What is free space medium?

What is meant by Free space(Vaccum) in Electromagnetics? Does Free space Medium, Perfect Dielectric Medium ,Non Conducting Medium, Lossless Medium all are same ?

Free space medium in electromagnetism is a standard medium in which it is believed that there is no obstruction to electromagnetic radiation which means that EM waves travel at the speed of light.
In free space, the superposition principle is said to be exactly true.
The permeability and permeativity is that of air and it is used to determine those of other medium.

The "free space" is the closest approach to a really free space around a radiation under consideration. NO obstacles of any kind at least "many" wavelengths around. Test ranges for antenna testing use wooden towers to get the tested antenna as far off the ground as possible. Instrumentation and cabling should be treated so as not to affect antenna radiation.

Where impossible, anti-echoic chambers are used with special provisions for attenuating stray radiation or dispersion from nearby objects.

Free space is kind of ideal condition for Propagation of EM wave and travels at speed of light. air is considered to be same as free space or vacuum as both of them have nearly equal permitivity. dielectric is an non conducting medium but mostly lossy in nature. everything can be considered as a dielectric medium with conductor being a special case of dielectric medium..!!
hope it helps,
Regards.

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Free space is kind of ideal condition for Propagation of EM wave and travels at speed of light. air is considered to be same as free space or vacuum as both of them have nearly equal permitivity. dielectric is an non conducting medium but mostly lossy in nature. everything can be considered as a dielectric medium with conductor being a special case of dielectric medium..!!
hope it helps,
Regards.