Concurrent Dual-Frequency Oscillators and Phase-Locked Loops

A dual-frequency oscillator employing a fourth-order tank is shown to have the ability to generate simultaneous oscillations at two frequencies. A nonlinear analysis to determine the steady-state and transient behavior of this oscillator is presented. Further, the phase-noise expression for the dual-frequency oscillator is derived and compared with that of a single-frequency oscillator. A dual-loop phase-locked loop (PLL) is designed to lock the frequencies of the dual-frequency oscillator to two external references independently. A prototype of a dual-frequency voltage-controlled oscillator (VCO) along with the dual-loop PLL is implemented in a BiCMOS SiGe technology. The dual-frequency VCO oscillates simultaneously at 2.33 and 4.98 GHz with 12.5% and 10.3% tuning ranges, respectively. The PLL has locking ranges of 4.2% and 3.6% for 2.33 and 4.98 GHz, respectively. Potential applications of concurrent multifrequency oscillators in multifunctional communication systems and multiband beam forming are discussed.      

A Beam-Steering Antenna Array Using Injection Locked Coupled Oscillators With Self-Tuning of Oscillator Free-Running Frequencies

The analysis and experimental results of an antenna array using injection locked coupled oscillators with self-tuning of oscillator free-running frequencies are presented. With the use of coupled type-II phase locked loops for tuning oscillator free-running frequencies and an external injection signal for stabilizing the array operating frequency, this antenna array can steer its beam through a single control voltage and hold its output frequency at the injection signal frequency in operation. In addition, its beam-pointing error arising from phase errors in coupled oscillators can be reduced and the array works well over a certain frequency band. Phase dynamics and stability are studied and experimentally verified. Experimental results of a three-element injection locked coupled oscillator array show that its uniform phase progression ranges between $-$16 $^{circ}$ and 52$^{circ}$ , and the phase errors are less than 5 $^{circ}$ at 2.7 GHz. The operation bandwidth is shown from 2.68–2.72 GHz. By loading the injection locked coupled oscillator array with rectangular patch antennas, the beam-steering radiation characteristics are measured at various control voltages.      

Two-dimensional array beam scanning via externally and mutuallyinjection-locked coupled oscillators

The use of arrays of injection-locked voltage-controlled oscillators coupled to nearest neighbors has been proposed as a means of controlling the aperture phase of one and two-dimensional (2-D) phased-array antennas. It has been demonstrated both theoretically and experimentally that one may achieve linear distributions of phase across a linear array aperture by injection locking to an external oscillator the end oscillators of an array of a mutually injection-locked oscillators. These linear distributions cause steering of the radiated beam. It is demonstrated theoretically here that one may achieve beamsteering in a similar manner in two dimensions by injecting appropriately phased signals into the perimeter oscillators of a 2-D array. The analysis is based on a continuum representation of the phase previously developed in the context of beamsteering via tuning of the perimeter oscillators     

On the dynamics of two-dimensional array beam scanning viaperimeter detuning of coupled oscillator arrays

Arrays of voltage-controlled oscillators coupled to nearest neighbors have been proposed as a means of controlling the aperture phase of one-dimensional (1-D) and two-dimensional (2-D) array antennas. It has been demonstrated, both theoretically and experimentally, that one may achieve linear distributions of phase across a linear array aperture by tuning the end oscillators of the array away from the ensemble frequency of a mutually injection-locked array of oscillators. These linear distributions result in steering of the radiated beam. It is demonstrated theoretically that one may achieve similar beamsteering in two dimensions by appropriately tuning the perimeter oscillators of a 2-D array. The analysis is based on a continuum representation of the phase in which a continuous function satisfying a partial differential equation of diffusion type passes through the phase of each oscillator as its independent variables pass through integer values indexing the oscillators. Solutions of the partial differential equation for the phase function exhibit the dynamic behavior of the array during the beamsteering transient     

Active antenna array lumped ring configuration

Coupled active antenna oscillator arrays are used for power-combining at microwave and millimeter-wave frequencies. It is known that the relative phase determined by the element separation distance ultimately determines the array operational mode and, hence, far-field radiation characteristics. Separately, it is known that coupled oscillator modal stability is achieved by coupling oscillators through lumped capacitive elements. In this paper, an arrangement whereby lumped capacitive elements (placed across the oscillator loads) and radiative coupling are employed concurrently is investigated. The arrangement takes the form of a ring of coupled oscillators used to excite a 2×2 antenna array. The effect that these couplings have on array behavior are evaluated using time-domain analysis and analytically derived equations. Experimental results for far-field radiation patterns are discussed in relation to coupled oscillator dynamical behavior. These suggest that the theoretical predictions are valid, offering a robust design tool for studies of larger power-combining arrays     

A demonstration of the coupled oscillator based agile beam receiver concept

The Cao-York concept of using a linear array of mutually injection locked oscillators to provide local oscillator signals for an agile beam receiver is demonstrated using a 15 circuit array of L-band voltage controlled oscillators coupled to nearest neighbors. The concept involves mixing each 1.265 GHz local oscillator (l-o) signal with a corresponding 1.950 GHz signal received by an element in an antenna aperture and combining the resulting 685 MHz intermediate frequency (i-f) signals. A normally incident wave is simulated using a power divider to provide 15 equal in-phase signals to the r-f ports of the mixers and the i-f combining is accomplished using a similar power divider in reverse. The "antenna beam" is steered through this "normally incident wave" by antisymmetrically detuning the end oscillators of the array and a plot of the i-f combiner output represents the receive beam shape. Finally, this system is used to demonstrate the Kott sidelobe suppression technique.     

