Development of a Broadband Integrated Optical Beamfomer for K u -Band Phased Array Antennas Topic: Mobile user - On the Move antennas (vehicular, train, maritime, aeronautical) General technology and techniques advances (Beamforming techniques) Chris Roeloffzen, Paul van Dijk SATRAX BV, University of Twente, Building 89, Hallenweg 6, 7522 NH, Enschede, The Netherlands c.g.h.roeloffzen@satrax.nl David Marpaung, Maurizio Burla, Leimeng Zhuang Telecommunication Engineering Group, CTIT Research Institute, University of Twente, P.O.Box 217, 7500 AE Enschede, The Netherlands I. INTRODUCTION Currently an integrated photonic beamformer for electronically-steered Ku-band phased array antenna (PAA) systems for satellite communications is being developed, targeting continuous reception of the full DVB-S band (10.7- 12.75 GHz), squint-free and seamless beam steering, and polarization agility. The use of an integrated photonic beamformer enables an antenna system with multi-gigahertz instantaneous bandwidth, compact form factor, light weight, and large beam scanning range, which are challenging requirements for beamformers using only electronics-based RF technologies. An important aspect tackled in this paper is to reduce the system cost such that it is commercially suitable for civil purposes in mobile satellite communications, particularly in aeronautic/avionic satellite communications, where low profile and light weight are essential requirements for the antenna system. The core of the photonic beamformer consists of an optical ring resonator (ORR) filter-based beamforming network (BFN). ORR filters are capable to provide continuously tunable true time delays (TTDs) with configurable bandwidth, and serve as delay elements in a BFN allowing squint-free and seamless beam steering for gigahertz bandwidth applications. Therefore, this approach is superior to the BFNs using phase shifters, discrete time delays or digital BFNs. This photonic beamformer also features optical single- sideband suppressed-carrier modulation and coherent optical detection techniques, resulting in a reduced number of ORRs in the BFN. Other system components such as the optical sideband filter, optical signal combining and carrier reinsertion circuitry are integrated with the ORRs in one photonic BFN chip. In the past, a laboratory demonstrator of such an antenna system has been realized as a proof-of-concept, incorporating individually packaged components, such as LNBs and optical modulators. Currently, substantial effort is put in the development of the key components, namely the antenna front- end, optical modulators, and photonic BFN, and the integration between them, aiming for the actual deployment of the antenna system. II. ANTENNA SPECIFICATIONS The intended operation of the PAA system is illustrated in Fig. 1. Antenna tiles (8x8), each consisting of 64 antenna elements (AEs), are arranged to form the total PAA system with a large number of AEs. As mentioned earlier this PAA is thus used to provide airplane passengers with live television service received from a satellite. To ensure proper signal receptions, the PAA should fulfil a set of requirements. The list of target specifications of the PAA is listed in Table 1. Figure. 1 Illustration of the system considered in this work. In order to provide airplane passengers with live television channels, a phased array antenna system is used for reception. The antenna consists of antenna tiles of 64 elements. Antenna parameter Target value Frequency range 10.7-12.75 GHz (K u -band) Frequency range after downconversion 950-3000 MHz (L-band) Inter-element distance 1.18 cm Steering type Electrical, continuous Beam steering angle Azimuth: 360 o Elevation: 60 o Beam tracking accuracy 0.1 o G/T 12.7 dB/K Antenna size Diameter: 60 cm Height: 10 cm Number of elements 2048 Antenna gain 35 dBi Polarization Linear (H/V) Table 1. The phased array antenna specifications targeted in this work. In this PAA, the received Ku-band signal is down- converted to the L-band and is subsequently processed in the beamformer. The beamformer delays and combines the signals from the AEs such that they are synchronized at the beamformer output. The time delay provided by the beamformer should be sufficient to incorporate the intended maximum scanning angle of this PAA system, which in this case is 360 o in the azimuth plane and 60 o in the elevation angle. Besides the maximum scanning angle, the factors that determine the required maximum time delay are the spacing between the AEs (1.18 cm in this case) and subsequently the size of the antenna. The size of the antenna will also determine the antenna gain. Here, the aim is to have an antenna with a diameter of 60 cm, with a gain in the order of 35 dBi. It has been shown that this dictates at least 1800 AEs incorporated in the system [1]. In this work we set the number of AEs to be 2048. Finally, a