A 60-GHz Dense Dielectric Patch Antenna Array - IEEE Xplore

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 62, NO. 2, FEBRUARY 2014

A 60-GHz Dense Dielectric Patch Antenna Array Yujian Li and Kwai-Man Luk

Abstract—The dense dielectric (DD) patch antenna is investigated at the 60-GHz band. By employing the printed circuit board (PCB) technology, a 4 4 aperture-coupled DD patch antenna array is designed, fabricated and studied. An impedance bandwidth of 23.7% from 51.3 to 65.1 GHz for , a gain up to 16.5 dBi with a 3-dB gain bandwidth of cross32.5%, and symmetrical broadside radiation patterns with polarization are achieved. Index Terms—60 GHz, antenna array, dense dielectric (DD) patch antenna, millimeter-wave, printed circuit board (PCB).

I. INTRODUCTION Development of wireless systems operated at the unlicensed 60-GHz frequency band has received a surge of attention in the last decade [1] attributed to the possibility to increase the network capacity [2] and the ability to support gigabit-per-second (Gbps) data rates in short range communications [3]. At such high microwave frequencies, various wireless applications such as uncompressed high definition video transfer and mobile distributed computing [4] can be implemented. Due to the high propagation loss caused by the atmospheric absorption around 60-GHz [5] and the limited transmit power enforced by the regulations of different countries [6], highly directional antennas are needed to meet the link budget requirement [7]. Up to now, different kinds of 60-GHz antennas and arrays have been investigated, which include patch [8], [9], dipole [10], slot [11], grid [12], helical [13], cavity [14], [15], and dielectric resonator (DR) [16] antennas and arrays. Recently, a novel antenna element designated as the dense dielectric (DD) patch antenna was proposed and tested [17], [18]. The DD patch antenna is a structure similar to the conventional microstrip patch antenna with the metallic patch replaced by a thin dielectric substrate of high permittivity. Because of the strong electromagnetic wave reflection between the supporting substrate and the DD patch, the conventional cavity mode is still excited in the region between the lower surface of the DD patch and the ground plane. According to the results in [18], the DD patch antenna operated at lower microwave frequencies shows a symmetrically unidirectional radiation pattern with low cross polarization and backlobe, and a gain of 5.5 dBi. However, the thin dense dielectric laminate with a very high permittivity of 82 as used in [18] is not easily available, which is an obstacle to practical applications. In addition, the DD patch antenna designed in [18] also suffers from a narrow bandwidth of 1%. In this communication, the performance of the DD patch antenna is investigated at millimeter-wave frequencies. A 60-GHz 4 4 wideband aperture-coupled DD patch antenna array is designed and measured. The proposed design demonstrates that the DD patch antenna can be realized by applying widely used PCB substrate with a permittivity of 10.2. Besides, by properly introducing the resonance of the feeding aperture, an impedance bandwidth of wider than 20% can also be achieved. Manuscript received 2013; revised August 29, 2013; accepted October 06, 2013. Date of publication November 19, 2013; date of current version January 30, 2014. This work was supported by a grant from the Research Grant Council of the Hong Kong SAR, China. [Project No. CityU 9041781]. The authors are with the State Key Laboratory of Millimeter Waves, and Department of Electronic Engineering, City University of Hong Kong, Hong Kong, China (e-mail: [email protected]). Color versions of one or more of the figures in this communication are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2013.2291558

Fig. 1. Side view of the DD patch antenna array.

