ISM 433-MHz Miniaturized Antenna Using the Shielding Box of Mobile Terminals

A miniaturized monopole antenna for ISM 433-MHz frequency band is designed, fabricated, and measured. The whole structure proposed in this letter consists of a metal shielding box for transceiver circuit, a rectangular ground for battery, and a meander-line monopole. The size of the structure is 51 × 82 mm², and the area left of the antenna itself is just about 49 × 13 mm². To make the antenna work in such a small area, and maintain good performance, the metal shielding box of the transceiver circuit in this work is connected to the meander-line monopole. Actually, the shielding box does not serve as a part of the ground, but a part of the antenna itself, which plays an important role in matching and increasing the antenna's electrical length. Meanwhile, no additional area is needed compared to the conventional design. The measured - 10-dB bandwidth is 5 MHz. The comparison between the traditional design and the proposed design as well as the critical parameter study is presented in this letter.