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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 the 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 nonlinear 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 $\theta _{\mathrm {d1}}$ and $\theta _{\mathrm {d2}}$. 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 $\theta _{\mathrm {d1}}\,\,= 90^{\circ }$ , $\theta _{\mathrm {d2}}\,\,= 110^{\circ }$ , and SLL = −20 dB centered at $f_{1}\,\,=2.1$ GHz and $f_{2}\,\,=3.5$ GHz is designed, fabricated, and tested. The simulated and measured results match well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

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, $\text{I}_{2}, \ldots $ , 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). [ABSTRACT FROM AUTHOR]

A wideband circularly polarized (CP) stacked patch antenna based on TM11 and TM10 is proposed in this article. This four-port antenna consists of a circular patch and a square patch, where the square patch is located above the circular patch. Taking into account the mutual coupling between four ports, the active reflection coefficient (ARC) is adopted to describe the impedance matching of the antenna, and a simplified form of ARC is derived. The abnormal electric field distribution generated in the square patch is attributed to the superposition of the electric fields of two orthogonal TM10 modes, which is theoretically verified. Due to the coupling between TM11 mode and TM10 mode, a new resonance mode appears in a square patch, where the abnormal electric fields on the two diagonals are generated simultaneously. The effect of the square patch on the circular patch is equivalent to a capacitor at the lower frequency end and the higher frequency end of −10 dB impedance bandwidth, while it acts as an inductor at the middle frequency band. Besides the horizontal patch of $\lceil $ -shaped feed is sandwiched between two radiators to enhance coupling. Finally, a wideband feed network composed of Wilkinson power divider and phase shifter is devised to provide four signals of equal magnitude and quadrature phase for proposed antenna. To verify the design concept, a prototype is fabricated and measured. The results show that left-hand circularly polarized (LHCP) radiation is achieved. The 3 dB gain variation bandwidth is 44.6%, ranging from 1.48 to 2.33 GHz, in which VSWR < 1.5 and AR < 1.5 dB. Besides the peak gain is 9.5 dBic and antenna efficiency is not less than 64%. [ABSTRACT FROM AUTHOR]

In this article, a low-profile and wideband circularly polarized patch antenna is proposed and developed, which is composed of the circular patch fed by four ports. A wideband property is achieved by utilizing TM11 and TM21 mode, as well as the orthogonal mode of TM11. The Γ-shaped feed is employed to stimulate the TM21 mode. Besides, due to the parasitic radiation from the face-to-face Γ-shaped feeds with opposite phase, the radiation peak of the circular patch under TM21 mode is along the broadside direction, which is different from the original radiation mechanism of TM21 mode. By loading shorting pins in the middle area of circular patch, the polarization orthogonal mode of the fundamental mode (TM11) is excited properly, which contributed to bandwidth enhancement. Cooperated with the quadrature phase feed network, a wideband circular patch antenna with unidirectional radiation and circular polarization properties is designed, fabricated, and measured. The size of the circular patch is 0.57λ0 × 0.57 λ0 and the height is only 0.053λ0 (λ0 is the free space wavelength at the center frequency). The measured results show that the 109% of fractional bandwidth is obtained under the condition of VSWR < 2, ranging from 0.94 to 3.18 GHz, and the 3 dB axial ratio fractional bandwidth is 95%, ranging from 1.04 to 2.93 GHz. Besides the realized LHCP gain >3 dBic from 1.27 to 2.99 GHz. [ABSTRACT FROM AUTHOR]

This article presents a synthesis method to design a new type of bandpass frequency selective surfaces (FSSs) with multiple transmission zeros (TZs). To briefly show the concept of our synthesis method, a generalized topology of the bandpass FSS based on cascaded slotline sections paralleled with bandpass resonators is first presented to map with an alternative $n$ th-order bandpass filtering network with $J$ -inverters and typical LC parallel resonators. Then, two kinds of composite LC parallel resonators, named as LC – LC and ${L}$ – LC parallel resonators, are introduced and discussed to replace the typical LC parallel resonators, which can produce TZs at skirts of the passband and increase the out-of-band selectivity. The derivations of equivalent relationships between the composite and typical LC resonators are given. Furthermore, for the exploration of bandpass FSS with multiple out-of-band TZs, the realization of these two discussed composite LC parallel resonators is exhibited by inductive and capacitive strip lines loading on slotline structures. The design curves and guidelines are given and discussed correspondingly. To validate our design concept, two FSS examples, a second-order bandpass FSS with four out-of-band TZs and a third-order one with five out-of-band TZs, are synthesized and designed. In final, these two designed bandpass FSS prototypes are fabricated and then measured by the free-space measurement method. The measured results show that the desired stable bandpass filtering performance and independently multiple out-of-band TZs are successfully realized. [ABSTRACT FROM AUTHOR]