Fig. I.Suspended stripline structure.In practical SSL circuits, grooves are used in the housing to support the dielectric substrate. For geometries in which the groove depth is a significant fraction of the channel width (often in the case at millimeter wave frequencies), this omission predicts a much higher cut-off frequency for the TE IO type waveguide mode than actually exist. A full wave simulation is necessary to determine the exact cut-off frequency of the higher order waveguide mode in the presence of strip conductor.The electric probe type transition consists of a rectangular electric probe inserted into the waveguide formed by an extension of the suspended stripline beyond the ground plane. The idea is very similar to the conventional waveguide to coaxial line transition. These types of transitions have been already developed at Kaband and W-band [1]-[4]. This paper describes the fabrication and performance of the above transition for D-band on 2 mil quartz substrate. Although fused quartz is an extremely brittle material, But for realizing millimeter wave circuits at these frequencies, fused quartz substrate is preferred due to its lower loss tangent, extremely good surface finish and tight control of relative permittivity. Proper and careful handling is required for fabrication ofMIC circuits on quartz. II. FABRICATIONBare fused quartz (Er=3.78) of 20 x 20 mm 2 size were cleaned and coated with 2 Jlm gold on one side by electron beam evaporation followed by electroplating.For better sticking of gold, 200 Achromium was coated before gold. Chrome mask were prepared using Laser Pattern Generator DWL66 and subsequent developing and etching. After photolithography process (resist coating, UV exposing, developing and wet etching), MIC circuit on quartz was fabricated. After dicing the Abstract -A back to back waveguide to suspended stripline transition for D-band has been fabricated on 2 mil (50.8 JUIl) fused quartz substrate by photolithography process and the performance of the transition has been studied. The excitation of transition probe has been done by placing the rectangular probe transversely across the WR6 waveguide and using a 50 JUIl fIXed short. To obtain low reflections over the whole operating frequency range of the transition, dimensional parameters, such as probe length, probe width, width and height of suspended stripline channel and thickness of quartz substrate have been optimized using electromagnetic simulation software HFSS. Insertion loss of less than 1.5 dB has been achieved for fabricated back to back transition on quartz over frequency range from 130 to 150 GHz.

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Design and development of thermistor based power meter at 140 gigahertz (GHz) frequency band have been presented. Power meter comprises power sensor, amplifier circuit and dialog based graphical user interface in visual C++ for the average power measurement. The output power level of a component or system is very critical design factor. Thus there was a need of a power meter for the development of millimeter wave components at 140 GHz frequency band. Power sensor has been designed and developed using NTC (Negative Temperature Coefficient) thermistors. The design aims at developing a direct, simple and inexpensive power meter that can be used to measure absolute power at 140 GHz frequency band. Due to absorption of 140 GHz frequencies, resistance of thermistor changes to a new value. This change in resistance of thermistor can be converted to a dc voltage change and amplified voltage change can be fed to computer through data acquisition card. Dialog based graphical user interface (GUI) has been developed in visual C++ language for average power measurement in dBm. WR6 standard rectangular waveguide is the input port for the sensor of power meter. Temperature compensation has been achieved. Moderate sensor return loss greater than 20 dB has been found over the frequency range 110 to 170 GHz. The response time of the power sensor is 10 second. Average power accuracy is better than ±0.25 dB within the power range from −10 to 10 dBm at 140 GHz frequency band.

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Simulation and experimental results at 35 GHz, for a single target of unit reflectivity, a concrete pillar and a gun shaped object placed in the central region  of 2-D scene , have been presented using circularly co-located transmit and receive co-arrays. Simulation program has been written in MATLAB to reconstruct the raw image using an improvised algorithm. Simulation and experimental results confirm the method of reconstruction of image. Reconstruction of a Gun-shaped object has also been shown with help of simulation and experimental results. Reconstruction of image has been performed using post data acquisition processing on the received scattered data. Experimental results confirm that the method can be used to reconstruct quality image for detection of concealed metallic objects using MM wave frequencies.