For resonant sections of a transmission line consisting of parallel silver rods extending vertically above a metal ground plane, the resonance curves of input admittance as a function of line length have been drawn by a synchronized recording meter apparatus, and the effective total resistance of each resonant line calculated. This has been done for frequencies between 300 Mcps and 1400 Mcps, for resonant line lengths up to several wavelengths, for line sections with both open‐circuit and short‐circuit termination at the top, and in each case with and without a large metal pipe shielding the test line. Radiation resistance is obtained as the difference between the resistance calculations for any one resonant line section unshielded and shielded.With a probable error of about 5 percent the radiation resistance is found to be proportional to the square of the frequency, and to be independent of line length and of whether the top termination is an open circuit or a short circuit. The absolute values agree reasonably well with the theory of Storer and King [Proc. Inst. Radio Engrs. 39, 1408 (1951)] and disagree conclusively with some predictions of earlier theories.

/pdf/the-radiation-resistance-of-resonant-transmission-lines-393pib0bb3.pdf

The Radiation Resistance of Resonant Transmission Lines

The problem of building a filter of ladder or lattice type wherein the elements are replaced by coaxial lines is shown to be largely one of geometrical arrangement. A method of designing and constructing such filters is described. Using this procedure, an experimental filter of the ladder type has been built for the television channel of 66 to 72 megacycles. The cutoff sharpness at the lower edge of its frequency range is 32 decibels per per cent of frequency change. This can be achieved with a very compact filter structure. The general performance and range of usefulness of this fiter type in television channels is discussed.

A Coaxial Filter for Vestigial-Sideband Transmission in Television

A coaxial line stabilized oscillator that is easily and rapidly adjustable over the frequency range from 70 to 700 Mc per sec. is described. Rugged mechanical construction, substantially complete shielding and coaxial line output connection are other features. With a 316A type vacuum tube, outputs of several watts are obtained over the entire range. Measurements indicate that for best stability it is necessary to tune precisely both filament leads, in addition to providing a high Q tank circuit. An optimum resonant length (λ/4, 3λ/4, ···) of line was not found. The stability decreases as the frequency increases, becoming very poor for frequencies near the limit of oscillation of the tube.

An Oscillator for Ultra‐High Frequencies

The first part of the paper describes a method of obtaining a picture of the damped vibrations of a quartz-plate resonator which occur when the excitation is removed by short-circuiting the electrodes between which the quartz plate lies. The build-up of vibrations after the short-circuit is removed is also shown. The quartz plate is short-circuited by means of a rotating commutator, and the resulting damped short-circuit current is caused to give a stationary damped-wave pattern on the cathode-ray-oscilloscope screen. Photographs of the patterns are easily obtained. Some interesting effects, such as variation of electrode air gap and pressure, are observed, and a few examples are shown. Since the damping or the Q of a circuit may be readily determined from the formula S = 1/n log A 1 /(A n+1 ) applied to n decaying amplitudes from A 1 to A n+1 the logarithmic decrement is readily found. The Q is also readily found since it is related to the reciprocal of δ. Amplitudes A 1 and A n+1 may be measured on the screen or photograph of the pattern for determination of δ or Q, but a more satisfactory method of measurement of these quantities was developed, incorporating a form of the commonly used momentary contactor, such as is sometimes used in the determination of wave form of an alternator. The speed of the contactor provides a ready determination of the number of vibrations from A 1 to A n+1 . A working formula [equation (3)] is developed for rapid measurements of Q of the quartz plate.

http://ieeexplore.ieee.org/iel5/10933/35670/01694253.pdf

Oscilloscope Patterns of Damped Vibrations of Quartz Plates and Q Measurements with Damped Vibrations

Radiation resistance, although ordinarily neglected, is actually of dominant importance in determining the selectivity factor Q and the input impedance Z s for both parallel-wire and concentric lines at high radio frequencies, and therefore materially changes the optimum design of the line, whether used as a low-loss inductive or capacitive reactance or to give high selectivity or high impedance as a resonant line Accurate design equations for maximum selectivity and for maximum impedance are developed in this paper for both parallel-wire and concentric lines, and curves are included showing radiation resistance, selectivity, input impedance, optimum values of spacing, conductor radius, etc It is shown that for maximum Q the optimum ratio of spacing to wire radius for parallel-wire lines is D/r = 6186, and the ratio of outer conductor radius to inner conductor radius for concentric lines is b/a = 422, as compared with values of about 36 for both ratios when radiation resistance is neglected For maximum impedance corresponding values are D/r = 2096 and b/a = 143, as compared with values of 8 and 92, respectively, predicted neglecting radiation resistance Moreover, Q and Z s are not proportional to D and b, as indicated in previous analyses; instead definite values of D and b give maximum Q and slightly larger values give maximum Z s , and even a small departure from the best value produces a large decrease in Q or in Z s 

Lester E. Reukema

Papers

Transmission Lines at Very High Radio Frequencies