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An omnidirectional wireless local area network (WLAN) loop-slot antenna with common-mode current (CMC) suppression is proposed in this communication. First, based on the analysis of the equivalent model of odd–even mode, the feeding coaxial line is led out at the voltage-zero point of the loop-slot element, which suppresses the CMC over the full band. Second, through the theory of array, three loop-slot elements form an array to obtain omnidirectional radiation. Finally, the physical size is reduced by loading Stubs T in the slot. The roundness of the radiation pattern is modified by the Stubs T and the chamfering edge of the antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the antenna achieves $\vert \text{S}_{11}\vert dB in bands of 2.15–2.65 and 4.85–5.92 GHz. In addition, the roundness is 0.95 dB at 2.4 GHz, 1.84 dB at 5.2 GHz, and 2.43 dB at 5.8 GHz. The antenna effectively suppresses the CMC to keep a favorable roundness over a wide band, showing its potential in WLAN communication systems.

A wideband and compact Fabry–Perot resonator antenna (FPRA) employing two layers of partially reflective surfaces (PRSs) is presented in this letter. The proposed PRSs with regular hexagonal units are used in wideband FPRA for the first time. Based on the compact arrangement of regular hexagon units and the addition of tripod branches, the size of FPRA is greatly reduced. Furthermore, the regular hexagonal units are arranged periodically along three directions on the 2-D plane, which means that one regular hexagon unit has six identical units around it. Therefore, there is a strong coupling between the PRS units, and units obtain a positive phase gradient in a wide range of 9.1–13.5 GHz, which is the basis for the formation of the wideband FPRA. The FPRA with dimensions of (2.2×2.2×0.6) λ03 (λ0 is the wavelength of the center frequency) has a 3 dB gain bandwidth over 9.2–13 GHz, relatively 34.2%, with a peak gain of 14.2 dBi. The prototype has been fabricated and tested, and validate the simulated results.

A wideband circularly polarized (CP) pyramidal horn antenna (PHA) is proposed. A +45° or −45° rotated spoof surface plasmon polariton (SSPP) waveguide, which serves as a circular polarizer, is inserted into the PHA. The vertically polarized wave in the PHA is decomposed into two orthogonal components with equal amplitude. One component perpendicular to the circular polarizer propagates along the PHA as a fast wave, and the other one propagates along the SSPP waveguide as a slow wave. When length of the SSPP waveguide is chosen appropriately, the phase difference between these two components is +90° or −90°, which makes the PHA radiate left-handed or right-handed (LH or RH) waves. Furthermore, the phase differences approximately equal to +90° or −90° over a wide frequency range. As a result, a wideband LH or RH CP PHA is implemented. Since the SSPP waveguide is completely inserted into a standard gain PHA, its volume does not increase at all, and its appearance does not change. Measured results show that the CP PHA achieves 26% 3 dB axial ratio (AR) bandwidth (from 8.7 to 11.3 GHz), its reflection coefficients are less than −10 dB, and its gains range from 14.9 to 16.6 dBic.

A dual-linearly polarized (LP) leaky-wave antenna (LWA) with low cross-polarization levels is proposed. The LWA with 14 circular patches is fed by symmetrical spoof surface plasmon polariton (S-SSPP) lines. When the S-SSPP lines are excited by a common mode, $ {z}$ -components of the magnetic fields are out-of-phase, and those of the electric fields are in-phase, due to the symmetrical structure. The radiation generated by the magnetic couplings (M-couplings) between these two SSPP transmission lines and the patch array strengthens each other, while the cross-polarized radiation produced by the electric couplings (E-couplings) cancels each other out. From another perspective, the M-couplings excite the horizontally polarized (H-pol) TM11 mode. The E-couplings excite the TM21 mode; thus, the E-couplings mainly appear at higher frequencies. As a result, the M-coupling and E-coupling mechanisms are separated successfully. Specifically, the LWA radiates H-pol waves with high purity. On the contrary, with the differential-mode excitation, the E-coupling patch array radiates vertically polarized (V-pol) waves. Finally, a dual-LP LWA with frequency-controlled scanning beams and suppressed cross-polarization levels is designed. Measured results show that the dual-LP beams scan from backward to forward. In the whole band, the cross-polarization levels are less than −30 dB in the scanning plane.

