dB Axial Ratio Bandwidth Research Articles

A Low-Cost Wideband Dual Circularly Polarized Aperiodic 2-D Phased Array

In this article, an aperiodic wideband high isolation dual circularly polarized (CP) scanning array is introduced. A novel aperiodic array optimization method based on the perturbation principle is proposed to solve the grating lobes of large spacing scanning array and thinning the number of array elements, thereby saving energy and reducing cost. The impedance bandwidth (IBW) of the proposed array element is 58%. Meanwhile, the bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{21}\vert &lt; -15$ </tex-math></inline-formula> dB is 42.5%, and the bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{21}\vert &lt; -20$ </tex-math></inline-formula> dB is 27.5%, which is better than previous reports. The 3 dB axial ratio bandwidth (ARBW) of both the left-hand circular polarization and the right-hand circular polarization is 55.4%. Furthermore, the formed 16-element aperiodic array can achieve a 2-D low side lobe level (SLL) with ±45° beam scanning across the entire operating band, improving the system’s ability to avoid interference. Compared with a 25-element compact uniform array of the same aperture, 36% transmitter and receiver components are saved. The proposed scanning array not only has high scanning performance but also has engineering versatility due to its low-cost implementation scheme.

Orthogonal Adjacent-Order Filtering Element-Based Wideband Transmissive Linear-to-Circular Polarization Converter

This article proposes a unified design method for a highly efficient wideband transmissive linear-to-circular polarization converter composed of two orthogonal adjacent-order bandpass filtering elements for the first time. First, the linear-to-circular polarization converter is constructed to convert two orthogonal linearly polarized (LP) spatial waves split from a 45°-slant incident plane wave into a desired circularly polarized (CP) wave. Taking advantage of the wideband filter synthesis method and phase shifter theory, polarization converter elements with prescribed specifications [e.g., fractional bandwidth (FBW) and Chebyshev passband ripple] are then synthesized by the corresponding low-characteristic-impedance bandpass filtering networks with the loading of shunt short-circuited stubs on quarter-wavelength transmission line (TL) sections. The adjacent-order phase difference function with a natural ±90° value at a center frequency can be simultaneously manipulated by a filtering bandwidth. The theoretical axial ratio (AR) curve is calculated by the synthesized magnitude responses and phase deviation (PD) function. The design guideline is then summarized. Finally, based on the third- and fourth-order bandpass filtering networks, a prototype of the proposed linear-to-circular polarization converter operating at 5 GHz with a designable 70% 3 dB AR bandwidth is implemented, fabricated, and tested by the free-space measurement method. The transmitted CP wave with three in-band AR minima and relatively stable angular performances can be efficiently converted from the incident LP spatial wave as well verified in the experiment. The AR curves and design requirements of different adjacent-order bandpass filtering combinations are further explored according to the proposed design guideline.

A Wideband High-Efficiency Transmit-Reflect-Array Antenna for Bidirectional Radiations With Distinct Circular Polarizations Based on a Metasurface

In this communication, we present the modeling, design, and experiments of a wideband high-efficiency transmit-reflect-array (TRA) antenna with independent manipulations for transmitted and reflected beams with distinct circular polarizations working in the millimeter-waveband. A polarization-dependent full-space metasurface is designed to transmit the left-handed circularly-polarized (LCP) wave for a transmitarray (TA) operation, and at the same time to reflect the right-handed circularly-polarized (RCP) wave for a reflectarray (RA) operation. The TRA is then optimized with a rectangular shape for a high aperture efficiency (AE) based on a system-level analysis combining the characteristics of a Fermi feed antenna. The experimentally measured results are in good agreement with the simulated ones, achieving a peak gain of 22 dBi (21.5 dBi), a 1 dB gain bandwidth of 18.2% (24.6%), and a 3 dB axial ratio (AR) bandwidth of 38.6% (38.5%) for TA (RA) operation. A total AE as high as 61.2% is realized by comprehensively considering TA and RA operations. The design strategy and the well-performed TRA may find promising applications in wireless and satellite communication systems with bidirectional communication scenarios.

