CN111030765B - Heterodyne frequency sweep type spectrum analysis system capable of identifying image frequency signals - Google Patents
Heterodyne frequency sweep type spectrum analysis system capable of identifying image frequency signals Download PDFInfo
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- CN111030765B CN111030765B CN201911234400.8A CN201911234400A CN111030765B CN 111030765 B CN111030765 B CN 111030765B CN 201911234400 A CN201911234400 A CN 201911234400A CN 111030765 B CN111030765 B CN 111030765B
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Abstract
The invention discloses a heterodyne frequency-sweeping type spectrum analysis system capable of identifying an image frequency signal, which is characterized in that a positive sign filter, a negative sign filter and an identification circuit module are added on the basis of the existing heterodyne frequency-sweeping type spectrum analysis system, and the magnitude relation between the local oscillation signal, namely the frequency of a frequency-sweeping signal, and the frequency of an input signal is judged according to the time sequence relation between the output signals of the positive sign filter, the output signals of the negative sign filter and an intermediate frequency filter, so that the identification of the image frequency signal is realized. Compared with the traditional heterodyne frequency sweep type spectrum analysis system, the heterodyne frequency sweep frequency mixing circuit module has the advantages that the low-pass filter is removed, the measured signal and the image frequency signal thereof can enter the heterodyne frequency sweep frequency mixing circuit module after being processed by the input circuit module, the working frequency band of the spectrum analysis system is not determined by the cut-off frequency of the low-pass filter of the input circuit module any more, the limitation of the bandwidth of the measured signal to the center frequency of the low-pass filter is eliminated, and meanwhile, the image frequency signal can be rapidly identified through one-time measurement.
Description
Technical Field
The invention belongs to the technical field of measurement and test, and particularly relates to a heterodyne frequency sweep type spectrum analysis system capable of identifying image frequency signals.
Background
The heterodyne sweep-frequency spectrum analysis technology is supported by the rapid development of basic subjects such as electronic systems, materials and devices, the working frequency band can reach the high-end terahertz and the resolution reaches the Hertz level, and the heterodyne sweep-frequency spectrum analysis technology becomes an indispensable important technology for testing, researching, developing and preparing signals and devices.
However, in order to prevent spectrum aliasing and suppress image interference, the conventional heterodyne swept-frequency spectrum analysis technique adds a low-pass filter to the input circuit module, and sets the center frequency of the intermediate frequency filter of the heterodyne swept-frequency mixer circuit module to a high intermediate frequency, as shown in fig. 1. Under the setting, in order to improve the frequency resolution of the spectrum analysis, a multi-stage mixing technology is adopted, that is, one or more subsequent heterodyne swept-frequency mixing circuit modules (only one is shown in fig. 1, and there may be more in practical application). The drawbacks of this design are: the complexity of a spectrum analysis system is increased, the index requirements of adopted devices are improved, for example, the requirements that the working frequency bands of a frequency mixer and a frequency sweeping local oscillator in a heterodyne frequency sweeping frequency mixing circuit are far higher than the frequency band of a measured signal are met, and meanwhile, the bandwidth of the measured signal is limited by the central frequency of a low-pass filter. In addition, due to the adoption of the multi-stage mixing technology, the single-sideband phase noise of the spectrum analysis system is increased, the sensitivity of the spectrum analysis system is reduced, and the dynamic range is reduced. High intermediate frequency techniques can therefore be considered to increase system complexity either directly or indirectly.
Meanwhile, with the development of modern microwave millimeter wave testing technology, the vector network analyzer gradually transits from a single instrument to a testing system, namely, the purpose of meeting various testing requirements in the technical field of microwave millimeter waves at present is achieved by fully utilizing a synthesized frequency sweep signal source, a signal receiving system (spectrum analysis system) and a combination of the synthesized frequency sweep signal source and the signal receiving system (spectrum analysis system) in the vector network analyzer, namely the vector network analyzer. However, compared with a common spectrum analyzer, the vector network analyzer has no low-pass filter in the input circuit module of the signal receiving system, so that the vector network analyzer cannot distinguish the signal to be measured and its image frequency signal, and cannot identify whether aliasing exists in the frequency spectrum of the signal to be measured, which greatly hinders the development of the vector network analysis technology.
