Suppression of harmonic radiation of tunable Planar Inverted-F Antenna by ferroelectric varactor loading

Low-cost ferroelectric varactors based on Barium-Strontium-Titanate (BST) thick-film technology have been implemented in a tunable planar Inverted-F antenna (PIFA). A prototype is realized and measured. The harmonic radiation is evaluated in detail. It is shown that, considerable RF voltage detunes the varactor and stimulates harmonic radiation in the varactor-loaded PIFA. It is discussed how such radiation can be suppressed by choosing the varactorpsilas tuning behavior. The passive BST thick-film varactors are proven to have advantages in reducing the harmonic excitation. When compared to a reference design using a silicon diode, the prototype shows suppressions on the second harmonic radiation up to 35.7 dB at -10 dBm input power. Possible suppression by BST thin-film varactors which are featured of low tuning voltages is also discussed.