In this letter, a low-profile wideband pattern diversity antenna based on metasurface (MTS) is proposed. Initially, based on the theory of characteristic mode (TCM), the two adjacent intrinsic modes, which correspond to the broadside and conical radiation pattern, respectively, are exploited to realize a wideband pattern diversity characteristic under a low profile. Then, by analyzing the modal current distribution on the MTS, the optimal locations, orientations and relative phases of the four L-shaped feeding probes are determined to excite the above two modes. However, the in-band high-order modes (HOMs) introduced by the feeding structure will deteriorate the radiation pattern. Therefore, chamfering corners on the MTS is used to suppress the HOMs for radiation pattern improvement. Finally, by combining TCM and MTS, the modes are manipulated to achieve a pattern diversity antenna with an extremely low profile of 0.06 λ0 (the free-space wavelength at the center frequency) and an isolation of better than 38 dB, which also maintains an operating bandwidth of 20.24%. Based on these excellent performances, the proposed antenna is an attractive solution for pattern diversity applications requiring low profile, especially in unmanned aerial vehicle communications.

A low-cost, wideband printed circuit boards (PCBs) manufactured antenna is proposed in this letter for 5G/6G antenna-in-package (AiP) applications with wideband common-mode current (surface-wave) choking characteristics. The antenna is based on a grounded, wideband, high-efficiency electromagnetic structure (WHEMS) and a backing cavity, in which a radiating choke is introduced. By changing the choking condition of a quarter-wave length, widely applied in traditional low-frequency baluns, wideband common-mode current suppression is achieved. The enclosing wall of the backing cavity is realized by a combination of isolated grounded vias and connected grounded vias based on current polarization on the wall. Finally, a 22% impedance bandwidth (60–75 GHz) and a relative gain of 8–10 dBi within the band is achieved.

High-precision positioning is critical for many Internet-of-Things (IoT) applications; however, most existing approaches are too expensive to be used in commercial products. A highly accurate differential global positioning system (DGPS) has not been widely used because of the difficulty in solving integer ambiguities in the single-frequency carrier phase. Multipath interference and receiver noise are the main reasons for limiting the DGPS accuracy and efficiency in solving integer ambiguities. In this article, we propose a combination of anti-multipath antennas and high-performance GPS receivers to effectively mitigate impairments due to multipath propagation and receiver noise. Furthermore, by exploiting more data available from high-performance GPS receivers, we can improve the efficiency of solving carrier-phase integer ambiguities. For applications in a smart snow blower, we installed two GPS receivers with a constant separation between them. The distance between the GPS receivers was used to verify the DGPS results. Furthermore, using the proposed DGPS technology, the smart snow blower can obtain a high-precision orientation estimation, with a standard deviation of 0.299 cm in positioning accuracy and 0.409° in orientation accuracy.

In this article, a rugged linear array is proposed for covering both the LTE and 5G bands with an intermediate gain. The antenna is composed of a driven element, a set of directors, and a set of reflectors, where the excited element is a wideband high-efficiency electromagnetic structure (WHEMS) and the parasitic elements consist of metal rods. To achieve a rugged design, similar to the classic Yagi antenna, all of the elements should be conductively connected, so that it can be welded. The weldable mechanism is started on the driven radiating element. In addition, a balun is introduced in the antenna to reduce the influence of unbalanced common-mode currents. A wind resistance analysis is also presented, where the drag force of the proposed antenna is approximately a quarter of that for an antenna with a metal plate. The antenna exhibits a gain of 10.8–13.3 dBi for a 78% fractional bandwidth (1.7–3.7 GHz), which is a sevenfold increase from that of the Yagi antenna, without sacrificing the gain or rugged design. The proposed antenna has the advantages of a simple feeding arrangement, low cost, lightweight, low-wind resistance, and rugged structure; and is suitable for all-weather large-scale Internet-of-Things (IoT) deployment at a rural site or in a harsh networking environment.

