Daniel J. Hoppe

A High-Power

A method of using low-loss waveguide septum combiners is developed into a high-power -band (31-36 GHz) amplifier producing 50 W at 33 GHz (Ka-band) using 32 low-power (>2 W) solid-state amplifier modules. By using low-loss waveguide combining and a packaged monolithic microwave integrated circuit with a low-loss microstrip-to-waveguide launcher, the output loss is minimized, allowing for the overall power-combining efficiency to remain high, 80% (average insertion loss of combiner < 0.7 dB and average insertion loss of launcher <0.3 dB) over 31-36 GHz. In the past, lower power-combining efficiencies have limited the number of modules that can be combined at -band, and hence, have limited the power output. The approach demonstrated in this paper, with high power-combining efficiency, allows a very large number (32) of solid-state amplifier modules to be combined to produce high powers. Greater than 50 W was demonstrated with low power modules, but even higher powers 120 W are possible. The current approach is based on corporate combining, using low-loss waveguide septum combiners that provide isolation, maintaining the true graceful degradation of a modular solid-state amplifier system.

Ka

A new symmetric formulation of the hybrid finite element method (HFEM) is described which combines elements of the electric field integral equation (EFIE) and the magnetic field integral equation (MFIE) for the exterior region along with the finite element solution for the interior region. The formulation is applied to scattering by inhomogeneous bodies of revolution. To avoid spurious modes in the interior region a combination of vector and nodal based finite elements are used. Integral equations in the exterior region are used to enforce the Sommerfeld radiation condition by matching both the tangential electric and magnetic fields between interior and exterior regions. Results from this symmetric formulation as well as formulations based solely on the EFIE or MFIE are compared to exact series solutions and integral equation solutions for a number of examples. The behaviors of the symmetric, EFIE, and MFIE solutions are examined at potential resonant frequencies of the interior and exterior regions, demonstrating the advantage of this symmetric formulation. >

-Band (31–36 GHz) Solid-State Amplifier Based on Low-Loss Corporate Waveguide Combining

Two novel high gain deployable reflectarray antennas to support CubeSat telecommunications are described and compared with other high gain CubeSat antenna technologies. The first reflectarray is the Integrated Solar Array and Reflectarray Antenna (ISARA), a K/Ka-band antenna that also incorporates a dense packing of solar cells used to provide electrical power for the spacecraft. The second is an X-band reflectarray designed to provide a bent pipe telecom link. These reflectarrays are ideal for CubeSat applications because they require negligible stowed volume and impose a modest mass increase. The antenna designs and measured performance results are presented.

A hybrid symmetric FEM/MOM formulation applied to scattering by inhomogeneous bodies of revolution

A new method for finding radiation patterns and the reflection coefficients associated with an axisymmetric waveguide fed horn is presented. The approach is based on a hybrid finite element method (FEM) wherein the electromagnetic fields in the FEM region are coupled to the fields outside by two surface integral equations. Because of the local nature of the FEM, this formalism allows for the presence of inhomogeneities to be included in the problem domain. The matrix equation which results from the application of this method is shown to be complex-symmetric. Comparisons of calculated and measured data for two different horns show good agreement.

Novel deployable reflectarray antennas for CubeSat communications

Direct imaging and characterization of exo-solar terrestrial planets require coronagraphic instruments capable of suppressing star light to 10-10. Pupil shaping masks have been proposed and designed1 at Princeton University to accomplish such a goal. Based on Princeton designs, free standing (without a substrate) silicon masks have been fabricated with lithographic and deep etching techniques. In this paper, we discuss the fabrication of such masks and present their physical and optical characteristics in relevance to their performance over the visible to near IR bandwidth.

