Printed Slot Loaded Bow-Tie Antenna With Super Wideband Radiation Characteristics for Imaging Applications

A super wideband printed modified bow-tie antenna loaded with rounded-T shaped slots fed through a microstrip balun is proposed for microwave and millimeter-wave band imaging applications. The modified slot-loaded bow-tie pattern increases the electrical length of the bow-tie antenna reducing the lower band to 3.1 GHz. In addition, over the investigated frequency band up to 40 GHz, the proposed modified bow-tie pattern considerably flattens the input impedance response of the bow-tie resulting in a smooth impedance matching performance enhancing the reflection coefficient (S₁₁) characteristics. The introduction of the modified ground plane printed underneath the bow-tie, on the other hand, yields to directional far-field radiation patterns with considerably enhanced gain performance. The S₁₁ and E-plane/H-plane far-field radiation pattern measurements have been carried out and it is demonstrated that the fabricated bow-tie antenna operates across a measured frequency band of 3.1-40 GHz with an average broadband gain of 7.1 dBi.

I. Introduction

Antennas offering ultra-wideband (UWB) radiation characteristics have been the subject of much research in recent years. Various antennas covering UWB have been studied in the literature including travelling-wave antennas, such as Vivaldi antennas; frequency-independent antennas, such as biconical antennas; self-complementary antennas, such as logarithmic spiral antennas; and multiple resonance antennas, such as fractal antennas. Among these, printed planar antennas have received much attention due to their planar structure, making them easily mountable on planar surfaces, and simple low-cost manufacturing. Bow-tie antennas, which are the planar version of biconical antennas, have the advantage of being considerably compact in size and offering good time domain and broad-band frequency domain radiation characteristics [1], [2]. UWB bow-tie geometries studied in the literature can be given as slot [3], [4], double-sided [5], self-complementary [6] and self-grounded [7].