So the limitations are the aircraft's structure reflecting back into the radar, and the terrain providing the aircraft is low to the ground and within the resolution cell?
Those are some of the limitations, to be sure. And your look down angle is also limited by your altitude. Without MTI (and these early radars did not have MTI) looking down will show you the ground out at the end of the range trace. The more you look down, for a given aircraft altitude, the shorter you maximum range to track or detect another aircraft will be.
I think you are using resolution cell incorrectly though. The resolution cell is the time occupied by the radar pulse. It is a moving space defined in depth by the duration of the pulse and in width and height by the beamwidth of the radar. The resolution cell is the area where a radar can detect a target is present but cannot resolve the number of targets present in the cell. And it has nothing to do with maximum range.
I thought you wanted to reduce the errors?
Errors are how the radar knows where the target is. Yes, you want to keep the errors as small as possible, but to do this you must first find the errors, so you can counter or null them. Every track has errors, no track is perfect, so you want to make the errors as small as possible.
The Conical scan is how the radar, in this case, derives the errors to know what direction to drive the antenna, so as to null the errors. There are other ways to develop these angle errors, Con scan is just one of the oldest techniques.
Kind of like this, only substitute target track for missile:
View: https://www.youtube.com/watch?v=F4Dvc1NrZJI
That I get, I said what I said because the palmer-scan was better for holding a lock, while the raster scan was faster for going left-right/up-down.
The Palmer scan is not better at anything, it is simply the combination of two different scan types at the same time. In this specific application the Conical scan is required to track, the Raster is required to search. When the radar has both types of scans active at the same time it is called a Palmer scan. The radar cannot both scan and track at the same time, it is one or the other.
So while searching, or scanning a large volume of space, it is using a Raster scan, it just so happens the beam also has a Conical scan at the same time. While tracking the radar stops the Raster scan, stares at the target, and uses its Conical scan to derive tracking errors.
I would not have thought the antenna would have carried that much inertia... learn something new everyday
For a bidirectional Raster scan, which by definition changes direction for every bar of the raster, you must overcome that inertia, no matter how small or large it may be. For a Helical scan there is no need to overcome anything except friction, the antenna just goes around and around in the same direction at the same rate, stepping up at some point in each revolution. A unidirectional Raster may do the same thing as a Helical, and have no inertia to overcome, or it might stop and retrace, having to overcome inertia each stop.
Meaning it's based on the device that swivels the antenna and rotates it? And I'm guessing the feed-horn is not designed to not rotate round and round, so it wouldn't be designed to simply center itself so it would be able to simply point in whatever direction the swivel is aimed so it just goes left, right, left, right, left, right, or left, right, up, left-right, up, left, right, up, left right, down... and so on?
No, the portion of the antenna mechanism that rotates the antenna and grossly moves the beam around in space in elevation and azimuth is unrelated to the skewed feed that provides the Conical scan.
A fixed feed antenna, like the SCR-720, just stares (with its beam) straight ahead of the dish. The device the antenna is mounted on (often called a pedestal) then moves the beam around in space, in the case of the SCR-720 in a Helical fashion (360 degrees of rotation, step up, 360 degrees of rotation, step up, etc), in the case of the APG-1/2 in a Raster.
Completely separate from that is the Conical scan. It rotates the beam of the antenna in small circles out in front of the antenna, independent of how the pedestal moves the dish. To do this it is intentionally skewed, mechanically, so that the beam does not go out directly ahead of, and on axis with, the dish. It goes slightly off center of where the dish is looking.
This explains the basic Conical portion of the operation pretty well
Conical scanning - Wikipedia
The key is above, when I said to do this the antenna feed is skewed, mechanically, to make this happen. This is a simple design. To allow the feed to index from this mechanically skewed position to on boresight would complicate the feed assembly. It is done on some systems, but not many at all.
More often when you want to allow both Conical scan (a spinning off boresight axis beam) and on boresight axis fixed beam operation you don't use a mechanically skewed feed assembly. Instead you wobble the dish itself to create the circular beam motion about the boresight axis. This would result in a nutating beam.
T!