CN1032238A - Method and system for testing electromagnetic parameters of microwave absorbing materials - Google Patents

Abstract

A method and system for testing complex permittivity ε and complex permeability μ of microwave absorbing materials. Scattering systems S ₁₁ and S ₂₁ are obtained by microwave interferometry, calibration technique and comparison measurement. The system includes a microwave signal unit, a sample loading device capable of performing four different measurement conversions and an S-parameter measurement unit. The latter consists of attenuators, standing wave measuring lines, isolators, power sensors and indicators. The system is easy to set up, easy to operate and low in price. Its measurement accuracy is not lower than that obtained by microwave vector network analyzer.

Description

The electromagnetic parameter test method of microwave absorbing material and system

The invention belongs to the complex permittivity of microwave absorbing material and the method for testing and the system of complex permeability.

Because radio frequency is to the microwave spectrum application and development, particularly as the research natural material, the important means of synthetic material and bio-tissue, and the application aspect communication and electronic countermeasure, complex permittivity ε=ε '-j the ε " and complex permeability μ=μ '-j μ " that measures various organic and inorganic dielectrics, semiconductor, ferrite etc. more and more increases its importance, in, the existing many reliable measuring methods of low-loss material; For high consumable material, the past is extensively adopted the open circuit-short-circuit method of slotted line, but when the sample loss was increased, the measuring error of this method significantly raise, and sensitivity descends, and its measurement result is difficult to meet the demands.ADA 100764, ADA120577 have introduced two scattering system S that utilize microwave vector network analyzer to measure setting-out product device ₁₁And S ₂₁, by the complex permeability of relevant formula calculating microwave absorbing material.This test macro is used to measure scattering coefficient S by microwave signal source ₁₁And S ₂₁Setting-out product device and microwave vector network analyzer constitute, utilize the computing machine accuracy to develop skill, can satisfy present requirement.

Yet microwave vector network analyzer does not possess the function of direct measurement material electromagnetic parameter, when the needs this respect is used, also will solve some special technique problem and calculation procedures.For example to design the setting-out product device of strip line or other structures voluntarily, and the X-over relevant with these structures; Or dispose high performance coaxial-waveguide transitions.These all are highly difficult work, and often are difficult to obtain satisfied result.Although the upper limiting frequency of microwave vector network analyzer has reached 100GHz, the highest frequency of measuring ε, μ with it is about 20GHz.In addition, such network analyzer cost an arm and a leg (the 8510A type of hp company is to 180,000 dollars of a complete set of instrument prices of 20GHz).

The purpose of this invention is to provide a kind of complex permittivity of microwave absorbing material and the method for testing and the system of complex permeability.Adopt common microwave device and electronic device to constitute interference unit and the setting-out product device that can carry out four kinds of different measurings conversions, adopt calibration technology and matching measurement method, realize basic electromagnetic parameter with the high consumable material of low price instrument high-acruracy survey.

In order to achieve the above object, the present invention has taked following measures:

S parameter measurement unit microwave interference method; Setting-out product device is used for reference signal to S ₁₁And S ₂₁Calibration measurement, reflection measurement, the conversion of transmission measurement; Utilize calibration technology and matching measurement method to obtain scattering coefficient S ₁₁And S ₂₁Said calibration technology and matching measurement method are to measure S ₁₁And S ₂₁Before, respectively reference signal is calibrated measurement, measure the variation that standing wave node after the signal of sample reflection and transmission and reference signal are interfered and attenuator reading correspond to when calibrating then respectively and obtain scattering coefficient S ₁₁And S ₂₁The S parameter measurement unit is made up of attenuator, standing wave measurement line, isolator, power sensor and indicator.The setting-out product device that can carry out four kinds of different measuring conversions contains the element that reference signal is carried out two kinds of calibrations.

