JPH08233875A - Image frequency-removing apparatus and spectrum analyzer using the apparatus - Google Patents

Abstract

PURPOSE: To display a spectrum of components of only a target measuring signal by removing an image spectrum generated by other higher harmonics. CONSTITUTION: A sweep offset control part 13 is provided to control a first local oscillator 56 for sweeping so that a sweep frequency fosc of the oscillator 56 is switched between a first sweep frequency fosc1 and a second sweep frequency fosc2=fosc1+2fif2/N at the sweeping time. A smaller data value of spectra data obtained with the sweep frequencies fosc1 and fosc2 by the control part 13 is selected and output by an image-removing/processing part 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring and displaying a spectrum of a frequency by mixing frequency signals to be measured with Nth harmonics in the field of spectrum measurement of the frequency.

[0002]

2. Description of the Related Art As an example of the prior art, a sweep frequency fosc signal of a first local oscillator 56 to be swept is output to an external output terminal 1.
20 having an input terminal 130 for receiving the intermediate frequency fif2 signal from the outside, and using an external mixer, the measured signal fhi in the frequency region N times higher than the upper limit frequency of the spectrum analyzer measurement frequency. Measure and display the spectrum. This will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, the configuration of the present device has a frequency conversion unit 50, an input switching unit 74, a second IF filter 66, a detection unit 68, an AD converter 82, an AD buffer memory 84, and a display process. It is composed of a section 86 and a display section 88. Externally, there is an external mixer 72 prepared by the user. The frequency conversion unit 50 includes an attenuator 42, a YT
F52, the first mixer 54, the first local oscillator 56,
The first IF filter 58, the second mixer 62, and the second local oscillator 64 are included.

First, the case of normal spectrum measurement using the internal frequency converter 50 will be described. The signal to be measured fin input to the input terminal 100 is attenuated to a desired level by the attenuator 42, passed through the target frequency component corresponding to the sweep by the YTF 52, and then supplied to the first mixer 54. Here, YTF (YIG-tuned filte
r) 52 is a tuning filter using YIG, and is a filter element whose tuning frequency is variable by an applied magnetic field, and frequency = fos with respect to the first local oscillator 56 to be swept.
By interlocking with the tuning frequency of c + fif1, only the target frequency component is passed and the filter function synchronized with the sweep is realized.

The first local oscillator 56 is an oscillator that sweeps the measurement frequency range. The first mixer 54 is the above YTF.
The intermediate frequency fif1 mixed with the signal from 52 and the first local oscillator 56 to be swept is output, and the intermediate frequency fif1 is passed through the first filter 58 and then supplied to the second mixer 62. . The second mixer 62 is the first mixer
Intermediate frequency fif1 from filter 58 and fixed oscillator 6
4 and the intermediate frequency fif2 = 421 in this example.
After down-converting to MHz, it is supplied to the second IF filter 66 via the input switch 74. The second IF filter 66 is a filter that can be set to an arbitrary bandwidth characteristic, and by this, after filtering under a desired band condition,
The wave is detected by the wave detector 68, quantized into a digital signal by the AD converter 82, and stored in the AD buffer memory 84. The display processing unit 86 reads the contents of the AD buffer memory 84, performs arithmetic processing according to various display forms, and then displays the display unit 8
Display the frequency spectrum etc. with 8.

Secondly, a case of measuring and displaying a frequency signal N times higher than the measurement upper limit of the spectrum analyzer by using the frequency conversion function of the external user will be described. The user sets the measurement specifications in advance by switching the input switching device 74 to the external input side and notifying the spectrum analyzer that N = 5th order. In this case, the sweep frequency fos
The Nth harmonic (fosc × N) contained in the c signal component is used. The Nth harmonic and the signal under test fhi are mixed and the absolute value of the intermediate frequency fif2 = fhi ± (fosc × N) is 2
Generate two signals. Input this intermediate frequency signal to input terminal 1
Connect and input to 30 to measure and display spectrum. An example of the spectrum waveform obtained as a result is shown in FIG. In this example, it is assumed that the measured signal fhi is a single signal of 30 GHz, the sweep frequency is fosc = 4 to 8 GHz, and N =
It is a spectrum waveform in the case of the 5th order. Looking at this spectrum, in addition to the spectra fN5a and fN5b of the target signal fhi to be measured, N = image spectra fN4a and fN4b of the fourth harmonic, N = image spectra fN6a and fN6b of the sixth harmonic, and N = Image spectra fN7a and fN7b due to the 7th harmonic are displayed. In this figure, for example, the image spectrum fN4a has a sweep frequency of (fosc × 4) = 30 GH
This is an image spectrum generated by z-fif2, and the image spectrum fN4b has a sweep frequency of (fosc × 4).
= 30 GHz + fif2, which is an image spectrum that produces two pairs of image spectra. In this way, two spectra are displayed with the target N = 5th order, and N
Image spectra other than = 5 are also displayed on the screen.