Low-Profile Wideband Circular Polarization Metasurface Antenna With Characteristic Mode Analysis and Mode Suppression

In this letter, a wideband circular polarization (CP) metasurface (MS) antenna is proposed, which is composed of a centrosymmetric structure with a mode suppressor and an asymmetric aperture-coupled feed structure separated by dielectric substrates. Based on the characteristic mode theory, the aperture-coupled feed structure consisted of an L-shaped slot and a microstrip line is employed to excite two orthogonal modes, which have a 90° phase difference to obtain CP radiation. Meanwhile, two methods have been proposed to expand CP bandwidth: one is the direct suppression of characteristic mode by decreasing the overlap frequency of operating and nonoperating mode. The other one is indirect suppression using a mode suppressor. Finally, the MS antenna with a low profile of λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.075 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at 5 GHz is fabricated and measured. The measured results show that the proposed antenna has a 3 dB axial ratio bandwidth of 45.2% from 4.1 to 6.5 GHz and an impedance bandwidth of 41.8% from 4.1 to 6.31 GHz, and a peak gain of 7.94 dBic at 5.9 GHz.

Substrate Integrated Waveguide Based Cavity-Backed Circularly-Polarized Antenna for Satellite Communication

This article presents the methodology to design a single-fed circularly-polarized antenna with low front-to-back ratio (FBR). A circular-patch (CPatch) antenna has been incorporated within the rectangular-cavity, made of, substrate integrated waveguide (SIW). The size of the CPatch and the SIW cavity has been chosen appropriately, in a manner, that the both resonators dominant mode coincide. This arrangement has been adopted to realize the basic radiating unit with no surface-wave and the significantly lower FBR. The circularly polarization has been excited through shorting the periphery of CPatch radiator to the “one of the two metallic grounds” of this SIW cavity. The patch periphery has been shorted from two distinct points, separated by the quarter wavelength—over center frequency of working band. The antenna has been designed and manufactured over Rogers RT/Duroid 5880 substrate with dielectric constant (εr) of 2.2, loss-tangent (tan δ, at 10 GHz) of 0.0009, and substrate height of 0.508 mm. Southwest® end launcher (SEL) along with SIW-to-GCPW (Grounded Co-Planar Waveguide) transition has been used here to facilitate the measurement of antenna’s electrical and the radiation performance. The designed antenna’s impedance bandwidth and the 3 dB axial-ratio (AR) bandwidth is 9.5% and the 2.3%, respectively. It’s simulated and the measured peak gain, within working frequency band, is higher than 8.5dBic. The proposed antenna’s FBR is antenna is significantly lower than the conventional circularly-polarized antennas. Through comparative study, with work in open literature, it has been demonstrated that the designed antenna, based on proposed method, can a potential candidate for applicable in satellite and in the other spaceborne communication system’s module—at ground and in the space station.

Novel Broadband Circularly Polarized Antenna based on Chamfered and Stair-Shaped Dielectric Resonator

A novel circularly polarized (CP) antenna with a chamfered and stair-shaped dielectric resonator (CSDRA) is introduced in this article, which introduces a chamfer in the stair-shaped resonator structure. This chamfer has hardly influence on the impedance bandwidth, but a distinct impact on the axial ratio (AR) bandwidth after its dimension is optimized by using HFSS. Simulated results show that the CSDRA has 10 dB return loss of 69.7% (3.91–8.10 GHz) and 3 dB AR bandwidths of 51.4% (3.87–6.55 GHz), respectively, and thus useable bandwidth of 50.4% (3.91-6.55 GHz) is obtained in this article. Moreover, the gain in the working frequency band exceeds 3.36 dBic.

