Lightweight doppler navigator

Claim 2

An FM/CW Doppler aircraft navigation system comprising; an antenna for radiating a beam of radio energy and for receiving Doppler shifted echo returns of said radiated energy; a transmitter for energizing said antenna; a modulator for frequency modulating said transmitter; whereby said transmitter will provide a frequency modulated signal at its output; a modulator control means for varying the frequency of said modulator; a receiver connected to said antenna; a mixer and filter means having two inputs and one output; one of said inputs being connected to said transmitter to receive unshifted frequency modulated signals therefrom; the other of said inputs being connected to said receiver to receive Doppler shifted echo returns therefrom; the output of said mixer and filter means providing a frequency spectrum in the range of said Doppler shift frequencies, the amplitude of said spectrum falling to substantially zero at Doppler frequencies associated with multiples of the half wavelength of said modulating frequency; and means for scanning said frequency spectrum and detecting said Doppler shift frequencies at said amplitude zeros.

Claim 3

An FM/CW Doppler aircraft navigation system as defined in claim 1 wherein said beam of radio energy comprises at least one narrow width fan shaped beam.

Claim 4

An FM/CW Doppler aircraft navigation system as defined in claim 2 wherein said frequency scanning and zero detecting means is adapted to detect a first Doppler shift frequency at an amplitude zero associated with an nth multiple of the half wavelength of said modulating frequency; and further comprising means for determining a second Doppler shift frequency of an amplitude zero associated with the nth multiple of a second modulating frequency; said first and second modulating frequencies being so related that no amplitude zeros will fall between said first and said second Doppler shift frequencies.

Claim 5

An FM/CW Doppler aircraft navigation system as defined in claim 3 wherein said modulator control means comprises means for stepping the frequency of said modulator means such that said first and said second modulating frequencies bear a fixed, predetermined ratio with one another; the output of said mixer and filter means being connected to the input of said frequency scanning and zero detecting means; one output of said frequency scanning and zero detecting means being connected to said modulator control means; whereby, when said frequency scanning and zero detecting means detects said first Doppler shift frequency at said first modulating frequency, a first signal is sent from said frequency scanning and zero detecting means to said modulator control means to cause said modulator control means to step the frequency of said modulator means to said second modulating frequeNcy; said frequency scanning and zero detecting means being further adapted to detect said second Doppler shift frequency; said frequency scanning and zero detecting means being still further adapted to detect a third Doppler shift frequency, immediately adjacent said second Doppler shift frequency, at an amplitude zero associated with the (n+1)th multiple of the half wavelength of said second modulating frequency; said frequency scanning and zero detecting means providing a second signal to said modulator control means when said third Doppler shift frequency is detected to cause said modulator control means to return said modulator to said first modulating frequency.

Claim 6

An FM/CW Doppler aircraft navigation system as defined in claim 3 wherein said modulator control means comprises means for varying the frequency of said modulator continuously; and further comprising means for preselecting said second Doppler shift frequency, said means comprising a second Doppler shift frequency filter and zero detecting means; and still further comprising a two position switch means, said switch means being adapted, in one position thereof, to connect the output of said mixer and filter means to said frequency scanning and zero detecting means, and, in the other position thereof, to said second Doppler shift frequency filter and zero detecting means; said switch being in said first position when said modulator is at said first modulating frequency; said frequency scanning and zero detecting means, and said second Doppler shift frequency filter and zero detecting means each being connected to said modulator control means and said switch means; said frequency scanning and zero detecting means being still further adapted to detect a third Doppler shift frequency, immediately adjacent said second Doppler shift frequency, at an amplitude zero associated with the (n+1)th multiple of the half wave length of said second modulating frequency; whereby, when said first Doppler shift frequency is detected by said frequency scanning and detecting means, a first signal is provided to said modulator control means to cause it to begin varying said modulator frequency continuously, and a second signal is provided to said switch means to cause it to acquire said second position; and wherein said second modulating frequency comprises that modulating frequency at which an amplitude zero is detected by said second Doppler shift frequency filter and zero detector means; and whereby, when said second Doppler shift frequency is detected by said second Doppler shift frequency filter and zero detector, a third signal is provided to said modulator means to cause it to remain at said second modulating frequency, and a fourth signal is provided to said switch means to cause it to acquire said first position; and whereby, when said third Doppler shift frequency is detected by said frequency scanning and zero detecting means, a fifth signal is provided to said modulator control means to cause it to return said modulator to said first modulating frequency.

Claim 7

An FM/CW Doppler aircraft navigation system as defined in claim 2 and further comprising; a variable filter and zero detecting means, said filter being in the range of said frequency spectrum and including zero Doppler frequency shift; a control unit; a switch means being adapted, in one position thereof, to connect said mixer and filter means to said variable filter and zero detecting means, and in the other position thereof, to connect said mixer and filter means to said frequency scanning and zero detecting means; said control unit being programmed to control said modulator control means and said switch means; a computer means receiving data from said modulator control means and from said frequency scanning and zero detecting means and providing information to said control means; whereby, at the start of an operating cycle, said control means causes said switch to be in said one position, and further causEs said variable filter means to be positioned at zero Doppler shift frequency, and still further causes said modulator control means to vary said modulating frequency continuously until said variable filter and zero detecting means detects an amplitude zero at zero Doppler shift frequency associated with an nth multiple of the half wavelength of a first modulating frequency; a value representative of said first modulating frequency being fed to said computer means; said control means causing said modulator control means to step the modulating frequency to a second modulating frequency, determined by said computer means, and causing said switch means to acquire its other position, when said zero Doppler shift frequency is detected; said frequency scanning and zero detecting means being adapted to scan upwards in frequency from said zero Doppler shift frequency and to detect a first Doppler shift frequency, said first Doppler shift frequency being the Doppler shift frequency next adjacent said zero Doppler shift frequency at which a zero amplitude appears, and which is associated with the nth multiple of said second modulating frequency; a value representative of said first Doppler shift frequency being fed to said computer means.