Apparatus and methods for synthetic aperture radar with digital beamforming

A method of operation of a digital beamforming synthetic aperture radar (SAR), the method comprising:

• receiving a first analog signal having a first center frequency and a first bandwidth;
• receiving a second analog signal having a second center frequency and a second bandwidth;
• mixing the first analog signal with a first local oscillator signal by at least one mixer to shift the first center frequency to a first intermediate frequency to generate a frequency-shifted first signal having a first spectral band;
• mixing the second analog signal with a second local oscillator signal by at least one mixer to shift the second center frequency to a second intermediate frequency to generate a frequency-shifted second signal having a second spectral band, the second spectral band of the second frequency-shifted signal positioned at a defined frequency offset from the first spectral band of the first frequency-shifted signal, and the second spectral band of the second frequency-shifted signal positioned non-overlapping with the first spectral band of the first frequency-shifted signal;
• combining the first and the second frequency-shifted signals by at least one combiner to generate a combined analog receive signal;
• and
• band-pass sub-sampling, via an analog to digital converter, the combined analog receive signal at less than the Nyquist rate to generate an aliased digital baseband signal having:
• i) a first guard band between a high frequency cut-off of the Nyquist bandwidth and the first spectral band of the first frequency-shifted signal, the first guard band having a width that exceeds a defined first width threshold;
• ii) a second guard band between the first spectral band of the first frequency-shifted signal and the second spectral band of the second frequency-shifted signal, the second guard band having a width that exceeds a defined second width threshold;
• iii) a third guard band between the second spectral band of the second frequency-shifted signal and a low frequency cut-off of the Nyquist bandwidth, the third guard band having a width that exceeds a defined third width threshold, and the digital baseband signal having a bandwidth that is less than the input bandwidth of the analog-to-digital converter which performs the sampling of the combined analog receive signal;
• and
• band-pass sampling the combined analog receive signal by the analog-to-digital converter having an input bandwidth to generate a digital baseband signal comprising digital signal data representative of the first analog signal and digital signal data representative of the second analog signal.