摘要
摘要
无源天线遵循带宽-效率-体积约束机制，使其难以同时实现减小体积、增加带宽和提高效率的目的。利用非福斯特有源电路的负斜率电抗特性设计宽带阻抗匹配，能够打破Bode-Fano准则限制，使得天线，尤其是短波频段的电小天线，获得更好的小型化和宽带化特性。此外，在室内复杂通信环境中，提高信道可靠性需要消除信号的多径衰落现象。分集技术是对抗多径衰落现象的一种有效手段，分集天线的相关研究具有重要的理论和工程应用价值。论文结合科研项目，围绕天线的有源匹配技术和分集技术展开研究工作，主要研究内容包括以下几个方面： 1、研究宽带有源电小单极子天线。首先，分析并实测验证电长度为0.075λ0的无源电小单极子天线，该天线辐射电阻小、输入电抗大，采用传统无源匹配网络只能实现窄带谐振。其次，研究了基于运算放大器的两种负阻抗变换器电路，得出同相输入端输出型NIC电路的输入电阻为负、反相输入端输出型NIC电路的输入电阻为正的结论，并对其关键参数进行仿真和测试分析，得出有规律的非福斯特特性曲线。在此基础上，设计有源二阶NIC匹配网络，通过改进和优化网络形式和参数，当它与电小单极子天线匹配时，天线电抗在整个短波频段得到了很大程度的抵消。在实测有源单极子天线输入阻抗的基础上，结合优化算法设计无源匹配网络，进一步展宽了天线带宽，实现127%的实测-6dB相对阻抗带宽。最后，采
用对比法测试有源单极子天线在几个具体频点的接收功率，证明了有源单极子天线与无源单极子天线相比具有更好的接收效果。
2、研究宽带有源半环天线。首先，采用特征模理论分析加载无源器件的半环天线，证明该天线只有单一的窄带谐振模，特征电流的分布和方向揭示了天线并联谐振特性。其次，通过调谐末端加载电容，分析了无源半环天线的两个关键特征模变化规律曲线，计算出具有负斜率特性的电纳曲线，设计出由理想非福斯特元件构成的非福斯特阻抗匹配网络。再次，将非福斯特阻抗匹配网络代替电容加载在半环天线的辐射体上，该有源半环天线的谐振模实现了连续谐振特性，同时保持几乎不变的特征方向图，展宽了天线的阻抗带宽和方向图带宽。最后，仿真分析和参数验证了基于晶体管的负阻抗变换器电路，在此基础上设计实际元件的非福斯特阻抗匹配网络，将其加载在半环天线辐射体上，并加工和测试有源半环天线。结果表明，有源半环天线的相对阻抗带宽是无源半环天线的6倍，从而实现了宽带化。
3、研究不同应用场景的分集天线。首先，设计一款双端口馈电的双模方向图分集天线。天线由带有双探针的方形贴片构成，通过改变馈电端口控制探针电流流向，实现定向宽波束辐射模式和锥形辐射模式的切换。通过设计鼠笼馈电网络和容性耦合
槽，两种工作模式具有21.8%的公共相对带宽。其次，设计一款低剖面水平全向覆盖的极化分集天线。天线采用圆环缝隙天线实现垂直极化，弧形偶极子阵列天线实现水平极化，通过将偶极子阵列天线摆放在圆环缝隙天线地板四周，天线的剖面高度仅为0.024λ0，通过设计互不影响的馈电形式，实现垂直极化和水平极化的水平全向覆盖。最后，设计一款细长型的方向图和极化双分集天线。天线由一个J型天线和两个偶极子天线组成，利用J型天线不需地的特点，实现了偶极子天线和J型天线组合而互不影响工作性能。偶极子天线采用弯折臂结构，减小了天线体积。当垂直于地板放置时，天线在WLAN频段可以实现水平极化和垂直极化的水平全向覆盖，同时在水平方向具有方向图分集特性。
关键词：非福斯特电路，有源天线，分集天线，电小天线
ABSTRACT
ABSTRACT
Due to the constraints of bandwidth, efficiency and volume of the passive antennas, it is usually difficult to reduce the antenna size, enhance the antenna bandwidth and increase the antenna efficiency, simutaneously. The reactance of non-Foster circuit reactance has negative slope characteristic. When using the non-Foster circuit in the matching network of antennas, the limit of Bode-Fano rule can be break. Thus, the antenna, especially the electrically small antenna in HF ban
d, can achieve better miniaturization and broadband characteristics. In addition, in the complex indoor communication environment, it is necessary to eliminate the multipath fading for improving the reliability of the channel. Diversity technology is an effective way to combat multipath fading, while the related research has important theoretical and engineering application value. Combining with the research project, this dissertation focuses on the active matching techniques and diversity techniques. The main academic contributions of this dissertation are as follows.
