Frequency analysis method and sweep type spectrum analyzer

A sweep type spectrum analyzer comprising:

• a time-to-frequency converter, said time-to-frequency converter comprising a local oscillator for generating a main swept-frequency signal;
• a first multiplier that multiplies the main swept-frequency signal generated from said local oscillator by a signal to be measured;
• and an intermediate frequency filter having a bandpass width, and being arranged such that a frequency component included in the signal to be measured is frequency-discriminated in accordance with a lapse of time associated with a sweep of the main swept-frequency signal thereby converting the frequency-discriminated components to intermediate frequency signals arranged by frequency according to the lapse of time;
• a second multiplier for multiplying each of the intermediate frequency signals outputted from said time-to-frequency converter by an inverse swept-frequency signal, said inverse swept signal having a frequency-sweeping span in which the frequency of the inverse swept-frequency signal changes in a direction inverse to that of changes in frequency of the associated intermediate frequency signal;
• and
• a resolution filter supplied with the results of the multiplications of said second multiplier for extracting a signal component having a constant frequency,
• wherein each signal extracted through said resolution filter is displayed on a display device as a frequency spectrum included in the signal to be measured.

A sweep type spectrum analyzer comprising:

• a time-to-frequency converter, said time-to-frequency converter comprising a local oscillator for generating a main swept-frequency signal;
• a first multiplier for multiplying the main swept-frequency signal generated from said local oscillator by a signal to be measured;
• and an intermediate frequency filter having a bandpass width, and being arranged such that a frequency component included in the signal to be measured is frequency-discriminated in accordance with a lapse of time associated with a sweep of the main swept-frequency signal thereby converting the frequency-discriminated components to intermediate frequency signals arranged by frequency according to the lapse of time;
• and
• a plurality of inverse chirp correction units provided in parallel with each other, each of said inverse chirp correction units comprising:
• a second multiplier for multiplying each of the intermediate frequency signals outputted from said time-to-frequency converter by an inverse swept-frequency signal, said inverse swept signal having a frequency-sweeping span in which the frequency of the inverse swept-frequency signal changes in a direction inverse to that of changes in frequency of the associated intermediate frequency signal;
• a resolution filter supplied for extracting a signal component having a constant frequency from a signal outputted from said second multiplier;
• a detector for detecting the signal component extracted through the resolution filter;
• and
• a sample-and-hold circuit for sampling and holding the detected output from said detector at the end of each sweep of the inverse swept-frequency signal;
• wherein said plurality of inverse chirp correction units are sequentially operated with a time difference therebetween, and sample-hold signals of the sample-and-hold circuits are sequentially outputted.

A sweep type spectrum analyzer comprising:

• a time-to-frequency converter, said time-to-frequency converter comprising a local oscillator for generating a main swept-frequency signal;
• a first multiplier for multiplying the main swept-frequency signal generated from said local oscillator by a signal to be measured;
• and an intermediate frequency filter having a bandpass width, and being arranged such that a frequency component included in the signal to be measured is frequency-discriminated in accordance with a lapse of time associated with a sweep of the main swept-frequency signal thereby converting the frequency-discriminated components to intermediate frequency signals arranged by frequency according to the lapse of time;
• a quadrature detector provided at the output side of said time-to-frequency converter;
• and
• a plurality of inverse chirp correction units provided in parallel with each other at the output side of said quadrature detector, each of said inverse chirp correction units comprising:
• a pair of second multipliers for multiplying an inverse swept-frequency signal by a real part signal and by an imaginary part signal outputted from said quadrature detector, respectively, said inverse swept signal having a frequency-sweeping span in which the frequency of the inverse swept-frequency signal changes in a direction inverse to that of changes in frequency of the associated intermediate frequency signal;
• a pair of low-pass filters each constituting a resolution filter, each of said low-pass filters extracting a base band signal obtained from the result of the multiplication of the associated second multiplier;
• a pair of squaring circuits for squaring the output signals from said pair of low-pass filters;
• an adder for summing up the results of said pair of squaring circuits to find a power of a frequency spectrum included in the signal to be measured;
• a detector for detecting the result of the addition of said adder;
• and
• a sample-and-hold circuit for sampling and holding the detected output from said detector at the end of each sweep of the inverse swept-frequency signal;
• wherein said plurality of inverse chirp correction units are sequentially operated with a time difference therebetween, and sample-hold signals of the sample-and-hold circuits are sequentially outputted.

A sweep type spectrum analyzer comprising:

• a time-to-frequency converter, said time-to-frequency converter comprising a local oscillator for generating a main swept-frequency signal;
• a first multiplier for multiplying the main swept-frequency signal generated from said local oscillator by a signal to be measured;
• and an intermediate frequency filter having a bandpass width, and being arranged such that a frequency component included in the signal to be measured is frequency-discriminated in accordance with a lapse of time associated with a sweep of the main swept-frequency signal thereby converting the frequency-discriminated components to intermediate frequency signals arranged by frequency according to the lapse of time;
• an analog-to-digital converter provided at the output side of said time-to-frequency converter and supplied with an intermediate frequency signal;
• a quadrature detector supplied with a digital output from said analog-to-digital converter;
• a memory for storing therein a digital output from said analog-to-digital converter obtained during the time interval of a sweep of the main swept-frequency signal;
• an inverse chirp correction unit for performing an inverse chirp correction operation using the data stored in said memory;
• and
• a resolution filter supplied with an output signal from said inverse chirp correction unit;
• wherein said quadrature detector, said memory, said inverse chirp correction unit, and said resolution filter are implemented by one or more digital circuits.

A frequency analysis method comprising the steps of:

• multiplying an input signal having signal components of different frequencies to be measured by a main swept-frequency signal to obtain a first result of multiplying;
• extracting an intermediate frequency signal containing the signal components included in said input signal from the first result of multiplying by an intermediate frequency filter having a bandpass width;
• multiplying said intermediate frequency signal by a second swept-frequency signal to obtain a second result of multiplying, said second swept-frequency signal having a frequency-sweeping span in which the frequency of the second swept-frequency signal changes in a direction inverse to that of changes in frequency of said intermediate frequency signal;
• extracting an output signal having a constant frequency component from the second result of multiplying by a resolution filter;
• and
• displaying an envelope of the output signal as a frequency spectrum of the signal components included in the input signal.

A sweep type spectrum analyzer comprising:

• a time-to-frequency converter that comprises:
• a main local oscillator for generating a main swept-frequency signal;
• a first multiplier that multiplies an input signal to be measured which contains signal components of different frequencies by the main swept-frequency signal and outputs a result of its multiplication;
• and
• an intermediate frequency filter connected to the first multiplier and having a bandpass width that outputs an intermediate frequency signal which contains the signal components in frequency-discriminated state arranged by frequency according to a lapse of time associated with a sweep of the main swept-frequency signal;
• an inverse chirp correction unit that comprises:
• a second local oscillator for generating a second swept-frequency signal;
• and
• a second multiplier that multiplies the intermediate frequency signals outputted from said time-to-frequency converter by the second swept-frequency signal and outputs a result of its multiplication;
• a resolution filter supplied with the result of the multiplication of said second multiplier that extracts an output signal containing signal components having a constant frequency;
• and
• a display device that displays the signal components contained in the output signal of said resolution filter as a frequency spectrum included in the input signal.