CN104101807A - Self intermodulation inhibition method for transmission passive intermodulation (PIM) test - Google Patents

Abstract

The invention provides a self intermodulation inhibition method for a transmission passive intermodulation (PIM) test. A phase position of a PIM product is measured through a PIM reference channel, and in allusion to the transmission PIM test of appliance parts such as antennae, a method for inhibiting transmission self PIM of a test system is provided and a novel method for inhibiting reflection self PIM can be provided. By means of the scheme, reflection self intermodulation and system transmission self intermodulation can be inhibited, thereby, excessive demands for intermodulation features of loads are not required, meanwhile, interference of transmission PIM and reflection PIM can be measured, and the dynamic range and the measurement uncertainty of the transmission PIM test of the system can be improved.

Description

A kind of self intermodulation suppression method of transmitting passive cross modulation test

Technical field

The invention belongs to passive cross modulation test technical field, in particular a kind of self intermodulation suppression method of transmitting passive cross modulation test.

Background technology

In Modern Communication System application, more outstanding to the interference of system by the non-linear passive intermodulation causing of passive device (PIM) product, linear characteristic requirement to passive devices such as antenna, connector, cables is more and more higher, and therefore PIM test macro is developed rapidly in the last few years.The main method of testing of PIM product comprises reflective and conveying type at present, and the object of reflective test is disturbing with the reciprocal PIM of multi-tone signal of tester parts generation, and general connector, cable are often weighed its linearity with this index; The object of conveying type test is disturbing with the equidirectional PIM of multi-tone signal of tester parts generation, and antenna is often weighed its linearity with this index.

The leading indicator of PIM test macro is self intermodulation, also referred to as residue intermodulation.The main method of system reduction self intermodulation is to adopt the low intermodulation device of low intermodulation explained hereafter parts, self intermodulation of at present-171dBc@2x (+43dBm) is almost the limit of low intermodulation technique,-128dBm, and can reach-135dBm of the sensitivity of receiver, obviously self intermodulation of system has limited the test specification of PIM greatly.

The another kind of method that reduces self intermodulation is that self intermodulation that instrument is produced is calibrated, and uses the method for system balance to suppress.The vector measurement method of the method based on PIM measured phase place and the amplitude of PIM simultaneously, and the PIM product of measuring system self first before test, carries out vector deduction (number of patent application: 201310689443.1) to it when test.But the method can only be calibrated reflected P IM, and low intermodulation load is had higher requirements, can not calibrate the transmission PIM test of the device parts such as antenna.

Therefore, there is defect in prior art, needs to improve.

Summary of the invention

Technical matters to be solved by this invention is for the deficiencies in the prior art, and a kind of self intermodulation suppression method of transmitting passive cross modulation test is provided.

Technical scheme of the present invention is as follows:

Self intermodulation suppression method of transmitting passive cross modulation test, wherein, comprises the following steps:

Step 1: signal source f1 and f2 form two-tone signal after amplifying, closing road, load in the antenna transmission system in microwave dark room the reflected P IM of generation by the Tx passage of first duplexer _rsending into receiver by Rx passage receives; Use another antenna horn to receive the signal transmission of antenna transmission system, transmission two-tone signal is absorbed by load by the Tx passage of the second diplexer, transmission PIM _trx passage via diplexer enters receiver;

Step 2: establish the transmission PIM signal receiving and can be expressed as PIM _tM, it is reflected P IM _tsynthetic with the vector of system self PIM, the transmission PIM signal receiving can be expressed as, formula one:

PIM _TM＝PIM _T+PIM _T1+PIM _T2；

Step 3: by the PIM in formula one _t1and PIM _t2from measured value, deduct;

Step 4: the reflection of test antenna self intermodulation is, formula seven: PIM _rM=PIM _r+ PIM _r1; Or reflection self intermodulation of the device parts such as test cable, than formula more than seven an error PIM _r2, its reflection intermodulation can be expressed as, formula eight:

PIM _RM＝PIM _R+PIM _R1+PIM _R2。

Step 5: testing standard part, try to achieve PIM _r1time gate position and PIM _r2with respect to the time gate position of standard component; Measured piece is accessed to standard component head end test reflection intermodulation, measurement standard part time shaft and PIM _r2time shaft;

Step 6: remove standard component test measured piece, according to formula five:

Method setup times door, try to achieve the PIM after calibration _r, deduction PIM _r1and PIM _r2

Realize reflection self intermodulation suppression.

