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Use of a Network of Phase Locked Oscillators in Phased Array Systems

IP.com Disclosure Number: IPCOM000091548D
Original Publication Date: 1968-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 17K

Publishing Venue

IBM

Related People

Gunn, JB: AUTHOR

Abstract

In phased array systems such as described by K.S. Molz in the article "Phased Array Radar Systems," Radio and Electronic Engineer 28, 331, 1964, the antennas or transducers, in the analogous acoustical case, forming a spatial array, are independently excited in controlled phases so as to radiate a plane wavefront having a desired orientation. This orientation can be altered, to provide a scanning action, by systematically varying the phases of individual radiators. The variation is normally achieved by a system of variable, passive phase-shifters. Either a phase-shifter or a mixer is required for each element of the array. The requirement to provide and control the many phase-shifters needed for a large array is a disadvantage of the system.

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Use of a Network of Phase Locked Oscillators in Phased Array Systems

In phased array systems such as described by K.S. Molz in the article "Phased Array Radar Systems," Radio and Electronic Engineer 28, 331, 1964, the antennas or transducers, in the analogous acoustical case, forming a spatial array, are independently excited in controlled phases so as to radiate a plane wavefront having a desired orientation. This orientation can be altered, to provide a scanning action, by systematically varying the phases of individual radiators. The variation is normally achieved by a system of variable, passive phase-shifters. Either a phase-shifter or a mixer is required for each element of the array. The requirement to provide and control the many phase-shifters needed for a large array is a disadvantage of the system. In these systems, the desired plane phase-fronts can conveniently be generated by a network of mutually coupled nonadjustable, identical phase-locked oscillators. With modern techniques, such oscillators may be very much more convenient to provide than phase-shifters or mixers.

Assume that each oscillator has the same free-running frequency f(o), but that its phase can be locked to that of a small signal at f(o) injected into its circuit, preferably at the output terminals.

For oscillators coupled together in such a way that each receives a phase-locking signal from a number of others, each oscillator is locked in phase to the vector sum of all the signals it receives. If the couplings are equal and none of the phase differences is as large as pi/2, the resulting phase is the mean of the phases of the locking signals. For a regular network of oscillators, each equally coupled only to its nearest neighbors by a path whose phase-shift is negligible modulo 2pi, the phase phi (r) of an oscillator at the position r in the interior of the network thus obeys the second difference equation
Delta/2/phi(r) = 0 where the second difference operator is given by Delta/2/phi(x) = phi(x) - 1/2>phi(x+1) + phi(x-1) |

Delta/2/phi(x,y) = phi(x,y) - 1/4>phi(x+1,y) + phi(x-1,y) + phi(x,y+1) + phi(x,y-1)|. for a linear chain or a square lattice, respectively. If a, b, c are arbitrary constants, the solution of the first equation has the unique form phi (x) = ax+c for the chain, while for the lattice phi (x,y) = ax+by+c is a solution, but there exist others. However, in this case the first equation has the property, similar to Laplace's equation, that if phi is prescribed at every point on the boundary of an array, then it is uniquely determined in the interior.

Thus both the chain and the lattice can be used to provide the signals to generate a desired phase front, by interpolation between externally controlled signals injected on the boundary. The chain of N oscillators can provide the signals for a linear phase front, using only a single phase-shifter to control the phase difference between the ends, instead of the N-1 phase-shifters or mixers...