ABSORPTIVE PIN ATTENUATORS

• US 3,859,609 A
• Filed: 07/23/1973
• Issued: 01/07/1975
• Est. Priority Date: 07/23/1973
• Status: Expired due to Term

• Current Assignee: James B. Couvillon, Roy E. Shipley
• Original Assignee: James B. Couvillon, Roy E. Shipley
• Inventors: Couvillon, James B., Shipley, Roy E.
• Primary Examiner(s): Gensler, Paul L.
• Application Number:
  US05/381,948
• Time in Patent Office: 533 Days
• Field of Search: 333/81R,81A,31R
• US Class Current: 333/81.00A
• CPC Class Codes: H01P 1/22 Attenuating devices dissipative terminating devices H01P1/26

Abstract

Variable attenuators for radio frequency (RF) signals in matched impedance transmission line systems are disclosed. Variable absorptive elements, PIN diodes, are used in shunt with the transmission line at quarter wavelength intervals. The impedance of the diodes which are coupled to input and output terminals is made equal at all attenuation levels to the impedance of the remaining diodes plus the characteristic transmission line impedance so that impedance mismatch with external devices is avoided.

Claims

1. An absorptive attenuator for RF signals in matched impedance systems comprising:

a plurality of transmission line segments, each having a length of one quarter wavelength at a preselected operating center frequency, said segments coupled between an RF input terminal and an RF output terminal for conducting RF energy from the RF input to the RF output, a plurality of PIN diodes coupled in shunt to the RF input and RF output terminals and junctions of transmission line segments for selectively absorbing part of the RF energy conducted by said transmission line segments, and a bias network for supplying unequal bias currents to said diodes to maintain the RF impedance of said diodes coupled to the RF input and RF output terminals at a value substantially equal to that of said diodes coupled to a common junction of transmission line segments plus the transmission line characteristic impedance over an operating range of attenuation levels.

2. An absorptive attenuator for attenuating RF signals between an input and an output terminal comprising, first and second transmission line segments each having a length of one quarter wavelengths at a preselected operating center frequency and each having one end coupled to a junction, a plurality of variable absorptive means, one side of a first absorptive means coupled to said input terminal and the other end of said first line segment, one side of a second absorptive means coupled to said output terminal and the other end of said second line segment, and a third absorptive means coupled in shunt to said junction, and, a bias network coupled to said junction for supplying current to said absorptive means which is related to the desired attenuation level of said RF signals, said bias network including resistors coupled between said junction and said input terminal and output terminal.

3. An attenuator according to claim 2 further including a plurality of capacitors coupled in series with the input and output terminals.

4. An absorptive attenuator for attenuating RF signals between an input terminal and an output terminal comprising:

fIrst and second transmission line segments each having a length of one quarter wavelength at a preselected operating center frequency and each having one end coupled to a junction, first and second variable absorptive means each comprising a PIN diode in series with a resistor having an impedance value equal to the transmission line characteristic impedance value, said first absorptive means coupled to said input terminal and the other end of said first line segment, and said second absorptive means coupled to said output terminal and the other end of said second line segment, third variable absorptive means comprising a PIN diode coupled to said junction, and attenuation control means for supplying substantially equal currents to all diodes in proportion to a desired attenuation level.

5. An attenuator according to claim 4 further including at least one additional attenuation stage comprising a quarter wavelength transmission line segment and a PIN diode interposed between said first and second segments.

6. An absorptive attenuator for attenuating RF signals between an input and an output terminal comprising, first and second transmission line segments, each having a length of one quarter wavelength at a preselected operating center frequency and each having one end coupled to a junction, a plurality of variable absorptive means, one side of a first absorptive means coupled to said input terminal and the other side of said first line segment, one side of a second absorptive means coupled to said output terminal and the other side of said second line segment, and a third absorptive means coupled in shunt to said junction, control means coupled to said junction for supplying current to said absorptive means in proportion to a desired attenuation level of RF signals, and impedance adjusting means coupled to said absorptive means for maintaining the RF impedance value of said first and second absorptive means equal to the RF impedance value of said third absorptive means plus the transmission line characteristic impedance.

7. An attenuator according to claim 6 wherein said absorptive means are PIN diodes.

8. An attenuator according to claim 7 wherein said control means and said impedance adjusting means is a bias network coupled to said junction and to said input and output terminals.