This paper investigates broadband planar antennas that consist of a wide rectangular slot with various tuning stubs. The antennas are fed by coplanar waveguides. Wide slots containing a, single tuning stub, V-shaped stubs, as well as inverted F-shaped stubs are investigated. Despite using a high dielectric constant substrate, the proposed antennas exhibit very broad bandwidth. They also have broadside bidirectional radiation. The radiation pattern stability with frequency for the various configurations is presented. One of the proposed configurations, the inverted F stub in a wide rectangular slot, produced very stable radiation patterns over its entire impedance bandwidth of about 40%. Also, an impedance bandwidth of 44% was obtained for the V-shaped stub in a rectangular slot. Simulations as well as experimental results are presented.