In this article, a class of bandpass frequency selective surfaces (FSSs) based on aperture-coupled dual-mode patch resonators (AC-DMPRs) are proposed to achieve single- and dual-band high-order ...filtering responses with low profiles. Initially, a basic resonator of a square patch with diagonal corner truncations is theoretically investigated so as to demonstrate that two orthogonal modes can be simultaneously excited in a single patch resonator. Then, to eliminate the cross-polarized reflection caused by the orthogonal modes, a composite resonator, including four of such corner-truncated patches with 90° rotation between each two adjacent patches, is constructed and analyzed. Furthermore, by arranging two of such composite resonators in a back-to-back manner through coupling apertures on the middle metallic layer, an FSS element of three-layer AC-DMPR is formed. Compared with traditional aperture-coupled patch resonators (AC-PRs), the resonant modes of AC-DMPR are increased twice, thus giving more design flexibility to achieve high-order performance. To validate the design concept, a single-band fourth-order bandpass FSS is designed by introducing magnetic couplings in the AC-DMPRs. Moreover, dual-band second-order bandpass FSSs with magnetic and/or electric couplings in the AC-DMPRs are also designed. Based on the even- and odd-mode analysis method, equivalent circuit models are established to explain the operating principles of the proposed structures. Finally, the designed FSSs are fabricated and measured. Good agreement between the measured and simulated results well validates the conceptual designs.
In this paper, a new class of wideband filtering phase shifters with a pair of controllable out-of-band transmission zeroes is presented for the first time. The proposed wideband filtering ...differential phase shifter consists of two stub-loaded multimode resonators (SLMMR) in the main and reference branches, which can provide a constant phase shift and self-realized generalized Chebyshev filtering function with controllable transmission zeroes by properly setting the impedance ratio <inline-formula> <tex-math notation="LaTeX">R_{\mathrm {z}} </tex-math></inline-formula> of the loaded stub. On the one hand, the prescribed phase shift value, phase deviation, and phase shift bandwidth are deduced that basically dominated by resonant modes of SLMMR together with electrical lengths of the phase-shifting lines. On the other hand, the phase properties of transmission zeroes are systematically investigated to demonstrate that they arouse little effect on the phase shift performance, but highly improve the frequency selectivity in theoretical analysis. Based on the presented synthesis method which simultaneously considers wideband phase shift and bandpass filtering function, the circuit parameters of the entire proposed phase shifter can be synthesized with prescribed phase shift value, phase deviation, bandwidth, return loss, and transmission zero positions. Besides, the phase shift and return loss bandwidth can be determined in the design process. As design examples, two 90° wideband filtering phase shifters with different specifications are synthesized, designed, and fabricated to validate our proposed approach.
In this article, a class of improved Schiffman phase shifters with two C-section coupled lines separately operating in the first and second phase periods is presented and analyzed. Theoretical model ...and closed-form synthesis formulae are utilized to analyze the phase performances of the proposed phase shifters, which reveals significant differences compared to the phase shifters solely operating in the first or second phase period. Compared to the traditional counterparts, the proposed phase shifters can achieve a larger phase shift value and a wider phase shift range at the same impedance ratio. Moreover, under the same impedance ratio, the phase shifter can obtain wider phase shift bandwidth. These features are believed to be very useful in the limitedly realizable coupling strength for a wide phase shift range case. Finally, two sets of comparative experiments, including the operations in the first phase period, second phase period, and the proposed type, are designed and fabricated to validate the proposed approach. The simulated and measured results agree well with the theory and achieve a 33.6% (36.7%) increase in phase shift bandwidth when the phase shift value is 90° (150°) under the impedance ratio of 1.5822 (2.0312).
In this paper, a new class of filtering differential phase shifters is proposed and developed, which can provide constant phase shift and self-embedded filtering function at the same time. In ...contrast to its traditional counterparts, the proposed phase shifter consists of two bandpass filter (BPF) branches and the phase properties of generalized nth-order BPF network are systematically studied at first time. With derived closed-form formula of phase slope, the synthesis method is presented to design the proposed filtering differential phase shifters with prescribed arbitrary phase shift value, passband ripple, and bandwidth. The filter order, which dominates frequency selectivity, is considered in the synthesis design of proposed phase shifter as well. The tradeoff between the frequency selectivity and phase shift is discussed. In addition to the advanced features of multifunction and simple geometry, the proposed filtering differential phase shifters can achieve compact size, low amplitude imbalance, and multiway polyphase capability. To validate the proposed concept and synthesis method, two filtering differential phase shifters with single-phase (90°) and five-way polyphase (45°, 90°, 135°, and 180°) are designed, fabricated, and measured. The simulated and measured results coincide well with the prescribed performances in phase shift and magnitude.
In this paper, a new design concept of Schiffman phase shifters under the operation of the second phase period in frequency domain is presented and analyzed. By investigating phase properties of the ...C-section structure, we first find that its second phase period is another independent and distinctive working region for Schiffman phase shifter, in addition to its first phase period. In contrast to traditional counterparts working on the first phase period, which are suitable for small phase shift from 0° to 90°, the Schiffman phase shifters on the second phase period are suitable for the large phase shift from 90° to 180°. It is because of the opposite phase variation property that the electrical length of reference line gets shortened as the phase shift value increases. Compared with the first phase period, the second phase period can achieve wider phase shift bandwidth under the same coupling degree. This feature is believed to be very useful in the limited realizable coupling degree cases. In this context, the closed-form synthesis formulas of Schiffman phase shifter on the second phase period are presented. Meanwhile, detail theoretical analysis of the phase shift bandwidth and phase deviation is carried out. In final, two Schiffman phase shifters on the first and second phase periods are designed and fabricated to validate our proposed concept and approach in the experiment.
