Signal analysis apparatus and signal analysis method
11463183 · 2022-10-04
Assignee
Inventors
Cpc classification
H04L25/03828
ELECTRICITY
International classification
Abstract
A signal analysis apparatus includes a first frequency conversion unit 10 that generates an intermediate frequency signal S.sub.IF2 and a second spurious signal S.sub.SP2 from a measured signal S.sub.RF of a frequency f.sub.RF (center frequency f.sub.c), and a second frequency conversion unit 25 that converts the intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 into an intermediate frequency signal S.sub.IF2′ of a frequency f.sub.IF2′ and a second spurious signal S.sub.SP2′ of a frequency f.sub.SP2′ by performing frequency shift of the intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 by a frequency shift amount Δf, in which the frequency shift amount Δf is a value that does not establish a relationship of −W/2≤f.sub.SP2′−f.sub.IF2′≤+W/2.
Claims
1. A signal analysis apparatus that analyzes a measured signal (S.sub.RF) having a frequency component f.sub.RF, the signal analysis apparatus comprising: a frequency setting unit that decides a first intermediate frequency f.sub.IF1, a frequency f.sub.LO1 of a first local oscillation signal, and a frequency shift amount Δf in accordance with a center frequency f.sub.c of the measured signal; a first local oscillator that outputs the first local oscillation signal (S.sub.LO1); a first mixer that generates a first intermediate frequency signal (S.sub.IF1) of the first intermediate frequency f.sub.IF1 by performing frequency mixing of the measured signal with the first local oscillation signal and generates a first spurious signal (S.sub.SP1) including a second harmonic component of the measured signal; a bandpass filter of a passed center frequency f.sub.0 into which the first intermediate frequency signal and the first spurious signal are input; a second local oscillator that outputs a second local oscillation signal (S.sub.LO2) of a frequency f.sub.LO2; a second mixer that generates a second intermediate frequency signal (S.sub.IF2) of a second intermediate frequency f.sub.IF2 by performing frequency mixing of the first intermediate frequency signal passing through the bandpass filter with the second local oscillation signal and generates a second spurious signal (S.sub.SP2) by performing frequency mixing of the first spurious signal passing through the bandpass filter with the second local oscillation signal; an AD converter that performs AD conversion of the second intermediate frequency signal and the second spurious signal; a frequency shift unit that performs frequency shift of the second intermediate frequency signal and the second spurious signal after the AD conversion performed by the AD converter by the frequency shift amount Δf on a frequency axis; a digital filter of a passed bandwidth W that allows a second intermediate frequency signal (S.sub.IF2′) after the frequency shift performed by the frequency shift unit to pass and removes a second spurious signal (S.sub.SP2′) after the frequency shift performed by the frequency shift unit; and a signal analysis unit that analyzes the second intermediate frequency signal passing through the digital filter, wherein the first intermediate frequency f.sub.IF1 is provided as f.sub.0+Δf, the second intermediate frequency f.sub.IF2 is provided as |f.sub.0+Δf−f.sub.LO2|, a second intermediate frequency f.sub.IF2′ of the second intermediate frequency signal after the frequency shift performed by the frequency shift unit is provided as |f.sub.0−f.sub.LO2|, the frequency f.sub.LO1 is provided as f.sub.c+f.sub.0+Δf, a frequency f.sub.SP1 of the first spurious signal is provided as 2×f.sub.RF, a frequency f.sub.SP2 of the second spurious signal is provided as |f.sub.SP1−f.sub.LO2|, a frequency f.sub.SP2′ of the second spurious signal after the frequency shift performed by the frequency shift unit is provided as |f.sub.SP1−f.sub.LO2−Δf|, and the frequency setting unit decides the frequency shift amount Δf that does not establish a relationship of −W/2≤|f.sub.SP1−f.sub.LO2−Δf|−f.sub.IF2′≤+W/2, and decides the first intermediate frequency f.sub.IF1 and the frequency f.sub.LO1.
2. The signal analysis apparatus according to claim 1, wherein in a case where a relationship of −W/2≤|f.sub.SP1−f.sub.LO2|−f.sub.IF2′≤+W/2 is not established, the frequency setting unit decides the frequency shift amount Δf as Δf=0.
