An X-band, high power dielectric resonator oscillator for future military systems

A 9.0-GHz dielectric resonator oscillator (DRO), generating a CW output power of 2.5 W at room temperature, has been designed and fabricated using a high-power GaAs MESFET and a dielectric resonator (DR) in a parallel feedback configuration. The oscillator exhibited a frequency stability of better than 130 ppm, without any temperature compensation, over the range -50 degrees C to +50 degrees C. The output power varied from +35 dBm (3.2 W) at -50 degrees C to +33 dBm (2 W) at +50 degrees C. The single-sideband phase noise levels were measured and found to be -105 and -135 dBc/Hz, at 10- and 100-kHz carrier offset frequencies, respectively. The oscillator output was then fed into a single-stage high-power MESFET amplifier, resulting in a total RF power output of 6.5 W. The overall DC to RF conversion efficiency of the 6.5-W unit was approximately 15.3%     

Optically controlled oscillators for millimeter-wave phased-arrayantennas

An approach for the design of optically synchronized millimeter-wave local oscillators based on a subharmonically injection-locked phase-lock-loop technique is introduced. The experimental results support the desired goal of frequency and phase coherency, phase shift control of millimeter-wave oscillators, and self-oscillating mixing to downconvert a millimeter-wave RF signal. Experimental results and theoretical analysis show the advantages of the proposed approach: large locking range of two subharmonically locked oscillators, lower FM noise degradation, and smaller phase error caused by frequency detuning     

Supporting Tele-Teaching: visualization aspects

A strong trend towards use of collaborative systems in teaching can be observed. Often first experience is gained by conducting seminars or lectures with existing tools, e.g. using the MBone. These tests generally find that the support of existing, mainly generic tools is not adequate for Tele-teaching. While some projects address learning aspects directly, these tend to be limited in scalability, mainly addressing smaller groups. Our approach is to develop a general framework (MACS: Modular Advanced Collaboration System) and basic components which can be used in a variety of scenarios. Currently the two main scenarios supported are a discussion group consisting of few (about 10) participants with equal rights, and a lecture scenario with more participants (up to 100) and a lecturer in control. For these scenarios, not only aspects of session control are relevant, but methods as well to provide feedback to the lecturer about the current session. This is achieved through a combination of visualization methods customized for the selected scenario. The session control uses a graphical representation of a room typically used in the specified scenario in order to provide feedback and to allow ease of use. The control marks tools currently in use allowing the lecturer and students to easily identify and participate in the corresponding media representation (e.g. audio and video). A special feedback tool allows rating, and can be used to gain feedback from the students about the received video and audio quality, the speed of presentation or any other resource one wants a rating on. These visualization measures combined with the floor control provided by MACS allow to conduct a lecture in an efficient manner.     

Direct optical frequency modulation and injection locking of resonant tunnel diode oscillator

Preliminary results indicate that a resonant tunnel diode (RTD) oscillator can be optically tuned, frequency modulated, and injection locked. Experiments were performed in which a 2.8 GHz RTD oscillator was frequency modulated from DC to 100 MHz and injection locked over a 150 kHz bandwidth with a laser diode via fibre optics.<>