1. The broadband active electrically small monopole antenna is studied. Firstly, a passive electrically small monopole with 0.075λ0 electrical length is analyzed. Because of its characteristics of small reactive and large reactance, the antenna only resonant at narrow bandwidth by using traditional passive matching network. Secondly, two kinds of negative impedance converter circuits based on operational amplifier are studied. It is concluded that the input resistance of the inverting input-output type NIC circuit is positive while that of the non-inverting input-output type NIC circuit is negative. By simulating and testing the key parameters of the circuits, the curves with non-Foster characteristic are obtained. On this basis, a active two stage NIC matching network is designed for the electrically small monopole antenna. By improving the network form, the antenna reactance has been largely offset in the short wave band. Thirdly, on the basis of the measured input impedance of the active m
onopole antenna, the passive matching network is designed with the optimization algorithm, and the bandwidth of the antenna is further widened. The measured -6dB relative impedance bandwidth can reach 127%. Finally, by applying the comparison method, the received power of the active monopole antenna is tested. Experimental results show that the active monopole antenna has a good effect in the whole working frequency band.
2. The broadband active half-loop antenna is studied. Firstly, by using characteristic mode theory, a passive loaded half-loop antenna is analyzed. Results show that the antenna
has a single narrowband resonant mode, and the distribution and direction of characteristics current reveal parallel resonant characteristics of the antenna. Secondly, by changing the value of the terminal loaded capacitance, the curves of two key characteristic modes is analyzed, and the admittance curve with negative slope characteristic is calculated. By applying co-simulation technique, the ideal non-Foster impedance matching network is designed to meet the requirements. Next, by replacing the Foster capacitor with the non-Foster network, the resonant mode of the active half-loop antenna turns the narrowband resonant mode into a continuous resonant mode with its radi稀疏化
ation pattern kept invariant over a wide bandwidth. Thus, both the impedance bandwidth and radiation bandwidth are widen. Finally, based on simulation verification and parameter analysis of the negative impedance converter circuit using transistors, the actual non-Forster impedance matching network is designed and loaded on the half-loop antenna. The active half-loop antenna is fabricated and tested. The results show that the impedance bandwidth of the active half-loop antenna is 6 times passive half loop antenna.
3. Three kinds of diversity antennas are studied. Firstly, a pattern diversity antenna is designed. The antenna is composed of a square patch with double probe, by control the current of the probe, the radiation pattern of the antenna can switch between the broadside and the conical radiation pattern. The overlapping relative bandwidth of two mode is 21.8%. Secondly, a polarization diversity antenna is designed. The antenna adopts ring slot antenna to achieve vertical polarization, while arc dipole array to achieve horizontal polarization. By placing the dipole array around the ground of ring slot antenna, and designing non-interference feeding networks, the antenna has a low profile of 0.024λ0, while achieving dual polarizations. Thirdly, a pattern and polarization diversity antenna is designed. The antenna consists of a J-pole antenna and two dipole antennas. Since the J-pole antenna requires no DC ground, the dipole antenna and J-pole antenna are combined without affecting each
performance. The arms of the dipole adopt a bent structure for size miniaturization. When placed perpendicular to the floor, the proposed antenna achieves available vertical and horizontal polarizations covering the whole horizontal plane, while has pattern diversity characterisitc in the horizontal direction.
Keywords: Non-Foster circuit, Active antenna, Diversity antenna, Electrically small antenna
插图索引
插图索引
图1.1 文献[1]中的非福斯特电路 (3)
图1.2 文献[4]中的非福斯特电路 (3)
图1.3 文献[5]中的非福斯特电路 (4)
图1.4 文献[10]中的非福斯特电路 (4)
图1.5 文献[11]中的非福斯特电路 (4)
图1.6 文献[12]中的非福斯特电路 (4)
图1.7 文献[15]中的非福斯特电路 (5)
图1.8 文献[18]中的非福斯特电路 (5)
图1.9 文献[20]中的负电容电路 (6)
图1.10 文献[21]中的非福斯特电路 (6)
图1.11 文献[22]中的负电容电路 (6)
图1.12 文献[24]中的非福斯特电路 (6)
图1.13 文献[49]中的有源天线 (7)
图1.14 文献[46]中的有源天线 (8)
水压力传感器图1.15 文献[51]中的有源天线 (8)
图1.16 文献[52]中的有源天线 (8)
润滑油分配器图1.17 文献[63]中的有源天线 (9)
图1.18 文献[64]中的有源天线 (9)
图1.19 文献[65]中的有源天线 (9)
图1.20 文献[78]中的有源天线 (10)tmch
图1.21 文献[127]提到的特征模的电磁场分析和设计的手持天线 (11)
图1.22 文献[131]提到的特征模电流特性和设计的手持天线 (11)
图1.23 文献[141]中提出的天线结构和特征模分析方法 (12)
图1.24 文献[146]中的天线 (13)
图1.25 文献[153]中的天线 (13)蚊子网
图1.26 文献[155]中的天线 (13)
图1.27 文献[156]中的天线 (13)
图1.28 文献[172]中的天线 (14)
图1.29 文献[173]中的天线 (14)
图1.30 文献[174]中的天线 (15)
图1.31 文献[178]中的天线 (15)
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