Home-made radar
Hi,
The range You need is high, so the ability to achieve it depends on some application details:
What is the height of the antenna?:
a). If the antenna is ground/marine-based and the hieght is limited to 10-30m then You will have to use VERY high power transmitter in decimeter wavelength range. In this case some birds/cats around such a radar and all of the neighbors TVs (as well as some neighbors
) will say good buy forever (if someone will allow You to power it on at all). The dimensions of such an antenna may be also in few good meters range and the weight is few tonns.
b). If the antenna is intended to be installed on the airborne object (even baloon, by the way), this may let You use santimeter wavelength RF. First, this will reduce the dimensions and weight of the antenna, then it will make Your radar more precise and less powerfull and will may help with legal issues (power/frequency)
I think You may try to use even GaAs HEMT or SiGe LNA this will help increasing the range, the only problem is that the minimum range will also be high, because it may be hard to achieve high dynamic range with these LNAs. If the frequency range will allow, You may use double gate FET LNA, this will give good dynamic range.
You should provide VERY good isolation between the transmitting and receiving path by using (even in combination) of circulators, gas discharge shorts and switching diode protection.
It may be good to modulate Your radar frequency by pseudo random noise sequence, this will let You determine the distance more precisely and also will help to increase overall system gain thus increasing maximum radius. Contras are the incresed bandwidth and complicated signal processing especcially at the reciever.
Regards,
F.S.