Darren S. Goshi

A compact digital beamforming SMILE array for mobile communications

A compact spatial multiplexing of local elements (SMILE) scheme smart antenna array with adaptive beamforming is presented. Low-noise amplifiers are implemented as switching elements to maintain a low system noise figure and allow fast switching. The switching scheme effectively reduces N RF channels to one, reducing the amount of costly RF hardware by a factor of N. The sampling rate must be higher than the signal bandwidth based on the Nyquist criterion to ensure proper restoration of the original signal. Measured data for destination of arrival estimation, beamforming, and digital data recovery demonstrate the capability and benefits of digital beamforming with this architecture.

A secure high-speed retrodirective communication link

A retrodirective array with adaptive interference rejection is developed to introduce additional functionality to conventional retrodirective arrays. This is the first retrodirective array to present an interference rejection mode, creating a secure wireless communication link. The array uses digital signal processing initially and periodically to determine the location of a jamming signal and directs sub-arrays to form a null in the corresponding direction. The continuous analog self-tracking of a desired source maintains the retrodirective arrays high-speed advantage over conventional smart antennas, requiring no computational algorithms for direction of arrival estimation and beamforming. It is demonstrated that interference is highly detrimental to retrodirective array performance, validating the need for such interference rejection. The application of this architecture is verified through a link test analyzing the reception and transmission of modulated data.

Integrated mixer based on composite right/left-handed leaky-wave antenna

This paper presents a novel balanced mixer receiver front-end design based on a metamaterial structure applicable to differential-/common-mode excitation. This metamaterial structure functions as a leaky-wave antenna and provides intrinsic common-mode suppression. Low LO leakage and high RF to LO isolation are achieved without additional filters for the LO and RF paths. The metamaterial is based on a unit-cell which under a differential-mode excitation behaves like a composite right/left-handed (CRLH) metamaterial. In contrast, the metamaterial unit-cell is below cut-off under a common-mode excitation. Experimental results are used to verify the proposed metamaterial’s differential-/common-mode characteristics. The metamaterial is integrated with a balanced mixer design resulting in an operation frequency range of 1.96 GHz – 2.40 GHz with an optimum mixer conversion loss of 21.1 dB at 2.4 GHz.

Optimization and Modeling of Sparse Conformal Retrodirective Array

Conformal scanning arrays are important for scanning ranges beyond ±90 degrees and the retrodirective array (RDA) is known as a promising candidate for this application. We discuss the optimization of a previously realized conformal sparse RDA by means of the genetic algorithm, and the RDA numerical model that is used in this approach. In particular, we improve the numerical model of the RDA by identifying practical factors that previous model failed to account for. The impact of each practical factor on the RDA monostatic pattern is visualized, and the improved model provides much better prediction of the monostatic pattern.

A retrodirective array with interference rejection capability

A retrodirective array with interference rejection capability is presented. Signals from two sources (one desired and one interfering) are first detected and then a null is formed in sub-arrays at each element in the retrodirective array and directed toward the unwanted signal. The null-forming sub- array pattern can be multiplied to the retrodirective pattern through application of the principle of pattern multiplication. The system continues to track the desired signal through its purely analog retrodirective function, requiring no digital signal processing and maintaining almost instantaneous self-tracking. Demonstration of interference suppression shows promise in furthering the functionality of retrodirective arrays in addition to the already high-speed self tracking benefits. Index Terms — Interference rejection, null-scanning, phased arrays, retrodirective arrays.

A Sparse Retrodirective Transponder Array With a Time Shared Phase-Conjugator

With the recent emergence of various radio frequency identification (RFID) applications, the desire for simpler, more efficient, and lower cost passive transponders has increased. Retrodirective arrays have been demonstrated as a good candidate for such systems due to their unique function of high-speed, automatic source tracking. A four-element, high-performance retrodirective transponder array is presented in this paper. The architecture uses a sparse array design to reduce the amount of radiating elements. A time sharing switching feature is used in conjunction with this architecture to further reduce RF hardware requirements and cost of the system. The switching network can also serve as a built-in modulator for simple data transfer tasks.

A Sparse Ka-Band Digital Beamforming Integrated Receiver Array

Digital beamforming smart antennas offer additional flexibility and precision within the digital domain in terms of beam control, source detection and calibration over conventional analog systems. With the continuous advancement in digital technology, specifically with the size and speed of analog to digital converters and FPGAs, the digital transceiver will persist to spread widely in use. We develop an 8-element sparse array design and implement it into Ka-band digital beamforming receiver architecture. The sparse design is briefly described. The array is realized in integrated planar microstrip circuitry with active MMIC surface mount die chips. Pattern synthesis and data recovery are demonstrated to validate its performance as a digital beamforming system

Interleaved Retrodirective Sub-Arrays for Null-Steering Interference Rejection

Retrodirective arrays have been established as a unique type of high-speed, self-steering array with the flexibility to integrate with a wide range of communication functions. However, their automatic phase reversal function prohibits the use of channel weighting prior to retransmission, greatly limiting its beamforming capabilities. In this work, an interleaved sub-array architecture is proposed to introduce a null-steering feature into retrodirective arrays for interference rejection. The system maintains its simple high-speed operation with a Butler matrix receiver rather than a digital receiver. A minimum number of phase shifters are required for null-steering. An 8-element prototype is fabricated to demonstrate this new feature. Measured pattern results validate the effectiveness of the introduced null-steering capability.

A Scheme for Hardware Reduction in Wireless Retrodirective Transponders

Typical transponders operate with an omnidirectional response to interrogation, with a single antenna element, resulting in inefficient use of available power. Conventional retrodirective array architectures require phase-conjugators at each element, placing a heavy burden on the amount of active circuitry required and limited real estate. In this paper, a switching feed network is integrated into a retrodirective array architecture to offer an N to 1 reduction in the amount of required phase-conjugating hardware, and therefore cost, while offering the directivity of an array architecture and maintaining omni-directional receive and transmit coverage. A four-element retrodirective transponder array is realized under this switching configuration. The introduced switching network can also serve as a built-in modulator for simple data transfer tasks

A Sparsely Designed Retrodirective Transponder

Retrodirective arrays have shown great potential for use as wireless transponders due to their automatic source tracking ability. A retrodirective transponder based on a sparse array is presented. The architecture uses a sparse array design to reduce the amount of elements, and thus circuitry required. A genetic algorithm is used to determine the optimal element positions in the array. The sparse architecture is compared with the uniform array architecture. Measured results verify the sparse concept as well as retrodirectivity