Ryan Y. Miyamoto

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

An active integrated retrodirective transponder for remote information retrieval-on-demand

A retrodirective transponder based on a novel compact phase-conjugating mixer with conversion gain has been developed. The active circuit uses one port for both incoming and outgoing signals, enabling a reduction of circuit size, and the balanced structure provides suppression of undesired signals. By using a modulated local oscillator, the circuit can modulate the received signal in order to retransmit local information to the remote site. A microstrip antenna is integrated with the phase conjugator and the whole system was fabricated on a single substrate, enabling a one-card system. A four-element prototype array with 0.5/spl lambda//sub 0/ array spacing demonstrated excellent measured retrodirectivity. Additionally, a simplified binary-phase-shift-keying signal transmitted by the array is recovered successfully at the source location, demonstrating great potential for remote tagging and wireless sensor applications.

Moving forward in retrodirective antenna arrays

Antenna arrays are individual radiating elements combined so that they function and perform like a single large antenna. Besides high radiating beam directionality, antenna arrays offer the capability to scan the main beam and control sidelobe radiation electronically. Retrodirective antenna arrays, as the name suggests, have a special feature. When receiving a signal from an unspecified direction, the array can automatically transmit a signal response to that same direction without any previous knowledge of the source direction. This function is performed automatically without the use of phase-shifters or digital circuitry. Compared to other array antennas that rely on digital signal processing (DSP) for beam direction control, this approach is much simpler and potentially faster because digital calculation is not needed. The automatic beam control nature of retrodirective arrays is well suited for RFID (radio frequency identification) and microwave tracking beacon applications. The article discusses the basic functionality as well as the ongoing research efforts and developments in retrodirective array architectures. Self-phasing attributes of different arrays are presented, as well as their applicability in practical communication systems.

A reconfigurable active retrodirective/direct conversion receiver array for wireless sensor systems

A reconfigurable active retrodirective/direct conversion receiver array is presented. The system can serve as both a retrodirective array transponder and a direct conversion receiver simply by changing the frequency of the LO applied to the mixers. In the retrodirective array mode, the circuit provides 20 dB gain and 20 dB RF-IF isolation. The mixers perform phase-conjugation and modulation simultaneously. When operating as a direct conversion receiver, both I and Q channels are successfully recovered.

Digital wireless sensor server using an adaptive smart-antenna/retrodirective array

A wireless sensor server is developed based on a reconfigurable active smart-antenna/retrodirective array. The system can serve as both a retrodirective array transponder and a smart-antenna receiver simply by changing the frequency of the local oscillator applied to the mixers, enabling it to utilize its hardware best to suit its communication environment. When operating as a direct-conversion receiver, the receiver array successfully demodulates a quaternary phase-shift keying (QPSK) modulated signal with circuit gain of 7 dB, and E/sub b//N/sub 0/ for BER=10/sup -4/ is approximately 12 dB without any error correction. In the retrodirective array mode, the system provides 20 dB circuit gain and 20 dB radio-frequency/intermediate-frequency isolation at the center frequency as well as phase conjugation, exhibiting excellent retrodirectivity. The mixers perform phase conjugation and modulation simultaneously, enabling the transmission of locally stored data. The local data is successfully extracted by an interrogator.

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.

Active retrodirective array for remote tagging and wireless sensor applications

A retrodirective array based on a novel, compact phase-conjugating mixer with conversion gain has been developed. A 4-element prototype array demonstrates excellent retrodirectivity. A simplified BPSK signal transmitted by the array is recovered successfully at the source location, demonstrating great potential for remote tagging and wireless sensor applications.

A retrodirective array using balanced quasi-optical FET mixers with conversion gain

A novel retrodirective array with intrinsic gain has been developed and demonstrated successfully for the first time. Each heterodyne scattering element employs a balanced FET mixer, which provides effective isolation between RF and IF signals with identical frequencies to realize phase conjugation. A 4-element array has been fabricated, which demonstrated excellent retrodirectivity.

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/.