Is this an antenna array on the new Chinese aircraft carrier?

[berkeman]

TL;DR Summary

I'm trying to figure out what the function would be for what looks like a dual antenna array lining the sides of the front of this new Chinese aircraft carrier...

I saw this photo at CNN.com today, and I'm trying to figure out what the function could be for what looks like a linear antenna array lining both sides of the aircraft ski-jump launching ramp. They look to be an array of about 10m verticals along each side of the bow, but with the base of some of the elements to the right curving up, it would seem to be a less-than-ideal array.

Does anybody know what these are and what functions they serve?

www.cnn.com

 

[Baluncore]

They are simply HF antennas, hinged at the base so they do not interfere with aircraft operations, or with docking.
They are not part of a DF system or array.
They have been used on aircraft carriers since WW2.

 

[berkeman]

Interesting. But since they are not coaxially mounted, one of them transmitting will swamp the other receivers, no?

 

[tech99]

I agree, I can't see a reason to mount them closely unless they form an array.

 

[Baluncore]

I agree, I can't see a reason to mount them closely unless they form an array.

The reason for several antennas is redundancy. They are built solid and distributed so one Kamikazi would be unlikely to disable more than one antenna. Each antenna was equipped for either transmission or reception.

Interesting. But since they are not coaxially mounted, one of them transmitting will swamp the other receivers, no?

HF transmit and receive antennas work OK near each other, so long as they are on different HF bands, or have very expensive selective equipment. Some co-located autotuned couplers can get confused and circulate a mid-frequency crossmod of the two, which can be fun to track down and identify.

The cold war Kusznetsov class carriers were designed in the 1970s, for construction by the Ukraine in the 1980s, for use by the USSR in the 1990s. With the move from HF to satellite communications, the WW2 style HF antennas are no longer needed, so we can expect them to disappear, as did the diagonal torpedo net support booms on battle ships following WW1.

 

[Klystron]

Assuming the structures make up an antenna or antennae, 10 meter wavelength supports ~~30 Megahertz (Mhz) frequencies. HF runs 3 to 30 Mhz. The installation placement suggests RF possibilities beyond backup communications. Some combinations and fractions of HF band sensitive to nearby jet engines, aircraft frames and engine hot exhaust streams. Launches could warble RF fields across the bow providing performance data.

It would be interesting to monitor shipboard HF band when aircraft scream up the ramp. Presuming mounted sensors; another WAG: emergency notification as wayward aircraft strike each antenna sensor pole.

 

[dlgoff]

I'm trying to figure out what the function would be for

My initial thought was the antenna are Very Low Frequency antenna.

VLF radio waves (3–30 kHz) can penetrate seawater to a few tens of meters and a submarine at shallow depth can use them to communicate. A deeper vessel can use a buoy equipped with an antenna on a long cable. The buoy rises to a few meters below the surface, and may be small enough to remain undetected by enemy sonar and radar. However these depth requirements restrict submarines to short reception periods, and antisubmarine warfare technology may be capable of detecting the sub or antenna buoy at these shallow depths.

 

[berkeman]

My initial thought was the antenna are Very Low Frequency antenna.

Interesting thought, but the antennas are probably too small to be useful/practical for VLF. More likely, they just use land-based VLF antennas for sub coverage and relay to the ships via satellite.

 

[tech99]

The antennas might be just transmitting ones and there might be an active receiving antenna at the stern of the ship, as far away as possible. VLF reception is very easy for a surface vessel using a small loop etc. and a whip is not necessary.

 

[Baluncore]

The antennas might be just transmitting ones and there might be an active receiving antenna at the stern of the ship, as far away as possible.

You have completely inverted the way the HF antenna system it is actually used.

The receive antennas are used in pairs for spatial diversity reception, one on each side of the flight deck. That is why they can be spaced closer together along the edge of the flight deck than would be the case for transmit antennas.

The transmit elements are not used in pairs. Transmission is from the individual more isolated whip elements, beyond the far end of the receive array, or at the other end of the vessel.

The elements only look like a vertical whip array while visiting port, when they are manually stowed in the vertical position. They are lowered into the horizontal operating position on return to sea. They are never vertical during flight operations.

