| 摘要 |
The invention discloses a variable attenuator consisting of a dielectric substrate supporting a microstrip layout plus some discrete components mounted on it, comprising: 1) a first branch connected between the input and output ports of the attenuator including a transmission line with a given characteristic impedance Zo along which two contiguous tracts of lambda /4 electrical length at the centre of the operating frequency band is delimited in order to constitute a first line section (LIN1); 2) a first pin diode connected across the first line section between the two lambda /4 tracts; 3) a second branch connected in parallel to the first one, including a series connection of a second line section (LIN2) having lambda /2 electrical length and impedance Z, and two fixed resistors Ro = Zo; 4) a second pin diode (R2) connected between ground and either the two fixed resistors Ro either one of the ends of the second line section (LIN2) when interposed between the two Ro resistors. The two diodes are serially biased. 5) pin diode DC-bias control means (AI) for varying the resistance of the two pin diodes of the same entity. The impedance Z of the second line section (LIN2) can be either equal to, or different from, Zo. In the former case the two microstrips can be either parallel straight-line or semicircular lines forming a ring. In the second case, Z NOTEQUAL Zo, the metallic layout is differently shaped (fig.3b and 3c). <IMAGE> <IMAGE>
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