Surface Electromagnetic Wave Characterization Using Non-Invasive Photonic Electric Field Sensors

Electromagnetic properties of aircraft and missile skins have a large effect on radar cross sections and determine the level of stealth that is achieved over the various RF bands currently in use. RF absorption, reflection, and propagation along the skin surface all serve as important measures of the electromagnetic performance of the coated surfaces. Non-invasive probing of the electromagnetic field just above the propagating wave at multiple spots along the propagation direction can be used to determine and measure wave propagation parameters, including effective RF index, loss per length, wave impedance, and frequency dependent material properties of the coatings. Wide-band photonic electric field sensors have been demonstrated for probing of dielectric layers by measuring the traveling waves along the coated aircraft surface. The photonic E-field sensors are extremely linear and produce an exact real time analog RF representation of the electric field, including phase information. These ultra-wideband (UWB) photonic RF sensors are very small and contain negligible metal content, allowing them to be placed at close proximity without perturbing the RF surface waves. This is very important in accurately characterizing highly damped surface waves on absorber layers. This paper discusses the linearity, bandwidth, polarization, and sensitivity of the unique UWB photonic E-field sensor design. Experimental results are presented on surface-wave characterization measurements using these sensors.