Wideband antennas and arrays for 60-GHz wireless communications

應用於 60GHz 無線通訊的寬頻天線與陣列

Student thesis: Doctoral Thesis

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Author(s)

  • Mingjian LI

Related Research Unit(s)

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date3 Oct 2014

Abstract

This thesis presents the design of wideband antennas and arrays for 60-GHz wireless communications. Because federal agencies across the world have allocated the 60-GHz band for unlicensed use, the innovation of 60-GHz radio technology has led to many promising commercial applications, including a high-definition multimedia interface, uncompressed video streaming, mobile distributed computing, rapid large-file transfer, and high-speed internet. This research investigates several microwave antenna designs with various polarizations. Among them, two designs that have linear and circular polarizations are developed for the 60-GHz band. Furthermore, a coplanar feed network is proposed. Using this network, a 60-GHz microstrip antenna array and a 60-GHz magneto-electric (ME) dipole array are designed and compared to each other. Finally, a wideband planar 60-GHz antenna array is developed. Firstly, a linearly polarized ME dipole antenna that is excited by a simple L-shaped probe is proposed for microwave frequency wireless communications. This antenna, which consists of four metallic plates, four metallic posts, and a planar reflector, exhibits a wide impedance bandwidth (SWR ≤ 2) of 93% and a boresight gain of approximately 9 dBi. Based on this antenna, a ± 45° dual-polarized ME dipole antenna is proposed. This dipole antenna, which is excited by two orthogonally placed Γ-shaped probes, provides a wide impedance bandwidth (SWR ≤ 1.5) of 48% and antenna gains of approximately 8.5 dBi. The isolation between the two ports exceeds 30 dB. The proposed antenna also achieves low cross-polarization and back radiation levels. A dual-fed circularly polarized ME dipole antenna is developed based on the dual-polarized antenna design. With a broadband 90° phase shifter and power divider, the antenna exhibits a wide impedance bandwidth (SWR ≤ 2) of 90%, which covers the entire 3-dB axial ratio (AR) bandwidth of 82%. Considering the common overlapped bandwidth that is limited by the input impedance, axial ratio, and gain, the proposed antenna features a wide effective bandwidth of 71%. Furthermore, a wideband circularly polarized antenna with a single feed is constructed by adjusting the shapes and dimensions of the proposed linearly polarized ME dipole antenna. The proposed antenna exhibits a impedance bandwidth (SWR ≤ 2) of 73.3%, a 3-dB axial ratio bandwidth of 47.7%, and an antenna gain of approximately 6.8 dBic. The results of this study clearly demonstrate that this design is promising for use at 60 GHz. After reviewing the designs operating at microwave frequencies, a wideband 60-GHz antenna with linear polarization is designed using printed circuit board (PCB) technology. This antenna, consisting of four metal patches, four sets of vias, and an L-shaped probe, achieves a wide impedance bandwidth of over 50% and a gain of approximately 8 dBi. Furthermore, a proposed 60-GHz antenna with circular polarization exhibits a wide impedance bandwidth (SWR ≤ 2) of 56.7% and a 3-dB axial ratio bandwidth of 41%, over which the antenna boresight gain varies from 5 to 9.9 dBic. The 60-GHz designs demonstrate that an ME dipole antenna can be realized on a single-layer PCB. Communications on the 60-GHz band are affected by the high free space propagation loss and strong atmospheric absorption. Thus, antennas typically must be high in gain to compensate for the attenuation of electromagnetic waves. This study proposes a coplanar waveguide (CPW) antenna array feed network. This network has a simple structure because it does not employ the traditional air bridges (wire bonds) above the CPW T-junctions; furthermore, the network provides pairs of broadband differential outputs. This feed network is used to excite two 60-GHz L-probe fed microstrip antenna arrays with different polarizations. The linearly polarized array exhibits an impedance bandwidth (SWR ≤ 2) of 25.5% and a gain of approximately 15.2 dBi. The circularly polarized array, employing a sequential rotation technique, achieves an impedance bandwidth (SWR ≤ 2) of 17.8%, a 3-dB axial ratio bandwidth of 15.6%, and a gain of approximately 14.5 dBic. This feed network is then used to develop a 60-GHz ME dipole array. This array provides a wide impedance bandwidth (SWR ≤ 2) of over 50% and a wide 3-dB gain bandwidth of 37.1%, over which the maximum gain is 18.1 dBi. Moreover, the cross-polarization and back radiation levels are low. A comparison of the two types of 60-GHz arrays reveals that the ME dipole array is superior because of its wider impedance and gain bandwidths, whereas the microstrip antenna array features a simpler structure and lower profile. When applying the same feed network, both types of arrays have a low cost during fabrication as they are constructed on a single-layer PCB. Finally, a wideband high-gain antenna element is developed by combining a printed reflector-backed one-wavelength bowtie antenna and a printed double loop antenna. This element can be used in an array environment because of its low-profile structure of approximately 0.05λ0. A series of antenna arrays operated at 60 GHz is designed and fabricated. The antenna arrays are fabricated on a single-layer PCB and achieve wide impedance bandwidths covering the unlicensed 57–64 GHz frequency band, over which the measured antenna gains range from 14.5 to 15.5 dBi, 18.3 to 20.1 dBi, and 22.5 to 25.2 dBi for the 4-, 14-, and 50-element antenna arrays, respectively.

    Research areas

  • Broadband communication systems, Wireless communication systems, Antennas (Electronics)