  Generation of extreme bright coherent synchrotron radiation in a short
wavelength range is of remarkable interest in the synchrotron light source
community. In this paper, a novel technique is adopted to produce the coherent
radiation which uses an angular dispersion to enhance the micro-bunch by a tiny
amplitude of energy modulation. This scheme can be inserted in a long straight
section of a storage ring. A lattice design of an extreme-low emittance storage
ring with 3.5 GeV energy is presented in this paper, which employs a higher
order achromat (HOA) concept. We show the design results for the multi-bend
achromat (MBA) lattice with an emittance of 20 pm-rad in about 900-meter
circumference. Numerical simulations demonstrated that this angular dispersion
induced micro-bunch scheme can be used to generate coherent radiation near soft
x-ray region, the repetition rate can reach 10 kHz and the spectral brightness
can reach 3*10^24phs/s/mm^2/mrad^2/0.1%BW.
