micro satellite transponder design

[bdoon esim]

Hi all,
I'm a communication engineering final year student, my project is about designing a low power consumption transponder..
I have to perform a matlab simulink for a ku or c band transponder and im having difficulties in that.. how to start and any help plz .. thx

 

[cct314]

Fundamental question: Do you want said transponder to be frequency-inverting or not?

 

[bdoon esim]

I am sorry i couldn't actually understand what u mean but I think no

 

[cct314]

I would recommend a bit of web research on your part.

What you seem to be asking about is a "bent pipe" type of transponder - that is, a signal that is put into the input of the transponder is frequency-converted and amplified, appearing on the output at a different frequency. These do not process the signal in any other way and are suitable for analog or digital signals.

The question about the "frequency inversion" has to do with a fundamental property of frequency conversion (say, via heterodyne) in which "high side" conversion (e.g. a local oscillator on a frequency above that of the input frequency) yields spectral inversion (e.g. increasing frequency components on the input translate to decreasing frequency components on the output) whereas "low-side" conversion does not: On the topic of Heterodyne, I would recommend this article:

https://en.wikipedia.org/wiki/Heterodyne

A typical "bent pipe" transponder usually implies a double conversion in which the input frequency is converted to a MUCH lower frequency (the "IF" or "Intermediate Frequency) a bandpass filter is applied, and then that frequency is converted up to the desired output frequency. The reason for this is that at the very high frequencies it is generally impractical to provide the necessary "brick wall" type of filtering necessary for frequency re-use found on typical space-link applications, but at lower frequencies (say, 10.7 MHz or 45 MHz) it is quite easy to have a very "sharp" filter that is just a few 10's of kHz or even a few MHz wide.

As you might suspect, as is the case with ordinary superheterodyne principles (e.g. ordinary radios) "front-end" filtering is required to suppress the "images" that would result in the heterodyne conversion process, both on the down-conversion to the IF and again in the up-conversion from the IF to the output frequency.


Finally, you did mention a "low power consumption" transponder and "C" and "Ku" band. For practical reasons, were one to design a microsat, one would not use C or Ku band, but rather a much lower frequency (say, L band or S band - or even something in the 435-438 MHz range where there are Amateur Radio Satellites) and this is due to constraints of "link budget" - that is, the limits of available RF output power, the sensitivity achievable in the receive *SYSTEM* (filters, amplifiers and other losses) and the gain figures of antennas that could be realized on a small microsat.

You have a lot of reading to do!

 

[bdoon esim]

Thx a lot.. mmm the ku and c band was chosen by my professor when i asked him what band should i consider s or even lower he said u may choose one of ku or c band !! I'm even confused now.. sure there is a lot of reading waiting for me..