The present invention can combine with ready-made microwave unit, device and electronic device, does not need to design in addition the device of setting-out product.Sample is the rectangular parallelepiped of processing easily, it is all fairly simple with operation to set up system, do not need computing machine to carry out error correction, be applicable to the broad frequency range of 3～40GHz, the price of each waveguide frequency range is no more than 30,000 yuans, but getable measuring accuracy is not less than the result who obtains with microwave network analyzer.

Be described in further detail below in conjunction with accompanying drawing.

Accompanying drawing is the block diagram of the electromagnetic parameter testing system of microwave absorbing material.

Microlock signal source (1) is passed through isolator (2), 10dB directional coupler (3) with the signal separated into two parts, after wherein a part enters the waveguide segment (19) of setting-out product by isolator (4), 3dB directional couple (5) and matched load (6) output source signal (II), absorbed by matched load (22).Its reflected signal (III) and transmission signal (IV) feed out by two 10dB directional couplers (15) and (21) respectively.Choose one of them by waveguide switch (23) and enter isolator (14) to standing wave measurement line (11).Export reference signal from another part signal (I) that directional coupler (3) comes out by isolator (7), variable attenuator (8) and precision rotating formula variable attenuator (9), enter isolator (10) to standing wave measurement line (11).The adjustable reference signal of amplitude is interfered with the reflected signal (or transmission signal) that comes out through directional coupler in slotted line (11), forms standing wave.With high sensitivity microwave power sensor (10 ^-9～10 ^-10Watt) (12) and power indicator (13) survey and indicate.Waveguide switch (16) is dressed up by two waveguide switches, can be operated in (a) and (b), (c) three positions, when (16) in the position when (a), with S ₁₁Scale elements (17) connect, be used for reference signal to S ₁₁Calibration measure.When (16) in the position when (b), with S ₂₁Scale elements (18) connect; When (16), are connected with the waveguide segment (19) of setting-out product when (c) in the position.(18), (19) be one section waveguide with same length, waveguide switch (20) can be connected with (18), (19) respectively.Locate at (b) when (16), (20) are located at (d), then are used for reference signal S ₂₁Calibration measure; Locate at (c) when (16), (20) are located at (e), cooperate waveguide switch (23) then can reflect respectively and transmission measurement.The element that reference signal is carried out two kinds of calibrations is to be led by a joint shortwave to constitute with short board and be made of a joint waveguide separately.

The effect of (1)～(6) is the two-way that microwave signal is divided into enough isolations in the system, i.e. reference signal (I) and source signal (II).(7)～(14) constitute the microwave interference unit, slotted line plays the fine phase meter here.(15)～(23) be configured for reference signal to S ₁₁And S ₂₁Calibration measurement, reflection and the setting-out product device of transmission measurement conversion.Wherein (15), (16), (18), (20), (21), (22) constitute S ₂₁The calibration branch road, (15), (16), (19), (20), (21), (22) constitute the branch road of setting-out product.When the latter did not contain sample, these two branch roads had identical decay and phase performance.And (15), (16), (17) constitute S ₁₁The calibration branch road, the branch road that it is constituted when the short circuit of setting-out product reference field MN place with (15), (16) and (19) has identical decay and phase performance.When utilizing these calibration branch roads to compare measurement with the sample branch road,, obtain scattering coefficient S accurately with regard to the phase place of energy removal system and the error of decay by calibration technology ₁₁And S ₂₁

Therefore, main points of the present invention are to measure, calibrating method: promptly measure with twice calibration, primary event is measured and a transmission measurement is asked for scattering coefficient S ₁₁And S ₂₁, promptly, just can carry out above-mentioned four kinds of different measurements when waveguide switch (16), (20) and (23) during at diverse location:

(1) reference signal is to S ₁₁Calibration measure: waveguide switch (16) is located at (a), and (23) are located at (f).

(2) reflection measurement: waveguide switch (16) is located at (c), and (23) are located at (f), and (20) are located at (e).

(3) reference signal is to S ₂₁Calibration measure: waveguide switch (16) is located at (b), and (20) are located at (d), and (23) are located at (g).