In this example, the simple case of a single frequency signal has been described, but the measured signal f including a plurality of frequency components is f.
When trying to measure hi, the original signal spectrum,
It becomes difficult to distinguish from the image spectrum, which is a great inconvenience in use.

[0007]

As described above, in the spectrum analyzer, in order to remove the image signal as described above, the YTF 52 which is a filter synchronized with the sweeping first local oscillator 56 is used as a mixer. 5
4 is inserted before 4 and is configured to eliminate the generation of unwanted image signals. However, the external mixer 7
In a configuration using 2, it is usually difficult to provide a filter synchronized with such a sweep. As a result, as shown in FIG. 4, a plurality of image spectra other than the original input signal fhi component are displayed on the screen, which is difficult to see and is erroneously recognized, which is a practical inconvenience.

Therefore, an object of the present invention is to eliminate the image spectrum generated by other harmonics and realize a spectrum display of only the target signal fhi component to be measured.

[0009]

FIG. 1 shows a first solution according to the present invention. In order to solve the above-mentioned problem, in the configuration of the present invention, the sweep frequency of the sweep frequency first local oscillator 56 is fosc, and the first sweep frequency is fosc.
The first local oscillator 56 of the sweep reference so that the sweep is performed by switching between 1 and the second sweep frequency fosc2 = fosc1 + 2fif2 / N.
A sweep offset control unit 13 for controlling the image removal processing unit 12 for selecting and outputting the smaller data value of the spectrum data values obtained at both sweep frequencies fosc1 and fosc2 by the sweep offset control unit 13 is output. It is a constituent means to be provided. Thereby, it has an external output terminal 120 for outputting the sweep frequency fosc signal of the swept reference first local oscillator 56 in the frequency conversion unit 50 to the outside, and an input terminal 130 for receiving the intermediate frequency fif2 signal from the outside. An input switch 74 is provided for switching between the intermediate frequency fif2 signal from the frequency conversion unit 50 or the intermediate frequency fif2 signal from the input terminal 130, and the Nth harmonic of the sweep frequency fosc of the swept first local oscillator 56 is provided. Using the signal under test fhi
Can be frequency-converted to an intermediate frequency fif2 and supplied to the input terminal 130 to perform spectrum measurement of the signal under test fhi to output only the spectrum signal from which the image signal is removed.

FIG. 5 shows a second solution according to the present invention. In order to solve the above-mentioned problem, in the configuration of the present invention, the sweep frequency of the sweep frequency fosc of the first local oscillator 56 is switched between the first sweep frequency fosc1 and the second sweep frequency fosc2 = fosc1 + 2fif2 / N. A sweep offset control unit 13 for controlling the first local oscillator 56 for sweeping is provided so that the sweep offset control unit 13
Then, the image removing processing unit 12 for selecting and outputting the smaller data value of the two spectrum data values obtained at the two sweep frequencies fosc1 and fosc2 is provided. As a result, the sweep frequency fosc of the swept reference first local oscillator 56 is
The signal to be measured fhi is frequency-converted into the intermediate frequency fif2 by using the Nth harmonic of the above, and the spectrum measurement of the signal to be measured fhi can be realized to output only the spectrum signal from which the image signal is removed.

