Werner Bächtold

Varactor-loaded transmission-line phase shifter at C-band using lumped elements

The design of varactor-loaded transmission-line phase shifters using lumped elements is discussed in this paper. A monolithic-microwave integrated-circuit (MMIC) phase shifter is fabricated to verify the proposed topology. Only one control voltage is required for phase control. Within a continuously adjustable phase-control range of 360/spl deg/ and a frequency range from 5 to 6 GHz, a low transmission loss of 4 dB/spl plusmn/1.7 dB is measured. The phase shifter is realized with a commercial 0.6-/spl mu/m GaAs MESFET process and requires a chip area of only 0.8 mm/sup 2/. To the knowledge of the authors, the best results reported to date are reached for a continuously adjustable passive phase shifter with comparable circuit size. The presented circuit is well suited to wireless adaptive antenna transceivers, operating in accordance with the 802.11a, high-performance radio local-area-network and high-speed wireless-access-network type-a standard.

Compact reflective-type phase-shifter MMIC for C-band using a lumped-element coupler

The design and results of an ultra-compact single-load reflective-type monolithic-microwave integrated-circuit phase shifter at 6.2 GHz for a satellite radar system is presented in this paper, which has been fabricated using a commercial 0.6-/spl mu/m GaAs MESFET process. A 3-dB 90/spl deg/ coupler with lumped elements enables significant circuit size reduction in comparison to former approaches applying microstrip branch line or Lange couplers. Phase control is enabled using MESFET varactors with capacitance control ratios (C/sub max//C/sub min/) of only four. Equations are derived to precisely describe the phase control ranges versus capacitance control ratios for different load configurations to allow efficient optimizations. Furthermore, the design tradeoff between low loss and high phase control range is discussed. Within a phase control range of 210/spl deg/, a loss of 4.9 dB/spl plusmn/0.9 dB and a 1-dB input compression point of higher than 5 dBm was measured for the designed phase shifter. The circuit size is less than 0.5 mm/sup 2/, which, to our knowledge, is the smallest reflective-type phase-shifter size reported to date.

A 5.2 GHz variable gain LNA MMIC for adaptive antenna combining

A variable gain LNA was designed for HIPERLAN I. A noise figure of only 1.7 dB is measured at a gain of 14.5 dB and a power consumption of 9 mW (V/sub DC/=3 V, I/sub DC/=3 mA). Over an amplitude control range of 20 dB, the third order intercept point at the input is higher than -10 dBm, the spurious free dynamic range is higher than 55 dB and noise performance does not effectively degrade. Noise and intermodulation performance of different amplitude control methods as well as the required resolutions for D/A converters are investigated.A variable gain LNA was designed for HIPERLAN I. A noise figure of only 1.7 dB is measured at a gain of 14.5 dB and a power consumption of 9 mW (V/sub DC/=3 V, I/sub DC/=3 mA). Over an amplitude control range of 20 dB, the third order intercept point at the input is higher than -10 dBm, the spurious free dynamic range is higher than 55 dB and noise performance does not effectively degrade. Noise and intermodulation performance of different amplitude control methods as well as the required resolutions for D/A converters are investigated.

Calibratable adaptive antenna combiner at 5.2 GHz with high yield for laptop interface card

This paper presents a calibratable adaptive antenna combiner with three branches for high-performance radio local area network at 5.2 GHz. The system was mounted on a reinforced duroid substrate and enables the integration in a laptop interface card. Each branch consists of a bent stacked slot antenna, a low-noise-amplifier monolithic microwave integrated circuit (MMIC) with antenna/calibration switching and a vector modulator MMIC with an amplitude control range of 15 dB and 3600 phase control range. The signals of the three branches are combined by an active adder MMIC. A calibration is proposed to significantly improve the phase and amplitude control resolution and the yield of the designed MMIC circuits, which were fabricated using a commercial GaAs process. Each branch has a maximum power gain of 16 dB, a noise figure of 3.3 dB, and a 1-dB output compression point of -4 dBm. The whole system draws less than 28 mA from a 2.7-V voltage supply. The total required MMIC chip size is 10.8 mm/sup 2/.

