Wayne A. Shiroma

A full-duplex dual-frequency self-steering array using phase detection and phase shifting

A full-duplex dual-frequency self-steering array using phase detection and phase shifting is presented. By RF decoupling the transmitter and receiver arrays, the proposed system promises greater system efficiency by ensuring a constant transmit power. This also allows for a separate low-frequency interrogating signal capable of various modulation schemes. A two-element prototype is demonstrated with interrogating and retrodirective frequencies of 1.425 and 2.85 GHz, respectively. Retrodirectivity is reported for angles of 0deg, -15deg, and +25deg. The power of the received signal is improved by up to 12 dB for -60deglesthetasles60deg when compared to a conventional two-element array

Continuous Electrowetting of Non-toxic Liquid Metal for RF Applications

Continuous electrowetting (CEW) is demonstrated to be an effective actuation mechanism for reconfigurable radio frequency (RF) devices that use non-toxic liquid-metal tuning elements. Previous research has shown CEW is an efficient means of electrically inducing motion in a liquid-metal slug, but precise control of the slugs position within fluidic channels has not been demonstrated. Here, the precise positioning of liquid-metal slugs is achieved using CEW actuation in conjunction with channels designed to minimize the liquid-metal surface energy at discrete locations. This approach leverages the high surface tension of liquid metal to control its resting position with submillimeter accuracy. The CEW actuation and fluidic channel design were optimized to create reconfigurable RF devices. In addition, solutions for the reliable actuation of a gallium-based, non-toxic liquid-metal alloy (Galinstan) are presented that mitigate the tendency of the alloy to form a surface oxide layer capable of wetting to the channel walls, inhibiting motion. A reconfigurable slot antenna utilizing these techniques to achieve a 15.2% tunable frequency bandwidth is demonstrated.

A 5-GHz high-efficiency class-E oscillator

A 5-GHz high-efficiency feedback oscillator using a class-E amplifier is presented. The oscillator is designed at 5.0 GHz for maximum conversion efficiency using only quasilinear simulation techniques. A maximum conversion efficiency of 59% is measured with an output power of 300 mW. The oscillator can also be biased for a maximum power of 600 mW with a conversion efficiency of 48%.

Self-Actuation of Liquid Metal via Redox Reaction

Presented here is a method for actuating a gallium-based liquid-metal alloy without the need for an external power supply. Liquid metal is used as an anode to drive a complementary oxygen reduction reaction, resulting in the spontaneous growth of hydrophilic gallium oxide on the liquid-metal surface, which induces flow of the liquid metal into a channel. The extent and duration of the actuation are controllable throughout the process, and the induced flow is both reversible and repeatable. This self-actuation technique can also be used to trigger other electrokinetic or fluidic mechanisms.

A Liquid-Metal Monopole Array With Tunable Frequency, Gain, and Beam Steering

A reconfigurable five-element Yagi-Uda monopole array is presented that utilizes pressure-driven liquid-metal elements. There is one centrally located driven element and six parasitic elements in the array, all of which utilize liquid metal so that their physical lengths can be varied. This allows the array to tune to different operational frequencies, vary the number of director elements, and change parasitic elements from reflectors to directors, and vice versa. The measured results show beam steering along a single axis and 1.33 dB of gain tuning at 2.4 and 3.87 GHz.

Coupling suppression in microstrip lines using a bi-periodically perforated ground plane

A perforated ground plane is used to suppress the coupling between adjacent and intersecting transmission lines. Experimental results indicate 40-dB suppression of broadside coupling between two adjacent 50-/spl Omega/ lines. A new option in the design of circuit routing schemes is proposed by demonstrating 28-dB coupling reduction between two intersecting 50-/spl Omega/ lines.

Multipath communications using a phase-conjugate array

A new microwave wireless communications scheme based on a phase-conjugating retrodirective antenna is introduced for maintaining a reliable radio link in a severe multipath environment. The method does not eliminate multipath, but uses it advantageously and is better suited to cope with mobile receivers than other methods. In the ideal case, the negative effects of multipath propagation can be completely avoided and multipath propagation only improves reliability of the radio channel. The principle is experimentally verified at 5.35 GHz and demonstrates that severe fading can be avoided and variation of received signal power can be reduced.

A Two-Element L-Band Quasi-Yagi Antenna Array With Omnidirectional Coverage

The design of a two-element quasi-Yagi antenna array with omnidirectional coverage is presented. The prototype array has a 50% bandwidth (|S11| les -10 dB) of 1.2-2.0 GHz. E-plane and H-plane radiation patterns of the single antenna element are shown at 1.3 and 1.7 GHz. The prototype two-element array exhibits an omnidirectional radiation pattern in the H-plane, with a maximum gain of 4.5 dBi at 1.3 GHz with ripples of less than 2.6 dB and 2.6 dBi at 1.7 GHz with ripples of less than 1.5 dB. The antenna has potential use in broadband mobile applications.

A quadruple subharmonic phase-conjugating array for secure picosatellite crosslinks

A retrodirective array for use in secure picosatellite networks is presented. This is the first reported array that uses quadruple subharmonic mixing which relaxes the requirements on a high-frequency local oscillator. The array demonstrates circular polarization and two-dimensional retrodirectivity for a free-floating satellite environment. Bistatic radiation-pattern measurements demonstrate the effectiveness of the design.

Frequency-tunable slot antenna using continuous electrowetting of liquid metal

This paper presents a frequency-tunable slot antenna which uses liquid metal to vary the electrical length of the radiating aperture. The liquid metal is driven by continuous electrowetting (CEW), a process by which motion is induced in a liquid-metal droplet through the application of a potential gradient across an electrolytic carrier fluid. The process is both fully reversible and repeatable, and the low-voltage electrical driving mechanism allows for simpler integration into electronic architectures than more common hydraulic methods. We believe this is the first instance of CEW being used to create a tunable RF device.