In this paper, a microstrip fed, L-shape slot antenna for dual polarization is proposed. The two arms of the slot generate electric fields of orthogonal polarizations. By properly sectioning the slot and the feed line, ultra wideband (UWB) behavior is obtained. The measured impedance bandwidth (S11< −10 dB) is more than 8.6 GHz (112%) and 8.2 GHz (104%) for Port 1 and Port 2, respectively. The measured isolation is better than 25 dB over most of the band. The aperture field distribution justifies the dual polarized nature. A modified version which implements a band-notch over 5.1–5.85 GHz wireless local area network (WLAN) band is also presented. With a compact, single substrate design, the antenna can be useful in MIMO transmission systems, polarimetric UWB radar, high performance microwave imaging, and other future wireless communications devices.

A compact dual ports antenna with high isolation is proposed for handheld radio frequency identification (RFID) reader which is rarely reported in open literatures. Different with conventional handheld RFID reader antennas with single port, the proposed antenna transmits and receives signal separately. The proposed antenna operating with full duplex mode can enhance effectively sensitivity of reader, since the strong transmitting signal of reader with single port is usually highly coupled with weak receiving backscatter signal of tag. The antenna utilizes E-shaped aperture-coupled patch structure that occupies less volume and provides further space-saving efficiency. The height of the proposed antenna is only 6.8 mm and the volume of that is 80 mm × 80 mm × 6.8 mm, which is easy to integrate in handheld RFID readers. The antenna uses two E-shaped coupling apertures to excite two orthogonal modes for dual-polarized operation. High isolation of around −30 dB is obtained by proper arrangement of the length of coupling apertures and the position of the stubs. The measured results show −10 dB matching band and −25 dB isolation band from 2.32 to 2.6 GHz and from 2.3 to 2.55 GHz, respectively. The antenna is suitable for applications in handheld RFID readers.

The substrate-integrated cavity-backed patch antenna embedded in dielectric-coated structure is presented. The aperture of antenna is covered with composite radome. The close proximity of radome to antenna severely degrades input impedance matching. The dielectric coating, a thick dielectric material, significantly deteriorates radiation pattern of antenna due to propagation of surface waves in the surrounding dielectric coating. The proposed planar electromagnetic bandgap structure reduces the propagation of surface waves in the dielectric coating recovering deterioration in the radiation pattern of the antenna. The problem of input impedance mismatching of antenna is resolved by placing a metallic strip on the top of the radome. The simulated results are in good agreement with measured results.

This paper proposes planar antennas with quadri-polarization diversity using a pair of orthogonal linear polarizations and a pair of orthogonal circular polarizations (CP). A novel feeding network with four input ports and four output ports is presented, allowing antenna polarization diversity by selecting different input ports, which can generate right-handed CP, left-handed CP, horizontal linear polarization, and vertical linear polarization. The first design uses two square patch resonators to synthesize the four polarizations; the second design comprises four circularly polarized patches to synthesize the four polarizations with an improved axial-ratio (the ratio of orthogonal components of an E-field) bandwidth. The proposed designs do not require for embedding PIN diodes and DC-biasing circuits, making them suitable for use in higher-frequency applications where using lump elements would be difficult. The novel antennas provide potential polarization diversity features which can be used for many applications. Details of the antenna design are shown, and the measurement and simulation results are also provided to validate the proposed concept.