The bow-tie antenna: Performance limitations and improvements

The simple planar shape and wideband input impedance of the bow-tie antenna make it suitable to diverse wideband applications. However, the radiation pattern of this kind of antenna is not stable and the gain in the broadside direction deteriorates with increasing frequencies. In this article, the operation of both the triangular and the rounded-edge versions of the bow-tie antenna is thoroughly investigated and the performance thereof is compared. A technique to maximise such performance, which consists of inserting radially aligned grooves in the radiators' ends, is presented. The bandwidth, defined by a broadside gain of at least 2 dBi and a reflection coefficient magnitude of less than −10 dB, is improved from 85.7% to 97.9% in simulations. Such an improvement is validated through the measurement of two prototypes, in which the presented technique also increases the broadside gain in up to 1.5 dB, with no significant change in the shapes of the radiation patterns and in the reflection coefficient magnitude.