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Individual faculty and institutions regularly develop novel educational materials that could benefit others, but these innovations often fail to gain traction outside the developers' circle as barriers to adoption are numerous. We present evidence that development targeting adaptation, rather than complete adoption, of innovative materials and methods may be a more successful approach. Specifically, if faculty members from multiple institutions are involved in the development, agility across diverse academic requirements and institutional cultures informs that process. in the described example, faculty members from multiple institutions developed online learning modules based on their individual areas of expertise related to the topic of wireless sensor networks. The modules integrated learning of systems thinking with traditional sub-disciplines in electrical and computer engineering and were delivered in a blended-learning format. While faculty from three institutions developed the original content for a single course, materials have been successfully utilized in multiple courses at several institutions.

The ability of a phase-conjugating array (PCA) to reduce fading in single-reflector, dual-reflector, and blocked-line-of-sight multipath environments is presented. Compared to a reference four-element antenna array, the PCA improves worst case signal fading by as much as 39 dB. Agreement between the experimental results and a ray-tracing model is observed, verifying the model as a viable method for characterizing array performance in multipath environments. Index Terms--Beam steering, fading channels, multipath channels, phase conjugation.

2-D retrodirective array hased on phase deteclion and heterodyne scanning is presented. The system integrates two single voltage-controlled oscillator phase-shifting networks that are autonomously controlled via a phase-detecting array and control circuit that eliminates the [R.sup.4] path loss typical of other retrodirective arrays. Retrodirectivity is reported for angles of 0 [degrees], + 15 [degrees], and -15 [degrees] at a transmitting frequency of 6.5 GHz. Index Terms--Phased arrays, retrodirective arrays.

The design of a two-element quasi-Yagi antenna array with omnidirectional coverage is presented. The prototype array has a 50% bandwidth ([absolute value of [S.sub.11] [less than or equal to] -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 [+ or -] 2.6 dB and 2.6 dBi at 1.7 GHz with ripples of less than [+ or -] 1.5 dB. The antenna has potential use in broadband mobile applications. Index Terms--L-band antenna, microstrip antenna, omnidirectional antenna, quasi-Yagi.

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 0[degrees], -10[degrees], and +20[degrees], and demonstrates high signal-to-interference ratio directivity, completely disabling interception [+ or -]20[degrees] from the direction of the interrogator. The system should find various applications where secure communications are required. Index Terms--Digital communication, microwave receivers, phase conjugation, phased arrays, transponders. Digital Object Identifier 10.1109/TMTT.2007.895405

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 0[degrees], -15[degrees], and +25[degrees]. The power of the received signal is improved by up to 12 dB for -60[degrees] [less than or equal to] [theta] < 60[degrees] when compared to a conventional two-element array. Index Terms--Antenna arrays, microwave antenna arrays, phased arrays, retrodirective array.

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 x 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 [phi] = 0[degrees], [phi] = -45[degrees], and [phi] = -90 plane for scattering angles of [theta] = -15[degrees], [theta] = 0[degrees], and [theta] = +30[degrees]. Index Terms--Antenna arrays, beam steering, microwave antenna arrays, phased arrays, retrodirective array, self-oscillating mixer (SOM).

Analytical and experimental results are presented that demonstrate the advantages of replacing the metal mirror of a C-band transistor-grid oscillator with two types of selective-feedback mirrors. The first mirror is a two-dimensional photonic crystal, whose frequency-, polarization-, and reflectivity-dependent characteristics result in higher radiated power, lower cross polarization, and improved locking. The second is a diode-loaded grating functioning as an electronically tunable mirror, which allows the oscillator to be amplitude-modulated. Index Terms - Photonic crystals, quasi-optical arrays.

A method for assessing and optimizing the feedback level in a transistor-grid oscillator is presented. based on the approximate large-signal S-parameters of the transistor, an equivalent circuit model for the grid is synthesized for maximum oscillator power. The resulting circuit serves as a convenient benchmark for determining the level of feedback for a given grid. Experimental results are presented for five different grid oscillators covering S through K a bands. By varying the substrate thickness and metallization pattern of the grid, the feedback can be optimized in accordance with the theory. A grid with an asymmetric unit cell is shown to deliver almost 60% more effective radiated power (ERP) than a grid with a symmetric unit cell. Index Terms - Active arrays, millimeter-wave oscillators, millimeter-wave power dividers/combiners, quasi-optical arrays.

This work investigates a spatially fed local oscillator (LO) for a retrodirective antenna array. Compared to conventional planar transmission-line feed networks, the spatial feed offers a more flexible array layout and easier implementation, especially in large two-dimensional (2-D) arrays. This method of delivery involves radiating the LO through free space to the back-side of the array where it is received by slot-coupled patch antennas and delivered to the mixing elements. A four-element linear retrodirective array utilizing this approach is demonstrated at an LO frequency of 10.7 GHz. Retrodirectivity is observed at scan angles from -40[degrees] to +40[degrees]. Index Terms--Antennas arrays, retrodirective antennas.