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-Internal dual-band planar inverted-F antenna (PIFA) diversity system for portable devices, operating in the 2.4-GHz band (2400-2484MHz) and 5.2-GHz band (5150-5350MHz), is presented. To reduce the mutual coupling and get the high isolation between the two internal dual-band antennas, we proposed the band-notched λ/4 slots on the ground plane.The optimized band-notched slots for high isolation, high radiation efficiency and high effective diversity gain are analyzed. The band-notched slots can be used to the small MIMO terminals which require high isolation between antennas.

In this article, we proposed a new balanced circulator structure having enhanced isolation characteristics between transmitter and receiver. Also, we show that the balanced circulator structure has little performance degradation for the varying load impedance. The balanced circulator consists of two branch‐line couplers and two circulators. The validity of the balanced circulator is confirmed by comparisons with the simulated and measured results obtained from the single circulator. The fabricated balanced circulator has about 50 dB isolation for the matched load impedance and above 30 dB isolation for the mismatched load impedance at 910 MHz, the center frequency of UHF RFID. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2389–2391, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23696

A multiple band-notched planar monopole antenna for multi-band wireless systems is presented. The proposed antenna consists of a wideband planar monopole antenna and the multiple U-shape slots, producing bandnotched characteristics. In order to generate two bandnotched characteristics, we propose that three U-shape slots are required. This technique is suitable for creating ultrawideband (UWB) antenna with narrow frequency notches or for creating multi-band antennas.

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