CN103884422A - Quasi-optics type probe for terahertz near-field measurement, detection system and detection method - Google Patents

Abstract

The invention discloses a quasi-optics type probe for terahertz near-field measurement, a detection system and a detection method based on the system. The quasi-optics type probe is arranged in front of a receiver and comprises a metal screen and a lens. The center of the metal screen is provided with a small hole with the diameter being D, and the thickness t of the metal screen is smaller than the diameter D of the small hole. The area outside the small hole is covered by a wave absorbing material, and the area of the surface of the screen is not smaller than the near-field range which is set to be scanned. The lens and the metal screen are arranged in parallel, the center of the lens and the central axis of the small hole of the metal screen are in the same line, and a quasi-optics focus in front of the lens and a quasi-optics focus on the rear of the lens are located in the small hole of the metal screen and on an antenna opening face of the receiver respectively. The quasi-optics type probe for the terahertz near-field measurement has the advantages of being low in loss and easy to machine, the quasi-optics type probe can be used in cooperation with the thermion mixing superconductivity receiver, and the high-sensitivity and high-resolution terahertz near-field measurement is achieved.

Description

For quasi-optical probe, detection system and the detection method of Terahertz near field measurement

Technical field

The present invention relates to a kind of quasi-optical probe, detection system and detection method based on this system for Terahertz frequency range (containing millimeter wave, submillimeter wave wave band) near field measurement, belong to Terahertz Research on measuring technique field.

Background technology

Near-field measurement technique is the important method during electromagnetic field field shape is measured, and has been widely used in the applications such as antenna radiation characteristics measurement, reflecting surface holographic measurement, microwave and millimeter wave imaging system and collimator optical system.With respect to far-field measurement technology, the advantage of near field measurement is that measuring system framework is more compact, and cost is lower, measures signal to noise ratio (S/N ratio) higher, and just can obtain the far-field distribution in different measuring distance upper near field distribution and full azimuth by one-shot measurement.

In near field measurement, field distribution to be measured is carried out to perception and the small receiving element of catching is called probe.In order to improve precision and the resolution of measurement, the physical size that probe receives actinal surface requires enough little, conventionally much smaller than the actinal surface size of radiation source to be measured.In microwave and millimeter-wave near-field measuring system, conventionally adopt the probe of open ended waveguide type.Such probe utilizes the opening section of rectangular waveguide to respond to radio-frequency electromagnetic signal, there is with low cost, advantages of simple structure and simple, but arrived higher submillimeter wave and the Terahertz frequency range of frequency, waveguide dimensions becomes submillimeter magnitude, and the Precision Machining of waveguiding structure becomes more difficult.Along with metal loss is in the phenomenal growth of high frequency, waveguide device is also higher in the loss of submillimeter wave and Terahertz frequency range, affects to a certain extent the performance of measuring system simultaneously.What is more important is in Terahertz frequency range, the detection sensitivity that semiconductor receives machine does not usually meet test needs, therefore usually need to adopt superconduction receiver in this frequency range, the detector of receiver is placed in airtight cooled cryostat, realizes and external electromagnetic signal coupling by the lens antenna of quasi-optical.Under this receiver configuration condition, the near field probes of waveguide type is no longer applicable, need to be equipped with for it probe of corresponding quasi-optical.

Summary of the invention

For problems of the prior art and deficiency, the present invention proposes a kind of quasi-optical probe for Terahertz frequency range (containing millimeter wave, submillimeter wave wave band) near field measurement, can be used in conjunction with thermoelectron mixing (HEB) superconduction receiver, realize high sensitivity, high-resolution Terahertz near field measurement.

For realizing above-mentioned technical purpose, technical scheme provided by the invention is:

A kind of probe of the quasi-optical for Terahertz near field measurement, before being arranged on receiver, is characterized in that, comprising:

One metal screen, metal screen center has the aperture that diameter is D, and thickness t is less than the diameter D of described aperture, and the region outside aperture is covered with absorbing material, and screen area is not less than the near field range of setting scanning;

One lens, the placement parallel with metal screen of described lens, the axis of lens center and metal screen aperture is located along the same line, and the quasi-optics focus (girdling the waist) of lens front and back drops on respectively on the Antenna aperture of metal screen aperture and receiver.

