By James T. Aberle, Robert Loepsinger-Romak, Constantine A. Balanis
Such a lot antenna engineers are inclined to think that antennas are one expertise that's kind of impervious to the speedily advancing semiconductor undefined. even though, as confirmed during this lecture, there's a solution to include lively parts into an antenna and rework it right into a new type of radiating constitution which can benefit from the most recent advances in analog circuit layout. The strategy for making this variation is to use non-Foster circuit parts within the matching community of the antenna. by way of doing so, we're not limited by way of the legislation of physics that follow to passive antennas. despite the fact that, we needs to now layout and build very sensitive energetic circuits. This new antenna know-how is now in its infancy. The contributions of this lecture are (1) to summarize the present cutting-edge during this topic, and (2) to introduce a few new theoretical and functional instruments for supporting us to proceed the development of this expertise.
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Additional info for Active Antennas with Non-Foster Matching Networks (Synthesis Lectures on Antennas)
In either case, these results confirm that conventional op-amps can be used to construct NICs, but faithful negative impedance will exist only to about 10 MHz or so. The use of op-amp-based NICs at higher frequencies must await the development of op-amps with significantly higher unity gain bandwidths than are currently available. Moreover, the parasitics of the device and circuit board will have to be minimized as much as possible. cls 17:23 ANTENNAS WITH NON-FOSTER MATCHING NETWORKS dB(Return_Loss_Measured) 0 dB(Return_Loss_Simulated) 30 January 19, 2007 -10 -20 -30 -40 -50 0 2 4 6 8 10 12 14 16 18 20 freq, MHz FIGURE 31: Simulated and measured return loss for the OPA690 NIC evaluation circuit Because an op-amp’s gain-bandwidth product severely limits the upper frequency at which negative impedance conversion can occur, we next focus on NIC realizations using current feedback amplifiers (CFAs) whose performance is (theoretically) not limited by their gain-bandwidth products, but mostly by their internal parasitic elements.
We simulated these circuits extensively and were able to obtain excellent performance in simulation with bandwidths greater than 1 GHz. Unfortunately, our attempts to physically implement these designs have all ended in failure. Other researchers have also reported a lack of success using this approach , and so we have abandoned it for the present. cls January 19, 2007 17:23 ANTENNAS WITH NON-FOSTER MATCHING NETWORKS 45 Return Loss (dB) -10 dB(S(1,1)) -15 -20 -25 -30 30 40 50 60 70 80 90 freq, MHz FIGURE 50: Return loss at input of optimized active matching network and antenna computed using Agilent ADS SIMULATED PERFORMANCE OF ESA WITH A PRACTICAL NON-FOSTER MATCHING NETWORK To illustrate the potential of non-Foster matching networks for ESAs, we designed and optimized in Agilent ADS a practical implementation of the active matching network shown in Fig.
G, Vol. 137, No. 2, pp. 78–87, Apr. 1990.  Texas Instruments, OPA690 Wideband Voltage-Feedback Operational Amplifier with Disable, 2005.  A. Sedra and K. C. , New York: Oxford University Press, 1998.  Maxim, MAX435/MAX436 Wideband Transconductance Amplifiers, 1993.  Texas Instruments, THS3202 Low Distortion, 2 GHz, Current Feedback Amplifier, 2004.  S. E. Sussman-Fort, “Matching network design using non-Foster impedances,” IEEE Long Island Section, Circuits and Systems Society [Online].