In this paper, we discuss the usage of image signal in the higher order Nyquist zone of 1-bit low-pass Delta-Sigma (LP-ΔΣ) return-to-zero (RZ)-DAC transmitter. We made a comparison between 3 types of 1-bit DAC signals (non-return-to-zero (NRZ), 50% duty RZ and 25% duty RZ in the simulation and the measurement. By using 1 Vp-p / 1 Gbps DAC output, we observe that the SNR degradation occurs in higher order (more than 5) Nyquist zone in the measurement, but the SNR of more than 50 dB can be obtained in the 7th Nyquist zone (around 3 GHz) for 50% duty RZ and 25% duty RZ conditions. From this measurement, higher SNR in higher Nyquist zone can be obtained by using 50% duty RZ-DAC output than that of 25% duty. Based on this study, we have successfully generated a 24 GHz-band signal by using a 1 Vp-p / 8 Gbps 50% duty RZ-DAC output and confirmed that the SNR of more than 40 dB can be obtained in the 7th Nyquist zone (around 24 GHz).