초록

A method for simulating a Doppler signal under stationary conditions is described. The method includes sampling a radar return signal at an integer multiple of the return signal frequency plus a fraction of the return signal period and generating a base band signal from the samples.

대표청구항 ▼

1. A method for simulating a Doppler signal under stationary conditions, in a radar altimeter, said method comprising:sampling a radar return signal at an integer multiple of the return signal frequency plus a fraction of the return signal period; andgenerating a base band signal from the samples. 2

1. A method for simulating a Doppler signal under stationary conditions, in a radar altimeter, said method comprising:sampling a radar return signal at an integer multiple of the return signal frequency plus a fraction of the return signal period; andgenerating a base band signal from the samples. 2. A method according to claim 1 wherein sampling a radar return signal comprises:down sampling a radar return signal to an intermediate frequency (IF) signal; andsampling the IF signal at an integer multiple of a period of the IF signal plus a fraction of the IF signal period. 3. A method according to claim 2 wherein sampling the IF signal comprises:receiving a decimation period that is an integer multiple of a period of the IF signal plus a fraction of the IF signal period;sampling the IF signal at the decimation period; andproviding a base band signal from the IF signal samples. 4. A method according to claim 1 wherein the fraction of the return signal period is a negative fraction of the return signal period. 5. A method according to claim 2 wherein the radar altimeter includes a processor receiving an IF signal, the processor including a decimation to base band function, decimation frequency logic, and a radar altimeter processing function, said method comprising:determining a decimation period in the decimation frequency logic that is an integer multiple of a period of the IF signal plus a fraction of the IF signal period;providing the decimation period to the decimation to base band function;sampling the IF signal at the decimation period with the decimation to base band function; andproviding a base band signal from the decimation to base band function to the radar altimeter processing function based on the IF signal-samples. 6. A radar altimeter comprising:a memory;a sequencer for modulating a first signal;a transmitter coupled to said sequencer for transmitting a radar signal including the modulated first signal toward the ground;a receiver for receiving a reflected radar signal from the ground, the received radar signal including the modulated first signal;a digitizer coupled to said receiver for generating digital samples of the modulated first signal at an intermediate frequency (IF), the IF digital samples being stored in said memory; anda processor coupled to said memory, said processor sampling the stored IF digital samples at an integer multiple of the period of the stored IF digital samples plus a fraction of a period of the stored IF digital samples. 7. A radar altimeter according to claim 6 wherein said processor comprises:a narrow band filter receiving the IF digital samples stored in said memory;a decimation to base band function receiving the filtered IF digital samples from said narrow band filter;decimation frequency logic causing said decimation to base band function to sample the IF digital samples received from said narrow band filter at a frequency whose period is at an integer multiple of the period of the IF signal plus a selected fraction of the period of the IF signal; anda radar altimeter processor to determine an altitude based on a base band signal received from said decimation to base band function, the base band signal being the samples taken by said decimation to base band function. 8. A radar altimeter according to claim 7 wherein the selected fraction of the period of the IF signal is programmable in said decimation frequency logic. 9. A radar altimeter according to claim 7 wherein the integer multiple of the period of the IF signal is programmable in said decimation frequency logic. 10. A radar altimeter according to claim 6 wherein the fraction of the period of the stored IF digital samples is a negative fraction of the period of the stored IF digital samples. 11. A decimation frequency logic unit for a radar altimeter, said unit configured to provide a sampling rate to an external device receiving an IF signal, the sampling rate at a frequency whose period is at an integer multiple of the period of IF signal plus a selected fraction of the period of the IF signal. 12. A decimation frequency logic unit according to claim 11 wherein the selected fraction of the period of the IF signal is programmable. 13. A decimation frequency logic unit according to claim 12 wherein the selected fraction of the period of the IF signal is negative. 14. A decimation frequency logic unit according to 11 wherein the integer multiple of the period of IF signal is programmable. 15. A method for sampling a signal to avoid a zero return, said method comprising sampling the signal at an integer multiple of a period of the signal plus a fraction of the signal period.