SPATIAL POWER COMBINING IN RECTANGULAR WAVEGUIDES USING DENSE FINLINE ARRAYS

Abstract

Spatial power combiners using dense finline arrays (tapered slot antennas) arranged in tray configuration and enclosed in a standard Ku band waveguide (WR-62) have been designed in this work. Tray approach offers higher device integration for a given area and better heat sinking for individual devices while standard Ku band waveguide allows only the dominant mode to propagate for the entire Ku band (12 till 18GHz), thus avoid multimoding problems. The design of the finline taper (or tapered slot antenna) is the most challenging aspect in this work. Before the tapers can be synthesized, a relationship between phase constant of the finline array and its geometrical parameters must be established which can only be achieved through full wave EM (electromagnetic) analysis. Matlab codes were developed using Spectral Domain Method (SDM) to extract this relationship for single-tray finline, two-tray finline and four-tray finline configurations. Results of SDM codes were also compared with Ansoft HFSS and were found to be in good agreement. SDM code parameters namely no. of spectral terms, order of basis functions etc. were optimized by first solving a known example. Finline array tapers for 25dB return loss were designed by extending the theory of small reflections to non-TEM lines and using the data generated by SDM to transform waveguide TE10 mode to independent slotlines. These tapers were simulated using Ansoft HFSS and results were close to the desired return loss. The slotline to microstrip transition was then designed using a model based on magnetic coupling between the two transmission media and again the structure simulated in HFSS. Finally the dielectric discontinuity between the WR-62 waveguide and dense finline array is minimized by quarter-wave matching using the homogeneous waveguide approximation. Components like waveguide probe transitions and waveguide terminations were also designed to enable testing of the spatial power combiners. Single tray finline, Two tray finline and Four tray finline tapers along with dielectric matching, connected back to back were fabricated and tested using Time Domain Gating feature of Network Analyzer. The results were found to be in good agreement with simulations. The results indicate measured return loss of 26.3dB as compared to simulated return loss of 23.5dB for single tray finline, 19dB as compared to simulated return loss of 18.6dB for two tray finline and 16dB as compared to simulated return loss of 15.5dB for four tray finline at 16GHz. Spatial Power Combining in Rectangular Wave