High-Frequency Broadband RF Transmit-Receive Switch for Pulsed Magnetic Field NMR

Abstract

The utility of high-field, high-frequency broadband pulsed magnetic field nuclear magnetic resonance (PMF-NMR) is significant in matter physics. The radio frequency (RF) transmit-receive (TR) switch is a kernel device used in nuclear magnetic resonance (NMR) spectrometers to switch signals between the two states of transmitting high-power RF pulses and receiving weak NMR signals. Most designs currently used in NMR have the disadvantages of a narrowband characteristic, low power capacity or large insertion loss, which make them unsuitable for high-frequency broadband PFM-NMR experiments. To improve the performance TR switches in PFM-NMR, a new design of an approximately symmetrical TR switch topology based on PIN diodes and multiple sections of coplanar waveguide lines with different impedances is introduced in this paper. By setting the parameters of the impedance lines and the values of the inductors and capacitors as variables and using the gradient optimization and the least square error evaluation function, we obtain excellent parameters for achieving the high-frequency broadband TR switch. The prototype of an active TR switch is designed and implemented for PMF-NMR with a band of 250 MHz-1 GHz, an insertion loss that is less than 0.56 dB, a switching time that is less than 0.9 μs and a high-power capacity of 200W.