Limitations of Noise temperature of Antenna, Feeder cable and LNA
I'm not 100% sure what you are driving at because what you've written seems to miss the word "below" like here: -


  1) Why can't the noise temperature of antenna and feeder cable be
  reduced a certain limit or in other words its limitations?


Is the word "below" missing between "reduced" and "a"? If it is then here's my attempt at an answer.

If what the antenna receives is non-man-made background noise, that noise will be at a power level dependant on the temperature of the stuff that made it. This means that you can cool your antenna and feeder as much as you want but you'll still end up with the noise from what you receive.

It's Planck's law that dictates the total power per Hz emitted from an object at temperature T: -

\$P_V = \dfrac{2\pi h f^3}{C^2} \times\dfrac{1}{e^{\frac{h f}{kT}}-1}\$

Where h is Planck's constant, f is frequency, K is Boltzmann's constant, T is temperature in kelvin and c is speed of light.

I don't 100% know if this answers your question given the word I've added to make sense of it. Please let me know if it isn't and I'll try and correct it.

This also seems to be quite a good paper on the subject. It's called "Noise in antennas" but I can't seem to fathom out who wrote it.