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This paper proposes a novel circularly polarized antenna operating at 2.4-2.48-GHz industrial, scientific, and medical (ISM) band for biomedical applications. This proposed structure is developed from a simple pin-loaded patch antenna, whose circular polarization (CP) is mainly attributed to the loading of shorting pins and L-shaped open-end slot. Based on this, pin-loaded annular ring (PLAR) with dual-mode operation is adapted to introduce another resonance. In addition, two closely coupled rectangular patches are added to bring these two resonant frequencies close to each other in muscle. Furthermore, by introducing arcshaped slots, CP property and improved impedance matching are achieved with size miniaturization. This proposed structure shows a simulated impedance bandwidth of 8% and a wide axial-ratio (AR) bandwidth of 19.1%. Finally, measurement is performed for the proposed antenna, and the results coincide well with the simulation ones, indicating that it is a good candidate for biomedical applications. INDEX TERMS Biomedical application, circular polarization, implantable antenna, pin-loaded annular ring.

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A compact dual-mode dual-band bandpass filter (BPF) for WLAN applications is presented. On the basis of a primary passband formed by a ring resonator, a second passband is introduced by taking advantage of its tightly coupled input and output structures. Therefore, a dualband performance is achieved without increasing the overall circuit size. Shorting vias and spurlines are adopted separately to realise the dual-mode excitation of each passband. Finally, a compact dualmode BPF centred at 2.4 and 5.2 GHz is designed and fabricated, along with four transmission zeros, leading to sharp skirts and a wide stopband. Experimental results reveal good agreement with simulation results.Introduction: To meet the multifunction demand of modern wireless communication systems, multiband filters are highly required as essential components. Therefore, many approaches have been studied based on dual-mode resonators for dual-band bandpass filters (BPFs) [1-6]. One method is to excite two different ordered resonant frequencies of a single resonator [1][2][3]. A modified ring dual-band filter using the stepped-impedance-resonator was proposed in [1], and its second passband can be adjusted by changing the impedance ratio. Nevertheless, the roll-off at the upper side of the second passband still needs improvement. Subsequently, a stub-loaded ring resonator was designed with good selectivity, and two pairs of the first-and second-order degenerate modes were excited to form two passbands [2], yet the two passbands were not independent and cannot be tuned separately. In [3], microwave C-sections were analysed and adopted to realise the dual-band characteristic. However, the designated frequencies of the structure have limitations. Another method is to cascade two resonators vertically or in the same layer [4][5][6], so that dual-band performance with controllable passbands can be achieved. However, it requires a relatively larger overall size.In this Letter, a novel dual-mode dual-band BPF with a wide stopband and sharp skirts is developed, working at 2.4 and 5.2 GHz for WLAN applications. Its two passbands are formed individually by two different resonators, whereas the resonator for the second passband also plays a role of the input and output (I/O) structure. Each passband is discussed separately, the dual-mode performance of which is excited by employing shorting vias or spurlines. Meanwhile, four transmission zeros are introduced at both sides of each passband to realise sharp roll-off.

A novel planar, dual-band antenna composed of a symmetrical dipole and balanced antipodal slot radiator with low ground plane effect is proposed and investigated. Operation principle of the antenna is analyzed and design equations are drawn first. Then, the return loss, surface current distribution, radiation patterns, and gain are numerically and experimentally studied in detail. The impedance bandwidth of the antenna is from 2.36 to 2.56 and 5.13 to 12 GHz for return loss larger than 10 dB. The antenna has omnidirectional pattern at the lower band and quasi-directional pattern at the higher band, and it has good immunity to a neighboring, large ground plane. The proposed antenna should be useful for dual-band communication or identification systems. V C 2012 Wiley Periodicals, Inc.Int J RF and Microwave CAE 00:000-000, 2012.