Self intermodulation suppression method of described transmission passive cross modulation test, wherein, in described step 2, the vector of described system self PIM is synthetic, be divided into two parts, a part is the transmission PIM that combiner, diplexer etc. form, and the vector disturbing for the PIM forming before first duplexer output port synthesizes, be defined as output port transmission PIM, use PIM _t1represent; Another part is self PIM that the second diplexer, receiver B etc. form, and is that the vector that disturbs of the PIM that forms after the second diplexer receiving port is synthetic, is defined as input port transmission PIM, uses PIM _t2represent.

Self intermodulation suppression method of described transmission passive cross modulation test, wherein, in described step 3, by the PIM in formula one _t1and PIM _t2the method of deducting from measured value is:

The first step: use low intermodulation cable, intermodulation standard component and low intermodulation load, instrument is connected; Standard component is the reference PIM source of a connector form, and reflected P IM is received by receiver A, and transmission PIM is received by receiver B; The measured value that now transmits PIM reception is expressed as, formula two:

or

Receiver is I/Q receiver, for testing the amplitude and the phase place that receive signal; | PIM _tM| obtained by the direct measuring amplitude of receiver B; can not directly measure, must have fixed phase just meaningful; This measuring method forms PIM reference source by double source frequency multiplication, difference frequency, and has reference receiver R to receive, and therefore vector measurement result is, formula three:

${\mathrm{PIM}}_{\mathrm{TM}}=\left|R\right|*\frac{B}{R};$

This measured value is with respect to the frequency response with reference to PIM signal phase; The CHIRP-Z inverse transformation that uses M unit, can obtain PIM _tMthe time domain response in relative reference PIM source, formula four:

${\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left({\mathrm{nT}}_s\right)=\frac{{\mathrm{\φ}}_0}{2\mathrm{\π}}{A}_0^n{e}^{{\mathrm{j\θ}}_0}\underset{k=0}{\overset{M_Z-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}\left(k\right)e^{{\mathrm{j\φ}}_0\mathrm{nk}},n=\mathrm{0,1},...,N_z-1;$

The virtual time position of trying to achieve standard component response, the top of response is standard component response position, is designated as t0; The PIM peak of negative sense time shaft is PIM _t2, the response time is designated as t1, t2; The PIM peak of positive time shaft is PIM _t1, the response time is designated as t3, t4;

Second step is by system under test (SUT) or measured piece access standard component rear end, the transmission intermodulation PIM of testing standard part and measured piece _tM, require the transmission PIM of standard component to be greater than the transmission PIM of measured piece, the CHIRP-Z of now note transmission PIM converts Plays part, PIM _t2and PIM _t1corresponding time shaft is t0 ', t1 ', t2 ', t3 ' and t4 ', so obviously t1=t1 ', t2=t2 ', t4-t3=t4 '-t3 ', t3-t0=t3 '-t0 '; Making time gate is formula five:

During by test measured piece or system under test (SUT), obtain measured value PIM _tM, CHIRP-Z contravariant is changed to PIM ' _tM, suppress so PIM _t1and PIM _t2measurement result be PIM ' _tM* the CHIRP-Z of Gate conversion, formula six:

${\mathrm{PIM}}_T=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left(n\right)*\mathrm{Gate}\left(n\right)\left(\frac{W_0^{\mathrm{nk}}}{A_0^n}\right)e^{-\mathrm{jn}({\mathrm{k\φ}}_0-{\mathrm{\θ}}_0)};$

PIM _tfor the frequency spectrum after self intermodulation suppression.

