Sanjay Nariyal

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.

An initial investigation on the use of carbon microfibers for conformal transmission lines

The use of carbon micro fiber tow (or bundle) for conformal transmission lines (TLs) is initially investigated in this work. Two different microfiber TLs have been synthesized and tested. A 28.2 mm long microfiber TL was manufactured to demonstrate the wave propagating properties. Once these characteristics were determined, a microstrip TL was prepared by attaching 1oz conducting copper tape to a conformal surface and a similar microfiber TL with the same length and on the same substrate was manufactured. This prototype was then used to compare the propagation characteristics of the microfiber TL to the traditional and well established microstrip TL. Overall, it has been shown that the microfiber TL can support wave propagation in a manner similar to a microstrip TL; however, the attenuation constant appears to be rather large for frequencies above 500 MHz.

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 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.

Strong coupling (crosstalk) between printed microstrip and complementary split ring resonator (CSRR) loaded transmission lines in multilayer printed circuit boards (pcb)

The coupling between a microstrip transmission line (TL) and a complementary split ring resonator (CSRR) loaded TL in a multilayer printed circuit board (PCB) is investigated in this paper. More specifically, how well analytical expressions derived from single cell layout simulations compares with schematic simulations and PCB measurements of a multi-unit cell layout. The power radiating off the PCB was measured as well. This work paves the way for future development of guidelines for reducing the effects of coupling between CSRR loaded TLs and other microstrip TLs.

Scanning characteristics of a self-adapting phased-array antenna on a wedge-shaped conformal surface

The scanning characteristics of a linear five-element antenna array on a wedge-shaped conformal surface is investigated in this work. In particular, the half-power beamwidth (HPBW) of a self-adapting array is studied for various changing conformal surfaces. A general array factor expression is derived and used to compute the HPBW. From these results, the self-adapting limitations of the array are outlined. Finally, analytical computations are validated with measurements.

An autonomous self-adapting conformal array for cylindrical surfaces with a changing radius

Conformal antennas are being used more often in modern wireless communication systems. Because of this increased usage, novel self-adapting arrays have been developed for improving the performance of wireless communication systems that use conformal antennas on changing surfaces. Among the changing surfaces of interest is a cylinder with a varying radius and in this work, the properties of an autonomous self-adapting 4 × 4 conformal array for changing cylindrical surfaces is presented. A sensor circuit is used to measure the radius-of-curvature of the cylindrical surface and this information is used to control phased-shifters in the 4 × 4 conformal array for phase-compensation of the radiation pattern. This array has been denoted as the SELF-adapting FLEXible (SELFLEX) array. Finally, the self-adapting characteristics of the array are validated with measurements and simulations.

On the use of amplitude tapering for pattern correction of conformal (Curved) antennas

Using amplitude tapering to improve the radiation pattern of a conformal antenna on a surface that changes shape with time has been studied and is presented in this paper. In particular, a six element array was attached to a wedge-shape conformal surface with bend angles 10 degrees, 20 degrees, 30 degrees, 40 degrees, 45 degrees and 50 degrees and the amplitudes of each element were changed to improve the broadside radiation pattern. The amplitude coefficients of each element were computed using the array factor of a conformal antenna and a search algorithm.