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A dual-band dual-polarization horn antenna array is proposed for Ku-band satellite communication (SATCOM) in this article. A miniaturized orthomode transducer (OMT) using the mutually perpendicular multistep waveguide transition and coupled transition to transmit TE10 mode and TE01 mode, respectively, is integrated into the radiation element. The high isolation characteristic of horizontal polarization in the transmitting band (Tx) and vertical polarization in the receiving band (Rx) desired for SATCOM is realized. Moreover, the sinusoid-tapered horn antenna and the radiating cross-shaped cavity are employed as the shared-aperture element to radiate orthogonal waves simultaneously, having the potential of wide bandwidth, low sidelobes, and high radiation efficiency. With the facility of the 3-D metal printing technology, a horn antenna array consisting of the proposed 4 $\times4$ radiation elements and feeding networks is demonstrated and fabricated. The gains up to 26.48 and 26.51 dBi with radiation efficiencies of around 94% and 90% are obtained at Tx- and Rx-bands, respectively. Benefitted from the advantages of compact size, high gain, and high efficiency, the proposed horn antenna array is suitable to tackle the high-throughput demand in Ku-band SATCOM systems. [ABSTRACT FROM AUTHOR]

In this communication, a high-order-mode (HOM)-fed open-ended rectangular waveguide antenna with high gain and broadband is proposed for fifth-generation (5G) applications. A miniaturized HOM cavity with four slots introduces hybrid modes of $TE_{340}$ and $TE_{140}$ , which act as a low loss feeding network. Furthermore, an open-ended waveguide is loaded above the HOM cavity to widen the impedance bandwidth. Compared with $TE_{340}$ HOM, hybrid modes of $TE_{340}$ and $TE_{140}$ HOM provide more compact size and higher gain. For the proof of concept, a $4\times $ 4 antenna array is designed and fabricated. The measured impedance bandwidth is 28.1% from 32.85 to 43.6 GHz. The measured peak gain is 21.7 dBi. Great compatibility between simulated and measured results is achieved. [ABSTRACT FROM AUTHOR]

In this letter, a compact wideband circularly polarized patch antenna array is proposed to cover the 57–71 GHz band. The antenna array is constructed by 45 $^\circ$ inclined slits loaded circular radiating patches with rectangular back cavities, two-layer sequential rotation feed networks, and a waveguide transition. Novel self-sequential rotation technology is introduced using a dual-high-order-mode cavity to improve the axial ratio (AR) and impedance bandwidths of the subarray. Compared with conventional sequential rotation feed networks, the proposed feeding scheme provides higher aperture efficiency. A 4 × 4 patch antenna array is fabricated using standard printed circuit board technology. Measured results show that the $-$ 10 dB impedance and 3 dB AR overlapped bandwidth is 23.8%(57–72.3 GHz). The measured peak gain is 20.5 dBic with an aperture efficiency of 87.7% at 66 GHz. [ABSTRACT FROM AUTHOR]

In this article, a novel structure of the high-order-mode cavity fed sequentially rotated patch antenna array is proposed for diverse polarizations. The diverse polarizations, including right-hand circular polarization (RHCP), left-hand circular polarization (LHCP), −45° linear polarization (LP), 0° LP, 45° LP, and 90° LP, are achieved based on the current distribution on the patches and different electric field modes in the high-order-mode cavity by adjusting the phase and amplitude of the two orthogonal feeding ports. Furthermore, from the electric field distribution in the high-order-mode cavity with different feeding schemes, arbitrary polarizations were analyzed and obtained. An $8\,\times \, 8$ dual-circularly polarized (dual-CP) antenna is demonstrated. Good agreement between the simulated and measured results is obtained, validating the design. The experimental results show that the impedance bandwidths (<−10 dB) for the two ports are 14.2% and 13.3%. The 3 dB axial ratio (AR) overlapping bandwidth is 10.5%. The maximum gain is 25 dBic. Attributed to its compact size, high gain, and high efficiency, the presented array is a good candidate for millimeter-wave applications. [ABSTRACT FROM AUTHOR]

