60 Ghz Omni-Directional Segmented Loop Antenna
Total Page：16
File Type：pdf, Size：1020Kb
60 GHz Omni-directional Segmented Loop Antenna Mohammad Hossein Ghazizadeh, and Mohammad Fakharzadeh Electrical Engineering Department, Sharif University of Technology Tehran,Iran ghazizadeh [email protected], [email protected] Abstract—The design, simulation and fabrication of a planar antennas [2]. These antennas have a simple and small size fragmented loop antenna with capacitive loads at 60 GHz structure and are cost-efficient but on the other hand, the are frequency band is reported in this paper. The loop antenna has linearly polarized, and only omni-directional in the horizontal a nearly omni-directional radiation pattern required for many IEEE 802.11ad applications, a simulated bandwidth of 6 GHz, plane and usually have nulls in the vertical plane radiation and a realized gain of 2 dBi. The measured input matching pattern limiting the spatial coverage of the antenna. Another bandwidth without deembedding the connector effect is nearly 2 famous structure is the Omni-directional Microstrip Antenna GHz. The HPBW in azimuth plane is 360◦. Array (OMAA) [3], which is a planar antenna based on the COCO antenna concept. Although it has a planar structure I. INTRODUCTION but since it comprises of several λ/2 sections, it has a large An emerging application of 60 GHz radio systems is es- physical size. A fairly small size antenna with omni-directional tablishing a short-range wireless network inside a room. As radiation pattern is the segmented loop antenna with capacitive described in IEEE 802.11ad standard a semi-omni antenna loadings introduced in [4]. The loop antenna has a periphery of coverage is required in discovery mode so that different users approximately λ corresponding to the resonant frequency. The inside the room can find each other. In the discovery mode a capacitive loadings are designed to limit the phase variation low-rate data is transmitted between stations, implying that a of the loop current to small amounts resulting in a relatively low SNR is sufficient for detecting this signal. The challenge omni-directional radiation. The capacitive loadings in this pla- is designing a planar omni-directional antenna which can be nar antenna is implemented by partially overlapping segments integrated in the same package where the 60 GHz radio is flip- constituting the loop antenna. The whole structure is excited chipped. Concerning the mobility of stations and any possible by a parallel plate feed line. Due to the rising interest in mm- orientation of the stations a circularly polarized (CP) antenna is wave applications [5], in this paper a 60 GHz loop antenna required to avoid polarization mismatch and significant drop with omni-directional radiation is designed using only 2 metal in antenna gain. Thus, regardless of the device position or layers. The antenna performance is optimized for operating orientation, the required SNR can be maintained. Another at 60 GHz frequency band. The designed antenna has been advantage of using omni-directional antennas in a wireless fabricated using regular PSB technology. network is that Non-Line-of-Sight signals can be used to establish a link when the line-of-sight path is blocked which II. OMNI-DIRECTIONAL SEGMENTED LOOP ANTENNA frequently happens in a mobile application. Figure 1 shows the top and bottom views of the propose Strictly speaking, an ideal omni-directional antenna has a omni-directional segmented loop antenna. The antenna con- unity gain in all directions (isotropic antenna), but such an sists of six overlapped copper arcs placed on both sides of a antenna is not physically feasible. A realistic omni-directional Rogers 4003 substrate with a relative dielectric coefficient of antenna is the one which has a low gain (around 2 to 3 dBi), r = 3.78 at 60 GHz and a thickness of 0.2 mm. The overall a circular pattern in one direction and a limited beamwidth circumference of the loop is 4.4 mm. The feed lines connected in the other direction. A good example is the half-wavelength to the loop structure in the top and bottom layers are optimized dipole antenna