Radar Block Diagram
This is a free printable radar block diagram: download the diagram as SVG or open it and print to paper or PDF.
Reference block diagram of a pulsed radar system showing the signal chain from transmitter through duplexer, antenna, receiver, and display subsystems.
A pulsed radar (Radio Detection And Ranging) system detects objects by transmitting short, high-power RF pulses and measuring the time delay before the reflected echo returns. The range to the target is calculated from the speed of light and this two-way transit time. A standard pulsed radar block diagram consists of five principal functional blocks.
1. Transmitter: generates high-power RF pulses at the operating frequency. In legacy systems, the transmitter consists of a magnetron oscillator driven by a modulator that shapes the pulse duration (pulse width) and repetition rate (Pulse Repetition Frequency, PRF). In modern solid-state radar, the transmitter uses power amplifiers driven by an exciter/synthesiser. Pulse width determines range resolution; PRF determines maximum unambiguous range.
2. Duplexer: a switching device that allows a single antenna to be shared between the high-power transmitter and the sensitive receiver. During transmission, the duplexer isolates the receiver from the transmitter output to prevent receiver damage. During the receive interval (after each pulse), it connects the antenna to the receiver. Gas-filled TR (transmit-receive) switches or solid-state diode switches are used depending on the system.
3. Antenna: radiates the transmitted pulse into space and collects the reflected echo. Most radar antennas are directional (parabolic dish, phased array, or slotted waveguide array) and rotate or scan to provide azimuth coverage. The antenna's beam width and gain are fundamental system parameters.
4. Receiver: amplifies the very weak echo signals returned by the antenna. A superheterodyne receiver architecture is typical: a low-noise amplifier (LNA) at the front end is followed by a mixer (down-converts RF to intermediate frequency), IF amplifier, detector, and video amplifier. The receiver sensitivity determines the minimum detectable signal and thus the maximum detection range.
5. Display (and signal processor): converts the detected echo signals into usable information. Traditional displays include the A-scope (amplitude vs time) and Plan Position Indicator (PPI). Modern radar systems use digital signal processors (DSP) and computer displays. Range is computed from time-of-flight; bearing from antenna position; and in Doppler radar, velocity from frequency shift.
This is an educational reference block diagram only.
How to wire radar block diagram
- Understand the timing master: the modulator/synchroniser All radar subsystems operate from a common timing reference. The modulator or synchroniser generates trigger pulses that initiate the transmit pulse, gate the receiver, and synchronise the display sweep. Trace the signal flow from this timing reference to understand the system.
- Trace the transmit path From the modulator, the transmit trigger fires the transmitter (magnetron or power amplifier chain), producing a high-power RF pulse. This pulse travels through the duplexer (in transmit mode) to the antenna, which radiates it as a directed beam.
- Understand the duplexer switching action The duplexer transitions from transmit to receive mode within nanoseconds after the pulse ends. During this transition (recovery time), nearby targets within a minimum range cannot be detected — this is the radar's minimum range limitation.
- Trace the receive path The echo arrives at the antenna, passes through the duplexer (now in receive mode) to the LNA, then to the mixer (where it is down-converted to IF), then through the IF amplifier, detector, and video amplifier. The output is a video signal proportional to echo amplitude.
- Understand signal processing and display The detected video signal is processed to reject clutter (ground returns, sea clutter) using MTI (Moving Target Indication) or Doppler processing. The processed signal drives the display, where range is represented by distance from the centre and bearing by antenna azimuth angle.
Specifications
| Radar type | Pulsed (monostatic — shared transmit/receive antenna) |
|---|---|
| Range calculation basis | Two-way time of flight at speed of light (~3 × 10⁸ m/s) |
| Range per microsecond of delay (one-way) | Approximately 150 metres |
| Key transmitter parameters | Peak power, pulse width, PRF (Pulse Repetition Frequency) |
| Key receiver parameter | Noise figure (determines minimum detectable signal) |
| Antenna scanning | Mechanical rotation or electronic (phased array beam steering) |
| Display types | A-scope (range vs amplitude), PPI (plan position indicator), digital |
Safety warnings
- Radar transmitters produce high-power RF radiation that can cause tissue heating and eye injury at close range. Maintain safe exclusion zones around operating antennas as defined by the system's RF hazard assessment and local regulations.