A novel wide-beamwidth rectangular dielectric resonator antenna (DRA) is proposed. By loading two pairs of higher-permittivity dielectric slabs symmetrically on two opposite surfaces of the rectangular DRA in one direction parallel to the feeding slot, the E-plane radiations from two opposite surfaces of the DRA are restrained. Dimensions and the relative permittivity of the dielectric slabs are adjusted, and the E-plane beamwidths of the DRA are expanded. Moreover, two sides of the metal ground plane in another direction perpendicular to the feeding slot are folded down, and the H-plane beamwidths are broadened. In order to verify the design feasibility and explain the operating principle, a wide-beamwidth rectangular DRA with $\text{TE}_{113}^y$ mode is designed and manufactured. Measured results indicate that its maximum half power beamwidths in E-plane and H-plane are 210° and 137°, respectively, while its gains are over 2.2 dBi throughout the usable bandwidth from 3.02 to 3.26 GHz (7.6%).

In this article, a dielectric resonator (DR) excited wideband metasurface (MTS) antenna with differential feeding is proposed, which uses two modes of the MTS and the fundamental mode of the DR to achieve multimode operation and obtain wide bandwidth. Initially, based on the characteristic mode theory, relevant modes of the MTS are analyzed. Then, a DR operating at the fundamental mode ( ${\mathrm {TE}}_{\delta 11}^{\mathrm {x}}$ ) is introduced as the magnetic current source to feed the MTS, exciting the dominant mode and high order mode (HOM) of the MTS simultaneously. However, this HOM has a weak gain at the broadside direction and large side lobes. According to the superposition principle of radiation patterns, the maximum at the broadside generated by the DR is utilized to enhance the boresight gain of the HOM, thus transforming the top-weak radiation pattern of this HOM into a broadside one and improving the gain flatness. Additionally, the differential feeding technique is introduced to improve the asymmetry of radiation pattern. Furthermore, by analyzing the out-of-phase currents and the periodicity of the MTS patches, three measures —loading transverse open-ended slots, shortening periodicity and loading longitudinal slots— are introduced to reduce the high side lobe level of the HOM while preserving radiation patterns undistorted and improving the gain stability. As a result, this HOM and the dominant mode of the MTS are combined with the fundamental mode of the DR, achieving multimode operation. Finally, the proposed antenna was fabricated and measured. The measured results agree well with the simulated ones, indicating an impedance bandwidth of 51.4% (4.38-7.41 GHz), a 5–9 dBi in-band gain and a 15 dB front-to-back ratio (FBR) within the operating band.

A novel two-state multi-lobe pattern-reconfigurable microstrip patch antenna (MPA) for wide beam coverage is proposed, where two states are realized by two higher modes, and a multi-lobe pattern is employed for each state. First, the equivalent transmission line model is used to analyze the input impedances of the dual-mode MPA. By adjusting sizes of the capacitive coupling patches and profile of the MPA, the frequency bands of TM30 and TM40 modes are controlled, yielding a band intersection. Second, by controlling the length of the radiating patch, the beam-level differences of TM30-mode and TM40-mode patterns are reduced, respectively. Third, two parasitic patches are also loaded. As a result, the mode-gain difference between TM30 and TM40 modes is small, and all the beam overlap levels are higher than −3 dB. The measured results show that the 3 dB beam coverage of the MPA at 2.9 GHz ranges from −68° to +73° in the xoz plane, and its maximum gain is 7.0 dBi. Furthermore, the two-state pattern-reconfigurable MPA has a 3-lobe pattern pointing at {0°, ±37°} for the first state and a four-lobe pattern pointing at {±17°, ±58°} for the second state. The measured results are in good agreement with the simulated ones.

A Wi-Fi dual-band directional antenna is presented herein. The proposed antenna consists of a bent ground-backed slot-loop structure to form a directional antenna. The aperture of the antenna element and the offset from the ground plane have opposing functional variation for the beamwidth adjustment. By utilizing both factors, a consistent Wi-Fi dual-band beamwidth is achieved. The antenna has high radiation efficiency over both bands. The proposed antenna achieves H-plane dual-band beamwidth consistency, which varies within 5° over the two bands. The gain is 9 and 9.5 dBi, respectively, in the 2.4 and 5 GHz bands, and a stable H-plane beamwidth of 66°–71° over the operating bands is achieved. The proposed antenna can be used for the sectorized Wi-Fi access point application or as an element to form an array.