3. The signal analysis apparatus according to claim 1, wherein in a case where a relationship of −W/2≤|f.sub.SP1−f.sub.LO2|≤f.sub.IF2′≤+W/2 is established, the frequency setting unit decides the frequency shift amount Δf capable of allowing the second intermediate frequency signal to pass and removing the second spurious signal at the digital filter.
4. A signal analysis method for analyzing a measured signal (S.sub.RF) of a frequency f.sub.RF, the signal analysis method comprising: a frequency setting step (S2) of deciding a first intermediate frequency f.sub.IF1, a frequency f.sub.LO1 of a first local oscillation signal, and a frequency shift amount Δf in accordance with a center frequency f.sub.c of the frequency f.sub.RF; a first local oscillation step (S3) of outputting the first local oscillation signal (S.sub.LO1) of the frequency f.sub.LO1; a first frequency mixing step (S4) of generating a first intermediate frequency signal (S.sub.IF1) of the first intermediate frequency f.sub.IF1 by performing frequency mixing of the measured signal with the first local oscillation signal, and generating a first spurious signal (S.sub.SP1) including a second harmonic component of the measured signal; a bandpass step (S5) of a passed center frequency f.sub.0 into which the first intermediate frequency signal and the first spurious signal are input; a second local oscillation step (S6) of outputting a second local oscillation signal (S.sub.LO2) of a frequency f.sub.LO2; a second frequency mixing step (S7) of generating a second intermediate frequency signal (S.sub.IF2) of a second intermediate frequency f.sub.IF2 by performing frequency mixing of the first intermediate frequency signal passing through the bandpass step with the second local oscillation signal, and generating a second spurious signal (S.sub.SP2) by performing frequency mixing of the first spurious signal passing through the bandpass step with the second local oscillation signal; an AD conversion step (S8) of performing AD conversion of the second intermediate frequency signal and the second spurious signal; a frequency shift step (S9) of performing frequency shift of the second intermediate frequency signal and the second spurious signal after the AD conversion performed in the AD conversion step by the frequency shift amount Δf on a frequency axis; a digital filter step (S10) of a passed bandwidth W in which a second intermediate frequency signal (S.sub.IF2′) after the frequency shift performed in the frequency shift step is allowed to pass, and a second spurious signal (S.sub.SP2′) after the frequency shift performed in the frequency shift step is removed; and a signal analysis step (S11) of analyzing the second intermediate frequency signal passing through the digital filter step, wherein the first intermediate frequency f.sub.IF1 is provided as f.sub.0+Δf, the second intermediate frequency f.sub.IF2 is provided as |f.sub.0+Δf−f.sub.LO2|, a second intermediate frequency f.sub.IF2′ of the second intermediate frequency signal after the frequency shift performed in the frequency shift step is provided as |f.sub.0−f.sub.LO2|, the frequency f.sub.LO1 is provided as f.sub.c+f.sub.0+Δf, a frequency f.sub.SP1 of the first spurious signal is provided as 2×f.sub.RF, a frequency f.sub.SP2 of the second spurious signal is provided as |f.sub.SP1−f.sub.LO2|, a frequency f.sub.SP2′ of the second spurious signal after the frequency shift performed in the frequency shift step is provided as |f.sub.SP1−f.sub.LO2−Δf|, and in the frequency setting step, the first intermediate frequency f.sub.IF1 and the frequency f.sub.LO1 are decided using the frequency shift amount Δf that does not establish a relationship of −W/2≤|f.sub.SP1−f.sub.LO2−Δf|−f.sub.IF2′≤+W/2.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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BEST MODE FOR CARRYING OUT THE INVENTION
(7) Hereinafter, an embodiment of a signal analysis apparatus and a signal analysis method according to the present invention will be described using the drawings.
(8) As illustrated in
(9) For example, the DUT 100 is a mobile terminal or a base station that includes a wireless communication antenna and an RF circuit and can output an analog RF signal. Examples of a communication standard of the DUT 100 include 5G NR, TD-LTE, FDD-LTE, LTE-Advanced, GSM (registered trademark), TD-SCDMA, W-CDMA (registered trademark), CDMA2000, and Bluetooth (registered trademark). The DUT 100 and the first frequency conversion unit 10 may be connected in a wired manner through a coaxial cable or the like, or may be connected in a wireless manner through a wireless communication antenna.
