An amplifier uses non-dissipative elements to provide current and voltage feedback. The base amplifier has two input terminals, and the current and voltage feedback signals are applied to respective input terminals. The non-dissipative elements may be either transformers or coupled-line pairs. These elements allow broad band operation with low noise. The feedback configuration results in higher input impedence.

A low noise RF input amplifier circuit has an input impedance Z.sub.IN for matched-impedance coupling to an antenna having a resistive impedance R.sub.A. The amplifier circuit has an input and output nodes, an inverting amplifier, and a feedback capacitor. The input node receives an antenna signal which the inverting amplifier amplifies by a frequency-dependent gain -A(s) approaching -A.sub.0 at low complex frequencies s. The feedback capacitor C couples the output node to the input node for negative feedback and is selected to match Z.sub.IN to R.sub.A. When the amplifier's gain A(s) has a rolloff approximated by ##EQU1## where p.sub.1 is a negative pole, the capacitance of C which matches Z.sub.IN to R.sub.A is approximately inversely proportional to both (A.sub.0 +1) and R.sub.A.

A low-noise, linearized double-balanced active mixer circuit is described, including a first input for a local oscillator (LO), a second input for an intermediate frequency (IF) signal, and an output for a resulting product radio frequency (RF) signal. The mixer circuit also includes a feedback transformer circuit for the purpose of improving the intermodulation (IM) performance. The lossless nature of the feedback topology gives the active mixer a lower noise figure (NF) characteristic than is realizable with conventional methods. According to a further embodiment, the mixer circuit includes an additional pair of complementary amplifier transistors for the purpose of further improving the IM performance.

An active window pane antenna for use in motor vehicles includes an antenna conductor arranged on the window pane and being connected via a conductor of negligible length to an input terminal of an active four terminal network also arranged on the pane. The output terminals of the network are connected via a first section of a transmission line to an antenna connector whose ground contact is connected for high frequencies to a ground point on the body of the motor vehicle. The impedance of the first section of the transmission line is not negligible for the received frequency bands and the input impedance of the four terminal network is balanced with respect to the first section. A second section of the transmission line extends from the antenna connector to a receiver.

The antenna of an RFID tag or label is disconnected from the balance of the RFID chip by means of a series switch activated in response to a logic command, CLOAK, generated by the RFID chip. Activation of the switch disconnects the antenna of the RFID tag for the remainder of the RFID chip and effects a high impedance resistance across the antenna terminals. An RC circuit is charged by activation of the CLOAK signal and thereafter discharges during a predetermined RC time period as determined by a high impedance series antifuse leakage transistor. The antenna is thus disconnected for a time sufficient to allow the remaining RFID tags in an RF interrogation field to be identified. Meanwhile, during the disconnection of the antenna from the RFID chip and its loading causes its effective absorption and scattering aperture to be reduced near zero so as to electromagnetically remove the RFID tag from the zone of interrogation during the predetermined time period. Hence, the interrogated tag remains disconnected and noninterferring with the RF field used to interrogate the remaining tags.