Ruina Lian

Broadband Circularly Polarized Patch Antenna With Parasitic Strips

A patch antenna with parasitic strips is presented for wideband circular polarization. In order to broaden the axial-ratio (AR) bandwidth of the original corner-truncated patch, four parasitic strips are sequentially rotated and gap-coupled around the patch. A capacitive-coupled feed with a small disc on the top of the feeding probe is utilized to obtain a wide impedance-matching bandwidth. Moreover, another disc-loaded shorting pin is placed at the center of the antenna to adjust the squint beams and improve the gains along +z-axis. Measured results show that the proposed antenna with a low profile of 0.13λ0 obtains a global bandwidth of 24% (2.32-2.95 GHz) for |S11| <; -10 dB, AR <; 3 dB, and average gain of 8 dBic.

A Miniaturized CPW-Fed Antipodal Vivaldi Antenna With Enhanced Radiation Performance for Wideband Applications

A miniaturized coplanar waveguide (CPW)-fed antipodal Vivaldi antenna (AVA) is presented in this letter. Elliptically shaped strip conductors are used to lower the antenna operating frequency. With two pairs of tapered slots and circularly shaped loads, the radiation performance in lower operating band can be greatly enhanced. The fabricated prototype of this proposed antenna with a size of 90 ×93.5 ×0.8 mm3 was measured to confirm the simulated results. The wide measured impedance band from 1.32 GHz to more than 17 GHz for can be obtained. Meanwhile, the good measured radiation patterns with gain 3.5- 9.3 dBi in end-fire direction achieve in the whole measured working band.

Design of a Low-Profile Dual-Polarized Stepped Slot Antenna Array for Base Station

In this letter, a microstrip-fed dual-polarized stepped-impedance (SI) slot antenna element with a low profile is first proposed. The antenna is composed of two pairs of SI slots excited by two orthogonal stepped microstrip feedlines. The broadband characteristic is achieved by combining the fundamental and spurious resonances of the SI slot resonators, while the good cross polarization is mainly due to the introduction of the shorting pins. Secondly, based on the proposed antenna, a four-element antenna array is designed, constructed, and measured for base-station applications. Measured results demonstrate the bandwidths (return loss ) of the antenna array are 46.9% (1.55-2.5 GHz) and 38.7% (1.69-2.5 GHz) for Port 1 and Port 2, respectively. The isolation between the two ports is greater than 35 dB, whereas the cross-polarization level maintains lower than -27 dB across the entire operating band. In addition, the antenna array prototype achieves average gains of 13.5 and 13.9 dBi for horizontal polarization and vertical polarization, respectively.

Wideband, Low-Profile, Dual-Polarized Slot Antenna with an AMC Surface for Wireless Communications

A wideband dual-polarized slot antenna loaded with artificial magnetic conductor (AMC) is proposed for WLAN/WIMAX and LTE applications. The slot antenna mainly consists of two pairs of arrow-shaped slots along the diagonals of the square patch. Stepped microstrip feedlines are placed orthogonally to excite the horizontal and vertical polarizations of the antenna. To realize unidirectional radiation and low profile, an AMC surface composed of 7 × 7 unit cells is designed underneath a distance of ( being the wavelength in free space at 2.25 GHz) from the slot antenna. Both the dual-polarized slot antenna and the AMC surface are fabricated and measured. Experimental results demonstrate that the proposed antenna achieves for both polarizations a wide impedance bandwidth (return loss 10 dB) of 36.7%, operating from 1.96 to 2.84 GHz. The isolation between the two input ports keeps higher than 29 dB whereas the cross-polarization levels basically maintain lower than −30 dB across the entire frequency band. High front-to-back ratios better than 22 dB and a stable gain higher than 8 dBi are obtained over the whole band.

Triband Frequency-Selective Surface as Subreflector in Ku-, K-, and Ka-Bands

A novel triband frequency-selective surface (FSS) is designed to be a subreflector for reflector antennas. The element of the proposed FSS structure consists mainly of two identical layers of a square loop combined with a hexagonal ring and a hexagon. The designed FSS reflects electromagnetic waves in Ku-band (12-15.2 GHz), but transmits electromagnetic waves in K-band (18-21.6 GHz) and Ka-band (29.3-32 GHz). Moreover, such an FSS has the merit of stable performance for various incident angles within 50° for both TE and TM polarizations. Simulated results show that the insertion losses in K-band are less than 0.5 dB when the incident angles vary from 0° to 45°, and less than 1 dB for the incident angles from 45° to 50°. In Ka-band, the insertion losses are less than 0.5 dB when the incident angles vary from 0° to 30°, and less than 1 dB when the incident angles are from 30° to 50°. For both TE and TM polarizations, the incident angle is up to 50° with S21 less than -15 dB in Ku-band. Both designed procedure and measured results of the FSS are presented and discussed.

Wideband Planar Inverted-F MIMO Antenna with High Isolation

A wideband planar inverted-F MIMO antenna with high isolation is proposed in this letter. The proposed MIMO antenna consists of two back-to-back planar inverted-F antennas and a fork- shaped decoupling stub. The two planar inverted-F antennas are merged together with a shorting strip connected to the ground plane. In order to enhance the isolation, a fork-shaped decoupling stub connected to the ground plane through shorting pins is introduced, and the impedance matching is significantly improved simultaneously. The proposed antenna prototype is fabricated and measured, and a compact size of 28 × 26 mm 2 makes the proposed antenna be easily integrated in a MIMO system. Measured results show that the measured bandwidth for |S11| less than −10 dB covers from 5.05 GHz to 6.23 GHz, and the measured isolation is higher than 20 dB in the whole working frequency band.

Wideband Fabry-Perot Resonator Antenna with Single-Layer Partially Reflective Surface

A single-layer partially reflective surface (PRS) structure is presented to design single-feed Fabry-Perot resonator antennas (FPRA) with a large gain bandwidth and compact size. The design of the PRS structure applied in this antenna is based on the theory of tightly coupled antenna arrays. Owing to strong mutual coupling between the overlapped patches, the proposed antenna obtains a wider bandwidth and more compact size. Experimental results show that the antenna obtains a 32% 3-dB gain bandwidth from 8.8 GHz to 12.2 GHz, with a peak gain of 13.5 dBi. Moreover, the relative impendence bandwidth is 40.9% for the voltage standing wave ratio (VSWR) less than 2 from 8.45 GHz to 12.8 GHz.

BROADBAND AND GAIN ENHANCED BOWTIE ANTENNA WITH AMC GROUND

A low-profile wideband bowtie antenna backed by artificial magnetic conductor (AMC) ground is presented for gain enhancement. The proposed bowtie antenna, loaded with an open stub in the upper layer, has broadband property. By using an AMC reflector, consisting of 6×9 metallic patches, the bidirectional radiation of the bowtie antenna is changed to unidirectional radiation. The distance between the bowtie antenna and the AMC surface is only λ/10 at 3.75 GHz. Both the bowtie antenna and the AMC surface are fabricated and measured. The measured results demonstrate good and stable performances, including maximum gain of 8.27 dBi, and flat gain response with variation of 0.6 dB in the wide impedance matching (S11 < −10 dB) band from 3.05 GHz to 4.35 GHz (35.1%). Furthermore, the maximum cross-polarization level is −17 dB for both E and H planes, and the measured front-to-back ratios are more than 18 dB. Good agreement between the simulated and measured results validates the proposed design approach.