Co-polar Patterns Research Articles

Parasitic Loaded Shorting Pin Based Compact Multi-slot LoRa Antenna for Military Application

In this paper, work on a compact multi-slot patch antenna with a parasitic load and shorting-pin has been presented for its use in long range (LoRa) defense applications. Initially the antenna is designed and simulated using HFSS and a parametric study has been carried out for achieving an optimized antenna configuration. This is followed by the fabrication of antenna prototype based on the optimal performances obtained from the simulated results. Further, the return loss along with free space co-polar and cross-polar radiation pattern measurements has been carried out for the fabricated antenna. The experimental results show a good comparison with that of the simulated one. The proposed antenna resonates at an operating frequency of 866 MHz, providing a -10 dB bandwidth from 856 MHz-877 MHz, which covers the wireless standard used for LoRa technology. Finally, a comparative analysis of the proposed antenna with the recently reported works is presented.

Mutual-Coupling Reduction of a Quad-Port Cross-Slot Antenna With Simultaneously Co-Polarized and Dual-Polarized Patterns

Mutual-Coupling Reduction of a Quad-Port Cross-Slot Antenna With Simultaneously Co-Polarized and Dual-Polarized Patterns

Irregular Subarray Tiling via Rotational Symmetry

To reduce the cost of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n\times n$</tex-math></inline-formula> polarimetric phased array antenna, an innovative subarray tiling technology is proposed based on a geometrical property called rotational symmetry. This property requires the tiling solution to remain unchanged after a series of rotations, and hence, a consistent scanning performance in multiple beam directions is guaranteed. By considering the rotation as the reordering of the array elements, an improved Algorithm X is proposed, which is computationally efficient to find the rotational symmetric exact tiling solutions (RSETS). Due to a compressed scale of the RSETS and a faster dimension reduction of the dictionary matrix, it is convenient to obtain an RSETS with the scanning performance approximated that of the optimal solution. A 12 × 12 X-band dual-polarized microstrip patch array antenna is simulated for the verification of the proposed method under mutual coupling effects. A desired scanning performance is accomplished on both copolarization and cross-polarization patterns of multiple beam directions, which is better than 99.75% of exact tiling solutions.

Coaxial Beam Rotating HPM Mode Converter Using Dielectrics Plates

The incorporation of the dielectric plates to produce phase delay for propagating waves is a widely employed technique in phase shifters and mode converters. In this article, a compact dielectric plate loaded coaxial beam rotating (CBR) mode converter having high gain and co-polarized (CP) pattern has been proposed for high-power microwave (HPM) applications at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band. Here, the input transverse magnetic (TM), i.e., TM01 mode, is converted to CP transverse electric (TE), i.e., TE11 likeness mode. The proposed design consists of a circular waveguide (WG) loaded with 12 dielectric polytetrafluoroethylene (PTFE) plates in a radial-azimuthal direction. For 5-mm plate thickness, the proposed design yielded a reflection loss of −20.01 dB with a radiation efficiency of 98.34% and a 17.9 dB gain at 10.084 GHz. Also, the power handling capacity of the proposed structure is predicted as 3.20 GW. Furthermore, the mode conversion is verified by measuring the far-field radiation pattern. Besides, the simulation studies of the thermal behavior of the proposed design are also discussed with the aid of CST Studio Suite.

Holographic Back-Projection Method for Calibration of Fully Digital Polarimetric Phased Array Radar