Therefore, the image frequency signal identification technology is an important problem which needs to be solved urgently in the field of modern microwave millimeter wave testing.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a heterodyne frequency sweep type spectrum analysis system capable of identifying an image frequency signal, can identify the image frequency signal, simultaneously eliminates the limitation of the bandwidth of a measured signal by the central frequency of a low-pass filter, breaks through the bottleneck of the development of the modern microwave millimeter wave testing technology, greatly improves the index parameters of the heterodyne frequency sweep type spectrum analysis system, and lays a good foundation for improving the technical level of vector network analysis.
In order to achieve the above object, the heterodyne swept-frequency spectrum analysis system capable of identifying image frequency signals of the present invention includes an input circuit module and a heterodyne swept-frequency mixing circuit module, and is characterized in that:
the input circuit module does not comprise a low-pass filter for suppressing the image frequency signal;
the heterodyne frequency sweep frequency mixing circuit module comprises a frequency mixer, a frequency sweep local oscillator, an intermediate frequency filter, a positive sign filter and a negative sign filter; the frequency passband of the intermediate frequency filter is not intersected with the frequency passbands of the positive sign filter and the negative sign filter; the positive sign filter is a band-pass filter with the center frequency larger than that of the intermediate frequency filter, and the negative sign filter is a band-pass filter with the center frequency smaller than that of the intermediate frequency filter;
the output signal of the input circuit module is input into a frequency mixer, and is mixed with the frequency sweeping signal output by the frequency sweeping local oscillator, and the obtained intermediate frequency signal is respectively input into an intermediate frequency filter, a positive sign filter and a negative sign filter;
the heterodyne frequency-sweeping system also comprises an identification circuit module, wherein output signals of the intermediate frequency filter, the positive sign filter and the negative sign filter are sent into the identification circuit module, and the magnitude relation between the frequency of the local oscillation signal (frequency-sweeping signal) and the frequency of the input signal is judged according to the time sequence relation between the output signals of the positive sign filter and the negative sign filter and the output signal of the intermediate frequency filter, so that the identification of the measured signal and the image frequency signal is realized.
The object of the invention is thus achieved.
The heterodyne frequency-sweeping type spectrum analysis system capable of identifying the image frequency signal is additionally provided with a group of sign filters (positive and negative sign filters) and an identification circuit module on the basis of the conventional heterodyne frequency-sweeping type spectrum analysis system, and the magnitude relation between the local oscillator signal, namely the frequency of the frequency-sweeping signal, and the frequency of the input signal is judged according to the time sequence relation between the output signals of the positive and negative sign filters and the intermediate frequency filter, so that the identification of the image frequency signal is realized.
The invention can bring the following beneficial effects:
(1) compared with the traditional heterodyne frequency sweep type spectrum analysis system, the heterodyne frequency sweep frequency mixer circuit module has the advantages that the low-pass filter is removed, so that the measured signal and the image frequency signal thereof can enter the heterodyne frequency sweep frequency mixer circuit module after being processed by the input circuit module, the working frequency band of the spectrum analysis system is not determined by the cut-off frequency of the low-pass filter of the input circuit module any more, the limitation of the bandwidth of the measured signal to the center frequency of the low-pass filter is eliminated, the bottleneck of the development of the modern microwave millimeter wave testing technology is broken through, the index parameters of the heterodyne frequency sweep type spectrum analysis system are greatly improved, and a good foundation is laid;
(2) the used frequency mixer, the used frequency sweep local oscillator and the used intermediate frequency filter are all original devices in the existing heterodyne frequency sweep type spectrum analysis system, when the frequency mixer, the used frequency sweep local oscillator and the used intermediate frequency filter are used, only a sign filter and an identification circuit module are needed to be added in the heterodyne frequency sweep type spectrum analysis system of the existing system, and a low-pass filter is removed from an input circuit module, so that the large-scale reconstruction of the existing heterodyne frequency sweep type spectrum analysis system is not needed, and the frequency mixer, the frequency sweep local oscillator;
(3) the image frequency signal can be rapidly identified through one-time measurement;
(4) the vector network analyzer can be combined with the existing vector network analysis technology, and only a simple symbol filter and a recognition circuit module are needed to be added in the existing system, so that the vector network analyzer is improved into a vector network analysis system, and the application range of the vector network analyzer is greatly expanded.
