Transmission-Line Transformers

The radio-frequency transformers described in this paper consist of matched transmission lines of equal length and characteristic impedance. The lines are connected according to rules given in the text. These transformers exhibit a very broad frequency response which can be readily estimated; two methods of analysis are presented. The computations agree well with the test results.     

Impedance Matching (Correspondence)

Matching an impedance to a transmission line by the use of a cascaded section of line is a well-known process. However, the range of terminating impedance that can be matched by this method, I believe, is not so well-known. Consider a lossless line of characteristic impedance R/sub0/ to which is to be matched an arbitrary impedance /bar Z/ = R + jX by means of another lossless line of lentgh d and characteristic impedance R/sub 1/ cascaded between the first line and the load as shown schematically in Fig. 1. The problem is to determine for what range of values of /bar Z/ a match can be thus obtained for any values of R/sub 1/, and d.     

Loss Calculations for Coupled Transmission-Line Structures (Correspondence)

Expressions are derived for computing loss in coupled TEM structures in terms of complex even- and odd-mode propagation constants and characteristic impedances of the lines. The attenuation due to conductor (series) and dielectric (shunt) losses in a given structure can be determined utilizing these expressions. The results may be particularly useful for computing conductor loss in microwave circuits with a large number of sections used in traveling-wave devices and as microwave circuit elements. The method is applied to some typical structures for computing conductor loss.     

Balanced Transmission-Line Measurements Using Coaxial Equipment (Correspondence)

The availability of commercial precision coaxial hybrids makes measurements on balanced two-conductor transmission lines as easy and as practical as on an unbalanced coaxial system. These hybrids, when used as a balun, transform an unbalanced coaxial system to a balanced shielded system and because of the nature of the balanced shielded system permit the measurement of the characteristics of loads connected thereto by the use of commercial coaxial test equipment. This technique has been successfully used from 600 MHz to 5 GHz, and with presently available components can be used at HF and VHF as well. The theory upon which the measurement technique is based is outlined and some results of an experimental verification included.     

Optimum Design of Stepped Transmission-Line Transformers

This paper describes the optimum stepped-transmission-line transformer structure for matching two unequal characteristic impedances. For any specified bandwidth, the steps are designed to yield a Tchebycheff-type (or equal-ripple) reflection-coefficient response. Over this band, the maximum vswr is less than that obtainable with any other stepped-transformer having the same number of steps. Design method and technique for eliminating discontinuity-capacitance effects are given. The measured results for a coaxial and a waveguide model are presented and found to verify the method.     

Group Delay and Dissipation Loss in Transmission-Line Filters (Correspondence)

Basic formulas for the group delay and for the dissipation loss are derived for transmission-line filters. The optimum number of resonators for minimum dissipation loss is found.     

A Versatile Phase Measurement Method for Transmission-Line Networks (Correspondence)

Current phase-measurement methods for transmission-line circuits fall into two general categories. The first is the comparison method, where the path under measurement is compared with another calibrated, variable one. The phase shift through the variable path is adjusted to equal that of the unknown path, and this condition is shown by a null detector. Null indication by both phase and amplitude adjustment is usually required; however, null indication by phase adjustment alone can be effected. The second category of phase measurements includes those measurements which provide voltage or meter output indication of phase angle. This category includes direct high frequency phase-dectector circuits of limited frequency phase-dectector circuits of limited frequency range or frequency-conversion methods where analog or digital circuits measure phase at a converted lower frequency.     

New Coaxial-to-Stripline Transformers Using Rectangular Lines (Correspondence)

The most common form of coaxial-to-stripline transition consists of a simple inline butt joint, as described by Barrett. A typical transition between a 50-ohm high-Q triplate and a standard N-type connector is shown in Fig. 1. This gives a VSWR<1.15 at frequencies up to 7000 Mc deteriorating to 1.25 at higher frequencies up to 11,000 Mc. While these results are acceptable for many types of stripline components and assemblies, it was felt that the design of a better transition would be necessary in order both to test and to maintain the performance of high grade components (e.g., hybrids, directional couplers, and filters) and to avoid the manufacture of a special stripline standing-wave detector.