Aiming to realize series-fed antenna array with good return loss, low sidelobe level (SLL), and small gain variation over a wide bandwidth, this article presents a unified synthesis method of ...designing series-fed networks (SFNs) under the equal/unequal distributions with the bandwidth enhancement. We find that the return loss and current distribution bandwidths of SFN are dominated by its input reactance slope. The ratio of SFN main line impedance Z0 and antenna impedance ZL plays an important role in it. When the optimal Z0/ZL makes the input reactance slope equal to zero at the center frequency, the bandwidth of SFN can be highly extended by 2-4 times compared with nonoptimal solutions. In this context, four classical types of SFNs are investigated and synthesized. The closed-form optimal formulas for these SFNs are further deduced under the specified element number N and current distributions I1, <inline-formula> <tex-math notation="LaTeX">\text{I}_{2}, \ldots </tex-math></inline-formula>, and IN. For experimental verification, an eight-element series-fed antenna array driven by the SFN with Dolph-Chebyshev current distribution is designed and fabricated based on the proposed design method. By virtue of the improved SFN, the designed series-fed array exhibits enhanced impedance and radiation bandwidths as predicted. The measured results show designed array achieves an impedance bandwidth of 52.2% (3.34-5.70 GHz) with S11 ≤ −10 dB and the radiation bandwidth with SLL ≤ −20 dB is 20.9% (3.85-4.75 GHz). The measured antenna gain is 11.3 dBi with a small variation of 1.3 dB and the efficiency of array is better than 82% over the operational bandwidth of 18.7% (3.88-4.68 GHz).
A new design of dual-band series-fed array (SFA) using coupled line sections with one series-fed network (SFN) and one port is proposed in this article. Compared with conventional array, the proposed ...design provides one more degree of freedom in antenna array synthesis. It can realize equal beam angles at two operational frequencies and reduce element spacing to eliminate the grating lobe by virtue of non-linear phase properties. The parameters have been extensively studied and considered in the analytical analysis. An assessment method of achievable beam angles for dual-band SFAs is proposed and conducted in the entire upper hemisphere. Compared with the conventional array, the proposed dual-band SFA can expand the achievable radiation range with regard to the θ d1 and θ d2 . Its limitations are also analyzed and discussed. Furthermore, in order to realize specified sidelobe level (SLL) at two operational frequencies, the closed-form design formulas are deduced for the proposed dual-band SFA with arbitrary N elements and amplitude distributions. To verify the proposed design concept and synthesis method, a prototype of proposed six-element dual-band SFA with specified θ d1 = 90°, θ d2 = 110° and SLL = -20 dB centered at the f 1 = 2.1 GHz and f 2 = 3.5 GHz is designed, fabricated and tested. The simulated and measured results match well with the theoretical predictions.
In this letter, a new compact filtering power divider (FPD) on the square substrate integrated waveguide (SIW) with wideband isolation is proposed. As the isolation network is embedded in a square ...SIW cavity, good in-band isolation, compact structure, and low insertion loss can be simultaneously attained. The proposed FPD consists of the coplanar waveguide feeding line of Port 1, the capacitor, a resistor, and the square SIW cavity. TE 101 , TE 201 , and slot-line modes can realize third-order filtering response. Center frequency (<inline-formula> <tex-math notation="LaTeX">f_{0} </tex-math></inline-formula>) and bandwidth of the filtering response can be independently adjusted. In order to achieve out-of-band isolation, Port 2/3 is placed in the specific position to suppress the high-order modes according to the electric-field distributions of these modes. Finally, a prototype with in-band return loss of 20 dB across 5.59-6.4 GHz is designed at 5.99 GHz. The bandwidths of isolation higher than 21 dB and upper stopband attenuation higher than 20 dB are extended to <inline-formula> <tex-math notation="LaTeX">2.79f_{0} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">2.83f_{0} </tex-math></inline-formula>, respectively.
In this article, a new class of wideband phase shifters with very compact size, large phase shift value, low insertion loss (IL), and low cost are presented and developed. The proposed phase shifter ...consists of <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> series and shunt resonators, which can achieve the magnitude and phase shift bandwidth of more than 120% thanks to <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> transmission poles. Besides the wideband property, the proposed phase shifter is able to achieve a small size of nearly 1/10 guided wavelength (<inline-formula> <tex-math notation="LaTeX">\lambda _{g} </tex-math></inline-formula>), which has a size reduction of more than 90% as compared with conventional wideband phase shifters on printed circuit board (PCB). Meanwhile, insertion phases for the both series and shunt resonators are zero at their resonant frequencies; thus, the length of reference line can be also greatly reduced. What is more, a detailed synthesis method with closed-form equations is presented and employed to determine all circuit parameters of the proposed phase shifter with the specified in-band return loss (RL), phase shift value <inline-formula> <tex-math notation="LaTeX">\Delta \Phi </tex-math></inline-formula>, and resonator number <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>. To validate the design concept, three design examples of 90° and 180° phase shifters on <inline-formula> <tex-math notation="LaTeX">N = 3 </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">N = 5 </tex-math></inline-formula> are synthesized and tested. Theoretical, simulated, and measured results are in a fairly close agreement. In particular, the proposed phase shifters feature very low IL. The measured maximum in-band IL is only 0.38 dB for <inline-formula> <tex-math notation="LaTeX">N = 3 </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">\Delta \Phi = 90^{\circ } </tex-math></inline-formula>) and 0.50 dB for <inline-formula> <tex-math notation="LaTeX">N = 5 </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">\Delta \Phi = 180^{\circ } </tex-math></inline-formula>).