Five-Band Millimeter-Wave Antenna of Circular/Linear Polarization for Forthcoming Generations of Mobile Handsets

A compact planar antenna is proposed to operate in five millimeter-wave frequency bands at 28, 51, 55, 59, and 63 GHz. The antenna is designed to produce circular polarization at 28 GHz and linear polarization at the other four frequencies. The 28 GHz frequency band is recommended for long range communications, whereas the other four frequencies are recommended for short range communications due to the atmospheric absorption in this range of the millimeter-wave frequencies and to provide more secure communications. The reasons behind the selection of the specific values of the higher frequency bands (51, 55, 59, and 63 GHz) are (i) to provide enough number of multiple bands at such unlicensed frequency range to be used as alternatives for different applications, (ii) to give about 4 GHz separation between the center frequencies of each band and, (iii) finally, to avoid the operation at 60 GHz, in particular, due to the peak atmospheric absorption of millimeter-wave encountered at this frequency. The antenna is constructed as a square patch surrounded by five parasitic elements that are capacitively coupled to the square patch so as to realize the location of the resonant frequencies of the higher frequency bands. The antenna is fabricated and its performance is experimentally evaluated. The proposed antenna is shown to operate efficiently over the five frequency bands 28, 51, 55, 59, and 63 GHz providing impedance matching bandwidths of 2.0, 0.9, 1.2, 1.1, and 1.6 GHz, respectively. The corresponding values of the maximum gain are 7.0, 6.8, 6.0, 6.0, and 8.0 dBi, respectively. Also, the corresponding radiation efficiencies are 90, 90, 91, 78, and 86%, respectively. The 3 dB-axial ratio bandwidth at 28 GHz is about 1.2 GHz.

Design of low-profile high-gain wideband circularly polarized low RCS single-layer metasurface antenna using characteristics mode analysis

AbstractIn this paper, a novel circularly polarized (CP) high-gain low-profile single-layer metasurface (MTS) antenna fed by a coplanar waveguide is presented for wideband low radar cross-section (RCS) applications. Characteristics mode analysis (CMA) technique is employed to simultaneously excite the useful modes rather than using conventional technique to achieve circular polarization in the wideband. By analyzing the characteristics modes of the antenna, gain of the antenna is also improved. Experimental results verify good performance of the proposed antenna with a compact size of 0.67λ0 × 0.67λ0 × 0.040λ0. The measured results of the antenna exhibit UWB impedance bandwidth of 96.93% in the frequency range of 3.7–10.65 GHz and 3 dB axial ratio bandwidth of about 41.8% in the frequency range of 5.3–8.1 GHz. The antenna shows a good radiation pattern with a measured peak gain of 7.9 dBic at 7.97 GHz. The proposed antenna achieves out-of-band scattering suppression in the wide range of 10–24 GHz because of MTS structure with peak RCS reduction of 19 dB at 12 GHz. The proposed antenna can be used for c- and x-band applications.

Toward High-Power Beam-Steerable Reflectarrays Using Tunable-Height Dielectric

A novel method for a high-power reconfigurable reflectarray (RRA) with a moderate 30° beam scanning is demonstrated. The proposed technique eliminates the need for mechanical steering of reflectors for satellite communication. A small mechanical movement of a patterned dielectric structure under multislot elements achieves beam steering by changing the coupling. Due to the unique shape of the multislot element, the unit cell is capable of tuning the phase for both linear polarization and circular polarization (CP) within a single design operating at 20 GHz. The maximum phase range obtained in this design is a continuous 280° for RHCP, LHCP, and two linear polarizations at 20 GHz. The phase of the reconfigurable unit cell is verified and measured using a waveguide simulator attached to a micromotor. Maximum element loss is simulated to be 0.5 dB. To demonstrate beam steering, three reflectarrays with frozen dielectrics and square array lattices composed of 400 elements ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\lambda _{0}\,\,\times 10\lambda _{0}$ </tex-math></inline-formula> ) are fabricated. The frozen reflectarrays demonstrate beams at 0°, 15°, and 30°. The measured gain is found to be 23.2 dB at broadside with 21.8 and 23.3 dB, respectively, when scanned to 15° and 30°. The 1 dB gain bandwidth is measured to be 7.45% with a 3 dB axial ratio bandwidth of 12.1%. Unlike other architectures that use nonlinear semiconductor devices, the proposed reflectarray uses a dielectric insert with a height that can be controlled by a micromotor suitable for high-power applications supporting up to 80 MW/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{2}$ </tex-math></inline-formula> .

