In modern microwave communication networks, how are signals efficiently and stably radiated from the antenna to the remote end and accurately received? The core answer to this question lies in a physical architecture that is often overlooked yet crucial—the antenna feed system. It is not only the transmission pathway for RF signals but also the cornerstone of the entire wireless communication link’s performance. For communication engineers, a deep understanding and precise maintenance of the antenna feed system are essential to ensuring high network availability and superior performance.
Core Components and Functions of the Antenna Feed System
A complete antenna feed system is far more than a simple cable. It is an integrated RF transmission link comprising various precision components.
Antenna: The Interface for Electromagnetic Wave Conversion
The antenna is the “gateway” of the entire system, responsible for efficiently converting guided waves (signals within the feed line) into space waves (electromagnetic waves propagating through the air). Commonly used parabolic or flat-panel antennas in microwave communication are designed to determine the signal’s directivity, gain, and coverage. Key performance parameters of the antenna, such as Voltage Standing Wave Ratio (VSWR) and radiation pattern, are primary indicators for assessing its health.
Feed Line: The “Highway” for Low-Loss Transmission
The feed line, typically a waveguide or low-loss coaxial cable, carries the critical task of transmitting high-frequency microwave signals between the transceiver and the antenna. Its core value lies in achieving extremely low transmission loss. At microwave frequencies ranging from several GHz to tens of GHz, losses in ordinary cables become prohibitive. Therefore, using feed lines with very low dielectric loss (such as air-dielectric waveguides or high-quality foam-dielectric coaxial cables) is essential. Any physical deformation, water ingress, or loose connections can significantly increase insertion loss, directly attenuating signal strength.
Supporting Components: Ensuring Integrity and Reliability
A robust system also includes a series of critical components:
- Connectors and Flanges: Ensure precise and secure mechanical and electrical connections between sections, with their machining accuracy directly affecting impedance matching.
- Lightning Arrestors (Surge Protectors): Protect expensive indoor units from damage caused by lightning-induced surges.
- Sealing Windows/Pressure Windows: In systems using pressurized waveguides, maintain internal dryness and constant air pressure to prevent performance degradation.
- Calibration Lines and Test Ports: Provide access points for routine maintenance and fault localization.
Antenna Feed Testing: Engineering Practices to Ensure System Performance
Even the best designs require rigorous testing and maintenance to guarantee long-term performance. Antenna feed testing is not a one-time task but a core engineering practice贯穿ning the entire lifecycle of installation, acceptance, and maintenance.
Installation and Acceptance Testing: Laying the Performance Foundation
Upon installation of a new system or after major adjustments, comprehensive acceptance testing is mandatory. This includes:
- Voltage Standing Wave Ratio (VSWR) Testing: Using a Vector Network Analyzer (VNA) to measure reflections across the entire antenna feed system within the operating frequency band. An ideal VSWR is close to 1:1. A higher value indicates impedance mismatch points (such as antenna damage, connector faults, or feed line deformation), causing signal energy to reflect back to the transmitter, reducing radiation efficiency and potentially damaging equipment. A study published in IEEE Transactions on Microwave Theory and Techniques emphasizes that VSWR is the most direct parameter for evaluating antenna system matching efficiency, and its deterioration serves as an early warning sign for link performance degradation (1-IEEE Trans. Microw. Theory Techn.-2018).
- Insertion Loss Testing: Quantifying the power attenuation of signals after passing through the entire antenna feed system. This value must be compared with the theoretical value from equipment manuals. An abnormally high increase often points to physical damage or connection issues in the feed line.
- Antenna Pattern and Polarization Isolation Testing: Verifying in an anechoic chamber or using field measurement techniques whether the antenna’s main lobe direction, side-lobe suppression, and cross-polarization discrimination meet standards. This is crucial for preventing co-channel interference.
Periodic Maintenance and Fault Diagnostic Testing
Environmental stresses (such as wind-induced vibration, temperature fluctuations, and rain erosion) can affect antenna feed performance over time. Regular preventive maintenance testing effectively prevents outages.
- Time-Domain Reflectometry (TDR) Function: The TDR function in modern vector network analyzers acts as an engineer’s “radar.” It converts frequency-domain measurements into time-domain responses, precisely locating faults in the feed line (such as open circuits, short circuits, or impedance discontinuity points) by their distance in meters from the test port, greatly enhancing troubleshooting efficiency (2-IEEE Antennas and Propagation Magazine-2020).
- Combined Power Meter and Spectrum Analyzer Measurements: During system operation, measuring the output power at the transmitter and the power at the antenna port allows for on-site calculation and monitoring of changes in actual link loss trends.
The Value of a Systematic Testing Strategy
Establishing end-to-end test baselines (from the transceiver output port to the antenna radiating surface) ensures that every maintenance data point is traceable. By comparing historical data, engineers can keenly identify gradual performance trends and intervene before failures occur, reflecting the advanced concept of predictive maintenance.
Optimization and Outlook: Building Reliable Links for the Future
To maximize the effectiveness of the antenna feed system, engineers must implement best practices throughout the entire process—from design and installation to maintenance. This includes selecting radomes and corrosion-resistant connectors suited to the environment; strictly adhering to engineering specifications during installation, ensuring proper feed line bend radii and waterproof sealing; and establishing a data-driven regular antenna feed system maintenance best practices plan.
With the development of 5G and future higher-frequency communication technologies (such as millimeter-wave), requirements for the precision and low loss of antenna feed systems will become even more stringent. Although integrated Active Antenna Systems (AAS) alter some aspects of the architecture, the fundamental physics and performance requirements of the RF transmission path remain unchanged. In fact, the core importance of RF transmission link quality assessment becomes even more pronounced.
Conclusione
The antenna feed system, serving as the bridge connecting the digital world with the physical space, directly determines the final quality of the microwave communication link. For communication network engineers, moving beyond perceiving it merely as simple “cabling” and instead applying the standards of a precision RF system to its design, testing, and maintenance is key to building highly reliable and high-performance communication infrastructure. Through rigorous antenna feed testing and scientific maintenance strategies, we can not only address current issues but also lay a solid physical layer foundation for future wireless communication demands that require higher speeds and lower latency.