Sayan Roy

A Self-Adapting Flexible (SELFLEX) Antenna Array for Changing Conformal Surface Applications

A phased-array test platform for studying the self-adapting capabilities of conformal antennas is developed and presented. Specifically, a four-port 2.45-GHz receiver with voltage controlled phase shifters and attenuators is designed along with four individual printed microstrip patch antennas attached to a conformal surface. Each antenna is connected to the corresponding receiver port with a flexible SMA cable. It is shown that with appropriate phase compensation, the distorted radiation pattern of the array can be recovered as the surface of the conformal array changes shape. This pattern recovery information is then used to develop a new self-adapting flexible 1 × 4 microstrip antenna array with an embedded flexible sensor system. In particular, a flexible resistive sensor is used to measure the deformation of the substrate of a conformal antenna array, while a sensor circuit is used to measure the changing resistance. The circuit then uses this information to control the individual voltage of the phase shifters of each radiating element in the array. It is shown that with appropriate phase compensation, the radiation properties of the array can be autonomously recovered as the surface of the flexible array changes shape during normal operation. Throughout this work, measurements are shown to agree with analytical solutions and simulations.

Phase-Compensated Conformal Antennas for Changing Spherical Surfaces

Self-adapting conformal antennas for changing spherical surfaces are investigated in this work. More specifically, the theory on the relationship between the radius of the spherical surface, element spacing of the conformal array and required phase compensation is developed. Initially, for theoretical validation, a 4 × 4 phased array antenna is assembled with individual microstrip antennas used as the radiators at 2.47 GHz. Each antenna is connected to a commercially available voltage controlled phase shifter with identical SMA cables and then each phase shifter is connected to a port on a sixteen-way power divider. This phased-array antenna allows for convenient placement of individual patches on the spherical surface and precise phase control. For further validation, a second 4 × 4 phased-array antenna with embedded phase shifters and a sensing circuit is manufactured. The sensing circuit is used to measure the radius of curvature of the spherical surface and use this information to autonomously apply the appropriate phase compensation, based on the previous theoretical developments, to recover the radiation pattern of the array for different spherical surfaces at 2.47 GHz. Overall, good agreement between theory, simulation and experimental data is shown and that it is possible to recover the radiation pattern autonomously.

Analysis of the Noise Voltage Coupling (Crosstalk) Between Right-Handed and Composite Right/Left-Handed (CRLH) Transmission Lines on Printed Circuit Boards

One aspect of the electromagnetic compatibility (EMC) analysis of RF circuitry is the accurate modeling of the coupling between printed transmission lines. Correct modeling of this coupling is essential because unwanted noise voltages can be substantial and create adverse effects on sensitive components. Recently, the development of composite right-/left-handed transmission lines (CRLHTLs) has received considerable attention due to the unique propagation characteristics. Because of this increase in applications, CRLHTLs are being implemented in RF systems with other printed circuitry, such as microstrip transmission lines, in very close proximity. In many of these instances, the coupling may not be intentional. To study this interaction between CRLHTLs and other printed circuitry from an EMC point of view, this paper presents derived analytical expressions for computing the nearand far-end voltage coupling between right-handed (printed microstrip transmission lines) and CRLHTLs. More specifically, these expressions are used to determine the nearand far-end voltages weakly coupled to the CRLHTL when the conventional microstrip right-handed transmission line is driven with a source and terminated with a load. These expressions are then used to illustrate how the induced voltages on the CRLHTL can be reduced by the capacitance and inductance values that support left-handed propagation. This can be a useful alternative to conventional shielding. Furthermore, design guidelines and tradeoffs are presented on the layout of CRLHTL near other printed transmission lines. The expressions derived in this paper are validated with simulations and measurements.

Half-power beamwidth of a self-adapting conformal 1 × 4 microstrip array

A new four element self-adapting conformal microstrip antenna array with an embedded sensor system and voltage controlled phase shifters is introduced. The sensor systems consists of a flexible resistive sensor used to measure the shape of the conformal surface and circuitry for measuring the resistance of the sensor. The voltage controlled phase shifters are controlled by the sensing circuitry and are used to introduce a specific phase compensation that dynamically preserves the radiation pattern of the array as the shape of the antenna changes. Specifically, in this work, the autonomous recovery of the half-power beamwidth (HPBW) of the four element array is investigated.

