A kind of coaxial cross oscillator array communications antenna and method for designing thereofTechnical field
The present invention relates to a kind of coaxial cross oscillator array communications antenna, this array antenna vertical guide has comparatively narrow beam, horizontal plane and has omnidirectional radiation performance, is therefore widely used in ADS_B communication system, AIS communication system and mobile base station, Vehicle mounted station etc. are various needs in the communication system of omnidirectional radiation.
Background technology
In the communications field such as mobile communication base station, Vehicle mounted station, in order to realize the comprehensive covering of signal, omnidirectional antenna be adopted.And in order to reach certain coverage, require that again this antenna has higher gain.Realize All-Round High Gain Antenna usually have and present and series feed two kinds of modes.And it is complicated to present mode feeding network, Project Realization is comparatively difficult, therefore series feed mode is widely adopted.
1989, Judasz. the people such as T. J proposes a kind of series feed high-gain omni-directional antenna in " Improved Theoretical and Experimental Models for the Coaxial Collinear Antenna " article, namely collinear antenna (Coaxial collinear antenna, is also COCO antenna) is coaxially intersected.It is made up of cross-coupled coaxial line segments, and every segment length is(wavelength in coaxial line), the outer conductor interconnection of its inner wire and next section, thus make every section of coaxial outer conductor outer wall electric current equal, reach the effect that homophase is series feed.
1998, the people such as Kiang. J. F proposed the concept of slotted coaxial antenna at article " Analysis of Linear Coaxial Antenna ", and have carried out computer sim-ulation.1999, the people such as Miyashita H propose slot-coupled coaxial dipole aerial (Electromagnetically coupled coaxial dipole antenna, i.e. ECCD antenna) in article " Electromagnetically Coupled Coaxial Dipole Array Antenna ".These two kinds of antennas are all the development of deformations of series fed antenna array, but coaxial collinear antenna and the tuning comparatively difficulty of slotted coaxial antenna and consistency is poor of intersecting, then there is the shortcoming of heavier-weight in slot-coupled coaxial dipole aerial.
Coaxial series feed oscillator battle array utilizes the half-wave dipole feed that on coaxial outer conductor, periodic annulus (interval is about 0.7 λ) is overlapped band chokes, and chokes cover is that oscillator arms plays inhibitory action to electric current on coaxial line outer wall again.Gap spacing is about 0.7 λ, and minor level can be made lower than-15 ~-20dB.Coated by dielectric between coaxial line internal and external conductor, makes adjacent slits spacing be, to ensure each array element current in phase.In the tubular cover that whole antenna packages is made at polytetrafluoroethylglass glass cloth, be used for protecting and strengthen rigidity.It is good, cheap and be easy to tuning feature that coaxial series feed oscillator battle array has consistency.Be widely used in each field of wireless communications.
Summary of the invention
The object of the invention is to: the problem lower for series fed antenna gain, azimuth plane omni-directional is poor, design a kind of high-gain, omni-directional is good, and the simple coaxial serial feedback vibrator antenna array of structure.
The present invention utilizes the half-wave dipole feed that on coaxial outer conductor, periodic annulus is overlapped band chokes, the coated by dielectric between coaxial line internal and external conductor, and chokes sleeve oscillator structure repeats at axis direction, improves antenna gain.Each is to half-wave dipole cross occurrence on metal chokes sleeve, and between often pair of neighbouring oscillator, angle is 90 °, and azimuth plane can be made better to reach omnidirectional radiation.
The concrete technical scheme realizing above-mentioned purpose is as follows.
1, according to lossless transmission line theory, on the transmission line of terminal short circuit, electromagnetic wave is pure standing wave state, and on it, electric current complex amplitude expression formula is:
Wherein, k is and line characteristic impedancerelevant plural number,.
The two-wire line that one section is opened a way is opened, can doublet antenna be obtained.DISTRIBUTION OF CURRENT on doublet antenna and two-wire line similar.Suitable length is got to the two-arm of separating, the electric current constant amplitude homophase in two-arm can be made.The electromagnetic field that two-arm electric current produces, to external radiation, forms doublet antenna.
Be greater than half wavelength when turning up partial-length, antenna will occur negative-phase sequence curent, the radiation of negative-phase sequence curent will be cancelled out each other.If folded up by the line segment of negative-phase sequence curent, two length aresymmetrical line segment, then folded part antenna can not produce radiation, and non-folded part electric current keeps inphase radiations.Material is thus formed the basic structure of sleeve stub.The CURRENT DISTRIBUTION on oscillator and input impedance can be calculated accordingly.
2, the feeding transmission line of antenna adopts the structure of coaxial line, the coated by dielectric between coaxial line internal and external conductor, makes adjacent slits spacing be, to ensure each array element current in phase.Impedance computation formula according to coaxial line:
(whereinthe characteristic impedance of coaxial transmission line,for the relative dielectric constant of loaded medium, a is inner wire radius, and b is loaded medium radius), the characteristic impedance needs of coaxial line and place communication system coupling, so characteristic impedance is known, can obtain the radius of inner wire and loaded medium thus.
