Microstrip fed printed dipole with an integral balun

Claim 1

A microstrip fed printed dipole with an integral balun comprising: a planar dielectric substrate having a first metallization layer disposed on the under surface and a second metallization layer disposed on the upper surface, (1) an unbalanced microstrip transmission line with a ground plane formed from said first metallization and a strip conductor formed from said second metallization, (2) a dipole radiating element having two spaced arms formed from said first metallization and exhibiting a first impedance at resonance, and (3) a transition in which a continuation of the ground plane of said unbalanced transmission line is bifurcated by a central slot extending to the arms of said dipole to form a first and a second ground plane, the bifurcated ground planes forming a balanced transmission line coextensive with the slot and exhibiting a characteristic impedance approximately matching said first impedance, and a continuation of the strip conductor of said unbalanced transmission line forming a three part strip conductor disposed over said bifurcated ground planes to continue said unbalanced transmission line, the continuation of said unbalanced transmission line exhibiting a characteristic impedance approximately matching said first impedance, said three part strip conductor having a "J" shaped configuration, a first part continuing over said first bifurcated ground plane toward said dipole radiating element, a second part extending across said slot over said dipole from said first bifurcated ground plane to said second bifurcated ground plane, and a third part extending back toward said unbalanced transmission line and ending in an open circuit, said dipole radiating element being formed as a diverging extension of said first and second bifurcated ground planes, the inner portions of the arms of said dipole underlying and strongly coupled to said second part, and the outer portions of said arms extending beyond said second part for efficient radiation, and wherein: the electrical length (theta b) of said unbalanced transmission line, measured from said slot to said open circuited end is approximately one-quarter wavelength so as to provide a low shunt RF impedance to unbalanced mode currents at the dipole load (Zl), and the electrical length (theta ab) of said balanced transmission line measured from the base of the slot to the half width of the dipole arm is approximately one-quarter wavelength so as to provide a high shunt RF impedance to balanced mode currents at the dipole load, thereby facilitating the conversion of RF current flowing in an unbalanced mode in said microstrip transmission line to a balanced mode in the dipole arms in transmission, the reverse occurring in reception.