Phased Array Radar (PAR) technology is rapidly rising as a candidate for future weather radars because it can provide focused, high-quality meteorological observations. Due to the need for precise measurements of polarimetric weather variables, it is desired that the radar simultaneously transmits and receives linearly polarized horizontal (H) and vertical (V) fields through beams that are well matched in gain and shape at every pointing direction. These scanning characteristics are difficult to achieve, especially with current methods such as the “park and probe” calibration, because the radiation patterns of PAR antennas are inherently dependent on their pointing direction. Thus, polarimetric array calibration is critical to produce matched H/V copolar antenna patterns. In this article, we present a polarimetric antenna calibration procedure for the fully-digital PARs based on the holographic back-projection of electric fields. The fully digital S-band Horus radar is used to implement and evaluate the proposed calibration method. First, near-field measurements of a fully active Horus antenna panel are back-projected onto the plane of the array to derive the copolar magnitude and phase of the H/V fields radiated by each antenna element. Then, digital calibration parameters are produced from back-projected fields to compensate for excitation differences and produce uniform radiation at the plane of the array. The performance of the back-projection calibration method is evaluated for broadside and for electronically scanned angles and compared to the more conventional park and probe calibration method. A robustness analysis is conducted using simulations to evaluate the impact of excitation amplitude and phase errors that could result from practical near-field environments and amplifier performance degradation. Preliminary results show that through precise digital calibration based on back-projected fields, beam matching can be significantly improved to achieve the desired polarimetric calibration levels. For electronically steered beams, back-projection calibration can reduce H/V beam mismatch biases by approximately 25%, from 0.34 dB to 0.08 dB. This improves measurement accuracy of fully digital PARs by mitigating antenna-induced biases in meteorological estimates.

Support Vector Regression-Enabled Optimization Strategy of Dual Circularly-Polarized Shaped-Beam Reflectarray With Improved Cross- Polarization Performance

This work presents the optimization of a dual circular-polarized (CP) shaped-beam reflectarray with improved performance. To that end, the design methodology leverages surrogate models based on support vector regression (SVR) of the electromagnetic response of the constituent unit cell for a direct layout optimization of the antenna. The dual CP capability is achieved using a linear polarization (LP) Jerusalem cross integrated with an LP-to-CP polarization converter. A full description of the reflectarray analysis in CP is given. We also provide a missing demonstration in the literature of the fact that the direct coefficients in CP shape the copolar (CO) pattern of the corresponding polarization. This is applied to the optimization of a dual CP reflectarray with an isoflux pattern, achieving a reduction of more than 9 dB in the crosspolar (XP) pattern.

Optimal Pattern Synthesis for Polarimetric Phased Array Antenna Using Representative Array Patterns

To reduce pattern measurements and synthesis computations for an optimal array pattern, a set of full array patterns, named as representative array patterns (RAPs), is proposed, the number of which is smaller than that of the active element patterns (AEPs). Each RAP corresponds to one beam named as the representative beam. By optimizing the directions of these representative beams, the measured RAPs can be a good substitute for all AEPs. Compared with using the AEPs, the measurement cost and the computation time of the proposed method are proportionally cut. Considering the results of multiple evaluated directions, the optimal arrangement of representative beams is analyzed. Relative to using the AEPs, a highly consistent performance is achieved, of which the correlation coefficient of copolarization patterns can exceed 98%. For the simulated 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10$ </tex-math></inline-formula> array antenna, since merely 67 RAPs are utilized, a 33% reduction in pattern measurements and synthesis computations is obtained. This relative reduction ratio reaches 39% for the 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 16$ </tex-math></inline-formula> array antenna and 50% for the 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 32$ </tex-math></inline-formula> array antenna. The stability of the proposed method under multiplicative and additive pattern measurement errors is presented. Moreover, the proposed method is verified on a practical C-band 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 4$ </tex-math></inline-formula> dual-polarized microstrip patch array antenna.

Rapid Test Method for Multi-Beam Profile of Phased Array Antennas.