(4) transmission measurement: waveguide switch (16) is located at (c), and (20) are located at (e), and (23) are located at (g).

Measure acquisition S from (one), (two) ₁₁

Measure acquisition S from (three), (four) ₂₁

Be described as follows with formula:

S ₁₁＝exp〔-（0.11513A _r+jφ _r）〕，φ _r＝π- (4πPr)/(λg) ;

S ₂₁＝exp〔-（0.11513A _t+jφ _t）〕，φ _t＝ (4πP _t)/(λ _g) + (2πl)/(λ _g) 。

λ in the formula _gBe waveguide wavelength (cm) that l is sample length (cm);

A _r=A _Ri-A _RoAttenuator reading (the dB)-S of=reflection measurement ₁₁The attenuator reading (dB) of calibration.

P _r=P _Ro-P _Ri+ n (λ _g)/2=(S ₁₁Standing wave node position (cm)+1/2 integral multiple waveguide wavelength of standing wave node position (cm)-reflection measurement is measured in calibration)＜1/2 waveguide wavelength.

A _t=A _Ei-A _EoAttenuator reading (the dB)-S of=transmission measurement ₂₁The attenuator reading (dB) that calibration is measured.

P _t=P _Ti-P _ToThe standing wave node position (cm) of=transmission measurement-to S ₂₁Standing wave node position (cm) when calibration is measured.

From S ₁₁, S ₂₁Calculate formula (but the Ma Ji Du E that ε, μ press the ADA100764 report ₀₁The difference of ripple and TEM ripple) carries out.So only need frequency f, thickness of sample l, scattering coefficient S with signal source ₁₁And S ₂₁The input computing machine is with regard to the printable complex permittivity ε=ε '-j ε " and complex permeability μ=μ '-j μ " that goes out material.

Compare as follows with the measurement result of teflon sample and the result of ADA100764 report:

Native system ADA100764

Frequency range (GHz): 8.2～12.4 9.2～19.2

Measure dot number 23 23 ^*)

ε ' mean value 2.052 2.057

ε ' standard deviation 0.088 0.139

ε " average fluctuation range+0.101～-0.133+0.159～-0.100

μ ' mean value 0.993 1.00

μ ' standard deviation 0.039 0.058

μ " average fluctuation range+0.0667～-0.0296+0.018～-0.0716

5.98mm

Thickness of sample 12.00mm 180mils

17.88mm

*) delete the point of three deviation maximums from 26 test points.

Claims (3)

1. A method for testing electromagnetic parameters of microwave absorbing materials, using the S parameter measuring unit to measure the two scattering coefficients S ₁₁ and S ₂₁ of the sample placement device (including the sample), and calculate the complex permittivity ε and complex magnetic permeability of the material μ, characterized in that said parameter measurement unit uses microwave interference method, said sample placing device can perform conversion of four different measurements, and obtain scattering coefficients S ₁₁ and S ₂₁ by using calibration technology and comparison measurement method. The said calibration technique and comparative measurement method are to perform calibration measurement on the reference signal to _S11 and _S21 respectively before measuring _S11 and _S21 , and then measure the signal reflected and transmitted from the sample to be compared with the reference signal respectively. Scattering coefficients S ₁₁ and S ₂₁ were obtained from interferometric standing wave nodes and attenuator readings relative to calibration. 2. An electromagnetic parameter testing system for microwave absorbing materials, consisting of a microwave signal unit, a sample placing device and an S-parameter measuring unit, characterized in that the said S-parameter measuring unit is composed of attenuators (8, 9), stationed A wave measuring line (11), an isolator (7, 10, 13), a power sensor (12), and an indicator (13). Two calibration elements (17, 18) for the reference signal are mounted on said sample loading device. 3. The electromagnetic parameter testing system of a microwave absorbing material according to claim 2, characterized in that the reference signal for two kinds of calibration components is composed of a short waveguide and a short circuit board (17) and is separately Consists of a section of waveguide (18).

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