With the progress of the electronics industry and radio communication technology, humans enjoy greater freedom in communicating. On the other hand, certain problems, such as electromagnetic interference (EMI), have arisen due to the increased use of electromagnetic (EM) waves. EM wave absorbers are used for constructing an anechoic chamber to test and measure EMI and electromagnetic susceptibility (EMS). Prior to 1998, international standards for anechoic chambers required that EM wave absorbers should absorb more 20 dB in the bandwidth from 30 MHz to 1,000 MHz. Since November 1998, however, the Comit International Special des Perturbations Radioelectrigne (CISPR) has required that the frequency bandwidth be extended from 1 GHz to 18 GHz for EMI measurement by the CISPR11. In this work, wide-band EM wave absorbers were designed by a theoretical model using the equivalent material constants method (EMCM). We designed a cross-shaped absorber which has a bandwidth from 30 MHz to above 2 GHz under the tolerance limit of -20 dB in reflection, the results of which were compared with the results analyzed using the finite-difference time-domain method (FDTD). The tapered cross-shaped absorber was also designed, which has a bandwidth from 30 MHz to 26 GHz under the same tolerance limit.