- High-voltage power supplies within radar transmitters (particularly magnetron-based systems) carry lethal voltages. Never service transmitter high-voltage circuits without specific training and appropriate PPE.
- Pulsed radar systems emit electromagnetic energy that may interfere with other electronic equipment, cardiac pacemakers, and other medical devices within range.
- Radar systems are regulated RF emitters. Transmission requires type approval and operating licences in all jurisdictions. Unauthorised radar operation is illegal.
- This block diagram is an educational reference only and does not represent a design for construction.
Tools needed
- RF power meter and directional coupler (for transmitter output measurement)
- Spectrum analyser (for frequency and spectral occupancy verification)
- Oscilloscope with RF capability (for pulse timing verification)
- Noise figure meter (for receiver LNA characterisation)
- RF test cables and attenuators rated for transmitter power levels
- High-voltage safety equipment (for magnetron transmitter maintenance)
Common mistakes
- Confusing the duplexer's function — it is not an antenna splitter; it is a time-gated switch that isolates the receiver during transmission.
- Misunderstanding PRF — a very high PRF reduces maximum unambiguous range, not increases it.
- Overlooking the receiver recovery time (duplexer TR switch recovery) which defines the radar's minimum range.
- Assuming the display directly shows raw echo amplitude — modern radar displays present heavily processed, clutter-rejected, and Doppler-filtered data.
- Confusing pulse width with PRF — pulse width determines range resolution; PRF determines maximum unambiguous range and data rate.
Troubleshooting
- No target returns visible on display despite targets known to be present
- Cause: Receiver noise figure degraded (LNA failure), duplexer TR switch not recovering, or transmitter power reduced Fix: Measure transmitter output power. Test receiver sensitivity with a calibrated signal generator at the antenna port. Verify duplexer recovery time with an oscilloscope.
- Range displayed for targets is incorrect
- Cause: Timing reference (synchroniser) clock error, or incorrect calibration of range scale Fix: Verify synchroniser timing against a known reference. Calibrate range scale using a target at a known range or a precision delay line.
- Strong fixed returns (clutter) masking genuine targets
- Cause: MTI or Doppler processing not functioning, or clutter filter threshold incorrectly set Fix: Verify the MTI or Doppler processing chain is operational. Adjust clutter rejection thresholds. Check that the coherent local oscillator (COHO) maintains phase stability between pulses.
Frequently asked questions
What is the function of the duplexer in a radar system?
The duplexer allows one antenna to serve both the transmitter and receiver by rapidly switching between transmit and receive modes. During the transmit pulse, it directs high power to the antenna and protects the sensitive receiver from damage. Between pulses, it connects the antenna output to the receiver input.
How does pulsed radar calculate the range to a target?
The radar measures the time elapsed between transmitting a pulse and receiving its echo. Since electromagnetic waves travel at the speed of light (approximately 3 × 10⁸ m/s), the two-way travel time divided by two, multiplied by the speed of light, gives the range. Every microsecond of delay corresponds to approximately 150 metres of range.
What is Pulse Repetition Frequency (PRF) and how does it affect radar performance?
PRF is the number of pulses transmitted per second. A higher PRF improves data update rate but reduces the maximum unambiguous range — if PRF is too high, a returning echo from a distant target may arrive after the next pulse has already been transmitted, causing range ambiguity.
What is the role of the Low-Noise Amplifier (LNA) in the radar receiver?
The LNA is the first gain stage in the receiver chain, immediately after the duplexer. Its function is to amplify the extremely weak echo signal before it enters the mixer and IF stages. The LNA's noise figure largely determines the overall receiver sensitivity and the radar's maximum detection range.
What is the difference between a monostatic and bistatic radar?
A monostatic radar uses the same antenna (or co-located antennas) for transmit and receive — this is the most common arrangement, requiring a duplexer. A bistatic radar uses physically separated transmit and receive antennas, often at different geographic locations, eliminating the need for a duplexer but requiring precise synchronisation.
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