In this letter, full circuit models are developed for the design of tightly coupled dipole arrays (TCDA) with Marchand baluns. It eliminates the difficulty in the conventional design that relies on parameter tunings with full-wave solvers. Based on the full circuit models, a dual-polarized TCDA achieving at least 10.5:1 bandwidth in the UHF– X -band and ±60° scanning range in the E -, H -, and D -planes is developed. A Marchand balun with over 10:1 bandwidth and operating up to 10 GHz is also developed from its corresponding circuit model. In addition, the dual-polarized TCDA possesses low cross-polarization level (<−20 dB) over the majority of the operating frequency. A 10 × 10 prototype TCDA is then fabricated and measured. The good agreement between the measurement results and simulation results validate the designs.