A Self-Structuring Impedance Matcher for In-Vehicle Digital Audio Broadcasting Applications

This paper proposes an adaptive impedance matching subsystem, called self-structuring impedance matcher (SSIM), for in-vehicle digital audio broadcasting (DAB) applications. The goal of the SSIM is to make antennas originally aiming at other vehicular applications, such as a digital television (DTV, 470-894 MHz) and an interphone car radio (136-174 MHz), operate in the targeted DAB frequency band (170-240 MHz), thereby lowering the startup cost of DAB devices. The SSIM consists of a template of a matching circuit, a microprocessor, and a receiving-type sensor. The template uses a nonuniform microstrip line interconnected with relay switches. To enhance the dynamic range and reduce the insertion loss for the template simultaneously, this work employs a new design technique based on solving the mathematical programming problem of matching requirements. The resultant matching domain covers a large area of the Smith chart, although only five switches are used. Experimental results show that the SSIM successfully adapts an interphone/DTV antenna into a DAB receiving mode. The operational bandwidth meets the DAB specification, and the transducer gain is larger than -1.83 dB.