Broad beamwidth stacked patch antenna with wide circularly polarised bandwidth

Abstract

A broad beamwidth stacked patch antenna with wide circularly polarised (CP) bandwidth is presented. The proposed antenna consists of a stacked structure with a rectangular shell under its ground structure to obtain CP characteristics and wide beamwidth. The radiation quality is excellent over the entire upper hemisphere. The 3 dB beamwidth of the proposed antenna on 2.4 GHz is larger than 140°. Moreover, the CP bandwidth, determined from the 3 dB axial ratio, is found to be about 240 MHz. CP bandwidth of 10.2% and the impedance bandwidth of 52.8% centred on 2.4 GHz are obtained. The proposed antenna is a good candidate for wide angle scanning phased arrays.Introduction: Microstrip patch antennas (MPAs) are widely used in current and future mobile communication systems which require small, low-profile and low-cost antennas. Moreover, with the development of communication and radar systems, wide beamwidth antennas have absorbed in burgeoning concern. To increase the 3 dB beamwidth of the MPA, many effective techniques have been employed. According to [1][2][3][4], many theoretical studies of the finite ground-plane effects on microstrip antenna radiation characteristics have been conducted. These studies have illustrated that the structure and dimensions of the antenna's ground plane can control the radiation patterns of the microstrip antenna.A circularly polarised (CP) microstrip antenna mounted on a threedimensional square structure is introduced in [5]. The antenna consists of a three-layer ground structure that makes the 3 dB beamwidth of CP radiation larger than 110°. In [6], it is illustrated that a curved grounding structure can increase both the impedance bandwidth and the beamwidth of the patch antenna. In [7], a corner-truncated squarepatch CP antenna mounted on a pyramidal ground plane and partially enclosed by a flat conducting wall is introduced. To make a wide beamwidth CP antenna lightweight and of low profile, the work presented in [8] uses a folded conducting wall to reduce the height of the CP antenna to about 0.04λ and meanwhile provides a 3 dB CP radiation beamwidth of about 106°. However, the inherent narrow bandwidth of the microstrip antennas is one of their major drawbacks. The CP bandwidth of the antenna presented in [5] is about 1.5% referenced to the centre frequency at 2323 MHz. Moreover, the impedance bandwidth and 3 dB axial ratio (AR) bandwidth of the antennas proposed in [7,8] are only about 2 and 5%. In the practical design of CP antennas, however, techniques for achieving wideband polarisation characteristics, as well as wideband impedance characteristics, are of great importance. A microstrip-monopole antenna is proposed in [9], where the beamwidth and bandwidth are obtained by loading four cylinders which are perpendicular to the radiating patch. Reference [10] illustrates a broadband dual CP patch antenna with wide beamwidth, which is excited by four crossslots via a microstrip line. The 10 dB impedance bandwidth is 24% and the 3 dB AR bandwidth is 16%. On the other hand, stack...

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