Modal beamformer for circular arrays, which is based on a circular harmonics decomposition of the sound field, is flexible for use because it is decoupled from the sensor positions. A time-domain implementation of broadband modal beamformer for circular arrays is presented in this paper. This beamforming structure consists of a real-valued circular harmonics transform and steering unit, followed by a pattern generation unit implemented by a set of real-valued finite impulse response (FIR) filters. The beam pattern is controlled through the FIR filters' tap weights, whose design is decoupled from beam pattern steering and can be formulated as a constrained optimization problem that can be solved efficiently. Multiple array performance measures such as array gain, sensitivity, mainlobe, and sidelobes can be taken into consideration in beamformer design, which is very important in practical applications. Simulation and experimental results are presented to illustrate the effectiveness of the proposed time-domain broadband modal beamforming approach. Performance comparisons between the proposed and the classical methods in weight coefficients, beam patterns, and quality of audio output are also provided. The results show that the proposed approach possesses high robustness and can achieve good frequency invariance.