Long slot array (LSA) antenna integrated with compact broadband coupled microstrip impedance transformer

In this paper, a miniaturized coupled microstrip impedance transformer has been developed and integrated with the long slot array (LSA) antenna as a feeding structure. The proposed impedance transformer offers low cost capability by employing printed circuit technology and compact size circuitries can be accomplished by a miniaturization technique, i.e. meandering. Conventional microstrip impedance transformers which can be designed to cover the frequency band of interest (225 MHz - 450 MHz) are too large to be directly implemented onto the LSA due to their limited space on the metallic strip section between feeds. To overcome this issue, miniaturization particularly the meandered transmission line is applied and the compact size (2.1 cm × 3.1 cm) impedance transformer has been developed. The developed impedance transformer provides less than 1 dB insertion loss over the operation frequency range and it is small enough to be directly implemented on the LSA. The developed impedance transformers were implemented to each port of the planar LSA as a feeding structure and their feasibility was tested by using HFSS. Simulation result shows that the LSA integrated with the developed impedance transformer provided very similar radiation pattern and gain as the LSA excited by ideal lumped ports.