The Radar Field Analyser - RFA641 is a highly portable instrument designed for on-site performance checks of Monopulse Secondary Surveillance Radar (MSSR), Primary Surveillance Radar (PSR), and Air Traffic Control (ATC) radars operating in L and S bands. It allows for continuous measurement and plotting of the transmission pattern (power) of Large Vertical Aperture (LVA) or horn-feed antennas versus azimuth or time, often used for regular check-ups or maintenance, especially when antennas are damaged or degraded. The device supports a frequency range of 900 MHz to 3.0 GHz, with an optional extension up to 3.5 GHz, making it versatile for a wide variety of radar systems.
Function Description:
The RFA641 serves multiple functions beyond its primary role as an antenna evaluation tool:
- Uplink (Transmission) Antenna Diagram Measurement: It measures the pulse power as a function of azimuth by receiving RF interrogations from the radar. The RFA641 is set up in the field without direct connection to the radar, picking up radar signals (P1-P2-P3 1030MHz or PSR transmissions) from the air. The Uplink software then calculates the Horizontal Polar Diagram (HPD) from this data. Pulses can be recorded in a condensed format (pulse mode) or in detail (scope mode), with HPD extraction performed through fingerprinting (stagger).
- Downlink (Reception) Antenna Diagram Measurement: It generates test pulses for reception pattern measurements. The RFA641 is set up in the field, transmitting Synchronous Amplitude Modulated (SAM) pulses at a selected frequency. These test pulses are then measured at the log video level at the output of the (M)SSR or PSR receiver using the Radar Interface Module (RIM782), with recording slaved to the antenna rotation.
- Receiver Sensitivity Sweeps: Measures receiver output voltage as a function of power.
- Receiver Bandwidth Sweeps: Measures power as a function of frequency and identifies spurious responses.
- STC (Sensitivity Time Control) Sweeps: Measures power as a function of delay after trigger.
- Sectorial STC/DSTC (Digital Sensitivity Time Control) Measurements: Measures power as a function of delay after trigger and azimuth, specifically for Quantised Video Receivers.
- Transmitter Analysis: Records transmitter power, spectrum, pulse shape, timing, mode, and stagger for verification.
- FRUIT (False Replies Unsynchronized In Time) Generation: Simulates environmental interference by generating out-beam FRUIT and/or CW interference scenarios.
- Mode-S Interrogation Generator: Used for transponder verification and quality checks.
- Primary Target Injection: Injects simulated primary targets for non-pulse-compression primary radars. The RFA641 generates a square pulse-shaped return with fixed power (depending on target range) and width after a given delay, based on precalculated power.
Important Technical Specifications:
Interfaces:
- Analog: 2x BNC (Ch1 out: video output from receiver log amplifier; Ch2 in: video input to acquisition system).
- Azimuth: DB15HD female (TTL input of ACP, ARP, trigger).
- Rf: 2x BNC (Rx, Tx; 50 Ohm).
- USB: USB2 (for remote programming and high-speed data throughput, 480 Mbit/s transfer rate).
Transmitter:
- Frequency Range: 900 MHz – 3.0 GHz (Oscillator Synthesiser stabilized; accuracy 100 KHz). Optional: up to 3.5 GHz.
- Max. Tx Power at Tx output port: 900 MHz – 3.0 GHz: > 10 dBm and < 18 dBm. Optional: 3 GHz – 3.5 GHz: > 5 dBm and < 15 dBm.
- Amplitude Pulse: 900 – 1500 MHz: 60 dB.
- Modulation: 1500 MHz: 50 dB.
- On/off Dynamic Range: > 70 dB.
- Bi phase modulation: 0 / 180 deg 5 deg.
- RFA Option A (Fruit Reply Code Generator): SSR pulse generator compliant with Annex 10. Pulse duration Mode A/C 450 ns 100 ns, Mode-S 500 ns 50 ns. Pulse rise time < 100 ns, Pulse decay time < 200 ns.
Receiver:
- Frequency Range: 900 MHz – 3.0 GHz. Optional: up to 3.5 GHz.
- Sensitivity: -75 dBm.
YIG Preselector Filter:
- Centre Frequency: 900 MHz – 3.0 GHz. Optional: up to 3.5 GHz.
- 3 dB Bandwidth: 25 MHz 2 MHz.
Usage Features:
- Self-Test/Calibration: Performs internal linear receiver measurements or uses an external log RF module for absolute power level measurements to calibrate the transmitter. This ensures accurate measurements before use.
- User-Friendly Software: The RASS-S Toolbox provides a graphical user interface for all functions, guiding the user through setup and measurement steps.
- Data Acquisition: Features a DSP processor and USB2 interface for direct spooling of captured pulse data to disk for later analysis, enabling a "one button" semi-automated measurement approach.
- Flexible Measurement Modes: Supports pulse, scope, and spectrum programs for Uplink measurements, allowing detailed pulse analysis or compact data recording.
- External Video Input: Allows using an external RF receiver or spectrum analyzer as an RF front-end for HPD measurements, extending the frequency range beyond the RFA641's internal capabilities.
- HPD Analysis: Tools for extracting HPDs from recorded pulses, including stagger pattern detection, threshold control, and boresight detection.
- OTD (Out of Tolerance Data) Calculation: Automatically evaluates HPD curves against Eurocontrol standards for Radar Performance, with user-definable limits.
- HPD Logfiles: Capable of reading, recognizing, and displaying Uplink and Downlink HPD logfiles, with the ability to overlay up to five layers for comparison.
- Scenario Generation and Replay: For Primary Target Injection and Remote Field Monitor, users can define and replay complex scenarios, simulating moving targets with programmable parameters.
- Interrogation List: For Transponder Interrogator, users can build and save lists of interrogations, which can then be played to sample and log transponder replies.
Maintenance Features:
- Self-Test/Calibration: Regular self-test and calibration procedures are advised before any measurements to ensure the RFA641 is performing as expected. The software guides through the process, including cable tests and YIG filter attenuation measurements.
- Troubleshooting: The manual provides guidance for common issues such as "File not found" errors, no pulses recorded, or flattened antenna diagrams, often pointing to connection checks, attenuation adjustments, or frequency settings.
- Calibration Files: The system uses calibration files for accurate power level calculations, which can be loaded, saved, and managed through the software.
- Data Export: Measurement data, including OTD parameters, limits, and error messages, can be exported to tab-separated files for external analysis.
- Firmware Updates: While not explicitly detailed as a user feature, the digital nature of the device implies potential for firmware updates to enhance functionality or address issues.
The RFA641 is designed for ease of use, portability, and comprehensive radar performance analysis, making it a valuable tool for radar maintenance and evaluation personnel.
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