In this letter, an 8 × 8 dual-polarized antenna array with high gain and broad bandwidth is proposed for $Q$ -band millimeter-wave (mm-wave) application. Metallic pillars and cavities act as magnetoelectric dipoles fed by a 1 to 4 backed cavity with cross-shaped slots. The cross-shaped slots are adopted to excite two orthogonal linear polarizations. A feeding network with shared vias is designed to construct the antenna array. An 8 × 8 dual-polarized antenna is fabricated and measured. The measured impedance bandwidths are 13.4% from 34.7 to 39.7 GHz and 14.4% from 34.6 to 40.1 GHz for the two ports, respectively. The 3 dB gain fluctuation bandwidth is 8% for the two ports. The maximum gain is up to 24.8 dBi due to less substrate loss in the radiation structure. Attributed to its high gain and high efficiency, the proposed antenna is a promising candidate for mm-wave applications. [ABSTRACT FROM AUTHOR]

In this article, a novel low-power notch-enhanced active filter is presented using the feedback notch-enhanced (FNE) technique. The active notch filter is proposed based on an area-saving second-order $LC$ series resonator. The passive devices’ loss can be effectively eliminated by the generated dc power-independent negative resistance by inserting a current feedback transistor. Moreover, the capacitive source degeneration (CSD) technique is proposed to boost the filter $Q$ by shifting the series resonant frequency to the negative-resistance region. To demonstrate the feasibility and practicability of the proposed notch filter, a 3.1–10.6-GHz IEEE 802.11a interferer rejected low-noise amplifier (IR-LNA) is fabricated in a 0.13- $\mu {\hbox {m}}$ CMOS process. The multistage structure, consisting of a common-gate (CG) stage with a dual-resonance load and a cascode stage with the proposed active notch filter, is employed for wideband input matching, gain flatness, and interferer rejection (IR) simultaneously. The measurements show that the IR-LNA provides a maximum of 16.05-dB power gain, 2.08–3.70-dB noise figure (NF) in the desired band, and a maximum of 40.9-dB IR ratio (IRR) at 5.77 GHz, with a power consumption of 10.2 mW, while the active notch filter only consumes 456- $\mu {\hbox {A}}$ current. [ABSTRACT FROM AUTHOR]

In this letter, a wideband circularly polarized high-order Bessel beam reflectarray composed of 30×30 elements with different spatial orientations is proposed. The element is formed by a multiple-ring-cascade structure printed on the top surface of FR-4 substrate, an air layer, and a metal ground plane. The multiple-ring-cascade structure supports the multiple resonance property, which contributes in achieving the wideband circularly polarized performance. The reflection phase of 360 $^\circ$ is achieved by continuously changing the spatial direction of the element. To validate the effectiveness of the proposed element, a high-order Bessel beam reflectarray with the size of 75 cm × 75 cm is designed, fabricated, and experimentally demonstrated. The measured results confirm that a high-order Bessel beam with $l$ = + 1 is successfully generated from 5 to 8 GHz, which has less divergence in near-field transmission as compared to the vortex beam carrying the same orbital angular momentum mode. [ABSTRACT FROM AUTHOR]

In this letter, a wideband circularly polarized reflectarray composed of 30 × 30 unit cells is proposed to generate dual-mode vortex beams. The element consists of two back-to-back semi-split-loop structures printed on the FR-4 substrate, an air layer, and a metal ground plane. The two back-to-back semi-split-loop structures provide the multiresonance property, which can effectively increase the bandwidth. A 360° phase range is achieved by changing the spatial orientations of the element. Based on the proposed element and the superposition design method of aperture field, a dual-mode square aperture vortex beams reflectarray is simulated, fabricated, and experimentally demonstrated. The measured results confirm that two vortex beams carrying +1 and –1 mode of orbital angular momentum are successfully generated in a wide range of frequencies from 5 to 8 GHz. The size of the proposed reflectarray is 75 cm × 75 cm, and the measured maximum gain is 22.2 dBic. The measured 1 dB gain bandwidth is 33.3%. [ABSTRACT FROM AUTHOR]

