It seems this one was built in 1958 here, next to New York International.. Dunno how long it’s been gone – decades, anyway. Why did they have to build such a massive structure just for an antenna? Why don’t they have to now?
The technology of radar has come a long way since the 1950s. Frequencies are higher. Which means resolution is greater and antennas are smaller. And therefore lighter. Needing a less substantial tower to support them.
Tech also now allows “radar mosaicing”. Where instead of the controller’s scope literally being fed the receive antenna’s amplified RF signal, a computer near the antenna receives the RF from the antenna, converts that into range, bearing, and altitude data, and that is forwarded as data to a centralized system that assembles the complete air picture for a region or a whole country from the “mosaic” of hundreds of different radars’ individual small snippet of the whole. Then the controller’s scopes anywhere can be set up to display the track data within whatever shard of the large picture is relevant to their duties.
A side effect of these two things is the radar serving an airport or a major city doesn’t need to be right nearby. And generally isn’t. The radar installations are also individually much smaller. So less obvious.
Here’s a modern approach / departure / airport area surveillance radar:
So one reason a 1958 antenna was larger was they needed it to cover a larger circle?
Maybe the prevalence of transponders has allowed smaller antennas too?
Not the greatest shot (is crop from larger image), but this is the radar tower at my home airport:
So, not too different. Just a bit smaller with the higher frequencies LSLGuy mentioned.
That bit is good thinking, but incorrect.
This ASR-9 - Wikipedia has a good close-up picture of a semi-modern ATC radar antenna. Even better if you click the pic for the expanded view of it. As the caption says, the larger parabolic antenna is the actual radar transmit & receive antenna. The smaller but wider flat grid riding atop it is the transponder system send/receive antenna.
If the transponder system wasn’t needed, the collective dual antenna & support tower would be even smaller. Conversely, if the radar wasn’t needed and they relied only on the transponder system, the installation would be even smaller and lighter yet.
You didn’t ask, but …
The latest expression of this progress is the Automatic Dependent Surveillance–Broadcast - Wikipedia system. Which is increasingly deployed around the world.
In that system, each aircraft broadcasts a short data packet containing its position, velocity, identity, etc., every couple seconds. And a simple fixed vertical stick antenna on the ground picks up all the signals from all the airplanes within a couple hundred miles.
In fact the ADS-B receive antenna and data decoder is simple and cheap enough that hobbyists put them up in their backyard and hook them up to their PC. And can watch their own private version of e.g. FlightAware.
All the other airplanes can also receive and understand every else’s transmissions. So for the first time the pilots can have the same traffic awareness ATC has. That is if their airplane is equipped to process and display it. Not all are, and the operational procedures for use of that awareness is still being fleshed out.
Of course this latest system depends on everyone playing nice and any airplane that isn’t broadcasting its ADS-B data is simply invisible to everyone else. So old -fashioned bidirectional pulsed radar bouncing signals off metal planes will be with us for a long time. For military uses if nothing else.
Also malfunctions. If the transmitter breaks or bugs out, then the system won’t receive anything.