Robin Sloan

A Ka-band indium-antimonide junction circulator

Following a brief overview of the underlying theory, experimental results are presented for the first time showing circulator action in a semiconductor junction structure. An axially magnetized indium-antimonide disc fixed in a three-port finline structure and cooled to the temperature of boiling nitrogen, 77 K gives circulation across K/spl alpha/-band. For a dc magnetic bias of 0.73 T, a 15-dB isolation is recorded from 28 to 40 GHz, or a fractional bandwidth of at least 35%. Typical insertion loss is less than 1.5 dB from the WG22 reference plane at the test fixture ports. Continued operation above 40 GHz is predicted, but has not yet been measured. Measurement suggests that circulation is evident even where the effective propagation constant is imaginary, although better theoretical agreement is achieved when this is a real quantity. This new device makes millimeter-wave broad-band circulation a possibility and confirms the current model based upon the Drude-Zener approximation. A theoretical example is then given for a design operating to 140 GHz, yielding a fractional bandwidth of 110%.

Predicted performance of semiconductor junction circulators with losses

A study of the circulation properties of a gyroelectric medium consisting of a high-quality n-type semiconductor is given. Losses due to electron collisions are modeled by inclusion of the collision frequency nu /sub c/ in the relative permittivity tensor. Broadband low-loss operation of a semiconductor slotline junction circulator above the extraordinary wave resonance frequency f/sub res/ appears possible at near-millimetric frequencies. Larger, applied static magnetic fields enable narrowband low-loss operation at frequencies below the resonance at f/sub res/. A 40-GHz design is described for GaAs cooled to 77 K. The minimum inband insertion loss is 0.82 dB. InSb theoretically possesses still lower losses for a reduced applied magnetic field. An example at an operating frequency of 75 GHz in InSb is given. >

Broadband theoretical gyroelectric junction circulator tracking behavior at 77 K

The perfect circulation conditions for the gyroelectric circulator are given for a gyroelectric ratio with magnitude in the range zero to two. Values of this ratio above unity given in this paper correspond to the frequency regions where the effective permittivity is negative. The subsequent Greens function analysis employs the modified Bessel function. In accordance with the Drude model of semiconductors, a theoretical low-loss GaAs design is presented with a 20 dB isolation bandwidth of approximately 90% at an operating temperature of 77 K. The theoretical broadband circulation tracking behavior of this design is demonstrated for gyroelectric ratios which may exceed a magnitude of unity. The operating frequency range for this particular circulator design is below the extraordinary wave resonance frequency. In order to measure the microwave properties of the magnetised semiconductor disk, a two port analysis is performed based upon the Drude model of semiconductors.

Semiconductor junction circulators

A semiconductor junction circulator is analyzed, and a predicted 25 dB isolation bandwidth of 6% at 94 GHz is shown using idealized, lossless GaAs at 77 K. A narrowband, lossy, theoretical design example at 40 GHz shows that losses do reduce performance but not to such a degree as to render the device useless. In this narrowband solution the losses due to electron collisions are modeled. The circulation conditions in this example are designed using intersecting impedance curves rather than the tracking solutions achieved in the lossless case. The technology discussed here may be compatible with high-T/sub c/ superconductors and with MMICs (monolithic microwave integrated circuits).<<ETX>>

A Ka-band InP MMIC 180/spl deg/ phase switch

A new type of Ka band (26 to 36 GHz) 180 degree phase switch (bi-phase modulator) monolithic microwave integrated circuit has been developed for the EC funded FARADAY radio astronomy project. This integral component forms part of a chip set for a very low noise switching radiometer operating at a temperature of approximately 15 K. To maximize the sensitivity of the radiometer lattice-matched indium phosphide HEMT technology has been used: all of the active components of the radiometer, with the exception of the detectors, have been manufactured on a single wafer process. Design principles are described, together with a comparison of modeled and measured results. The results show an average insertion loss of 3.5 dB, return loss of better than 10 dB and an average phase difference close to 170/spl deg//spl plusmn/10/spl deg/ the 26-36 GHz band.

Broadband millimetric semiconductor junction circulators at 77 K

Broadband circulation at millimetric frequencies is currently unavailable. However on utilising the gyrotropic behaviour of the magnetised semiconductor this appears possible. Low-loss theoretical results are presented which suggest GaAs and InSb circulators are feasible with bandwidths greater than an octave and operating up to 125 GHz at a temperature of 77 K.

A Three-Dimensional Positioning Algorithm for Networked Wireless Sensors

An ultrawideband 3-D positioning technique is described here for locating wireless sensor nodes in extreme multipath environments. These typically form part of a network of sensors used to monitor salient parameters such as temperature and humidity in large industrial storage vessels. The novelty of this approach is twofold. First, a leading ultrawideband pulse edge detection method is combined with a series of spatially diverse measurements to isolate the line-of-sight component from the unwanted multipath interference from the vessel walls. Second, a new location algorithm based on the statistical analysis of spherical function intersection points is applied to the received time-domain data to improve the estimation of the time of flight at each measurement location. These two features combine to facilitate both precision positioning and cumulative error source estimation and yield resolutions approaching 2 cm in rich scattering environments. The results of the application of the new spherical technique compares favorably with those obtained using a conventional hyperbolic positioning method where it was demonstrated to provide a marginally superior resolution for the applied experimental conditions.

A Positioning Algorithm for Wireless Sensors in Rich Multipath Environments

A novel positioning algorithm is described for locating wireless sensor nodes in the extreme multi-path conditions encountered in industrial storage vessels. Here, pulse leading edge detection is combined with high-resolution spatial diversity, to facilitate both precision positioning and cumulative error estimation. The 2-D prototype described within may be readily adapted for 3-D full scale commercial applications.

Measurements of V-band n-type InSb junction circulators

A V-band n-type indium antimonide (InSb) junction circulator supported in a three-port finline structure has been fabricated and measured. Broad-band operation for a semiconductor junction circulator over the frequency range 50-75 GHz at a temperature of 77 K has been demonstrated for the first time. With an applied magnetic flux density of 0.88 T, approximately 10 dB of differential isolation has been measured over the entire waveguide frequency band. The measured results also indicate that circulation is possible when the semiconductor material has /spl epsiv//sub eff/<0. In principle, broader bandwidths are predicted since frequency tracking can be achieved from /spl epsiv//sub eff/<0 to /spl epsiv//sub eff/>0, but the bandwidths of the circulators measured are restricted by the cutoff frequency of the V-band waveguide. Experimental evidence also showed that a disc or triangular-shaped semiconductor suspended in an E-plane junction without the finline circuit provides circulation. The experimental results clearly illustrate the broad-band behavior of semiconductor junction circulators for operation beyond 40 GHz, which is difficult to achieve with ferrite-based circulators.

Distributed coupling model of the dielectric resonator to microstrip line

A three-dimensional (3-D) electromagnetic (EM) study shows that the magnetic coupling between a dielectric resonator (DR) and a microstrip line is appreciable over a length greater than the diameter of the DR. The effect of this distribution should be considered when modeling the coupling. A new circuit model is introduced representing the coupling as distributed, and an integral method is used to calculate circuit parameters efficiently. Numerical comparison shows that the new model provides better results than the conventional lumped model. In the calculated example, the 3-dB frequency response is reduced from 31 MHz (via the conventional model) to 9.0 MHz (new distributed model) which approaches 6.6 MHz, the result from EM calculation. The equivalent distributed circuit can be easily included in circuit simulators such as Libra/sup TM/, and could prove invaluable in the design of DR oscillators.