GB1263624A - Coaxial microwave detector - Google Patents

Abstract

1,263,624. Matching impedances. TAVKOZLESI KUTATO INTEZET. 14 May, 1969 [15 May, 1968], No. 24679/69. Heading H1W. [Also in Division G1] A microwave signal detector for measuring the signal power in a coaxial line by converting the signal to a direct current comprises a first, central, conductor 6, second, third and fourth conductors 9, 8, 11 coaxial with and surrounding the first conductor, a connecting element 4 for connecting the first and second conductors, which together form an inner coaxial line, to the line carrying the signal to be measured, a diode 5 arranged within the inner coaxial line with one electrode connected to the first conductor 6, and a metal disc 7 connecting the other diode electrode to the third conductor 8, the disc being spaced from the second conductor 9 by an axial gap which is a small fraction of a wavelength at the centre frequency of the operating frequency range of detector. The disc constitutes a short circuit to microwave frequencies but not to D.C. A further metal disc 12 interconnects the second and fourth conductors but is axially spaced from the third conductor. Dielectric 10 spaces the second and third conductors so that the two form a middle coaxial line whose characteristic impedance is a small fraction of that of the inner coaxial line and whose length is about a quarter wavelength at the centre frequency. The third and fourth conductors constitute an outer coaxial line whose characteristic impedance is about ten times that of the middle coaxial line. To reduce microwave radiation, a microwave damping material, e.g. ferrite, is placed in the outer coaxial line, and the fourth conductor 11 is extended axially and closed by a metal disc 13 to form a cavity 14 whose resonant frequency, in any oscillating mode, is outside the operating frequency range of the detector. The cavity may accommodate resistor(s) which form part of the detector circuit. To improve matching, the characteristic impedance of the inner coaxialline (formed by conductors 6, 9) equals the real part of the diode forward impedance, and a short tube 14 of iron or ferrite powder is disposed between conductors 6, 9. Electrical contact between the diode 5 and the disc 7 is maintained under pressure by means of a split conical bush compressed into a conical hole in the disc 7 by the tightening of a nut (not indicated).