CN106483384B

CN106483384B - Dielectric constant microwave measuring device

Info

Publication number: CN106483384B
Application number: CN201610980643.6A
Authority: CN
Inventors: 刘伟娜; 邢孟女
Original assignee: Henan Normal University
Current assignee: Henan Normal University
Priority date: 2016-11-08
Filing date: 2016-11-08
Publication date: 2023-03-10
Anticipated expiration: 2036-11-08
Also published as: CN106483384A

Abstract

The invention discloses a dielectric constant microwave measuring device, which comprises a mixing ring with a slot line structure, wherein the mixing ring comprises an input port, an isolation port and two in-phase output ports, and the quarter wavelength part of the mixing ring is a slot line; the input port and the two in-phase output ports both adopt symmetrical coplanar waveguide transmission lines, and a plurality of groups of array branch nodes are symmetrically loaded on a middle guide belt of the two in-phase output ports, and the array branch nodes are constructed by coplanar waveguide transmission lines with open-ended terminals; two signal transmission branches are formed from the input port to the in-phase output ports with two open terminals, wherein a plastic pipe used for containing a solution to be detected is arranged on the signal transmission branch on one side; the isolation port adopts a slot line, and a balun coplanar with the slot line is manufactured by adopting an etching process to complete balanced/unbalanced signal conversion. The measuring device provided by the invention is a dual-port measurement, and can avoid the problem of multi-solution, so that the measurement result of the dielectric constant is more accurate and reliable.

Description

Microwave measuring device for dielectric permittivity

Technical Field

The invention belongs to the technical field of dielectric constant microwave measuring devices, and particularly relates to a dielectric constant microwave measuring device.

Background

The dielectric constant of a substance is always a fundamental and important problem in the research of the interaction between the substance and microwaves. There are many methods for measuring the dielectric constant, and the methods can be mainly classified into a resonance method and a non-resonance method. Among them, the non-resonant method, in which the transmission-emission method is widely used in broadband measurement, is relatively simple, and is even used to measure the dielectric constant of a low-loss substance. The measurement method is to complete the calculation and extraction of the dielectric constant of the material by a complex de-embedding or inversion algorithm through loading the information of the amplitude and the phase of the scattering parameters of the test device before and after the tested object. The scattering parameters must therefore be acquired accurately during the measurement. Especially when the dielectric constants of two media are very close, the information of the measured scattering parameters are also very close, and the traditional output-reflection method like the axis measurement cannot accurately distinguish the information of the small changes, thereby influencing the judgment of the dielectric properties of the substances. The invention provides a novel measuring device based on open circuit of an output port terminal of a hybrid ring structure, which adopts a two-way comparison method to improve the test sensitivity and realizes the test of distinguishing the micro-change information of dielectric constant.

Disclosure of Invention

The invention provides a dielectric constant microwave measuring device based on a composite open-ended hybrid ring structure, which is formed by loading an array additional structure consisting of open-ended stubs at the tail ends of two output ports of a broadband hybrid ring, namely, the open-ended stubs are loaded on the two output ports, so that a novel structure consisting of an array structure form and the hybrid ring with the two output ports open is formed, and the purpose of improving the dielectric constant measuring sensitivity of the whole measuring device is achieved.

The invention adopts the following technical scheme to solve the technical problem, and the dielectric constant microwave measuring device is characterized by comprising a mixing ring with a slot line structure, wherein the mixing ring comprises an input port, an isolation port and two in-phase output ports, a quarter wavelength part of the mixing ring is connected with each port by a slot line, the input port and the two output ports adopt symmetrical coplanar waveguide transmission lines, a plurality of groups of array branch nodes are symmetrically loaded on a middle guide belt of the two output ports, the array branch nodes are constructed by coplanar waveguide transmission lines with open terminals, two signal transmission branches are formed from the input port to the two in-phase output ports with open terminals, a plastic pipe for containing a solution to be measured is arranged on the signal transmission branch at one side, and the isolation port adopts a microwave slot line. In the testing process, the input port and the isolation port are connected with the vector network analyzer through the SMA connector respectively.

