  We present the design, construction and measurements of the electromagnetic
performance of a wideband space beam splitter. The beam splitter is designed to
power divide the incident radiation into reflected and transmitted components
for interferometer measurement of spectral features in the mean cosmic radio
background. Analysis of a 2-element interferometer configuration with a
vertical beam splitter between a pair of antennas leads to the requirement that
the beam splitter be a resistive sheet with sheet resistance {\eta}o /2, where
{\eta}o is the impedance of free space. The transmission and reflection
properties of such a sheet is computed for normal and oblique incidences and
for orthogonal polarizations of the incident electric field. We have
constructed such an electromagnetic beam splitter as a square soldered grid of
resistors of value 180 Ohms (approximately {\eta}o /2) and a grid size of 0.1
m, and present measurements of the reflection and transmission coefficients
over a wide frequency range between 50 and 250 MHz in which the wavelength well
exceeds the mesh size. Our measurements of the coefficients for voltage
transmission and reflection agree to within 5% with physical optics modeling of
the wave propagation, which takes into account edge diffraction.
