Quasi-optical power-combining techniques have been developed to address fundamental limitations in solid-state devices and circuits. These techniques have been applied to oscillators, amplifiers, frequency-conversion components, and control circuits. This paper surveys progress in the development of quasi-optical array systems operating in the microwave and millimeter-wave regime, focusing primarily on the progress in power amplifiers.

Quasi-optical and spatial power combining

Power combining of TM surface waves by a planar active-lens amplifier is the subject of this paper. An amplifier gain of 11 dB at 8.25 GHz with a 3-dB bandwidth of 0.65 GHz has been demonstrated. Gain is measured from input to output connector to facilitate comparisons with more conventional amplifiers. Measurements of output power versus input power are also presented. The amplifier behaved in a linear manner and no problems with spurious oscillations were encountered. Construction of the amplifier is compatible with planar fabrication technologies. A key component of the combiner is a microstrip-fed Yagi-Uda slot-array antenna for TM surface-wave excitation of a thick dielectric slab. Design and optimization guidelines for the antenna are presented as well as detailed spectral-domain and finite-difference time-domain (FDTD) analysis results. Measured and simulation results show an input return loss and front-to-back ratio better than 10 dB over a 5% bandwidth. Calculated and measured results for the fields radiated by the antenna confirm forward radiation of the dominant TM mode in the thick dielectric slab. Integration of the computed radiated fields shows the antenna has a surface-wave launching efficiency of 85%.

TM surface-wave power combining by a planar active-lens amplifier

Active integrated antennas (AIAs) provide a new paradigm for designing modern microwave and millimeter-wave architecture with desirable features such as compactness, light weight, low cost, low profile, minimum power consumption, and multiple functionality. This paper reviews recent research and development related to this emerging technology with emphasis on its applications in high-efficiency radio-frequency (RF) front-end, millimeter-wave power combining, beam steering, and retrodirective arrays, as well as wireless sensors. Optical controlling techniques for AIA's are also described.

Progress in active integrated antennas and their applications

Unified dynamic equivalent-circuit model for characterizing planar unbounded discontinuities is reported for use in the field-theory-based computer-aided design and optimization of high-frequency integrated circuits and structures such as monolithic and hybrid microwave integrated circuits (M(H)MIC's). The proposal of the circuit model is stemmed from a new scheme called the short-open calibration (SOC) technique. This SOC technique is directly accommodated in a full-wave method-of-moments (MoM) algorithm. The developed MoM algorithm is applied to the modeling of unbounded planar discontinuities that can be segmented into two distinct sections: static model of feed lines and dynamic model of circuit discontinuity. In this paper, the MoM, is formulated in such a way that the port voltages and currents are explicitly represented through relevant network matrices. The SOC technique is used to remove or separate unwanted parasitics brought by the approximation of the impressed voltage source and also the problem of resulting consistency between the two-dimensional and three-dimensional simulations. Results for a class of planar circuit discontinuities are very well compared with measurements and also available publications. Generalized end-to-end coupling structure having offset and unequal input/output lines (to name a specific example) is studied to indicate the parametric and dispersion effects on its equivalent capacitance and radiation conductance. Advantageous features of the proposed unified circuit model suggests its practical usefulness and high accuracy in the design and optimization of a wide range of M(H)MIC's and planar antennas.

Unified equivalent-circuit model of planar discontinuities suitable for field theory-based CAD and optimization of M(H)MIC's

An efficient and rigorous method for the analysis of planarly layered geometries with vertical metallizations is presented. The method is based on the use of the closed-form spatial-domain Green's functions in conjunction with the method of moments (MoM). It has already been demonstrated that the introduction of the closed-form Green's functions into the MoM formulation results in significant computational improvement for the analysis of planar geometries. However, in cases of vertical metallizations, such as shorting pin's, via holes, etc., there are some difficulties in incorporating the closed-form Green's functions into the MoM formulation. In this paper, these difficulties are discussed and their remedies are proposed. The proposed approach is compared to traditional approaches from a theoretical point of view, and the numerical implementation is demonstrated through some examples. The results are also compared to those obtained from the commercial software em by SONNET.

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Efficient use of closed-form Green's functions for the analysis of planar geometries with vertical connections

Real power gain from a quasi-optical power combining dielectric slab waveguide amplifier system is reported for the first time. The system employs four MESFET amplifiers located under the slab, and a small signal gain of 10.5 dB was achieved. Measurements of insertion loss and E-field patterns are presented.

A quasi-optical dielectric slab power combiner

In this paper, the design of a 2D quasi-optical power combining structure is presented. Convex and concave phase transformers were used in the system comparing their scattering losses. The amplifier array is placed underneath the dielectric slab to reduce insertion loss and allow beam scanning by tuning the input signal frequency.

Two-dimensional quasi-optical power combining system: performance and component design

A full-wave moment-method technique developed for the analysts of quasi-optical (QO) systems is used to model finite grid structures in a lens system. This technique incorporates an electric-field dyadic Green's function for a grid centered between two lenses. This is derived by separately considering paraxial and nonparaxial fields. Results for the driving point reflection coefficient of a 3/spl times/3 and 5/spl times/5 grid in the lens system are computed and compared with measurements.

Analysis of finite grid structures with lenses in quasi-optical systems

A new full-wave, space-domain moment method implementation is developed for the analysis and circuit-characterization of passive microstrip elements (in an open environment) at microwave frequencies. The computational time and memory requirements are significantly reduced by filling the moment matrix efficiently utilizing closed-form Green's functions and symmetries in the problem formulation, such that a circuit of moderate electrical size can be analyzed in reasonable time on a personal computer. © 1994 John Wiley & Sons. Inc.

Efficient analysis of passive microstrip elements in MMICs

A full-wave moment method implementation, using a combination of spatial and spectral domains, is developed for the analysis of quasi-optical systems. An electric field dyadic Green's function, including resonant and nonresonant terms corresponding to coupling from modal and nonmodal fields, is employed in a Galerkin routine. The dyadic Green's function is derived by separately considering paraxial and nonparaxial fields and is much easier to develop than a mixed, scalar and vector, potential Green's function. The driving point impedance of several antenna elements in a quasi-optical open cavity resonator and a 3/spl times/3 grid in free space are computed and compared with measurements.

T.W. Nuteson

Papers

A quasi-optical dielectric slab power combiner

Two-dimensional quasi-optical power combining system: performance and component design

Analysis of finite grid structures with lenses in quasi-optical systems

Efficient analysis of passive microstrip elements in MMICs

Full-wave analysis of quasi-optical structures