Harish Rajagopalan

Conformal Ingestible Capsule Antenna: A Novel Chandelier Meandered Design

This paper investigates a conformal antenna for the ingestible bio-telemetric capsule system. This system has the potential to provide real-time biological information from within the human body via a radio frequency link. The balanced planar meandered dipole (concept used for antenna miniaturization through space-filling) is discussed along with the offset planar meandered dipole, which facilitates better matching. The conformal chandelier meandered dipole antenna (CCMDA), which is an extension of the offset planar meandered dipole and envelopes the capsule surface, is then investigated. The return loss, input impedance, and radiation pattern characteristics of the CCMDA are discussed in detail at the operating frequency of 1.4 GHz. Additionally, electrical components (specifically the batteries) are modeled inside the capsule to investigate their effects on the conformal antenna performance in free space. The capsule antenna is then inserted into a simple box model (a simplification of the human torso) and a 4-mm precision human-body model (Ansoft) where the detuning effects are observed and discussed. Finally, a circularly polarized receiver antenna design consisting of orthogonal dipoles is suggested which provides polarization diversity and is miniaturized to fit into a personal digital assistant (PDA) for portability of the data telemetric link.

RF MEMS Actuated Reconfigurable Reflectarray Patch-Slot Element

This paper describes the design of a reconfigurable reflectarray element using commercially available radio frequency micro-electromechanical system (RF MEMS) switches. The element consists of a microstrip patch on the top surface and a slot with an actuated variable length in the ground plane. RF MEMS switches are mounted on the slot to electronically vary the slot length by actuating the switches and thus obtaining the desired phase response. Waveguide measurements and high frequency structure simulator (HFSS) simulations are used to characterize the reflectarray element. The four MEMS switches element gives 10 independent states with a phase swing of 150 deg and a loss variation from 0.4 dB to 1.5 dB at 2 GHz (more switches can provide larger phase shift). The loss is mainly attributed to the dielectric loss and the conductor loss, which occur due to the relatively strong electric fields in the substrate region below the patch and the large currents on the top surface of the patch, respectively, close to the patch resonance. Detailed analysis is performed to characterize the effect of the switches by taking into consideration the switch model and wire bonding effects.

MEMS Reconfigurable Optimized E-Shaped Patch Antenna Design for Cognitive Radio

Reconfigurable antennas offer attractive potential solutions to solve the challenging antenna problems related to cognitive radio systems using the ability to switch patterns, frequency, and polarization. In this paper, a novel frequency reconfigurable E-shaped patch design is proposed for possible applications in cognitive radio systems. This paper provides a methodology to design reconfigurable antennas with radio frequency microelectromechanical system (RF-MEMS) switches using particle swarm optimization, a nature-inspired optimization technique. By adding RF-MEMS switches to dynamically change the slot dimensions, one can achieve wide bandwidth which is nearly double the original E-shaped patch bandwidth. Utilizing an appropriate fitness function, an optimized design which works in the frequency range from 2 GHz to 3.2 GHz (50% impedance bandwidth at 2.4 GHz ) is obtained. RF-MEMS switch circuit models are incorporated into the optimization as they more effectively represent the actual switch effects. A prototype of the final optimized design is developed and measurements demonstrate good agreement with simulations.

On the Reflection Characteristics of a Reflectarray Element with Low-Loss and High-Loss Substrates

This paper revisits the loss phenomenon (particularly, the dielectric loss) for a microstrip patch in reflectarray mode, and discusses the reflection characteristics (magnitude and phase) for a reflectarray element with low- and high-loss substrates. First, the dielectric losses that occur in a lossy slab backed by a perfect electric conductor are both analytically and numerically investigated. Using similar numerical analysis, the reflectarray element (a patch on top of a slab backed by a conductor) is characterized, based on dielectric losses and reflection behavior. It is observed that for low-loss substrates, the dielectric loss decreases with increasing substrate thickness (as previously suggested in the literature). More importantly, for high-loss substrates, the dielectric loss no longer follows the expected trend (decreasing loss with increasing substrate thickness). The dielectric loss becomes a complex phenomenon, involving the dielectric loss tangent and substrate thickness. It is therefore noted that it is important to recognize the well-behaved and misbehaved phase-swing region for high-loss substrates for a reflectarray element. A simple circuit-model representation is provided for the reflectarray element. The anomalous phase behavior observed for high-loss substrates is explained using pole-zero analysis. Waveguide measurements are performed to quantify these reflectarray losses for low- and high-loss substrates. Finally, the loss mechanisms in a patch reflectarray (scattering mode) are compared to a patch antenna (radiation mode), using parameters such as reflection power and radiation efficiency, and similar loss mechanisms for both structures are apparent.

