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A novel dual-band circularly polarized (CP) planar endfire antenna with the front-to-back ratio (FBR) enhancement is proposed. First, a half-mode substrate integrated waveguide cavity serving as a magnetic dipole (M-dipole) is devised for the dual-band vertical polarizations, and four slots are etched on the M-dipole to adjust the frequency ratio reasonably. Two independent electric dipoles (E-dipoles) are introduced for the dual-band horizontal polarizations. Then, the M-dipole and the E-dipoles are connected by the parallel double-side compensate lines to adjust their amplitudes and phase differences, thus dual-band CP waves are radiated. A two-stage reflector is also loaded behind the M-dipole, which improves FBRs of the antenna in two bands. Finally, a 2.4/5 GHz prototype antenna is designed, fabricated and measured to validate our design idea. A reasonable agreement between simulated and measured results is obtained. Measured FBRs of the propose antenna at 2.42 GHz and 5.02 GHz are 15 dB and 14.2 dB, respectively.

Ideal dipole antennas are desirable for antenna calibration. However, real-world implementation issues introduce inevitable non-ideal effects that can significantly affect the quality of calibration. In this communication, a 2-GHz standard dipole (SD) antenna is presented with an excellent overall performance. This result is achieved by an innovative design with an optimized element shape and an embedded (shielded) balun. The designed feeding structure is a balanced structure that transitions from parallel strip lines to coaxial lines. The feeding method avoids the impact of electromagnetic environment asymmetry while achieving an appropriate balance. The measured relative bandwidth of the dipole exceeds 15%, and the antenna gain is approximately 2 dBi. The cross-polarization ratio is greater than 27 dB in the horizontal plane, and the horizontal gain variation is less than 0.2 dB. The dipole has a symmetrical vertical plane pattern, and the maximum gain point does not deviate from the horizontal plane. The high performance of this SD makes it suitable for antenna calibration.

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.

In this paper, decoupling of a compact isosceles triangular array is performed by a hybrid method consisting of loaded parasitic element (LPE) in combination with decoupling and matching network (DMN). By introducing a reactively loaded parasitic element at a suitable position on the axis of symmetry of the isosceles triangle, not only are the mutual couplings between the element at the vertex and the two elements on the base eliminated but also the circuit parameters of the base elements are well prepared for a DMN of a simpler form. Thus, the impedance matching of the vertex element and the decoupling and matching of the base elements can be implemented independently. The DMN of base elements comprises two impedance-transforming sections (ITS) and a $\pi $ -shaped neutralization section (NS). The ITSs inserted between the antennas and NS convert the self-conductance to the system admittance and the trans-conductance to zero. The trans-susceptance is then compensated through the main line of the NS independently, and self-susceptance is canceled out by adjusting the tapped stubs subsequently. With all the explicit formulas derived, the design is systematic and straightforward. The presented compact isosceles triangular array with element separations of $0.1\lambda $ and $0.2\lambda $ is fabricated and measured. The results show that sound isolation of 35 dB and return loss of 21 dB is obtained with ECCs less than 0.02, validating the effectiveness of the hybrid decoupling technique.

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.

In order to achieve high accuracy in measurements of the multiple probe antenna measurement system (MPAMS), an omnidirectional calibration antenna with a small gain variation in the horizontal polarization (named calibration loop antenna, in convention) is required. This article presents such an antenna design. The proposed calibration loop antenna consists of four arc-folded dipoles with dimensions of 52 mm $\times52$ mm $\times 1$ mm, balun structures for suppressing common mode current, and four parasitic strips for impedance matching on each of the top and bottom planes. The experimental results show that the proposed calibration loop antenna has a small gain variation in the horizontal polarization less than 0.16 dB in a bandwidth of 20% (2.25–2.75 GHz), and its 10-dB return loss bandwidth is 18.2%. Also, the cross-polarization ratio in the operating bandwidth is greater than 24 dB. Along with the desired omnidirectional radiation pattern, the low profile and compact design further make the proposed calibration loop antenna a suitable selection for calibration in MPAMS.

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%).

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.

In this paper, a novel wideband omnidirectional cone-shaped monopole antenna is proposed. The presented antenna is composed of two patches etched on dielectric substrate and a metal ground. Several metal pins are inserted between them to connect the above metal areas, which forms a simplified cone-shaped monopole antenna. By adjusting the diameters of the above two metal patches, the operation frequency and bandwidth can be designed for different requirements. The proposed antenna was simulated by HFSS with its relative bandwidth reach 61.5% for| S11| L (wavelength of lower frequency) and good omnidirectional vertically polarized property make it a good candidate for wireless communications.