Compact Series-Fed Microstrip Patch Arrays Excited With Dolph–Chebyshev Distributions Realized With Slow Wave Transmission Line Feed Networks

Abstract

Compact series-fed microstrip patch arrays are presented that are excited with Dolph–Chebyshev distributions realized with periodic stub-loaded slow wave transmission line (SW-TL) feed networks. The methodology to design these SW-TL feed networks is described in detail. The developed equivalent circuit representation reveals that their characteristic impedance can be modulated while maintaining their propagation constant (guided-wavelength) simply by modifying the widths of their stubs. These stub-loaded SW-TL feed networks are seamlessly integrated with uniformly spaced microstrip patch arrays. The desired Dolph–Chebyshev excitations are realized simply by modulating the widths of their stubs. Moreover, the slow wave property of the SW-TLs facilitates an advantageous closely spaced Dolph–Chebyshev current distribution, i.e., a very compact array with $0.3\lambda _{0}$ spacing between the array elements is attained. The Dolph–Chebyshev SW-TL feed networks are employed to excite microstrip patch arrays that radiate a broadside main beam with −30 dB sidelobe levels and a grating-lobe-free 50° tilted main beam. A measured prototype of the broadside-radiating array confirms its simulated performance characteristics. In comparison with conventional Dolph–Chebyshev arrays implemented with standard microstrip transmission line (MTL) feed networks, the optimized designs are grating-lobe-free and have enhanced bandwidths.