2.45 GHz end-loaded dipole backed by a high impedance surface

Abstract

An end loaded planar open sleeve dipole (ELPOSD) antenna over an electromagnetic band gap (EBG) high impedance surface is presented. An ELPOSD consists of a printed dipole with two parasitic elements (sleeves) along its sides and capacitive loading at the end. This antenna is fed from beneath the ground plane by live vias connected to a microstrip to coplanar strip balun. The EBG structure is based on the Jerusalem Cross geometry and is sandwiched between two 1.27 mm-thick substrate layers, resulting in a total antenna thickness (excluding the feed layer) of ~λ/50. Measured performance of the antenna demonstrates a bandwidth of 30 MHz at 2.45 GHz, with a gain of ~3.5 dB. IntroductionHerein a low-profile planar antenna operating at 2.45 GHz with uni-directional radiation is presented. The goal of this effort was to establish a baseline approach for realizing a flexible antenna with moderate bandwidth that can be used in applications such as bodyworn sensors. For electromagnetic sensing, e.g. in the case of radiometric sensors, reduction in backside radiation is important in order to maximize the detection sensitivity. Accordingly, a design incorporating a backing ground-plane is appropriate. Furthermore, in this particular effort, the ability to tune the operating frequency is desirable as this allows real-time adjustment of the sensing depth. For this reason, the architecture has been conceived with the aim of facilitating eventual integration of varactor-based tuning.Among the choices for antenna elements satisfying the above criteria are various forms of microstrip patch antennas. Standard, single-layer patches are typically narrow-band [1] and tuning approaches usually involve devices that are exposed on the outer surface [2], contrary to the embedded solution that is desired in this work. Multi-layer patches may offer instantaneous bandwidth covering the frequency range of interest [e.g. 3] however the thickness conflicts with the desire to achieve a flexible, low-profile design.The approach taken in this work was to integrate an end-loaded planar open sleeve dipole (ELPOSD) into a multi-layer substrate that includes a back ground-plane and an intervening high-impedance, electronic band-gap (EBG) layer. The ELPOSD is naturally broad-band, typically ~25% bandwidth, and compact in size. The Jerusalem Cross Frequency Selective Surface (JC-FSS) geometry was selected for the EBG layer, due to its wide angular stability and the potential for convenient frequency tuning and substrate thickness reduction. Previous authors have investigated the combination of an ELPOSD with patch-type electronic band-gap (EBG) layers [e.g. 4, 5]. Antenna Design and PerformanceThe ELPOSD antenna design consists of a printed dipole that is loaded with two parallel sleeves, and has parasitic capacitive loading at the ends of the dipole arms; the loading 978-1-4244-4968-2/10/$25.00 ©2010 IEEE elements offer design miniaturization. The dipole was designed for a 1.27 mm-thick Rogers RT6010 substrate, with a dielectric constant of 10.2, that...

One dimensional capacitive loading in a frequency selective surface for low profile antenna applications

“…1). Previous works have demonstrated that dipole-type antennas above FSS ground planes tend to be narrowband [1], [2]. In [2] it was shown via simulation that the bandwidth can be increased by positioning the dipole in free space above the FSS; the typical bandwidth with this approach is 4.3% for a total antenna and FSS thickness of ~λ/25.…”

“…The primary objective of this effort is to study the impact on antenna bandwidth and planar size when capacitive loading is introduced into the FSS. This work builds upon the design presented by Cure [1] with the goal of achieving bandwidths on the order of 10%.…”