The diameter of described aperture can be chosen to be 2～5 λ, and the wavelength that λ is radiation source to be measured is setting value.In this interval, higher spatial resolution can be realized in less aperture, and larger aperture is conducive to realize higher detection sensitivity and signal to noise ratio (S/N ratio).

As preferably, described absorbing material can select loss factor to be not less than 100dB/cm(thickness) absorbing material, as high loss silica gel thin film etc.

As preferably, described lens are HDPE (high density polyethylene) lens.In the near field measurement of Terahertz, above-mentioned quasi-optical probe is used in conjunction with superconduction receiver, two dimensional surface scanning bracket, has formed overall detection system, and concrete scheme is as follows:

For a quasi-optical detection system for Terahertz near field measurement, it is characterized in that, comprise following composition member:

Two dimensional surface scanning bracket, comprises the platform of fixing radiation source to be measured and controls the mobile device of platform at two dimensional surface X-axis and Y-axis top offset;

Above-mentioned quasi-optical probe, the metal screen of described quasi-optical probe parallels with the two dimensional surface of two dimensional surface scanning bracket;

Thermoelectron mixing (HEB) superconduction receiver, the axis of the center of receiver antenna and probe lens center, metal screen aperture is on same straight line.

In order to realize the maximum quasi-optics coupling between probe lens and metal screen aperture, the waist radius w at the quasi-optics focus place of described lens on aperture ₁should meet w ₁≈ D/3, preferably w ₁=0.34D.

As preferably, the antenna of described superconduction receiver can adopt lens antenna.If receiver antenna is silicon lens antenna, in order to realize the maximum quasi-optics coupling between probe lens and silicon lens antenna, probe lens are positioned at the waist radius w at the quasi-optics focus place on Antenna aperture ₂should meet w ₂≈ 0.4D _a, preferably w ₂=0.4D _a, in above formula, D _afor the actinal surface diameter of lens antenna.

A detection method of measuring for THz electric field shape, is characterized in that, comprises the following steps:

1) radiation source to be measured of setting wavelength is fixed in two dimensional surface scanning bracket, in the plane that need to measure near field distribution, the metal screen of aperture is driven at placement center, makes the two dimensional surface keeping parallelism of metal screen and described two dimensional surface scanning bracket;

2) place successively the superconduction receiver of HDPE lens and employing silicon lens antenna at the opposite side of the metal screen relative with radiation source to be measured, and the quasi-optics focus of HDPE lens both sides is dropped on respectively on the silicon lens Antenna aperture of metal screen aperture and receiver;

3) utilize superconduction receiver read output signal intensity, adjust the collimation between metal screen, HDPE lens and superconduction receiver antenna according to signal intensity, make metal screen aperture, HDPE lens and silicon lens center of antenna point-blank, complete after adjustment, fixing metal screen, lens and superconduction receiver are motionless;

4) mobile device of startup two dimensional surface scanning bracket, makes radiation source to be measured translation on two dimensional surface, and in scanning process, signal amplitude and the phase place that receiver is read recorded in pointwise;

5), after having scanned, obtain the two-dimensional vector near field distribution of radiation source to be measured.

In said method, metal screen and the HDPE lens of opening aperture have formed described quasi-optical probe.

In step 5), can obtain by nearly Far-Zone Field Transformation afterwards the far field antenna pattern of radiation source to be measured.

In above-mentioned steps, the optics between metal screen, HDPE lens and receiver and design of Structural Parameters adopt following methods:

(A) the hole diameter D of metal screen is taken as 2～5 λ, the wavelength (given value) that λ is radiation source to be measured;

(B) utilize following formula (1), formula (2) to calculate the waist radius at quasi-optics focus place, HDPE lens both sides:

w ₁=0.34D （1）

w ₂=0.4D _A （2）

In above formula, w ₁for waist radius, the w at the quasi-optics focus place of lens on aperture ₂for the waist radius at the quasi-optics focus place of lens on receiver silicon lens Antenna aperture, D _afor the actinal surface diameter of silicon lens antenna;

By w ₁, w ₂bring into respectively in formula (3), formula (4), try to achieve R ₁, R ₂:

${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="140326090456.png"\; state="\{\{state\}\}">R</figure-callout>}}_1=d_1[1+{\left(\frac{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="w"\; filenames="140326090456.png"\; state="\{\{state\}\}">w</figure-callout>}}_1^2}{\mathrm{\&lambda;}{d}_1}\right)}^2]---\left(3\right)$

