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Future NASA deep space missions able to provide tens of kilo-watts of spacecraft DC power, make it feasible to employ high power RF telecommunications systems. Traditional flight systems (e.g., Cassini), constrained by limited DC power, used a single high-gain 4m Cassegrain reflector fed by a single lower power (20W) transmitter. Increased available DC power means that high power (1000 W) transmitters can be used. Rather than continue building traditional single-transmitter systems it now becomes feasible to engineer and build multi-element active arrays that can illuminate a dish. Illuminating a 2m dish with a spherical wavefront from an offset 1kW active array can provide sufficient ERP (Effective Radiated Power) when compared to a larger Cassegrain dish. Such a system has the advantage of lower mass, lower volume, improved reliability, less stringent pointing requirements, lower cost and risk. We propose to design and build a prototype Ka-band transmit antenna with an active sub-array using 125W TWTAs. The system could be applied to a telecommunications downlink or radar transmitter used for missions such as JIMO.

This paper describes a set of experimental measurements designed to test the predictions of the continuum theoretical model concerning the dynamics of a linear array of mutually in-jection-locked voltage-controlled oscillators.

In many communications and radar applications, one is confronted with interfering signals orginating in a predefined angular sector.

Our purpose in coupling oscillators is to achieve high radiated power through the spatial power combining which results when the oscillators are injection locked to each other.

Our purpose in coupling oscillators together is to achieve high radiated power through the spatial power combining which results when the oscillators are injection locked to each other.

It has been shown that arrays of voltage controlled oscillators coupled to nearest neighbors can be used to produce useful aperture phase distributions for phased array antennas. However, placing information of the transmitted signal requires that the oscillations be modulated.

This presentation will begin with a description of the previous published work contributing to the results reported here. The previously developed one dimensional continuum model will be generalized to two dimensions and a Green's function for the resulting differential equation will be obtained as an eigenfunction expansion. This will be used to obtain dynamic solutions relevant to the steering of the radiated beam. Finally, some remarks concerning limitations on the interoscillator phase difference will be provided.

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Some years ago, Stephan proposed an approach to one dimensional (linear) phased array beam steering which requires only a single phase shifter.

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This paper describes the design, fabrication, and testing of a seven element S-band phased array in which the beam is steered by means of a coupled oscillator technique.

Arrays of coupled oscillators have been proposed as means of realizing high power rf sources via coherent spatial power combining.

Mutually injection locked arrays of electronic oscillators provide a novel means of controlling the aperture phase of a phased array antenna thus achieving the advantages of spatial power combining while retaining the ability to steer the radiated beam. In this work we develop a continuum model which results in a single partial differential equation for the aperture phase as a function of time.

The behavior of arrays of coupled oscillators has been previously studied by computatinal solution of a set of non-linear differential equations describing the time dependence of each oscillator in the presence of signals coupled from neighboring oscillators.

Quasi-optical oscillators were proposed a little more than ten years ago as a means of developing the power levels needed for applications at millimeter frequencies using large numbers of individual semiconductor devices each of which produces only a modest amount of power [J.W. Mink, IEEE Trans. MTT., vol. 34, p. 273, 19861. An operating system was demonstrated soon after [Z.B. Popovic et. al, Int. J. Infrared and Millimeter Waves, v. 9, p. 647, 1988] in the form of a so-called grid oscillator. This device constituted a rectangular array of oscillating devices that are mutually coupled so that they oscillator coherently. The interconnecting lines in one direction serve as radiators so that the oscillators radiate directly, and the radiated fields add. Subsequently, coupled oscillators using resonant transmission line lengths was demonstrated by Mortazawi and Itoh [IEEE Trans. MTT., vol. 38, p. 86,1990). In recent work, coupled-oscillator power combiners have received less attention, with amplifier/combiners receiving more attention. Specific weaknesses of spatial-combining oscillators have motivated this transition. Namely, the oscillators employ low-Q resonators (resulting in low signal quality) and no clear means of modulation has been identified until recently. In this presentation, we review coupled-oscillator combiners in broad terms, indicating the features that make particular systems viable. We indicate how these features can be reconciled to functional requirements for system applications. Comparisons are drawn between two approaches to obtain mutual coupling: One employs low-Q oscillator circuits at each site, with concomitantly high propensity for the oscillators to couple. The other approach employs moderate-Q oscillators at each site with the concomitant requirement to tune the oscillators so that they share a range of frequencies over which they can couple and lock. In either case, precise frequency control and modulation can be achieved through locking to an external frequency source that ensures high quality signals. A recent development in coupled-oscillator arrays provides a means for beam-steering the radiation field of coupled oscillators through de-tuning of the edge elements in the array. This detuning introduces a progressive phase shift across the oscillator array. This 0 suggests architectures that can replace the functionality of a phased array without the cost 0 incurred by phase shifters. A comprehensive theory of the phase interactions among devices in such arrays is under development [e.g., Pogorzelski, York, and Maccarini, 1998 AP-S International Symposium, Atlanta, GA. June, 19981.

