Miniaturized dipole antennas for ground-penetrating radar using metamaterial techniques

该项目的目标是研究小型化超材料偶极子天线取代现有探地雷达系统中大偶极子天线的可行性，同时研究“超物质化”对脉冲色散、天线电流分布、辐射方向图、带宽、辐射效率和极化纯度的影响。负折射率传输线(NRI-TL)超材料已被证明在小型化器件中是有效的，其性能取决于其相对于工作波长的尺寸。NRI-TL方法非常适合高频平面印刷电路板TL技术，如微带，并已使小型化微带耦合器、分频器、巴伦，甚至小型化印刷偶极子天线的开发成为可能。然而，这些平面超材料技术可能不适合与探地雷达系统相关的高压或低频条件。探地雷达可以在低至几十兆赫的频率下工作，这需要几米长的天线。通常，这些天线是简单的线偶极子天线，它们的小型化需要开发和表征一种合适的超材料拓扑结构，能够处理缩小频率下的高压信号。此外，探地雷达以脉冲的传输为基础，脉冲由一系列频率分量组成。因此，所设计的超材料技术还必须提供宽带性能。然而，使超材料能够提供小型化的相同性质也引入了很强的频散，这必须通过根据所设计的超材料的已知频散对发射和接收的信号进行前处理或后处理来充分表征和补偿。综上所述，该项目将研究以探地雷达天线小型化为目标的NRI-TL超材料拓扑结构，并将大量时间用于脉冲色散、恢复和色散补偿的理论研究。

The goal of this project is to examine the feasibility of miniaturized, metamaterial-based dipole antennas in replacing the large dipole antennas in existing ground-penetrating radar (GPR) systems, while examining the effect of `metamaterialization' on pulse dispersion, antenna-current distributions, radiation pattern, bandwidth, radiation efficiency, and polarization purity. The negative-refractive-index transmission-line (NRI-TL) metamaterial has proven itself effective in miniaturizing devices whose performance relies on their size with respect to the wavelength of operation. The NRI-TL approach is ideally suited to high-frequency planar PCB TL technologies, such as microstrip, and has enabled the development of miniaturized microstrip couplers, dividers, baluns, and even miniaturized printed dipole antennas. However, these planar metamaterial technologies may be unsuitable for the high-voltage or low-frequency conditions associated with GPR systems. GPR can operate at frequencies as low as the tens of megahertz, requiring antennas that can be several metres long. Typically, these antennas are simple wire dipole antennas, and their miniaturization will necessitate the development and characterization of a suitable metamaterial topology capable of handling high-voltage signals at scaled-down frequencies. Furthermore, GPR is based on the delivery of pulses, which consist of a spectrum of frequency components. The designed metamaterial technology must also, therefore, provide broadband performance. However, the same property which enables metamaterials to provide miniaturization also introduces strong frequency dispersion, and this must be adequately characterized and compensated for by either pre- or post-processing both the transmitted and received signals according to the known frequency dispersion of the designed metamaterial. In summary, this project will investigate robust NRI-TL metamaterial topologies aimed at GPR-antenna miniaturization and will devote significant time to the theoretical investigation of pulse dispersion, recovery, and dispersion compensation.