Switchable microwave step attenuator with compensation for linear operation over wide frequency range

摘要

A programmable microwave card-type step attenuator is compensated for switch capacitance to render its attenuation response effectively insensitive to frequency over most of its dB range and comprises a plurality of cascaded attenuator sections disposed on a microstrip card with each attenuator section including a deposited film microstrip resistive network adapted to be switched into or out of the signal line by a miniature relay switch, a minimum loss transmission line being inserted into the signal line when the resistive network is switched out. Each of the microstrip resistive networks includes a reactive element connected thereto to compensate the frequency response of the resistive networks due to deviations from the optimum electrical length, thereby minimizing the frequency sensitivity of the attenuation characteristic of the section. Inductive effects are achieved by use of suitably shaped conductive areas or by removal of portions of the resistive networks. Capacitive effects are achieved by use of capacitances integrally formed with the resistive network. In addition, a window opening arrangement is provided which enables the required electrical connections of the attenuator circuit to be achieved with minimal length conductors. Compensation at the low levels of attenuation, i.e., 1 dB, 2 dB and perhaps 4 dB, cannot be effectively compensated by the aforesaid method alone and the attenuator may further comprise resistance stubs added to the minimum loss line to provide an additional increase in loss with frequency that parallels the attenuation sensitivity with frequency of the uncompensated lower dB attenuator networks.