传输线变压器的机理及宽带阻抗匹配的设计

传输线变压器具有频带宽、易于制作的特点，在通信领域得到了广泛的应用。但在超声换能器与超声信号源之间采用传输线变压器实现阻抗匹配的报道较少。文章对传输线变压器实现宽带阻抗匹配的机理进行了详细的分析，通过一个简单的等效电路阐明了传输线变压器如何巧妙地利用传输线间的分布电容，使其由影响高频能量传输的不利因素而转换为电磁能量转换必不可少的条件，从而达到宽频带传输的目的。以500kHz-2MHz范围内的超声换能器的阻抗匹配变压器的设计为例，具体给出了确定传输线变压器特性阻抗、线长、磁心、导线型号和匝数的方法。

Mechanism of broadband transmission line and design of impedance match transformer

With its broadband characteristic and the ease of manufacturing, transmission line transformers have been widely used in communication. However, few articles have been published to mention the fact that impedance match between an ultrasonic transducer and the signal source can be achieved by using a transmission line transformer. Analysis is given in this article on how a transmission line transformer can realize broadband impedance match. Through a simple equivalent circuit it is illustrated that distributed capacitance along the transmission line can be utilized, turning an adverse factor in the transmission of high-frequency energy to an advantage. As a result, transmission of energy over a broad frequency band is realized. As an example, design of an impedance match transformer of an ultrasonic transducer working in the frequency range of 500kHz-2MHz is described. The characteristic impedance, wire length, magnetic core, specifications of wire, and winding turns are determined.