(10) The first frequency conversion unit 10 performs frequency conversion of a frequency of the analog RF signal as the measured signal S.sub.RF output from the DUT 100 and includes a first local oscillator 11, a first mixer 12, a BPF 13, a second local oscillator 14, and a second mixer 15.
(11) For example, the first local oscillator 11 is configured with a PLL circuit and receives a control signal from the frequency setting unit 30, described later, and outputs a sine wave of a frequency f.sub.LO1 that is higher than the original frequency f.sub.RF of the measured signal S.sub.RF by a frequency of a conversion result, to the first mixer 12 as a first local oscillation signal S.sub.LO1.
(12) The first mixer 12, by performing frequency mixing of the measured signal S.sub.RF of the frequency f.sub.RF with the first local oscillation signal S.sub.LO1 of the frequency f.sub.LO1 output from the first local oscillator 11, generates output signals of a sum component and a difference component of the frequencies of the two signals, that is, output signals of frequencies f.sub.RF+f.sub.LO1 and |f.sub.RF−f.sub.LO1|. In addition, the first mixer 12 generates an output signal including a second harmonic component of the measured signal S.sub.RF. Hereinafter, the frequency |f.sub.RF−f.sub.LO1| will be referred to as a “first intermediate frequency f.sub.IF1”, and the output signal of the frequency |f.sub.RF−f.sub.LO1| will be referred to as a “first intermediate frequency signal S.sub.IF1”. In addition, the signal including the second harmonic component of the measured signal S.sub.RF will be referred to as a “first spurious signal S.sub.SP1”.
(13) The BPF 13 is a bandpass filter of a passed center frequency f.sub.0 disposed between the first mixer 12 and the second mixer 15, and output signals including the first intermediate frequency signal S.sub.IF1 and the first spurious signal S.sub.SP1 output from the first mixer 12 are input into the BPF 13. The BPF 13 allows the first intermediate frequency signal S.sub.IF1 of the first intermediate frequency f.sub.IF1 and the first spurious signal S.sub.SP1 to pass among the output signals from the first mixer 12, and removes the sum component, a third or higher harmonic component of the measured signal S.sub.RF, and a harmonic component of the first local oscillation signal S.sub.LO1 among the output signals from the first mixer 12.
(14) For example, the second local oscillator 14 is configured with a PLL circuit and outputs a sine wave of a frequency f.sub.LO2 to the second mixer 15 as a second local oscillation signal S.sub.LO2. Here, the frequency f.sub.LO2 is a fixed value.
(15) The second mixer 15, by performing the frequency mixing of the first intermediate frequency signal S.sub.IF1 of the first intermediate frequency f.sub.IF1 passing through the BPF 13 with the second local oscillation signal S.sub.LO2 of the frequency f.sub.LO2 output from the second local oscillator 14, generates output signals of a sum component and a difference component of the frequencies of the two signals, that is, output signals of frequencies f.sub.IF1+f.sub.LO2 and |f.sub.IF1−f.sub.LO2|. In addition, the second mixer 15, by performing the frequency mixing of the first spurious signal S.sub.SP1 of the frequency f.sub.SP1 passing through the BPF 13 with the second local oscillation signal S.sub.LO2 of the frequency f.sub.LO2 output from the second local oscillator 14, generates output signals of a sum component and a difference component of the frequencies of the two signals, that is, output signals of frequencies f.sub.SP1+f.sub.LO2 and |f.sub.SP1−f.sub.LO2|.
(16) Hereinafter, the frequency |f.sub.IF1−f.sub.LO2| will be referred to as a “second intermediate frequency f.sub.IF2”, and the output signal of the frequency |f.sub.IF1−f.sub.LO2| will be referred to as a “second intermediate frequency signal S.sub.IF2”. In addition, the frequency |f.sub.SP1−f.sub.LO2| will be referred to as a “frequency f.sub.SP2”, and an output signal of the frequency f.sub.SP2 will be referred to as a “second spurious signal S.sub.SP2”. That is, the second spurious signal S.sub.SP2 is an unnecessary wave signal downconverted from the first spurious signal S.sub.SP1 by the second mixer 15.
(17) The AD converter 20 performs AD conversion of output signals including the second intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 output from the second mixer 15 into binary digital data having a predetermined number of bits by sampling the output signals at a predetermined sampling frequency.
