Antenna A Control Signal Computer Tx XBee Wireless Connection Arduino Pro Mini Rx XBee Ant. 4 Ant. 3 Ant. 2 Ant. 1 Control Signal Wireless Control of Reconfigurable Antenna Arrays Mina A. Iskander * and Dimitris E. Anagnostou ECE Dept. South Dakota School of Mines and Technology Rapid City, SD 57701 USA, Email: mina.anwar@ieee.org Abstract— We developed a system that allows a user to wirelessly control reconfigurable antenna arrays using software. The array consists of four coplanar folded slot antenna elements and its different states can be activated or deactivated remotely on- demand to alter the entire array’s resonant frequency. The array alters its operating frequency by changing the status of eight couples of p-i-n diodes simultaneously (four diodes per antenna element). The control system is described and the performance of the reconfigurable array was measured and discussed. I. INTRODUCTION Reconfigurable antennas are of interest because they enable to use a single antenna structure that can change on demand one or more of its characteristics (i.e. radiation pattern, operating frequency and polarization) by using low-power biasing or control signals. Many frequency reconfigurable antennas with p-i-n diodes have been implemented in the past. This work was inspired by the reconfigurable antenna in [1] where the p-i-n diodes act as switches that can be turned ‘on’ or ‘off’ by applying a DC voltage at their terminals. The Coplanar Folded Slot Antenna (CFSA) was first described in [2] and [3] and its matching is shown in [4]. The antenna can also be wideband or dual-band as shown in [5], as well as reconfigurable [1] without the need to design a separate biasing network. The biasing network is realized simply and does not affect the RF signal by connecting the diodes to the ground of the antenna. The wireless control system that we developed is applied here on a new reconfigurable CFSA array that consists of four independently reconfigurable antenna elements. The array is fabricated on a 16-mil (406.4 μm) thin and flexible RO4003C substrate, and is controlled remotely through a wireless channel. II. THE WIRELESS CONTROL SYSTEM The reconfigurable antenna array is controlled remotely using software through the Reconfigurable Antenna Control System (RACS) that we developed. A MATLAB M-file code was written to work as a user input interface. The code asks for a decimal (i.e. 5) or 4-bit binary number (i.e. [0101]), where a ‘1’ sends 3.3-Volts to the terminals of a specific pair of p-i-n diodes that are connected together on one side of the slot (since they share the ‘+’ patch conductor and the ‘-’ ground) and turns them ‘on’, while a ‘0’ sends a 0-Volts signal that turns them ‘off’. The M-file sends the desired p-i-n diode control states to the computer’s serial COM port where a Xbee transceiver transmits them to a remotely located Arduino I/O board through a XBee wireless channel. The block diagram of the developed system and a photograph of the implemented system with all hardware components connected and functioning are shown in Fig. 1. The first wireless XBee transceiver is connected to the computer’s COM port through a USB connection. Then the wireless signal is picked up by the other (receiving) Xbee that is connected to the remote Arduino microcontroller board. The Arduino controller interprets the MATLAB command, and sets the digital output terminals / pins accordingly. A code for the Arduino was also developed to interpret the received commands from MATLAB. The code uses mainly the serial.read() Arduino command to read incoming serial data, the pinMode() command to configure the specified pins to behave as (only) outputs, and the digitalWrite() command to write or sent an output ‘high’ or ‘low’ value to the Arduino pins. These outputs are used to control the states of all the diodes of the array. Figure 1. Photo and block diagram of the wirelessly controlled reconfigurable antenna array system developed. III. WIRELESS CONTROL OF RECONFIGURABLE ANTENNA ARRAYS The developed wireless control system was tested by connecting it to a reconfigurable 4x1 antenna array that we designed. A photo of the fabricated array after the soldering of the p-i-n diodes and of the control lines is shown in Fig. 2. Note that the length of the control lines does not affect the behavior of the antenna elements or of the array itself [2], and therefore they can be made as long as necessary to be connected to the Arduino output pins. The array is designed with a microstrip corporate feed network that is transitioned to a Coplanar Wave-Guide (CPW) feedline at the terminals of each antenna element. The microstrip corporate network matches each antenna element at their feeding point using a stepped CPW matching transformer. The corporate network ensures maximum radiation at the 978-1-4673-0462-7/12/$31.00 ©2012 IEEE