See; Title: HF Receiving Antenna Arrangement on Flight-Deck Edge of Aircraft Carriers. Performances of Antennas in Different Locations and Paired Combinations are Compared. [Full text is not available]. Abstract “Five possible sites were studied for placement of 2-30 MHz twin-whip antennas on the deck edge of ships of the CVA 59 to CVAN 68 types. … It was found that siting of the antennas did not appreciably affect their performance, provided they were more than quarter wavelength at 2 MHz, approximately equal to 125 feet from the forward and after ends of the flight deck and from the island. In pairing the antennas to achieve space diversity, the most important factor is the distance between them, which should be at least 200 feet.” https://apps.dtic.mil/sti/citations/AD0888366

Anyone serve on an aircraft carrier or in the know about them?
“I served as an electronics tech onboard the USS Nimitz for three years and those were my babies. Those are two piece 35 foot HF whip antenna. They are in the down position during flight operation (and generally when underway) to keep jet wings safe. They are manually lifted when in close confines. They have nothing to do with HFDF or fall arrest.”
https://engineering.stackexchange.c...e-side-off-this-aircraft-carriers-flight-deck

 

[berkeman]

The receive antennas are used in pairs for spatial diversity reception, one on each side of the flight deck.

I guess I'm not following. Spatial diversity in Rx is used to combat multipath issues, AFAIK. If the antennas were vertical I could believe that multipath interference would be an issue due to the Pri-fly tower and the movement of aircraft on the flight deck. But in the horizontal position, what would cause multipath issues requiring spatial diversity in Rx?

Also, it does seem that use in the horizontal position is the normal mode when under way, but doesn't that provide poor coverage in the port/starboard directions? It seems like the antenna patterns are redundantly fore and aft, with little coverage out the sides of the ship. At least a vertical HF antenna will have a pattern that is consistent with Tx/Rx in all directions on the surface of the water.

Sorry if these are dumb questions -- I haven't dealt with antennas much in operations at sea.

 

[Baluncore]

Spatial diversity in Rx is used to combat multipath issues, AFAIK.

That may be true for VHF on the same ground plane, but in this case the antenna patterns are different due to being mounted in different positions on the vessel. One antenna on each side reduces directional data dropouts.
Land based HF spatial diversity is also achieved by having HF receive sites in different locations, connected to the central station by shorter communication data links.

At least a vertical HF antenna will have a pattern that is consistent with Tx/Rx in all directions on the surface of the water.

That is the theory for ground-plane based vertical systems, but the antennas are not operated from the surface of the sea water. The conductivity of the immediate vessel is more important than the conductivity of the undulating sea water at an unspecified distance measured in multiple partial wavelengths.

The HF system used on WW2 aircraft carriers was a compromise that worked 80 years ago, but it is now a couple of decades past it's use-by-date.

 

[tech99]

You have completely inverted the way the HF antenna system it is actually used.

The receive antennas are used in pairs for spatial diversity reception, one on each side of the flight deck. That is why they can be spaced closer together along the edge of the flight deck than would be the case for transmit antennas.

The transmit elements are not used in pairs. Transmission is from the individual more isolated whip elements, beyond the far end of the receive array, or at the other end of the vessel.

The elements only look like a vertical whip array while visiting port, when they are manually stowed in the vertical position. They are lowered into the horizontal operating position on return to sea. They are never vertical during flight operations.

See; Title: HF Receiving Antenna Arrangement on Flight-Deck Edge of Aircraft Carriers. Performances of Antennas in Different Locations and Paired Combinations are Compared. [Full text is not available]. Abstract “Five possible sites were studied for placement of 2-30 MHz twin-whip antennas on the deck edge of ships of the CVA 59 to CVAN 68 types. … It was found that siting of the antennas did not appreciably affect their performance, provided they were more than quarter wavelength at 2 MHz, approximately equal to 125 feet from the forward and after ends of the flight deck and from the island. In pairing the antennas to achieve space diversity, the most important factor is the distance between them, which should be at least 200 feet.” https://apps.dtic.mil/sti/citations/AD0888366

Anyone serve on an aircraft carrier or in the know about them?
“I served as an electronics tech onboard the USS Nimitz for three years and those were my babies. Those are two piece 35 foot HF whip antenna. They are in the down position during flight operation (and generally when underway) to keep jet wings safe. They are manually lifted when in close confines. They have nothing to do with HFDF or fall arrest.”
https://engineering.stackexchange.c...e-side-off-this-aircraft-carriers-flight-deck

Thank you for very good information.

 

[nsaspook]

Transmit whip and dual receiver whips on the USS USS Midway CV-41


I worked on those and many other antenna systems as a US Navy Radioman and Electronic Technician. We used whips and long wire/fan antennas for both HF receive and transmit functions from one end of the ship to the other.