The reflection of test antenna self intermodulation is, formula seven: PIM _rM=PIM _r+ PIM _r1; Or reflection self intermodulation of the device parts such as test cable, than formula more than seven an error PIM _r2, reflection intermodulation can be expressed as, formula eight:

PIM _RM＝PIM _R+PIM _R1+PIM _R2。Adopt such scheme, based on the vector measurement method of PIM, PIM standard component, low intermodulation testing cable and low intermodulation load are used, use the method for similar " time domain door " that the transmission PIM of system is disturbed to " deduction ", can inhibitory reflex self intermodulation can inhibition system transmit self intermodulation again, and needn't too require the intermodulation characteristic of load, and measure transmission PIM and reflected P IM simultaneously and disturb, improve dynamic range and the uncertainty of measurement of the transmission PIM test of system.

Brief description of the drawings

Fig. 1 is that PIM test and error schematic diagram are reflected and transmit in the present invention.

Fig. 2 is that PIM test self intermodulation suppression principle and connection diagram are transmitted in the present invention.

Fig. 3 is that in the present invention, CHIRP-Z conversion realizes schematic diagram.

Fig. 4 is PIM time domain response figure in the present invention.

Fig. 5 is the transmission intermodulation schematic diagram of testing standard part and measured piece in the present invention.

Fig. 6 is the reflection intermodulation schematic diagram of testing measured piece and standard component in the present invention.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

Embodiment 1

The present invention is based on the vector measurement method of passive intermodulation (PIM) test, measure the phase place of PIM product by a PIM reference channel, for the transmission PIM test of the device parts such as antenna, a kind of method that suppresses test macro transmission self PIM is provided, and the new method of a kind of inhibitory reflex self PIM is provided.

Passive cross modulation test principle is generally divided into two kinds of mode of operations, reflective and conveying type.The object of reflective test is disturbing with the reciprocal PIM of multi-tone signal of tester parts generation, and general connector, cable are often weighed its linearity with this index; The object of conveying type test is disturbing with the equidirectional PIM of multi-tone signal of tester parts generation, and antenna is often weighed its linearity with this index, and two kinds of method of testings can be measured simultaneously.Taking antenna transmission system as example, reflection and transmission PIM test philosophy and error illustrate as shown in Figure 1, and in Fig. 1, signal source f1 and f2 form two-tone signal through amplification, after closing road, load in the antenna transmission system in microwave dark room the reflected P IM (PIM of generation by the Tx passage of first duplexer _r) send into receiver reception by Rx passage; Use another antenna horn to receive the signal transmission of antenna transmission system, transmission two-tone signal is absorbed by load by the Tx passage of the second diplexer, transmission PIM (PIM _t) enter receiver via the Rx passage of diplexer.

If the transmission PIM signal that receiver B receives can be expressed as PIM _tM, it is reflected P IM (PIM _t) and the vector of system self PIM synthetic.System self PIM can be divided into two parts, and the one, the transmission PIM that combiner, diplexer etc. form, synthetic for the vector that the PIM forming before first duplexer output port disturbs, may be defined as output port transmission PIM, use PIM _t1represent; Another part is self PIM that the second diplexer, receiver B etc. form, and is that the vector that disturbs of the PIM that forms after the second diplexer receiving port is synthetic, may be defined as input port transmission PIM, uses PIM _t2represent.The transmission PIM signal that receiver B receives so can be expressed as, formula one:

PIM _TM＝PIM _T+PIM _T1+PIM _T2。(1)

For by the PIM in formula one _t1and PIM _t2from measured value, deduct, the present invention adopts the vector measurement method of PIM, and the first step is used low intermodulation cable, intermodulation standard component and low intermodulation load, and instrument is connected by Fig. 2 mode.

Standard component is the reference PIM source of a connector form, access test macro, and reflected P IM is received by receiver A, and transmission PIM is received by receiver B.

Adopt the measured value that PIM reception is now transmitted in vector method expression to be expressed as, formula two:

or

Receiver is I/Q receiver, can test the amplitude and the phase place that receive signal.| PIM _tM| can be obtained by the direct measuring amplitude of receiver B; can not directly measure, must have fixed phase just meaningful.This measuring method forms PIM reference source by double source frequency multiplication, difference frequency, and has reference receiver R to receive, and therefore vector measurement result is, formula three:

${\mathrm{PIM}}_{\mathrm{TM}}=\left|R\right|*\frac{B}{R}.---\left(3\right)$

This measured value is with respect to the frequency response with reference to PIM signal phase.

