M.G. Stubbs

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.

A novel compact uniplanar MMIC Wilkinson power divider with ACPS series stubs

Short-circuit series stubs realized in the signal conductor of an asymmetric coplanar stripline (ACPS) transmission line are investigated as a circuit element in order to achieve a significant size reduction of a MMIC Wilkinson divider. A simple ideal transmission line equivalent circuit is used to model the ACPS line/stub combination yielding good agreement with EM simulation. The stubs are then utilized to shorten the /spl lambda//4 transmission lines by approximately 35% in a Wilkinson divider application at 23 GHz.

An enhanced on-wafer millimeter-wave noise parameter measurement system

A novel on-wafer resistive noise source, useful for noise characterization of microwave devices with the cold noise power measurement technique, is described. The noise source enhances measurement accuracy by providing a calibrated noise temperature directly at the device reference plane. A procedure for determining the excess noise ratio of the noise source is presented and validated up to 40 GHz. The noise source is employed in an on-wafer measurement system, allowing the noise parameters of two-port devices to be extracted. Following a description of the apparatus and measurement procedure, an example of a high-electron-mobility transistor noise parameter measurement at millimeter-wave frequencies is presented.

Micromachined Hemispheroidal Cavity Resonators

A high quality factor ( factor) -band micromachined hemispheroidal cavity was designed for use in low phase-noise oscillators. The cavity is micromachined using self-limited isotropic etching of a silicon wafer, which is then metallized with gold and soldered to an alumina wafer using a thin layer of indium. The alumina is patterned with a microstrip feed line having an aperture in the ground plane for coupling to the cavity since the ground plane also forms the top wall of the cavity. An analysis based on equivalent energy aperture coupling theory, and perturbation techniques, was used to design the cavities. The resonant frequency, the unloaded factor, and the loaded factor of the fully assembled micromachined cavity can be calculated using simple equations that agree with both finite-element simulations and measurements. The prototype micromachined cavity has a single measured resonance at 76.39 GHz with a measured unloaded factor of 1426 and a measured loaded factor of 909.

A novel compact multi-layer MMIC CPW branchline coupler using thin-film microstrip stub loading at 44 GHz

A very compact 90/spl deg/ CPW branchline coupler at 44 GHz for Ka/K-band, advanced SATCOM terminal systems operating in the 20/44 GHz frequency bands is reported. This coplanar coupler structure using two metallization layers separated by a thin dielectric sheet on GaAs was investigated. This arrangement provides additional degrees of freedom compared to standard coplanar line structures resulting in extremely compact couplers suitable for monolithic integration. The proposed method takes advantage of the coexistence of the CPW lines and shunt thin film microstrip stubs. The coupler does not use lumped inductors or capacitors and, subsequently, has the advantages of excellent design accuracy even at high frequencies. In comparison with conventional hybrid couplers, this coupler offers lower insertion loss, higher compactness (a significant 65% reduction of the circuit area) and additional degrees of freedom by the inclusion of the shunt thin film microstrip stubs. These stubs are the sole reason for the major reduction in size.

A novel uniplanar 44 GHz MMIC subharmonic mixer using CPW series stubs

The design of a subharmonically pumped (SHP), monolithic microwave integrated circuit (MMIC) mixer for Satcom applications is described. The mixer uses an anti-parallel diode pair to achieve frequency translation by mixing the IF signal with the second harmonic of the fundamental local oscillator (LO) pump. The circuit was fabricated using OMMICs ED02AH foundry process and contains two pairs of 0.18 /spl mu/m PHEMT based diodes, each, having two 15-/spl mu/m cathode fingers. The measured conversion loss is 8 dB for an RF output signal of 44.51 GHz and the RF port return loss is better than 13 dB over the RF frequency range (43.5 to 45.5 GHz). The 2*f/sub LO/ suppression is better than 17 dB over the RF range of 43.5 to 45.5 GHz.

A 30 GHz, HEMT, Active Antenna Structure in MMIC Technology

A novel MMIC active antenna structure has been demonstrated by closely integrating a HEMT device and a slot antenna on opposite sides of a GaAs substrate. To our knowledge, this is the first time that such components have been integrated on the same MMIC. It is also the first time that circuit components have used both sides of an MMIC with via holes providing the through substrate connections. This active transmit antenna was developed for 30 GHz operation.

3D MMIC compact semi-lumped loaded CPW stubs for spurious suppression fabricated with a standard air bridge process

Compact and harmonic suppression semi-lumped stubs based on a CPW/thin film microstrip combination using 3D on-chip air-core solenoid and elevated symmetric inductors are proposed. The stubs are implemented using an MMIC airbridge process to realize an elevated transmission line and 3D inductors. These 3D inductors are used to load open circuit CPW/TFMS stubs in order to reduce their sizes. In addition to size reduction, an excellent suppression of spurious harmonic responses are achieved with improved dielectric loss which are inherent in these types of semi-lumped stubs. The experimental results presented in this paper demonstrate the validity of the design method.

A Novel Reduced-Size Uniplanar Wilkinson Power Divider Using ACPS Series Stubs

Short-circuit series stubs realized in the signal conductor of an asymmetric coplanar stripline (ACPS) transmission line are investigated as a circuit element in order to achieve a significant size reduction of a Wilkinson divider. A simple ideal transmission line equivalent circuit is used to model the ACPS line/stub combination yielding good agreement with EM simulation. The stubs are then utilized to shorten the ¿/4 transmission lines by approximately 33% in a Wilkinson divider application at 22.25 GHz.

Design of a Ka-band upconverter using a heterojunction bipolar transistor

Heterojunction bipolar transistors (HBTs) are attracting interest around the world, finding use in power amplifiers and low phase noise oscillators. There is little information, however, on the performance of HBT devices as mixers, specifically as upconverters in the transmitter path. Using a proprietary HBT model implemented on Libra/sup TM/ by the Communications Research Centre, the HBT is investigated for its suitability as a mixer. A single-ended microwave monolithic integrated circuit (MMIC) upconverter is designed with the IF and LO fed through the base and emitter, respectively, thereby eliminating the need for a diplexer. The simulated upconverter (IF=3.6 GHz and RF=30.1 GHz) yields a conversion gain greater than 2 dB over a bandwidth of 300 MHz. At the RF port, the IF, LO and image frequency isolations are 19 dB, 18 dB and 13 dB respectively, while at the IF port, the RF, LO and image frequency isolations are all greater than 40 dB.