CN1913220A - Three-D resonant cavity capable of reducing cut-off frequency - Google Patents

Abstract

This invention relates to a 3-D resonance cavity reducing the cut-off frequency including a metal wall closing to a cavity and medium in the cavity characterizing that: the surface of the metal wall in the cavity includes one or 2-3 artificial magnetic surfaces composed of a copper-spreading layer, a dielectric layer and a metal copper layer, in which, the copper-spreading layer is composed of a period unit structure kind meeting the selected working wave length and period structure geometrical parameter, the periodic unit structure kind can be types of square mushroom, UC-PBG, parting of H, parting of Hilbert or Spiral plane screws, the metal wall is replaced by a metal copper layer of artificial magnetic surface and the cut-off frequency is not limited by the geometrical diameter of the cavity.

Description

A kind of three-D resonant cavity that reduces cut-off frequency

Technical field

A kind of three-D resonant cavity that reduces cut-off frequency relates to a kind of cavity resonator, relates in particular to a kind of undersized resonant cavity of microwave band, this resonant cavity particularly suitable microwave communication system.

Background technology

We know that resonant cavity is a device of can implementation pattern selecting, and also are ancient, a basic notion in basic research fields such as physics simultaneously.In a broad aspect, resonant cavity can be defined as the electromagnetic environment of a sealing, has limited physical dimension, and isolation, as the hohlraum that defines in the statistical physics.If from the angle in the microphysics world, the environment of this finite size has determined the discrete characteristic that this maximum system energy distributes, and this viewpoint also is quantum-mechanical basis.Have in mind from the engineering application of classical ripple category, resonant cavity can provide the model selection and the identification of very high quality factor, is widely used for example microwave communication system in all many-sides such as human science and technology and even daily lifes.Theoretically, the boundary condition of traditional resonant cavity generally is considered desired electrical conductor (PEC) boundary condition, the desired electrical conductor is the infinitely-great nothing consumption of a conductivity conductor, electromagnetic wave is when running into this surface, reflected wave electric field tangential component and incident wave electric field tangential component have the phase jump of half wavelength, causing tangential total electric field is zero, and the response surface impedance is zero.This moment, the pattern in chamber was bulk-mode (being made up of six faces).Be respectively d with the length of side _x, d _y, d _zThe cuboid resonant cavity be example, six faces of resonant cavity are respectively LRUDFB (about the left-right and front-backs), the pattern in chamber is decided by following equation:

-2k _xd _x+2π＝m _x2π

-2k _yd _y+2π＝m _y2π (1)

-2k _zd _z+2π＝m _z2π

(m wherein _x, m _y, m _z)=m is the integer sequence of corresponding modes exponent number.This moment, the operating frequency in this chamber satisfied:

${\mathrm{\ω}}_m=c\sqrt{{((m_x-1)\mathrm{\π}/d_{m_x})}^2+{((m_x-1)\mathrm{\π}/d_{m_y})}^2+{((m_x-1)\mathrm{\π}/d_{m_z})}^2}---\left(2\right)$

Lowest operating frequency is decided by the size of cavity, works as d _zBe minor face when long, its lowest operating frequency is by expression formula: $f_c=\frac{c}{2\mathrm{\π}\sqrt{{\mathrm{\ϵ}}_r}}\sqrt{{\left(\frac{1}{d_x}\right)}^2+{\left(\frac{1}{d_y}\right)}^2}$ Decision, c is the light velocity in the vacuum in the formula, ε _rBe the dielectric constant of the medium of filling in the chamber, at this moment, this resonant cavity all is not less than effective operation wavelength (c/f in the size on both direction at least _c) 1/4th.With the cube resonant cavity is example (d _x=d _y=d _z), medium is an air in the chamber, cut-off wavelength λ _c= d _xThis shows that the resonant cavity lowest operating frequency is by the physical dimension decision in chamber, this frequency is the lowest limit operating frequency of traditional classical resonant cavity.So far, resonant cavity all adopts copper (because its high conductivity can be regarded desired metallic as) to make, and this resonant cavity can reach the effect of model selection and identification, that is: cut-off frequency is low more, and then the physical dimension in chamber is big more.For example be the resonant cavity of 21mm for size dimension, corresponding cut-off frequency is about 10.10GHz, and when the length of side shortened to 14mm, corresponding cut-off frequency rose to 21.43GHz.If the microwave band that cut-off frequency drops to as mobile communication is 0.9-1.8GHz, so, the size dimension of resonant cavity will increase to 210-140mm.Although at certain characteristic frequency, in the chamber, adopt the medium of high-k can effectively reduce the size in chamber, the medium of high-k has bigger loss usually, thus the resonance that can't realize ideal still is unfavorable for miniaturization of devices.Yet indexs such as the miniaturization of microwave communication system, lightness and high-performance are the developing direction of modern short-wave communication tedhnology.Therefore research and development has very high economic and social benefit at microwave band low-frequency range and small-sized resonant cavity.