$R_2=d_2[1+{\left(\frac{\mathrm{\&pi;}{w}_2^2}{\mathrm{\&lambda;}{d}_2}\right)}^2]---\left(4\right)$

In above formula, d ₁for the HDPE lens of setting and the distance of metal screen, d ₂for the distance between HDPE lens and the receiver antenna actinal surface set;

By R ₁, R ₂bring in formula (5), try to achieve the equivalent focal length f of HDPE lens:

$f=\frac{1}{\frac{1}{R_1}+\frac{1}{R_2}}---\left(5\right)$

Then according to the equivalent focal length of trying to achieve, can select corresponding HDPE lens.

Beneficial effect of the present invention:

1) utilize the small via hole on metal screen to realize local electromagnetic wave field shape detection, its difficulty of processing is simple compared with open ended waveguide;

2) utilize HDPE lens to realize the maximum quasi-optics coupling between aperture and receiver detector, further improved detection sensitivity and signal to noise ratio (S/N ratio);

3) adopt the method for pasting high loss absorbing material on metal screen, effectively reduce disturbance and the reflection of metal screen to be measured shape.

To sum up, quasi-optical probe of the present invention has advantages of low, the easy processing of loss, is applied in detection system of the present invention and detection method, can coordinate with thermoelectron mixing superconduction receiver, realizes high sensitivity, high-resolution Terahertz near field measurement.

Accompanying drawing explanation

Fig. 1 is the structural representation of quasi-optical probe;

Fig. 2 utilizes quasi-optical probe to realize the exemplary configuration structural representation of vector near field measurement at 850GHz.

Embodiment

In order further to illustrate technical scheme of the present invention and technique effect, below in conjunction with drawings and the specific embodiments, the present invention is described further.

A kind of quasi-optical probe as shown in Figure 1, comprises square-shaped metal screen and convex lens that a length of side is a.

Described metal screen center offers the aperture that diameter is D, can allow local electromagnetic wave pass through.The screen body thickness t of metal screen is less than the diameter D of described aperture, and now metal screen thickness is less to projecting electromagnetic disturbance.The region of metal screen both sides outside aperture is all pasted with absorbing material, for absorbing the electromagnetic wave energy that projects aperture exterior domain.The area of metal screen should be enough large, to cover the near field range of required scanning.

Described convex lens adopt HDPE lens, placement parallel with metal screen, the axis of lens center and metal screen aperture is located along the same line, and by the curvature mirror of design HDPE lens, the quasi-optics focus (girdling the waist) of lens both sides is laid respectively on metal screen aperture and receiver antenna actinal surface.

Above-mentioned quasi-optical probe is used in conjunction with thermoelectron mixing superconduction receiver, can carries out the near field measurement of Terahertz.As shown in Figure 2, take the example of realizing vector near field measurement at 850GHz as example explanation, specific as follows:

As shown in the figure, radiation source to be measured is a Terahertz frequency multiplication amplification module, by the outside radiation power of diagonal horn antenna.

The detector of thermoelectron mixing superconduction receiver is placed in 4K cooled cryostat that (Dewar is provided with window, make to be detected signal and can arrive detector), by helical lens antenna and the external electromagnetic signal coupling of silicon materials, described helical lens antenna is the lens antenna that is equipped with an elliposoidal before helical antenna, the actinal surface diameter D of described lens antenna _afor 10mm.

Metal screen adopts the square stainless steel thin slice of 100 × 100 × 0.4mm, and center-hole diameter is 1mm.HDPE lens diameter is 30mm, and equivalent focal length is 20.5mm, and quasi-optics focal length lens center, both sides is respectively 22mm and 186mm, and the waist radius at bifocal place is respectively 0.35mm and 4mm.

