Novel Wideband Millimeter-wave Open Slot Antennas

新型寬帶毫米波開放式縫隙天線

Student thesis: Doctoral Thesis

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Award date18 Sep 2019

Abstract

This thesis presents novel wideband open slot antennas for millimneter-wave (mmW) applications. A novel open slot structure, which contains only two metal boundaries, is proposed to effectively enhance the bandwidth of slot antennas. All antennas in this thesis use open slots as radiators, and exhibit advantages including wide bandwidth, planar structure, and ease of fabrication. A substrate integrated waveguide (SIW) fed open slot antenna is firstly explored, and this design is then extended to the development of antenna arrays. Further, the SIW fed open slot antenna design is modified to a substrate integrated horn (SIH) fed stacked open slot antenna, which exhibits enhanced gain and maintains the wide bandwidth. Finally, a wideband multi-beam open slot antenna is demonstrated. The presented antennas are attractive for millimeter-wave applications.

Firstly, an SIW fed open slot antenna with a very wide bandwidth is proposed. A new structure of an open slot antenna excited by an SIW feed is introduced to obtain a wide bandwidth of about 60%. Different from conventional slot antennas, two short sides of the slot are open which do not connect to any metal. To excite the open slot, an SIW section is used as the feed. In this way, the antenna is constructed on a single laminate that includes the feeding structure and the radiator. The open slot structure serves as a single-mode resonator with a low Q-factor, and thus contributes a much wider bandwidth than that of conventional slot antennas and simultaneously maintains stable radiation performance. Intensive parametric studies are implemented to provide design guidelines, and antenna prototypes are fabricated and measured to verify the design. The measured results confirm that the antenna achieves a wide impedance bandwidth of 59.3% from 50.8 to 93.6 GHz with stable radiation patterns over the entire operating frequency band. The average gain of the antenna is approximately 5.7 dBi.

The proposed SIW fed open slot antenna is then extended to a 4 × 2 antenna array. The antenna array is single-layered and differentially fed by 1-to-4 SIW power dividers. The impedance bandwidth of the radiating part with an ideal feed covers from 53.6 to 86.9 GHz for S11 < -10 dB, which is narrower than that of the single antenna element due to the mutual coupling effect. To feed the radiating part, two sets of feeding networks are designed to cover the V-band and W-band individually. Prototypes of the V- and W-band antenna arrays are fabricated and measured. The measured impedance bandwidths of the two arrays cover frequency ranges of 54.0 to 74.8 GHz (32.3%) and 75.0 to 89.9 GHz (18.1%) for S11 < -10 dB, respectively. Measured gains of the two arrays vary from 11.3 to 15.6 dBi and from 12.3 to 15.0 dBi within the frequency range of 54 to 90 GHz, respectively. It is concluded that the bandwidth of the whole array is limited by the feeding network.

Furthermore, to achieve enhanced gain and wide bandwidth simultaneously, SIH fed stacked open slot antennas are proposed. Initially, the SIW fed open slot antenna is modified to a double-layered stacked open slot antenna that is long in the H-plane, and an SIH is incorporated as the feed that can generate a quasi-TEM wave. A pair of stacked open slot antennas are then combined front-to-front and differentially fed by two SIHs. Finally, the feeding SIHs are folded to reduce the size of the whole antenna. A prototype of the folded SIH fed stacked open slot antenna is fabricated and measured. An impedance bandwidth of 54.4% (52.3 to 91.4 GHz) for S11 < -10 dB and a gain up to 16.3 dBi are achieved. In addition, stable symmetrical radiation patterns with low cross-polarization, side lobe, and back lobe levels are obtained over the whole working frequency band. 

Finally, a wideband multi-beam open slot antenna is developed. The antenna is composed of a stacked open slot radiator and a pillbox feeding system to generate multiple beams. A prototype of the antenna is fabricated and measured. Due to the radiator’s wideband performance, the bandwidth of the multi-beam antenna can reach 34.3% for S11 < -10 dB. Five beams are generated with a scanning angle of ±32° and a peak gain of 21 dBi.