A continuum model of the dynamics of coupled oscillator arrays forphase-shifterless beam scanning

The behavior of arrays of coupled oscillators has been previously studied by computational solution of a set of nonlinear differential equations describing the time dependence of each oscillator in the presence of signals coupled from neighboring oscillators. The equations are sufficiently complicated in that intuitive understanding of the phenomena which arise is exceedingly difficult. We propose a simplified theory of such arrays in which the relative phases of the oscillator signals are represented by a continuous function defined over the array. This function satisfies a linear partial differential equation of diffusion type, which may be solved via the Laplace transform. This theory is used to study the dynamic behavior of a linear array of oscillators, which results when the end oscillators are detuned to achieve the phase distribution required for steering a beam radiated by such an array     

Microstrip Antenna–Oscillators Integrated with a Waveguide Built in a Dielectric Substrate

The design of a microwave oscillator based on a microstrip log-periodic antenna integrated with a field effect transistor and a waveguide built in a dielectric substrate has been developed and analyzed. The waveguide geometry provides the possibility of propagation and radiation at both the fundamental frequency of the log-periodic antenna and harmonics. Computer simulation of the oscillator design in a frequency range near resonance frequencies of the log-periodic antenna is conducted. The possibility of summation of powers of several antenna–oscillators arranged ias a linear phased array is investigated.     

Effect of Coupling Phase on Mutual Injection Locking Range in Coupled Oscillator Arrays

The performance of a coupled oscillator array depends critically on the coupling network. Determination of the optimal coupling phase depends on the oscillator equivalent circuit and the location of mutual coupling between the oscillators. In this paper, the authors examine the effects of coupling phase on the mutual injection locking range. Three element coupled oscillator arrays (COAs) were mutually coupled at two different locations, with each coupling location presenting a different resonance to the coupling network, and the optimal coupling phase required to generate a linear phase shift in the range of $-90^{circ}$ to 90$^{circ}$ was determined. For each coupling location, when the coupling phase was off by 180$^{circ}$ , the arrays were shown to lock with a limited range and operate in a mode other than the in-phase mode.      

Active antenna array behavior

It has been recently demonstrated that arrays of coupled active antenna oscillating elements can be locked together by mutual radiation in order to form spatial power combining and beam steered arrays. In this paper a nonlinear coupled oscillator theory is developed which accounts for both the amplitude and phase behavior of an array of distributed coupled active antenna oscillators. In its canonical form the theory can be used to describe the behavior of any number of spatially displaced coupled elements placed in a chain. These elements can have unequal spacing and they can have arbitrary free-running oscillation frequencies. Unequal free-running amplitudes are also permitted. Experimental validation of the theory is presented for some basic cases in terms of frequency and amplitude variation under mutual injection locked conditions. In its particular form the theory developed is suited for use with recently reported active antenna imaging methods     

A beam-scanning and polarization-agile antenna array using mutually coupled oscillating doublers

In this paper, a two-dimensional mutually coupled oscillator array is studied for the application of a beam-scanning and polarization-agile antenna array. In the design of antenna array, a two-dimensional oscillator array is implemented in x-y plane, the polarization agility is provided by one dimension (or y-direction) and the other dimension (or x-direction) is for beam scanning. By properly tuning the free-running frequencies of these oscillators, the array radiation direction can be scanned at the selected polarization states including linearly polarized, left-hand and right-hand circularly polarized states. The maximal phase difference of /spl plusmn/180/spl deg/ between coupled oscillating signals is acquired by utilizing their second-harmonic signals. This then gives well-defined phase differences among oscillators for beam scanning in addition to the required quadrature phase difference for circular polarization. The performances of polarization agility and beam scanning for a four-element antenna array are verified experimentally and shown to have the potential for adaptive antenna array applications.     