The communication is organized as follows. Section II introduces the geometries of the DD patch antenna array. Section III discusses the design and fabrication of the antenna. Then the performances of the antenna array are analyzed in Section IV. Finally, Section V gives a brief conclusion. II. ANTENNA GEOMETRY Fig. 1 shows the geometry of the DD patch antenna array which consists of three PCB substrates. In this design, substrates 1 and 2 are ) with thickness of 0.127 and Rogers 5880 PCB laminates ( 0.254 mm respectively, while substrate 3 is a Rogers 6010 PCB lami) with thickness of 0.635 mm. Substrate 1 works as the nate ( feeding network consisted of microstrip lines with coupling apertures on the ground plane. Substrate 2 is the dielectric material between DD patches and the ground plane. Besides, the DD patch array is realized through substrate 3. The spacing between adjacent patch elements is 2.9 at 60 GHz) in both and directions. For the measuremm ( ment, by modifying the structures in [20] and [21], a microstrip line to coaxial connector transition is designed on substrate 1. With the transition, the antenna array is able to be fed by a coaxial connector from the back side so that the influence of the coaxial connector on the radiation pattern of the antenna is relatively small. The transition first converts a microstrip line into a grounded co-planar waveguide (GCPW), and then feeds to a coaxial connector. Four screws with 1 mm diameter and a fixture are used to fix the three layers together. In order to decrease the back radiation from the coupling slots, a reflector is mounted under the fixture. The details of the antenna structure on the three substrates, the fixture and the reflector are exhibited in Fig. 2 along with the dimensions. It should be noted that as shown in Fig. 2(a) the grid-shaped connecting strips are also added to the substrate 3 to connect the DD patch arrays together. By introducing the connecting strips, the 16 DD patches are able to be manufactured on the single substrate and their positions can also be precisely determined. The widths and the lengths of the connecting strips as well as the positions of the fixing screws should be carefully tuning to avoid the influence on the radiation performance of the antenna array. The details of a single radiating element and the feeding network will be given and discussed in the Section III. III. ANTENNA DESIGN AND FABRICATION The antenna and array are analyzed by using the full-wave electromagnetic solver Ansoft HFSS [19]. A. Single Radiating Element The DD patch antenna element is fed by a 50 microstrip line with width of as shown in Fig. 3. The dimensions of the antenna are and radiation gain of the DD patch listed in Table I. The simulated antenna are shown in Fig. 4. It is seen that there are two resonances over the operating band of the DD patch antenna. Based on the result of parametric studies, it is determined that the lower resonance is from

0018-926X © 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.


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Fig. 4. Simulated

and gain of a single DD patch antenna against frequency.

TABLE I DIMENSIONS OF DD PATCH ANTENNA (UNITS: mm)

Fig. 5. Simulated -parameters of the feeding network.

Fig. 2. Geometry of the DD patch antenna array. (a) Top view of DD substrate 3. (b) Top view of substrate 2. (c) Top view of substrate 1. (d) Top and side views of fixture and reflector.

Fig. 6. Geometry of the fabricated DD patch array.

the feeding network is less than from 50 to 67 GHz as shown in Fig. 5. The input power from port 1 is almost equally divided to the outputs 2 to 17 with a 1.46 dB average insertion loss. C. Fabrication of Dense Dielectric Patch Array

Fig. 3. Geometry of a single DD patch antenna.

the DD patch, while the higher one is the resonance of the coupling aperture. The two resonances combine together to achieve an impedance bandwidth of 33% from 50.27 to 70 GHz, which is much wider than the 1% impedance bandwidth in [18]. The simulated maximum gain of the antenna is 7.5 dBi at 52 GHz with a variation of 2.4 dB. Since the resonance of the coupling aperture leads to a bidirectional radiation, the broadside gain of the antenna around the higher resonance is about 5.5 dBi, which is lower than the gain around the resonance of the DD patch. B. Feeding Network The conventional parallel feeding network consisted of microstrip lines is applied to the design of the antenna array. Quarter wave transformers with 100 characteristic impedance are introduced to the T of junctions to match microstrip lines with 50 to 200 . The

How to conveniently and precisely fabricate the DD patch array is the main challenge of the design. A method of drilling overlapped holes on substrate 3 is employed to construct the needed patch array. The diameter of the holes is set to 0.7 mm to meet the fabricating limitation. As shown in Fig. 6, the overlapped hollow circles indicate the pattern of drilled holes. After fulfilling the fabricating process, the undesired portions on the substrate can be removed and the DD patch array is obtained. IV. ANTENNA PERFORMANCE To verify the simulated results, a prototype of the DD patch antenna array was fabricated and measured, which is exhibited in Fig. 7. The input impedance of the array was measured by a millimeter wave band Agilent Network Analyzer (E8361A with N5260-60003 waveguide T/R module). The radiation performance was measured by an in-house far-field millimeter wave antenna measurement system as depicted in [10]. The input signal is generated by an Agilent E8257D Signal Generator and an OML S15ms-GA 50–75 GHz MMW Source Module, and is fed to the AUT (antenna under test) through a WR-15

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Fig. 7. Photograph of the fabricated DD patch antenna array.