After above-mentioned member installs, the concrete implementation step of carrying out THz electric field shape (near-field/far-field) measurement is:

1) radiation source to be measured is fixed in two dimensional surface scanning bracket, in the plane that need to measure near field distribution, places metal screen, and metal screen parallels with the two dimensional surface of described two dimensional surface scanning bracket;

2) place successively HDPE lens and receiver at the opposite side of metal screen, and the quasi-optics focus (girdling the waist) of HDPE lens both sides is dropped on respectively on the lens antenna actinal surface of metal screen aperture and receiver;

3) utilize receiver read output signal intensity, adjust the collimation between probe and superconduction receiver antenna according to signal intensity, make metal screen aperture, HDPE lens and lens antenna center point-blank, complete after adjustment, probe and receiver are maintained static;

4) mobile device of startup two dimensional surface scanning bracket, makes radiation source to be measured translation on two dimensional surface (realizing the relative motion between radiation source to be measured and probe), and in scanning process, signal amplitude and the phase place that receiver is read recorded in pointwise;

5) after having scanned, obtain the two-dimensional vector near field distribution of radiation source to be measured, then obtain the far field antenna pattern of radiation source to be measured by nearly Far-Zone Field Transformation.

In above-mentioned steps, probe and receiver, in the time of design optics and structural parameters, can adopt and first select probe lens, then design the method for lens and metal screen and receiver distance, also can first setpoint distance, then extrapolate the lens of appropriate size.A kind of rear method can realize by following steps:

(A) the hole diameter D of metal screen is taken as 2～5 λ, the wavelength (given value) that λ is radiation source to be measured;

(B) utilize following formula (1), formula (2) to calculate the waist radius at quasi-optics focus place, HDPE lens both sides:

w ₁=0.34D （1）

w ₂=0.4D _A （2）

In above formula, w ₁for waist radius, the w at the quasi-optics focus place of lens on aperture ₂for the waist radius at the quasi-optics focus place of lens on receiver silicon lens Antenna aperture, D _afor the actinal surface diameter of silicon lens antenna;

By w ₁, w ₂bring into respectively in formula (3), formula (4), try to achieve R ₁, R ₂:

${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="140326090456.png"\; state="\{\{state\}\}">R</figure-callout>}}_1=d_1[1+{\left(\frac{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="1"\; label="w"\; filenames="140326090456.png"\; state="\{\{state\}\}">w</figure-callout>}}_1^2}{\mathrm{\&lambda;}{d}_1}\right)}^2]---\left(3\right)$

$R_2=d_2[1+{\left(\frac{\mathrm{\&pi;}{w}_2^2}{\mathrm{\&lambda;}{d}_2}\right)}^2]---\left(4\right)$

In above formula, d ₁for the HDPE lens of setting and the distance of metal screen, d ₂for the distance between HDPE lens and the receiver antenna actinal surface set (to Antenna aperture distance foremost), the wavelength that λ is radiation source to be measured;

By R ₁, R ₂bring in formula (5), try to achieve the equivalent focal length f of HDPE lens:

$f=\frac{1}{\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="140326090456.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\frac{1}{R_2}}---\left(5\right)$

According to the equivalent focal length of trying to achieve, select corresponding HDPE lens, as improper in parameter designing such as distances, can logarithm value adjust, repeatedly select and calculate, until extrapolate suitable lens specification.

More than show and described ultimate principle of the present invention, principal character and advantage of the present invention.The technician of the industry should understand, the present invention is not restricted to the described embodiments, that in above-described embodiment and instructions, describes just illustrates principle of the present invention, and without departing from the spirit and scope of the present invention, the present invention also has various changes and modifications.The claimed scope of the present invention is defined by appending claims, instructions and equivalent thereof.

Claims (10)

1. the probe of the quasi-optical for Terahertz near field measurement, before being arranged on receiver, is characterized in that, comprising:

One metal screen, metal screen center has the aperture that diameter is D, and thickness t is less than the diameter D of described aperture, and the region outside aperture is covered with absorbing material, and screen area is not less than the near field range of setting scanning;

One lens, the placement parallel with metal screen of described lens, the axis of lens center and metal screen aperture is located along the same line, and the quasi-optics focus of lens front and back drops on respectively on the Antenna aperture of metal screen aperture and receiver.

2. a kind of probe of the quasi-optical for Terahertz near field measurement according to claim 1, is characterized in that, the diameter of described aperture is 2～5 λ, the wavelength that λ is radiation source to be measured.

3. a kind of probe of the quasi-optical for Terahertz near field measurement according to claim 1, is characterized in that, the loss factor of described absorbing material is not less than 100dB/cm.

4. a kind of probe of the quasi-optical for Terahertz near field measurement according to claim 3, is characterized in that, described absorbing material is silica gel thin film.

