a little explanation.
Tanks, when they move, they move in platoon or company size, I think.
Forces are divided into units and formations.
Units are tactical groups of troops up to division in strength.
Formations are larger groups.
When these units and formations transit between Areas of Operation (AO), they do so in a march configuration called Order of March. During this movement the AD elements are deployed to provide AD envelope over the route.
When the force reaches an area close to where the combat is taking place, it assumes an area where the various parts of the force form up into sub-groups according to the overall plan of deployment. From this area the sub-groups Manoeuvre independently to achieve their missions and tasks in securing planned objectives. AD assets are at this time attached to various sub-groups.
These are small autonomous units.
When manoeuvring, the vehicles within the group are positioned within a given tactical formation appropriate to the combat situation, terrain or based on intelligence about the enemy. The place of AD assets attached to these groups of vehicles is determined by particular formation and situation, however in general the AD assets lack armour and are therefore not positioned as a forward element (proviso – unless there is solid intelligence on operation of enemy attack helicopters)
It is very rare to have AD assets attached to a group smaller then a company. Even in the case of a company, the group will usually be made up of various other arms and combat support elements so the group is rarely less then two reinforced companies in strength, and usually a battalion group.
In western armies, regarding local air defence, are these units accompanied by AA tracked vehicles, like the Gepard, at all times, or do they move without any defence, besides that provided by SAM units, in the rear?
There are no hard and fast ways to define tactical AD operations in ‘Western’ armies because these include NATO and non-NATO forces.
The systems used even by NATO countries are only standardised in terms of digital battle information sharing and Identification Friend or Foe (IFF) signal transmission. In general the NATO forces use more surface to air missiles (SAM) then guns. The reason is that modern attack aircraft can deploy their weapons out of effective gunnery range.
If so, how do they cope with attacks by enemy helicopters and aircraft?
However the threat of attack helicopter using tactics to negate missile capabilities are a serious threat, and so most armies combine missile equipped vehicles with automatic cannon vehicles (either tracked or wheeled) in the 20mm to 40mm calibre.
Is there any site where I can find out about current doctrine for armoured vehicles deployments and organic composition of units?
This is hard. Much of AD doctrine has to do with technology they employ. Both missile and gun vehicles use advanced radar, data, and computational systems which are always in transition due to development. Much of this has to do with developments in aerospace technology, air weapons, and jamming of all these systems, as well as countermeasures to negate the jamming, and counter-countermeasures in turn to negate the work of own electronic warfare supporting units.
Most tactical units deploy in teams of two, or batteries of four, usually mixed missile/gun.
At higher echelon of command (above division), the AD units are usually static, and deploy by batteries with four to eight launchers and a fire control centre (FCC) which includes much more powerful radar and target acquisition and tracking systems.
The above is a start.
AD is a vast area of defence science. It would be very difficult to summarise it here.
There are some useful books you can begin with.
Guided Weapons (Land Warfare, Brassey's New Battlefield Weapons Systems and Technology Series Into the 21st Century, V. 5) (Hardcover)
by T. K. Garland-Collins, C. A. Sparkes, R. G. Lee (Editor), J. F. Rouse (Editor)
You should be aware that AD of ground units is part of an integrated multi-service doctrine. NATO forces in general expected (during Cold War) to not have to face the full brunt of air attacks without air cover from their air forces.
There was, and is a greater reliance on short range man-portable missiles and longer range vehicle mounted systems such as Roland used by German and French armies. German Gepard was designed based on German experience in WW2. American Army took a leaf out of the Air Force book by mounting what is essentially an aircraft weapon in a Gatling configuration atop one of the most used APCs in the World, the M113 to come up with the M163 Vulcan. The new Linebacker combines a 25mm auto cannon with a SAM system. The French used a tank chassis to design the AMX30 DCA twin 30 mm AFV. The variety of self-propelled AD vehicles is truly astounding.
With the introduction of the infantry fighting vehicle (IFV), the infantry tactical formation has acquired a relatively lethal ‘hedgehog’ of short range anti-helicopter gunnery capability with a company at full strength being able to open fire with from 8 to 14 single barrel weapons.
Many other vehicles in a tactical formation have less powerful AD weapons in the shape of heavy machine gun (HMG) in the NATO standard 12.7mm or 0.5 inch calibre. These are last resort, very short range (1000m) weapons with Mark 1 eyeball for Fire Control
NATO tactic is to have someone in the group on helicopter overwatch. The battlegroup HQ depends on warning of approaching enemy aircraft from radars at higher echelon in the rear to be available via their battle management systems.