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. >

Active antenna array behavior

Arrays of coupled active antenna oscillators can be used for power-combining at microwave and millimetre-wave frequencies. It is known that the relative phase angle between active antenna oscillators placed in an array and hence their far-field radiation pattern can have certain discrete values depending on the separation distance between elements. Thus in order to characterise an active array an accurate method of evaluating the coupling between oscillators and a knowledge of the available modes that exist within the array are required. In this paper the available modes for an array of mutually coupled active antenna elements are evaluated by examination of the eigenvectors of the impedance matrix of the passive element components in the active array. Time domain numerical simulations are performed and the resulting predictions compared to those obtained by experiment and by the eigenvalue approach.

Eigenvalue mode confirmation in a mutually coupled active antenna chain array

This paper describes the design and performance of 30 GHz low noise amplifiers (LNAs) integrated with slot antennas on GaAs monolithic microwave integrated circuits (MMICs). Various designs are compared, showing the tradeoffs between achievable noise figure, gain and overall chip size. The smallest chip size, measuring 8.6 mm/sup 2/, would provide a 2.1 dB noise figure with 9.5 dB associated gain.

https://ieeexplore.ieee.org/iel3/4660/13246/00602962.pdf

30 GHz GaAs monolithic low noise amplifier-antennas

This paper discusses the design and operational properties of a circular array of slot coupled active GaAs metal-semiconductor field-effect transistor (MESFET) rectangular microstrip patch antennas arranged for quasioptical power combining at X band. The active antenna radiating elements are injection locked by slot coupling to a radial cavity waveguide. Spatial power combining efficiency of 75% and dc to radio frequency (RF) conversion efficiency of 10% at 28 dBm EIRP was achieved at 10.38 GHz. Retrodirective action was also demonstrated by using the active elements as self-oscillating mixers pumped at 20.76 GHz.

Radial cavity-fed spatial power combiner with retrodirective array behavior

A software tool for active antenna array dynamical evaluation

This article discusses the application of a synthesis method for, and the subsequent experimental characterization, of an active microstrip patch antenna. The active antenna incorporates a GaAs MESFET on the patch periphery and the circuit acts as a self-oscillating radiating element. The MESFET and the antenna are mounted on the same side of the circuit, thereby preserving the conformal nature of the structure. The synthesis approach described is based on the method of harmonic balance and allows optimal FET terminations to be selected for a predefined, added power at a specified frequency of operation. Application of a time domain simulator is illustrated in order to demonstrate start-up performance and limit cycle formation in the presence and absence of a frequency entrainment signal. The issue of stability of the active element is also addressed using a modified device/load line method. Theoretical and experimental results are presented for the external quality factor, locking power/phase variation, and power and frequency pushing characteristics of the active antenna. Finally, the effect on oscillator behavior of the mutual coupling between the microstrip patch and the active antenna distributed embedding elements is discussed.

D. Stewart McDowall

Papers

Synthesis and performance of an active microstrip antenna