Summary of the invention

The objective of the invention is to disclose a kind of three-D resonant cavity, this resonant cavity is compared with the existing resonant cavity of same size, cut-off frequency is not limited by resonant cavity size, satisfy the index requests such as miniaturization, lightness and high-performance of microwave communication system, changed the rule that the physical dimension with increasing resonant cavity that prior art follows realizes the low operating frequency of resonant cavity.

In order to achieve the above object, the present invention finds when studying for a long period of time artificial magnetic surface (magnetic metamaterialsurfaces) and confirms that it has following characteristic: this artificial magnetic surface belongs to a quefrency and selects the surface, generally be (to see B.A.Munk by the magnetic response that the plane resonance structure is implemented on the specific wave band, " Frequency Selective Surfaces; Theory and Design " Wiley, New York, 2000).A kind of common artificial magnetic surface is wherein arranged for square mushroom-shaped, the reflection position of this magnetic surface frequency change that accompanies (is seen DF Sievenpiper, et.al., IEEE Trans.onAntennas ﹠amp; Prop.47,2059 (1999)), the effective permeability of this body structure surface can come equivalence with following formula: ${\mathrm{\μ}}_{\mathrm{eff}}\left(\mathrm{\ω}\right)=1-\frac{{\mathrm{F\ω}}^2}{{\mathrm{\ω}}^2-{{\mathrm{\ω}}_0}^2+\mathrm{i\Γ\ω}}.$ In fact, the artificial structure surface that can regulate and control reflected wave position phase all belongs to and the artificial magnetic surface, this artificial magnetic comes from the metal patch array of periodic structure and the loop current vibration that the resonance current on the metal substrate lower surface forms, thereby forms effective magnetic near this resonance frequency.UC-PBG (the K.P.Ma that except that square mushroom-shaped magnetic surface, has metal substrate in addition, F.R.Yang, Y.Qian, and T.Itoh, " Nonleaky conductor-backed CPW using anovel 2D-PBG lattice; " presented at the Asia-Pacific Microwave Conf., Yokohama, Japan, Dec.8-11,1998.) and (F.R.Yang, Y.Qian, R.Coccioli, and T.Itoh, " A novel low loss slow wave microstrip structure; " IEEEMicrowave Guided Wave Lett., vol.8, pp.372-374, Nov.1998.), fractal (the W.Jia et al. of H type, Phys.Rev.Lett.89,23901 (2000)) and (L.Zhou, et al., Appl.Phys.ett.82,1012 (2003)), fractal (the Zhu of Hilbert, J., A.Hoorfar, N.Engheta IEEE Antennas and Wireless Propagation Letters, 2,2 (2003) and (Hongqiang Li, etc., A photonic bandgap filter using metallic Hilbertcurves, Chinese Physics Letters, 22,1439 (2005)), (Volume 3 for HaiquanYang Hongqiang Li, Multi-Band Subwavelength Magnetic Reflectors Based onSpiral for the Spiral snail, 4-7Dec.2005Page (s): 3pp.Digital Object Identifier10.1109/APMC.2005.1606738) and (Zeyong Wei, Hongqiang Li, Multi-bandreflectivity from metallic photonic crystals containing spiral-likepatterns, Proceedings of the SPIE, Volume 6029, pp.482-487 (2006)) etc. the magnetic surface.We can realize reducing the three-D resonant cavity of cut-off frequency to utilize this class surface.

Below we are that example is made the principle type and set forth with the one dimension resonant cavity at first.Classical one dimension resonant cavity is made of two parallel desirable electrically conductor (PEC) surfaces, can see Fabry-Paro resonant cavity as, it is zero that the desirable electrically boundary condition on surface requires tangential electric field, basic mode is a standing wave mode, so the antinode of field (electric field is zero position) drops on the surface just, at this moment cut-off wavelength λ _cBe the twice of two conductive surface spacing d, λ _c=2d.When we substitute one of them PEC surface with a desirable magnetic conductor surface (PMC), because it is zero that the boundary condition on PMC surface requires tangential magnetic field, we only need the field spatial distribution of half standing wave mode just can obtain basic mode like this, the node of this pattern (position of electric field maximum) is in the PMC surface, antinode then still drops on another PEC surface, this moment, the wavelength of this basic mode was the twice of above-mentioned cut-off wavelength, λ _c=4d.Further again, if the reflection position on a surface is the function about frequency mutually, then this surface is magnetic surface (M).For certain characteristic frequency, M surface reflection electromagnetic phase shift may be [π, π] in arbitrary value, this moment is for the pattern of cut-off wave strong point work, this one dimension chamber thickness that satisfies phase-matching condition can be far smaller than operation wavelength, can prove thus and can form the ultra-thin resonant cavity of one dimension that its lowest operating frequency (in other words by operation wavelength) also be can't help the physical dimension of this resonant cavity and decided with artificial magnetic surface.

