Alireza Foroozesh

Investigation Into the Effects of the Patch-Type FSS Superstrate on the High-Gain Cavity Resonance Antenna Design

Results of modeling, design, simulation and fabrication are presented for a high-gain cavity resonance antenna (CRA), employing highly-reflective patch-type superstrates. In order to determine the resonant conditions, the antenna is first analyzed using the transverse equivalent network (TEN) model, as well as the well known simple ray-tracing method. Prior to that, a highly-reflective patch-type frequency selective surface (FSS) is designed in order to be employed as the superstrate layer of the CRA. Next, a 2.5-D full-wave analysis software package, based on the method of moments (ANSOFT Designer v4.0), is utilized to analyze the antenna structure. Using this full-wave analyzer, the input impedance properties of an actual antenna are investigated as well. Then, a 3-D full-wave analyzer, based on the finite element method (ANSOFT HFSS), is used to extract the directivity and radiation patterns of the CRA, taking into account the finiteness of the substrate, superstrate and ground plane. Some previously unaddressed issues, such as the effects of the FSS superstrate on the input impedance characteristics of the probe-fed microstrip patch antenna, acting as the excitation source of the CRA are also studied. The effects of the highly-reflective FSS superstrate size on the CRA directivity, and explicitly its aperture efficiency, are investigated as well. A comparative study is also performed between CRAs with patch-type FSS and high permittivity dielectric superstrates. Measurement results are provided to support the modelings and simulations.

Investigation Into the Application of Artificial Magnetic Conductors to Bandwidth Broadening, Gain Enhancement and Beam Shaping of Low Profile and Conventional Monopole Antennas

The reflection coefficient phase is investigated for several different artificial magnetic conductors (AMCs) having canonical FSS-type shapes. Three of them are selected, each representing a different class, and fine tuned to exhibit identical resonant frequency. Polarization and angular dependence as well as the effects of losses on these structures are studied. Next, a low-profile inverted L-shape monopole antenna (ILSMA) is placed horizontally above the ground plane. Vertical monopole antenna (VMA) is also placed above them. It is shown that using some of the aforementioned AMCs, the input impedance of both ILSMA and VMA can not only be matched, but also the input impedance bandwidth enhancement as wide as 27% and 35% are obtained, respectively. The VMA study on AMC ground planes which reveals a counter-intuitive phenomenon has not been explored in the literature, previously. It is revealed that the broadband characteristics can also be achieved for smaller size of the AMC ground planes, which enables the antenna to be designed in compact size. It is also illustrated that reflection characteristics of the AMC is not sufficient to evaluate AMC performance when it is used as an antenna ground plane. This is illustrated through extensive simulation and measurement results.

Application of combined electric- and magnetic-conductor ground planes for antenna performance enhancement

This paper investigates the application of three different ground planes for antenna performance enhancement. They are the conventional perfect electric conductor (PEC), the perfect magnetic conductor (PMC), and their combination. A half-wavelength dipole in free space is considered as the reference case, and its performance over these ground planes is investigated and compared. It is shown that by using a combined PMC-PEC ground plane, one can achieve a better performance. Next, a microstrip patch antenna is considered as the source and is placed over a high-impedance surface (HIS) or an artificial magnetic conductor (AMC). Here too, adding a PEC ground plane on the periphery of the HIS or AMC improves the antenna gain significantly. As well, the superiority of AMC ground planes, consisting of grounded dielectric slabs loaded with periodic metallic patches without shorting pins (vias), is investigated in detail. Simulation results show that use of such artificial ground planes can enhance the microstrip patch antenna gain and bandwidth remarkably. These enhancements are confirmed by measurement, and high gains of 10.4 dBi and input impedance bandwidths of 28% are measured.

Effects of Artificial Magnetic Conductors in the Design of Low-Profile High-Gain Planar Antennas With High-Permittivity Dielectric Superstrate

Cavity resonance antennas with dielectric superstrate are considered with different ground plane types namely, perfect electric conductor (PEC), perfect magnetic conductor (PMC), and artificial magnetic conductor (AMC). Radiation properties of these antennas are computed using transverse equivalent network (TEN) model. It is shown that the effects of angular and polarization dependency of artificial ground planes can be beneficial or detrimental to the antenna performance in directivity.

