A free-space method is in wide spread use for the reflectivity measurement of electromagnetic wave absorbers (EMA) in VHF and UHF range. In the free-space method, the reflection levels from EMA and from the metal plate with same size as the EMA are measured, and the reflectivity is calculated from their ratio. The incident angle such as normal or oblique must be defined, and the polarization of electromagnetic (EM) wave must be specified to be TE, TM, or circularly-polarized mode. In this paper, a parallel EM wave beam method using dielectric lenses in front of horn antennas was studied experimentally. Electromagnetic wave absorption was measured with the vertical and the oblique incidence by using this parallel EM wave beam. This measurement system has following features:• It is compact because equiphase parallel EM wave beam was obtained in a short distance from the dielectric lens.• It requires no anechoic chamber because of little multi-reflection due to high directivity of parallel EM wave beam.• It allows a large oblique incident measurement by using high directive parallel EM wave beam.

An epoxy-modified urethane rubber mixed with carbon particles is now chosen as the millimeter-wave absorber material in our study. The absorption characteristics of the absorber is measured under temperature changes. The weatherability of our absorber is also clarified based on absorption characteristics, thickness and hardness of the sample. As a result of the temperature characteristics of the absorber, the difference of the maximum absorption frequency under temperature changes is about 1 GHz, however the absorption of 20 dB or more is obtained between 54 and 58 GHz. The result of accelerated artificial exposure test is that 2.8% of the thickness of our sample is shrunk after 1000 hour exposure, and the hardness of rubber is hardened with increasing test time. It is also confirmed that the deterioration of the absorption ranges from 1 to 3 dB, although the absorption of about 20 dB is kept at the frequency range. As a consequence, it is confirmed that the wave absorber using the epoxy-modified urethane rubber mixed with carbon particles has good weatherability including our desired temperature characteristics, and it is suitable for outdoor use.