency signals. The core advantages of medium and low-frequency bands lie in low propagation loss and wide coverage. Many industrial IoT, outdoor sensing and municipal monitoring devices rely on the 868MHz band to realize long-distance wireless communication of several kilometers, while link loss is the key bottleneck restricting the transmission quality of medium and low-frequency networking. Ordinary medium and low-frequency filters generally have an insertion loss of more than 1.5dB. Accessing the link will greatly reduce the effective transmission power, weaken the natural long-distance coverage advantages of medium and low-frequency bands, and cause problems such as weak remote equipment signals, data packet loss and communication disconnection. Optimized for medium and low-frequency transmission characteristics, the 868 mhz cavity filter strictly follows the industry-standard 50Ω impedance with an ultra-low insertion loss of ≤1.0dB and a passband ripple as low as 0.2dB. The in-passband signal transmission is extremely stable without obvious power fluctuation and energy loss. The ultra-low access loss maximizes the retention of 868MHz medium and low-frequency signal propagation energy, gives full play to the advantages of diffraction, penetration and long-distance transmission of this band, effectively improves the coverage radius and transmission stability of wireless networking, and perfectly meets the core requirements of long-distance and wide-range networking for medium and low-frequency bands.

　　Aiming at the multi-device compatible networking scenarios of medium and low-frequency bands, the 868 mhz cavity filter solves the problem of public frequency band signal crosstalk with high-selectivity filtering capability. As a license-exempt public ISM medium and low-frequency band, the 868MHz band has low access thresholds and a wide variety of equipment. A large number of LoRa gateways, IoT sensors, wireless remote controls and UHF-RFID reading and writing devices reuse this frequency band, which easily causes co-frequency interference, adjacent frequency crosstalk, intermodulation distortion and other problems. Medium and low-frequency signals have long wavelengths and strong penetration and diffraction capabilities, leading to wider coverage and higher difficulty in avoiding interference signals. Insufficient filtering and isolation will cause full-network communication lag, data disorder and equipment offline, seriously affecting the stability of medium and low-frequency networking systems. Featuring a steep frequency response transition band with clear and accurate passband truncation, the 868 mhz cavity filter can accurately screen 868MHz target signals in complex dense medium and low-frequency electromagnetic environments and deeply attenuate all out-of-band interference signals. Meanwhile, the device has excellent linear characteristics and will not generate additional harmonics and intermodulation interference in multi-signal superimposed complex medium and low-frequency electromagnetic environments. It supports high-density multi-device networking of shared medium and low-frequency spectrum, enables stable cooperative operation of multiple terminal devices, and greatly improves the spectrum utilization and networking reliability of public medium and low-frequency bands.

　　From the perspective of working condition adaptation and long-term stability of medium and low-frequency bands, the hardware structure of the 868 mhz cavity filter adapts to the all-weather outdoor operation characteristics of medium and low-frequency equipment. Most 868MHz medium and low-frequency networking devices are deployed in open scenarios such as outdoor factory areas, municipal roads, field monitoring points and building exterior walls, operating for a long time in complex working conditions with alternating high and low temperatures, humid rain, dust erosion and slight vibration, which puts forward high requirements for the temperature stability, structural firmness and parameter consistency of filters. Most ordinary medium and low-frequency filter devices adopt simple patch and miniaturized structures with large temperature drift coefficients, which are prone to resonant frequency offset and filtering performance attenuation in variable temperature environments, failing to maintain long-term stable operation. Adopting an all-metal sealed cavity structure, the 868 mhz cavity filter features firm mechanical structure, deformation resistance, vibration resistance, temperature and humidity resistance, and an ultra-low temperature drift coefficient. It can maintain constant filtering parameters of the 868MHz medium and low-frequency band in a wide temperature range of -40℃ to 85℃, without frequency band offset, isolation failure or increased loss caused by environmental changes. Meanwhile, the device supports stable high-power operation up to 30W, adapting to the operating requirements of medium and low-frequency gateways and high-power transmitting equipment, and avoiding device saturation and performance distortion under high-power working conditions, perfectly fitting the all-weather, high-load and long-term operation scenarios of medium and low-frequency outdoor networking equipment.