(18) The second frequency conversion unit 25 performs frequency conversion of the output signals from the AD converter 20 and includes an NCOM unit (frequency shift) 26 and a digital filter 27.
(19) For example, the NCOM unit 26 includes a numeric controlled oscillator modulator (NCOM), a digital up converter (DUC), and a digital down converter (DDC) and performs frequency shift of the output signals including the second intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 after the AD conversion performed by the AD converter 20 by a frequency shift amount Δf on a frequency axis.
(20) For example, the digital filter 27 is a bandpass filter of a passed center frequency f.sub.D and a passed bandwidth W and allows a second intermediate frequency signal S.sub.IF2′ after the frequency shift performed by the NCOM unit 26 to pass and removes a second spurious signal S.sub.SP2′ after the frequency shift performed by the NCOM unit 26. Here, the passed center frequency f.sub.D is a fixed value equal to f.sub.IF2′ described later.
(21) The first intermediate frequency f.sub.IF1, the second intermediate frequency f.sub.IF2, the second intermediate frequency f.sub.IF2′ after the frequency shift performed by the NCOM unit 26, the frequency f.sub.LO1 of the first local oscillation signal S.sub.LO1, the frequency f.sub.SP1 of the first spurious signal S.sub.SP1, the frequency f.sub.SP2 of the second spurious signal S.sub.SP2, and a frequency f.sub.SP2′ of the second spurious signal S.sub.SP2′ after the frequency shift performed by the NCOM unit 26 are provided by Expressions (1) to (7) below.
f.sub.IF1=f.sub.0+Δf (1)
f.sub.IF2=|f.sub.IF1−f.sub.LO2|=f.sub.0+Δf−f.sub.LO2| (2)
f.sub.IF2′=f.sub.D=|f.sub.0−f.sub.LO2| (3)
f.sub.LO1=f.sub.c+f.sub.IF1=f.sub.c+f.sub.0+Δf (4)
f.sub.SP1=2×f.sub.RF (5)
f.sub.SP2=|f.sub.SP1−f.sub.LO2| (6)
f.sub.SP2′=|f.sub.SP1−f.sub.LO2−Δf| (7)
(22) The frequency setting unit 30 decides the first intermediate frequency f.sub.IF1 of the first intermediate frequency signal S.sub.IF1 and the frequency f.sub.LO1 of the first local oscillation signal S.sub.LO1 in accordance with the center frequency f.sub.c of the measured signal S.sub.RF depending on Expressions (1) and (4) above. Furthermore, the frequency setting unit 30 sets the decided frequency f.sub.LO1 and the frequency f.sub.LO2, which is a fixed value, in the first local oscillator 11 and the second local oscillator 14, respectively.
(23) Here, the frequency setting unit 30 decides the frequency shift amount Δf that does not establish a relationship in Expression (8) below, in accordance with the center frequency f.sub.c of the measured signal S.sub.RF such that the frequency f.sub.SP2′ of the second spurious signal S.sub.SP2′ after the frequency shift performed by the NCOM unit 26 is not included in the passed bandwidth W of the digital filter 27. In addition, the frequency setting unit 30 calculates Expressions (1) to (7) using the decided frequency shift amount Δf.
f.sub.IF2′−W/2≤f.sub.SP2′≤f.sub.IF2′+W/2−W/2≤|f.sub.SP1−f.sub.LO2−Δf|−f.sub.IF2′≤+W/2 (8)
(24) For example, in a case where a relationship in Expression (9) below is not established, the frequency setting unit 30 decides the frequency shift amount Δf as Δf=0. Meanwhile, in a case where the relationship in Expression (9) below is established, the frequency setting unit 30 decides the frequency shift amount Δf that satisfies Δf≥2W/3 or Δf≤−2W/3.
f.sub.IF2′−W/2≤f.sub.SP2≤f.sub.IF2′+W/2−W/2≤|f.sub.SP1−f.sub.LO2|−f.sub.IF2′≤+W/2 (9)
(25) For example, an example of f.sub.c, f.sub.SP1, Δf, f.sub.IF1, f.sub.LO1, f.sub.LO2, f.sub.SP2, f.sub.IF2, f.sub.SP2′, f.sub.IF2′, and a value of a passed band of the digital filter 27 in a case where the passed center frequency f.sub.0 of the BPF 13 is 9 GHz and the passed center frequency f.sub.D of the digital filter 27 is 1.95 GHz is illustrated in
(26) In this example, in a case where the center frequency f.sub.c of the measured signal S.sub.RF is within a range of 4.45 GHz≤f.sub.c≤4.5 GHz, setting 0.2 GHz as the frequency shift amount Δf not establishing the relationship in Expression (8) results in the first intermediate frequency f.sub.IF1 of 9.2 GHz. Furthermore, the NCOM unit 26 performs the frequency shift of the second intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 by 0.2 GHz.