Preferably, the isolation port is provided with a balun coplanar with the microwave slot line by adopting an etching process, so as to complete balanced/unbalanced signal conversion between the coaxial interface and the slot line structure.

Compared with the prior art, the invention has the following beneficial effects: the mixed ring measuring device with the novel structure, which is provided by the invention, has the advantages that the tail ends of the two in-phase output ports are opened and the array branch nodes are loaded, the solution to be measured with different concentrations is measured under the experimental condition that the measuring device keeps the same volume, the limit of the measuring device for sensing the weak change information of the dielectric constant is explored by adopting an FEM numerical algorithm, the sensitivity of the mixed ring measuring device is far higher than that of the traditional transmission line method, and compared with a single-port coaxial line measuring method, the measuring device provided by the invention is a double-port measuring device, the multi-solution problem can be avoided, and the measuring result of the dielectric constant is more accurate and reliable.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic diagram of a hybrid ring with open output ports and loaded array stubs in accordance with the present invention;

FIG. 3 is a schematic diagram of scattering parameters of the hybrid ring with an open output port and loaded array stubs during no-load operation;

FIG. 4 is a schematic diagram of scattering parameters when the output port is open and the hybrid ring of the array stub is loaded.

In the figure: 1. the device comprises a vector network analyzer, 2, a plastic pipe, 3, a solution to be detected, 4, an input port, 5, an isolation port, 6, a same-phase output port, 7, an array branch node, 8, a slot line, 9, an SMA joint, 10, a transmission line, 11, a reference line, 12 and a balun.

Detailed Description

The present invention is described in further detail below with reference to examples, but it should not be construed that the scope of the above subject matter of the present invention is limited to the following examples, and that all the technologies realized based on the above subject matter of the present invention belong to the scope of the present invention.

As shown in fig. 1-2, the dielectric permittivity microwave measuring apparatus includes a mixing ring having a slotline structure, the mixing ring includes an input port 4, an isolation port 5 and two in-phase output ports 6, a quarter wavelength portion of the mixing ring is connected to each port by a slotline 8, wherein the input port 4 and the two in-phase output ports 6 both use symmetrical coplanar waveguide transmission lines, a plurality of sets of array stubs 7 are symmetrically loaded on a middle conducting strip of the in-phase output ports 6, the array stubs 7 are coplanar waveguide structures with open terminals, two signal transmission branches are formed from the input port 4 to the two in-phase output ports 6 with open terminals, a plastic pipe 2 for containing a solution 3 to be measured is disposed on one signal transmission branch, the isolation port 5 uses a microwave slotline, a balun 12 coplanar with the slotline is formed on the isolation port 5 by an etching process, and balanced/unbalanced signal conversion between the coaxial interface and the slotline structure is completed. And in the test process, the balun 12 and the input port 4 are respectively connected with the vector network analyzer 1 through the SMA connector 9.

The whole measuring device is simulated by adopting a Finite Element (FEM) numerical method, a measuring device model structure shown in figure 2 is built according to actual size, and scattering parameters when the two in-phase output ports 6 are open and the mixing ring of the array branch section 7 is loaded are simulated respectively, and no solution to be measured is placed in the mixing ring, as shown in figure 3.

Ideally, microwave signals are input from the input port 4, most of the signals are converted by quarter wavelength, have equal amplitude and are in phase, and reach the two in-phase output ports 6, and no signal is output from the isolation port 5. The two signal transmission branches that transmit the signal from the input port 4 to the non-inverting output port 6 are referred to as a transmission line 10 and a reference line 11, respectively. When ethanol solutions with different concentrations are placed in the plastic pipe 2 in the transmission line 10, equivalently a discontinuity structure is introduced into the measuring device, the original signal transmission equilibrium state is broken, and therefore scattering parameter information of the input port 4 and the isolation port 5 of the measuring device is changed.

