Distance measuring apparatus and distance measuring method

A distance measuring apparatus comprising:

• means for generating a first pseudo random signal whose clock frequency is f1;
• means for generating a second pseudo random signal having the same pattern as that of the first pseudo random signal and a clock frequency f2 slightly lower than the clock frequency f1;
• a first multiplier multiplying the first pseudo random signal and the second pseudo random signal together;
• means for generating a carrier wave of a microwave;
• means for phase modulating the carrier wave by the first pseudo random signal;
• means for transmitting the phase modulated carrier wave as an electromagnetic wave to a target;
• means for receiving the electromagnetic wave reflected from the target to obtain a received signal;
• a second multiplier multiplying the obtained received signal and the second pseudo random signal together;
• a hybrid coupler receiving part of the carrier wave to output an I signal and a Q signal as two components whose phases are orthogonal to each other;
• a third multiplier multiplying signal R1 which is one of the two signals obtained by dividing the output signal of the second multiplier into two and the I signal together;
• a fourth multiplier multiplying the signal R2 which is the other of the two signals obtained by dividing the output signal of the second multiplier into two and the Q signal together;
• a first low-pass filter subjecting the output signal of the first multiplier to the low-pass filtering process;
• a second low-pass filter subjecting the output signal of the third multiplier to the low-pass filtering process;
• a third low-pass filter subjecting the output signal of the fourth multiplier to the low-pass filtering process;
• first and second squaring devices squaring the output signals of the second and third low-pass filters individually;
• an adder adding the output signals of the first and second squaring devices;
• means for generating a first pulse when detecting the maximum amplitude value of the output signal of the first low-pass filter;
• means for generating a second pulse when detecting the maximum amplitude value of the output signal of the adder;
• means for measuring a time from the time at which the first pulse is generated and the time at which the second pulse is generated;
• a rough distance measuring portion in which ½ of the measured time and the propagation speed of the electromagnetic wave are multiplied together to obtain the product as a first computation value, a difference of frequency obtained by subtracting the clock frequency f2 from the clock frequency f1 is divided by the clock frequency f1 to obtain the quotient as a second computation value, and the first computation value and the second computation value are multiplied together to obtain the product as a third computation value which is a distance to the target;
• a phase difference computing unit, in which, assuming that the output of the second low-pass filter is I′ and the output of the third low-pass filter is Q′, a phase difference θ=tan−1(Q′/I′) is obtained;
• and
• a precise distance measuring portion, in which, assuming that the wavelength of the carrier wave is λ, a precise distance=θλ/2π is obtained.