A wideband Vivaldi antenna array

Abstract

The need for wideband antenna arrays have increased due to the number of devices that are connected to wireless networks. One of the main limitations of current corporate fed antenna arrays is the narrow band response, due to the limited bandwidth of the feed network, radiating element, or the combination thereof. This narrow band response can be increased by implementing a wideband radiating antenna element along with a feed network with an increased impedance bandwidth. From literature it is evident that current wideband antenna arrays use a single transmission line or combinations of different types of transmission lines as feed networks in the array structure. One example of a single transmission line feed network obtained an impedance bandwidth of 10.69%. In another study a four-element antenna array was fed using a combination of microstrip to slotline transitions (MST) and obtained a maximum bandwidth of 60%. The same feed network was used in another study to feed Vivaldi antennas and obtained an 83.8% bandwidth. As Vivaldi antennas can achieve large bandwidths exceeding 100%, the feed network is typically the limiting factor. Therefore, the aim of this study is to improve the bandwidth of the feed network of a Vivaldi antenna array to achieve a bandwidth of more than 100%. The proposed feed network design consists of a coplanar waveguide (CPW) line that transitions to a slotline and two slotline to microstrip transitions in a linear array configuration. The feed design reduces the number of microstrip to slotline transitions compared to existing feed networks found in literature and achieves an impedance bandwidth greater than 100%. The feed network achieves a 160% bandwidth from 1 GHz to 9 GHz. In contrast to conventional corporate feeding networks, the output ports of the feed network has a phase difference of 180°. The phase difference will result in unequally excited antenna elements. The feed network was used to feed four Vivaldi antenna elements in a linear array configuration. The phase difference between the output ports were mitigated with a 180° rotation of the outer two Vivaldi elements in the four element linear array. This orientation resulted in a slight offset in distance between the inner and outer Vivaldi antennas. The feed network design had to be adjusted and optimised further to achieve the uniformly equal spaced linear antenna array. The final antenna array achieved a bandwidth of 144.6% with desirable radiation patterns. The array also achieved a better than 8 dBi boresight gain over the frequency band, with a peak boresight gain of 13.8 dBi. This design outperforms other corporate fed antenna arrays available in literature.