Tongfeng Guo

Coupling Matrix Synthesis of Nonreciprocal Lossless Two-Port Networks Using Gyrators and Inverters

A coupling matrix technique is presented for the synthesis of nonreciprocal lossless two-port networks. This technique introduces complex inverters to build the nonreciprocal transversal network corresponding to the nonreciprocal coupling matrix. It subsequently transforms this matrix into canonical topologies through complex similarity transformations. The complex inverters in the final topology are transformed into real inverters and gyrators for implementation simplicity. A second-order network example and a fourth-order network example, as well as an experimental validation, are then provided to illustrate the proposed technique. Finally, other possible implementations of the nonreciprocal gyrators are discussed.

Single-Step Tunable Group Delay Phaser for Spectrum Sniffing

This letter presents a single-step tunable group delay phaser for spectrum sniffing. This device may be seen as a “time filter”, where frequencies are suppressed by time separation rather than by spectral attenuation. Compared to its multiple-step counterpart, this phaser features higher processing resolution, greater simplicity, lower loss and better channel equalization, due to the smaller and channel-independent group delay swing. A two-channel example is provided for illustration.

Dispersive Feeding Network for Arbitrary Frequency Beam Scanning in Array Antennas

This paper introduces a dispersive feeding network that allows arbitrary frequency beam scanning in array antennas. The key component in this network is a dispersive element based on phasers, which are electromagnetic components providing arbitrary dispersive phase responses. The proposed feeding network is suitable for both the parallel-fed and series-fed arrays. Both the uniform and nonuniform scanning applications are demonstrated in the stripline technology via full-wave simulations. Finally, an experimental validation is presented.

Shunt-Stub and Stepped-Impedance Broadband Reflective Phasers

This letter introduces two new broadband reflective phasers, one based on shunt stubs and the other one based on stepped-impedance lines, respectively. In these phasers, broad bandwidth is achieved by using electrically short (λ/8 long or less), and therefore non-resonant, transmission line sections. A corresponding design procedure is presented, and three numerical and two experimental examples are subsequently provided to validate the proposed phasers.

DOA Estimation for Mixed Uncorrelated and Coherent Sources in Multipath Environment

A novel direction-of-arrival (DOA) estimation method is proposed to cope with the scenario where a number of uncorrelated and coherent narrowband sources simultaneously impinge on the far-field of a uniform linear array (ULA). In the proposed method, the DOAs of uncorrelated sources are firstly estimated by utilizing the property of the moduli of eigenvalues of the DOA matrix. Afterwards, the contributions of uncorrelated sources and the interference of noise are eliminated completely by exploiting the improved spatial differencing technique and only the coherent components remain in the spatial differencing matrix. Finally, the remaining coherent sources can be resolved by performing the improved spatial smoothing scheme on the spatial differencing matrix. The presented method can resolve more number of sources than that of the array elements and distinguish the uncorrelated and coherent sources that come from the same direction as well as improving the estimation performance. Simulation results demonstrate the effectiveness and efficiency of the proposed method.

Capacitor-Loaded Spoof Surface Plasmon for Flexible Dispersion Control and High-Selectivity Filtering

This letter proposes a new spoof surface plasmon transmission line (SSP-TL) using capacitor loading technique. This new SSP-TL features flexible and reconfigurable dispersion control and highly selective filtering performance without resorting to configuration change. Moreover, it requires much smaller linewidth than the conventional SSP-TL for achieving an extremely slow wave (or a highly confined field), which is quite useful for a compact system. To illustrate the design principle, several examples are designed within the frequency range of 2–8 GHz. Both numerical and experimental results are given in comparison with the conventional SSP-TL. It is demonstrated that the proposed technique provides a better performance in size reduction and dispersion reconfigurability.

Design of a dispersion-switchable phaser for chirping modulation

This paper presents a new switchable reflective phaser (which is a component providing arbitrary dispersive group delay response) for the first time. It is used for chirping modulation in real-time analog signal processing. Timedomain signals are modulated with two different dispersive group delay responses in correspondence to two different switch states. To efficiently design this new component with two different states, we transfer these two circuits into a single symmetrical filter network by applying odd/even-mode analysis, and subsequently apply the classic filter approaches. A design example is provided to illustrate the design approach. The result is in a good agreement with the prescribed response.

Design of nonreciprocal antenna array

A new non-reciprocal antenna array has been proposed in this paper for operation in microwave frequencies. The antenna array has been configured using a gyrator with the antenna patch elements through a T-type structure. Implementation of gyrator in the structure, that provides a phase shift of 180 degrees, results in a same beam direction of the forward and backward signals in the proposed antenna array. This proposed novel structure provides high radiation efficiency with beam steering and reduced side lobe levels.

Design of high efficiency rectifier operating at 2.4 GHz

This letter proposes a new rectifier circuit design operating with a reasonable efficiency for RF energy harvesting at 2.45GHz. The circuit is composed of an impedance matching network, a voltage-doubler for converting RF power into DC voltage and a low-pass filter. Our device outperforms other published counterparts with a maximum conversion efficiency up to 73.4% when the input power is 4.5dBm. The simulation is implemented and a prototype is fabricated. The measured maximum RF-DC conversion efficiency of the prototype is about 52% at 4.5dBm input power.

Miniaturized probing antenna for near-field microwave imaging

In this paper, we describe a single port probe for miniaturized imaging system. The probe antennas are optimized using computer simulation technology (CST) Microwave Studio (MWS) to achieve a good sensitivity to permittivity over a bandwidth of 15–20GHz. Comparing with others, our design can be applied to the near field imaging and the resolution becomes higher than the far-field imaging.