Michelle Champion

Experimental validation of a partially-overlapped, constrained-feed network for Limited-Field-of-View (LFOV) applications

This paper presents an experimental verification of the partially-overlapped, constrained- feed network first introduced in (Mailloux, 2001). Unlike (Mailloux, 2001), we chose to operate the network in a LFOV mode to significantly reduce the amount of measured data. A GA was used to optimize the complex weights of the network, resulting in a system that is capable of at least 25-dB sidelobe suppression over angular bandwidths as large as 11.54deg. Furthermore, at least 30-dB sidelobe suppression is achievable for bandwidths as large as 8.05deg. One of the major benefits of this system is that the weights at both the constituent-beam and subarray levels can correct for phase errors within the network. Since it is difficult (and/or expensive) to maintain consistent phase at this frequency, this self-calibration capability provides a big advantage.

Materials for liquid RF electronics: Long term operation of gallium liquid metal alloys in reconfigurable RF applciations

Room temperature liquid electronics offers the potential of rewiring and reconfiguring functionality in real-time. One of the most promising materials recently explored for these components is gallium liquid metal alloys (GaLMAs) because of their non-toxic and self-healing properties. Unfortunately the reactive nature of the surface, with both oxygen to form a thin viscoelastic skin and alloy formation with solid metal electrodes, results in the need for better control over these interfaces. This control needs to be achieved while maintaining appropriate RF properties and reliability of the fluidic electronic components. In this work, we provide a new material set to control the interface of GaLMAs and characterize the effects on RF performance.

Considerations in the design of parallel plate lüneburg beamformers and cylindrical arrays

We present a new concept for a low-profile, low cost integrated multi-beam cylindrical array. It consists of a parallel plate 2D Luneburg beamformer feeding a cylindrical aperture. The concept incorporates a number of novel features, such as low profile, and highly directive excitations. All these features are introduced in order to reduce volume, weight and ultimately cost. The paper discusses the various challenges this concept presents, and ways to mitigate these difficulties.

Polarization Reconfigurable Antennas Using a Liquid Metal Switching Mechanism

This paper describes the use of a pressure-actuated liquid metal switching mechanism to alter the polarization characteristics of printed circuit antennas. The mechanism is applied to a truncated corner patch antenna and an annular slot antenna to provide switching between linear and circular polarization.

A conformal rotman lens

One of the challenges of designing UAVs is the limited amount of interior space for components. The communication, navigation, and radar systems all compete for this limited space. Phased array antenna systems, in turn, save space, weight, and power by steering the antenna electrically versus mechanically. Rotman lens devices (Fig. 1) are a particularly efficient means providing the correct amplitude and phase waveform inputs to a phased array antenna to allow this steering. However, the elongated, flat shape of a Rotman lens makes it cumbersome to fit the confines of a UAV.

A low-profile VHF dual band printed antenna

We present a new design of a low-profile small VHF dual-band omnidirectional antenna made on a compact ARLON board. The antenna was optimized using full-wave EM simulations to provide an omnidirectional radiation pattern. A reactive impedance matching circuit was synthesized to operate the antenna in two VHF bands around 150 and 450 MHz with high efficiency. Several prototypes of the antenna have been fabricated and tested.

Antennas operating in close proximity of textured surfaces

In this paper a new method to reduce the interaction between antennas and nearby objects is proposed. It involves the use of a thin textured surface similar to a high-impedance layer that is wrapped around the objects that are in close proximity of the antenna (ground planes, various platforms, etc.). The textured surface acts as a “diffuser” spreading the reflected fields from the close objects and thereby reducing the power otherwise directed in the specular reflections. This method allows reducing the profile of endfire antennas working in close proximity to various platforms.

Array calibration and health/status check using a “reverse” transmit/receive module

A method for in situ evaluation of the health and status of individual array elements within a large phased array has been developed and demonstrated at the subarray level. The technique utilizes a special radiating element located in the center of each subarray. This center element is fed with a “reverse” T/R module that operates in the opposite sense of the regular elements in the subarray; that is, for dual-band communications arrays, it transmits at the receive frequency and receives at the transmit frequency of the other elements in the array. A similar technique can also be applied to arrays for radar. By operating in this manner, the “reverse” element can be used to self-test the regular elements in the subarray, without requiring an external RF source. This method allows for detection of element faults and failures so that error correction or repairs can be applied without significant impact to operation of the array.

Analysis of sparse trifilar array antenna

A sparse trifilar antenna can support two independent beams while, to reduce the interference between the beams, each array element supports only one beam. To minimize the grating lobe effects each beam is formed by three spiral arms resulting in a sparse random array arrangement. In this paper we investigate the impedance and radiation characteristics of such an array. We have shown that the active reflection coefficients are somewhat degraded in comparison to a fully populated array, however the directivity remains approximately the same, making the trifilar array a viable solution for multi-frequency, multi-beam communication applications.

A new omnidirectional shaped beam antenna

A new type of antenna, the omnidirectional polyrod shaped beam antenna with a shaped-beam radiation pattern in elevation is presented. It is based on the typical polyrod antenna, which can have a shaped beam realized by the appropriate physical shaping of the radiating polyrod. The antenna can be used as an airborne omnidirectional radiator with a requested sectoral coverage.