4G Fiberglass Antenna for Vehicle Mounting

　　In-vehicle 4G fiberglass antenna: design features and application adaptation

　　4G communication in the in-vehicle environment faces multi-dimensional challenges - metal shielding of the vehicle body causes signal attenuation (up to 20dB), Doppler frequency deviation caused by high-speed vehicle movement (up to ±1.2kHz@120km/h), and performance drift caused by vibration and impact (10-2000Hz/10g). Fiberglass antennas have become an ideal solution for in-vehicle communications due to their material properties and directional radiation design. Its core advantage is to avoid vehicle shielding through radiation pattern optimization, while taking into account lightweight (<2kg) and vibration resistance, ensuring the communication continuity of the vehicle under complex road conditions.

　　Optimized design of radiation pattern for vehicle-mounted scenarios

　　Dialectical choice between omnidirectional and directional

　　For urban commuting vehicles (such as taxis and private cars), a low-profile omnidirectional radiation design is adopted, with the horizontal beam width maintained at 360° and the vertical beam width expanded to 25° (10° more than the traditional omnidirectional antenna), ensuring that the signal is not interrupted when the vehicle turns and pitches (such as uphill and downhill). Actual measurements show that when the vehicle body tilts ±15°, the signal strength attenuation of this design is ≤3dB, which is much better than directional antennas (attenuation 8-10dB).

　　For long-distance freight vehicles (such as container trucks), a dual-polarization directional radiation solution is adopted, with the horizontal beam width compressed to 80° and the main lobe pointing to the sky (elevation angle 5°-10°). By suppressing the ground reflection signal (front-to-back ratio ≥25dB), the communication jamming caused by multipath interference is reduced. Its radiation pattern presents a "forward-leaning" distribution in the 700MHz low-frequency band, which can compensate for the signal lag when the vehicle is driving at high speed (Doppler effect compensation efficiency is increased by 40%).

　　Frequency band adaptation and radiation efficiency

　　The vehicle-mounted antenna needs to cover the full frequency band of 698-2690MHz, and the radiation efficiency in each frequency band must be consistent:

　　700MHz (low frequency band): radiation efficiency ≥85%, using diffraction ability to penetrate urban buildings

　　1800MHz (mid-frequency band): radiation efficiency ≥90%, balancing coverage and signal bandwidth

　　2600MHz (high frequency band): radiation efficiency ≥80%, and high-frequency attenuation is compensated by narrow beam design

　　Through three-dimensional electromagnetic simulation (HFSS software) to optimize the layout of the radiation unit, the standing wave ratio of each frequency band is <1.6, ensuring that the RF energy is efficiently converted into the radiation field and avoiding power loss caused by vehicle body impedance mismatch (controlled at ≤0.5dB).

　　Mechanical and electrical adaptation for vehicle installation

　　Anti-vibration structural design

　　The elastic damping bracket (rubber hardness 50 Shore A) is used to reduce the vibration transmission rate to less than 15%. In the low-frequency vibration range of 10-50Hz (engine resonance frequency band), the relative displacement between the antenna and the body is ≤0.1mm, avoiding fatigue fracture of the connector solder joint (test life ≥100,000 vibration cycles). The shell is made of basalt fiber reinforced material, and the structural weak points are eliminated through the molded one-piece molding process, and the impact resistance reaches 1000g/6ms (meets MIL-STD-883H standard).

　　Installation location and signal penetration

　　Installation in the center of the roof: suitable for omnidirectional antennas, which can obtain 360° unobstructed radiation, and the signal strength is 5-7dB higher than that installed on the edge of the roof, but the height needs to be controlled (≤15cm) to meet the height limit requirements

　　Installation integrated in the rearview mirror: a concealed choice of directional antennas, which avoids A-pillar obstruction through beam tilt (elevation angle 15°), and the signal receiving sensitivity reaches -112dBm, which is suitable for passenger cars with requirements for appearance

　　Installation on the side of the container: for freight vehicles, a 7dBi directional antenna is used, and the loss is controlled within 8dB when the beam penetrates the side plate of the container (thickness ≤5mm steel plate), ensuring stable communication with base stations along the way

　　Lightning protection and EMC compatibility

　　Integrated multi-level lightning protection circuit (gas discharge tube + TVS diode), which can withstand 5kA/8/20μs lightning current impact, residual voltage ≤30V, protecting the vehicle-mounted 4G module from overvoltage damage. By wrapping the feeder with a metal shielding layer (316L stainless steel mesh), the electromagnetic compatibility (EMC) radiation value is controlled below 30dBμV/m (30MHz-1GHz) to avoid interference with vehicle-mounted radar and navigation systems.

　　Performance optimization and scenario adaptation case

　　Special antenna for emergency communication vehicles

　　The high-gain array antenna (12dBi) designed for emergency command vehicles adopts MIMO 2×2 architecture, with a horizontal beam width of 65°, and real-time tracking of the base station direction through an electric angle adjustment mechanism (±30°). At a vehicle speed of 60km/h, the data transmission rate remains at 30Mbps (download)/5Mbps (upload), supporting 4-way 1080P video concurrent transmission and return, with an interruption time of < 50ms/24 hours.

　　Built-in antennas for new energy vehicles

　　New energy logistics vehicles use hidden fiberglass antennas (integrated in the roof rack), which are only 8mm thick, with a dielectric constant of 3.2 (close to glass) and a GPS signal attenuation of ≤0.5dB. Its radiation pattern forms a "dumbbell-shaped" distribution in the horizontal direction, avoiding the metal shell of the battery pack, and the 4G communication availability reaches 99.9% (urban environment).

　　Rail transit vehicle antennas

　　High-speed trains use streamlined fiberglass antennas (drag coefficient Cd=0.4), which are installed near the roof pantograph, with a horizontal beam width of 70°. They track base stations along the line through beam locking technology (response time < 100ms). At a speed of 350km/h, the switching success rate is ≥99.5%, and the bit error rate is < 10⁻⁶.

　　Installation specifications and performance test

　　Key points of mechanical installation

　　Base fixing torque: M6 bolts use 15N・m torque, with anti-loosening gaskets (made of spring steel) to ensure no loosening on bumpy roads at 120km/h

　　Feeder direction: Arrange along the keel of the vehicle body, with a bending radius ≥10 times the cable diameter (RG-58 cable ≥50mm), avoid parallel with high-voltage harnesses (such as 380V cables of new energy vehicles) (spacing ≥30cm)

　　Grounding treatment: Connect to the vehicle body ground through copper tape (cross-sectional area ≥4mm²), grounding resistance ≤2Ω, reduce electrostatic interference

　　Performance verification standard

　　Each vehicle-mounted antenna must pass:

　　Dynamic test: Continuous communication for 4 hours on a circular runway (speed 80km/h), call drop rate ≤0.1%

　　Environmental test: -40℃ to 85℃ temperature cycle (20 After 10-2000Hz sweep vibration, the main lobe shift of the radiation pattern is ≤2°. The core value of the vehicle-mounted 4G fiberglass antenna is to transform the vehicle from a communication obstacle to a mobile node through the integration of material science and electromagnetic design. Its application in emergency command, logistics tracking, intelligent networking and other fields is promoting the Internet of Vehicles technology from concept to practical use. In the future, by integrating the 5G NR frequency band (3.5GHz) and the V2X protocol, the application boundaries of vehicle-mounted communications will be further expanded.