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

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.