(27) In addition, in a case where the center frequency f.sub.c of the measured signal S.sub.RF is within a range of 4.5 GHz<f.sub.c≤4.55 GHz, setting −0.2 GHz as the frequency shift amount Δf not establishing the relationship in Expression (8) results in the first intermediate frequency f.sub.IF1 of 8.8 GHz. Furthermore, the NCOM unit 26 performs the frequency shift of the second intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 by −0.2 GHz.
(28) Consequently, the frequency f.sub.SP2′ of the second spurious signal S.sub.SP2′ after the frequency shift performed by the NCOM unit 26 deviates out of a range of f.sub.IF2′−W/2≤f.sub.SP2′≤f.sub.IF2′+W/2, that is, out of a range of 1.855 to 2.045 GHz. Meanwhile, in a case where the center frequency f.sub.c of the measured signal S.sub.RF is within a range of f.sub.c<4.45 GHz or 4.55 GHz<f.sub.c, the relationship in Expression (9) is not established. Thus, Δf=0 is satisfied.
(29) For example, in a case where the center frequency f.sub.c of the measured signal S.sub.RF is 3 GHz, the frequency f.sub.SP2 of the second spurious signal S.sub.SP2 is not within a range of 1.855 to 2.045 GHz. Thus, the frequency shift amount Δf is set to Δf=0 Hz. Here, the frequency f.sub.LO1 is 12 GHz, and the first intermediate frequency f.sub.IF1 is 9 GHz. The first spurious signal S.sub.SP1 having the frequency f.sub.SP1 of 6 GHz is converted into the second spurious signal S.sub.SP2 having the frequency f.sub.SP2 of 4.95 GHz by the second mixer 15. In addition, the first intermediate frequency signal S.sub.IF1 having the first intermediate frequency f.sub.IF1 of 9 GHz is converted into the second intermediate frequency signal S.sub.IF2 having the second intermediate frequency f.sub.IF2 of 1.95 GHz by the second mixer 15.
(30) Thus, the second spurious signal S.sub.SP2 after the AD conversion performed by the AD converter 20 passes through the NCOM unit 26 and then, is removed by the digital filter 27. Meanwhile, the second intermediate frequency signal S.sub.IF2 after the AD conversion performed by the AD converter 20 passes through the NCOM unit 26 and then, passes through the digital filter 27.
(31) In addition, in a case where the center frequency f.sub.c of the measured signal S.sub.RF is 4.5 GHz, the frequency f.sub.SP2 of the second spurious signal S.sub.SP2 is within a range of 1.855 to 2.045 GHz. Thus, the frequency shift amount Δf is set to, for example, Δf=0.2 GHz. Here, the frequency f.sub.LO1 is 13.7 GHz, and the first intermediate frequency f.sub.IF1 is 9.2 GHz. The first spurious signal S.sub.SP1 having the frequency f.sub.SP1 of 9 GHz is converted into the second spurious signal S.sub.SP2 having the frequency f.sub.SP2 of 1.95 GHz by the second mixer 15. In addition, the first intermediate frequency signal S.sub.IF1 having the first intermediate frequency f.sub.IF1 of 9.2 GHz is converted into the second intermediate frequency signal S.sub.IF2 having the second intermediate frequency f.sub.IF2 of 1.75 GHz by the second mixer 15.
(32) The second spurious signal S.sub.SP2 after the AD conversion performed by the AD converter 20 is converted into the second spurious signal S.sub.SP2′ having the frequency f.sub.SP2′ of 2.15 GHz by the NCOM unit 26 and then, is removed by the digital filter 27. Meanwhile, the second intermediate frequency signal S.sub.IF2 after the AD conversion performed by the AD converter 20 is converted into the second intermediate frequency signal S.sub.IF2′ having the frequency f.sub.IF2′ of 1.95 GHz by the NCOM unit 26 and then, passes through the digital filter 27.
