The phase noise of the microwave synthesizer is one of the considerable limitations on the short-term stability of microwave atomic clocks through Dick effect. We present a dedicated microwave frequency synthesizer at 6.834 GHz in place of the commercial microwave signal generator. A phase-locked loop (PLL)-based direct digital synthesizer (DDS) generates a 134 MHz signal, which is mixed with a 6.7 GHz signal output from a phase-locked dielectric resonant oscillator (PDRO), to deliver a 6.834 GHz signal to the rubidium atomic sample for microwave interrogation. We measured the phase noise behavior of the 6.834 GHz signal to be −91 dBc/Hz and −122 dBc/Hz at 100 Hz and 1 kHz offset frequencies, respectively, which induced an instability contribution of 5.5×10 −14 at 1s averaging time to the clock. The dedicated microwave frequency synthesizer helps to improve the compactness and low-consumption of the engineering rubidium atomic clocks.