In this paper, a novel configurable loop array antenna based on resonator-loaded microstrip lines (RLML) is proposed to enlarge the interrogation zone of the reader antenna for near-field ultrahigh-frequency (UHF) radio frequency identification (RFID) system. The proposed loop array antenna is composed of a number of RLML loop units. By configuration of the RLML loop units sharing a common side with its adjacent RLML loop units which carry reverse-direction flowing current in the ${x}$ -axis and ${y}$ -axis directions, loop array antennas are created to generate a strong and uniform magnetic-field distribution over a large configurable interrogation area. As an example, loop array antennas with $1\,\times \,8$ and $2\,\times \,3$ RLML loop units implemented onto a piece of an FR4 printed circuit board (PCB) are designed, fabricated, and measured. The measured bandwidth ranges from 894 to 964 MHz for a $1\times 8$ array antenna with a reading area of $570 \,\,{\mathrm{ mm}}\times 150\,\,{\mathrm{ mm}}$ and 917–932 MHz for a $2\times 3$ array antenna with a reading area of $270 \,\,{\mathrm{ mm}}\times 240\,\,{\mathrm{ mm}}$. The reading distances of an $1\times 8$ array antenna for loop-like tag, dipole-like tag, and antimetal tag are achieved up to 22, 42, and 45 mm, respectively. For a $2\times 3$ array antenna, the reading distances of three tags are achieved up to 23, 43, and 40 mm. [ABSTRACT FROM AUTHOR]

A dielectric-slab-loaded hollow substrate-integrated waveguide (HSIW) $H$ -plane horn antenna with improved impedance matching is proposed based on printed circuit board material FR-4. HSIW is utilized to avoid high dielectric loss. Apart from that, a dielectric slab is added by directly extending the substrates for gain improvement. Moreover, two coupling lines are added above and below the horn aperture for better impedance matching. The proposed HSIW $H$ -plane horn antenna shows a maximum realized gain of 11.2 dBi with 77.6% radiation efficiency and 32.9% bandwidth (27.7–38.6 GHz). Based on the antenna element, a $1\times 4$ HSIW $H$ -plane horn antenna array is proposed. The array shows a maximum realized gain of 17.2 dBi with 66.5% radiation efficiency and 31.9% bandwidth (27.6–38.1 GHz). Good agreements of the measured and simulated results are achieved for both designs. The proposed antenna and array can be good candidates for low-cost millimeter-wave wireless communication systems. [ABSTRACT FROM AUTHOR]

A wideband vortex beam reflectarray is designed and fabricated to generate the orbital angular momentum (OAM) waves for an $\boldsymbol{l} = 2$ mode. A quarter-wavelength element is proposed to achieve a reflection phase of 360° at the designed frequency of 6 GHz. The element consists of a loop patch, a cross-dipole patch, and four square patches. The symmetric structure of the element makes it suitable for dual polarization. It is revealed that the OAM mode purity and operational bandwidth of the reflectarray are increased by using the quarter-wavelength element. The array size is $\text{50} \times {\text{50 cm}}^2$ , which achieves measured gain of 18.98 dBi at 6 GHz and operational OAM bandwidth of 42%. [ABSTRACT FROM AUTHOR]

A “back-to-back” structured common port is proposed with high isolation obtained between the two channels. This port has the advantage of being able to easily achieve a low external quality factor ( Qe ). By introducing this type of port, a “back-to-back” structured diplexer with wide bandwidth is designed and fabricated. The bandwidths of each passband are 9.5% and 13.6%. Each channel filter is optimized by using the Cauchy method. Guided by a real-time Cauchy extracting system, the diplexer is tuned. The measured reflection coefficient in the passbands is below −23 dB, and the average insertion losses are 0.7 and 0.55 dB. The measured isolation between the two passbands is higher than 34 dB. An agreement is found between measured and simulated results. [ABSTRACT FROM PUBLISHER]