With the above configuration, the sweep offset control unit 13 sets the first sweep frequency fosc1 and the second sweep frequency f.
By controlling the swept first local oscillator 56 to alternately sweep osc2 = fosc1 + (2fif2 / N),
By outputting the frequency conversion signal that is shifted by exactly the intermediate frequency fif2, there is an action of generating and outputting a spectrum signal at a position where only the target signal fhi is overlapped by both sweeps. The image removal processing unit 12 removes unnecessary image signals by selecting and outputting the smaller data value of the spectrum data values obtained by alternately sweeping by the sweep offset control unit 13. There is.
As a whole, it is possible to realize the function of removing the image spectrum generated by other Nth harmonics and displaying the spectrum of only the target signal fhi component to be measured.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to Examples.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention uses an N times swept signal of a swept reference first local oscillator 56 to receive an intermediate frequency fif2 mixed by an external mixer and receive an image other than the signal under test fhi. This is a case where a signal is removed and a measurement display is realized. This will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the configuration of this apparatus is a configuration in which an image removal processing unit 12 and a sweep offset control unit 13 are added to the conventional configuration.

The principle of removing the image signal is realized by a procedure of identifying the image signal other than the target mixed component with the Nth harmonic and then performing the removal processing of this image signal. Here, as in the conventional example, the intermediate frequency fif2 =
421MHz, the measured signal fhi is a single 30GHz
Assuming a signal, the sweep frequency fosc = 4 to 8 GHz,
The measurement will be described as N = 5th order.

First, the identification of the image signal will be described.
The intermediate frequency fif2 is generated by fif2 = 421 MHz = fhi
Two components with absolute values of ± (fosc × N) are generated.
Therefore, normal sweep frequency fosc and intermediate frequency fif2 ×
When each sweep is performed with the sweep frequency fosc + 2fif2 shifted by 2, the positions of the detection points coincide with each other only in the case of the target signal fhi among the obtained signal components. Identification is performed by utilizing matching of the detection points. That is, when two sweep frequencies are used as the sweep frequency fosc and the sweep is alternately executed and controlled, four signals fN5a, fN5b, fN5c, and fN5d are generated as shown in FIG. Here, if the first sweep frequency is fosc1, and the relationship of the second sweep frequency fosc2 = fosc1 + (2fif2 / 5), the frequency of the fifth harmonic becomes 5 × fosc1 and 5 × fosc2 + 2fif2, and the second sweep frequency fosc2 is just swept by shifting the intermediate frequency 2fif2. As a result, the spectrum position due to the second sweep frequency fosc2 appears shifted to the positions of fN5c and fN5d in FIG. Here, noteworthy is that fN5b and fN5c exist at the overlapping position because they are just shifted by the intermediate frequency 2fif2.

The sweep offset control unit 13 sets the first sweep frequency fosc1 and the second sweep frequency fosc2 = f as described above.
The swept reference first local oscillator 56 is controlled so as to alternately sweep osc1 + (2fif2 / N).

The image removal processing unit 12 compares the respective data points in the arrangement of the spectrum data strings obtained by alternately sweeping, and displays the data having the smaller value as the display processing unit 8.
By outputting to 6, the image is removed.
As a result, the four signals fN5a, fN5b, fN5 described above are obtained.
When this processing is performed on c and fN5d, only the signals fN5b and fN5c existing at the overlapping positions are output as one spectrum and displayed as shown in FIG. 2 (b). Similarly, the spectrum signal generated by N = 4, 6, 7 has a shift frequency of 4 × (2fif2 / 5) or
It becomes 6 × (2fif2 / 5) or 7 × (2fif2 / 5), and since the positions are shifted from the positional relationship shifted by the intermediate frequency fif2 × 2, they are removed by the image removal processing unit 12. As a result, the spectrum display of FIG. 2A is changed to the spectrum display of FIG. 2B, and only the target signal is obtained as a spectrum.

In the description of the above embodiment, the measured signal f in the frequency region N times the sweep frequency of the spectrum analyzer is f.
Although the description has been given in the case of removing the image signal of the hi spectrum, in addition to this, as shown in FIG.
Even when the hi signal is supplied to one side of the mixer and the sweep frequency fosc signal is supplied to the other side of the mixer and mixed to obtain spectrum data, the Nth harmonic of the sweep frequency fosc and an unknown frequency fhi signal It is also applicable in the case of an image frequency removing device that generates a signal and can be implemented in a similar manner.