Fig. 8. Simulated and measured frequency.

of the DD patch antenna array against

waveguide-to-coaxial adaptor. A Quinstar QWH-VPRR00 SG horn is used as the receive antenna at a far field distance of 50 cm. An Agilent 11974V MMW Mixer and an Agilent E4448A Spectrum Analyzer are connected to the receive antenna to detect the receiving RF power. The gain is obtained by the conventional gain comparison method through the use of two identical standard horns.

Fig. 9. Simulated and measured radiation patterns of the DD patch antenna . (b) . (c) . array. (a)

A. Impedance Bandwidth of the DD patch antenna array The simulated and measured are shown in Fig. 8 with good agreement. The simulated and measured bandwidths are 23% from 51.1 to 64.5 GHz and 23% from 51.3 to . The measured rises to 65.1 GHz for across the range from 53.7 to 54.5 GHz. Generally, the bandwidth of the antenna array can cover the unlicensed 60-GHz band from 57 to 64 GHz. It should be noted that since no glue was added between the dielectric substrates 2 and 3, a small air gap would exist in practice. Several studies have been dedicated on the air gap effect on dielectric resonator antennas (DRAs). According to the results in [22], an air gap operating wavelength thickness results in significantly with 0.7 changes in resonant frequency and input impedance of DRAs. In order to demonstrate the effect of the air gap on the DD patch antenna, the of the array with a 0.05 mm ( at 60 GHz) thicksimulated ness air gap is given in Fig. 8. It can be seen that the air gap does not is with an upper shift but lead to a frequency shift. The simulated over the whole operating band. So the air still almost below does not significantly affect the gap with a thickness less than DD patch antenna, which is an advantage in practical applications.

Fig. 10. Simulated and measured gains and simulated radiation efficiency of the DD patch antenna array against frequency.

which is mainly caused by fabrication tolerance and the effect of the feeding setup near to the AUT. Besides, the simulated backlobe over the whole operating band. level of the array is less than However, the backlobe at the higher portion of the operating band is larger than that at the lower portion. This is because the resonance from the coupling aperture is close to the higher end of the operating band and leads to the increase of the radiation in back direction. Due to the limitation of the measurement system, the measured back radiations are not available.

B. Radiation Pattern

C. Gain and Efficiency

Fig. 9 depicts the simulated and measured radiation patterns of the DD patch antenna array, which are in good agreement in both and - planes. The radiation patterns of the array are symmetric and the mainlobe keeps pointing to the broadside throughout the whole impedance bandwidth. Meanwhile, the first sidelobe level of the . The measured cross-polarization level varies array is around to across the operating band. Slight discrepancy between between simulated and measured cross-polarizations can be observed,

The simulated and measured radiation gains of the array are compared in Fig. 10. The simulated and measured maximum gains are 17.2 dBi and 16.5 dBi with 3-dB gain bandwidths of 33% and 32.5%, respectively. The 1.1 dB gain drop between the simulated and measured results is partially from deviation of the dielectric and metallic losses considered in simulations, the measurement setup, as well as the possible air gap between the dielectric substrates. Besides, the tolerance of the fabricated DD patch array is also the reasons for the discrepancy


in gain, which can be seen from the photograph of the DD patch array. The simulated radiation gain of the array without adding the reflector is also shown in Fig. 10. By applying the reflector, a 1.2 dB increase of radiation gain is achieved, but the gain drops 1.3 dB at 61 GHz. The simulated radiation efficiency of the array is between 71% and 83% over the operating band. V. CONCLUSION The investigation on the novel dense dielectric patch antenna has been extended to the 60-GHz band. The results demonstrate that the DD patch antenna can be realized by applying widely used PCB substrate with a permittivity of 10.2. A 4 4 dense dielectric patch antenna array has been designed, fabricated and measured using the conventional low-cost PCB technology. By introducing the resonance of the coupling aperture, a wide impedance bandwidth of 23.7% is achieved. The maximum radiation gain of the array is 16.5 dBi with a 3-dB gain bandwidth of 32.5%. It is believed that the advantages of the dense dielectric patch antenna array will be more noticeable at higher millimeter wave frequencies.

