This paper describes the effects of changing the magnet shape of permanent magnets (PMs) in a Halbach array applied in a slotless tubular actuator. More specifically, the square shaped magnets are replaced by trapezoidal shaped magnets. A semi-analytical magnetic field solution of regular square shaped magnets is presented and used to approximate the airgap field produced by the trapezoidal shaped PMs. The method is based on dividing the magnets into several radial layers and superposition of the fields to calculate the total magnetic field. The results are compared to finite element analysis (FEA) and show excellent agreement. Using this magnetic field solution, the effect of the shape of the magnets on the magnetic field waveform is analyzed by means of a parametric search.