An intimate relation is established between non-Foster reactive elements and loss-compensated negative-group-delay (NGD) networks. It is shown that any possible network configuration containing a class of non-Foster elements operates as an NGD network. Likewise, it is demonstrated that a loss-compensated NGD network represents a reactive network with a non-Foster behavior. Consequently, these two properties can be intimately linked together and NGD networks can be utilized to implement non-Foster elements, such as negative capacitors and inductors. This result introduces another perspective in realizing non-Foster reactive elements, leading to new designs that are well behaved and more predictable in terms of stability and operation than traditional designs using negative impedance inverters and negative impedance converters. Based on this concept, loss-compensated NGD networks are proposed for realizing high-quality non-Foster reactive elements. Furthermore, entirely passive non-Foster elements with a limited quality ( Q) factor are proposed for which the minimum Q factor and the maximum achievable bandwidth are inversely related. It is shown that the design of non-Foster reactive elements using NGD networks can lead to the realization of standalone unilateral non-Foster reactive elements in a certain bandwidth. Examples of such non-Foster reactive elements and networks are demonstrated experimentally and shown to be stable.

Realizing Non-Foster Reactive Elements Using Negative-Group-Delay Networks

Application of retrodirective antenna arrays in wireless power transmission is proposed in this paper. The time reversal or phase conjugate theory and design considerations of the array factors are examined in GHz regime and meter range. The wireless power transmission efficiency is analyzed in the 2-D case with full-wave electromagnetic (EM) solution and validated by analytical array theory. The design factors of array size, array spacing, element size, and specific choice of the industrial, scientific and medical (ISM) band frequency are investigated to optimize the transmission focus. Design guidelines are provided for those factors and the impact of manufacturing variability is discussed. The proposed approach can also be extended to wireless power transfer with active retrodirective rectenna array and passive RFID systems.

Design of Retrodirective Antenna Arrays for Short-Range Wireless Power Transmission

This paper proposes two new circularly polarized retrodirective rectenna arrays, including a 2 /spl times/ 2 array and a 4 /spl times/ 4 array. A proximity-coupled microstrip ring antenna is used as the retrodirective rectenna array element, which can automatically block harmonic signals up to the third order from reradiating by the rectifying circuit. These arrays are printed on a Rogers Duroid 5880 substrate of /spl epsiv//sub r/=2.2 with a two-layer structure, with a total thickness of 1.5748 mm (or 62 mil). The new retrodirective rectenna array can track the incoming power source signals automatically and is less sensitive to the power incident angle variations, i.e., main-beam alignment deviation. It can provide a nearly constant dc output voltage within /spl plusmn/10/spl deg/ and 90% dc output voltage within /spl plusmn/45/spl deg/. The conversion efficiencies of the two arrays are 73.3% and 55%, respectively, when the power density is 10 mW/cm/sup 2/. The retrodirective rectenna array can be used in the low-power density applications for microwave wireless power transmissions.

New 5.8-GHz circularly polarized retrodirective rectenna arrays for wireless power transmission

A full-duplex dual-frequency self-steering array using phase detection and phase shifting is presented. By RF decoupling the transmitter and receiver arrays, the proposed system promises greater system efficiency by ensuring a constant transmit power. This also allows for a separate low-frequency interrogating signal capable of various modulation schemes. A two-element prototype is demonstrated with interrogating and retrodirective frequencies of 1.425 and 2.85 GHz, respectively. Retrodirectivity is reported for angles of 0deg, -15deg, and +25deg. The power of the received signal is improved by up to 12 dB for -60deglesthetasles60deg when compared to a conventional two-element array

A full-duplex dual-frequency self-steering array using phase detection and phase shifting

Backscatter modulation in radio frequency identification (RFID) tags will potentially connect billions of tomorrow’s devices to the Internet-of-Things. Current passive RFID systems have power constraints that limit RFID tag communication to short ranges, but these limitations can be overcome by employing reflection amplifiers. In this paper, we show that negative differential resistance devices, such as tunnel diodes, exhibit 27 dB more gain and 10 dB lower power consumption than state-of-the-art reflection amplifiers. Two 5.8 GHz prototypes using off-the-shelf tunnel diodes show reflection gains of 40 dB and 29 dB for a total biasing power consumption of 45 ${\mu }\text{W}$ and 39 ${\mu }\text{W}$ , respectively, at impinging RF power levels as low as −84 dBm. A 5.8 GHz RFID link of 23 m was achieved when transmitting only −14 dBm of effective isotropic radiated power from a transceiver with a sensitivity of −90 dBm.

Tunneling RFID Tags for Long-Range and Low-Power Microwave Applications

A novel two-port bi-directional amplifier, which may simultaneously amplify the waves coming from both ports, is proposed and demonstrated in this paper Using this amplifier, a two-element active Van Atta retrodirective array is implemented and compared to a four-element passive array The bi-directional amplifier is constructed by two identical one-port reflection-type amplifiers and a 3-dB 90/spl deg/ hybrid The reflection-type amplifier is designed using an FET with a single-power-supply configuration A quarter-wavelength microstrip radial stub is connected to the device's source terminal to narrow down the negative-resistance frequency range so as to avoid oscillation at undesired frequencies The fabricated bi-directional amplifier provides the transmission gain over the frequency band from 576 to 688 GHz, with a peak value of 91 dB at 604 GHz Printed Yagi antennas with four directors are adopted to build both the active and passive Van Atta arrays The 3-dB back-scattering beamwidth of the active array is measured as wide as 74/spl deg/ Finally, it is observed from the measurements that, although only half of the antenna elements are used, the active Van Atta array produces a back-scattering field level 45 dB, on average, higher than the passive one does This verifies the performance of the bi-directional amplifier

https://ir.nctu.edu.tw:443/bitstream/11536/28112/1/000180980100030.pdf

Shing-Ming Chen

Papers

A novel bi-directional amplifier with applications in active Van Atta retrodirective arrays