Broadband circularly polarized folded transmitarray antenna based on polarization conversion metasurfaces

In this communication, a novel design of compact and low-profile broadband circularly polarized folded transmitarray antenna (CPFTA) is reported. A broadband linear-to-circular polarization conversion metasurface (PCM) with multi-mode operation is initially developed as the sub-reflector, to reflect the y-polarized waves and transmit x-polarized waves into right-handed circularly polarized waves. Additionally, by rotating the circularly polarized transmitters, geometric phase can be exploited for phase compensation. Then, a linear-to-linear PCM with high efficiency is designed as the main reflector. As verification, a CPFTA integrated with a broadband planar feed source and the proposed high-efficiency PCMs at X band is designed, fabricated, and experimentally characterized. The measured results are in good accordance with the simulated ones, revealing a −10 dB impedance bandwidth of 28.7%, a 3 dB gain bandwidth of 22.9%, and a 3 dB axial ratio bandwidth of 31.9%. Meanwhile, the achieved peak gain is 25.2 dBi at 10.35 GHz with a maximum aperture efficiency of 28.3%. Combining the advantages of broadband operation, flat gain, and ease of integration, the proposed CPFTA is an attractive candidate for modern wireless communications.

A Mesh-Type Shared-Aperture Dual-Band Circularly Polarized Transmit- Reflect-Array Antenna

This article proposes a dual-band bidirectional circularly polarized transmit-reflect-array (TRA) antenna, which consists of an oblique 45° feed horn and a shared-aperture TRA. The TRA is an optically transparent mesh-type structure consisting of 14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times14$ </tex-math></inline-formula> three-dimensional (3-D) cross-shaped elements. The cross-shaped element assembled from two orthogonal vertical layers is independent of polarization and can adjust the phase of reflected and transmitted waves. Due to the polarization and frequency independence of the element, the TRA is able to convert the linearly polarized waves radiated by the feed horn into circularly polarized reflected and transmitted waves in the lower and higher frequency bands, respectively. The measurement results show that in the reflection band, the TRA antenna has a maximum gain of 21.3 dBi at 6.2 GHz (corresponding to an aperture efficiency of 32.1%) and a 3 dB axial ratio (AR) bandwidth of 11.2% (5.9–6.6 GHz). In the transmission band, the TRA antenna has a maximum gain of 23.1 dBi at 8 GHz (corresponding to an aperture efficiency of 29.1%) and a 3 dB AR bandwidth of 16.0% (7.5–8.8 GHz). The proposed TRA antenna has potential applications in dual-band, circularly polarized, and bidirectional communications.

A Wideband Circularly Polarized Antenna Based on Anisotropic Metamaterial

This article presents a novel circularly polarized (CP) antenna based on an anisotropic metamaterial. The antenna is capable of performing linear-to-circular polarization conversion over a wideband of frequencies in the X-band (8–12 GHz). The proposed antenna was constructed from a metamaterial-based polarizer mounted above the aperture of a rectangular waveguide. The polarizer was oriented at 45° to E-plane of the waveguide. The proposed polarizer is composed of multiple metamaterial layers. The unit cell of the proposed polarizer consists of a single dielectric slab incorporating a series of rectangular split ring resonators that are printed on both sides of the slab. Impedance matching layers (IML) are introduced to enhance the axial-ratio (AR) bandwidth. The polarizer has a low profile in terms of electrical length (thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.41 \lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at 10.5 GHz). A full-wave electromagnetic simulator was used to verify the anisotropic characteristics of the unit cell. This was achieved by showing that the metamaterial exhibits two different refractive indices along the orthogonal components of the incident electric field. The prototype of the proposed design is fabricated and measured to validate the performance. The measured results agree with the simulated ones and demonstrated a wide impedance bandwidth of 62.4% ranging from 7.08 to 13.5 GHz with a 3 dB AR bandwidth of 29.9% (9.25–12.5 GHz).

