Electromagnetic modeling of a waveguide-based spatial power amplifier array with hard horn feeds

A generalized scattering matrix (GSM) approach, which utilizes finite difference time domain (FDTD) and mode matching (MM) techniques, is used to analyze waveguide based spatial power combiners with hard hom feeds. The simulation results are experimentally verified for a complete spatial power dividingkombining system with a 3x3 patch antenna array and a hard hom. This analysis provides information for the to the waveguide walls in order to increase the power combining efficiency of the waveguide-based spatial power combiners. Introduction Despite the continuous advances in vacuum electronics [I], due to their fault tolerance against device failures, low bias requirement and linearity, spatial power amplifiers have the potential to replace traveling wave tubes (TWTs) in moderate power communications applications at millimeter wave fkequencies. After a decade of developmental stage, the latest research in spatial power combining has been concentrating on understanding the fundamental concepts in spatial power amplifiers. Accurate modeling of spatial power amplifiers is essential for optimal design, and due to the complex electromagnetic structures involved, full wave analysis is required. Even with today's powerful computers, full wave analysis of spatial power combiners with custom codes can be hampered by large memory requirements, so modeling of spatial combining arrays continue to be a very challenging task. Although significant progress has been made in modeling of spatial amplifiers, most of the designs are still based on the unit cell approach. For grid structures, it is more convenient to follow this approach with an infinite array assumption, which neglects the edge effects [2]. Modeling of a finite grid array [3] as well as a finite folded slot array [4] has also been demonstrated. There have been successful attempts at modeling waveguide-based spatial power combining arrays as shown in Fig. 1 using the GSM approach as well [5,6]. GSM approach suits well to the waveguide problems since the complexity is reduced by partioning the system into smaller blocks that can be simulated using different numerical techniques. There has been limited amount of work that relates the performance of the spatial power amplifiers to the array parameters [7-91. Issues that have not been previously addressed are the detailed optimization of the parameters such as inter-element spacing and the distance of the array This work was supplied by an Army Research Ofice MURI grant under the contract number DAAG-55-97-0132. 400 O7803-733O-8/02$17.O@2W IEEE modeling of spatial power combining arrays inside dielectric loaded oversized waveguides, optimization of array parameters (such as inter-element spacing) for higher power combining efficiency, and the effect of the proximity of the m y to the hard hom walls on the m y behavior (bandwidth, driving point impe+mces of the array elements). Transmit Hom f 7 YReceiveHom Input antenna array ' \ Output antenna Amplifier layer array