The CHIRP-Z inverse transformation that uses M unit, can obtain PIM _tMthe time domain response in relative reference PIM source, formula four:

${\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left({\mathrm{nT}}_s\right)=\frac{{\mathrm{\φ}}_0}{2\mathrm{\π}}{A}_0^n{e}^{{\mathrm{j\θ}}_0}\underset{k=0}{\overset{M_Z-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}\left(k\right)e^{{\mathrm{j\φ}}_0\mathrm{nk}},n=\mathrm{0,1},...,N_z-1.---\left(4\right)$

Above-mentioned CHIRP-Z inverse transformation can utilize Fast Fourier Transform (FFT) to realize, and rudimentary algorithm as shown in Figure 3.

Therefore can be in the hope of the virtual time position of standard component response, as shown in Figure 4, the top responding in Fig. 4 is standard component response position to simulation result, is designated as t0; The PIM peak of negative sense time shaft is PIM _t2, the response time is designated as t1, t2; The PIM peak of positive time shaft is PIM _t1, the response time is designated as t3, t4.Because reference planes are virtual plane, response time plane is not through calibration, and therefore time shaft only has relative meaning.

Second step is by system under test (SUT) or measured piece access standard component rear end, the transmission intermodulation PIM of testing standard part and measured piece _tM, its connection diagram as shown in Figure 5.Require the transmission PIM of standard component to be greater than the transmission PIM of measured piece, the CHIRP-Z of now note transmission PIM converts Plays part, PIM _t2and PIM _t1corresponding time shaft is t0 ', t1 ', t2 ', t3 ' and t4 ', so obviously t1=t1 ', t2=t2 ', t4-t3=t4 '-t3 ', t3-t0=t3 '-t0 '.Because standard component is connector, its time domain yardstick can be ignored, and therefore can make time gate be, formula five simultaneously:

While testing measured piece or system under test (SUT) as Fig. 1, obtain measured value PIM _tM, CHIRP-Z contravariant is changed to PIM ' _tM, suppress so PIM _t1and PIM _t2measurement result be PIM ' _tM* the CHIRP-Z of Gate conversion, formula six:

${\mathrm{PIM}}_T=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left(n\right)*\mathrm{Gate}\left(n\right)\left(\frac{W_0^{\mathrm{nk}}}{A_0^n}\right)e^{-\mathrm{jn}({\mathrm{k\φ}}_0-{\mathrm{\θ}}_0)}---\left(6\right)$

PIM _tfor the frequency spectrum after self intermodulation suppression.

It should be noted that and why select CHIRP-Z transfer pair, mainly because can select time period, arbitrfary point arbitrarily to carry out time-domain analysis, here time-frequency switch technology that can use other completely, as Fourier Transform Technique replaces, carry out-Ts/2, to the time series analysis of Ts/2 (inverse that Ts is sample frequency), tries to achieve gate function and suppresses.

In addition, also can be conveniently carry out self intermodulation suppression to reflection intermodulation with " time gate " of the present invention method, instead of vector subtraction method, advantage is to suppose that self PIM of connecting system load is enough good again, and can suppress self intermodulation of load.

As shown in Figure 2, the reflection of test antenna self intermodulation is, formula seven:

PIM _RM＝PIM _R+PIM _R1。(7)

This is a kind of special circumstances, and more general situation is reflection self intermodulation of the device parts such as test cable, than formula (7) many an error PIM _r2, it produces position as shown in Figure 2, and reflection intermodulation can be expressed as, formula eight:

PIM _RM＝PIM _R+PIM _R1+PIM _R2。(8)

First testing standard part, uses frequency-time domain converter technique to try to achieve PIM _r1time gate position and PIM _r2with respect to the time gate position of standard component; Afterwards measured piece is accessed to standard component head end test reflection intermodulation, as shown in Figure 6, measurement standard part time shaft and PIM _r2time shaft.

