Malcolm G. Stubbs

Compact MMIC CPW and asymmetric CPS branch-line couplers and Wilkinson dividers using shunt and series stub loading

Circuit size may be reduced by up to 60% by embedding series and shunt uniplanar stubs inside the main uniplanar line since this reuses physical space in the longitudinal direction. This size-efficient stub loading of the main uniplanar line results in robust options for designing compact K-band 90/spl deg/ hybrid couplers and Wilkinson dividers. The approach is confirmed by experimental results that agree well with theory up to at least 30 GHz using both coplanar waveguide (CPW) and asymmetric coplanar stripline (ACPS). Furthermore, these couplers and dividers do not use lumped inductors or capacitors and, consequently, have excellent design accuracy even at millimeter-wave frequencies. Additionally, it is shown that it is possible to design an ACPS 90/spl deg/ branch-line coupler without the conventional CPW quarter wavelength transformers used to match the input and output port characteristic impedances.

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.

The integration of thin-film microstrip and coplanar technologies for reduced-size MMICs

This paper proposes the integration of coplanar waveguide (CPW) and thin-film microstrip transmission lines to achieve size reduction of monolithic microwave integrated circuits (MMICs). The proposed structures take advantage of the multilevel metallization processes offered in MMIC technology. A very compact 90/spl deg/ CPW branchline coupler, operating at 44 GHz, is used to illustrate the technique. In comparison with conventional hybrid couplers, this coupler offers lower insertion loss and significantly smaller dimensions. The area of the coupler is approximately 65% of a conventional coupler. This paper also presents a family of novel series/shunt matching stub structures based on the CPW/thin-film microstrip combination. The technique allows a reduction in the length of matching stubs of approximately 50% by collocating multiple stubs together. Simulated and experimental results are presented in support of the novel structures.

Size-reduction techniques for CPW and ACPS structures

In coplanar-waveguide technology, there is a possibility of locating shunt and series matching stubs inside the center conductor of the transmission line. This principle can be used to reduce of the dimensions of microwave components such as monolithic microwave integrated circuits. This paper discusses the concept and presents the design of a reduced-size Wilkinson divider based on the realization of short-circuit series stubs in the signal conductor of an asymmetric coplanar stripline.

Size Reduction of a MMIC Direct Up-Converter at 44 GHz in Multilayer CPW Technology Using Thin-Film Microstrip Stubs Loading

This paper proposes a novel compact multilayer 44.5-GHz coplanar waveguide (CPW) single-sideband (SSB) subharmonically pumped (SHP) mixer for direct up-conversion GaAs monolithic microwave integrated circuit. It uses previously developed thin-film microstrip (TFMS) and CPW structures for capacitive and inductive loading techniques to drastically reduce its size. The SSB SHP mixer uses 50-MHz in-phase and quadrature signals to directly modulate the second harmonic of a 22.25-GHz carrier to produce the required 44.55-GHz RF output. Two pairs of antiparallel diodes reduce feedthrough of the fundamental 22.25-GHz signal to the RF output while novel CPW/TFMS-based structures provide matching. This 1.2times1.5 mm2 chip uses a lumped Wilkinson divider as a local-oscillator divider and a previously developed reduced size 90deg coupler. The SSB SHP mixer acts as an up-converter with a measured conversion gain of -10plusmn1 dB and the lower sideband suppression is greater than 23 dB across the RF bandwidth of 43.5-45.5 GHz. Additionally, it is shown that the RF port return loss is better than 20 dB, and 2timesfLO was suppressed by 21 dB over the same band. The circuit also does not require any dc bias. Compared to the conventional SSB SHP mixer, a 70% reduction in circuit area was achieved with better performances

