Billy Wu

On the Selection of the Number of Bits to Control a Dynamic Digital MEMS Reflectarray

The benefit of low loss exhibited in utilizing MEMS variable capacitors in a reconfigurable reflectarray is undermined by the inconsistency of the fabricated devices. A digitally controlled reflectarray with MEMS capacitive switches is proposed. This paper aims to determine an appropriate number of phase shifting bits for such implementation. Using array theory, the influence of the number of bits on the beam pointing performance is evaluated. A common feed horn is used to illuminate the reflectarrays. In addition, broadside plane wave illumination is also considered for comparison with existing works in phased arrays. Though at certain scan angles the results are different from those for traditional phased arrays, in general the results are found to be similar. This information lays the groundwork for designing a cost-effective digital MEMS reflectarray cell.

A Pneumatically Controlled Reconfigurable Antenna With Three States of Polarization

Many of the existing antennas described in current literature utilize PIN diodes to achieve switchable polarization. In realizing more elaborate reconfigurable antennas, the biasing structures for these DC-controlled components become more complex, which leads to limitations in the RF design as well as losses and undesired radiation. Other reconfigurable technologies, such as MEMS switches and liquid crystals, could be chosen for a particular application depending on various trade-offs, for example efficiency and ease of implementation. An alternative system is a recently developed scheme of using pneumatically controlled solid dielectric slugs, which is low-loss and immune to RF distortion, and eliminates the need for DC biasing structures. To demonstrate the viability of this system, it was incorporated in the design of a reconfigurable ring slot antenna capable of three polarization states (LP/LHCP/RHCP) at 2.4 GHz. The measured axial-ratio bandwidth was 5%, which is comparable to similar low-profile antennas. The simulated and measured antenna performance at all three states showed strong correlation. The pneumatic actuation of four slugs inside a channel to realize the three different states was successfully implemented, demonstrating that pneumatic slug control technology is suitable for inclusion in reconfigurable antennas.

Configuration design of MEMS switches in a digitally controlled reflectarray element

This paper introduces a circuit of MEMS capacitive switches, which yields a set of phase states that are close to being equally separated. The optimal capacitance values of the switches are determined using a genetic algorithm (GA). In addition, a ternary design for controlling the switches is proposed to reduce the number of control lines required without decreasing the number of realizable phase states.

Design and Fabrication of a Ternary Switch for MEMS-Controlled Reflectarray Elements

For a digitally controlled reflectarray consisting of many elements, the cost and complexity increase considerably with every additional control line in each element. A ternary design for controlling microelectromechanical systems (MEMS) capacitive switches is proposed to reduce the number of lines required without decreasing the number of states realized. Three distinct capacitance states are realized with custom-fabricated shunt switches having different pull-in voltages. To increase the versatility of the concept, the capability of designing the pull-in voltage and the capacitance of a switch independently of each other is also demonstrated. This design can be applied to any digital tuning circuit involving MEMS switches for the reduction of biasing layout complexity.

Comparing the simulated and measured results of a pneumatically controlled antenna

The simulated and measured results of a reconfigurable antenna with switchable polarization, using pneumatic control of solid dielectric slugs, are compared. The antenna structure and materials used for fabrication are described. The realization of each polarization state (LP/LHCP/RHCP), given a specific manipulation of the slug positions, is explained. The gain values, antenna patterns, and axial ratio and impedance bandwidths were found to be very consistent between simulations and measurements.

Reconfigurable ring slot antenna with polarization diversity using pneumatic control

In designing reconfigurable antennas, pneumatic control of solid dielectric slugs offers an alternative to established technologies of reconfigurability, such as PIN diodes and MEMS switches, that require biasing feedlines embedded in the radiating structures. A pneumatically controlled ring slot antenna capable of switching between LP, LHCP, and RHCP is described, in which the dielectric slugs and their enclosing channel are fabricated on a different layer. The positions of the slugs, controlled by the pressure gradient within the channel, determine the polarization state. An axial ratio bandwidth of 5% was measured, which is slightly greater than those of similar antennas with polarization diversity using PIN diodes. The measured performance was found to be similar to existing reconfigurable antennas, demonstrating that a device using pneumatic actuation is a viable alternative.

Determining an appropriate number of bits for a digitally controlled reflectarray cell with MEMS switches

The trade-off between the reduction in directivity and the number of bits of a digitally controlled reflectarray cell was considered for the case of broadside plane wave illumination. The study was performed with a number of simplifying assumptions to allow for fast analysis and insight into general trends. A 3-bit design was determined to be a good compromise between beam pointing accuracy and cell biasing layout simplicity. This information lays the groundwork for the physical design of the cell.

Design of a pneumatically controlled frequency switchable patch antenna

A pneumatically controlled patch antenna with resonant frequency that can be switched to either 3.05 GHz or 5 GHz is introduced. The resonant frequency of the device is determined by the dimension of the patch that is excited. To select a particular frequency, a pneumatically-operated copper-plated swinging arm is moved to cover one of two orthogonal slots on the ground plane. The uncovered slot allows energy to be coupled from the microstrip feedline to the corresponding dimension of the patch. Simulated results from HFSS are provided.

Reconfigurable antenna designs using micro-pneumatic control of dielectric slugs

The designs of a single-fed circularly-polarized (CP) microstrip antenna with switchable polarization and a tunable dielectric resonator antenna (DRA), using metal-plated dielectric slugs, are described. The scheme of micro-pneumatic control of solid slugs presents an alternative to the existing methods in realizing reconfigurable antennas. The radiation polarization of the CP antenna and the resonant frequency of the DRA are determined by the position of the slugs inside the substrate. Both antennas have been simulated and the results demonstrate the viability of this new antenna reconfiguration method.