A Low-Profile, Circularly Polarized, Metasurface-Based Antenna With Enhanced Bandwidth and Stable High Gain

A low-profile circularly polarized (CP) metasurface-based (MS-based) antenna with enhanced axial-ratio bandwidth (ARBW) and stable high gain is developed. The developed antenna has a stacked layout with the MS containing 3 × 3 patch lattices, which are placed above a custom-designed driven element. The driven element comprises a patch with an etched slot and a parasitic ring strip with shorting pins, which can excite the MS to generate multiple resonances and three AR minimum points, thus resulting in enhanced ARBW and stable high gain. Finally, an antenna prototype is designed to confirm the simulation results. The experimental (simulated) results demonstrate that the MS-based antenna is low-profile: 0.03 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> corresponds to the operating central frequency at 2.63 GHz, achieving a −10 dB fractional bandwidth (FBW) of 20.48 (19.81)%, and 3 dB ARBW of 10.2 (11)% along with a stable gain of 8.1–8.8 (8.0–9.2) dBic, respectively.

Penta-band rectangular slot antenna for multi-function wireless communication with linear and circular polarizations

AbstractThis paper presents a multi-band rectangular slot antenna, which can be used in Beidou navigation system, 4G, WLAN and 5G system. The proposed antenna adopts a single feeding line, generating circular polarization for satellite navigation, and linear polarization for mobile communication systems. The proposed antenna consists of three c-type resonators and three rectangular loop slots. A c-type resonator and a rectangular loop slot work together to produce a usable frequency band. Multiple frequency bands can be generated by increasing the number of c-type resonator and rectangular loop slots. It is found that the c-type resonator changes the current distribution on the antenna surface, making the axial ratio less than 3 dB in the low frequency bands. Eventually, five operation frequency bands are realized. Experimentally, it is verified that the impedance bandwidths of each frequency band are 11.8% (1.12–1.26 GHz), 15.4% (1.5–1.75 GHz), 11.9% (2.36–2.66 GHz), 19.7% (3.15–3.84 GHz) and 2.6% (4.47–4.59 GHz), respectively. The measured 3 dB axial ratio bandwidths are 20 MHz at 1.2 and 1.56 GHz, fully covering BDS B1 and B2 bands. The measured gains are 3, 3.59, 4.07, 4.2 and 4.35 dBi, respectively.

Characteristic mode analysis of a compact circularly polarized rotated square slot antenna

AbstractPresented in this paper is a circularly polarized (CP) wide 45° rotated slot antenna with a broad bandwidth. Characteristic mode analysis is initially carried out to show that, by simply rotating a square slot, CP waves can be radiated if it is properly excited. A simple 50 Ω feedline is then designed to excite the slot for the generation of broadband CP waves. The antenna has a total volume of 30 × 30 × 1.6 mm3. Measurement results indicate a broad S11 ≤ −10 dB impedance bandwidth of 85.7% (3.2–8 GHz), a broadband 3 dB axial ratio bandwidth of 57.1% (3.5–6.3 GHz) and a peak gain of 3.6 dBi are obtained by the antenna. The proposed antenna possesses stable radiation patterns as well as relatively flat gain over its operational bandwidth in addition to being compact. It can thus be used for wireless technologies such as WiMAX 3.5 and 5.5 GHz, WLAN 5.2 and 5.8 GHz in addition to Industrial, Scientific, and Medical 5.8 GHz.

A compact dual-sense circularly polarized SIW textile antenna for body-centric wireless communication

In this communication, a dual-sense circularly polarized textile antenna that operates at the centre frequency of 5.8 GHz is presented for body-centric wireless communication. The proposed textile antenna is realized using a substrate integrated waveguide (SIW) cavity. Circular polarization is achieved by exciting two orthogonal quarter mode apertures in 900 phase differences. A metallic via is employed to control the magnetic field coupling between the two orthogonal quarter mode apertures. The feed point and dimensions of two-quarter mode apertures can be changed to realize both left-hand and right-hand circular polarization. The proposed textile antenna has a 4.8 % impedance bandwidth covering from 5.62 to 5.90 GHz. Moreover, the textile antenna has a 2.9 % 3 dB axial ratio bandwidth covering from 5.725 to 5.875 GHz frequency bandwidth. The textile antenna has exhibited good reflection characteristics when bent on the surface of a cylindrical structure. The textile antenna has a lesser than 1.27 W/Kg SAR value in the proximity of the human phantom model for a 1 W source and also has exhibited a minimum peak gain of 5 dBi, making it conducive for integration with body-centric wireless communication.

