Design of a cavity‐based filtering antenna with dual‐polarization operating at Ka‐band

The contribution of this work is to propose a cavity‐based antenna with both dual‐polarization and bandpass filter characteristics. Proper cavity resonators and antenna based on the substrate integrated waveguide (SIW) technology are designed utilizing the low temperature co‐fired ceramics (LTCC) for demonstration. By properly arranging and coupling the cavities, a shaping of filter‐like response for the antenna gain and input return loss can be obtained. Measures for achieving a good isolation and a low cross‐polarization level have also been taken into account during the design procedure. A 4th‐order prototype working in the Ka‐band is designed and fabricated. Investigations show that the antenna presents a good isolation below ‐29 dB across the operating bandwidth, together with a cross‐polarization level lower than ‐25 dB at the center working frequency. The performance of the prototype has been verified in the measurement.     

Dual‐band CPW fed MIMO antenna with polarization diversity and improved gain

A dual‐band MIMO slot antenna with polarization diversity and improved gain is proposed in this article. The antenna is composed of two C‐type back‐to‐back connected slot resonators and offers resonances at 3.5 and 5.2 GHz. This antenna element is further used to design a MIMO antenna. By introducing one U‐shaped slot between two antenna elements, isolation between the ports of this MIMO antenna is improved further. Finally, an artificial magnetic conductor (AMC) is placed below the MIMO antenna to enhance its gain. Gain enhancement of 1.5 and 2.2 dB is achieved at lower and upper band, respectively. S‐parameters, radiation patterns, gain, envelope correlation coefficient, and channel capacity loss are investigated to conclude about its performances in MIMO applications. Dual band dual polarization (circular and linear), improved isolation, polarization diversity (right‐hand circular polarization and left‐hand circular polarization), gain enhancement all are presented in a simple design represents the novelty of the proposed MIMO antenna.     

A polarization reconfigurable CPW fed monopole antenna with L‐shaped parasitic element

A coplanar waveguide fed polarization reconfigurable monopole antenna is proposed in this letter. The proposed antenna consists of L‐shaped stubs placed on either side of a monopole, two p‐i‐n diodes and a slot in the ground plane. In the proposed antenna structure, the switching element is not directly connected to the feed line. Depending on the switching state of the p‐i‐n diodes, the antenna either radiates left/right circular polarization or linear polarization. To validate the proposed design, the antenna was fabricated and its performance was measured. Since the ground plane is electrically small, the effect of the cable and SMA connector on the performance of the antenna is also investigated. The measured impedance bandwidth is 66.78% (3.67 GHz to 7.35 GHz) and the axial ratio bandwidth is 13.62% (4.24‐4.86 GHz) for circular polarization and 23.61% (3.81‐4.83 GHz) impedance bandwidth for linear polarization.     

Extremely low‐profile wideband dual‐polarized microstrip antenna for micro‐base‐station applications

A wideband dual‐polarized microstrip antenna is presented. By designing the coplanar parasitic patches and modified feed probes, antenna profile is decreased significantly. Shorted pins are used and 34 dB isolation between input ports is then achieved. A phase difference feed network is introduced to suppress higher‐order modes and reduce the cross polarization to ?27 dB. To verify the design, a prototype of the antenna is fabricated and experimentally studied. Measured results show that 30.3% operating bandwidth (VSWR < 1.5) and good dual linear polarization characteristics with a profile height as low as 0.08λ are achieved. Due to the very compact configuration, the proposed antenna is suitable for micro‐base‐station applications.     

Investigation of factors contributing depolarization in offset reflector antenna and trimmed‐reflector offset parabolic antenna with lower cross‐polarization

This article outlines impact of various factors on cross‐polarization characteristics of offset reflector antenna for communication spacecraft with smaller sized bus at C band. Effects of different parameters are considered in rigorous analysis of the antenna. Measured and predicted performances are found in agreement. To fulfill specific requirement of higher edge‐of‐coverage gain (>26 dBi) and higher cross‐polarization discrimination (XPD > 30 dB) over a wider coverage and dual linear polarization under the imposed constraints, a novel trimmed‐reflector offset parabolic antenna (TROPA) is devised. This interesting configuration is obtained by trimming both sides parallel to symmetrical plane of a parabolic offset reflector antenna. Parametric study of trimming distance versus its impact on cross‐polarization is also presented. The TROPA acquires wider bandwidth, simplification in its mechanical design and manufacturing, and offers low weight and compactness. It is also shown that trimmed reflector has almost even RF performance in presence of spacecraft body and other antenna. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Double triangular monopole‐like antenna with reconfigurable single/dual‐wideband circular polarization