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(36) The signal analysis unit 40 illustrated in
(37) The storage unit 41 stores digital data of the second intermediate frequency signal S.sub.IF2′ passing through the digital filter 27.
(38) The baseband module 42 generates orthogonal signals I(t) and Q(t) that are orthogonal to each other, by orthogonally demodulating the digital data of the second intermediate frequency signal S.sub.IF2′ stored in the storage unit 41. In addition, the baseband module 42 performs a predetermined signal analysis process on the generated orthogonal signals I(t) and Q(t). Examples of the signal analysis process executed by the baseband module 42 include temporally changing an amplitude (power), a phase, a frequency, or the like of the measured signal SRF and obtaining a channel power (CHP), an occupied bandwidth (OBW), an adjacent channel leakage ratio (ACLR), a burst average power, modulation accuracy (EVM), a spectrum emission mask (SEM), a transmission power level, and a transmission spectrum mask.
(39) The display unit 50 is configured with a display device such as an LCD or a CRT and displays various display contents such as a result of the signal analysis process performed by the signal analysis unit 40 in accordance with a display control performed by the control unit 52. Furthermore, the display unit 50 displays operation targets such as a button, a soft key, a pull-down menu, and a text box for setting a measurement condition and the like in accordance with a control signal output from the control unit 52.
(40) The operation unit 51 receives an operation input of a user and is configured with, for example, a touch panel that is disposed on a surface of a display screen of the display unit 50. Alternatively, the operation unit 51 may be configured to include an input device such as a keyboard or a mouse. The operation input provided to the operation unit 51 is detected by the control unit 52. For example, the user can arbitrarily designate the center frequency f.sub.c of the measured signal S.sub.RF, the passed center frequency f.sub.0 of the BPF 13, and the passed bandwidth W of the digital filter 27 using the operation unit 51.
(41) For example, the control unit 52 is configured with a microcomputer or a personal computer including a CPU, a ROM, a RAM, an HDD, and the like and controls an operation of each of the units constituting the signal analysis apparatus 1. In addition, at least a part of the frequency setting unit 30 and the baseband module 42 can be configured in a software manner by causing the control unit 52 to move a predetermined program stored in the ROM or the like to the RAM and execute the predetermined program. At least a part of the frequency setting unit 30 and the baseband module 42 can be configured with a digital circuit such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). Alternatively, at least a part of the frequency setting unit 30 and the baseband module 42 can be configured by appropriately combining a hardware process performed by the digital circuit and a software process performed by the predetermined program.
(42) Hereinafter, an example of a process of the signal analysis method using the signal analysis apparatus 1 of the present embodiment will be described with reference to the flowchart in
(43) First, various information related to the frequency conversion, that is, information such as the center frequency f.sub.c of the measured signal S.sub.RF, the passed center frequency f.sub.0 of the BPF 13, and the passed bandwidth W of the digital filter 27, are input by the operation input provided to the operation unit 51 by the user (step S1).
(44) Next, the frequency setting unit 30 decides the frequency shift amount Δf not establishing the relationship in Expression (8) above in accordance with the center frequency f.sub.c of the measured signal S.sub.RF. Furthermore, the frequency setting unit 30 decides the first intermediate frequency f.sub.IF1 of the first intermediate frequency signal S.sub.IF1 and the frequency f.sub.LO1 of the first local oscillation signal S.sub.LO1 in accordance with the center frequency f.sub.c of the measured signal S.sub.RF depending on Expressions (1) and (4) above (frequency setting step S2).
(45) Next, the first local oscillator 11 outputs the first local oscillation signal S.sub.LO1 of the frequency f.sub.LO1 (first local oscillation step S3).
(46) Next, the first mixer 12 generates the first intermediate frequency signal S.sub.IF1 of the first intermediate frequency f.sub.IF1 by performing the frequency mixing of the measured signal S.sub.RF with the first local oscillation signal S.sub.LO1, and generates the first spurious signal S.sub.SP1 having the frequency f.sub.SP1 of the second harmonic component of the measured signal S.sub.RF (first frequency mixing step S4).