Drawings
FIG. 1 is a functional block diagram of a conventional heterodyne swept-frequency spectrum analysis system;
FIG. 2 is a schematic block diagram of an embodiment of a heterodyne swept-frequency spectrum analysis system capable of identifying image signals according to the present invention;
fig. 3 is a graph of the time-frequency and timing relationships of input and output signals when identifying an image frequency signal.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
According to the common practice of the technical personnel in the field, when the frequency of an input signal is less than the frequency of a local oscillation signal, the signal is defined as a measured signal; when the frequency of the input signal is greater than the local oscillator signal and is symmetrical to the frequency of the measured signal relative to the frequency of the intermediate frequency signal, the frequency is defined as the image frequency signal of the measured signal.
FIG. 2 is a schematic block diagram of an embodiment of a heterodyne swept-frequency spectrum analysis system capable of identifying image signals according to the present invention.
In this embodiment, as shown in fig. 2, the heterodyne swept-frequency spectrum analysis system capable of identifying an image frequency signal according to the present invention includes an input circuit module 1, a heterodyne swept-frequency mixing circuit module 2, and an identification circuit module 3.
In this embodiment, as shown in fig. 2, the input circuit module 1 includes an impedance matching circuit 101 and a signal conditioning circuit 102, and the input signal is matched by the impedance matching circuit 101 and conditioned by the signal conditioning circuit 102 and then output to the heterodyne swept-frequency mixer circuit module 2. The input circuit block 1 may preferably include an impedance matching circuit block and a signal conditioning circuit block. Compared with the traditional heterodyne frequency sweep type spectrum analysis system, the heterodyne frequency sweep type spectrum analysis system has the advantages that a low-pass filter for suppressing the image frequency signal is eliminated, so that the measured signal and the image frequency signal thereof can enter the heterodyne frequency sweep frequency mixing circuit module 2 after being processed by the input circuit module 1, the working frequency band of the spectrum analysis system is not determined by the cut-off frequency of the low-pass filter of the input circuit module 1 any more, and the limitation of the bandwidth of the measured signal by the cut-off frequency of the low-pass filter is eliminated.
In the embodiment, as shown in fig. 2, the heterodyne swept frequency mixer circuit module 2 includes a mixer 201, a swept local oscillator 202, an intermediate frequency filter 203, and a sign filter 204 (including a sign filter f)+And a negative sign filter f-) The frequency passband of the intermediate frequency filter 203 does not intersect the frequency passband of the sign filter 204. An output signal of the signal conditioning circuit 102 in the input circuit module 1 is input into the mixer 201, and is mixed with a swept frequency signal output by the swept frequency local oscillator 202, and the obtained intermediate frequency signal is input into the intermediate frequency filter 203 and the positive and negative sign filter 204, respectively.
The intermediate frequency filter 203 and the positive and negative sign filters 204 are all band-pass filters, the center frequency of the positive sign filter is greater than that of the intermediate frequency filter, and the center frequency of the negative sign filter is less than that of the intermediate frequency filter, and the setting can be determined according to actual working requirements. On the premise that the frequency passband of the intermediate frequency filter 203 and the frequency passband of the sign filter 204 are not intersected, the specific bandwidth may also be determined according to the actual working requirement, and the frequency sweep local oscillator 202 generates a frequency sweep signal with a frequency periodically and linearly changing with time.
