Sean M. Duffy

A dual-band circularly polarized aperture-coupled stacked microstrip antenna for global positioning satellite

This paper describes the design and testing of an aperture-coupled circularly polarized antenna for Global Positioning System (GPS) applications. The antenna operates at both the L1 and L2 frequencies of 1575 and 1227 MHz, which is required for differential GPS systems in order to provide maximum positioning accuracy. Electrical performance, low-profile, and cost were equally important requirements for this antenna. The design procedure is discussed, and measured results are presented. Results from a manufacturing sensitivity analysis are also included.

Accurate modeling of dual dipole and slot elements used with photomixers for coherent terahertz output power

Accurate circuit models derived from electromagnetic simulations have been used to fabricate photomixer sources with optimized high-impedance antennas. Output powers on the order of 1 /spl mu/W were measured for various designs spanning 0.6-2.7 THz. The improvement in output power ranged from 3 to 10 dB over more conventionally designed photomixers using broad-band log-spiral antennas. Measured data on single dipoles, twin dipoles, and twin slots are in good agreement with the characteristics predicted by the design simulations.

MEMS microswitches for reconfigurable microwave circuitry

The performance is reported for a new microelectromechanical structure (MEMS) cantilever microswitch. We report on both dc- and capacitively-contacted microswitches. The dc-contacted microswitches have contact resistance of less than 1 /spl Omega/, and the RF loss of the switch up to 40 GHz in the closed position is 0.1-0.2 dB. Capacitively-contacted switches have an impedance ratio of 141:1 from the open to closed state and in the closed position have a series capacitance of 1.2 pF. The capacitively-contacted switches have been measured up to 40 GHz with S/sub 22/ less than -0.7 dB across the 5-40 GHz band.

MEMS microswitch arrays for reconfigurable distributed microwave components

A revolutionary device technology and circuit concept is introduced for a new class of reconfigurable microwave circuits and antennas. The underlying mechanism is a compact MEMs cantilever microswitch that is arrayed in two-dimensions. The switches have the ability to be individually actuated. By constructing distributed circuit components from an array, the individual addressability of the microswitch provides the means to reconfigure the circuit trace and, thus, provides the ability to either fine-tune or completely reconfigure the circuit elements behavior. Device performance can be reconfigured over a decade in bandwidth in the nominal frequency range of 1 to 100 GHz. In addition, other circuit-element attributes can be reconfigured such as instantaneous bandwidth, impedance, and polarization (for antennas). This will enable the development of next-generation communication, radar and surveillance systems with agility to reconfigure operation for diverse operating bands, modes, power levels, and waveforms.A novel MEMS switch design for use in microwave circuits is presented. The microswitch is capable of being configured in a multi-element X-Y array for use in tunable distributed circuits. Circuit design concepts using microswitch arrays and measurements of single microswitch performance are given.

Design considerations and results for an overlapped subarray radar antenna

Overlapped subarray networks produce flat-topped sector patterns with low sidelobes that suppress grating lobes outside of the main beam of the subarray pattern. They are typically used in limited scan applications, where it is desired to minimize the number of controls required to steer the beam. However, the architecture of an overlapped subarray antenna includes many signal crossovers and a wide variation in splitting/combining ratios, which make it difficult to maintain required error tolerances. This paper presents the design considerations and results for an overlapped subarray radar antenna, including a custom subarray weighting function and the corresponding circuit design and fabrication. Measured pattern results will be shown for a prototype design compared with desired patterns.

An enhanced bandwidth design technique for electromagnetically coupled microstrip antennas

This paper describes a method of enhancing the bandwidth of two different electromagnetically coupled microstrip antennas by utilization of a tuning stub. An approximate theory and equations are developed to demonstrate the potential bandwidth improvement and required stub impedance characteristics. A novel dual-stub design is presented that achieves better characteristics than a conventional quarter wavelength open-end stub. As examples, the bandwidth (VSWR<2) of a conventional proximity-coupled microstrip antenna is increased from 4.8 to 8.4% and the bandwidth of a stacked aperture-coupled microstrip antenna is increased from 27.5 to 34.5% using this technique.

Low cost Multifunction Phased Array Radar concept

MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.

Multifunction Phased Array Radar (MPAR) for aircraft and weather surveillance

MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.

Advanced architecture for a low cost multifunction phased array radar

MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordable Multifunction Phased Array Radar (MPAR) technology for Next Generation air traffic control and national weather surveillance services. Aggressive cost and performance goals have been established for the system. The array architecture and its realization using custom Transmit and Receive Integrated Circuits and a panel-based Line Replaceable Unit (LRU) will be presented. A program plan for risk reduction and system demonstration will be outlined.

A modified transmission line model for cavity backed microstrip antennas

Spatial power combining of many MMIC amplifiers at millimeter wave frequencies using a fixed array of microstrip antenna elements places unique demands on the dielectric media. The substrate must be relatively thick to allow space for MMIC placement, must provide rather high thermal conductivity to dissipate MMIC heat, and be of high dielectric constant to shrink the circuit element dimensions. Presently, microstrip antenna models require a low dielectric constant substrate to be valid. This paper presents a modified transmission line model based on the model of Pues and Van de Capelle (1984) which addresses the problems of thick, high dielectric constant substrates as applied to proximity coupled, cavity backed microstrip antenna elements. The goal of the model was to guide the design of a microstrip array antenna suitable for a spatial power combined module.