1 introduction
Along with the modern military communications system in technical and so on frequency-hopping, wide frequency applications, the antenna takes communication facility’s front end part, is playing the very important role to the correspondence quality. However the traditional antenna form and the function cannot follow the communications system miniaturization to a certain extent the development demand, seeks antenna’s isotropic, the miniaturization, the wide band, to use in common turns into for the antenna research in an important topic. Single-pole sub-antenna by its structure simple and spherical radiation characteristic, is widely applied in the wireless communication domain, because the single-pole sub-antenna has the electricity oversize and the frequency band narrow characteristic, already could not satisfy the design well the request. And antenna’s input impedance is quite big along with the frequency shift, causes the antenna to present the very high input reactance (to accommodate nature), is very difficult and 50 OMEGA coaxial line matches. The people use many kinds of measures to improve antenna’s performance, the load adapts this kind of miniaturized antenna’s typical technology. In recent years had the massive literature development to this, on the one hand research.
The load technology is in the antenna works the commonly used miniaturization and the wide band method, through, in antenna’s appropriate position load resistance, the reactance or the conductor improve in antenna’s current distribution, thus achieves changes antenna’s resonance frequency or reduces the antenna under the similar operating frequency highly as well as changes antenna’s goals and so on transmitting pattern. The load part may be the passive component may also be the active network, may be the linear element may also be misalignment, what in the actual project is most commonly used is the passive load, for example: The crown loads, the medium to load, the series distribution to load, the centralism load and so on. Often uses the centralism regarding the operating frequency not high situation to load, but the operating frequency is high time uses the distribution load. Therefore realizes the antenna miniaturization most effective way through the load technology.
2 load applications
The predecessor had already done many about loaded antenna’s research, the Altshuler first basis transmission line theory, regards as the dipole antenna to lead the way approximately the transmission line, from opening terminal 1/4 wave length place series one was equal to that the open-circuited line characteristic impedance the resistance, may obtain the traveling wave electric current on the antenna, thus causes the dipole antenna to match good in the wide frequency band. Because the antenna request loading point to the terminal distance is 1/4 wave length, if this condition is dissatisfied, the load resistance’s function will be weakened has even an effect. This continues in the HF, V/UHF frequency band to reduce antenna’s size very difficultly. Recently, BOag and Mittra et al. proposed that implements the partition load with the RLC parallel circuit to the single-pole sub-antenna. Simultaneously drew support from the genetic algorithm and the computer simulation overall situation search best load position and the loading unit value, the success has designed 30~450 MHz Shan Bian and the double whip loaded antenna. Dr. Sun Baohua was synthesizing the above method, the union loads the optimization design methods design which the fast processing technology as well as GA and SA unified to manufacture the single whip antenna, further optimized antenna’s performance index. Although R, L, C and the combination load may reduce the antenna size, stretches the antenna bandwidth. But will have consumes part’s introduction to will certainly to cut antenna’s radiation efficiency. The impedance loaded antenna is obtains the wideband characteristic through the sacrifice gain, therefore between the band width and the gain is pair of contradictory, particularly works as the frequency to be low, the antenna electrical length is small, this kind of contradiction displays prominently. In the actual correspondence, often requests the antenna both to have the good band width and to have the acceptable gain. Therefore, when design must makes a suitable choice between the band width and the gain. 3 loads and other technical unions
Because pure RLC loads to the miniaturized antenna design has the limitation. Under the guarantee certain efficiency’s premise, must further reduce the single-pole sub-antenna’s size, but also needs to do the further research. And the curvature antenna and the fractal adapt the design development another computing technique. As shown in Figure 1.
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The fractal technology has filled effectively the finite space region, thus increased antenna’s electrical length. This characteristic may cut antenna’s resonance frequency greatly, meanwhile may obtain the multi-frequency bands or the wideband characteristic. Unifies the crown load technology to be possible to design the structure compact three dimensional fractal tree single pole sub-antenna, the resonance frequency must lower a lot compared to the same high single-pole sub-antenna. Literature [1] Ruan completed a ceremony professor to propose one kind loaded the fractal single-pole sub-antenna, the antenna work in 3~30 MHz frequency range, his electricity size must be smaller than the general load single pole sub-antenna.
Fractal’s construction has the relative complexity, comparatively, loads both and the economy simply with the curvature structure in the plane single pole sub-antenna peak, in can satisfy under the antenna design target performance premise, the curvature is the first choice load structure not only increases antenna’s input resistance, but also sharpens the emissivity. Literature [2] Li the Xu equality proposed one kind of new rectangular plane single pole sub-antenna, as shown in Figure 3, the upper extreme used the curvature to increase antenna’s electrical length, and in the suitable position load, has realized antenna’s wide band miniaturization design requirements.
The curvature and the fractal line are increase the antenna electrical length the effective measure, is not only advantageous adjusts the low frequency band standing wave characteristic to be also advantageous to loading unit’s introduction, can cause the antenna to obtain the very good performance requirement.
Literature [6] used a blending inheritance algorithm design load normal mold spiral antenna, this kind improved the partial search ability with the load union’s method to be bad, the convergence rate slow shortcoming, caused to load the multi-objective function optimization efficiency to enhance many.
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4 load optimization designs
Antenna loading’s optimization design is a misalignment question, involves the variable including loads the position, the loading unit, the load combination form and so on, is a multivariable question. Must establish an appropriate optimized function, when achieves the antenna needs the characteristic, this function has a minimum. Because antenna characteristic and antenna parameter related, therefore the optimized function is also these parameter function. Simultaneously seeks the appropriate optimized method, enables the optimized function to achieve minimum. Seek the load with the aid of the computer simulation and the optimized technology the optimal solution.
Because the optimized function is very difficult with a simple analytic function to indicate that but the traditional optimized algorithm or needs the objective function the derivative, either is only the partial optimization, although either is but oversized for the overall situation optimization computation load, causes commonly used optimized algorithms and so on gradient method, simplex method to realize with difficulty in the antenna loading optimization design. One new closed region optimization reconnaissance method genetic algorithm’s appearance has solved the above some problems. He is simulates the nature organic evolution process and mechanism solution minimum problem one kind from the organization, the auto-adapted artificial intelligence technology. He only needs to use the objective function the value information, but does not need high price information and so on gradient, suits in not having the expression or has the expression any kind of objective function, has the achievable parallel computing behavior. 5 conclusions
Along with the antenna miniaturization, the wide band further development, the load technology obtains more applications. However the pure load already could not satisfy the antenna integration the development demand, what are more is loads the technology and the fractal technology, converts into the single pole, the wideband matching network, the genetic algorithm combination application, like this may design a more ideal antenna fast effectively. Will unify the antenna miniaturization technology is the future antenna design tendency effectively, will wait for the further research, he will have the widespread application prospect.