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[16] Q. H. Lai, C. Fumeaux, W. Hong, and R. Vahldieck, “Substrate integrated waveguide cavity-backed wide slot antenna for 60-GHz bands,” IEEE Trans. Antennas Propag., vol. 60, no. 12, pp. 6023–6026, Dec. 2012. [17] K. M. Luk and H. W. Lai, “Dense dielectric patch antenna,” in Proc. Eur. Conf. on Antenna and Propag., 2012, pp. 1346–1348. [18] H. W. Lai, K. M. Luk, and K. W. Leung, “Dense dielectric patch antenna – A new kind of low-profile antenna element for wireless communications,” IEEE Trans. Antennas Propag., vol. 61, no. 8, pp. 4239–4245, Aug. 2013. [19] HFSS: High Frequency Structure Simulator Based on the Finite Element Method. Canonsburg, PA, USA, Ansoft Corp. [Online]. Available: http://www.ansoft.com/ [20] W. C. Wu, E. Y. Chang, R. B. Hwang, L. H. Hsu, C. H. Huang, C. Kärnfelt, and H. Zirath, “Design, fabrication, and characterization of novel vertical coaxial transitions for flip-chip interconnects,” IEEE Trans. Adv. Packag., vol. 32, no. 2, pp. 362–371, May 2009. [21] Z. Zhou and K. L. Melde, “Development of a broadband coplanar waveguide-to-microstrip transition with vias,” IEEE Trans. Adv. Packag., vol. 31, no. 4, pp. 861–872, Nov. 2008. [22] G. Drossos, Z. Wu, and L. E. Davis, “The air gap effect on a microstrip-coupled cylindrical dielectric resonator antenna,” Microwave Opt. Technol. Lett., vol. 20, no. 1, pp. 36–40, Jan. 1999.

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Compact Circularly Polarized Antenna Based on Quarter-Mode Substrate Integrated Waveguide Sub-Array Cheng Jin, Zhongxiang Shen, Rui Li, and Arokiaswami Alphones

Abstract—A compact and circularly polarized planar antenna is presented in this communication based on a quarter-mode substrate integrated waveguide sub-array. The operating principle and design guidelines of the proposed antenna are discussed with the aid of an isosceles right triangular cavity with two magnetic side walls and one electric side wall. The mode solutions are determined and the resonant frequencies of the triangular cavity are calculated. The designed antenna is fabricated and its radiation characteristics are measured. Measured results are in good agreement with predicted ones. It is demonstrated that the proposed structure is a simple and compact candidate of high-performance circularly polarized antenna. Index Terms—Circularly polarized antenna, half-mode/quarter-mode substrate integrated waveguide, isosceles right triangular waveguide, planar antenna.

I. INTRODUCTION Circularly polarized (CP) antennas are widely employed to mitigate the polarization mismatch and multi-path interference problems in radar and wireless communication systems. One class of the CP antennas is the microstrip patch antenna with a slight perturbation in the antenna at a specific location to excite two orthogonal modes with 90 Manuscript received April 19, 2013; revised July 05, 2013; accepted November 14, 2013. Date of publication November 20, 2013; date of current version January 30, 2014. C. Jin is with the School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China (e-mail: [email protected]). R. Li is with the Institute of Microelectronics (IME), Singapore 117685, Singapore (e-mail: [email protected]). Z. Shen and A. Alphones are with the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore (e-mail: [email protected]; [email protected]). Color versions of one or more of the figures in this communication are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2013.2291574

0018-926X © 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.