A polarization and frequency reconfigurable circularly polarized (CP) antenna is proposed based on a novel bilateral switching mechanism. Two triangular monopole antennas are connected to each other in an L‐shaped form by a narrow link to produce a CP operation. In the proposed technique, 4 PIN‐diode‐based switches are designed with desired insertion loss and isolation, and only 2 DC‐voltage controllers. These switches are located on the links and the feed lines to realize a polarization reconfigurable feature including both right‐hand CP (RHCP) and left‐hand CP (LHCP) modes. Moreover, 2 CP states, a single wideband operation and a dual‐band operation, can be supported by this mechanism. In a special performance of the switches, CP reconfigurability can be obtained in a narrow‐band mode around 2.45 GHz. Two general simulations are performed based on the simple microstrip links and a diode‐circuit model. The measured results exhibit a wide overlapped bandwidth (AR < 3 dB and VSWR < 2) of 44.4% (1.63–2.56 GHz) with a peak gain of 2.88 dBi in the first state and 5.5% (1.22～1.29GHz) and 20.6% (2.12–2.61 GHz) with the peak gains of 0.52 and 3.0 dBi in the second state, respectively. A wide beamwidth is obtained more than 75°. This work is appropriate for L‐ and S‐band CP diversity applications.     

A low‐profile wideband dual‐polarization patch antenna with antisymmetric feeding network

In this paper, a novel broadband dual‐polarization patch antenna is proposed. Antisymmetric Γ feeding network is applied to excite the radiating patch etched on the upper side of the horizontal substrate, which could minimize the undesired radiation from the probe and extend the impedance bandwidth. For verifying the proposed approach, a prototype is fabricated and measured, the simulated and measured results show the antenna has a wide impedance bandwidth of 48% (1.66‐2.71 GHz) for S11 < ?10 dB, as well as stable radiation gain around 9.5 dBi with low cross‐polarization. In addition, the total height of the antenna is only 0.17 λ₀ ( λ₀ is the free space wavelength of central frequency) and high port‐to‐port isolation is better than 30 dB. The characteristics of the proposed antenna illustrate it can be an indication for a micro base station in the mobile communication system.     

A wideband polarization reconfigurable isosceles trapezoidal monopole antenna

In this article, a polarization reconfigurable isosceles trapezoidal monopole antenna for the circular polarization (CP) is presented. A trapezoidal monopole and the ground plane are on the same side of the dielectric substrate. The monopole is excited by a reconfigurable T‐shaped 50 Ω microstrip feed line and reconfigurable vertical slots are incorporated in the ground plane to realize switchable wideband CP. For the different switching states of the p‐i‐n diodes, linear polarization, left‐handed and right handed CP can be achieved in the boresight direction (+z direction). The antenna prototype is fabricated and tested. The measured reflection coefficient bandwidth (|S11| < ?10 dB) is 31.2% (2.13 ‐ 2.91 GHz) and axial ratio bandwidth (axial ratio < 3 dB) is 22% (2.18 ‐ 2.72 GHz) for the CP. The measured reflection coefficient bandwidth is 18.56% (2.15 ‐ 2.59 GHz) for linear polarization.     

Annular ring slot antenna design with reconfigurable polarization

A microstrip‐fed conventional annular ring slot (ARS) antenna with linear polarization (LP) is initially studied. To generate two orthogonal degenerate modes for circular polarization (CP) radiations, two identical meandering perturbation slots (MPS) are symmetrically loaded into the ARS. By further incorporating a PIN diode switch across each MPS, the proposed antenna can switch between left‐hand CP (LHCP), right‐hand CP (RHCP), and LP. All three polarizations have shown good impedance bandwidth and broad CP bandwidth that can satisfy the wireless local area network (WLAN) 2.4‐GHz operating band (2400–2480 MHz). Furthermore, desirable gains of 1.8–2.0 dBi and 2.40–2.84 dBic are also exhibited at LP and LHCP/RHCP, respectively. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:110–120, 2016.     

A Dual‐band and dual‐polarized antenna array for 2G/3G/LTE base stations

A dual‐band antenna array is proposed for the application of base station (BS) in 2G/3G/long term evaluation (LTE) mobile communications. This antenna consists of two independent ±45° dual‐polarized arrays, one of which operates from 1.71 to 2.17 GHz, and the other of which is designed from 2.5 to 2.69 GHz. The proposed BS antenna array has a high isolation of greater than 29 dB and high front‐to‐back ratio of more than 26 dB at the operating frequencies. The measured peak gain is 17.9 and 18.1 dBi for the lower and upper bands, respectively, and the cross polarizations isolation (CPI)(within ±60º of the mainlobe) is 16 dB lower than the broadside co‐polarization. It was confirmed that the proposed antenna array meets the communication standards in China. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:154–163, 2016.     