Remove standard component test measured piece, because standard component is that therefore connector is ignored and removed its impact on time shaft, according to the method setup times door of formula five, when use-switch technology can be tried to achieve the PIM after calibration frequently _r, realize reflection self intermodulation suppression.

Adopt such scheme, based on the vector measurement method of PIM, PIM standard component, low intermodulation testing cable and low intermodulation load are used, use the method for similar " time domain door " that the transmission PIM of system is disturbed to " deduction ", can inhibitory reflex self intermodulation can inhibition system transmit self intermodulation again, and needn't too require the intermodulation characteristic of load, and measure transmission PIM and reflected P IM simultaneously and disturb, improve dynamic range and the uncertainty of measurement of the transmission PIM test of system.

Embodiment 2

On the basis of above-described embodiment, further, a kind of self intermodulation suppression method of transmitting passive cross modulation test, wherein, comprises the following steps:

Step 1: signal source f1 and f2 form two-tone signal after amplifying, closing road, load in the antenna transmission system in microwave dark room the reflected P IM of generation by the Tx passage of first duplexer _rsending into receiver by Rx passage receives; Use another antenna horn to receive the signal transmission of antenna transmission system, transmission two-tone signal is absorbed by load by the Tx passage of the second diplexer, transmission PIM _trx passage via diplexer enters receiver;

Step 2: establish the transmission PIM signal receiving and can be expressed as PIM _tM, it is reflected P IM _tsynthetic with the vector of system self PIM, the transmission PIM signal receiving can be expressed as, formula one:

PIM _TM＝PIM _T+PIM _T1+PIM _T2。

Step 3: by the PIM in formula one _t1and PIM _t2from measured value, deduct;

Step 4: the reflection of test antenna self intermodulation is, formula seven: PIM _rM=PIM _r+ PIM _r1; Or reflection self intermodulation of the device parts such as test cable, than formula more than seven an error PIM _r2, its reflection intermodulation can be expressed as, formula eight:

PIM _RM＝PIM _R+PIM _R1+PIM _R2。

Step 5: testing standard part, try to achieve PIM _r1time gate position and PIM _r2with respect to the time gate position of standard component; Measured piece is accessed to standard component head end test reflection intermodulation, measurement standard part time shaft and PIM _r2time shaft;

Step 6: remove standard component test measured piece, according to formula five

Method setup times door, try to achieve the PIM after calibration _r, deduction PIM _r1and PIM _r2

Realize reflection self intermodulation suppression.

In said method, in described step 2, the vector of described system self PIM is synthetic, be divided into two parts, a part is the transmission PIM that combiner, diplexer etc. form, and the vector disturbing for the PIM forming before first duplexer output port synthesizes, be defined as output port transmission PIM, use PIM _t1represent; Another part is self PIM that the second diplexer, receiver B etc. form, and is that the vector that disturbs of the PIM that forms after the second diplexer receiving port is synthetic, is defined as input port transmission PIM, uses PIM _t2represent.

In said method, in described step 3, by the PIM in formula one _t1and PIM _t2the method of deducting from measured value is:

The first step: use low intermodulation cable, intermodulation standard component and low intermodulation load, instrument is connected; Standard component is the reference PIM source of a connector form, and reflected P IM is received by receiver A, and transmission PIM is received by receiver B; The measured value that now transmits PIM reception is expressed as, formula two:

or

Receiver is I/Q receiver, for testing the amplitude and the phase place that receive signal; PIM _tMobtained by the direct measuring amplitude of receiver B; can not directly measure, must have fixed phase just meaningful; This measuring method forms PIM reference source by double source frequency multiplication, difference frequency, and has reference receiver R to receive, and therefore vector measurement result is, formula three:

${\mathrm{PIM}}_{\mathrm{TM}}=\left|R\right|*\frac{B}{R};$

This measured value is with respect to the frequency response with reference to PIM signal phase; The CHIRP-Z inverse transformation that uses M unit, can obtain PIM _tMthe time domain response in relative reference PIM source, formula four:

