Quarter-wavelength Impedance Transformer Research Articles

Coupling behaviors of quarter-wavelength impedance transformers for wideband CPW bandpass filters

Quarter-wavelength coplanar waveguide (/spl lambda//4-CPW) impedance transformers with low and high characteristic impedance are characterized via fullwave method of moments short-open calibration (MoM-SOC) approach and further utilized as alternative K- and J-inverter networks with enhanced coupling. Network parameters are obtained and compared with those of two traditional lumped-CPW elements, demonstrating tightened coupling behaviors. The two improved /spl lambda//4 CPW bandpass filters are then constructed and their performances are optimized via cascaded topology. Predicted results show us a few attractive features, i.e., wide passband and first-order harmonic suppression as confirmed by experiment.

Millimeter-wave MMIC passive HEMT switches using traveling-wave concept

This paper describes the design of millimeter-wave wide-band monolithic GaAs passive high electron-mobility transistor (HEMT) switches using the traveling-wave concept. This type of switch combined the off-state shunt transistors and series microstrip lines to form an artificial transmission line with 50-/spl Omega/ characteristic impedance. A 15-80-GHz single-pole double-throw (SPDT) switch in conjunction with quarter-wavelength impedance transformers demonstrates an insertion loss of less than 3.6 dB and an isolation of better than 25 dB. Another type of wide-band switch was designed by using a series HEMT switch to replace the quarter-wavelength transformer, and the operating band can be extended to dc. With this scheme, dc-80-GHz single-pole single-throw (SPST) and dc-60-GHz SPDT switches are also developed with compact chip size. From dc to 80 GHz, the insertion loss and isolation of the SPST switch are better than 3 and 24 dB, respectively. The SPDT switch has an insertion loss of better than 3 dB and an isolation of better than 25 dB from dc to 60 GHz. The analysis of circuit characteristics and design procedures are also included. It is concluded that the device periphery can be selected for the desired bandwidth, while the number of transistors is decided to achieve the isolation.

A General Design Procedure Inhomogeneous Impedance for Quarter-Wavelength Transformers Having Approximately Equal-Ripple Performance

A general design procedure for quarter-wavelength inhomogeneous impedance transformers having approximately equal-ripple performance is presented, based on the simplifying assumptions that the relative impedance of two waveguides of slightly different widths is a constant and that tan /spl Theta//sub i/= k/sub i/ tan /spl Theta//sub 0/ in the vicinity of /spl Theta//sub i/ and /spl Theta//sub 0/ = 90/spl deg/. The calculation of the design parameters depends on the fact that the insertion-loss function can be expressed, in closed form, in terms of the unknown parameters. When this is identified with the permissible equal-ripple function, a set of simultaneous equations in the unknown parameters results. The solution of these equations is approximated by the solution to the corresponding homogeneous transformer problem. Thus a set of simultaneous linear equations in the small differences can be obtained which provides an approximate solution to the problem. An experimental design is described and the resulting data are presented.