(47) Next, the output signals including the first intermediate frequency signal S.sub.IF1 and the first spurious signal S.sub.SP1 output from the first mixer 12 are input into the BPF 13, and the BPF 13 allows the first intermediate frequency signal S.sub.IF1 and the first spurious signal S.sub.SP1 to pass (bandpass step S5).
(48) Next, the second local oscillator 14 outputs the second local oscillation signal S.sub.LO2 of the frequency f.sub.LO2 (second local oscillation step S6).
(49) Next, the second mixer 15 generates the second intermediate frequency signal S.sub.IF2 by performing the frequency mixing of the first intermediate frequency signal S.sub.IF1 passing through bandpass step S5 with the second local oscillation signal S.sub.LO2. In addition, the second mixer 15 generates the second spurious signal S.sub.SP2 by performing the frequency mixing of the first spurious signal S.sub.SP1 passing through bandpass step S5 with the second local oscillation signal S.sub.LO2 (second frequency mixing step S7).
(50) Next, the AD converter 20 performs the AD conversion of the second intermediate frequency signal SIF2 and the second spurious signal SSP2 output from the second mixer 15 (AD conversion step S8).
(51) Next, the NCOM unit 26 performs the frequency shift of the second intermediate frequency signal S.sub.IF2 and the second spurious signal S.sub.SP2 after the AD conversion in AD conversion step S8 by the frequency shift amount Δf on the frequency axis (NCOM step S9). Here, the second intermediate frequency f.sub.IF2′ of the second intermediate frequency signal S.sub.IF2′ after the frequency shift performed in NCOM step S9 is provided as |f.sub.0−f.sub.LO2| as illustrated in Expression (3). In addition, the second spurious signal S.sub.SP2′ after the frequency shift performed in NCOM step S9 is provided as |f.sub.SP1−f.sub.LO2−Δf| as illustrated in Expression (7). In addition, NCOM step S9 may be referred to as frequency shift unit.
(52) Next, the digital filter 27 allows the second intermediate frequency signal S.sub.IF2′ after the frequency shift in NCOM step S9 to pass and removes the second spurious signal S.sub.SP2′ after the frequency shift in NCOM step S9 (digital filter step S10).
(53) Next, the signal analysis unit 40 analyzes the second intermediate frequency signal S.sub.IF2′ passing through digital filter step S10 (signal analysis step S11).
(54) As described above, the signal analysis apparatus 1 according to the present embodiment decides the frequency shift amount Δf, the first intermediate frequency f.sub.IF1, and the frequency f.sub.LO1 in accordance with the center frequency fc of the measured signal S.sub.RF depending on Expressions (1), (4), (8), and the like, performs an analog signal process using the first frequency conversion unit 10, and then, performs a digital signal process using the second frequency conversion unit 25. Accordingly, by varying the frequency shift amount Δf, the first intermediate frequency f.sub.IF1, and the frequency f.sub.LO1, the signal analysis apparatus 1 according to the present embodiment can analyze the measured signal S.sub.RF while avoiding a spurious harmonic of the measured signal S.sub.RF generated by the first mixer 12, without changing a configuration of hardware related to the frequency conversion. Furthermore, even in a case where a standard that uses a new band is established in the future, the signal analysis apparatus 1 according to the present embodiment can perform measurement that avoids a spurious harmonic, without changing the configuration of the hardware related to the frequency conversion.
(55) In addition, since the first intermediate frequency f.sub.IF1 and the frequency f.sub.LO1 can be separately used by shifting the first intermediate frequency f.sub.IF1 and the frequency f.sub.LO1 by the frequency shift amount Δf, the signal analysis apparatus 1 according to the present embodiment can receive a desired wave of the second intermediate frequency f.sub.IF2′ while removing an unnecessary spurious harmonic of the frequency f.sub.SP2′ using the digital filter 27 of the passed bandwidth W. In other words, the signal analysis apparatus 1 according to the present embodiment can separate the first intermediate frequency f.sub.IF1 and the frequency f.sub.SP1 of the first spurious signal S.sub.SP1 generated by the first mixer 12, using the digital filter 27 of the rear stage.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
(56) 1: signal analysis apparatus 10: first frequency conversion unit 11: first local oscillator 12: first mixer 13: BPF 14: second local oscillator 15: second mixer 20: AD converter 25: second frequency conversion unit 26: NCOM unit 27: digital filter 30: frequency setting unit 40: signal analysis unit 100: DUT