Non-Foster circuits (NFC), in conjunction with the effect of negative impedance, have been applied to design broadband radio frequencies (RF) due to their wideband impedance matching ability. There are many approaches to designing non-Foster circuits that use transistors with loops inside to obtain negative reactance. Hence, conventional NFC has some problems, including complex connectivity and power consumption. In this paper, we analyse other properties of NFC phase and group delay, and we realize that these properties are related to properties of negative group delay (NGD) networks. Therefore, we proposed a new design of passive nonFoster circuits, that is less complicated and does not require power.

A high-efficiency microwave power transmission (MPT) system based on an inverted class F (F −1 ) rectifier for microwave wireless charging applications is presented in this paper. A left-hand circular polarization (LHCP) transmitting antenna (Tx) is designed based on a modified sequential phase rotation (SPR) divider integrated with a 2 × 2 array. The proposed Tx exhibits compact size with LHCP maximum gain of 11.85 dBi at 5.8 GHz. Furthermore, the receiver is composed of an LHCP receiving antenna (Rx) and a microwave F −1 rectifier. To realize the power radiated region of the Tx, an Rx with a wide beamwidth for minimizing distance loss is proposed, which has a 3-dB axial ratio (AR) beamwidth of 165.55 0 and 175.17 0 in the x-z and y-z planes, respectively. In addition, to improve the RF to DC conversion efficiency (η), the class F −1 harmonic processing network is utilized at the load of the rectifier that can process the voltage and current waveforms without using a DC pass filter. The proposed F −1 rectifier circuit occupies a compact area of 15.3 x 12.7 mm 2 , and it exhibits an average η of 50% for the input power range from 4 to 20 dBm with a peak efficiency of 77.9% at 18 dBm. Overall, the experimental results show that our proposed system achieves a maximum power transmission efficiency (PTE) of 8.8% for wirelessly charging low-power multiple devices at a distance of 60-200 mm. INDEX TERMSCircularly polarized antenna, harmonic processing, microwave rectifier, wireless power transmission (WPT), wireless charger.

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Negative impedance converter (NIC) is a broadband matching technique in radio frequency (RF) based on the non‐Foster theory. This technique in conjunction with the effect of negative impedance has been proven to achieve a wider impedance matching bandwidth than other techniques. However, it still has problems in the areas of flexible connectivity, and mismatch in the real part of negative impedance and power consumption. Those problems have led to non‐Foster circuits (NFC) not being trusted as much as high unload Q module for broadband matching. In this paper, we propose a new idea for NFC that uses balun transformers to achieve negative reactance in 0.8 GHz to 1.2 GHz with the real part of the impedance is matched to 50 Ω when the imaginary part (normally, it is the reactance of negative impedance circuit) does not change. Finally, we show and compare our results with the ideal impedance of negative lump components in both the Smith Chart and reactance. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1801–1806, 2016

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