${\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left({\mathrm{nT}}_s\right)=\frac{{\mathrm{\φ}}_0}{2\mathrm{\π}}{A}_0^n{e}^{{\mathrm{j\θ}}_0}\underset{k=0}{\overset{M_Z-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}\left(k\right)e^{{\mathrm{j\φ}}_0\mathrm{nk}},n=\mathrm{0,1},...,N_z-1;$

The virtual time position of trying to achieve standard component response, the top of response is standard component response position, is designated as t0; The PIM peak of negative sense time shaft is PIM _t2, the response time is designated as t1, t2; The PIM peak of positive time shaft is PIM _t1, the response time is designated as t3, t4;

Second step is by system under test (SUT) or measured piece access standard component rear end, the transmission intermodulation PIM of testing standard part and measured piece _tM, require the transmission PIM of standard component to be greater than the transmission PIM of measured piece, the CHIRP-Z of now note transmission PIM converts Plays part, PIM _t2and PIM _t1corresponding time shaft is t0 ', t1 ', t2 ', t3 ' and t4 ', so obviously t1=t1 ', t2=t2 ', t4-t3=t4 '-t3 ', t3-t0=t3 '-t0 '; Making time gate is formula five:

During by test measured piece or system under test (SUT), obtain measured value PIM _tM, CHIRP-Z contravariant is changed to PIM ' _tM, suppress so PIM _t1and PIM _t2measurement result be PIM ' _tM* the CHIRP-Z of Gate conversion, formula six:

${\mathrm{PIM}}_T=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left(n\right)*\mathrm{Gate}\left(n\right)\left(\frac{W_0^{\mathrm{nk}}}{A_0^n}\right)e^{-\mathrm{jn}({\mathrm{k\φ}}_0-{\mathrm{\θ}}_0)};$

PIM _tfor the frequency spectrum after self intermodulation suppression.

The reflection of test antenna self intermodulation is, formula seven: PIM _rM=PIM _r+ PIM _r1; Or reflection self intermodulation of the device parts such as test cable, than formula more than seven an error PIM _r2, its reflection intermodulation can be expressed as, formula eight:

PIM _RM＝PIM _R+PIM _R1+PIM _R2。

Adopt such scheme, based on the vector measurement method of PIM, PIM standard component, low intermodulation testing cable and low intermodulation load are used, use the method for similar " time domain door " that the transmission PIM of system is disturbed to " deduction ", can inhibitory reflex self intermodulation can inhibition system transmit self intermodulation again, and needn't too require the intermodulation characteristic of load, and measure transmission PIM and reflected P IM simultaneously and disturb, improve dynamic range and the uncertainty of measurement of the transmission PIM test of system.

Should be understood that, for those of ordinary skills, can be improved according to the above description or convert, and all these improvement and conversion all should belong to the protection domain of claims of the present invention.

Claims (3)

1. self intermodulation suppression method of transmitting passive cross modulation test, is characterized in that, comprises the following steps:

Step 1: signal source f1 and f2 form two-tone signal after amplifying, closing road, load in the antenna transmission system in microwave dark room the reflected P IM of generation by the Tx passage of first duplexer _rsending into receiver by Rx passage receives; Use another antenna horn to receive the signal transmission of antenna transmission system, transmission two-tone signal is absorbed by load by the Tx passage of the second diplexer, transmission PIM _trx passage via diplexer enters receiver;

Step 2: establish the transmission PIM signal receiving and can be expressed as PIM _tM, it is reflected P IM _tsynthetic with the vector of system self PIM, the transmission PIM signal receiving can be expressed as, formula one:

PIM _TM＝PIM _T+PIM _T1+PIM _T2；

Step 3: by the PIM in formula one _t1and PIM _t2from measured value, deduct;

Step 4: the reflection of test antenna self intermodulation is, formula seven: PIM _rM=PIM _r+ PIM _r1; Or reflection self intermodulation of the device parts such as test cable, than formula more than seven an error PIM _r2, its reflection intermodulation can be expressed as, formula eight:

PIM _RM＝PIM _R+PIM _R1+PIM _R2；

Step 5: testing standard part, try to achieve PIM _r1time gate position and PIM _r2with respect to the time gate position of standard component; Measured piece is accessed to standard component head end test reflection intermodulation, measurement standard part time shaft and PIM _r2time shaft;

Step 6: remove standard component test measured piece, according to formula five:

Method setup times door, try to achieve the PIM after calibration _r, deduction PIM _r1and PIM _r2realize reflection self intermodulation suppression.