[0019]

Since the present invention is configured as described above, it has the following effects. The sweep offset control unit 13 sets the first sweep frequency to fosc1.
And the second sweep frequency fosc2 = fosc1 + (2fif2 / N) are alternately controlled to control the first local oscillator 56 of the sweep reference to output a frequency conversion signal shifted by exactly the intermediate frequency fif2 × 2. As a result, the effect of generating the spectrum signal at the overlapping position by both sweeps can be obtained. The image removal processing unit 12 removes only unnecessary image signals by selecting and outputting the smaller data value of the spectrum data values obtained by alternately sweeping by the sweep offset control unit 13. The output effect can be obtained. As a result of these, the N of the first local oscillator 56
In the spectrum measurement of the signal under test fhi using the second harmonic, the effect of removing the image spectrum generated by other harmonics and realizing the spectrum display of only the target signal under test fhi component can be obtained. Excellent visibility is obtained and the convenience for the user is greatly improved.

[0020]

[Brief description of drawings]

FIG. 1 is a configuration diagram of a spectrum analyzer for measuring a signal under measurement fhi in which an image signal is removed by an external mixer according to the present invention.

FIG. 2 (a) is a spectrum display screen before image signal removal according to the present invention. (B) It is a spectrum display screen after removing an image signal of the present invention.

FIG. 3 is a configuration diagram of a conventional spectrum analyzer for measuring a signal under test fhi by an external mixer.

FIG. 4 is a conventional spectrum display screen for measuring a signal under test fhi by an external mixer.

FIG. 5 is a block diagram of an image frequency removing apparatus for removing an image signal and measuring a signal under test fhi according to the present invention.

[Explanation of symbols]

 12 image removal processing unit 13 sweep offset control unit 42 attenuator 50 frequency conversion unit 52 YTF (YIG-tuned filter) 54 mixer 56 first local oscillator 58 filter 62 second mixer 64 oscillator 66 second IF filter 68 detection unit 72 external mixer 74 input switching device 82 AD converter 84 AD buffer memory 86 display processing unit 88 display unit 100, 130 input terminal 120 external output terminal fin, fhi frequency fosc sweep frequency fif2 intermediate frequency

Claims (2)

[Claims] 1. An external output terminal (120) for outputting a sweep frequency (fosc) signal of a swept reference first local oscillator (56) in a frequency conversion section (50) to an external intermediate frequency ( fif2) signal has an input terminal (130) and receives the intermediate frequency (fif2) from the frequency converter (50).
2) An Nth order of the sweep frequency (fosc) of the swept reference first local oscillator (56) having an input switch (74) for switching between a signal or an intermediate frequency (fif2) signal from the input terminal (130). Signal under test using harmonics (fhi)
In the spectrum measurement of the signal under test (fhi) performed by converting the frequency of the signal to the intermediate frequency (fif2) and supplying it to the input terminal (130), the sweep frequency (fosc) of the swept reference first local oscillator (56)
The sweep frequency of the first sweep frequency is (fosc1)
Sweep frequency (fosc2) = (fosc1) + ((2fif2) /
Sweep offset control unit (13) for controlling the first local oscillator (56) for sweeping so as to switch between and
Is provided, and both sweep frequencies (f
A spectrum analyzer characterized by comprising an image removal processing unit (12) for selecting and outputting the smaller data value of the two spectrum data values obtained by osc1 and fosc2). 2. The signal under test (fh) using the Nth harmonic of the sweep frequency (fosc) of the swept reference first local oscillator (56).
In the spectrum measurement of the signal under test (fhi) performed by frequency conversion of i) into the intermediate frequency (fif2), the sweep frequency (fosc) of the swept reference first local oscillator (56)
The sweep frequency of the first sweep frequency is (fosc1)
Sweep frequency (fosc2) = (fosc1) + ((2fif2) /
Sweep offset control unit (13) for controlling the first local oscillator (56) for sweeping so as to switch between and
Is provided, and both sweep frequencies (f
The image frequency removing device is provided with an image removing processing unit (12) for selecting and outputting the smaller data value of the two spectrum data values obtained by osc1 and fosc2), and including the above. .