In this paper, we present terahertz bandpass filters composed of resonant arrays of crossed slots in lossy metal films deposited on dielectric membranes. The filters exhibit insertion loss as low as 1.9 dB at room temperature and 1.2 dB at 77 K at a center frequency of 2.2 THz. It is found that the dielectric substrate introduces a downward shift in frequency not predicted by standard mean dielectric-constant approximations. This shift is proportional to the permittivity and thickness of the substrate, and is accurately modeled for polyester, fused quartz and silicon substrates using a finite-difference time-domain (FDTD) model. It is also found that the insertion loss and-factors of the filters vary with the product of the thickness and conductivity of the metal film for lead and gold films, even in cases when the thickness is several skin depths at the center frequency. The FDTD theory presented here accounts for some of the conductor losses.
The design and measured results of a single-substrate transceiver module suitable for 76-77-GHz pulsed-Doppler radar applications are presented. Emphasis on ease of manufacture and cost reduction of commercial millimeter-wave systems is employed throughout as a design parameter. The importance of using predictive modeling techniques in understanding the robustness of the circuit design is stressed. Manufacturing techniques that conform to standard high-volume assembly constraints have been used. The packaged transceiver module, including three waveguide ports and intermediate-frequency output, measures 20 mm 22 mm 8 mm. The circuit is implemented using discrete GaAs/AlGaAs pseudomorphic high electron mobility transistors (pHEMTs), GaAs Schottky diodes, and varactor diodes, as well as GaAs p-i-n and pHEMT monolithic microwave integrated circuits mounted on a low-cost 127-m-thick glass substrate. A novel microstrip-to-waveguide transition is described to transform the planar microstrip signal into the waveguide launch. The module is integrated with a quasi-optical antenna. The measured performance of both the component parts and the complete radar transceiver module is described.
-Scanning in arrays is conventionally achieved through phase shiften. Recent work has indicated that scanning can be achieved with significantly reduced complexity and cost using coupled-oscillator techniques. However, the scan range has been somewhat limited using this tecbnique. This paper describes a simple method to greatly enhance the scan range using varactor frequency doublers, which has the added advantage of simplifying the fimdamental mode oscillator design.In an effort to combine power in an efficient way the field of quasi optical power combining was born.[3]-[6] A large number of solid state oscillators can be integrated in such a way that their respective outputs coherently add in free space. The low loss properties of free space, especially at higher frequencies, along with the reliability of solid state devices make this approach particularly attractive.Extensive work, theoretical [1,7,8] and experimental [1,2] on the coupling dynamics of these discrete oscillators has already been performed. A significant breakthtough of this research was the discovery of a simple way to induce beam scanning in such an array of coupled oscillators [2]. This can be achieved by frequency &tuning the end elements of the array. Since conventional beam steering mandates the use of one phase shifter per array element, the simplicity of implementation of this new technique becomes obvious. There is no more need for a cumbersome control network to create a phase shift between successive elements. Never&heless, the phase shift and therefore the scan angle is now limited by coupled oscillator dynamics. Some concem has been expressed over these limitations. In this paper we are proposing a slight modification on the coupled oscillator beam scanning array that will drastically enhance its scanning characteristics. A small inclrease in implementation complexity is expected, but is somewhat offset by other advantages. A frequency doubler is inserted between each oscillator and its respective antenna Fig. 1. The phase shift generated between each oscillator is doubled along with the oscillator's frequency. The radiating elements are phase shifted with respect to each other, tsvice as much as the oscillators feeding them are. Clearly the scan angle is increased. Furthermore, the oscillators need to be designed, at only half of the array 0peratiOeal frequency.As was shown in [ 1,7] the theoretical phase shift At) that can be generated between successive coupled oscillators lies within -900 Sit) S900. In an array of element ~7803-27145/95/s4.000 1995 IEEE 1308
Most reported spatially combined or quasioptical amplifier arrays exhibit resonant narrowband performance (<10%) and have not addressed thermal management issues. We report a waveguide-based spatial combining scheme using broadband tapered-slot transitions, capable of realizing full waveguide band coverage (40% fractional bandwidth) with good thermal properties. An X-band prototype using eight mediumpower GaAs monolithic microwave integrated circuits (MMIC's) produced an output power of 2.4 W and 9-dB power gain at 1-dB compression, with a combining efficiency of 68% and <61-dB gain variation over the full waveguide band (8-12 GHz).
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