More for less: reconfigurable antenna arrays

The recent rapid development of wireless communication systems has created a strong need for the development of new antenna structures. Researchers at the Universiti Teknologi MARA in Malaysia have introduced the concept of reconfigurable antennas with switching beam control, operable at 5.8 GHz.

Reconfigurable antennas are attractive for wireless communications because they enable the use of a single antenna for multiple systems. In this project, a new reconfigurable antenna design was proposed; namely, a reconfigurable antenna array (RAA). In the RAA configuration, the behaviour of the reconfigurable multiple element linear antenna array system was investigated with respect to the beam shaping characteristics. Two different beam patterns were achieved by reconfiguring the number of patch elements.

The project, led by Mohd Tarmizi of Universiti Teknologi MARA, developed reconfigurable, multiple-element, micro-strip, rectangular linear array antennas integrated with radio frequency (RF) switches. Reconfigurable beam shaping is ideal for the detection of small and large targets at both short and long ranges, including where the antenna is mounted on a high tower or hillside. “Reconfigurable antennas have been applied to many military and mobile communication applications where it is necessary to have a single antenna that can be dynamically reconfigured to transmit or receive on same or multiple frequency bands,” says Tarmizi.

The team had to investigate antenna design, fabrication and measurement in order to develop the optimum type of antenna. The objectives were to study, design and fabricate an innovative RAA with respect to the control of beam shape characteristics at a resonant frequency of 5.8 GHz. Another aim was to develop and design programmable interface controller (PIC) power microcontroller circuits that can be used to supply the DC voltage to activate the PIN diode switch circuits.

The team eventually succeeded in getting simulation data to demonstrate the concepts of a reconfigurable number of elements that produced broadened beam and narrowed beam radiating pattern characteristics. By using a modified Wilkinson Power Divider (WPD) in the antenna structure, better performance in terms of return loss was produced. The researchers say the design solves some of the problems of the original Wilkinson power divider design. The addition of transmission lines in between two quarter-wave transformer arms has been shown to absorb unwanted waves generated due to mismatch at the switches.

The research took advantage of techniques of flexibly manipulating the number of elements. The reconfigurable dual-beam antenna pattern at fixed frequencies across the entire 5.7-5.9 GHz band showed excellent radiation patterns, with the measured results illustrating that the radiation pattern characteristic of the antenna had been tuned efficiently. The reconfiguration of radiation patterns for four- and eight-element structures at 3 dB half power produced a beamwidth (HPBW) of 290° and 210° respectively. Meanwhile, the return losses for both structures were -20.57 dB.

The comparison of gain between both reconfigurable modes can be observed from the results: the eight-element mode had 2 to 3 dB higher gain compared to the four-element mode. It shows clearly that when the numbers of elements are increased, the beamwidth becomes narrower with lower sidelobe and higher magnitude.