Antenna properties of glow-discharge detectors of microwave radiation

Investigations of X-band directionality of response by sensitive d.c. glow-discharge detectors of microwave radiation indicate no noticeable dependence on the d.c. field being parallel or perpendicular to the microwave field, thus supporting a previously developed modol of detection by the plasma. However, if the microwave frequency is such that the electrode dimension tangential to the microwave field approaches one-half the wavelength, changes in response directionality occur which appear to result possibly from diffraction and scattering by the glass envelope, resulting in mode conversion and transmission line resonance by the electrodes. Lack of noticeable antenna properties by these devices at X-band suggests the detection mechanism is based primarily in the discharge itself and that ‘ probe ’ rectification by the anode, though not excluded completely, is not too significant at X-band (⋍ 3 cm wavelength) in view of the small inter-electrode space (≈ 1–2 mm) of such devices. Inter-electrode distances are such that phase differences in the signal incident at each electrode are important at millimetre wavelengths. Further investigation is suggested, particularly at millimetre wave frequencies, in order to optimize electrode geometry for maximum detector response.