Phase noise in externally injection-locked oscillator arrays

Previous investigations of noise in mutually synchronized coupled-oscillator systems are extended to include the effects of phase noise introduced by externally injected signals. The analysis is developed for arbitrarily coupled arrays and an arbitrary collection of coherent injected signals, and is illustrated with the specific case of linear chains of nearest neighbor coupled oscillators either globally locked (locking signal applied to each array element) or with the locking signal applied to a single-array element. It is shown that the general behavior is qualitatively similar to a single injection-locked oscillator, with the output noise tracking the injected noise near the carrier, and returning to the free-running array noise far from the carrier, with intermediate behavior significantly influenced by the number of array elements and injection strength. The theory is validated using a five-element GaAs MESFET oscillator array operating at S-band     

Mechanical load cell based on cavity-controlled microwaveoscillators

A device consisting of a rectangular resonator to which two oscillators are coupled at right angles to each other is described. The frequency of each oscillator is controlled by the cavity, and distortions caused by mechanical load change the two frequencies in opposite directions. The detector, which is arranged at an angle of 45° to the probes of the two oscillators, picks up a beat signal whose frequency in the MHz range is linearly related to the mechanical load applied across the cavity. The oscillators using GaAs MESFETs have been designed to detect small distortion in the cavities by a mechanical load     

Nonlinear antenna technology

Nonlinear antennas combine advances in nonlinear dynamics, active antenna design, and analog microelectronics to generate beam steering and beam forming across an array of nonlinear oscillators. Nonlinear antennas exploit two phenomena typically shunned in traditional designs: nonlinear unit cells and interelement coupling. The design stems from nonlinear coupled differential equation analysis that by virtue of the dynamic control is far less complex than the linear counterparts by eliminating the need for phase shifters and beam forming computers. These advantages arise from incorporating nonlinear dynamics rather than limiting the system to linear quasisteady state operation. A theoretical framework describing beam shaping and beam forming by exploiting the phase, amplitude, and coupling dynamics of nonlinear oscillator arrays is presented. Experimental demonstration of nonlinear beam steering is realized using analog microelectronics     

V-band MMIC oscillator array

A V-band strongly-coupled single-chip MMIC oscillator array is presented. For wide bandwidth and easy biasing to push-pull type oscillators, modified 2-port microstrip parasitic coupled antennas are employed. When measured in a closed oversized waveguide, the MMIC oscillator array with two 2-port antennas and four oscillators radiated an output power of 4.4 dBm with excellent spatial power combining efficiency of 93% at 58.59 GHz.     

Nonlinear Mode Analysis and Optimization of a Triple-Push Oscillator

The triple-push oscillator architecture is an attractive application of a three element coupled oscillator array for high frequency signal generation. The desired solution to combine the power at the third harmonic and reject the first and second harmonics requires a 120 $^{circ}$ phase shift among the system elements. However, depending on the coupling strength and delay between the oscillators, the phase distribution varies, giving rise to different operating modes. Harmonic balance analysis is used to trace these multiple coexisting modes and their stability is investigated using envelope transient simulation. A design methodology is presented where optimum coupling parameters guarantee the operation of the system in the desired mode. A 13.8 GHz triple push oscillator is fabricated, and the various modes are investigated verifying the analysis.      

A study of steering capability of a microstrip phased array using inter-injection locked oscillators

An innovative, phase coherent, power combining method, known as inter-injection locking applied to linear limited scan phased arrays is investigated. In this novel method, each antenna element in the array is supplied by power from a separate oscillator. However, the oscillator phases are allowed to be synthesized coherently by means of a coupling network and injection currents, being the input controls to the system of coupled phases oscillators. The inter-injection-locked phased arrays studied in this paper provide more design freedom than conventional phased arrays. They also result in systems more adapted to solid state monolithic integration technology.     

Indirect Subharmonic Optical Injection Locking of a Millimeter-Wave IMPATT Oscillator

Large aperture phased-array antennas operating at millimeter-wave frequencies are designed for space-based communications and imaging. Array elements are composed of active transmit-receive (T/R) modules that are phase and frequency synchronized to a reference signal at the central processing unit by a fiber-optic (FO) distribution network. The implementation of FO links, synchronizing the millimeter-wave Iocal oscillators (LO's), imposes a great challenge. This paper presents results of indirect optical injection locking of a free-running 38-GHz (Ka-band) IMPATT oscillator over the Iocking range of 2-132 MHz, depending on the injected power level (amplifier gain). In the experiment, the nonlinearity of both the laser diode and the IMPATT oscillator is exploited to achieve 12th subharmonic injection locking. The overall system FM noise degradation of the reference signal is 16 dB at 500-Hz offset. The FM noise degradation is dominated by the theoretical limit of 20 log N, where N is the frequency multiplication factor used in subharmonic injection locking. Methods by which optical injection locking may be extended into 60 and 90 GHz are demonstrated.     

Frequency Sources in W-band Radar Front-end with Low Phase Noise

A W-band coherent stepped-frequency pulsed radar front-end is developed. It consists of a millimetre wave transmitting source, a mm-wave local source, a DDS with multi frequency points output and two microwave sources serving as local oscillators. All the sources are coherent with the 120 MHz referenced crystal oscillator. The mm-wave sources are realized by frequency multiplier chain, up-conversion and injection locking. The phase noise of fundamental-wave injection-locked W-band harmonic Gunn oscillator output signal achieves ?98 dBc/Hz at 10 kHz offset and the spurious output is less than ?50 dBc. The received intermediate frequency signal is also presented.