Nature-Inspired Optimization Techniques in Communication Antenna Designs

This paper summarizes the primary features inherent in current optimization methods typically applied to antenna designs and demonstrates their effectiveness by applying particle swarm optimization (PSO), a nature-inspired global optimization technique, to novel antenna design solutions in wireless communications. The concept of the PSO technique is briefly introduced and an outline of the important parameters that are utilized is summarized. Next, an implementation strategy combining PSO with numerical algorithms for electromagnetic solutions, namely the finite element method (FEM) and the method of moments (MoM), is discussed. In both realizations (PSO-FEM and PSO-MoM), the PSO technique drives the design variables, such as the antenna dimensions, geometrical features, etc., and the full-wave electromagnetic analysis engines evaluate the fitness function for the optimizer. Optimized antenna designs including a multiband handset antenna and an E-shaped patch antenna for circularly polarized (CP) applications are presented. Measurement results of prototype optimized designs are shown to demonstrate the functionality and effectiveness of the methodologies presented in this paper.

Dielectric and Conductor Loss Quantification for Microstrip Reflectarray: Simulations and Measurements

The conductor and dielectric loss mechanisms in microstrip reflectarray are described using simulation models and waveguide measurements. The dielectric constant and loss tangent variation with frequency is obtained for a particular substrate using existing datasheets. Variable size patch reflectarray element was studied for loss characterization. The effect of these losses is characterized and the potential cause for the loss phenomenon is provided. It is observed that the dielectric loss and copper loss occur near the patch resonance due to strong electric fields in the substrate region below the patch and the large currents on the top surface of the patch, respectively.

Ingestible RFID bio-capsule tag design for medical monitoring

The use of electromagnetics in medicine has facilitated the design of advanced biological systems and has also helped evolve medical treatments and diagnostic procedures significantly [1]. Electromagnetics, in particular radio frequency identification (RFID), can become a major player in medicine and thus, in health care. Due to the non line-of sight operation, larger read range and ability to store more information, RFID tags serve as a possible replacement to bar codes. By implementing RFID technology in health care and medicine, the dream of continuous medical monitoring of patients, storage of patient statistics, medicine tracking, drug delivery control and efficient medical management can be realized. RFID wrist-bands have been successfully used to identify patients in hospitals. Implantable RFID chips [2] have been reported for storing information and tracking location.

Design and Implementation of Broadband MEMS RHCP/LHCP Reconfigurable Arrays Using Rotated E-Shaped Patch Elements

A novel broadband RHCP/LHCP reconfigurable patch antenna array using an E-shaped patch antenna element is investigated. By applying particle swarm optimization (PSO), a challenging, combined S11-AR bandwidth of 17% was achieved and verified through measurement for the isolated element using MEMS switches at an overall substrate thickness of 0.092λ0. The achieved bandwidth is significantly higher than the current state-of-the-art in single-layer, single-feed circularly polarized (CP) patch element designs with similar substrate thickness. A small percentage of the upper frequency band experiences a pronounced beam squint similar to other thick substrate CP patch antennas. To overcome the beam squint, a novel rotated-element configuration is implemented to force pattern symmetry. Derivations of pattern symmetry and network effects are also shown. The final design prototype using rotated elements provides a measured 20% S11-AR bandwidth with good radiation pattern stability.

On Understanding the Radiation Mechanism of Reflectarray Antennas: An Insightful and Illustrative Approach

This article presents a unique point of view for microstrip reflectarrays. Through the effective utilization of graphical visualization of the scattered fields from the reflectarrays, one can gain insightful understanding into the fundamental workings of these antennas. The most important part of the reflectarray analysis and design is the accurate characterization of the individual reflectarray element for reflection phase performance. Using this visualization approach, reflectarray elements are characterized in unit-cell environments. This exercise aids in identifying the important geometrical parameters of the element that contribute to the reflection phase shift. These elements are then placed in an actual reflectarray environment, and the performance of the reflectarray is evaluated through full-wave electromagnetic simulations and measurements. It is validated that this technique can be successfully used to analyze, design, and potentially diagnose reflectarray antennas.

A novel reflector surface distortion compensating technique using a sub-reflectarray

In this paper, the concept of a novel reflector surface distortion compensating approach using a sub-reflectarray is introduced.