Millimetre-Wave Intelligent Antennas for Wireless Systems Qi Luo*, Zhang Long*, Steven Gao* *School of Engineering and Digital Arts, University of Kent ([email protected]; [email protected]) Introduction Millimetre-wave intelligent antennas attract increasing interests for their applications in wireless systems including satellite and mobile broadband communications [1, 2]. For an intelligent antenna system, a high efficiency array antenna with beam steering or switching capability is always desirable. Several millimetre-wave array antennas have been reported for the application of intelligent antenna, including direct radiating beam-steering array using millimetre-Wave Radio over Fibre [3], multi-layered reflectarray [4], antenna system based on substrate integrated waveguide (SIW) technology [5] and etc. In this paper, two millimetre-wave array antennas that are suitable for the intelligent antenna systems are presented. One is a beam-steering folded reflectarray (FRA) and the other one is a beam switching array-fed reflector (AFR). Beam-steering folded reflectarray with large scan angles Fig.1 presents the configuration of the beam-steering FRA and the layout of the array unit cell [4]. The array element is a dual-polarized slot antenna with multi-layered PCB structure and the FRA is designed to operate at 29.5-30.8GHz band for both transmitting and receiving with single linear polarization. The objective of this work is to design a reflectarray that is capable of scanning its beam within large angle range and continuous beam steering can be obtained after the FRA is integrated with the monolithic microwave integrated circuit (MMIC) and phase shifters. To realize the wide scan angle, Vias are introduced on the antenna elements in order to to suppress the surface wave propagation and reduce the mutual coupling between adjacent array elements spaced by 0.5λ30GHz. The measured radiation pattern of the passive demonstrators consisting of 116 elements are shown in Fig.1.The experimental results o show that the presented reflectarray is capable of steering the beam up to ±60 in both E- and H-planes. 2.4mm E Polarizer Vias E Back drilling holes 5mm 1.9mm Printed reflectarray Feed Stripli nes 4.6mm E MMIC Slot antenna E Phase shifter MMIC Fig.1: The configuration of the beam-steering folded reflectarray, the layout of the unit cell and measured radiation patterns with different beam scanning angles Beam-switching array-fed reflector with an interleaved feeding array antenna Fig.2 presents the configuration of the interleaved array antenna for a beam-switching AFR. The feeding array is designed to operate at dual frequency band within K band with circular polarizations. Equilateral triangular patches of two different sizes are grouped into a subarray with Hexagonal configuration: three for higher band and three for lower band. Shielding vias were introduced to increase the isolation between adjacent subarrays. Then, seven subarrays forms a feeding cluster in a septet configuration as demonstrated in Fig.2. The single patch is fed by two microstrip lines connected to the outputs of the branch line coupler which o provides the desired 90 phase shift to excite the CP waves [6]. To evaluate the beam-switching performance of the AFR, the radiation pattern of the feeding cluster was used as the feeding source of a reflector with diameter of 300mm. The simulated beam-switching performance of the AFR in symmetry plane at 20.1GHz by de-focusing the feed array is given in Fig.2. As can be seen, the beam can be o switched to ±15 with small gain variation. With the subarray concept, the number of the RF chain required can be reduced by a factor of three. Vias 3 Antenna for band 2 1 6 4 2 7 5 Be am f or mi ng net wo rk Antenna for band 1 Fig.2: The layout of the feeding array for a beam-switching AFR and simulated radiation patterns of the AFR with different beam scanning angles Conclusion In this paper, some recent developments in millimetre-wave intelligent antennas for the advanced wireless system have been presented. Two array antennas, including one linearly polarized Ka-band folded reflectarray with wide-angle beam steering capabilities for and one K-band circularly polarized beam-switching array-fed reflector are described. Both of these two array antennas show promising radiation performance with reduced system complexity compared to the conventional direct radiating arrays. Acknowledgement The authors acknowledge the financial support through EC FP7 program under the FLEXWIN (contract number 257335) and GANSAT (contract number 606981) project. References 1 P. Zhouyue and F. Khan, "An introduction to millimeter-wave mobile broadband systems", IEEE Communications Magazine, vol.49, no.6, pp. 101-107 2011. 2 W. A. Imbriale, S. Gao and L. Boccia, Space antenna handbook, John Wiley & Sons, Chichester, West Sussex ; Hoboken, 2012. 3 M. Oishi, Y. Nishikawa, S. Akiba, J. Hirokawa and M. Ando, "2-dimensional beam steering by 2x3 photonic antenna using millimeter-wave radio over fiber", in 2013 International Topical Meeting on Microwave Photonics (MWP), pp. 130-133, 2013. 4 Q.Luo, S. Gao, C. Zhang, D. Zhou, T. Chaloun, W. Menzel, V. Ziegler and M. Sobhy, "Design and analysis of a reflectarray using slotantenna elements for ka band satcom", submitted for publication in IEEE Transactions on Antennas and Propagation 2015. 5 F. F. He, K. Wu, W. Hong, L. Han and X. P. Chen, "Low-cost 60-ghz smart antenna receiver subsystem based on substrate integrated waveguide technology", Ieee T Microw Theory, vol.60, no.4, pp. 1156-1165, Apr 2012. 6 S. S. Gao, Q. Luo and F. Zhu, Circularly polarized antennas, Wiley-IEEE Press, 2014.
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