Three miniaturized lumped-element power dividers with a filtering function for use in quadrature mixers are described. Simulation results showed that they can be miniaturized, as compared to conventional ones with open/short stubs, while maintaining the filter characteristics. A fabricated 0.95-GHz 0power divider with a filtering function had a chip size about half that of a conventional lumped-element one. Its insertion loss at 0.950.05 GHz was 4.00.1 dB.

This paper presents some structures of artificial coplanar waveguide with very slow phase velocity and their applications to a design of compact 3-dB branch-line couplers. The slow-wave structure is constructed by periodically loading both of series inductance and shunt capacitance. First, a basic miniature branch-line coupler is designed and consequently considerable size-reduction of about 1/4 is obtained. Next, a broadband design technique is described using open-circuited quarter-wavelength series-stubs added at each port as a matching network. By size-reducing the series-stubs and branchline sections, a very compact broadband coupler with a good hybrid performance over a wide bandwidth of 31 percent or more is realized. The design concepts and procedures are verified both numerically and experimentally.

For a highly nonlinear circuit design such as an active frequency multiplier, performing an input impedance "match" is not a straightforward problem. In this work, an analysis of nonlinear input impedance matching in active microwave frequency multipliers is presented. By utilizing harmonic balance simulation of an idealized device model, fundamental aspects of performing an input "match" are explored for classical frequency doubler and frequency tripler configurations. The analysis is then repeated using a realistic device model, verifying the efficacy of using nonlinear input impedance matching to improve the output power and return loss characteristics of a multiplier.

This paper describes a radial open stub and its application to a simple design of a four-element planar Butler matrix. In the first stage of our work, we propose a 45-degree phase shifter composed of an eighth-wavelength delay line and a serial connection of a quarter-wavelength straight line and a quarter-wavelength straight open stub. Next, in order to improve relative-phase characteristics between output ports, we propose a 45-degree phase shifter configuration using a quarter-wavelength radial open stub instead of using a quarter-wavelength straight open stub. It is shown by simulation that relative-phase characteristics of the configuration using the radial open stub are better than that using the straight open stub at the high frequencies. Finally, an experimental UHF-band four-element planar Butler matrix is presented. Over the frequency range from 0.83 to 0.92 GHz, the experimental four-element planar Butler matrix exhibits power splits of -6.510.29 dB, return losses of greater than 13 dB, errors in the desired relative-phase difference between output ports of less than 2 degrees.

This paper describes a simple design of a broad-band four-way power divider with 45-degree phase differences between output ports. In the first stage of our work, we present a new broad-band 90-degree power divider. The phase error of the power divider here is less than one-tenth of the conventional 90-degree branch-line hybrid. Next, an experimental UHF-band four-way power divider using a broad-band 90-degree power divider and two broad-band 45-degree power dividers is presented. Over the frequency range from 0.86 to 1.06 GHz, the experimental four-way power divider exhibits power splits of -6.420.25 dB, return losses of greater than 15 dB, errors in the desired relative-phase difference between output ports of less than 1 degree, and isolation between output ports of greater than 15 dB. This divider is useful for realizing low distortion and high efficiency amplifiers without the need for an isolator.

Silicon-based monolithic microwave integrated circuits (MMICs) present an interesting option for low-cost consumer wireless systems. SiGe/Si heterojunction bipolar transistors (HBTs) are a major driving force behind Si-based MMICs, because they offer excellent microwave performance without aggressive lateral scaling. This article reviews opportunities for receiver frontend components (low-noise amplifiers and mixers) using SiGe HBTs.