suspended in air, which has 2.2 dBi gain and to provide good impedance matching without degrading the 78◦ half-power beamwidth in one direction and almost 360◦ omni pattern. The whole antenna structure is excited with a in the other direction. Planar antennas have usually a narrower parallel plate transmission line. pattern compared to the half-wavelength dipole antenna due to fabrication limits and the non-homogeneous propagation III. SIMULATION AND MEASURED RESULTS environment (air-dielectric) around them. Moreover, dipole The proposed antenna was optimized and simulated with is a linearly polarized antenna. Our target in this paper is HFSS. The antenna was fabricated in a two-layer PCB. and to design a planar CP antenna with at least 180◦ degree measured. Figure 2 (a) depicts the fabricated loop antenna. The beamwidth in one plane and of 90◦ degree beamwidth in measurement was conducted by exciting the antenna element the orthogonal plane. Additionally the radiation pattern should through a 1.85 mm plug end-launched connector shown in Fig have no deep nulls in the wide beam plane imitating a semi- 2 (b), using a PNA-X as a signal source. omni pattern. Several omni-directional antennas have been The simulated 10 dB impedance bandwidth of the antenna, introduced such as printed monopole antennas [1] and slot shown in Fig. 3 is 6 GHz which covers 3 channels in 60 Fig. 3. Measured and simulated S11 of the loop antenna. Fig. 1. (a) Top view, and (b) bottom view of the proposed loop antenna. GHz band. However, the measurement results indicate that the antenna plus connector have an input match bandwidth of 2 GHz. The discrepancy between the simulated and measured S11 is partially due to the connector effect which can be de- embedded with more measurements, fabrication errors and inaccurate calibration of PNA-X, which can be seen from the ripples in measured S11. The simulated radiation patterns of the proposed loop antenna at the resonant frequency in horizontal and azimuthal planes are shown in Fig. 4. Radiation pattern measurement is underway. It is seen that the gain in both planes is 2 dBi. The beam in xy plane (θ = 90◦) is nearly omni with a half power beamwidth (HPBW) of 360◦ The HPBW in yz plane (φ = 90◦) is approximately 90◦. These relatively wide beams provide omni-directional spatial coverage. Fig. 4. Antenna radiation pattern in xy (solid red) and yz (dashed blue) planes assuming antenna is along y-axis in xy plane. ACKNOWLEDGEMENT The authors would like to thank Peraso Technologies, Toronto, Canada for supporting this project. REFERENCES - [1] W. Zhou, and T. Arslan, “Planar monopole antenna with Archimedean spiral slot for WiFi/Bluetooth and LTE applications”, Antennas and Fig. 2. (a) Fabricated omni-directional loop antenna and (b) end-launch Propagation Conference (LAPC), pp. 186–189, November 2013. connector used to measure antenna. [2] X. Qing, Z. N. Chen, and C. K. Goh, “A horizontally polarized om- nidirectional slot antenna array”, Antennas and Propagation Society International Symposium (APSURSI), pp. 1–2, July 2012. [3] L. Bras, N. B. Carvalho, and P. Pinho, “Planar omnidirectional microstrip In summary, a six segmented planar loop antenna at 60 GHz antenna array for 5 GHz ISM and UNII band”, Antennas and Propagation frequency band has been proposed based on the technique of Society International Symposium (APSURSI), pp. 1590–1591, July 2013. [4] R. Hasse, W. Hunsicker, and K. Naishadham, “Design of a planar inserting capacitive loads on the loop periphery to attain an segmented circular loop antenna for omnidirectional radiation at 5.8 omni-directional radiation pattern. Simulation results show an GHz”, IEEE Antennas and Wireless Propagation Letters, vol. 11, pp. impedance bandwidth of 6 GHz and an omni-directional radi- 1402–1405, November 2012. [5] M. Fakharzadeh, and M. Mohajer, “An integrated wide-band circularly ation pattern with a gain of 2 dBi. The proposed antenna could polarized antenna for millimeter-wave applications”, IEEE Transactions be used in wireless devices for IEEE 802.11ad applications. on Antenna and Propagation, vol. 62, no. 2, pp. 925–929, February 2014..