GPS Antenna Selection Guide: Technical Characteristics and Application Adaptation

　　GPS Antenna Selection Guide: Technical Characteristics and Application Adaptation

　　As the core component for receiving satellite signals, the performance of GPS antenna directly determines the positioning accuracy (from sub-meter level to meter level), cold start time (25-45 seconds) and capture capability in weak signal environment (-160dBm to -165dBm). The selection needs to focus on the core elements such as space limitations, transmission distance, environmental interference, etc. of the application scenario, and accurately match the passive and active solutions, while taking into account the balance between cost and power consumption.

　　Technical characteristics of passive GPS antenna

　　Core structure and performance indicators

　　The passive antenna is based on the ceramic radiating unit (dielectric constant εr=9.8-11.0), and the gain adjustment is achieved by optimizing the diameter of the ceramic sheet (15-25mm): 25mm ceramic sheet can provide 2.5dBi gain (1575.42MHz), which is 1.2dB higher than the 15mm model. The antenna adopts vertical polarization, and the horizontal half-power beam width is ≥100°, ensuring efficient capture of satellite signals within the range of ±45° at the zenith.

　　The impedance matching network is integrated on the PCB substrate (FR4 material), and the 50Ω system matching is achieved by adjusting the microstrip line length (λ/4=38mm@1.575GHz), and the standing wave ratio needs to be controlled within 1.5:1 (1.55-1.60GHz frequency band). The RF output end uses an SMA or IPEX connector, and the lead length is strictly controlled within 30mm (the loss increases by 0.2dB for every 10mm increase) to avoid signal attenuation affecting the receiving sensitivity.

　　Applicable scenarios and design points

　　Consumer electronics: Smart phones, smart watches and other devices use 15-18mm miniature passive antennas, and improve radiation efficiency through PCB ground planes (area ≥ 2 times the antenna size). The positioning accuracy can reach 3-5 meters in an open environment, and the cold start time is ≤35 seconds

　　Compact terminal: The Bluetooth GPS module uses a 20mm ceramic antenna, with an LNA front end (noise factor ≤1.5dB), and the signal capture rate in an urban canyon environment is ≥90% (when ≥4 satellites are visible)

　　Low-power devices: IoT terminals (such as trackers) use passive solutions, with static power consumption ≤1μA (active antenna is 5-10mA), and intermittent positioning mode can extend battery life to more than 12 months

　　Design needs to avoid electromagnetic interference: Strong radiation sources such as clock circuits (10-100MHz) and power inductors are prohibited within 5cm around the antenna, and 5mm is required at the edge of the PCB Clearance area, through the ground shield layer (copper thickness ≥ 35μm) to reduce the motherboard noise coupling (≤-80dBc/Hz@1kHz offset).

　　Technical enhancement plan for active GPS antenna

　　Signal amplification and transmission compensation

　　The active antenna has a built-in two-stage low noise amplifier (LNA). The first stage uses GaAs PHEMT devices (noise figure NF=0.8dB), and the second stage is a SiGe BiCMOS amplifier (gain 20dB). The total gain is controlled at 28-32dB (excessive gain is prone to introduce saturation distortion). Noise coefficient is the core indicator. The high-quality solution can be controlled below 1.5dB (typical value 1.2dB), ensuring effective amplification of -163dBm weak signals.

　　The transmission line uses RG-174 coaxial cable (loss ≤0.5dB/m@1.575GHz), supports 1-10 meters of transmission, and provides 3-5V DC power supply (current 3-5mA) through the inner core of the cable. The connector uses a waterproof N-type or TNC interface (IP67 protection), which can withstand temperature fluctuations from -40℃ to 85℃ in vehicle scenarios, and the performance attenuation after vibration testing (10-2000Hz/10g) is ≤0.5dB.

