Differential‐fed UWB microstrip antenna with improved radiation patterns

Abstract

A differential-fed microstrip antenna, which is characterised with an ultra-wideband (UWB) of 120% (3-12 GHz), improved radiation patterns, stable gains and compact size, is proposed. Two symmetrical trapezoid-shaped slots and four triangle-cut corners on the ground are used to improve the impedance matching over the UWB frequency band. To clarify the improved radiation characteristics, the simulated 3D radiation patterns of the proposed antenna are also shown. The measured results show that, in the entire frequency band, the designed antenna exhibits a stable radiation pattern and the gain variation is < 2.5 dB. Furthermore, the polarisation purity is increased compared with the conventional ones, especially in the high-frequency band.Introduction: Since the Federal Communication Commission (FCC) released the frequency band 3.1-10.6 GHz for commercial ultrawideband (UWB) systems, both industry and academia have conducted tremendous efforts on the UWB radio technology. As an important component of the communication system, the UWB antenna is required to have a simple structure, wide impedance bandwidth, easy integration, stable radiation patterns, constant gain and so on. Planar monopole antennas, as one of the most attractive candidates for UWB antennas, have recently been paid more attention due to their small size and easy integration. So far, various single-ended feed planar UWB antennas have been presented [1][2][3]. Although this type of antenna can be matched over the entire UWB bandwidth with ease, there exists a common deficiency of deterioration of radiation pattern. The radiation patterns of these antennas may deviate from the broadside direction at high frequencies (above 9 GHz), which may cause problems for the applications that require a stable radiation pattern. To alleviate this problem, several techniques have been proposed to improve the radiation pattern of the UWB antenna [4][5][6]. However, although the radiation pattern in the upper frequency band has improved to some extent, the cross-polarisation of the antennas is in high level in the H-plane, and the polarisation purity still needs to be improved.To reduce the cross-polarisation, which is caused by the transverse currents of higher-order mode, some efforts have been made by the researchers. It is found that higher-order mode can be suppressed greatly when the antenna is symmetrically driven using differential feeding systems [7]. Hence, in this Letter, a compact differential-fed microstrip antenna is presented for UWB applications. Furthermore, owing to the differential feeding technique, the balun is not needed when the antenna is driven using differential signals. More importantly, over the entire UWB band, the proposed antenna presents stable omnidirectional radiation patterns in the H-plane, compared to dipole-like radiation patterns in the E-plane. By employing the differential feeding systems, the crosspolarisation level is kept low over the whole operating frequencies, which result in high polarisation purity of the antenna.

Differential‐fed printed monopole antenna loaded with half cylindrical DR for UWB handheld device application

“…The design procedure is described as follows. First, referring to the current antennas in, a differential‐fed printed monopole is designed to get a wideband characteristic. Then, a half sector cylindrical DR is added, and by referring to parameters studies and using the HFSS simulation, all the parameters are adjusted such that the differential reflection coefficients, gains and radiation efficiencies for the antenna meet the specifications.…”

“…When the differential‐fed antennas connected to the differential‐fed systems, no baluns are needed, which decreases the design complexity and increases system stability. Some kinds of differential‐fed antennas have been proposed . However, all those antennas have omnidirectional radiation patterns in H ‐plane and dipole‐like radiation patterns in E ‐plane.…”

A compact size 2.9‐23.5 GHz microstrip patch antenna with WLAN band‐rejection

“…The main focus of the microstrip antennas are the bandwidth improvement and can be classified into three categories. One is the manipulation of the field distribution in the patch with tampered shape and other is the feeding schemes to achieve multiple resonances . The third type uses different shapes of slots and apertures in such a way that generate wide bandwidth .…”

A compact planar antenna with extended patch and truncated ground plane for ultra wide band application

“…Various designs have been suggested and demonstrated for the UWB and WLAN range of frequency. A fork‐shaped radiating patch in Reference , differentially fed partially cut elliptical patches in Reference , elliptical patch with circularly symmetric slot in References 3 and 4, open‐ended T‐shaped slot with feed line extension in Reference , double L‐slot patch in Reference , lobster‐shaped ground plane with multiple slots have been reported recently. The partial ground plane and slots impact the overall bandwidth of the antenna and its return loss characteristics.…”