Hi, Jesús, Here are a few more comments for you...
On Mon, 2012-06-18 at 14:57 +0200, Jesús García LLedó wrote: > > The idea is to implement an Antenna Array to receive signals from > geostationary satellites. These kind of satellites can be seen a signal > source fixed in the sky. > Now, to make things simpler, we only want to implement a two antenna > correlator. > The signal from the Satellite arrives to each of the antennas, but as these > antennas are separate in the space, we have some delay between these two > signals. > So what we have to do is just to correct this delay, and them sum these two > signals. Making this we would improve the Signal to Noise ratio of the > resultant signal in 3dBs. > > We want to make this with broadband communication signals. At least with a > bandwidth of 100MHz. 1. For (nearly) geostationary satellites, the fringe rate will be (nearly) 0. 2. In order to add the signals in the time domain you need to align them in both time and phase. If you add them in the frequency domain, you can essentially think of each frequency channel as a narrowband time domain signal with a slower sample rate, so you still need to time align and phase align the signals before summing. If the two signals are misaligned in time by 1 ADC sample before the frequency channelization, they will be misaligned by a fraction of a frequency domain sample after channelization. Phase aligning digitized signals essentially requires the data be in complex form, so you will want to convert to complex form by using one of: I/Q sampling, Digital Down Converter, or PFB. 3. If there are mixers in the signal path, you will likely have to deal with a phase offset across the band in addition to a phase slope across the band. 4. Whether to add the signals together in the time domain or frequency domain depends on how you will use the summed data downstream. 5. Every beamformer needs a correlator of some sort (preferably built-in) for calibration. Hope this helps, Dave
