RADIOENGINEERING, VOL. 23, NO. 1, APRIL 2014 165 An Efficient Beam Steerable Antenna Array Concept for Airborne Applications Hadi ALIAKBARIAN 1,3 , Ewald VAN DER WESTHUIZEN 2 , Riaan WIID 2 , Vladimir VOLSKIY 1 , Riaan WOLHUTER 2 , Guy A. E. VANDENBOSCH 1 1 ESAT-TELEMIC, KU Leuven, Kasteelpark Arenberg 10 3001, Leuven, Belgium 2 E&E Engineering Dept., Banghoek Road, Stellenbosch University, Stellenbosch, 7600, South Africa 3 Dept. of ECE, K.N.Toosi University of Technology, Tehran, Iran h.aliakbarian@ieee.org, ewaldvdw@sun.ac.za Abstract. Deployment of a satellite borne, steerable an- tenna array with higher directivity and gain in Low Earth Orbit makes sense to reduce ground station complexity and cost, while still maintaining a reasonable link budget. The implementation comprises a digitally beam steerable phased array antenna integrated with a complete system, comprising the antenna, hosting platform, ground station, and aircraft based satellite emulator to facilitate conven- ient aircraft based testing of the antenna array and ground-space communication link. This paper describes the design, development and initial successful interim test- ing of the various subsystems. Due to the increase in signal level, our two-element prototype raises the signal-to-noise ratio (SNR) by about 3 dB which is corresponding to a more than 10 times better bit error rate (BER). Keywords Space deployed phased array antenna, beam steering, DSP software defined radio modem, embedded FPGA channel coding. 1. Introduction One of the best methods to improve the link budget of a Low Earth Orbit (LEO) satellite or an airborne system is to use an expensive tracking antenna system on the ground station. On the other hand for environmental monitoring purposes, it is commonly required that such stations be deployed over a large area and in significant numbers, with small size and low cost. In such situations, the alternative way is to transfer tracking capability to the airborne or satellite borne side of the link. It would, therefore, be greatly advantageous to use a fixed antenna with wider polar radiation characteristics, but lower associated gain [1]-[3]. This however, implies a higher antenna gain for the satellite, if the power budget is to remain. It should also be steerable, to cater for the greatly varying overflight geometry [4]-[5]. These characteristics are in line with the research ob- jectives of the ESAT-TELEMIC division of the Dept. of Electrical Engineering, of the Katholieke Universiteit Leu- ven, Belgium. This group is developing advanced tech- niques for the design of electronically beam steerable an- tenna arrays, intended for satellite deployment. Directivity and associated higher gain, together with convenient steer- ability, will allow specific ground stations to be scheduled during satellite overflight with improved link budget, com- pensating for a fixed, more omnidirectional ground station antenna. The project is carried out in partnership with the Dept. of Electrical and Electronic Engineering of Stellenbosch University, South Africa, who is developing the rest of the LEO satellite payload, ground station and accompanying ground-space communications link. Ground station coordi- nates and a per station communications schedule will be uploaded to the satellite via the telecommand link. Satellite position and orientation information will be made available from the satellite bus, in order to enable beam steering and aiming of the antenna axes towards the appropriate ground station. The purpose of this paper is to report on the develop- ment of the communications link, Steerable Antenna Array (SAA) and the calibration method. Some initial test results are also presented; using an aircraft based satellite emulator (ASE) [6]. The rest of the paper is structured as follows. An overview of the systems design is presented in Section 2, followed by an overview of the various subsystems and their functionality, in Section 3. The satellite payload de- sign is also covered in Section 3, with Section 4 presenting a brief review of the communications link and protocol implementation. The ground station re-uses much of the space segment embedded design, but not being restricted to space qualified hardware, and also utilizes some more standard submodules. The configuration thereof is dis- cussed in Section 5. Evaluation and test results were ob- tained from both simulations and an actual flight simulator. These are presented in Section 6. Section 7 contains a summary of the work performed, and actions planned for the immediate future are discussed in Section 8.