Marine Radar Signal Sensitivity – Understanding radar means grasping its extreme sensitivity: detecting a 2 μV echo amid the overwhelming power of its own 50 kW transmission—the classic “needle in a haystack.”
A clear PAL TV picture needed about 1,000 μV. A usable radar blip appeared at just 2–4 μV, right at the edge of the thermal noise floor. Rectangular copper waveguides were mandatory for the high-power path; coax would arc over instantly under 50 kW pulses. Satellite systems avoid this issue by down-converting at the dish with an LNB.
Incoming Signals Compared
Satellite signals from geostationary orbit (or ~550 km for Starlink) are astonishingly faint by the time they reach a backyard dish—often measured in power flux density rather than microvolts. A typical -100 dBm signal equates to roughly 2.2 μV on a 75 Ω feed, but the massive bandwidth (27–36 MHz for DVB-S2) floods the system with thermal noise.
The LNB is the hero: it amplifies and converts the 12 GHz signal to L-band (950–2150 MHz) immediately, before cable losses can swallow it. Modern HEMT technology (and earlier liquid-nitrogen cooling in high-end setups) allows receivers to extract data even at negative signal-to-noise ratios through sophisticated correlation.
For perspective, here’s how input signal strengths stack up:
Device
Typical Signal at Input
Perspective
Analog Colour TV (1980s)
1000uV
A loud shout (benchmark)
Marine Radar Echo (36 nm
~2.2uV
A clear whisper (the echo)
Satellite TV Dish
1-3uV
A faint breath from space
GPS Receiver
~0.07 μV (or weaker)
A ghost of a thought
The LNB does for satellite what the GaAs/GaN front-end does in modern radar: amplify at the antenna before the signal travels any distance.
A disassembled LNB. A waveguide carrying the microwave signal from the external dish antenna enters at the hole in the center, where two pins act as internal antennas (for two different polarizations). Here the microwave signal is coupled into microstrips on the LNB’s circuit board, in order for the RF signal to be amplified and downconverted into lower frequencies, which are output at the two F connector sockets at the bottom.
Low-noise block downconverter (LNB) from a satellite television dish, disassmbled. This is mounted at the focus of the satellite dish and converts the microwave ku band signal from the satellite to a lower intermediate frequency which is sent down the coaxial cable into the house to the set-top box at the user’s TV. A feed horn collects the microwaves from the dish into a circular waveguide which passes through the hole in the circuit board. The two metal pins visible at the edge of the hole act as antennas to receive the two orthogonal circularly polarized microwave signals. On the circuit board a local oscillator creates a signal which is mixed with the microwave signal, creating the intermediate frequencies, which are output to the coaxial cable through the connectors at bottom.
Why Waveguides for Radar but Coax for Satellite?
Radar is “heavy metal” transmission. A 50 kW pulse creates voltages that would arc across coax dielectric and cause catastrophic loss at X-band frequencies due to skin effect and dielectric absorption. Hollow air-filled copper waveguides eliminate the center conductor and plastic, allowing near-lossless propagation with high-voltage insulation provided by air.
Satellite reception, by contrast, deals with picowatts after down-conversion to lower frequencies where coax excels. No transmit pulse means no arcing risk, and the LNB handles the frequency shift upfront.
S-band radars often used flexible elliptical waveguides to navigate ship masts—larger “pipes” for the longer 10 cm wavelength, but still hollow for the same physics.
In short: radar needs a high-pressure fire hose; satellite makes do with a soda straw after clever frequency conversion.
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Credits
Research assistance provided by Grok xAi and Google’s Gemini. All facts, personal experiences, and final editing remain the responsibility of the author.
Image Credits
Featured Image: AN/SPS-46(V)9 radar antenna on the USS Theodore Roosevelt aircraft carrier. This is an X-band (8-12 GHz) marine navigational radar similar to types on civilian ships, used to detect other ships in the vicinity. It has a peak power of 7 kW, a range of somewhere around 35 nautical miles. This type of antenna is called a slot antenna and radiates a narrow vertical fan-shaped beam of microwaves, about 15° high and 2.2° wide. A motor in the housing below rotates the bar-shaped antenna to scan the beam around the horizon. Author US Navy.
Low Noise Block – Wiki Commons – No Author/User