Overlapping, multiple CPW stub structures for high density MMICs

This paper proposes a robust option for developing a new class of very compact matching stub configurations. It demonstrates that an overlapping technique, involving different MMIC CPW stubs built into a single line section, can provide size and cost reductions up to 60%, while also providing performance enhancements. The high flexibility of uniplanar technology allows the development of possible transmission line shapes and removes a number of limitations inherent in conventional design approaches, thus providing varying degrees of miniaturization. The experimental prototypes presented in this paper demonstrate the efficiency of the design method and the feasibility of creating multistub configurations in a single line section to get ultra compact structures. The principle of achieving such high-quality circuits is detailed and is also confirmed by experimental and theoretical results which are in good agreement up to at least 40 GHz. This good agreement validates the design procedure and shows that complex circuit functions can be implemented by means of relatively inexpensive compact structures. This study was completed by producing a very compact 90/spl deg/ CPW branchline coupler for Ka/K-band, advanced SATCOM terminal systems operating in the 20/44 GHz frequency bands, which demonstrated that the concept can be easily used.

44.5 GHz MMIC direct I&Q modulator in coplanar waveguide technology for an EHF Satcom terminal phased array

A MMIC (monolithic microwave integrated circuit) 44.5-GHz direct I&Q modulator has been developed for implementation in a low-cost EHF SATCOM terminal phased array. In this paper, the performance of the MMIC modulator is reported and the integration aspects are discussed. The K-band even-harmonic quadrature modulator conversion loss was measured to be less than 10 dB, sideband suppression better than 28 dB, carrier (2f/sub LO/) suppression around 15 dB, and IM3 (2f/sub LO/-3f/sub IF/) suppression better than 38 dB over the 43.5 to 45.5 GHz frequency band of interest.

A miniature high gain and broadband MMIC distributed amplifier

A new miniature MMIC distributed amplifier, which combines conventional distributed amplifier (CDA) to extend wider bandwidth and a single-stage cascode amplifier (SSCA) as a gain stage for high gain over several octaves of bandwidth (called CDA-SSCA) is presented in this paper. The low pass filter (LPF) configuration is adopted between the CDA and SSCA while resistive terminations are used in the biasing circuitry to provide broadband matching. The measured small signal gain is 22±1.5 dB from 0.5 to 27 GHz with a chip size of 1.5 × 1 mm2. Another two broadband distributed amplifiers are also designed for comparison and with the same chip size. One is cascaded the two single-stage distributed amplifiers, called two-cascaded single-stage distributed amplifier (2-CSSDA), and the other is a CDA cascaded with a CSSDA, called (CDA-CSSDA). This CDA-SSCA produces a significantly higher gain than the other two designs 2-CSSDA and CDA-CSSDA within the same bandwidth. The flat group delay of this design also proves the feasibility for digital optical communication applications.

Design of a 60 GHz subharmonic mixer MMIC

The design of a subharmonically pumped (SHP), monolithic microwave integrated circuit (MMIC) mixer for future wireless communications applications is described. The mixer uses an anti-parallel diode pair to achieve frequency translation by mixing the RF signal with the second harmonic of the fundamental LO pump. The circuit was fabricated by Triquint Semiconductor Inc. using their GaAs MMIC PHEMT process. The overall chip size is 1.2 mm × 1.3 mm. Measured conversion loss is 13 dB with a 61 GHz RF input signal and RF port return loss is better than 10 dB over a 61.4 to 62.5 GHz frequency range. Simulation predicts a conversion loss of 13 dB over 59 to 61 GHz band and an RF port return loss of better than 10 dB over this range. The simulated 1-dB compression point occurs with an RF input power level of 5 dBm.

New Types of Very Compact 90° ACPS Branchline Couplers using CPW Shunt Stubs

A very compact 90° ACPS branchline coupler for Ka/K-band, advanced SATCOM terminal systems is reported. The proposed method takes advantage of the integration of coplanar waveguide (CPW) shunt stubs and asymmetric coplanar stripline (ACPS) lines. The coupler does not use lumped inductors or capacitors and, consequently, has the advantages of excellent design accuracy even at high frequencies. In comparison to conventional hybrid couplers, this coupler offers lower insertion loss, higher compactness (a significant 55% reduction in circuit area) and does not require a CPW quarter wavelength transformer in order to overcome the input and output port characteristic impedances. Additional degrees of design freedom can be obtained by the inclusion of shunt CPW stubs and these are the reason for the major reduction in size. The reduced size couplers are potential building blocks for the growing wireless communications market.