　　Deployment advantages and performance

　　Onboard navigation system: The active antenna is arranged on the roof (unobstructed area) through a 3-meter cable, with a horizontal beam width of 120° and a gain of 3dBi. The positioning continuity in weak signal areas such as tunnel entrances (signal strength - 158dBm) is improved by 40%

　　Industrial equipment: The container tracker uses a magnetic active antenna, with an anti-interference filter (suppressing clutter outside the 1.5-1.6GHz frequency band ≥40dB), and the positioning error in a metal-intensive environment is ≤10 meters

　　Long-distance transmission: The UAV ground station is connected to the active antenna through a 10-meter cable, and the LNA gain of 30dB compensates for the transmission loss, ensuring that the high-altitude (1000 meters) positioning refresh rate is ≥10Hz and the delay is ≤100ms

　　Special design of navigation-grade GPS antenna

　　Enhanced environmental adaptability

　　Navigation antennas in the fields of navigation and aviation use a fiberglass sealed shell (thickness 3-5mm), with a dielectric constant εr=3.2±0.1, signal penetration loss ≤0.3dB. Salt spray protection (1000 hours of corrosion-free according to ASTM B117 test) is achieved through fluorocarbon coating (thickness 50μm), waterproof level reaches IP68 (2 meters underwater / 24 hours), and adapts to high humidity (95% RH) and salt spray (35mg/m³) environments in the ocean.

　　The mechanical structure adopts a stainless steel 316L base, with a wind load of ≥1500Pa (equivalent to a level 10 typhoon), vibration tolerance of 10-2000Hz/20g, ensuring that the beam pointing deviation is ≤5° when the ship sways ±30°, and the signal attenuation is controlled within 1dB.

　　Performance parameters and reliability guarantee

　　Gain and beam: horizontal beam width ≥110°, vertical beam coverage - 5° to 90° (zenith direction), gain 4dBi, cross-polarization discrimination ≥20dB

　　Multipath suppression: The multipath error is reduced from 2 meters to 0.5 meters through the choke design (4-ring λ/4 structure), which is particularly suitable for near-ground environments (such as ports and buildings)

　　Redundant design: key equipment uses dual antenna hot backup, switching time ≤10ms, and year-round availability ≥99.99%, meeting the safety requirements of marine navigation

　　Technical framework for selection decision

　　Core parameter comparison

　　The passive antenna has a gain of 1.5-2.5dBi, no independent noise coefficient (depending on the back-end LNA), a transmission distance of ≤0.3 meters, an operating temperature range of -40℃ to 85℃, power consumption ≤1μA, and a positioning accuracy of 3-5 meters.

　　The active antenna gain reaches 28-32dB (including LNA), the noise figure is ≤1.5dB, supports a transmission distance of 1-10 meters, the operating temperature is also -40℃ to 85℃, the power consumption is 3-10mA, and the positioning accuracy is improved to 2-3 meters.

　　The navigation-level antenna gain is 3-4dBi, the noise figure is ≤1.2dB, the transmission distance is 1-5 meters, the operating temperature is extended to -55℃ to 85℃, the power consumption is 5-15mA, and the positioning accuracy can reach 1-2 meters.

　　Scenario Adaptation Principles

　　Space Limitation: When the internal installation space of the device is < 30cm³, choose a passive antenna (such as a wearable device). When external installation is allowed, give priority to active solutions

　　Transmission Distance: When the distance between the antenna and the receiving module is > 0.3 meters, an active antenna must be used. For every additional 1 meter of cable, the gain compensation must be increased by 1dB

　　Environmental Conditions: Basic active antennas can be used for outdoor open scenes, and navigation-level products (protection level ≥ IP66) are required for harsh environments such as oceans and industries

　　Accuracy Requirements: Passive or basic active antennas can be selected for consumer-level positioning (5-10 meters), and professional-level applications (1-3 =Meters) need a high-gain active solution

　　Key points of engineering deployment

　　Installation location: The antenna needs to point to the sky without obstruction (obstruction angle ≤ 15°), away from metal structures (distance ≥ λ/2 = 38cm), to avoid multipath errors caused by signal reflection

　　Grounding treatment: The shielding layer of the active antenna needs to be reliably connected to the device casing (impedance ≤ 0.1Ω) to reduce the impact of electromagnetic interference (EMI) on LNA

　　Cable selection: RG-174 (diameter 1.32mm) is used for transmission distances within 5 meters, RG-58 (loss 0.3dB/m) is used for 5-10 meters, and the joints need to be waterproofed (heat shrink tube + sealant)

　　The core of GPS antenna selection is to balance performance, cost and environmental adaptability. By accurately matching the technical requirements of the application scenario, the optimal solution is found between the low power consumption advantage of the passive solution and the long-distance capability of the active solution. At the same time, the RF optimization of the installation link is emphasized to give full play to the performance potential of the satellite positioning system.