A compact wideband high gain directional antenna is proposed in this paper for marine communications. The antenna consists of a back plane (reflector), a slot-loop antenna (driven element), and a director of rod. Based on the current distribution, the slot-loop antenna is equivalent to an array of three linear current dipoles. The dipole acts as an element of the director, which provides a high efficient director for slot-loop antenna according to theoretical analysis. Both the impedance bandwidth and the 1 dB gain bandwidth are 45% covering 1.7–2.7 GHz in this design. A gain of 11.2 to 12.2 dBi is obtained in the working band with only one set of directors. The directors have a dimension less than the antenna aperture in the H-plane, which can be seen as one director in the end-fire direction. Compared with the classic Yagi antenna with the same gain level, the newly proposed antenna is only half of the size in radiation direction, which is a breakthrough for the Yagi antenna design. This size reduction can significantly minimize the interference between ship-borne antennas. The antenna is fabricated using only metal of low cost, which is useful for the ship-to-shore/ship communicating applications and desirable for the large-scale deployment.

With emerging wireless communication technology, undesired interference caused by passive intermodulation (PIM) becomes a major obstacle to the network efficiency and the electromagnetic compatibility (EMC) of the devices. Accurate measurement techniques for PIM are fundamental to identify and characterize the electromagnetic interferences (EMIs). Anechoic chambers are commonly used in the antenna PIM test. The noise of PIM test chamber usually determines the accuracy of PIM measurement. The additional PIM sources caused by the chamber can be classified into three classes: those due to the absorbers, those due to the design of the shielded enclosure, and those due to the extraneous signals caused by an ineffective shielding. In this paper, a measurement method is proposed for the performance verification of PIM test chamber. The proposed method has two key points. One is adjusting the measurement distance between antenna and absorbers for gain compensation, which can evaluate the maximum measurable antenna gain of the PIM test chamber. The other is choosing the multiple measurement points according to the beamwidth of antenna, which can define the PIM level in worse case of the chamber. Theoretical analysis of the proposed method and measured results for two PIM chambers by the method are given in this paper.

A novel circularly polarized (CP) dielectric resonator antenna (DRA) array is introduced. The DRA element operating at the desired frequency is determined by the dielectric waveguide model (DWM), and two orthogonal modes are generated to excite CP waves. A 4 × 4-element DRA array is then developed. The array is fed by the cavity-backed slotted substrate integrated waveguide, without using extra feeding network. Experimental results show that the array obtains a bandwidth of 240 MHz (9.88–10.12 GHz) for reflection coefficients and axial ratios (ARs) less than −10 dB and 1 dB, respectively. Moreover, the array obtains a 16 dBic peak gain, a −33.6 dB cross-polarization level at the boresight, namely 0.5 dB AR at the center frequency, which demonstrate the desirable array performance. In addition, above 62.5% aperture efficiency and above 90% radiation efficiency are realized over the operating bands, with about 76% peak aperture efficiency and about 94% peak radiation efficiency. The proposed array can be regarded as an element to form large planar arrays, which will be useful in beamforming systems. Our design idea may open a new way for developing high-efficiency large millimeter-wave arrays.

A low-profile broadband circularly polarized (CP) microstrip antenna with a wide beamwidth is proposed for a global navigation satellite system. Four claw-shaped parasitic branches are placed on the corners of the ground to widen the impedance bandwidth (IBW) and half-power beamwidth (HPBW) simultaneously. Several slots are etched on the radiation patch to obtain impedance matching. The proposed antenna is fabricated and measured. The experimental results show that the IBW for VSWR ≤ 2 is 72.5% from 1.02 to 2.18 GHz, and the 3 dB axial-ratio bandwidth is 54% from 1.15 to 2 GHz. The HPBW is beyond 100° overall CP bandwidth. Its dimensions are 70 mm × 70 mm × 12 mm, (0.35 × 0.35 × 0.06) λ03, where λ0 is the wavelength of the center frequency.

