Influence of substrate configuration on the angular response pattern of infrared antennas

The far-field angular response pattern for dipole antenna-coupled infrared detectors is investigated. These devices utilize an asymmetric metal-oxide-metal diode that is capable of rectifying infrared-frequency antenna currents without applied bias. Devices are fabricated on both planar and hemispherical lens substrates. Measurements indicate that the angular response can be tailored by the thickness of the electrical isolation standoff layer on which the detector is fabricated and/or the inclusion of a ground plane. Electromagnetic simulations and analytical expressions show excellent agreement with the measured results

Angular Resolution Improvement Of Infrared Phased-Array Antennas

Measured and simulated angular response patterns at 10.6 μm demonstrate considerable improvement in angular resolution with a four-element phased-array antenna versus that of a two-element array. Due to propagation loss in the transmission line that connects the antenna elements, further resolution improvement is minimal with a six-element phased array. Additional measurements of a two-element array with increased metal thickness indicate that further improvement in angular resolution is possible by reducing propagation loss in the transmission line. With the combination of additional antenna elements and reduced propagation loss, substantial improvement in the angular resolution of off-broadside performance is also observed. All devices use a metal-oxide-metal tunnel diode as the detector element. © 2006 IEEE

Infrared Phased-Array Sensor

Metal-oxide-metal (MOM) tunnel diode detectors when integrated with phased-array antennas provide determination of the angle of arrival and degree of coherence of received infrared radiation. Angle-of-arrival measurements are made with a pair of dipole antennas coupled to a MOM diode through a coplanar strip transmission line. The direction of maximum angular response is altered by varying the position of the MOM diode along the transmission line connecting the antenna elements. Phased-array antennas can also be used to measure the degree of coherence of a partially coherent infrared field. With a two-element array, the degree of coherence is a measure of the correlation of electric fields received by the antennas as a function of the element separation. Antenna-coupled MOM diode devices are fabricated using electron beam lithography and thin-film deposition through a resist shadow mask. Measurements at 10.6 μm are substantiated by electromagnetic simulations and compared to analytic results. © 2011 SPIE

Design Of An Mom Diode-Coupled Frequency-Selective Surface

This article presents the design of a slot-antenna-based frequency selective surface coupled with metal-oxide-metal diodes integrated into the structure. This design takes advantage of a single self-aligned patterning step using shadow evaporation. The structure is optimized at 10.6 μm to have less than 2% reflection with 70% of the incident energy dissipated into the oxide layer. Initial experimental results conducted with e-beam lithography are presented. The fabricated structure is shown to produce a polarization sensitive unbiased DC current. This design will be useful for both infrared sensing and imaging as well as direct conversion of thermal energy. © 2012 Wiley Periodicals, Inc

Directional control of infrared antenna-coupled tunnel diodes

Directional control of received infrared radiation is demonstrated with a phased-array antenna connected by a coplanar strip transmission line to a metal-oxide-metal (MOM) tunnel diode. We implement a MOM diode to ensure that the measured response originates from the interference of infrared antenna currents at specific locations in the array. The reception angle of the antenna is altered by shifting the diode position along the transmission line connecting the antenna elements. By fabricating the devices on a quarter wave dielectric layer above a ground plane, narrow beam widths of 35 degrees FWHM in power and reception angles of +/- 50 degrees are achieved with minimal side lobe contributions. Measured radiation patterns at 10.6 mu m are substantiated by electromagnetic simulations as well as an analytic interference model

Evaporation Of Uniform Antireflection Coatings On Hemispherical Lenses To Enhance Infrared Antenna Gain

Infrared dipole-coupled bolometers receive radiation more efficiently when illuminated through a high permittivity, antireflection (AR) coated, hemispherical immersion lens. To maintain the enhanced responsivity for all illumination angles, the AR coating must be uniform over the hemispherical surface. An evaporation method for depositing a uniform AR coating on the hemispherical surface is presented. The lens is tilted relative to the source, which can be either electron-beam or thermal, and rotated throughout the deposition. Evaporation at an angle of 70° yields a uniform film with less than 10% thickness variation over a 120° full angle of the hemispherical surface. A theoretical model is developed and compared to profilometer measurements. In all cases, there is general agreement between theory and measurement. A single dipole is fabricated onto the flat surface of an AR-coated germanium immersion lens and the responsivity is measured for both substrate-side and air-side illumination. With a zinc sulfide (ZnS) single-layer AR coating, substrate-side illumination yields a broadside antenna response 49 ± 2.7 times greater than air-side illumination. © 2009 Elsevier B.V. All rights reserved