Above-mentioned thought can be generalized to three-dimensional, can remove the conventional three-dimensional resonant cavity size to the restriction by operation wavelength, and this mainly realizes that by the inwall that the artificial magnetic surface is used for three-D resonant cavity the physical dimension in chamber can be far smaller than by operation wavelength.Still be respectively d with the length of side _x, d _y, d _zThe cuboid resonant cavity be example, when the reflection position of six faces of resonant cavity was function about frequency mutually, we had:

-2k _xd _x+Δφ _+x+Δφ _-x＝m _x2π

-2k _yd _y+Δφ _+y+Δφ _-y＝m _y2π

-2k _zd _z+ Δ φ _{+ z}+ Δ φ _-z=m _z2 π are Δ φ wherein _{+ i}, Δ φ _-i(i=x, y z) are respectively normal along x, y, the reflection position phase of two parallel chambeies of z direction wall, k _x, k _y, k _zBe respectively x, y, the wave vector on the z direction, integer m _x, m _y, m _zBe respectively x, y satisfies the exponent number of the standing-wave condition of phase matched on the z direction, and at this moment, the resonance frequency in chamber can be determined by following formula:

${\mathrm{\&delta;}}_{\left\{m_i\right\}}\left(\mathrm{\&omega;}\right)=c\sqrt{\underset{i=x,y,\mathrm{<figure-callout\; id="1"\; label="z"\; filenames="A20061003049000101.png"\; state="\{\{state\}\}">z</figure-callout>}}{\mathrm{\&Sigma;}}\frac{1}{4d_i^2}{({\mathrm{\&Delta;\&phi;}}_{+\hat{i}}\left(\mathrm{\&omega;}\right)+{\mathrm{\&Delta;\&phi;}}_{-\hat{i}}\left(\mathrm{\&omega;}\right)-2\mathrm{\&pi;}{m}_i)}^2}-\mathrm{\&omega;}=0$

M=(m wherein _x, m _y, m _z).If get ${\mathrm{\&Delta;\&phi;}}_{\&PlusMinus;\hat{i}}=\mathrm{\&pi;},$ Then can get back to the situation of traditional resonant cavity, the lowest operating frequency in chamber is decided by the size in chamber at this moment.The same with above-mentioned unidimensional system, the yardstick of this cavity on three dimensions can be arbitrarily small with respect to it by operation wavelength.Our experimental result shows that for the three-dimensional resonant cavity that mushroom-shaped artificial magnetic surface constitutes, the size of this resonant cavity can be less than ending 1/4th of operation wavelength.

The concrete structure of resonant cavity of the present invention is: comprise medium in the metallic walls that surrounds coelosis and the chamber, be characterized in: the surface of the metallic walls in the chamber is fixed with 1 or 2-3 piece artificial magnetic surface.

Described artificial magnetic surface comprises the metal copper layer that is commonly called as to " metal patch " copper-clad, dielectric layer and bottom (patch) successively, and wherein copper-clad is made of periodic unit structure type that can satisfy selected operation wavelength and periodic structure geometric parameter.

The periodic unit structure type of the copper-clad on described artificial magnetic surface is square mushroom-shaped, UC-PBG type, the H type is fractal, Hilbert is fractal or Spiral snail type.

Described metallic walls can be substituted by the metal copper layer on artificial magnetic surface.

Resonant cavity of the present invention has the following advantages:

1. because the intrinsic artificial magnetic of the chamber wall surface in the resonant cavity of the present invention, therefore, the cut-off frequency of this resonant cavity is not subjected to the restriction of the physical dimension in chamber itself, broken through of the restriction of the size of traditional classical resonant cavity to cut-off frequency, resonant cavity of the present invention has been broken through traditional resonant cavity lowest limit operating frequency, helps miniaturization of devices.

2. because the operating frequency of resonant cavity can be controlled by selecting suitable period cellular construction type and geometrical parameters in the intrinsic artificial magnetic of the chamber wall surface of resonant cavity of the present invention, therefore on the basis that guarantees miniaturization, can also make the wavelength of the present invention can be by the instructions for use of different field, align corresponding wavelength parameter, low to can be used as filter or the cavity type antenna uses.