On the Characteristics of the Highly Directive Resonant Cavity Antenna Having Metal Strip Grating Superstrate

Various resonant cavity antennas (RCAs) having different metal strip gratings (MSGs) as their superstrates are studied in terms of their directivity and scanning properties using transverse equivalent network (TEN) model in conjunction with the periodic method of moments (MoM). It is shown that radiation patterns in E- and H-planes coincide over a wide angle range in RCAs when their MSG superstrates are free-standing and highly reflective, as reported in the previous literature. However, using less reflective MSG or employing dielectric support in the MSG superstrate degrades the equality of E- and H-plane radiation patterns. Moreover, as the scan angle increases, radiation patterns in E- and H-planes become noticeably different. It is elucidated that this is due to the angular dependence of the reflection coefficient phase of the MSG superstrates. A comparative study is also performed on a few different RCAs based on both simulation and measurement results. It is illustrated that in practice when the excitation source of the RCA is a probe-fed microstrip antenna and the RCA is finite in size, cross-polarization increases considerably as opposed to the RCAs having ideal sources and, infinite ground plane and MSG superstrate in the transverse direction.

Size reduction of a microstrip antenna with dielectric superstrate using meta-materials: artificial magnetic conductors versus magneto-dielectrics

Planar antenna gain can be enhanced using a high-permittivity cover as the superstrate (D.R. Jackson and N.G. Alexopolous, 1985). As well, partially reflecting sheets (PRSs) have been used as the superstrate layer for gain enhancement (T. Zhao et al., 2005). In addition, artificial magnetic conductors (AMCs) as the ground plane have been able to reduce the microstrip antenna size with a PRS cover (A. Fresidis et al., 2005). On the other hand, a class of novel materials called magneto-dielectrics has recently been introduced which can simulate both high permittivity and permeability, while being low-loss (H. Mosallaei and K. Sarabandi, 2004) (A. Buerkle and K. Sarabandi, 2005). Thus, these novel materials hold promise in antenna miniaturization (H. Mosallaei and K. Sarabandi, 2004) (A. Buerkle and K. Sarabandi, 2005). In this paper, initially a conventional microstrip antenna with the high-permittivity dielectric superstrate is designed. Then, using a periodic structure of metallic patches, acting as an AMC, the antenna size is reduced. Furthermore, another size reduction method for this class of high-gain antennas is proposed using magneto-dielectrics. The results are presented and discussed

APPLICATION OF ARTIFICIAL GROUND PLANES IN DUAL-BAND ORTHOGONALLY-POLARIZED LOW-PROFILE HIGH-GAIN PLANAR ANTENNA DESIGN

Application of artificial ground planes in design of compact cavity-resonance dual-band high-gain antennas is presented. The artificial ground plane consists of periodic strip grating on grounded dielectric slab. A code based on method of moment (MoM) is developed to analyze and design such artificial ground planes. The reflection parameters obtained using the MoM code are employed to characterize the surface impedance of the artificial ground plane for different incident angles and both TE and TM polarizations. Then, this impedance surface is used in transverse equivalent network (TEN) model of the cavity-resonance antenna with high-permittivity dielectric superstrate. Using TEN model radiation properties of such antennas are analyzed. Finally, the antenna with the compact size is designed to demonstrate the maximum directivity. An interesting characteristic of this antennas is that when the antenna ground plane acts as an artificial magnetic conductor the height of the antenna is almost reduced by a factor of two, while its directivity is increased by about 1 dB compared to the conventional antennas of this class having PEC ground plane.

Investigation Into the Effects of the Reflection Phase Characteristics of Highly-Reflective Superstrates on Resonant Cavity Antennas

First we describe two frequency selective surfaces (FSSs), one capacitive and the other inductive, that are designed to exhibit identical high-reflection magnitude at an arbitrary frequency. These two FSSs are then employed as the superstrate of two RCAs having identical microstrip patch source. In order to determine the resonant conditions and obtain approximate values for the antenna directivity, RCAs are initially analyzed using the well known simple ray-tracing method. Next, a full-wave analyzer (ANSOFT Designer v4.0), based on the method of moments (MoM), is utilized to thoroughly analyze the RCAs. Experimental results are provided to support the full-wave simulations, as well. In contrast to the prediction of the ray-tracing modeling, which is merely based on the reflection magnitude of the FSSs, it is pointed out that their phase properties have noticeable effects on the RCA gain. Second, two other RCAs are designed based on high permittivity and high permeability superstrates with identical contrast. There, too, it is shown that the reflection phases of the RCA superstrates determine the air-gap heights which in turn affect the RCA gains.

2-D truncated periodic leaky-wave antennas with reactive impedance surface ground planes

In this paper, first, the idea of using reactive impedance surfaces (RISs) as the ground plane of such leaky wave antennas is proposed and studied through a few examples. Next, the effect of a typical source antenna position on the directivity is investigated through a parametric study. Then, the radiation characteristics of these different antennas are determined and compared. Finally, the conclusion is drawn

Performance enhancement of the compact microstrip antennas using AMC ground planes

In this paper, using AMC ground planes the performance of the miniature microstrip antennas were enhanced in both input impedance bandwidth and gain. Simulations demonstrate the input impedance of 8.6% and aperture efficiency of 104% in the best cases. Measurements on the fabricated antennas are currently being conducted and will be presented at the conference time.