Jim S. Wight

A Microstrip and Stripline Crossover Structure (Letters)

A microstrip or stripline four-port structure which allows two signal paths to physically cross over while maintaining high isolation is described in this letter.

A 28 GHz HBT Vector Modulator and its Application to an LMCS Feedforward Power Amplifier

A vector modulator employing four amplitude modulated orthogonal channels is presented. Operating at 28 GHz, this device consists of a four-way 6 dB power divider, four GaAs HBT MMIC variable gain amplifiers, and a 4-to-1 power combiner All of the passive functions were realised on alumina ceramic while the amplifier chips were fabricated at Nortel Technologies using a 3.5 ¿m × 6 ¿m GaInP-GaAs HBT process. By testing a vector modulator prototype, we were able to evaluate the architecture and be the first to assess its suitability as a gain/phase control element for a Ka-band MCS adaptive feedforward lineariser.

On the conception and analysis of a 12-GHz push-push phase-locked DRO

This paper describes the design and behavior of a 12-GHz push-push dielectric resonator oscillator in a phase-locked environment. This phase-locked dielectric resonator oscillator (PLDRO) differs from conventional designs on many fronts. First, it uses a push-push oscillator for its improved phase noise and reduced fundamental frequency. Second, the phase detection is implemented at a 3-GHz IF as an alternative to detecting at RF using a sampling phase detector (PD). Finally, the push-push PLDRO is tuned via coupled microstrip lines to minimize oscillator loading. These modifications are intended to minimize the risk of PLDRO lock failures by maintaining a constant PD gain via amplifiers operating at P1dB, and by halving the DRO fundamental frequency using the push-push approach. Experimental results indicate a fundamental suppression of 27 dBc, and single-sideband phase noise densities of -105, -110, and -125 dBc/Hz at 10-kHz, 100-kHz, and 1-MHz offsets, respectively, from a 12-GHz carrier

Computer aided design of square spiral transformers and inductors (MIC application)

A simple, yet accurate, lumped-element model for four-port planar rectangular spiral structures has been developed. Closed-form expressions were used to generate frequency-dependent parameter values, resulting in an equivalent circuit which is easily incorporated into existing analysis packages. The method can easily be implemented in a commercial microwave computer-aided design program, allowing its use in the optimization of various types of active circuits. The technique was applied to standard and center-tapped transformer configurations, as well as to spiral inductors to 20 GHz. Comparison with measured results shows good agreement up to the first resonant frequency of the structures.<<ETX>>

Vertical transitions in low temperature co-fired ceramics for LMDS applications

To realize the advantages of low temperature co-fired ceramics (LTCC), such as highly integrated and low cost microwave packages, a library of repeatable and low loss vertical transitions is necessary. This paper presents measured results of three LTCC vertical transitions: stripline to coplanar waveguide (CPW), CPW to CPW, and CPW to microstrip. A novel grounding structure for intermediate ground planes is presented and discussed. The measured results demonstrate vertical transitions with good performance across the LMDS range.

Frequency agile RF feedforward noise cancellation system

A frequency agile feedforward noise cancellation system (FFCS) concept was developed to increase the isolation between the transmitter and receiver which share a common antenna in a frequency division duplex (FDD) radio front-end. A cancellation performance of 50 dB was achieved in a bandwidth of 4.5 MHz. The performance was maintained throughout a tuning bandwidth of 25 MHz, centered at 836.5 MHz. The FFCS has applications in communication systems requiring tunable notch filters with wideband performance. The research on the FFCS is aimed at developing technology to complement a cellular base station (BTS) duplexer of reduced order and reduced size and capable of operating in any CDMA cellular bands. The FFCS component is envisioned as enabling technology to implement frequency agile duplexers.

Investigation of various feed structures for linear arrays of dielectric resonator antennas

Experimental investigations carried out at 20 GHz on various linear arrays of dielectric resonator antennas with different feeding mechanisms are reported. Linear arrays with microstrip feed, dielectric image guide feed, and slot aperture feed were fabricated and their performance was evaluated. A discussion of the practicality of each array is included.

Equivalent Circuits of Microstrip Impedance Discontinuities and Launchers

Experimental results obtained indicate that an excess phase shift is the most pronounced high-frequency parasitic effect resulting from a microstrip quarter-wave transformer impedance discontinuity. An empirically derived design-oriented model describing the dominant parasitic reactance associated with a microstrip impedance discontinuity at X-band frequencies is described. A description is also given of the dominant parasitic reactance associated with a number of commercially available coaxial-to-microstrip launchers.

Experimental Analysis of a 60 GHz Compact EC-CPW Branch-Line Coupler for mm-Wave CMOS Radios

A 60 GHz reduced-size branch-line coupler has been developed using elevated-center coplanar waveguide (EC-CPW) transmission lines. The coupler is fabricated in a 90 nm CMOS technology and has a chip area of 0.102 mm2. The measurements indicated an amplitude-imbalance of 0.7 dB and a phase difference of 88 degrees at 60 GHz, a return loss of greater than 15 dB at every port over the 60 GHz band (57-64 GHz), and an isolation better than 17 dB. A 73% size-reduction compared to a conventional CPW coupler design has been achieved using capacitively loaded high-impedance EC-CPW lines. The proposed coupler is well suited for the design of millimeter-wave (mmW) CMOS subsystems including: balanced amplifiers, vector modulators, and balanced mixers.

A Systematic Study of Varying Reference Phase in the Design of Circular Fresnel Zone Plate Antennas

A circular Fresnel zone plate antenna was simulated using a finite difference time domain software to study the effect of changing the reference phase from the standard 0deg to any value between 0deg and 180deg. Several prototypes were built to validate the simulations using four different focal-length-to-diameter (F/D) ratios. It was found that a significant improvement in the level of the first sidelobe, up to about 9 dB according to the simulations, could be achieved without sacrificing gain or cross-polarization levels