A compact, wideband, omnidirectional, vertically polarised antenna without electrostatic discharge problems is proposed in this study for 4G long-term evolution applications. The proposed antenna is composed of three identical basic radiators separated by an angle of 120°. The basic radiator is based on a slot loop which is a wideband and DC ground structure. By bending the basic radiators, the antenna achieves better impedance matching and lower gain variation in the horizontal plane in a compact size. The proposed antenna reaches a fractional bandwidth of 45.5% for the voltage standing wave ratio (VSWR)

A multiband dual-polarized omnidirectional antenna for 2G/3G/Long Term Evolution (LTE) mobile communications is proposed in this letter, which consists of horizontal polarization (HP) and vertical polarization (VP) element with separate feeds. The VP element consists of three polygonal radiation patches with three equally spaced legs shorted to the ground plane. The HP element consists of three wideband slot loop structures, which is nested on the top of the VP element. Three slot loop structures provide a 360° coverage for HP and enhance its bandwidth. Both the simulated and measured results indicate that the frequency bands of 1650–2900 MHz for HP and 780–2700 MHz for VP can be achieved. The reflection of VP improves the gain of the HP element at least 1 dBi after nesting. The gain of HP element is more than 3 dBi for LTE, and the gain of VP element is more than 5 dBi in the LTE band and 1.5 dBi in the 2G band. Port isolation larger than 30 dB and low-gain variation levels are also obtained. The proposed antenna can be applied in mobile communications.

A novel dual-wideband dipole directional antenna with double reflecting floors is presented in this letter. By using a dipole with crooked arms and parasitic Γ-shaped branches, the antenna achieves two wide impedance bandwidths of 40.5% from 0.68 to 1.03 GHz and 50.6% from 1.67 to 2.8 GHz for VSWR ≤ 1.5, respectively. With the help of double reflecting floors, the reverse currents are reduced, and the radiation patterns in the upper band are improved. The proposed antenna has peak gains ranging from 6.7 to 7.5 dBi and from 6.6 to 10.1 dBi in the lower and upper bands, respectively, and shows good directionality. The antenna can be used in the wireless communication systems.

A novel loop linear array for circularly polarized (CP) radiation with low sidelobe levels (SLLs) and high gains is proposed in this letter. The resonant element consists of a pair of loops fed by a slot. Moreover, two square patches are added on the opposite corners of both loops to implement circular polarization. Fed by the slotted substrate integrated waveguide, a 10-element linear array with Taylor distribution is then designed, manufactured, and measured. Measured results show that the fabricated array has bandwidths of 350 MHz (9.76–10.11 GHz) with the reflection coefficients better than −10 dB and 280 MHz (9.82–10.10 GHz) with the axial ratios (ARs) less than 3 dB, respectively. In addition, −22 dB peak SLL, 15.4 dBic gain, −29.6 dB cross-polarization level, namely 0.57 dB AR at the boresight, and 65% aperture efficiency are experimentally obtained at the center frequency.

A new single-fed wide dual-band circularly polarized (CP) dielectric resonator antenna (DRA) is presented in this letter. The DRA is excited by a microstrip line through the narrow underneath rectangular aperture, and its HE 111 and HE 11δ (2

A compact unidirectional slot antenna with front to back ratio (FBR) enhancement is proposed. The antenna consists of a novel compact slot driven antenna, a stepped reflector and a vertical balun from a microstrip to a parallel strip line. Better FBRs are obtained by optimizing the stepped reflector. Impedance bandwidths are enhanced by applying the balun and a pair of microstrip stub etched on the opposite side of the slot. Then, the antenna is manufactured and measured. Measured results show that the proposed antenna has a bandwidth of 76% (1.53-3.41 GHz) for VSWR ≤ 1.5. In addition, from 1.7 to 3.2 GHz, the antenna gains are higher than 8.6 dBi, and the FBRs are greater than 22 dB. Good agreement between the simulated and measured results is obtained. All above indicates that the proposed antenna can be widely used in wireless communications.

A low-profile dual-polarized omnidirectional antenna is presented. The antenna is a combination of a vertically-polarized (VP) antenna and a horizontally-polarized (HP) antenna. The VP antenna is composed of a circular ground plane, a cross-shaped metal patch with four shorted legs and a top-loading circular ring. The printed dipoles of the HP antenna are fed through a three-way power divider etched on an FR4 substrate. To maintain stable radiation and reflection characteristics, the HP feed coaxial cable is soldered on one patch of the VP antenna to reduce the parasitic current on the feed cable. The VP antenna covers the frequency bands for GSM/2G/3G/4G LTE, and the HP antenna works in an overlapping frequency bands for 3G and 4G LTE communication systems with high isolation. The VP antenna achieves a wide bandwidth of 108% from 800 MHz to 2700 MHz, and its gains are larger than 2 dBi in 800∼960 MHz band and greater than 4 dBi in 1710∼2700 MHz band, respectively. The HP antenna works in the frequency band from 1700 MHz to 2700 MHz, and its gains are greater than 3 dBi. The proposed dual-polarized antenna is simulated, fabricated and measured. Measured results are in good agreement with the simulated ones.

