Constantine G. Kakoyiannis

Design and implementation of printed Multi-Element Antennas on wireless sensor nodes

The design and implementation of sensor nodes equipped with low-complexity multi-element antennas (MEApsilas) is considered in this work. The design restrictions imposed by the size limits of the sensors, as well as the requirements for the antenna elements employed have been investigated. In the process of implementing such a system, there are a number of critical issues, such as the geometry and arrangement of the elements on the PCB. Accurate simulation models have been built into a full-wave electromagnetic simulator. These models have provided insight into the degree of degradation when two printed radiators share the same small PCB. We have calculated quantities that serve as benchmarks of array performance under realistic operating conditions, such as mutual coupling between elements and the degradation of total radiation efficiency. The prototype MEApsilas have been fabricated, and characterized by measurement in a full anechoic chamber.

A compact microstrip antenna with tapered peripheral slits for CubeSat RF Payloads at 436MHz: Miniaturization techniques, design & numerical results

We elaborate the design and simulation of a planar antenna that is suitable for CubeSat picosatellites. The antenna operates at 436 MHz and its main features are miniature size and the built-in capability to produce circular polarization. The miniaturization procedure is given in detail, and the electrical performance of this small antenna is documented. Two main miniaturization techniques have been applied, i.e. dielectric loading and distortion of the current path. We have added an extra degree of freedom to the latter. The radiator is integrated with the chassis of the picosatellite and, at the same time, operates at the lower end of the UHF spectrum. In terms of electrical size, the structure presented herein is one of the smallest antennas that have been proposed for small satellites. Despite its small electrical size, the antenna maintains acceptable efficiency and gain performance in the band of interest.

Co-design of Antenna Element and Ground Plane for Printed Monopoles Embedded in Wireless Sensors

This work presents the results of a study on Euclidean and fractal small antennas operating in the 2-3 GHz range, which were designed according to the size and bandwidth constraints imposed by wireless multimedia sensor networks. The performance of small antennas depends heavily on their electrical size, which is controlled by the size of the ground plane. We cannot design small antennas for tiny sensor nodes without considering the effect of the ground plane. The tested schemes have been characterized in terms of electrical size, fractional VSWR bandwidth, and broadband total radiation efficiency. A suitable figure-of-merit is also suggested, which is an attempt to gather all fundamental antenna parameters in a single scalar quantity. The results show that a large ground plane does not necessarily produce a better printed antenna. Moreover, each antenna element couples to the ground plane in its own unique way. Meander-line antennas manage to outperform more involved antenna configurations in a fair comparison.

Ground Plane Considerations for Printed Monopole Antennas Integrated into Wireless Sensor Devices

This work presents the results of a parametric study on small integrated antennas for wireless sensor network (WSN) devices operating in the 2-3 GHz range. The performance of small antennas depends heavily on their electrical size, which is controlled by the size of the ground (GND) Plane, since the GND plane is an integral part of the overall radiator. Therefore, we cannot design small antennas for tiny sensor nodes without considering the GND plane effect. We examined the performance of Fractal and Euclidean antenna configurations located on device-sized ground planes. The electrical performance of the tested schemes was characterized in terms of VSWR bandwidth and broadband total radiation efficiency. A suitable figure-of- merit (FOM) is also suggested for a fair comparison. This FOM is an attempt to gather all fundamental antenna parameters in a single scalar quantity. The results show that (a) every element couples to the GND plane in its own unique way, (b) a large ground plane does not produce optimal antenna performance. Although the results shown are for specific element sizes, the parametric analysis aids the designer to estimate the effect of the ground plane for various sizes of sensor nodes.

Comparison of efficient small antennas for wireless microsensors through simulation and experiment

This work presents the results of a study on a set of small antennas for wireless microsensor devices. We consider antennas that are small compared to the wavelength, and can be fitted on a small PCB. The key point regarding small antennas is that their performance is heavily dependent on their electrical size. The product of the bandwidth and the gain is a function of the size of the antenna, so that the gain can only be increased at the expense of bandwidth, and vice versa. Our goal was not only to miniaturize the elements, but to maintain acceptable radiation characteristics as well. A reasonable figure of merit is suggested, in an attempt to gather all fundamental antenna parameters in a single quantity. The behavior of the examined schemes was characterized through simulation and experimental validation.

Hybrid antenna efficiency measurements in fixed-geometry wheeler caps by wideband Q-factor estimation

An end-to-end methodology for wideband efficiency measurements in fixed-geometry Wheeler caps is described. The post-processing of measured data is based on a modified Q-factor method, which exploits inherently wideband Q-calculation formulas that are based on frequency derivatives of antenna input impedance and on the concept of matched VSWR bandwidth. The wideband WCap/Q-factor method is useful both for narrowband and wideband antennas, regardless of whether the latter exhibit closely or widely spaced multiple (anti)resonances. Experimental verification of the method includes the characterization of a small antenna in a 40%-wide, cavity-resonance-free band, as well as the measurement of a multi-band antenna in an 8:1 band (156%). Despite the bandwidth, the requirements for the hybrid WCap/Q-factor method are a properly designed cavity and two full-band input impedance measurements on a vector network analyzer.

Coupling and Correlation Reduction in Compact Arrays for WSN Nodes via Pre-fractal Defected Ground Plane

We studied compact printed arrays built with sinusoidal monopoles. The antennas were designed at 2-3 GHz according to the size and bandwidth constraints of broadband sensor networks. Their performance was characterized in terms of VSWR bandwidth, broadband radiation efficiency, mutual coupling and broadband envelope correlation. Results show that densely-packed compact arrays feature controllable element detuning, whereas envelope correlation stays below 0.5 even for lambda 0/10 spacing. Finally, if coupling and correlation suppression is needed, we describe a simple yet effective technique that offers multi-decibel gains. It is based on disturbance of the ground currents by insertion of a defect.