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A new trapezoid-shaped Frisch-grid ionization chamber (TFG-IC) has been built as a part of a $$\varDelta {E}-E$$ Δ E - E telescope system for the detection and identification of charged particles at energies down to a few MeV. To study the effect of the drift electric field uniformity, two types of sealed windows, namely a pair of SSA (split-strip aluminized mylar film) and a pair of DSA (double-sided aluminized mylar film) sealed windows have been investigated. The detector’s performances were studied using a standard $$^{241}$$ 241 Am source at different gas pressures, and the total energy-deposit resolution achieved is about 1.1%(FWHM). The $$\varDelta {E}-E$$ Δ E - E telescope, which was composed of TFG-IC and a DSSSD (double-sided silicon strip detector), has been tested using a three-component $$\alpha $$ α source and the $$^{241}$$ 241 Am source under laboratory conditions. The results show that the energy resolution with the SSA sealed windows which provide uniform drift electric field has a smaller fluctuation than that with the DSA ones; the fluctuations are about 1% and 4% for the former and the latter, respectively. Simulations using the COMSOL software also confirmed the electric-field distortion at the edge of the detector with the DSA windows. A correlation curve between energy resolution and energy deposit of charged particles at various gas pressures and for two gas species is derived for TFG-IC with the SSA sealed windows using the measurement with the $$^{241}$$ 241 Am source. Incorporating the above results, we performed Monte Carlo simulations to evaluate the particle-identification capability of the telescope. The results show that the telescope can be extended to the identification of low-energy particles.