With the widespread use of vehicles, finding an empty parking space in a parking lot has become a problem that most drivers encounter daily, particularly in urban environments. In this article, a 3-D printing high-gain dielectric lens $K$ -band antenna is designed for a smart parking radar system that performs dual-mode detection by using a magnetic sensor to improve the accuracy of parking space detection. The proposed antenna uses a wideband high-efficiency electromagnetic structure (WHEMS) as the primary feed antenna. The primary antenna is etched on a substrate and can be easily integrated with a radio frequency (RF) circuit. The WHEMS antenna has a wide bandwidth that is not influenced by instability in the substrate permittivity. Benefiting from low-cost, fast prototyping 3-D printing technology, a conformal flat semiclosed perforation dielectric lens is designed to achieve a high gain; this lens avoids the measurement unreliability caused by large penetration losses in the $K$ -band. The $K$ -band radar operates at 24–24.25 GHz, with a measured gain of 18.4 dBi. Measurements obtained from the developed system reveal that the proposed high-gain, low-cost, lightweight, durable, integrated design approach is well-suited for a $K$ -band radar smart parking system.

A metal rim integrated open slot antenna with a band-stop matching circuit for LTE/WWAN smartphones is presented in this letter. The proposed antenna comprises two branch slots which share a same opening disposed at the top edge of the ground board, the longer open slot structure is excited by a $\mathbf{50-\Omega}$ microstrip line with a band-stop matching circuit. By adjusting the length of the slot, position of the microstrip line, values of the capacitor and the inductor, the antenna can cover the LTE/WWAN operations in the 698–960 MHz and 1710–2690 MHz bands. Simulated and measured results of the antenna are presented and discussed.

A planar multiband antenna based on composite right-and-left-handed transmission line (CRLH-TL) zeroth-order resonator (ZOR) for 4G compact mobile terminals is proposed in this letter. The proposed antenna consists of a monopole, a CRLH-TL structure and a triangular radiation patch. Among them, the monopole antenna can cover GSM850/950 (824–960 MHz) and LTE2500 (2500–2690 MHz); capacitive excitation of the CRLH-TL structure can produce ZOR mode to cover LTE band 12 (698–746 MHz); triangular radiation patch can cover high-frequency DCS, PCS, UMTS, LTE2300 (1710–2490 MHz). Since the antenna has the advantage of multiband, compact size and ease to fabricate, it can be applied to design 4G compact mobile terminals.

A Dual-band MIMO antenna for the 5G communication is proposed in this paper. The proposed antenna consists of four antenna, it operating at 3300–3600 MHz and 4800–5000 MHz. The antenna designed in this letter are different from traditional 5G antennas, the antenna of this paper is perpendicular to the edge of the system circuit board, it can be applied to the popular full-screen mobile phone. According to the simulation results, reflection coefficient of the modulus is less than −6 dB, and the isolation is better than 12 dB over the band-frequency of 3300–3600 MHz and 4800–5000 MHz, it will met the needs of future 5G applications.

A circularly polarized dielectric resonator antenna (DRA) millimeter wave array (MMW) with cavity-backed substrate integrated waveguide (SIW) feeding is proposed. This antenna is excited by a coaxial probe. The implemented antenna exhibits a simulated gain of almost 16 dBi and good radiation efficiency of around 96% are also obtained. The best axial ratio is almost less than 0.5 dB. It shows a good performance in radiation pattern.

A novel multilayer bidirectional linear array with the same sense circularly polarised (CP) radiation patterns are proposed. The CP resonant unit consists of a pair of loops and two square patches added on their opposite corners. With a feeding slotted substrate integrated waveguide (SIW) sandwiched between two back-to-back mirror rotated resonant units, a radiating element is designed, and same sense bidirectional CP waves are generated. Along the longitude direction, the radiating elements are arranged alternately from the centre line of the slotted SIW. Then, an 8-element linear array with uniform distribution is designed. Identical right-hand CP waves are achieved in both front and back directions. The array is fabricated, and measured results are in good agreement with simulated ones.