A New Printed Quasi-Landstorfer Antenna

A recently developed compact planar Quasi-Landstorfer antenna is presented here. For this design, the reflector element was removed from the original Landstorfer antenna and the ground plane was modified to have the same behavior as the removed reflector element. By using the ground plane as a reflector, the overall size of the planar Landstorfer antenna was reduced by 44%. The smaller prototype Quasi-Landstorfer antenna presented here had a measured return loss of -42.7 dBi and measured gain of 6.6 dBi at the resonant frequency of 2.44 GHz. Furthermore, a Quasi-Landstorfer antenna design with an extended ground plane was also investigated and is presented. Simulations and measurements of a prototype antenna have shown that by adding conducting strips to the end of the ground plane, approximately 1 dBi of gain could be added without changing the overall dimensions. Throughout this work, it is shown that the measured values agree well with simulations.

A note on the fundamental maximum gain limit of the projection method for conformal phased array antennas

New expressions for comparing the maximum gain of a phase-compensated conformal antenna have been analytically derived and validated to measurements. In particular, the newly derived analytical expressions were validated with a conformal phased-array antenna prototype attached to a wedgeand inverted-wedged shaped surface. Phase-compensation techniques based on the projection method were used to correct the radiation pattern. These expressions can be used by a designer to predict the maximum theoretical gain of a phase-compensated conformal antenna on a surface that changes shape with time.

A model for 3D-printed microstrip transmission lines using conductive electrifi filament

New research on wearable electronics, domotics, flexible circuits, and RF applications on conformal surfaces have used the advancements of material science and additive manufacturing technology. Parallelly, the limited design specifications of industrially available PCB substrates (i.e., flat substrates) has stimulated a de novo exploration for more complex electronic circuits with versatile geometries. In this paper, the development of a microstrip transmission line using additive manufacturing technology and Electrifi conductive filament is reported for the first time. The simulated and measured transmission properties of the design are also compared and presented.

A dual band balanced planar inverted F antenna (PIFA) for mobile applications

A new low profile dual-band balanced planar inverted F antenna with meandered lines resonating in the 1800 MHz and 2100 MHz bands is proposed. The antenna size is 50 × 12 × 10mm3 allowing it to be easily housed in mobile handsets. The return loss, radiation pattern, gain and current distribution of the proposed antenna is presented. Furthermore, agreement between simulations and measurements is shown for a balanced feed with zero phase difference. Then, the design with differential feeding is simulated for various feeding phase angles and the benefits of minimized current flow on the ground plane are highlighted.

Gain limits of phase compensated conformal antenna arrays on non-conducting spherical surfaces using the projection method

Previously, it has been shown that the projection method can be used as an effective tool to compute the appropriate phase compensation of a conformal antenna array on a spherical surface. In this paper, the projection method is used to study the gain limitations of a phase-compensated six-element conformal microstrip antenna array on non-conducting spherical surfaces. As a metric for comparison, the computed gain of the phase-compensated conformal array is compared to the gain of a six-element reference antenna on a flat surface with the same inter-element spacing and operating frequency. To validate these computations, a conformal phased-array antenna consisting of six individual microstrip patches, voltage controlled phase shifters and a power divider was assembled and tested at 2.22 GHz. Overall, it is shown how much less the gain of the phase-compensated antenna is than the reference antenna for various radius values of the sphere.

On using biocomposite filaments to additively manufacture substrates for microstrip transmission lines

As the requirements for wireless systems become more complex, researchers and designers are turning to unique technologies for solutions. In support of this, a new design that uses biocomposite filaments to additively manufacture substrates for microstrip transmission lines is presented here. In particular, the measured complex permittivity of the material manufactured with three different biocomposite filaments; namely Buzzed, Entwined and Wound Up is determined. This information is then used to design prototype 50Ω microstrip transmission lines. Overall, simulations and measurements compare well and show that biocomposite filaments can be used to support propagation up to 3.0 GHz on the microstrip transmission lines.