Differential-fed Wang-shaped patch antenna using narrowband and wideband baluns

The rapid growth of wireless communications has demanded technology development in addressing the narrow bandwidth of microstrip patch antennas. Various impedance bandwidth broadening techniques such as U-slotted patch [1], E-shaped patch [2]-[3], suspended patch [4], and L-shaped probe feed [5]-[6] have been invented to overcome the impedance matching and bandwidth issues. Nevertheless, wide impedance bandwidths are often accomplished at the cost of distorted copolarized (Co-pol) radiation patterns and high cross-polarization (X-pol) levels within the achieved impedance bandwidth, which in turn leads to a narrow operating bandwidth. Recently, the novel differential-fed wideband patch antennas featuring symmetrical, non-distorted radiation patterns with low X-pol levels have been proposed [7]-[9], one of them is known as the Wang-shaped patch antenna [8]-[9]. The innovation of the Wang-shape comes from the disadvantages of the E-shaped patch which is inherently asymmetric in one plane and produces high X-pol off boresight. Moreover, when the feed mechanism of wideband patch antennas involves a vertical probe, the used air/foam substrate is found to be limited at -0.1 operation wavelength (λ) in height [l]-[5]. This paper presents a novel differential L-probe fed Wang-shaped patch antenna with the use of an air substrate that goes beyond 0.2λ. High-order modes and cross-polarization levels are suppressed to minimum by separately using two different feeding networks: a narrowband and a wideband balun. The operating bandwidths of the two antennas are 30% and 40% at 2 GHz, in which the X-pol levels are suppressed below -17dB and -20 dB, respectively.