Gain enhancement of circularly polarized antenna with dual‐polarization conversion transmitarray

A dual‐polarization conversion transmitarray is proposed for a circularly polarized (CP) transmitarray antenna. The designed transmitarray realizes the polarization conversion and gain enhancement for the circular polarization incident wave. The transmitarray can transform the left‐hand circularly polarization (LHCP) wave and the right hand circularly polarization (RHCP) wave into RHCP and LHCP waves, respectively. Two CP patch antennas are designed as source antennas to illuminate the transmitarray and form the transmitarray antenna. The experimental and simulation results show that the designed transmitarray realizes the polarization conversation and the gain enhancement for two CP antennas indeed.     

A low‐profile wideband dual‐polarized antenna with gain enhancement,low gain variations,and low cross polarization for 5G indoor communications

A low‐profile wideband dual‐polarized antenna with high gain, low gain variations, and low cross‐polarization for the fifth generation (5G) indoor distribution system is proposed. By using circular‐thread vase‐shaped structure, a low profile of 0.23λ₀ (λ₀ is the free‐space wavelength at the starting frequency) as well as low gain variation feature can be achieved by the vertically polarized (VP) radiating element. An eight‐way power divider network is employed to feed the horizontally polarized (HP) dipoles so that wideband performance is obtained. Here, eight pairs of arc‐shaped parasitic strips are used to broaden the bandwidth, and eight pairs of director elements are introduced to enhance the gain and reduce the gain variations. In addition, the protruded stubs that are extended from the circular ground plane will help to reduce the cross polarization in the VP direction. Measured results show that a bandwidth of 46.5% (3.3‐5.3 GHz) (S₁₁ < ?10 dB) with a gain of 0.85 ± 0.35 dBi, and another bandwidth of 85.0% (2.5‐6.2 GHz) with a gain of 4.75 ± 1.75 dBi can be realized in the HP and VP directions, respectively. Furthermore, high isolation (>27 dB) and low cross polarization (<?24 dB) can also be attained. Therefore, the proposed antenna is a good candidate for 5G indoor distributed system.     

Dual‐band reconfigurable circularly polarized monopole antenna

A microstrip antenna with dual‐band reconfigurable circular polarization (CP) characteristics in Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) bands is presented in this article. The proposed antenna has a symmetrical U‐shaped slot with PIN diodes on the ground plane. The slotted ground generates a resonant mode for broad impedance‐band width, and excites contrary CP state at 2.45 GHz for WLAN and 3.4 GHz for WiMAX, respectively. Because switching the states of PIN diodes on the slot can redirect the current path, the CP state of the proposed antenna can be simply switched between the right‐handed CP and left‐handed CP. The proposed antenna has a low profile and a simple structure. Measured results of the fabricated antenna prototype are carried out to verify the simulation analysis. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:109–114, 2015.     

Compact planar frequency reconfigurable multiple‐input‐multiple‐output antenna with pattern and polarization diversity characteristics for WiFi and WiMAX standards

A compact planar frequency reconfigurable dual‐band multiple‐input‐multiple‐output (MIMO) antenna with high isolation and pattern/polarization diversity characteristics is presented in this article for WiFi and WiMAX standards. The MIMO configuration incorporates two symmetrically placed identical antenna elements and covers overall size of 24 mm × 24 mm × 0.762 mm. Reconfiguration of each antenna element is achieved by using a PIN diode which allows antennas to switch from state‐1 (2.3‐2.4 GHz and 4.6‐5.5 GHz) to state‐2 (3.3‐3.5 GHz and 4.6‐5.5 GHz). In state‐1, the configuration offers isolation ≥18 dB and 20 dB in lower band (LB) and upper band (UB) respectively; whereas, in state‐2, isolation ≥21 dB and 20 dB in LB and UB respectively is achieved. The same decoupling circuit provides high isolation in dual‐band of two states, which makes overall size of the proposed design further compact. The antennas are characterized in terms of envelope correlation coefficient, radiation pattern, gain, and efficiency. From measured and simulated results, it is verified that the proposed frequency reconfigurable dual‐band multi‐standard MIMO antenna design shows desirable performance in both operating bands of each state and compact size of the design makes it suitable for small form factor devices used in future wireless communication systems.     