Description of drawings

Fig. 1 is a profile schematic diagram of the present invention

Fig. 2 is the front view that removes the metallic walls of front of the present invention

Fig. 3 is the attached view that removes top metallic walls of the present invention

Fig. 4 is the end view that removes the metallic walls on the left side of the present invention

Fig. 5 is the structural representation on the square mushroom-shaped artificial magnetic surface that is made of nine unit of the present invention

Fig. 6 is that the resonant cavity cut-off frequency of the embodiment of the invention 1 calculates and graph of measured results

Fig. 7 is that the resonant cavity cut-off frequency of the embodiment of the invention 2 calculates and graph of measured results

Fig. 8 is the reflection position phase result of calculation curve chart under the surperficial normal incidence condition of square mushroom

Fig. 9 is for calculating the equivalent permeability graph of a relation on square mushroom surface with reflection coefficient under the normal incidence condition

Embodiment

Embodiment 1

Be of a size of the resonant cavity of cube shaped on artificial magnetic surface of fixed two 3 * 3 copper-clads of inwall of 21mm.At first, see also Fig. 1 ~ 5.Resonant cavity of the present invention is surrounded by 6 metallic walls 1 before and after up and down and forms, and air is arranged in the chamber.The lower surface of the metallic walls 1 in its lumen and right surface respectively are fixed with 1 and amount to 2 artificial magnetic surfaces, magnetic surface be shaped as square mushroom-shaped that 3 * 3 nine unit form, form by copper-clad 4, dielectric layer 3 and metal copper layer 2 successively.This magnetic surface is of a size of 21mm, the cycle of periodic unit structure (copper-clad and slit) p=7mm, slit=0.4mm, the thick h=0.035mm of two kinds of metals (copper-clad and as the metal copper layer of base plate), DIELECTRIC CONSTANT _r=2.2, dielectric layer thickness d=1.6mm.Constitute thus and be of a size of the cut-off frequency of the cubical resonant cavity of the present invention of 21mm at 8GHz.The return loss of passing through of Fig. 6 has confirmed this point (result of calculation curve and measurement result have correlation) to resonant cavity cut-off frequency measurement result of the present invention.But the cut-off frequency of the existing resonant cavity of identical size is more than 10GHz.

Embodiment 2

Be of a size of the resonant cavity of cube shaped on artificial magnetic surface of fixed two 2 * 2 copper-clads of inwall of 14mm.

Except artificial magnetic surface size and copper-clad 4 are 2 * 2, all the other are all identical with embodiment 1.Constitute thus be of a size of the cubical resonant cavity of the present invention of 14mm cut-off frequency at 5.5GHz, the resonant cavity of identical size (referring to not have the prior art of artificial magnetic surface) cut-off frequency is more than 15GHz.The cut-off frequency measurement result of resonant cavity of the present invention shown in Figure 7 has confirmed this point (result of calculation curve and measurement result have correlation).

Embodiment 3

Size is respectively the resonant cavity of two kinds of cube shaped on fixed two 3 grades snail type artificial magnetics of the inwall surface of 21mm and 14mm.Except artificial magnetic surface size and copper-clad 4 are two 3 grades snail type artificial magnetic surfaces, the length of side of the periodic unit structure of each artificial magnetic surface is 7mm, the width of copper-clad 4 (bonding jumper) is 0.5mm, distance between the adjacent two parallel metal bars is 0.5mm, dielectric layer thickness is 2.0mm, so for the cut-off frequency (by operating frequency) of 3 * 3 resonant cavity at 3.95GHz, the resonant cavity for 2 * 2 by operating frequency at 3.20GHz.All satisfy the filtering device instructions for use.

Claims (4)

1. three-D resonant cavity that can reduce cut-off frequency comprises medium in the metallic walls (1) that surrounds coelosis and the chamber, and it is characterized in that: the metallic walls in the chamber (1) surface is fixed with 1 or 2-3 piece artificial magnetic surface.

2. a kind of three-D resonant cavity that reduces cut-off frequency according to claim 1, it is characterized in that: described artificial magnetic surface is made up of copper-clad (4), dielectric layer (3) and metal copper layer (2) successively, and wherein copper-clad (4) is made of periodic unit structure type that can satisfy selected operation wavelength and periodic structure geometric parameter.

3. a kind of three-D resonant cavity that reduces cut-off frequency according to claim 1 is characterized in that: the periodic unit structure type of the copper-clad (4) on described artificial magnetic surface is for square mushroom-shaped, UC-PBG type, the H type is fractal, Hilbert is fractal or Spiral snail type.

4. a kind of three-D resonant cavity that reduces cut-off frequency according to claim 1 is characterized in that: described metallic walls (1) is substituted by the metal copper layer (2) on artificial magnetic surface.

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