Design of a simple three-element quasi-Yagi antenna with a broad impedance bandwidth up to 2.4 : 1

Abstract

This paper introduces a method for designing a broadband three-element quasi-Yagi antenna (QYA) with a simple geometry and compact size. The proposed QYA consists of simple strip-type elements with unequal widths and distances between them to obtain the desired performance. The proposed QYA fed by a microstrip (MS) line is compact because it has an MS line-to-coplanar strip (CPS) line transition integrated on the CPS line, without requiring additional space for the transition. When a rectangular patch-type director is placed close to the driver dipole fed by a CPS line, the antenna becomes a triple resonance structure, and the impedance bandwidth is extensively increased up to 2.4 : 1 (82.3%) for a VSWR < 2. An example design for a QYA with a gain >4 dBi and a frequency band of 1.6–3.6 GHz is presented. The optimized antenna is fabricated on an FR4 substrate with dimensions of 90 mm × 90 mm and is tested experimentally. The results demonstrate an impedance bandwidth of 2.4 : 1 (1.56–3.74 GHz, 82.3%) for a VSWR < 2, a realized gain of >4 dBi, a cross-polarization level of <−21 dB, and a front-to-back ratio of >13.6 dB within the bandwidth.