James Vian

Smart lens antenna arrays

This paper describes a smart lens antenna array in which a portion of the signal processing is implemented at the analog front end, resulting in reduced processing load. The design of constrained lens arrays is described, and simulations of optimal receiver placement in the array are shown. As an example, the signal-to-noise ratio (SNR) is calculated when a least-mean-square (LMS) adaptive algorithm is applied to different-size lens arrays. The complex weight trajectories are compared to those in a standard planar antenna array, and if is shown that fewer weights are needed in the case of a lens array. The resulting adapted radiation patterns in multi-user and multi-path communication environments are calculated for realistic antenna elements, and a reduction in processing load is shown as compared to standard arrays.

A bi-directional quasi-optical lens amplifier

A 10-element bi-directional quasi-optical lens amplifier array is presented. The amplifier is designed for X-band, and operates in transmission mode. SPDT switches are used to switch between transmit and receive amplifiers. An ON/OFF ratio of 25 dB is measured for both transmitting and receiving modes with associated amplifier gains of 5 and 10 dB.

Science Instrumentation for the Student Nitric Oxide Explorer

The student nitric oxide explorer (SNOE) is a small satellite to be designed built and operated at the University of Colorado under the student explorer demonstration initiative from the Universitys Space Research Association (STEDI). The goal of the STEDI program is to demonstrate that low cost satellite missions can be done with large student involvement. The primary science goals of SNOE are to measure thermospheric nitric oxide (NO) and its variability over the lifetime of the mission. SNOE will also monitor the solar irradiance at soft x-ray wavelengths and the auroral energy deposition at high latitudes. Three science instruments are required to achieve the simultaneous measurements: an ultraviolet spectrometer for NO; a solar soft x-ray photometer; and a far ultraviolet photometer for studying the aurora. The instruments are designed to represent a minimum impact on the spacecraft, particularly in terms of data storage and interactions with the command and data handling system. The focus of this paper is the outline of the design of the science instruments. We discuss why these instruments are well suited for smaller, lower cost satellite missions.

A transmit/receive active antenna with fast low-power optical switching

An X-band active antenna element for half-duplex transmit/receive (T/R) applications with efficient optical switching is presented. The antenna element is designed to be a unit cell of a quasi-optical array with fast switching between T and R and with built- in phase-shifterless beamforming. The measured performance of the active element is 14 dB gain contributed by the power amplifier (PA) in transmission, 16 dB gain contributed by the LNA in reception, with 30 dB isolation between T and R. The switching is accomplished with only 1 /spl mu/W of optical power for 1.7 /spl mu/s switching time, and a rise time of 2 ns at 10 GHz with 7 mW of optical power. The design, implementation and measured performance of the optically-controlled transmit/receive circuit are presented here in detail.

Identification and compensation of Wiener-Hammerstein systems with feedback

Efficient operation of RF power amplifiers requires compensation strategies to mitigate nonlinear behavior. As bandwidth increases, memory effects become more pronounced, and Volterra series based compensation becomes onerous due to the exponential growth in the number of necessary coefficients. Behavioral models such as Wiener-Hammerstein systems with a parallel feedforward or feedback filter are more tractable but more difficult to identify. In this paper, we extend a Wiener-Hammerstein identification method to such systems showing that identification is possible (up to inherent model ambiguities) from single- and two-tone measurements. We also calculate the Cramér-Rao bound for the system parameters and compare to our identification method in simulation. Finally, we demonstrate equalization performance using measured data from a wideband GaN power amplifier.

Performance bounds on cooperative radar and communication systems operation

A theoretical framework that embraces the competing objectives of cooperative radar-communication operations is proposed that engages the apparent trade-space in an optimal fashion. Specifically, minimization of a cooperative risk metric that extends the Neyman-Pearson criterion to include communication data rate is explored. Hence, establishing performance bounds for cooperative interaction. Ideal informed reception where simultaneous access to received data from both the radar and communication (comm.) system is shown to yield a structured covariance-based water-filling solution. Unlinked cooperation where codebooks, waveforms, and schedules are known by all, but received data is not relayed between radar and comm. conveys a complex tradespace dependent on the rate of information transmitted by the comm. system relative to the capacity of the radar-comm. data link.

Double-stub impedance matching algorithm

The use of wireless communication systems is becoming more prevalent in the military. In addition, these systems are located in environments where the antennas experience an ever changing load environment. This is especially true for sea-based antennas which float on top of or are mounted near the surface of the water. This paper presents an algorithm which efficiently controls a double-stub impedance matching network (IMN) for matching an antenna with an unknown load.

Efficient optical control of microwave circuits, antennas and arrays

We present an overview of work at the University of Colorado in the area of optical control of microwave circuits, antennas and active antenna arrays. Specifically, we present X-band examples of two types of optically controlled microwave components: those where the optical device is used as a microwave component; and those where a standard optical component is combined with standard microwave components. The former is a slot antenna controlled with a PD in the feedline; and the latter example is that of a photodiode that controls the bias to a microwave SPDT switch. This switch is integrated with a transmit/receive (T/R) active antenna, which is then used as an element of a quasi-optical T/R array.

Test Platform for Millimeter-wave Amplifier Linearity Characterization

Many existing and proposed military satellite communication waveforms use spectrally confined modulations to increase the number of users that occupy a limited bandwidth. These modulations are non-constant modulus and require linear operation of the transmitters. Linearity requirements necessitate that amplifiers operate well below their saturated output power, which often requires devices larger in size and weight than acceptable for mobile terminals, such as those in vehicles. The Lincoln Laboratory Amplifier Testbed (LLAT) is a measurement platform designed to quantify the effects of amplifiers on spectrally confined waveforms. LLAT is capable of measuring amplifiers at millimeter-wavelengths with saturated output powers ranging from a few Watts to hundreds of Watts. To allow maximum flexibility in modem design, LLAT uses virtual modems running on a multiprocessor grid. The LLAT enables investigation of technology advances that may solve the size, weight and power constraints of small mobile terminals.

A K-band full-duplex transmit-receive lens array

A K-band full-duplex transmit-receive lens antenna array using uniplanar circuitry is reported. The array transmits at 19 GHz and receives at 21 GHz by means of two independent unit cells. Orthogonal antenna polarization and bandpass circuitry provide a simulated isolation of 42 dB between transmit and receive channels. The measured gains of the active array are 3.0 and 8.3 dB above passive with an on-off ratio of 10 and 15 dB for transmit and receive modes respectively.