Study and Design Optimization of Multiharmonic Transmission-Line Load Networks for Class-E and Class-F

A design-oriented analysis of microwave transmission-line class-E and class-F amplifiers is presented in this paper. Multiharmonic transmission-line load networks are analyzed and compared in terms of harmonic suppression and their effects on output power and efficiency. Based on this study, a design of highly efficient monolithic-microwave integrated-circuit amplifiers has been carried out. To allow circuit optimization and to simplify the design process, analytic expressions were derived for the most practical multiharmonic transmission-line networks. Fabricated amplifiers achieve state-of-the-art efficiency of 56.2% and 59.0% for class-E and class-F operation at K-band for power levels of 19.1 and 20.0 dBm, respectively. Moreover, without the need for supplementary filtering sections, harmonic suppression for operation well into compression is better than -25 and -30 dBc for the transmission-line class-F and class-E amplifiers, respectively.

K

We have investigated the cross-sectional electric field and potential distribution of a cleaved n+-InP/InGaAsP/p+-InP p–i–n laser diode using Kelvin probe force microscopy (KFM) with a lateral resolution reaching 50 nm. The powerful characterization capabilities of KFM were compared with two-dimensional (2D) physics-based simulations. The agreement between simulations and KFM measurements regarding the main features of the electric field and potential is very good. However, the KFM yields a voltage drop between n- and p-doped InP regions which is 0.4 times the one simulated. This discrepancy is explained in terms of surface traps due to the exposure of the sample to the air and in terms of incomplete ionization. This hypothesis is confirmed by the 2D simulations.

-Band MMIC Power Amplifiers

Backscatter modulation is frequently used in microwave tagging or sensor systems for interrogating remote devices. This paper describes, in the first part as an overview, three commonly used interrogator setups for backscatter modulation systems. In the second part, a novel interrogator topology is presented which is part of an active read/write microwave tagging system. A combination of backscatter modulation with frequency hopping methods is applied in the presented tagging system in order to cope with multiple reader multiple tag environments. Measured results of an experimental tagging system setup operating in the 2.4-GHz ISM band are presented which show the performance of the proposed interrogator.

Investigation of the cleaved surface of a p–i–n laser using Kelvin probe force microscopy and two-dimensional physical simulations

The design and performance of a vector-modulator-based phase shifter for high-performance radio local area networks at 5.2 GHz is presented in this paper. Low power consumption is achieved using a 0.6-/spl mu/m GaAs MESFET process. At a voltage supply of 1.4 V and with a current consumption between 3.5-7 mA, the gain is 0.6 dB and the 1-dB input compression point is -9 dBm. A full 360/spl deg/ phase control range is achieved by combining two of the three vectors, which have phase offsets of 120/spl deg/, with variable amplitude. Chip size is only 1.3 mm/sup 2/. The proposed vector modulator applies a new circuit configuration of variable-gain amplifiers to compensate their transmission phase errors. Within a gain control range of 20 dB, the phase error can be reduced to /spl plusmn/3/spl deg/, which is about a factor of eight better than the results obtained by single FET amplifiers. A simple calibration procedure for the proposed vector modulators is presented to improve the manufacturing yield and to decrease the impact due to temperature changes and aging. A maximum gain error of /spl plusmn/0.8 dB and a maximum phase error of /spl plusmn/7/spl deg/ have been measured after applying this calibration to the designed vector modulator.

Microwave backscatter modulation systems

We propose a highly efficient spatiotemporal vertical-cavity surface-emitting laser (VCSEL) model aimed at optimizing entire optical links. It is based on two-dimensional (2-D) rate equations, which allow the computation of dynamic gain competition resulting from inhomogeneous field and carrier spatial distributions in the cavity. The equations are mathematically transformed so as to remove any explicit spatial dependency from their formulation. This modified model reduces the computational time by several orders of magnitude. Resulting 2-D dynamic intensity profiles allow investigating effects related to improper fiber coupling due to transverse misalignment between laser beam and fiber. Self-consistent implementations of feedback and chirping, thermal effects, and noise are presented as well. A variety of advanced simulations showing results consistent with theory and experiments confirm the validity of the model.

An antenna diversity MMIC vector modulator for HIPERLAN with low power consumption and calibration capability

As the gate lengths of silicon MOSFETs become smaller and smaller, these devices are usable to frequencies in the gigahertz range. The nonlinear MOSFET model presented in this paper is based on S-parameter measurements over a large bias range, and has been implemented in a SPICE simulator. The improvements consist of new equations for the nonlinear capacitances and output conductance of the MOS transistor. This new large-signal model shows very good agreement between measured and simulated S-parameters of single transistors at various bias points up to 10 GHz. Intermodulation (IM) and circuit performance are also well predicted. Simulated S-parameters of a simple amplifier showed excellent agreement with measured results, confirming the performance of this model.