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Drone gps antennais a terminal device that receives satellite signals for positioning or navigation. Antennas are essential for signal reception.
GPS satellite signals are divided into L1 and L2 bands, operating at frequencies of 1575.42 MHz and 1228 MHz respectively.
The L1 band is an open civil signal with circular polarization. The signal strength is approximately -166 dBW, making it relatively weak. These characteristics necessitate specialized antennas for GPS signal reception. Currently, GPS antennas play a vital role in agriculture, aviation, environmental monitoring, maritime navigation, public safety and disaster relief, railways, space exploration, surveying, and mapping. The receiving antenna is the first component in a GPS receiver to process satellite signals, converting the electromagnetic waves emitted by GPS satellites into voltage or current signals for processing by the receiver's RF front end. Satellite antennas possess directional capabilities, meaning the signal power originally dispersed in all directions is concentrated and directed toward Earth. This directionality is also referred to as gain. Larger antennas generally achieve higher gain. I. Classification of GPS Antennas According to research by Thomas Seiler, CEO of Swiss company u-blox, over 20 types of GPS antennas exist globally. Despite Mr. Seiler's two decades of research in this field, standard ceramic antennas remain the recommended choice for their balanced performance in size, sensitivity, and cost. GPS receiver antennas feature various structural types, such as monopole, dipole, helical, microstrip, and choke coil designs. Patch antennas belong to the microstrip antenna category.1. By polarization method, GPS module antennas are categorized into vertical polarization and circular polarization. Based on current technology, circular polarization delivers superior performance. Therefore, except in special cases, GPS module antennas adopt circular polarization! 2. Based on installation placement, GPS module antennas are categorized as internal or external. With GPS modules increasingly miniaturized and integrated, internal installation and placement are now predominant. In such cases, the antenna must be positioned above all metal components. The enclosure must be plated and properly grounded, and kept away from EMI sources like CPUs, SDRAM, SD cards, crystal oscillators, and DC/DC converters. 3. Based on power supply methods, built-in GPS module antennas are further categorized into active and passive antennas. Passive antennas lack low-noise amplifiers and require no power supply. However, due to the weak signal strength of unamplified GPS signals, the cable length from passive antennas to receivers should generally not exceed 1 meter. The figure shows an integrated passive antenna with a GPS module:(1) Silver Layer: The silver coating on ceramic antennas influences resonance frequency. The ideal frequency point is 1574.42 MHz, which can be adjusted during manufacturing by modifying the silver surface shape. (2) Ceramic Disc: The quality of ceramic powder and sintering process directly affects performance. Larger ceramic discs achieve higher resonance frequencies. Active Antenna: Typically refers to an antenna module requiring power supply. It consists of a ceramic antenna, LNA (Low Noise Amplifier), cables, connectors, and an additional sealed waterproof ring, commonly known as the G-mouse. II. Differences Between Active and Passive Antennas for GPS Modules 1. Conceptual Distinction Passive Antenna: A purely metallic structure, representing the common antennas seen in everyday applications. Active Antenna: Features an amplifier added to this basic antenna, along with a dedicated power supply for the amplifier. The amplifier enhances sensitivity and reduces the signal-to-noise ratio.2. Shape DistinctionDue to the added amplifier, active antennas offer higher gain and are generally larger in volume and dimensions than passive antennas. Crucially, active antennas typically display a voltage indicator (VCC) on their exterior, whereas passive antennas do not.III. Factors Affecting GPS Antenna Performance1. Ceramic Element: The quality of ceramic powder and sintering process directly impacts performance. Commonly used ceramic elements measure 25×25mm, 18×18mm, 15×15mm, or 12×12mm. Larger ceramic elements have higher dielectric constants, resulting in higher resonance frequencies and better reception. Most ceramic plates are square-shaped to ensure consistent resonance in both X and Y directions, achieving uniform satellite reception. 2. Silver Layer: The silver coating on the ceramic antenna surface affects its resonance frequency. Ideally, the GPS ceramic chip's frequency should precisely match 1575.42 MHz. However, the antenna's frequency is highly susceptible to environmental interference, especially when integrated into a device. Adjusting the silver coating's shape is necessary to recalibrate the frequency back to 1575.42 MHz. Therefore, GPS device manufacturers must collaborate with antenna suppliers during procurement, providing device samples for testing.3. Feed Point: The ceramic antenna collects resonant signals via the feed point and transmits them to the backend. Due to impedance matching requirements, the feed point is typically not centered on the antenna but slightly offset in the XY directions. This impedance matching method is simple and cost-effective. Offset in a single axis is termed single-polarization antenna, while offset in both axes is called dual-polarization.4. Amplifier Circuit: Determines the PCB shape and area supporting the ceramic antenna. GPS signals exhibit ground bounce characteristics; patch antennas achieve peak performance when mounted on a 7×7 cm uninterrupted ground plane. While constrained by appearance and structure, maintain a sufficiently large, uniformly shaped area. Amplifier gain selection must match the rear-end LNA gain. Sirf's GSC3F requires total gain before signal input not to exceed 29dB; otherwise, signal oversaturation may cause self-oscillation. GPS antennas have four critical parameters: Gain, VSWR (Voltage Standing Wave Ratio), Noise Figure, and Axial Ratio. Axial ratio is particularly emphasized as a key indicator measuring the device's signal gain variation across different directions. Since satellites are randomly distributed across the hemispherical sky, ensuring the antenna maintains similar sensitivity in all directions is crucial. Axial ratio is influenced by antenna performance, physical structure, internal circuitry, and EMI factors.