Rapid development in wireless communication demands the multifunctional antennas with cognitive functionalities. Reconfigurable antennas are the suitable candidate to the aforementioned problem via its notching characteristics. There are several reconfigurable antennas with several mechanisms are exploited in the open literature. Based upon the application, the re-configuration will be with respect to frequency, pattern or polarization. The reconfigurable mechanisms should not affect the radiation characteristics of the antenna and also the complexity. Ultra-wideband technology is recommended for applications like satellite networks, biomedical detection, microwave imaging, military and radar systems. Multifunctional characteristics can be obtained by incorporating multiple antennas or by re-configurable antennas. Vivaldi antennas are the one among the end fire antenna family and it has been explored in many ways in many applications. In our research, we have implemented antipodal Vivaldi antenna (AVA) to become a reconfigurable antenna with the help of PIN diodes.
Since Gibson unveiled the Vivaldi antenna in 1979, due to its benefits such as wide bandwidth, flat shape, relatively high directivity, radiation efficiency and simple to manufacture, it has gained more and more popularity in the field of science [1, 2]. The Vivaldi antenna is most commonly used for aircraft missiles, ships and other airborne applications. It is a standard UWB antenna, the bandwidth of the antenna is limited by its complicated feed setup and the width of the slot [3]. The AVA has low input impedance relative to the conventional Vivaldi antenna. So it can reliably match the characteristic impedance of 50 Ohm [4]. A Vivaldi antenna is a best option for UWB applications and it has strong end-of-fire radiation compared to the planar monopole antenna [5, 6]. Studies demonstrates that depending on the antenna size the lowest operating frequency is regulated and that the antenna size should be at least one half the wavelength, equivalent to the lowest operating frequency in free space, in order to receive effective radiation[7, 8]. In order to resolve the restriction, several techniques have been used and recorded to minimize the size of the Vivaldi antenna, the slotted edge has been used [9]. Adding a high-permittivity dielectric director will greatly increase antenna gain at various operating frequencies [10]. Improved radiation characteristics can be obtained by inserting slots to its boundary, it provides light weight and reduced structure [11]. Recently, the clustering of several networks in one antenna using antenna reconfiguration has gained a lot of coverage. In the antenna opening at different positions the PIN diodes and slots are inserted. This antenna is suitable for applications using UWB and narrow band switching [12, 13]. At the receiver side, the interference level can be reduced by applying antenna reconfiguration and it can be used in cognitive radio applications [14, 15]. Frequency reconfiguration is typically accomplished by means of lumped elements, such as PIN diodes and MEMS switches, in a particular location to monitor the distribution of current [15–16]. The slot antenna's various designs are presented in [17, 18].The proposed dual mode antipodal Vivaldi antenna is designed by the introduction of rectangular slots to operate in ultra-wide band and two narrow bands [19].With the ground plane input change and placing a slot resonator on ground plane will provides a customized ultra wide band AVA [20]. By adding the lumped elements in the proposed miniaturized Vivaldi antenna will enhance impedance features [21]. A small wide band AVA is created by loading convex lens and director in an arc type radiator for high frequency performance enhancement [22].
This article outlines the design and implementation of dual mode antenna. Conventional AVA is implemented with a rectangular slots on its inner radiating structure and semi-circular slots on its outer radiating edges. To exhibit the dual mode characteristics, PIN diodes are implemented on the rectangular slits and the characteristics were studied. This paper is organized as follows. The antenna design with diode implementations are discussed in Sect. 2. Results and discussions are carried out in Sect. 3. Section 4 is the summary of our design and future potential.