represents the resolution along the platform (satellite and UAV) flight path and is determined by the antenna length in the azimuth direction. The antenna beamwidth is inversely proportional to the antenna length [10]. Second, the range resolution is the resolution where the beam is being emitted. Thus, the waveform characteristic affects the range resolution [11; 12]. The waveform imbalance (e.g., amplitude, phase, and delay) was calibrated for a very high resolution with three sub-band frequencies [11]. In [12], a new equation was derived based on wavenumbers. The ground-range resolution was derived by the wavenumber, platform velocity, and locations. There are further studies using nonlinear frequency modulation for improvement of the signal-to-noise ratio [13; 14; 15]. Nonlinear frequency modulation can suppress the sidelobes and save transmitting power without losing the signal-to-noise ratio. In the radar system, the shorter the pulse, the smaller is the target that can be discriminated [16]. However, because the implementation of a very short pulse has a system limitation, SAR adopted a chirp waveform [17]. In a SAR system, the wider the bandwidth, the higher the resolution that can be acquired. In the case of the L-band SAR, which is relatively low in frequency and has a narrow band, the range resolution is tens of meters, even though the system has a large antenna. In contrast, the X-band SAR using a relatively small antenna can have high-resolution capability due to the wideband waveform [9; 16; 17; 18]. Generation of the wide bandwidth depends on the signal generation clock. However, high-speed systems, such as field programmable gate array (FPGA) and digital analog converter (DAC), cost a lot of money. Thus, we propose a high-speed system scheme using a relatively low system load for generation of a wide bandwidth waveform. A waveform generator generates a specific waveform using a commercial product or the desired waveform based on the environment using an FPGA. Conventional SAR studies used commercial chips or test equipment for efficiency with the experiments. The equipment is limited due to its unchangeable characteristics, making it challenging to use experimental parameters, such as wide bandwidth and different shapes of the waveform. In the case of a study using a DDS chip, the researchers used the multiplier or reference source to expand the bandwidth [14; 19]. The multiplier can output multiple bandwidths without an FPGA burden, but the distortion in the frequency also expands such that spectrum quality is decreased. The other problem in conventional systems is the radio frequency (RF) imbalance. RF imbalance and nonlinearity cause waveform distortion and image degradation. The RF linearity analysis and digital pre-distortion produced by a high-power amplifier were compensated for in [20; 21]. In this study, we describe a wideband waveform generation method and demonstrate the results using a developed waveform generator. We modified the conventional multi-DDS (MDDS) method to compensate for the phase center error generated at the baseband. Pre-distortion was also applied to improve X-band spectrum quality. The waveform generator was designed based on an MDDS structure that can generate a wide bandwidth without a system clock burden. Moreover, the developed waveform generator can output the desired waveform based on the environment because we programed the FPGA accordingly. Finally, the compensated phase center and the pre-distorted phase are verified by the experimental results. The main contributions of this study include:  
* **Proposal for an improved MDDS method**: We propose an improved MDDS method for wideband waveform generation to satisfy the desired clock cost and reduce the phase error. * **Development and verification of the waveform generator for wideband**: For a high-speed and low-cost system, we propose a hardware structure in accordance with the improved MDDS method.