Reflect–Transmit-Array Antenna With Independent Dual Circularly Polarized Beam Control

In this letter, we propose a dual circularly polarized reflect–transmit-array (RTA) antenna with independent beam control. It can transmit left-hand circularly polarized (LHCP) wave as transmitarray antenna and reflect right-hand circularly polarized (RHCP) wave as reflectarray antenna at 8.7–10.2 GHz. In addition, 360° phase shift for each circularly polarized wave can be achieved by rotating the top and bottom patches. A 20 × 20-unit cell RTA is designed, fabricated, and measured. For the LHCP radiation, the measured results show that the 3 dB gain bandwidth and axial ratio (AR) bandwidth are 13.7% (8.8–10.1 GHz) and 15.9% (8.7–10.2 GHz), respectively. For the RHCP radiation, the measured 3 dB gain bandwidth and AR bandwidth are 11.4% (9.1–10.2 GHz) and 12.6% (8.9–10.1 GHz). The peak aperture efficiencies for LHCP and RHCP radiations are 45.5% at 9.2 GHz and 41.8% at 9.6 GHz, respectively.

Wearable Polarization Conversion Metasurface MIMO Antenna for Biomedical Applications in 5 GHz WBAN

This paper presents a wearable metasurface multiple-input multiple-output (MIMO) antenna for biomedical applications in a 5 GHz wireless body area network (WBAN) with broadband, circular polarization (CP), and high gain. The physical properties of the MIMO antenna element and the principles of polarization conversion are analyzed in-depth using characteristic mode analysis. For the proposed MIMO antenna, the measured -10 dB impedance bandwidth is 34.87% (4.76-6.77 GHz), and the 3 dB axial ratio bandwidth is 22.94% (4.9-6.17 GHz). By adding an isolation strip, the measured isolation of the two antenna elements is greater than 19.85 dB. The overall size of the MIMO antenna is 1.67λ0 × 0.81λ0 × 0.07λ0 at 5.6 GHz, and the maximum gain is 7.95 dBic. The envelope correlation coefficient (ECC) is less than 0.007, with the maximum diversity gain greater than 9.98 dB, and the channel capacity loss is less than 0.29 b/s/Hz. The specific absorption rate (SAR) of the wearable MIMO antenna is simulated by the human tissue model, which proves that the proposed antenna conforms to international standards and is harmless to humans. The proposed wearable metasurface MIMO antenna has CP, broadband, high gain, low ECC, and low SAR, which can be used in wearable devices for biomedical applications.

Broadband Millimeter-Wave Circularly Polarized Open-Ended Waveguide Antenna Using Stubs and Its Application in Forming an Array

A new broadband circularly polarized (CP) antenna using an open-ended waveguide is proposed in this article. By using two stubs at different positions of the open-ended waveguide, the amplitude and phase of the orthogonal fields are effectively adjusted. The method is applied to the millimeter-wave bands, and a single element as well as a four-element array are presented. Reasonable agreement between the measured and simulated results has been observed. The antenna element has a wide overlapping impedance bandwidth of 50% and a 3 dB axial ratio (AR) bandwidth of 50% covering 24–40 GHz, making it a promising candidate for wideband applications. The measured realized gains at 28 and 38 GHz are 6.7 and 6.9 dBic for an element and 12.3 and 13.9 dBic for an array, respectively.

Circularly Polarized Single-Layer Microstrip Reflectarray Fed With a 2x2 Microstrip Patch Array

The design of a single-band singly-layered reflectarray fed by a circularly polarized 2x2 microstrip patch antenna array with corporate feeding to be used in K-band (18.7–19.2 GHz) is proposed in this paper. It is demonstrated by simulations and measurements that the axial ratio bandwidth performance of the reflectarray depends strongly on the circularly polarization purity of the feeder. Simulated and measured results revealed that the complete reflectarray exhibits good performance in terms of input impedance with -10 dB input reflection coefficient bandwidth of 19.0 %, radiation pattern with 3 dB axial ratio bandwidth of 10.55 % and 3 dB gain bandwidth of 2.64 %.