Dual-mode patch antenna switched by PIN diode

Since various wireless communication services are available, it is required to make a mobile terminal which can handle several such services. Therefore, it is necessary to design a multimode, multifrequency antenna which has different polarization and radiation patterns at each band; the switching of the resonant modes should be controlled electronically. We propose a dual-mode patch antenna where a PIN diode switch is used to change the resonant mode of the antenna. The basic structure of the antenna is a planar inverted F-shape antenna (PIFA) with a PIN diode at the open terminal of the patch. The PIN diode is switched by the DC bias which is provided at the RF feed. When the PIN diode is biased forward (ON), the antenna operates as a loop antenna, while when the PIN diode is biased backward (OFF), the antenna works as a PIFA. The characteristics of the antenna, such as resonant frequency, radiation pattern, and radiation efficiency are investigated experimentally and numerically. The antenna's resonant frequency and radiation characteristics can be changed by using the PIN diode switch, and the radiation efficiency degrades when forward-bias is added to the diode. The degradation of the radiation efficiency is mainly caused by high forward-bias resistance, which indicates that it is necessary to use a PIN diode with low forward-bias resistance.