3, according to the designing gain requirement of antenna element, the gain of series feed array is calculated.First model is equivalent to half-wave doublet.According to aerial array basic theories, have:
Gain=Ge+Ga
In formula, Gain, Ge, Ga are respectively the gain of antenna element, doublet antenna and aerial array.Therefore, the designing gain requirement of aerial array can be obtained.In order to reach the designing requirement of array, considering the convenience in Project Realization simultaneously, the form of coaxial series feed oscillator battle array being equivalent to equidistantly evenly excitation limit here and penetrating formation formula.Like this, the direction coefficient that battle array is penetrated on the first limit of N is:
In formula, d is array element distance,for free space wave number.According to above formula, N unit can be obtained and equidistantly evenly encourage limit to penetrate the relation of direction coefficient with the change of electric spacing of battle array.The unit interval d under designing gain and each chokes length sleeve and oscillator number can be selected accordingly.
The Advantageous Effects of inventive antenna is embodied in following several aspect:
1, antenna adopts the basic model of coaxial transmission line, to realize the good impedance match with each communication system, obtains wider standing wave working band.And easy to process, be easy to realize;
2, on coaxial outer conductor, periodically have annulus (interval is about 0.7 λ), can to the half-wave dipole feed of band chokes cover, chokes cover is that oscillator arms plays inhibitory action to electric current on coaxial line outer wall again.Serve the function of impedance matching and capable radiation;
3, each is to half-wave dipole cross occurrence on metal chokes sleeve, and between often pair of neighbouring oscillator, angle is 90 °, ensure that the omnidirectional performance of antenna on azimuth plane.
Below in conjunction with accompanying drawing, the present invention is described in further detail.
Accompanying drawing explanation
Fig. 1 is the structure full figure of inventive antenna.
Fig. 2 is the local structural graph of inventive antenna.
Fig. 3 is the antenna structure dimensional drawing of example one.
Fig. 4 is the standing wave curve of the antenna port of example one.
Fig. 5 is the antenna three-dimensional figure of example one.
Fig. 6 is the directional diagram of antenna at azimuth plane of example one.
Fig. 7 is the directional diagram of antenna in pitching face of example one.
Embodiment
Specific implementation method of the present invention is as follows.
See Fig. 1 and Fig. 2, a kind of series feed sleeve stub array antenna, antenna element adopts the form of half-wave doublet, and whole antenna comprises metal inside 1, medium inner core 2, metal shell 3, metal oscillator 4, base 5.The present invention adopts following concrete technical measures as follows.
1, coaxial series feed oscillator battle array available equivalents network technique carrys out analytical calculation.Can following relationship be obtained according to coaxial transmission line principle:
In formula, I and V represents coaxial line two-end-point 1,2, and subscript 1,2 represents at 1 end or 2 ends, and subscript i represents coaxial line internal current,for the characteristic impedance in coaxial line.
The pass obtaining the inside and outside electric current of coaxial line according to principle of continuity of electric current is:
Can be tried to achieve by above a few formula
The input impedance of coaxial series feed a period of time antenna can be obtained thus:
Computable to the size of chokes sleeve and the spacing in gap according to the input impedance of antenna.
2, the feeding transmission line of antenna adopts the structure of coaxial line, the coated by dielectric between coaxial line internal and external conductor, makes adjacent slits spacing be, to ensure each array element current in phase.Impedance computation formula according to coaxial line:
(whereinthe characteristic impedance of coaxial transmission line,for the relative dielectric constant of loaded medium, a is inner wire radius, and b is loaded medium radius), the characteristic impedance needs of coaxial line and place communication system coupling, so characteristic impedance is known, can obtain the radius of inner wire and loaded medium thus.
3, the gain of coaxial series feed array is calculated.First model is equivalent to half-wave doublet, the gain of half-wave doublet antenna is about 2dB.According to aerial array basic theories, have:
Gain=Ge+Ga
In formula, Gain, Ge, Ga are respectively the gain of antenna element, doublet antenna and aerial array.The designing gain of aerial array can be obtained thus.In order to reach the designing requirement of array, considering the convenience in Project Realization simultaneously, the form of coaxial series feed oscillator battle array being equivalent to equidistantly evenly excitation limit here and penetrating formation formula.Like this, the direction coefficient that battle array is penetrated on the first limit of N is:
In formula, d is array element distance,for free space wave number.According to above formula, N unit can be obtained and equidistantly evenly encourage limit to penetrate the relation of direction coefficient with the change of electric spacing of battle array.The unit interval d under designing gain and each chokes length sleeve and oscillator number can be selected accordingly.
Example 1: one is operated in the coaxial series feed oscillator array antenna of L frequency range.The all version of this antenna element is identical with Fig. 1, and adopt the feeding classification of coaxial transmission line, the dielectric constant of loaded medium is 2.02, antenna total length L=656mm, antenna diameter d=12mm, the long l=168mm of chokes sleeve oscillator, oscillator brachium 61mm, gap width 8mm.Antenna structure as shown in Figure 3.
Fig. 4 is the antenna standing wave curve of example one, and in working band, active standing wave is all less than 1.5 as seen, meets index request well.
Fig. 5 is the antenna gain three-dimensional figure of example one, and gain is about 6dB.
Fig. 6, Fig. 7 are that the aerial array of example one is at the azimuth plane of center frequency point and pitching face directional diagram.