The heterodyne swept-frequency system further comprises an identification circuit module 3, the output signals of the intermediate frequency filter 203 and the sign filter 204 are fed into the identification circuit module 3, in accordance with the sign filter 204 (positive sign filter f)+And a negative sign filter f-) The timing relationship with the output signal of the if filter 203 determines the magnitude relationship between the local oscillator signal (sweep frequency signal) frequency and the input signal frequency, and identifies the measured signal and the image frequency signal, that is, identifies the image frequency signal, specifically:
if the time sequence of the output signal of the filter is respectively a negative sign filter, an intermediate frequency filter and a positive sign filter, the frequency of the input signal is less than the frequency of the sweep frequency signal, and the input signal is a measured signal; if the time sequence of the output signal of the filter is respectively a positive sign filter, an intermediate frequency filter and a negative sign filter, the frequency of the input signal is greater than the frequency of the sweep frequency signal, and the input signal is an image frequency signal.
The measured signal with the same frequency causes the positive and negative sign filters and the intermediate frequency filter to generate outputs at different moments, and the time difference of the output signals of the filters is determined by the central frequencies of the positive and negative sign filters and the intermediate frequency filter and the sweep frequency speed of the sweep frequency oscillator, and is independent of the measured signal.
In the present embodiment, as shown in fig. 2, the identification circuit block 3 includes an intermediate frequency detector 301, a sign detector 302, an intermediate frequency analog-to-digital conversion circuit 303, a sign analog-to-digital conversion circuit 304, and a digital circuit block 305.
The output signal of the intermediate frequency filter 203 is detected by an intermediate frequency detector 301, is subjected to analog-to-digital conversion by an intermediate frequency analog-to-digital conversion circuit 303, and is sent to a digital circuit module 305; the output signal of the symbol filter 204 is detected by a positive/negative symbol detector 302, analog-to-digital converted by a positive/negative symbol analog-to-digital conversion circuit 304, and then sent to a digital circuit module 305. The digital circuit block 305 recognizes the signal to be measured and the image frequency signal, that is, recognizes the image frequency signal.
In addition, in the implementation, the output of the if filter 203 is connected to one or more subsequent heterodyne swept-frequency mixer circuit modules (not shown in fig. 2), and then is detected by the if detector 301, analog-to-digital converted by the if analog-to-digital conversion circuit 303, and then sent to the digital circuit module 305. The subsequent heterodyne frequency sweep frequency mixing circuit module comprises circuits such as a frequency mixer, a frequency sweep local oscillator, an intermediate frequency filter and the like, but does not comprise a positive and negative sign filter.
FIG. 3 is a graph of the time-frequency and timing relationships of input and output signals when identifying an image signal.
As shown in FIG. 3, the frequency of the measured signal is set to fxCenter frequency of the IF filter is fifFrequency of the sweep signal is f0(t) a + bt, where a and b are normal numbers, and the image frequency of the measured signal is fimg。
The center frequency of the negative sign filter is set to be f when being smaller than that of the intermediate frequency filter-(ii) a The center frequency of the positive sign filter is set to be f when being larger than that of the intermediate frequency filter+If the frequency of the measured signal is fxIf the frequency of the mixed frequency (difference frequency) signal obtained by mixing the frequency sweep signal and the measured signal is f0(t)-fx＝a+bt-fxOutputting the mixed signal at t1、t3And t4The frequencies of the moments respectively reach the center frequency f of the minus sign filter-Center frequency f of intermediate frequency filterifAnd the center frequency f of the positive sign filter+So that the negative sign filter, the intermediate frequency filter and the positive sign filter are respectively at t1、t3And t4And outputting a signal at a moment. If the frequency of the input signal is fimgFrequency of a mixing (difference) signal mixed with the sweep signal is fimg-f0(t)＝fimg- (a + bt), outputting the mixed signal and outputting the mixed signal at t2、t3And t5The frequencies of the instants of time respectively reach the center frequency f of the positive sign filter+Center frequency f of intermediate frequency filterifAnd the center frequency f of the minus sign filter-So that the positive sign filter, the intermediate frequency filter and the negative sign filter are respectively at t2、t3And t5And outputting a signal at a moment.
