Do helicopters carry radar equipment? Is so, where is it placed and what type is used?
Most helicopter don't carry radar; there is no need for it. 

In civil helicopters radar is typically used for weather detection. In most use cases there is not real need for it because helicopters are usually operating under daytime Visual Flight Rules (VFR) and are staying away from clouds. For maritime helicopters that are used in search and rescue operations or off-shore operations on oil-rigs, weather is often installed. The typical location is in a radome in the nose of the helicopter. Examples are the Honeywell Primus 660 or Rockwell Collins RTA-4100

Military helicopters use radar for detecting objects. Depending on the nature of the mission the helicopter is designed for, the radar is underneath (usually for navy operation, providing sea surface detection capabilities, see for example the navy version of the NH90) or on top of the rotor (to look over obstacles such a hills / trees  and provide fire control to their missiles). An example is the AN/APG-78 longbow fire control radar.