Reykowski A, Wright S M, Porter J R
Department of Electrical Engineering, Texas A&M University, College Station 77843-3128, USA.
Magn Reson Med. 1995 Jun;33(6):848-52. doi: 10.1002/mrm.1910330617.
This paper discusses matching networks that minimize inductive coupling between the antennas within an array while simultaneously insuring minimum noise contributions from preamplifiers. Typical low noise preamplifier designs require a strong mismatch between the source impedance and the amplifier input impedance (reflection coefficient close to one) to achieve optimal noise performance. This is in contrast to the familiar impedance match known from communication theory where input and source impedances have complex conjugate values for maximizing the power transfer from source to amplifier. The high input reflection coefficient of low noise amplifiers can be exploited to reduce antenna currents by using lossless impedance transformations to create a high impedance at the coil terminals while simultaneously maintaining a low noise figure for the amplifier. The networks presented here constitute an improvement over previous work because they give additional freedoms regarding the values of the network components and the amplifier input impedance. The technique has been formalized and coded in MathCad, making the design of realizable networks a simple process.
本文讨论了匹配网络，该网络可使阵列内天线之间的电感耦合最小化，同时确保前置放大器产生的噪声贡献最小。典型的低噪声前置放大器设计要求源阻抗与放大器输入阻抗之间存在很大失配（反射系数接近1），以实现最佳噪声性能。这与通信理论中熟知的阻抗匹配相反，在通信理论中，输入阻抗和源阻抗具有复共轭值，以最大化从源到放大器的功率传输。通过使用无损阻抗变换在线圈端子处创建高阻抗，同时保持放大器的低噪声系数，可以利用低噪声放大器的高输入反射系数来降低天线电流。本文介绍的网络是对先前工作的改进，因为它们在网络元件值和放大器输入阻抗方面提供了更多自由度。该技术已在MathCad中形式化并编码，使可实现网络的设计成为一个简单的过程。
