Dajun Lei

A Nonreciprocal Multi-Channel Bandstop Filter Using the Generalized Fibonacci Multiferroic Superlattices with the Silver-Mean Sequence

The generalized Fibonacci multiferroic superlattices (GFMS) are composed of single-phase multiferroic domains with simultaneous polarization and magnetization and are defined by the binary substitutional rule (B −→ BmA, A −→ B, m = 2, 3). We propose to construct a nonreciprocal multichannel bandstop filter by the GFMS. The couplings between electromagnetic waves and lattice vibration of multiferroic material with ferroelectric and ferromagnetic (or antiferromagnetic) orders can be invoked either through piezoelectric or piezomagnetic effects and can lead to the creation of polaritonic band structure. The plane wave expansion method with first-order approximation predicts the existence of multiple band gaps, and electromagnetic waves lying within the band gaps are prohibited, and the band gaps with respect to forward electromagnetic waves (FEWs) and backward electromagnetic waves (BEWs) are asymmetric. The forbidden band structures with FEWs and BEWs are calculated by the transfer matrix method and multiple frequency channels with unidirectional transmission of electromagnetic waves can be further confirmed. Nine and twenty transmission dips in transmission spectra for the BEWs in the frequency range of ω = 0.4–0.6 (17.06 GHz–25.59 GHz) are found in the GFMS with m = 2 and 3, respectively, in which the BEWs are prohibited while the FEWs can travel. Thus, the GFMS has all the conditions for the nonreciprocal multi-channel bandstop filter. Besides, the GFMS can also be applied to construct compact multi-channel one-way electromagnetic waveguides.

Accurate Extraction of High Quality Factor of Dielectric Resonators from Measurements

We present a revised Cauchy method to accurately extract the high quality factor of dielectric resonators from measurements. Since the losses displace all the zeros and poles of the transfer function horizontally to the left in the complex plane, the accurate evaluation of the unloaded quality factor of microwave resonators can be achieved based on the complex frequency transformation. The results show that if the three-point method is employed, the accuracy of the quality factor values deteriorates when the input/output coupling is strong. Nevertheless, a nearly constant factor value can be obtained by our proposed technique whether the input/output couplings are weak or strong. This algorithm provides an alternative method to measure the unloaded quality factor when the signal-tonoise ratio is high.

A Novel Method from Bandpass to Dual-Band for Microwave Filter and Diplexer Design

A novel method for a dual-band filter and quad-channel diplexer design is presented in this paper. This method, by altering the gap between resonators, realizes a transformation from bandpass to dual-band for the filter and diplexer. At first, a high selectivity bandpass filter (BPF) with four controllable transmission zeros (TZs) is designed. Then altering the gap between resonators, a band gap is generated and utilized to split the passband of the proposed BPF into two bands, which transform the BPF to a dual-band filter with a narrow passband separation. The center frequency and bandwidth of the new dual-band filter are controllable by adjusting the frequency and width of the band gap. Based on the dual-band filter, a quad-channel diplexer with stepped impedance T-junction is designed, and it can be transformed to a wideband diplexer. For demonstration, the dual-band filter and quad-channel diplexer are fabricated and measured.

Novel Circularly Polarized SIW Cavity - Backed Antenna with Wide CP Beamwidth by Using Dual Orthogonal Slot Split Rings

A circularly polarized (CP) substrate integrated waveguide (SIW) cavity-backed antenna based on dual concentric, orthogonal slot split ring resonators is proposed and experimentally studied. The circularly polarized wave is generated by two split ring-slots etched in the upper metal layer of the SIW cavity resonator. These two slots are excited by a coaxial probe located in the gap of the external slot split ring to radiate the right-handed circularly polarized (RHCP) wave. By rotating the dual split slot ring resonators and the probe by 45 degrees relative to the backed cavity, a better match characteristic and a slightly higher radiation gain are obtained. Because of the concentricity of radiant split ring slots, the beamwidth of the circular polarization is obviously increased. From the experimental results, the impedance bandwidth was 10.8% for the reflection coefficient less than −10 dB, the axial ratio (AR) bandwidth was 1.54% for the AR less than 3 dB, and the RHCP gain was 4.44 dBic. Moreover, the 3-dB axial ratio beamwidth at the centre frequency of 10.40 GHz has been extended to 142◦ in the angular range from −78◦ to +64◦.