Since the interface connected to the vector network analyzer 1 is a coaxial line interface with a characteristic impedance of 50 Ω, the coaxial line interface is a standard interface for most instruments and signal generators. Since the balanced transmission characteristics of the coaxial unbalanced interface and the slotline structure are not matched, a balanced/unbalanced conversion is required between the coaxial interface and the slotline structure. The invention provides a balun for balanced/unbalanced conversion in a broadband range, namely, the balun 12 coplanar with a microwave slot line of an isolation port 5 is manufactured by adopting an etching process according to different parameters, so that the optimal matching effect is achieved, and balanced/unbalanced signal conversion is completed.

In order to verify the effectiveness of the mixed ring measuring device of the present invention, which opens at the in-phase output port 6 and loads the array stub 7, in sensing a small change in dielectric constant, the following embodiments perform some related measurements, that is, ethanol solutions with molar concentrations of 0.05 (x 1), 0.09 (x 2), 0.12 (x 3), and 0.14 (x 4) are respectively placed in the plastic tube 2, and the calculated scattering parameter information of the measuring device is shown in fig. 4, and it can be seen from fig. 4 (a) and (b) that when the measuring device is placed on the solution 2 to be measured, the scattering parameter of the port of the whole measuring device changes significantly. And figure 4 also illustrates that the minimum molar concentration difference of the ethanol solution perceivable by the measuring device is 0.02. The invention is very effective in sensing the weak change of the dielectric constant in the microwave band by the broadband of the hybrid ring measuring device with the open-circuit in the in-phase output port 6 and the loaded array branch section 7.

Research shows that a two-line comparison test method is adopted. One is a reference line 11 on which a reference material is placed, and the other is a transmission line 10 on which a material to be tested is placed, so that the test sensitivity can be greatly improved. The invention does not need any reference object, the reference object and the measured object are the same, namely the whole measuring device does not contain task substances (no load), the measured object is called as load when being placed in a plastic tube, and the dielectric constant of the solution to be measured is obtained by comparing scattering parameters under the two conditions of no load and load. The measuring device provided by the invention loads the array branch joints 7 at the tail ends of the two in-phase output ports 6, enhances the effect of an electromagnetic field on a solution to be measured, and sensitively senses weak scattering parameter information caused by small change of dielectric constant, so that the sensitivity of the whole measuring device can be greatly improved.

While the foregoing embodiments have described the general principles, features and advantages of the present invention, it will be understood by those skilled in the art that the present invention is not limited thereto, and that the foregoing embodiments and descriptions are only illustrative of the principles of the present invention, and various changes and modifications can be made without departing from the scope of the principles of the present invention, and these changes and modifications are within the scope of the present invention.

Claims

1. The dielectric permittivity microwave measuring device is characterized by comprising a mixing ring with a slot line structure, wherein the mixing ring comprises an input port, an isolation port and two in-phase output ports; the quarter-wavelength part of the hybrid ring is connected with each port by a slot line, wherein the input port and the two in-phase output ports both adopt symmetrical coplanar waveguide transmission lines, and a plurality of groups of array branch nodes are symmetrically loaded on a middle guide belt of the two in-phase output ports, and the array branch nodes are constructed by coplanar waveguide transmission lines with open-circuit terminals; two signal transmission branches are formed from the input port to the in-phase output ports with two open terminals, wherein a plastic pipe used for containing a solution to be detected is arranged on the signal transmission branch on one side; the isolation port adopts a slot line, and the input port and the isolation port are connected with the vector network analyzer through the SMA connector respectively in the test process; the isolation port is provided with a balun coplanar with the slot line by adopting an etching process to complete balanced/unbalanced signal conversion between the coaxial interface and the slot line structure, and the interface connected with the vector network analyzer is a coaxial line interface with characteristic impedance of 50 omega; ideally, a microwave signal is input from an input port, most of the signal is converted by quarter wavelength to reach two in-phase output ports in equal amplitude and in phase, no signal is output from an isolation port, two signal transmission branches for transmitting the signal from the input port to the in-phase output ports are respectively called a transmission line and a reference line, when ethanol solutions with different concentrations are placed in a plastic pipe in the transmission line, a discontinuity structure is equivalently introduced into a measuring device, the original signal transmission balance state is broken, and therefore scattering parameter information of the input port and the isolation port of the measuring device is changed, and the dielectric constant of the solution to be measured is calculated according to the change information.