According to the analysis, if the time sequence of the output signal of the filter is a negative sign filter, an intermediate frequency filter and a positive sign filter, the frequency of the input signal is less than the frequency of the sweep frequency signal, and the input signal is a measured signal; if the time sequence of the output signal of the filter is a positive sign filter, an intermediate frequency filter and a negative sign filter, the frequency of the input signal is greater than the frequency of the sweep frequency signal, and the input signal is an image frequency signal.
In summary, according to the time sequence relationship between the output signal of the positive and negative sign filter and the output signal of the intermediate frequency filter, whether the frequency of the input signal is less than or greater than the local oscillation signal can be judged, so as to identify whether the input signal is a detected signal or an image frequency signal.
The technical personnel in the field can easily apply the invention to the spectrum analysis technology in the prior art and the vector network analysis technology in the prior art, realize the identification of the image frequency signal in a simple and efficient way, improve the technical level of the spectrum analysis, and greatly enlarge the application range of the vector network analysis technology. In addition, the person skilled in the art can also apply the present invention to other scenarios according to the actual working needs, so as to identify the image frequency signal in a simple and efficient manner.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (2)
1. A heterodyne frequency sweep type spectrum analysis system capable of identifying image frequency signals comprises an input circuit module and a heterodyne frequency sweep frequency mixing circuit module, and is characterized in that:
the input circuit module does not comprise a low-pass filter for suppressing the image frequency signal;
the heterodyne frequency sweep frequency mixing circuit module comprises a frequency mixer, a frequency sweep local oscillator, an intermediate frequency filter, a positive sign filter and a negative sign filter; the frequency passband of the intermediate frequency filter is not intersected with the frequency passbands of the positive sign filter and the negative sign filter; the positive sign filter is a band-pass filter with the center frequency larger than that of the intermediate frequency filter, and the negative sign filter is a band-pass filter with the center frequency smaller than that of the intermediate frequency filter;
the output signal of the input circuit module is input into a frequency mixer, and is mixed with the frequency sweeping signal output by the frequency sweeping local oscillator, and the obtained intermediate frequency signal is respectively input into an intermediate frequency filter, a positive sign filter and a negative sign filter;
the heterodyne frequency-sweeping system also comprises an identification circuit module, wherein output signals of the intermediate frequency filter, the positive sign filter and the negative sign filter are sent into the identification circuit module, and the magnitude relation between the local oscillator signal, namely the frequency of the frequency-sweeping signal, and the frequency of the input signal is judged according to the time sequence relation between the output signals of the positive sign filter and the negative sign filter and the output signal of the intermediate frequency filter, so that the identification of the measured signal and the image frequency signal is realized: if the time sequence of the output signal of the filter is respectively a negative sign filter, an intermediate frequency filter and a positive sign filter, the frequency of the input signal is less than the frequency of the sweep frequency signal, and the input signal is a measured signal; if the time sequence of the output signal of the filter is respectively a positive sign filter, an intermediate frequency filter and a negative sign filter, the frequency of the input signal is greater than the frequency of the sweep frequency signal, and the input signal is an image frequency signal.
2. A heterodyne swept-frequency spectrum analysis system capable of image frequency signal identification as recited in claim 1, wherein the same frequency signal under test causes the positive and negative sign filters and the if filter to produce outputs at different times, and the time difference between the filter output signals is determined by the center frequencies of the positive and negative sign filters and the if filter and the sweep speed of the swept frequency oscillator, independently of the signal under test.
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| CN113376434A (en) * | 2021-06-07 | 2021-09-10 | 电子科技大学 | Frequency spectrum analysis method based on chirp transformation architecture and rapid digital pulse pressure algorithm |
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