Implicit space mapping method for dual-band filter and wideband diplexer design

In this paper, open-stub loaded resonator and short-stub loaded resonator are adopted to design a novel wideband diplexer and dual-band filter. To accelerate simulation speed, implicit space mapping method is firstly applied in multi-mode filter and diplexer design. To demonstrate it, a novel dual-band filter with central frequency at 1.8/2.5GHz and relative bandwidths of 16.7%/12%, and a diplexer with central frequency at 1.9/2.5GHz and relative bandwidth of 30%/24% are designed and fabricated and the measured S-parameters agree with the simulated one.

Compact dual-band filter using two layered dual-mode substrate integrated waveguide resonator

In this paper, a compact dual-band filter using multilayer dual-mode substrate integrated waveguide (SIW) resonators is presented. Resonators are vertically stacked to reduce surface area and dual-mode resonator is applied to decrease the dimension. Moreover, the central frequencies of dual-band filter and coupling coefficient can be adjusted independently. For demonstration, A dual-band filter with central frequency located at 7.4GHz and 7.8GHz is designed and the measured S-parameters agree well with the simulated ones.

Conceptual design of a nonreciprocal bandstop filter using metamaterial Thue-Morse multiferroic superlattices

A novel nonreciprocal bandstop filter (NBF) using metamaterial Thue-Morse multiferroic superlattices (MTMMS) is presented, where the multiferroic domains with polarization and magnetization simultaneous are arranged along x-axis according to the iterative rule of the Thue-Morse sequence. The dispersion relation is obtained by the transfer matrix method and indicates that the band gaps for the forward wave (FW) and the backward wave (BW) are not symmetrical. Transmission spectrum is utilized to illustrate the band gaps clearly. Two band gaps in the frequency ranges of ω = 20.9 - 23.03 GHz and ω = 63.98 - 64.41GHz can be observed in the MTMMS with the sequence of l=2 for the FW. However, the band gaps for the BW appear in the frequency ranges of ω = 19.49 - 21.92 GHz and ω = 63.12 - 63.98 GHz. The maximum bandwidth of 2.1GHz and an obvious nonreciprocity with respect to the FW and BW can be obtained in this case. The S-parameters can verify this property further. In addition, the NBSF is easy to integrate into practical systems since its size of forming stable band gaps is about one centimeter.

Compact Hexa-Mode Resonator and its Application on WiFi Dual-Band Filter

This letter presents a compact hexa-mode microstrip resonator which is originated from a traditional stub-load resonator (SLR). Stub in SLR is replaced by a couple of square-loops in the proposed resonator. The advantage of this replacement is that six modes emerge to realize a compact size, and more transmission zeros are generated in its application on filter to enhance the frequency selectivity. For demonstration, a compact dual-band microstrip filter using the proposed resonator is designed in 2.4 GHz/5.2 GHz of WIFI channel, and six transmission zeros are generated to enhance the frequency selectivity.

Compact Coaxial Probe-Fed CP Substrate Integrated Waveguide Cavity-Backed Antenna Utilizing Slot Split Ring

A circularly polarized (CP) substrate integrated waveguide (SIW) cavity-backed slot antenna is proposed. A slot split ring (SSR) etched on the top metal surface of an SIW resonator is employed to generate the right-handed circularly polarized (RHCP) wave. The proposed antenna is excited directly by a coaxial probe with a proper distance from the symmetric axis of the SSR resonator. A prototype of the proposed CP antenna at the center frequency of 10 GHz is manufactured. As a result, the proposed antenna exhibits the advantages of both conventional planar antennas and metallic cavity backed antennas, including simple structure, compact size of 15.8×15.8 mm 2 , light weight, easy fabrication, high gain and wide axial ratio bandwidth. It is proved by experiment that an impedance bandwidth of 10.2% for the reflection coefficient less than −10 dB, an axial ratio (AR) bandwidth of 1.72% for AR less than 3 dB, and a RHCP gain 5.5 dBi have been obtained.

Extraction of the Q factor of dielectric resonators from S-parameters using the cauchy method

A modified Cauchy method to generate an accurate rational model of lossy systems from the S-parameters is presented. Based on the property that the losses displace all the zeros and poles of the transfer function horizontally to the left in the complex plane and the complex frequency transformation technique, the accurate evaluation of the unloaded quality factors of microwave resonators can be realized using the Cauchy method. Whether the input/output couplings are weak or strong, nearly the same unloaded quality factors can be obtained by the proposed technique. This algorithm provides an alternative method to measure the unloaded quality factor without the limits of weak coupling strength.