In the present work we use the contiuum model to study the dynamic behavior of the oscillator array when an injection signal having a time dependent frequency is applied for modulation purposes.

Linear and planar arrays of coupled oscillators have been proposed as means of achieving high power rf sources through coherent spatial power combining. In such - applications, a uniform phase distribution over the aperture is desired. However, it has been shown that by detuning some of the oscillators away from the oscillation frequency of the ensemble of oscillators, one may achieve other useful aperture phase distributions. Notable among these are linear phase distributions resulting in steering of the output rf beam away from the broadside direction. The theory describing the operation of such arrays of coupled oscillators is quite complicated since the phenomena involved are inherently nonlinear. This has made it difficult to develop an intuitive understanding of the impact of oscillator tuning on phase control and has thus impeded practical application. In this work a simpl!fied theory is developed which facilitates intuitive understanding by establishing an analog of the phase control problem in terms of electrostatics.

The virtual spacecraft concept is embodied in a set of subsystems, either in the form of hardware or computational models, which together represent all, or a portion of, a spacecraft. For example, the telecommunications transponder may be a hardware prototype while the propulsion system may exist only as a simulation. As the various subsystems are realized in hardware, the spacecraft becomes progressively less virtual. This concept is enabled by JPL's Mission System Testbed which is a set of networked workstations running a message passing operating system called "TRAMEL" which stands for Task Remote Asynchronous Message Exchange Layer. Each simulation on the workstations, which may in fact be hardware controlled by the workstation, "publishes" its operating parameters on TRAMEL and other simulations requiring those parameters as input may "subscribe" to them. In this manner, the whole simulation operates as a single virtual system. This paper describes a simulation designed to evaluate a communications link between the earth and the Mars Pathfinder Lander module as it descends under a parachute through the Martian atmosphere toward the planet's surface. This link includes a transmitter and a low gain antenna on the spacecraft and a receiving antenna and receiver on the earth as well as a simulation of the dynamics of the spacecraft. The transmitter, the ground station antenna, the receiver and the dynamics are all simulated computationally while the spacecraft antenna is implemented in hardware on a very simple spacecraft mockup. The dynamics simulation is a record of one output of the ensemble of outputs of a Monte Carlo simulation of the descent. Additionally, the antenna/spacecraft mock-up system was simulated using APATCH, a shooting and bouncing ray code developed by Demaco, Inc. The antenna simulation, the antenna hardware, and the link simulation are all physically located in different facilities at JPL separated by several hundred meters and are linked via the local area network (LAN).

A novel means of achieving cophasal far-field radiation has been demonstrated for a curcularly polarized microstrip reflectarray with elements having variable rotation angles. Two Ka-band, half meter microstrip reflectarrays have been fabricated and tested.

One of the major concerns of antenna design for spacecraft applications is the effect of surrounding structures which can reflect and diffract the antenna's radiated energy and cause degradation in the antenna directivity, beam shape, and sidelobe levels.