Split band signal processing

1. A system for processing a broadband input signal, comprising:

a signal divider that divides the input signal into at least a higher frequency band and a lower frequency band;

a lower frequency circuit path that processes the lower frequency band;

a higher frequency circuit path that processes the higher frequency band, the higher frequency circuit path having a group delay substantially equal to the lower frequency circuit path; and

a signal combiner capable of combining the processed lower frequency band and the processed higher frequency band into an output signal.

2. A system as in claim 1 , further comprising a delay element in the higher frequency circuit path to equalize group delay between the higher frequency circuit path and the lower frequency circuit path.

3. A system as in claim 2 , wherein

the input signal or the output signal is a digital signal; and

the delay element includes a digital memory element.

4. A system as in claim 3 , wherein

the lower frequency circuit path includes a data converter,

the higher frequency circuit path includes a data converter, and

the delay element delays a digital signal in the higher frequency circuit path.

5. A system as in claim 2 , wherein

the input signal or the output signal is an optical signal; and

the delay element is an optical waveguide.

6. A system as in claim 1 , wherein the signal combiner or the signal divider includes a diplexer.

7. A system as in claim 6 , wherein:

the signal combiner or the signal divider includes an odd-order diplexer, and

a 180 degree phase shift is included in either the higher frequency circuit path or the lower frequency circuit path.

8. A system as in claim 1 , wherein the signal combiner or the signal divider includes a power divider.

9. A system as in claim 1 , wherein

the signal divider is a first diplexer;

the signal combiner is a second diplexer; and

the delay element is selected from the group consisting of a transmission line, a lumped-element ladder, a bulk acoustic wave device, and an optical waveguide.

10. A system as in claim 1 , wherein the lower frequency band covers 0 Hertz.

11. A system as in claim 1 , wherein the higher frequency band includes microwave frequencies.

12. A system as in claim 1 , wherein a transfer function H(jω) for the output signal and input signal has a substantially that magnitude response.

13. A system as in claim 1 , wherein the transfer function H(jω) for the output signal and input signal has linear phase.

14. A system as in claim 1 , wherein the lower frequency band has a smaller bandwidth than the higher frequency band.

15. A method for processing a broadband input signal, comprising:

receiving an input signal;

dividing the input signal into at least a higher frequency band a lower frequency band;

processing the lower frequency band in a lower frequency circuit path;

processing the higher frequency band in an higher frequency circuit path;

when the lower frequency circuit path has a different group delay than the higher frequency circuit path, equalizing the group delays of the lower frequency circuit path and the higher frequency circuit path; and

recombining the processed higher frequency band and the processed lower frequency band into a single output signal.

16. A method as in claim 15 , wherein equalizing the group delay includes delaying the higher frequency band.

17. A method as in claim 16 , wherein delaying the higher frequency band includes delaying a digital signal by storing the digital signal in memory.

18. A method as in claim 16 , wherein delaying the higher frequency band includes delaying an optical signal.

19. A system as in claim 16 , further comprising delaying the higher frequency band by a time delay of .tau., where .tau. is the group delay of the lower frequency circuit path.

20. A system as in claim 15 , wherein the lower frequency band covers 0 Hertz.