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Antenna Electronically Steered Using MEMS Phase Shifters

This work contributes to development of relatively inexpensive electronically steerable antennas.

An experimental phased-array microwave antenna assembly includes an array of eight patch antenna elements connected to Microelectromechanical System (MEMS) phase shifters, by means of which the directional radiation pattern of the antenna can be controlled electronically. The antenna and the MEMS-based phase shifters were designed for a nominal operating frequency of 17 GHz. In addition, some 35-GHz MEMS phase shifters were designed, built, and tested. This work is part of a continuing effort to develop relatively inexpensive electronically steerable antennas.

Figure 1. This Reflection-Type Phase Shifter for 17 GHz includes six electrostatically actuated MEMS shunt switches and an integrated CPW Lange directional coupler. The overall dimensions are 2.75 by 4 mm.

The phase shifters are based on the concept of delay lines having various lengths selectable by use of electrostatically actuated MEMS switches. A reflection-delay-line phase-shifter architecture was chosen to make best use of the performance of the MEMS switches and to help minimize the overall dimensions of each phase shifter.

The phase shifters were fabricated on high-resistivity silicon substrates. Both two- and three-bit phase shifters were designed and built. Figure 1 shows one of the 17- GHz two-bit phase shifters as it looks before it is packaged. Each phase shifter includes a coplanar-waveguide (CPW) Lange directional coupler and two delay lines with shunt switches at the locations appropriate for switching the desired increments of phase. The switches are actuated in left-right pairs to obtain in ascending sequence phase increments of 0°, 90°, 180°, and 270°, respectively. Assuming that the delays along the two delay lines are equal, the microwave signals reflected from the closed switches add in phase with each other at the output terminal of the directional coupler with a phase shift equal to twice the delay associated with length of one delay line. The transmission line shown as a vertical line at the top, which is terminated in a CPW short circuit, is used in the 270° switch state.

In tests, the MEMS switches alone exhibited insertion loss <0.3 dB and isolation greater than 20 dB from DC to 40 GHz. The MEMS phase shifters were enclosed in packages that include external connectors for DC switching control signals and for the radio-frequency (RF) signals to be phase-shifted. The 17-dB MEMS phase shifters were tested and found to function with average insertion loss ≈2.5 dB and return loss >20 dB. The average insertion loss of the 35-dB phase shifters was found to be ≈3.3 dB.

Figure 2. These Views of the Antenna Array are representative of stages of assembly and of testing in an anechoic chamber.

Eight packaged two-bit, 17-GHz MEMS phase shifters, tested and selected to be functional and nearly identical in operational characteristics, were mounted on a dielectric board that holds the array of antenna patches and the associated feed array of microstrip transmission lines (see Figure 2). The phase shifters were connected to a switch panel to provide DC switching signals to the MEMS switches. In a test in which the array was operated in a receiving mode, the array functioned well, exhibiting steering of the radiation beam to five available positions: 0°, +25°, -25°, +55°, and -55°.

This work was done by Ronald G. Polcawich, Daniel Judy, Jeffrey S. Pulskamp, and Steve Weiss of the Army Research Laboratory.

ARL-0033

Topics:
Antennas Connectors and terminals Electrical systems Electronic equipment Hazardous materials Hazards and emergency operations Microelectromechanical devices Physical Sciences RF & Microwave Electronics Radiation Sensors and actuators
This Brief includes a Technical Support Package (TSP).
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Antenna Electronically Steered Using MEMS Phase Shifters

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    Magazine cover
    RF & Microwave Technology Magazine

    This article first appeared in the April, 2008 issue of RF & Microwave Technology Magazine (Vol. 2 No. 2).

    Read more articles from the archives here.

    Overview

    The document titled "Ku-Band Radio Frequency Microelectromechanical System Enabled Electronically Scanned Antenna" is a technical report authored by Ronald G. Polcawich, Daniel Judy, Jeffrey S. Pulskamp, and Steve Weiss, published by the U.S. Army Research Laboratory in October 2007. It presents research conducted between May 2005 and April 2006, focusing on advancements in antenna technology utilizing microelectromechanical systems (MEMS).

    The report outlines the development of a Ku-band electronically scanned antenna, which is designed to enhance communication and radar capabilities for military applications. The introduction highlights the significance of electronically scanned antennas in modern warfare, where rapid and precise targeting is crucial. The use of MEMS technology allows for miniaturization and integration of components, leading to improved performance and reliability.

    The experimental procedure section details the methodologies employed in the research, including the design and fabrication processes of the MEMS devices. The report discusses the electrostatic shunt switch and MEMS phase shifter, which are critical components in achieving the desired antenna performance. These devices enable dynamic control of the antenna's beam direction and shape, allowing for agile and adaptive communication systems.

    Results and discussions are presented in a structured manner, with specific sections dedicated to the performance of the electrostatic shunt switch and MEMS phase shifter. The findings indicate that the developed components exhibit promising characteristics, such as low insertion loss and high isolation, which are essential for effective antenna operation. The report also includes a detailed analysis of the antenna's performance metrics, including gain, bandwidth, and efficiency.

    The conclusion summarizes the key findings and emphasizes the potential impact of MEMS-enabled antennas on future military communication systems. The report suggests that these advancements could lead to more versatile and efficient systems capable of meeting the demands of modern military operations.

    Overall, the document serves as a comprehensive resource for understanding the integration of MEMS technology in antenna design, highlighting its implications for enhancing military capabilities. It is approved for public release, ensuring that the findings can contribute to broader research and development efforts in the field of advanced communication systems.

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