Varactor controlled frequency and polarization reconfigurable microstrip antenna

A single feed compact microstrip antenna achieving frequency and polarization diversity using a varactor is presented. A simple patch antenna with an X‐slot constitutes the fundamental structure. The frequency and polarization agility is realized by varying the reactance of an embedded varactor at the center of the X‐slot with respect to the biasing from 0 to 25 V. The prototype fabricated on a substrate of dielectric constant (ε_r) 4.4 and height (h) 1.6 mm is fed by a proximity feed fabricated using the same substrate. By controlling the bias voltage of the varactor, the polarization of the antenna can be switched between linear and circular polarization. Furthermore, the proposed antenna offers stable broadside radiation characteristics without any extra impedance matching circuit. The frequency and polarization diversities of this design could potentially improve the reliability of wireless communication systems. The details of the antenna are presented and discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.     

Microstrip patch antenna feed for offset reflector antenna for dual band application

In this article, details of a dual band microstrip patch antenna (MPA) array feed for an offset reflector antenna is presented. The main objective of the proposed structure is to achieve low cross‐polarization at Φ = 90° plane in the reflector pattern. Low cross‐polar levels in the reflector pattern are achieved by illuminating the reflector with fields of the proposed dual band feed structure. A centered circular array as the dual band feed structure is proposed in which the central radiating element is a dual mode circular MPA operating at 6 GHz and the surrounding circular ring of eight circular MPA elements operating at 4 GHz in the dominant mode. The dual mode central antenna uses the concept of conjugate field matching for cross‐polarization reduction. TM₂₁ mode is excited at an appropriate ratio with the TM₁₁ mode to achieve the proper field matching at 6 GHz. The radius of the surrounding circular array is varied to obtain cross‐polarization better than ?30 dB at both the resonant frequencies. The offset reflector gain is found to be better than 37 dB with a 2.5 m parabolic reflector and F/D = 0.8 at both the operating frequencies.     

Radiated cross‐polar levels and mutual coupling in patch radiators

This article presents the relation between the cross‐polar signal radiated by a dual feed patch antenna and the mutual coupling existing between the antenna feeds. The theoretical analysis is based on the S‐parameters of the antenna element, providing a clear understanding of the physical relation between cross‐polar level and coupling. Analytical expressions are given for the radiation pattern computation, including the cross‐polar level and the effect of higher order modes on the pattern. Finally, the results of the study are illustrated with measured patterns. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 342–352, 2000.     

Analysis and design of dual‐polarized microstrip antenna array

A new dual‐polarized microstrip antenna array is presented. Diagonal feeding of the square patch with two ports is proposed to obtain dual linear polarization. A novel coplanar feedline network is also presented for the dual‐polarized array. For engineering purposes, a CAD‐oriented method of analysis is developed. The measured results demonstrate high isolation between the two input ports. The array has simple structure and is easy to further combine to form larger coplanar arrays. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 42–48, 1999.     

A substrate integrated cavity‐fed dual‐polarized filtering patch antenna with high isolation

This article presents a dual‐polarized filtering patch antenna, which uses two orthogonal modes (TE₂₁₀/TE₁₂₀) of the substrate integrated cavity (SIC) to couple with two orthogonal modes (TM₁₀/TM₀₁) of the patch by the cross slot, respectively. The second‐order filtering response on dual polarizations can be achieved by using just one SIC resonator and one slotted square patch, which display simple structure of the proposed antenna. The slotted square patch provides a new way to obtain same external quality factor of the radiator on dual polarization, which makes the performances on two polarizations agree well with each other when changing the bandwidth. High isolation can be achieved by controlling the space of the vias of the SIC. Radiation nulls can be produced by connecting the coupled lines with the feeding lines in parallel. A prototype with the entire height of 0.019 λ₀ (λ₀ is the free‐space wavelength at center frequency) achieves a 10‐dB bandwidth of 1.6%, the gain of 4.9 dBi at the center frequency, the port isolation of 43 dB, and the out‐of‐band rejection level of 25 dB.     

Self‐diplexed antenna based on loading asymmetric grounding‐vias

This article presents a simple and efficient method for the design of a self‐diplexed antenna based on loading asymmetric grounding‐vias. The structure consists of two antenna elements loaded with two asymmetric grounding‐vias, specifying the uplink and downlink operation frequencies. By choosing the appropriate positions of the two grounding‐vias, high isolation between the two antennas can be achieved. To validate the feasibility of the proposed structure, two self‐diplexed antennas with different operational frequencies have been fabricated and tested. Experimental results verify the multi‐functionalities of the proposed compact structure in terms of high isolation and low cross‐polarization discrimination.