Why do the Royal Navy's AD radars rotate?

And not act in the manner of the Tics / AEGIS ships, who have flat panels for their AD / search radars?

Is it all about height of eye, per the T45s?

Apologies if I've duffed the terms...
 
And not act in the manner of the Tics / AEGIS ships, who have flat panels for their AD / search radars?

Is it all about height of eye, per the T45s?

Apologies if I've duffed the terms...

@Ravers won’t have the answer, but he will have a dit about it, probably involving alcohol and nakedness.
 
They would have been in service years ago, but they could not decide which direction they should rotate.
 

Ravers

LE
Kit Reviewer
Book Reviewer
More than one way to skin a cat.

We chose to use big spinny things, the yanks chose flat panels.

One big spinny thing that covers all directions is probably cheaper than 4 flat panel things.

Either way, I think we can all agree that Samson (T45) is the best air defence radar on the planet. We’re doing something right.
 
You can get a single Panel array that rotates higher than multiple arrays that don't increasing the radars horizon. However you then have gaps when the array is pointed in the wrong direction.

The entire design of T45 revolves (see what i did there) around getting that Sampson radar as high as possible while still steady in most sea conditions.
 
They will still rotate like that as by procurement procedures they were probably designed when Watson Watt just finished his drawings and are attached to the back wheel of a bike with some poor matelot pedalling like fcuk
 

Yokel

LE
And not act in the manner of the Tics / AEGIS ships, who have flat panels for their AD / search radars?

Is it all about height of eye, per the T45s?

Apologies if I've duffed the terms...

The radio horizon is dictated by antenna height, and in the case of a radar the height of a target (of a specified size). I suspect that there may be something in your idea that it is going to be challenging to mount a large array at the same height above sea level.

It is possible to combine mechanical and electronic scanning.
 
My best guess is that as the ship/boat is undulating that the radar picks up multiple scans and then the processor can work out an average, the azimuth would not change but the height would. I am interested to know the answer myself to be honest, every day is a school day and having worked with radar for many years albeit firmly land based, it is not something I have ever had to think about. Surely whether it is a surveillance or tracking radar must make a difference, are they mounted on a gimbal? I honestly don't know. Surely there must be someone on here that does.
 

Hairy-boab

Old-Salt
More than one way to skin a cat.

We chose to use big spinny things, the yanks chose flat panels.

One big spinny thing that covers all directions is probably cheaper than 4 flat panel things.

Either way, I think we can all agree that Samson (T45) is the best air defence radar on the planet. We’re doing something right.

Assuming you are attacked by cricket balls.
 
The T45 has two active phased array radars back to back, which allows it to 'see' each target twice in one revolution. The Arleigh Burkes' phased arrays are those large octagonal(?) panels on the superstructure, ie, fixed. I don't know how they manage to cover their stern arcs efficiently with this set up. I do know that there is MILES of 'pipework' behind each array - check out the pictures of Cole after the attack.

Sampson has a lot, if not all the processing done in the mast, ie right beside the aerial, cutting down extensively on 'plumbing' (except for chilled water!).

So, radar 101 - height and rotation good.



The hull is sloped so that any cricket balls that get through bounce off.
 
Has anybody said "to get to the other side yet"? Oh well.....

It isn't just the RN - note that both the Fr and IT variants of Horizon use a rotating array - with the EMPAR radar in their case.

The reasoning behind it is primarily to extend radar horizon in order to counter high-speed sea skimming threats, for which you need to mount the radar as high as possible in the ship. The higher you mount the radar, the more impact it has on the overall ship design. The mast has to be stiffer, which means it has to be heavier and cumulatively that can start getting tricky from a ship stability (not ship motion) perspective.

A planar array - particularly an older one like the original SPY1 - is a heavy beast (with a fair bit of volume behind it), so trying to mount three or four of them at the end of a relatively slender mast gets very tricky. You basically end up with a choice between fixed quadrant style arrays (like SPY, APAR and CEAFAR which is a bit of an oddity) mounted at a lower height, or one or two face rotating arrays mounted atop the mast. Single-sided arrays struggle to get the update rate unless rotating at very high speed (meaning more powerful and heavier motors up the mast), so you tend to see back to back two faced arrays.

It is not true that the radar and mast height drove the T45 increase in size compared to T42, T23 - that is primarily down to accommodation and escape and evacuation standards, but it certainly had a bearing on the design. Interestingly the Australians appear to be struggling with getting the CEAFAR radar into their T26 variant - because the CEAFAR is mounted higher than most fixed arrays in order to get performance. They managed it on the ANZAC mods with a f8ckton of ballast and I suspect some certification concession tomfoolery. Not something you do voluntarily. Just goes to show that even on a beamy (nigh-on 20m!) hull with well over 8000te displacement, it's not easy.
 

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