 

[tech99]

Thank you. I also notice from the shapes displayed that your ship was constrained in her ability to maneouvre!

 

[anorlunda]

I notice in the picture in #1, the ship is anchored to stand away from the dock by 10m or so. I presume that some of those structures hanging over the side below the flight deck could be damaged if the dock came up underneath them. Such anchoring is not simple, and perhaps not dependable in all weather, so that looks like a weakness.

Do other warship designs share that feature/fault?

 

[nsaspook]

Don't know about that class of ship but my old rust bucket (LPH-3) of about the same size could dock to just about anything.



(16 Mar 1980) The US Warship USS Okinawa has docked in Singapore and its crew have gone on shore leave.

 

[davenn]

Don't know about that class of ship but my old rust bucket (LPH-3) of about the same size could dock to just about anything.(16 Mar 1980) The US Warship USS Okinawa has docked in Singapore and its crew have gone on shore leave.

what a wonderful piece of history

Makes you wonder where these guys are now ?

 

[Klystron]

View attachment 279589

The parabolic section mounted on the far left of the third photo appears to be a radar antenna. Given that the parabolic section is mounted 'on its side' and rotates horizontally, it is part of an azimuth direction finder. Estimating relative wavelength, I imagine the radar system paints other ships, medium and larger boats on the surface, most aircraft, and shoreline features above the ship's horizon.

Typical height finder radar antenna also rotates horizontally but the 'orange peel' parabolic section is mounted and pivots vertically to discriminate elevation. Depending on feedhorn design, the pictured antenna likely supplies enough elevation data depending on target range for ship operations. Compared to fixed ground radars, very cool visualizing antenna motions on a moving ship.

There must be several methods to allow for the radar antenna sweeping past the metal structures in the center of the photo. Mechanical: stop the antenna from pointing in proscribed directions or inhibit TX within proscribed azimuths. Electronic: protect RX from super close returns and/or train the system to recognize and eliminate returns from ship structures.

Thanks for explaining how the HF antennae in the OP pivot for operations.

 

[nsaspook]

https://en.wikipedia.org/wiki/AN/SPS-49
The third photo was the superstructure of this class of ship.

 

[nsaspook]

what a wonderful piece of history

Makes you wonder where these guys are now ?

A few of us from that 6 month cruise keep track online. The timeline of that trip is a piece of history as our task group was off the coast of Iran in a support mission during the failed 1980 embassy rescue mission later that year.

Some bad pictures from the flight deck of the USS Nimitz in 1980. I hitched a ride on a Marine helicopter from the USS Okinawa that landed on her during a repair mission for some communications equipment for the task group.


You can see the SPS-48 3D flat radar up front on the superstructure.
https://en.wikipedia.org/wiki/AN/SPS-48

 

[sophiecentaur]

Thank you. I also notice from the shapes displayed that your ship was constrained in her ability to maneouvre!

I can see an Anchor Ball, which would be appropriate. They also seem to have been washing their party shirts.

 

[Klystron]

https://en.wikipedia.org/wiki/AN/SPS-49
{.snip...}

From:

In 1998, the Inspector General of the Department of Defense reported that SPS-40 and SPS-49 radars in Bahrain were "unusable because the equipment operates on a frequency that interferes with the Bahrain telecommunications services". [

Something similar happened around 1975 when the US attempted to sell a dual FPS-20 air traffic control radar system to our friends, the Thais. For years FM radio in the southern basin squealed when the ATC radar beam rotated past. Interference could have been caused by a sideband or an ancillary system .

The Italians, IMS, supplied the ATC radar system at the new airport after listening to local concerns.

 

[tech99]

I can see an Anchor Ball, which would be appropriate. They also seem to have been washing their party shirts.

The shapes shown are Ball-Diamond-Ball in a vertical line, which means "constrained in her ability to maneouvre".

 

[sophiecentaur]

The shapes shown are Ball-Diamond-Ball in a vertical line, which means "constrained in her ability to maneouvre".

Right. I'll have a closer look. . . . . I see one ball and one diamond only. I remember learning 'shapes' one time and I forgot the details soon after through lack of use. However, I do remember that fishing boats used to display their cones permanently, whatever they were doing. But, in my experience, fishing boats are the 'scaffolders of the sea' when it comes to safety and regs. They had similar views against recreational sailors!But isn't any ship 'a bit constrained' when in dock?