David Cure

Study of a Low-Profile 2.4-GHz Planar Dipole Antenna Using a High-Impedance Surface With 1-D Varactor Tuning

A theoretical and experimental study has been performed on a low-profile, 2.4-GHz dipole antenna that uses a frequency-selective surface (FSS) with varactor-tuned unit cells. The tunable unit cell is a square patch with a small aperture on either side to accommodate the varactor diodes. The varactors are placed only along one dimension to avoid the use of vias and simplify the dc bias network. An analytical circuit model for this type of electrically asymmetric unit cell is shown. The measured data demonstrate tunability from 2.15 to 2.63 GHz with peak gains at broadside that range from 3.7- to 5-dBi and instantaneous bandwidths of 50 to 280 MHz within the tuning range. It is shown that tuning for optimum performance in the presence of a human-core body phantom can be achieved. The total antenna thickness is approximately λ/45.

Low-Profile Tunable Dipole Antenna Using Barium Strontium Titanate Varactors

In this paper, a 2.4 GHz low-profile dipole antenna that uses a frequency-selective surface (FSS) with interdigital barium strontium titanate (BST) varactor-tuned unit cells is presented. The tunable unit cell is a square patch with a small aperture on either side to accommodate the BST devices. The Ba0.6Sr0.4TiO3 varactors were fabricated on alumina substrates and demonstrate capacitance tuning of 1.5:1 (33%) at 90 V. The varactor chips were placed only along one dimension of the FSS to avoid the use of vias and simplify the dc-bias network. The measured data of the antenna demonstrate tunability from 2.23 to 2.55 GHz with a peak gain at broadside that ranges from 3 to 3.7 dBi, and instantaneous bandwidths of 50 to 160 MHz within the tuning range. The total antenna thickness is approximately λ/47.

A comparison between Jerusalem Cross and Square Patch Frequency Selective Surfaces for low profile antenna applications

In this paper, a comparison between Jerusalem Cross (JC) and Square Patch (SP) based Frequency Selective Surfaces (FSS) for low profile antenna applications is presented. The comparison is aimed at understanding the performance of low profile antennas backed by high impedance surfaces. In particular, an end loaded planar open sleeve dipole (ELPOSD) antenna is examined due to the various parameters within its configuration, offering significant design flexibility and a wide operating bandwidth. Measured data of the antennas demonstrate that increasing the number of unit cells improves the fractional bandwidth. The antenna bandwidth increased from 0.8% to 1.8% and from 0.8% to 2.7% for the JC and SP structures, respectively. The number of unit cells was increased from 48 to 80 for the JC-FSS and from 24 to 48 for the SP-FSS.

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

In this paper, the impact of adding discrete capacitive loading along one dimension of a frequency selective surface for low profile antenna applications is presented for the first time. The measured data demonstrates comparable performance between a non-loaded and a capacitively-loaded FSS with a significant reduction in the number of cells and/or cell geometry size. Additionally, the provision of discrete capacitive loads reduces the FSS susceptibility to fabrication tolerances based on placement of a fixed grid capacitance. The bandwidth increased from 1.8% to 7.3% for a total antenna thickness of ∼λ/22, and from 1.5% to 9.2% for a thickness of ∼λ/40. The total antenna area for each case was reduced by 55% and 12%, respectively.

A Quasi-Yagi Antenna Backed by a Jerusalem Cross Frequency Selective Surface

A quasi-Yagi antenna is developed to operate at 2.4 GHz (ISM band) presenting a low profile and off-axis radiation when packaged over a metal ground plane. The off-axis radiation is realized by incorporating a Jerusalem cross frequency selective surface (JC-FSS) as the ground plane for the antenna. A JC-FSS is preferred because of its frequency stability in the operating band for a large angular spectrum (≈70°) of TE- and TM-polarized incident waves. In this research, the substrate of the antenna flush-mounted on top of the FSS is added to the JC-FSS model and allows for a smaller cell grid. The prepared quasi-Yagi antenna over the JC-FSS offered 260 MHz of functional bandwidth and 54° of beam tilt towards the end-fire direction. To the best of the authors’ knowledge this is the first instance that these two structures are combined for off-axis radiation. Additionally, to support the preferred use of the JC-FSS, the quasi-Yagi is backed by a square patch (SP) FSS for comparison purposes.

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

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.

Non-uniform bias enhancement of a varactor-tuned FSS used with a low profile 2.4 GHz dipole antenna

In this paper a low profile antenna using a nonuniformly biased varactor-tuned frequency selective surface (FSS) is presented. The tunable FSS avoids the use of vias and has a simplified DC bias network. The voltages to the DC bias ports can be varied independently allowing adjustment in the frequency response and enhanced radiation properties. The measured data demonstrate tunability from 2.15 GHz to 2.63 GHz with peak efficiencies that range from 50% to 90% and instantaneous bandwidths of 50 MHz to 280 MHz within the tuning range. The total antenna thickness is approximately λ/45.

Low profile tunable dipole antenna using BST varactors for biomedical applications

In this paper a 2.4 GHz low profile (λ/47) tunable dipole antenna is evaluated in the presence of a human core model (HCM) body phantom. The antenna uses a frequency selective surface (FSS) with interdigital barium strontium titanate (BST) varactor-tuned unit cells and its performance is compared to a similar low profile antenna that uses an FSS with semiconductor varactor diodes. The measured data of the antenna demonstrate tunability from 2.2 GHz to 2.55 GHz in free space and impedance match improvement in the presence of a HCM at different distances. This antenna has smaller size, lower cost and less weight compared to the semiconductor varactor diode counterpart.