Grant S. 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

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.

A high-directivity transponder using self-steering arrays

A high-directivity transponder system based on self-steering arrays is introduced. The system consists of retrodirective and self-null-steering arrays. When interrogated, the retrodirective array steers a beam containing data toward the interrogator, while the null-steering array points a null toward the interrogator and a jamming signal in all other directions. The system effectively provides super-high directivity, disabling interception.

A 16-element two-dimensional active self-steering array using self-oscillating mixers

A 16-element two-dimensional (2-D) retrodirective array using self-oscillating mixers (SOMs) is presented. SOMs allow for easier implementation of larger 2-D arrays by eliminating the complex local-oscillator (LO) feed structure. A 4 /spl times/ 4 element retrodirective array using SOMs is demonstrated at an LO frequency of 7.68 GHz. Each element is phased locked at the LO frequency with an accompanying RF frequency isolation of 17.9 dB between adjacent horizontal elements and 22.2 dB between adjacent vertical elements. A -10-dBm external injection-locking signal is applied to reduce the phase noise of the 16-element array to -68.2 dBc/Hz at 10-kHz offset. Retrodirectivity is observed in the /spl phi/=0/spl deg/, /spl phi/=-45/spl deg/, and /spl phi/=-90 plane for scattering angles of /spl theta/=-15/spl deg/, /spl theta/=0/spl deg/, and /spl theta/=+30/spl deg/.

A High-Directivity Combined Self-Beam/Null-Steering Array for Secure Point-to-Point Communications

A high-directivity combined self-beam/null-steering array for secure point-to-point binary phase-shift keying communications is introduced. The system provides high directivity and reduced probability of interception using just two antenna elements. Using quadrature phase-shift keying modulators allows for compact single-layer fabrication. The 2.4-GHz prototype is tested at interrogation angles of 0deg, -10deg, and +20deg, and demonstrates high signal-to-interference ratio directivity, completely disabling interception plusmn20deg from the direction of the interrogator. The system should find various applications where secure communications are required

Antennas for distributed nanosatellite networks

Distributed nanosatellite networks have the advantage of being reconfigurable, redundant, and readily deployable. Two types of antennas designed for this application are presented: a flexible UHF antenna for Earth-to-satellite communications, and an X-band retrodirective array for secure satellite-to-satellite crosslink communications.

An active self-steering array using self-oscillating mixers

A retrodirective array using self-oscillating mixers (SOMs) is presented. SOMs allow for easier implementation of larger two-dimensional arrays by eliminating the complex local-oscillator (LO) feed structure. A four-element linear retrodirective array using SOMs is demonstrated at a LO frequency of 8.87 GHz. Each element is successfully phased locked at the LO frequency while 33 dB of isolation between adjacent elements is measured at the RF frequency. The LO power generated by a single SOM element at the fundamental frequency is +3 dBm. Retrodirectivity is successfully observed for scattering angles of -30/spl deg/, 0/spl deg/, and +15/spl deg/.

Retrodirective antenna technology for CubeSat networks

In the spring of 2003, the University of Hawaii (UH) began participation in the University NanoSat Program, a multi-university effort sponsored by NASA and the USA Air Force Research Laboratories to encourage small-satellite research and development. Undergraduate engineering students at UH have been involved in small-satellite development for the past two years, particularly for a class of picosatellites known as CubeSat, which has a mass no greater than 1 kg and a volume of 1000 cm/sup 3/.