5. a kind of probe of the quasi-optical for Terahertz near field measurement according to claim 1, is characterized in that, described lens are HDPE lens.

6. for a quasi-optical detection system for Terahertz near field measurement, it is characterized in that, comprise following composition member:

Two dimensional surface scanning bracket, comprises the platform of fixing radiation source to be measured and controls the mobile device of platform at two dimensional surface X-axis and Y-axis top offset;

Quasi-optical probe as described in arbitrary claim in claim 1-5, the metal screen of described quasi-optical probe parallels with the two dimensional surface of two dimensional surface scanning bracket;

Thermoelectron mixing superconduction receiver, the center of receiver antenna is located along the same line with the axis of probe lens center, metal screen aperture.

7. a kind of quasi-optical detection system for Terahertz near field measurement according to claim 6, is characterized in that:

The waist radius w at the quasi-optics focus place of described lens on aperture ₁=0.34D; Described receiver antenna is silicon lens antenna, and the lens of popping one's head in are positioned at the waist radius w at the quasi-optics focus place on Antenna aperture ₂=0.4D _a, in above formula, D _afor the actinal surface diameter of lens antenna.

8. a detection method of measuring for THz electric field shape, is characterized in that, comprises the following steps:

1) radiation source to be measured of setting wavelength is fixed in two dimensional surface scanning bracket, in the plane that need to measure near field distribution, the metal screen of aperture is driven at placement center, makes the two dimensional surface keeping parallelism of metal screen and described two dimensional surface scanning bracket;

2) place successively the superconduction receiver of HDPE lens and employing silicon lens antenna at the opposite side of the metal screen relative with radiation source to be measured, and the quasi-optics focus of HDPE lens both sides is dropped on respectively on the silicon lens Antenna aperture of metal screen aperture and receiver;

3) utilize superconduction receiver read output signal intensity, adjust the collimation between metal screen, HDPE lens and superconduction receiver antenna according to signal intensity, make metal screen aperture, HDPE lens and silicon lens center of antenna point-blank, complete after adjustment, fixing metal screen, lens and superconduction receiver are motionless;

4) mobile device of startup two dimensional surface scanning bracket, makes radiation source to be measured translation on two dimensional surface, and in scanning process, signal amplitude and the phase place that receiver is read recorded in pointwise;

5), after having scanned, obtain the two-dimensional vector near field distribution of radiation source to be measured.

9. a kind of detection method of measuring for THz electric field shape according to claim 8, is characterized in that:

In step 5), obtain the far field antenna pattern of radiation source to be measured by nearly Far-Zone Field Transformation.

10. according to a kind of detection method of measuring for THz electric field shape described in power 8 or 9, it is characterized in that, in above-mentioned steps, the optics between metal screen, HDPE lens and receiver and design of Structural Parameters adopt following methods:

(A) the hole diameter D of metal screen is taken as 2～5 λ, the wavelength that λ is radiation source to be measured;

(B) utilize following formula (1), formula (2) to calculate the waist radius at quasi-optics focus place, HDPE lens both sides:

w ₁=0.34D （1）

w ₂=0.4D _A （2）

In above formula, w ₁for waist radius, the w at the quasi-optics focus place of lens on aperture ₂for the waist radius at the quasi-optics focus place of lens on receiver silicon lens Antenna aperture, D _afor the actinal surface diameter of silicon lens antenna;

By w ₁, w ₂bring into respectively in formula (3), formula (4), try to achieve R ₁, R ₂:

$R_1=d_1[1+{\left(\frac{\mathrm{\&pi;}{w}_1^2}{\mathrm{\&lambda;}{d}_1}\right)}^2]---\left(3\right)$

$R_2=d_2[1+{\left(\frac{\mathrm{\&pi;}{w}_2^2}{\mathrm{\&lambda;}{d}_2}\right)}^2]---\left(4\right)$

In above formula, d ₁for the HDPE lens of setting and the distance of metal screen, d ₂for the distance between HDPE lens and the receiver antenna actinal surface set;

By R ₁, R ₂bring in formula (5), try to achieve the equivalent focal length f of HDPE lens:

$f=\frac{1}{\frac{1}{R_1}+\frac{1}{R_2}}---\left(5\right)$

Then according to the equivalent focal length of trying to achieve, select corresponding HDPE lens.

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