Low profile double resonance frequency tunable antenna using RF MEMS variable capacitor for digital terrestrial broadcasting reception

It is difficult to realize the built-in antenna for wideband systems, because a frequency bandwidth of the low profile antenna is narrow. A frequency tunable antenna is a technique for wideband characteristics. In this paper a low profile double resonance frequency tunable antenna using MEMS variable capacitors is presented. It has high efficiency over a wide frequency band. Through both resonant portions from 465 to 665 MHz, the efficiency of more than −4 dB and the VSWR of less than 3 are observed in the measurement using the variable capacitor of 0.4–0.9 pF.

I. Introduction

The DTB (Digital Terrestrial Broadcasting) service for mobile devices has been widespread. A built-in antenna for DTB reception is demanded for durable and neat mobile devices. However, such an antenna usually has the demerits of narrower operation bandwidth and lower radiation efficiency because the wavelength of the DTB band, 470 MHz through 710 MHz in Japan, is much longer than the size of mobile devices. As a technique generally useful for wideband characteristics, tunable antennas using variable capacitors have been developed [1]–[3]. But as the value of the capacitor becomes larger, the operation frequency becomes lower and the efficiency seriously degrades because the power consumption in the parasitic resistance of the capacitor becomes larger due to the increase of the current in the capacitor. Some papers report that the RF current on the printed circuit boards of the mobile device can be employed to enhance the efficiency [2], [3].