| Modern electromagnetism, after more than three hundred years of development, is improving continuously.As the key equipment to achieve radio applications, antennas continuous development, conforming to required at different stages of telecommunications, broadcasting, radar, the guidance system and other radio applications.Nowadays, antenna have a great change on the function,design and manufacturing process than before.However, the rapid development of microelectronic technology and the large scale integrated circuit make the question obviously, which antenna become huger, more unwieldy part's in the electronic installation, thus the needs for small antenna which can coordinate with equipment size and have effective electrical characteristics has become more urgent.The research of practical and small microstrip antenna become the focus of research, especially the antenna for the third generation mobile communication system,Bluetooth and wireless positioning system.In present, PIF antenna, because of it's small-size, light-weight, and small-backward radiation and so on merits, become the main form of built-in antenna's in the portable equipment. To decrease passive antenna's size will cause the radiation resistance and the efficiency fell. To use the amplification and impedance compensation technology of active network could compensate for target drop caused by the antenna minification.But the active antenna must consider of noise and the nonlinear distortion.Based on the above situation, this article has designed small active antenna which was integrated a miniaturized PIF antenna and a low noise amplifier based on MMIC.This article has analyzed and studyd antenna build in handset and applied in the blue tooth frequency band.It put emphasis on the analysis of PIF antenna's and the low noise amplifier's characteristics and design methods, then designed the active PIF antenna.which has met the challenge of the handset built-in antenna. This article has designed and analyzed on the PIF antenna and low noise amplifier separately, then analyzed active antenna's characteristic . The active antenna enhanced the gain and enhanced the radiation signal-to-noise ratio, with keeping passive antenna intrinsic band width, the directivity, in the polarized characteristic situation.It has achieved a good effect.Specific work are as follows:1,Firstly, this article introduced the evolution of PIF antenna.Secondly, in HFSS, it described the design process of blue tooth antenna in detail.This part summarizes the influence rule of antenna's length L, width W and short circuit piece width WS to antenna's resonance frequency, the input impedance.Based on this, I have optimized a PIF antenna with good performance, its volume is 4*29.5*10mm3, the resonance frequency is 2.4GHz, the input impedance presents a pure resistance condition on the resonance point, the relative bandwidth was 13.7%, the front tropism and the cross polarization characteristic could satisfy the miniaturized blue tooth handset antenna's request, the antenna design are convenient and flexible.The deficiency was the gain on the maximum radiation direction only– 6dB, waited for solving.2,Because the antenna's gain is small, the signal quality is bad, this paper has designed a low noise amplifier (LNA), used to increase antenna's power input, make its gain increase and reduce the noise effect of component, enhance the radiant signal quality.This part has completed by ADS.The simulation result indicated that the LNA input and output was matched with 50 ohm, the gain was 15.45dB, noise factor was 0.22dB, the gain smoothness was smaller than 0.02dB in each 100MHz, the performance was good.3,The simulation of LNA in ADS discovered three things:on the frequency domain, the LNA has amplified the signal which was in the transmission bands and kept down the singal which was out of the transmission bands;On the time domain.The input and output's phase is opposite, the voltage gain was about 7;with electric capacity C1in the inputs port of LNA to be bigger, the lower frequency gain was bigger and the gain change was steeper in the frequency band, when the capacitance value is 0.46pF, the gain change was smoothest, when it was reduced sequentially, the low-frequency gain is smaller than the high frequency gain, reduced sequentially, gain change was steeper in the frequency band.On the other hand.When the inductance L2 in the output port was bigger, the high-frequency gain was lower; On the contrary, when the value of L2 was smaller, the low frequency gains was lower.Therefore, the output gain smoothness can be increased by adjusting inductance and electric capacity.Through the above analysis and design, the LNA electric circuit was optimized.4,The active antenna was come from a passive antenna which integrated active circuit. So this part connected lower noise amplify circuit with PIF antenna.this part have completed by IE3D.The simulation result indicated that gain was bigger than original antenna, the gain on the maximum radiation direction was from -6dB to 4dB after signal was through the amplifier, and gain smoothness was to be batter in the bandwidth range than before. Moreover, compared to the passive antenna, the active antenna has suppressed the backward radiation better.This active PIF antenna has small volume, big band width, high gain, good gain smoothness, such a series of advantages.Moreover, it suppressesed the backward radiation effectively, so it reduced the value of SAR to human body, that was beneficial to human health.Then, it reduced the component noise, at the same time, increased the gain.thus it enhanced the signal-to-noise ratio of radiation, the signal quality obtains promotion. |