2. self intermodulation suppression method of transmission passive cross modulation test as claimed in claim 1, it is characterized in that, in described step 2, the vector of described system self PIM is synthetic, be divided into two parts, a part is the transmission PIM that combiner, diplexer etc. form, and the vector disturbing for the PIM forming before first duplexer output port synthesizes, be defined as output port transmission PIM, use PIM _t1represent; Another part is self PIM that the second diplexer, receiver B etc. form, and is that the vector that disturbs of the PIM that forms after the second diplexer receiving port is synthetic, is defined as input port transmission PIM, uses PIM _t2represent.

3. self intermodulation suppression method of transmission passive cross modulation test as claimed in claim 1, is characterized in that, in described step 3, by the PIM in formula one _t1and PIM _t2the method of deducting from measured value is:

The first step: use low intermodulation cable, intermodulation standard component and low intermodulation load, instrument is connected; Standard component is the reference PIM source of a connector form, and reflected P IM is received by receiver A, and transmission PIM is received by receiver B; The measured value that now transmits PIM reception is expressed as, formula two:

or

Receiver is I/Q receiver, for testing the amplitude and the phase place that receive signal; | PIM _tM| obtained by the direct measuring amplitude of receiver B; can not directly measure, must have fixed phase just meaningful; This measuring method forms PIM reference source by double source frequency multiplication, difference frequency, and has reference receiver R to receive, and therefore vector measurement result is, formula three:

${\mathrm{PIM}}_{\mathrm{TM}}=\left|R\right|*\frac{B}{R};$

This measured value is with respect to the frequency response with reference to PIM signal phase; The CHIRP-Z inverse transformation that uses M unit, can obtain PIM _tMthe time domain response in relative reference PIM source, formula four:

${\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left({\mathrm{nT}}_s\right)=\frac{{\mathrm{\φ}}_0}{2\mathrm{\π}}{A}_0^n{e}^{{\mathrm{j\θ}}_0}\underset{k=0}{\overset{M_Z-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}\left(k\right)e^{{\mathrm{j\φ}}_0\mathrm{nk}},n=\mathrm{0,1},...,N_z-1;$

The virtual time position of trying to achieve standard component response, the top of response is standard component response position, is designated as t0; The PIM peak of negative sense time shaft is PIM _t2, the response time is designated as t1, t2; The PIM peak of positive time shaft is PIM _t1, the response time is designated as t3, t4;

Second step is by system under test (SUT) or measured piece access standard component rear end, the transmission intermodulation PIM of testing standard part and measured piece _tM, require the transmission PIM of standard component to be greater than the transmission PIM of measured piece, the CHIRP-Z of now note transmission PIM converts Plays part, PIM _t2and PIM _t1corresponding time shaft is t0 ', t1 ', t2 ', t3 ' and t4 ', so obviously t1=t1 ', t2=t2 ', t4-t3=t4 '-t3 ', t3-t0=t3 '-t0 '; Making time gate is formula five:

During by test measured piece or system under test (SUT), obtain measured value PIM _tM, CHIRP-Z contravariant is changed to PIM ' _tM, suppress so PIM _t1and PIM _t2measurement result be PIM ' _tM* the CHIRP-Z of Gate conversion, formula six:

${\mathrm{PIM}}_T=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{\mathrm{PIM}}_{\mathrm{TM}}^{\′}\left(n\right)*\mathrm{Gate}\left(n\right)\left(\frac{W_0^{\mathrm{nk}}}{A_0^n}\right)e^{-\mathrm{jn}({\mathrm{k\φ}}_0-{\mathrm{\θ}}_0)};$

PIM _tfor the frequency spectrum after self intermodulation suppression.