Varactor Loaded Tunable Printed Pifa

Varactor tuned printed planar inverted-F antennas (PIFA) are investigated. The low-profile printed antennas are fabricated together with the layouts of its DC control circuits and other RF/baseband circuit footprints. A surface mounted (SMT) varactor is applied as a frequency-tuning element at the middle of the long radiating arm in PIFA. Passive lumped DC bias circuits are implemented with good isolation. Both single and dual-band varactor tuned PIFA antennas are investigated. For a single-band PIFA, prototype designs show the in-band frequency (return loss is <10 dB) is tunable from 1.6GHz to 2.3 GHz when the bias voltage varies from 0 V to 9.5 V. Measured results show about 70∼75% efficiency and 2∼3 dB maximum gain. For a dual band PIFA with two varactor loadings, both the 800∼900MHz and 1.7∼2.2GHz bands are tuned individually by a varactor. By varying low-band capacitance, the operation frequency is tuned from 780MHz to 1020 MHz, with little change on the higher frequency band. By varying high-band capacitance, the operation frequency is tuned from 1700 MHz to 2140MHz, with little change on the lower frequency. Measurement shows antenna radiation efficiencies within operation bands are about 55% at the low band and about 45% at the high band. The proposed frequency reconfigurable antennas could be useful for personal mobile terminal applications.