Help in designing of Dickei Radiometer

[amit261287]

Any body help me out to design a DIckei Radiometer..>!!!
how to make it compact as far as possible
currently i m reading neil skou..!!

mail: amit261287@gmail.com

 

[davenn]

weclome to the forum

any particular frequency in mind ?

Dave

 

[amit261287]

weclome to the forum

any particular frequency in mind ?

Dave

FREQUENCY: 6.93 GHz
I WANT TO KNOW WHAT CHANGESMENT I HAVE TO MAKE IN DIKE RADIOMETER SO THAT ITS ACCURACY AND RELIABILITY WILL INCREASE AS WELL AS I WANT TO MAKE IT COMPACT AS FAR AS POSSIBLE.
I ALSO WANT TO REPLACE WAVEGUIDES WITH COAXIAL CABLES TO REDUCE ITS SIZE.
CAN U PLZZ GIVE ME SUGGESTION FOR THAT?
THANKSS..!!

 

[jiripolivka]

I am ready to help you and answer your questions. I built several Dicke radiometers, now I am running a 33 GHz one as a solar radio telescope.
At 6.3 GHz you can find good components in coax and microstrip. The most difficult is to find a good Dicke switch. A switching circulator is best but not easy to find. My radiometers utilized mechanical switches like Dicke used, only my attenuating vane is like a propeller. It is mechanically balanced and the waveguide attenuator has two cycles per revolution. A photosensor controls the synchronous detector.
With a satellite LNB having electrically switched polarization I found easy to use it as a polarization-switching Dicke or a polarimeter. If you can design such device at 6.3 GHz, the switching frequency can be up to 30-40 Hz.
If you wish I have a published paper on such design, in Czech, and an English translation of the text. I can send it to your e-mail.
Best regards, "jpolivka@spaceklabs.com".

 

[amit261287]

I am ready to help you and answer your questions. I built several Dicke radiometers, now I am running a 33 GHz one as a solar radio telescope.
At 6.3 GHz you can find good components in coax and microstrip. The most difficult is to find a good Dicke switch. A switching circulator is best but not easy to find. My radiometers utilized mechanical switches like Dicke used, only my attenuating vane is like a propeller. It is mechanically balanced and the waveguide attenuator has two cycles per revolution. A photosensor controls the synchronous detector.
With a satellite LNB having electrically switched polarization I found easy to use it as a polarization-switching Dicke or a polarimeter. If you can design such device at 6.3 GHz, the switching frequency can be up to 30-40 Hz.
If you wish I have a published paper on such design, in Czech, and an English translation of the text. I can send it to your e-mail.
Best regards, "jpolivka@spaceklabs.com".

hey thanxx a lot for your help..!!
i just want to know that now coaxial cables are coming within the range of 18ghz so can i use them instead of waveguides in my Dicke Radiometer operating on freq of 6.93Ghz .
please please send me your published papers. Thanxx :-D
Email: amit261287@gmail.com

 

[davenn]

FREQUENCY: 6.93 GHz
I ALSO WANT TO REPLACE WAVEGUIDES WITH COAXIAL CABLES TO REDUCE ITS SIZE.
CAN U PLZZ GIVE ME SUGGESTION FOR THAT?
THANKSS..!!

not a good idea coax cable at that frequency is VERY lossy, short waveguide feeds right at the antenna would be your best choice

Dave

 

[amit261287]

not a good idea coax cable at that frequency is VERY lossy, short waveguide feeds right at the antenna would be your best choice

Dave

hey bro ,
i want to know which is the best material suitable for my radiometer case (box)??
which material should i use plzz help,,,,,!!!!
what type of switch should i use for best result...!!!

 

[jiripolivka]

Hello Amit:

I saw the claims above that coaxial devices are not suitable as they are lossy.
Everything depends upon what your specifications are. For a radiometer, temperature resolution is usually specified. It is a function of system noise temperature, predetection bandwidth and integration constant. So even with lossy devices you can design a good radiometer for your purpose.
Waveguides are preferred but for frequencies < 2-3 GHz they are bulky and short coaxial sections can serve you well.
Concerning the radiometer case there are many different situations and advices to follow.
Best of all, if you let me know more about your radiometer, I can better advise you.

 

[amit261287]

Hello Amit:

I saw the claims above that coaxial devices are not suitable as they are lossy.
Everything depends upon what your specifications are. For a radiometer, temperature resolution is usually specified. It is a function of system noise temperature, predetection bandwidth and integration constant. So even with lossy devices you can design a good radiometer for your purpose.
Waveguides are preferred but for frequencies < 2-3 GHz they are bulky and short coaxial sections can serve you well.
Concerning the radiometer case there are many different situations and advices to follow.
Best of all, if you let me know more about your radiometer, I can better advise you.

Hey Bro,
Please Help me out .
Listen, i am designing radiometer (Dicke type) working in CJ band so, i want to know the best type of Dicke switch that can i use which have minimum loss.

 

[jiripolivka]

Hello Amit:

I do not know what "CJ" band is. If it is C-band, ~4 GHz, you can find several solutions:
1. Original Dicke modulator utilized an attenuating disk rotated by a motor so it entered a waveguide section to attenuate by ~20 dB, or was pulled out to get 0 dB loss. I used a similar design but instead of a round disk I used a "propeller" with two symmetrical wings. This offers no vibration and twice the frequency, two per revolution. The position of the propeller is sensed with a photosensor and drives the sync detector. The photosensor should be mounted so the phase of the "reference" pulses can be adjusted for the best output.
2. There are MMIC switches now available, by Analog Devices, Linear Technology and RFMD, with a low loss and a good isolation, to be used as switches. You can also buy or design a PIN-diode switch. All such switches have >1 dB loss which makes them worse than the above having 0 dB loss.
3. A nice solution was used by Paglione, also at 4 GHz: to avoid switch loss, he used two LNAs before his mixer. He switched LNA DC bias to alternate, one of the LNAs was connected to antenna, the other, to reference noise source.
You can see that I chose a similar approach in my Dicke radiometer at 11 GHz. The LNB I used can switch the linear polarization of input signal, also by having two alternating LNAs before mixer.
Then I inserted a Mylar attenuating foil in the LNB input pipe so its emission only gets into one LNA while the other input is exactly perpendicular. The result is excellent. Maybe you could also find a C-band LNB with this feature, or, you can design it.