The latest marine radar buzz words are “HD Radar” and “Broadband Radar,” now
being advertised by reputable radar manufacturers as the latest and greatest
technology. But how are they different from the radar we have come to know over
the past decade? Here is a quick overview of these two technology advances.
The term HD rides along with the recent high definition television wave. HD TV
has brought enhanced reality to the screen: favorite TV personalities are
presented life-sized or larger, with amazing details plainly visible. This has
been a remarkable step forward for television viewing. In marine radar, the step
is not so large, but it is noticeable. HD processing in radar display is a
manipulation of the video output of the received radar signal that can make the
echo image appear sharper. Neither the transmitter nor receiver is radically
changed to accomplish this, instead video processing after the receiver stage
and the use of a color palette to display echo strength are used to make the
target edges more defined. The result is a pleasing display appearance that
lends confidence to the interpretation and may enhance target separation in some
cases. In short, this is an improvement in the display and not a change in the
target detection capabilities of the radar.
Broadband Radar is an arguable marketing term, intended to differentiate one
manufacturer’s technology from others’. Marketing folks come up with these terms
that sometimes convey the opposite of their intent. We suspect this is the case
here. We could argue that this version of radar technology is not at all
broadband, and that, in fact, it depends beneficially on an extremely narrow
receiver selectivity (i.e., the opposite of broadband) to function.
Nevertheless, this has been a good choice of terms as it has caught on and is
The technology is indeed radically different from that used previously in the
marine industry, although it has been used in aviation applications for decades.
The first change to note about this new marine application of a not-so-new
technology is that it dispenses with the radar’s traditional high-power output
vacuum tube–the magnetron. Instead, it uses a very low-power solid-state device
as the transmitter’s main power generating element. A solid-state, low-power
transmitter is a radical step forward in our industry.
The high-power magnetron is notoriously wasteful of energy: it splatters its
output pulse across a wide band of the frequency spectrum. Talk about broadband!
Adding disadvantage on top of disadvantage, the magnetron’s output pulse is not
stable. Its transmitting frequency varies from pulse to pulse, and even within a
pulse. This method of generating two thousand or more watts of pulsed power
requires its paired radar receiver to have a wide selectivity that allows a lot
of electrical noise to enter the receiver along with the faint target echoes.
A solid-state transmitter as in the new broadband radars generates energy that
is more stable in frequency, and does not waste its energy in sidebands as much.
This allows the radar engineers to design a receiver with very narrow
selectivity that prevents much noise from entering the receiver where it
competes with the very faint target echoes. If a magnetron radar can be called a
blunderbuss, a solid-state radar is a rifle–that is, frequency-stable energy
applied efficiently versus magnetron energy splattered inefficiently. What has
kept magnetron radars alive so long is their low cost. Microwave ovens we cook
with need high power to warm the soup, so a solid-state power device would not
serve well in the galley. On deck, though, magnetron technology has about run
The second change in broadband radar is that it doesn’t transmit a single output
pulse. It transmits a continuous energy wave (called CW) that gradually sweeps
across a frequency spectrum. If you could listen to the sound, it might be
similar to a police siren’s whoop, whoop, sweeping in tone from low to high. Its
paired receiver follows that frequency sweep with very narrow selectivity. In
this it is very much like the function of an aviation product that we know of as
the CW radio altimeter. As the transmitter sends out its constantly sweeping
energy, its receiver keeps track of that output and compares it to the energy
reflected from a target. When the incoming signal matches the outgoing, that
identifies a target. Thus we come to the more generic name of this type of radar
technology: Frequency Modulated Continuous Wave (FMCW).
One of the touted advantages of broadband radar is that it can see echoes
virtually up to the rubrail of the boat. Much is made of this as a collision
avoidance benefit; however, my own 2 kW radar mounted at the spreaders can
readily see a small buoy barely 70 feet in front of the bow. My feeling is that
that any situation within that distance that depends on radar to ameliorate is a
collision that is unlikely to be avoided. Collision avoidance depends on proper
watch at distances far beyond boat-length range–a virtue that some competitors
still argue are lacking in the low-powered FMCW technology.
Today’s second generation broadband radars, however, are advertising much
improved long-distance operation, which indicates that the first gen product
probably wasn’t a great performer. There is no reason why a low-power
solid-state radar cannot have long range performance equivalent to traditional
multi-kW magnetron radars. The “No Substitute for Power” mentality in radar is
based on myth. What matters is not transmitter power; what matters is Loop Gain,
which is a function of transmitter effectiveness teamed with receiver
sensitivity and selectivity, and modern video processing.
Eliminating the magnetron will reduce system power consumption because the
filaments of the magnetron are a power-hog. Sailors will appreciate this power
reduction, but the antenna drive motor and display back lighting, two other
significant power consumers, remain unaffected. Radiation exposure due to radar
is a topic that wins too little consideration, in my opinion. Solid-state radar
would certainly reduce or eliminate any perceived hazard in this area, which has
to be considered a virtue. Accepted values of radiation exposure seem to go down
with each improved study.
The most serious disadvantage of broadband radar, in our opinion, is that its
low transmitter output power is insufficient to trigger a RACON. This is a
serious weakness, especially in challenging navigational environments where many
vessels operate. Aside from this one major drawback, we believe that FMCW
(“Broadband”) radar is worth consideration if one were contemplating a purchase.
Modern magnetron radars are darn reliable. On a delivery this writer has used an
old monochrome CRT Decca to cross the Columbia River Bar at 0300 in pea-soup
fog, a radar that has probably performed flawlessly for 30-plus years. And so
long as the radiation hazard is recognized and respected, a magnetron radar will
serve just fine.
But progress marches on. When the magnetron was removed from aviation weather
avoidance radar, many “experts” stated that low power (e.g., 25 watts peak
power) aviation radar would never work properly. Today, thousands of such radars
perform exceptionally well, providing pilots and passengers with benefits they
only dreamed of—such as Doppler turbulence detection—which were not available on
high power magnetron radars.
Technological progress in the marine radar field will eventually herald the
demise of the venerable “maggie.” And along with the frequency stability of
solid-state transmitters may come a host of new advantages, such as Doppler
analysis of squall winds, or even Doppler analysis of wind gusts based on radar
reflection from the water surface. Stay tuned. There is a new radar world coming
over the horizon.