September 26, 2005
YEAHHH
I done ... yess .. master saya officially dah abis with my last poster presentation .. yahuuuuuu
September 01, 2005
endless thot
hahahahaha .. i'm doing something impossible... my sv shud award me with dr if i able to make it possible.. :)
Dear xxx,
Many direct detect microwave radiometers have been successfully built. The xxx and xxx spaceborne radiometers, both of which I am involved with, use them. Many other ground based sensors do, too. It isn't possible to build one without a significant amount of amplification before the detector. This is because the natural thermal emission signal is too weak for the detector without it. In Dicke's case, the amplification was made after a frequency downconversion for the same fundamental reason - his signal was also too weak. Direct detection at W-Band will be very difficult because low noise amplifiers at that frequency are rare and expensive and because higher power gain stages at that frequency (needed after the low noise amplifier) are also problematic. If you need to build a W-Band radiometer, it will be much more economical to do so using frequency downconversion. To decide how much amplification you will need, look at the Tangential Signal Sensitivity (Tss) value of your detector. You will need the signal to be detected at least 10 times bigger (in power) than Tss so you can reliably measure it.
Good luck,
xx
Quoting "xxx":
> Thanks xx on your mail. Actually I plan to construct a radiometer
> receiver using a direct detection ( crystal value) architecture. I
> have a diode detector with zero bias, antenna .. Both at W band. As I
> don't have amplifier at W band for the pre-detection amplifier, I plan
> to use a lock in amplifier after diode detector to improve diode
> detector sensitivity. Do you know any succesfull radiometer using a
> direct detection ( crystal value)? I saw them in theory but I'm not
> sure if it applicable to make it real. I've read a paper from Dicke on
> Microwave radiometer. He was using a lock in amplifier but with super
> heteorodyne receiver. Do you think without amplification before
> detection, it will be possible for me to detect the emission?
> Thanks in advance.
Dear xxx,
Many direct detect microwave radiometers have been successfully built. The xxx and xxx spaceborne radiometers, both of which I am involved with, use them. Many other ground based sensors do, too. It isn't possible to build one without a significant amount of amplification before the detector. This is because the natural thermal emission signal is too weak for the detector without it. In Dicke's case, the amplification was made after a frequency downconversion for the same fundamental reason - his signal was also too weak. Direct detection at W-Band will be very difficult because low noise amplifiers at that frequency are rare and expensive and because higher power gain stages at that frequency (needed after the low noise amplifier) are also problematic. If you need to build a W-Band radiometer, it will be much more economical to do so using frequency downconversion. To decide how much amplification you will need, look at the Tangential Signal Sensitivity (Tss) value of your detector. You will need the signal to be detected at least 10 times bigger (in power) than Tss so you can reliably measure it.
Good luck,
xx
Quoting "xxx"
> Thanks xx on your mail. Actually I plan to construct a radiometer
> receiver using a direct detection ( crystal value) architecture. I
> have a diode detector with zero bias, antenna .. Both at W band. As I
> don't have amplifier at W band for the pre-detection amplifier, I plan
> to use a lock in amplifier after diode detector to improve diode
> detector sensitivity. Do you know any succesfull radiometer using a
> direct detection ( crystal value)? I saw them in theory but I'm not
> sure if it applicable to make it real. I've read a paper from Dicke on
> Microwave radiometer. He was using a lock in amplifier but with super
> heteorodyne receiver. Do you think without amplification before
> detection, it will be possible for me to detect the emission?
> Thanks in advance.
Subscribe to:
Posts (Atom)