A hybrid finite-element method for axisymmetric waveguide-fed horns

The recent introduction of 35-nm gate length InP MMIC low-noise amplifiers has enabled significant advances in Earth remote sensing. These low-noise amplifiers achieve 2-dB and 3-dB noise figure at 180 GHz and 90 GHz, respectively, at room temperature. For Earth remote sensing using ocean surface altimeters, the design of new millimeter-wave radiometers is motivated by the fact that these missions include nadir-viewing, co-located 18–37 GHz microwave radiometers to measure wet-tropospheric path delay. However, due to the substantial area of the surface instantaneous fields of view (IFOV) at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 50 km from the coasts. In addition, conventional microwave radiometers do not provide wet-path delay over land. For a maximum antenna aperture size on Earth observation satellites, the addition of higher-frequency millimeter-wave (90–170 GHz) radiometers to current Jason-class radiometers is expected to improve retrievals of wet-tropospheric delay in coastal areas and to increase the potential for over-land retrievals.

Fabrication and characteristics of free-standing shaped pupil masks for TPF-coronagraph

The development of stellar coronagraphs for exoplanet detection requires apodized occulting masks to effectively remove the light from the central star while allowing planet light to propagate past. One possible implementation, a gray-scale mask, includes the placement of micron-scale neutral density light absorbing patterns using High Energy Beam Sensitive (HEBS) glass. A second implementation, binary masks, uses micron-scale diffractive/reflective patterns. Coronagraph performance will be influenced by wavefront phase shifts introduced by the masks, hence accurate characterization of the fundamental optical properties, namely optical density (OD), phase advance/delay and optical constants of the material is needed for occulter design, development and modeling. In this paper we describe an interferometric apparatus that measures wavefront phase advance/delay through grey-scale and binary masks as functions of wavelength and optical density, which is also measured. Results for HEBS gray-scale masks will be presented along with ellipsometric measurements of optical constants.

InP HEMT low-noise amplifier-based millimeter-wave radiometers from 90 to 180 GHz with internal calibration for remote sensing of atmospheric wet-path delay

A TE/TM modal solution for a longitudinally corrugated rectangular waveguide is developed. These longitudinal corrugations can be used to excite a quasi-TEM wave and form a hard waveguide by correctly choosing the impedance at the guide wall. The correctly chosen impedance is referred to as the hard boundary condition. The modal solution developed here solves the problem of longitudinal corrugations filled with a dielectric material by first finding and solving the characteristic equation for a complete TE/TM modal set. It is shown that this TE/TM mode solution can be used to achieve the hard boundary condition resulting in the quasi-TEM wave in a hard waveguide for discrete values of corrugation depth. Beyond each of these depths, a mode becomes a surface wave. The theoretical mode set is amenable to the solution of problems using the mode-matching method. A combination of the mode-matching method and the TE/TM modal solution will allow the solution of larger problems.

Measurement of wavefront phase delay and optical density inapodized coronagraphic mask materials

The Terrestrial Planet Finder Coronagraph (TPF-C) for observing and characterizing exo-solar planets requiring star light suppression to 10-10 level demands optical aberrations and instrument stability to sub-nm levels. Additionally, wavefront polarization has to be tightly controlled over the 8m x 3.5m primary mirror aperture and 500nm - 800nm minimum bandwidth because the Deformable Mirror (DM) employed to control the wavefront can not correct simultaneously for the different wavefronts presented by two orthogonal uncorrected polarization fields. Further, leakage of cross polarization fields introduced by the various optical surfaces can degrade the image contrast. The study reported here shows mirror coating designs that reduce the phase difference between orthogonal polarizations reflected by a mirror surface to less than 0.6 deg over the bandwidth and aperture which may encounter a maximum angle of incidence of about 12 deg at a curved mirror. Such designs mitigate the contrast degradation due to cross polarization leakage. Simulations show that required contrast levels can be achieved with such coatings.

A TE/TM modal solution for rectangular hard waveguides

The scattered fields from axisymmetric problems containing anisotropic media are found by a hybrid finite element method. In particular a symmetric formulation for bodies of revolution that incorporates a finite element formulation for axially magnetized ferrite materials is presented. The method is applied to a ferrite cylinder with quartz matching layers. A Gaussian beam input is used to predict the Faraday rotation through the ferrite cylinder and display it visually. >