The measurement of the phased array antenna (PAA) is completely different from the traditional antenna, due to its multi beam patterns. Usually, each beam pattern of the PAA needs a separate measurement, which makes the overall time extremely long. Thus, the traditional method can no longer meet the efficiency and cost requirements of new PAA measurement. In this paper, a pattern reconstruction method is proposed which significantly reduce the measurement time of multi-beam PAAs. With the known array element patterns (AEP) and theoretical weighted port excitation of the beams, any beam pattern can be predicted by measuring only a certain beam pattern, due to the element excitation coefficient (including the matching, mutual coupling, and manufacturing factors, etc.) of the specific PAA being calculated. The approach has low reconstruction error in term of beam pointing accuracy, side lobe, and co-polar and cross-polar patterns while being validated for large scanning range. Through theoretical derivation and experiments, the effectiveness of the method is verified, and the testing efficiency of the phased array antenna can be improved by 10 times or even more.

Cross-polarization pattern diversity of patch antenna using recessed dielectric layer

In this article, the H-plane cross-polarization (XP) pattern diversity is realized using an air-filled recessed dielectric layer without disturbing the co-polarized (co-pol) pattern and reflection coefficient (S11) of the conventional square patch antenna. Instead of suppressing XP over the entire tracking angle (−60° to +60°) at a stretch, an effective approach of shifting the minima of the XP pattern has been conceived. Considering the possibilities of substrate field alteration, a recessed dielectric layer is integrated between the patch and ground planes. In this middle layer of thickness 0.8 mm, five air cavities are excavated to reduce the effective dielectric constant (εreff) of the substrate locally for the improvement of radiation properties. As the air-filled dielectric layer is moved upwards from the ground plane, the null of the XP pattern is shifted towards the right and left of the boresight for the Type A and Type B antenna, respectively, in a specific manner. The design concept has been validated through proper measurement, and the measured results are in good agreement with the simulated results.

Pattern Reconstruction for Polarimetric Phased Array Antenna by Efficient Beam Measurement

To reduce the pattern measurement cost of the polarimetric-phased array antenna (PPAA), this letter proposes a novel method to reconstruct the array pattern using that of beam positions fewer than the elements. The method is based on the induced reconstruction matrix, thereby estimating the pattern of any beam position within the scanning range. Our approach has low reconstruction error for both copolarization and cross-polarization patterns while being valid for the beam positions in a wide range. A 6 × 6 dual-polarized microstrip patch array is designed to verify the effectiveness of the method. The near-field measurement of a 4 × 4 microstrip patch array confirms that our method could not only effectively reconstruct an approximate pattern meeting the actual requirements, but also proportionally reduce the pattern measurement cost of the PPAA.

The Effect of the OMT in Electromagnetic Simulations of MeerKAT Primary Beams

Until recently, full-wave electromagnetic (EM) primary beam simulation results for MeerKAT’s offset-Gregorian reflector antennas in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -band (856–1711 MHz) differed systematically and inexplicably from high-precision field measurements. The measured beam patterns exhibit unexpected frequency- and polarization-dependent pointing offsets (squint) in both horizontal (H) and vertical (V) directions for the copolarization patterns, as well as distinctive asymmetries in the horizontal direction for the cross-polarization patterns in the upper half of the band. These effects were not predicted by design stage simulations that are based on the excitation of the fundamental waveguide mode only. Conventional large reflector simulation strategies used in the literature idealize the orthomode transducer (OMT) and waveguide and exclude this module from primary beam simulations entirely. This research shows that the inclusion of MeerKAT’s wide-bandwidth OMT and waveguide in the simulation is critical to the excitation of the TE21 mode, which results in the asymmetric features observed in the measurements. It is found that the characteristic frequency-dependent asymmetries of the primary beams are a consequence of the design of the OMT and cannot be attributed to manufacturing tolerances, reflector collimation errors, nor the coupling to conductive structures near the feed horn.

A Crossed Dipole Phased Array Antenna Architecture With Enhanced Polarization and Isolation Characteristics

A dual-polarized planar phased array antenna with enhanced polarization and isolation characteristics for multifunction applications is presented. A bent crossed dipole is selected as the element of the array antenna. The bend angle is optimized to widen the E-plane active element pattern of the dipole resulting in a pair of matched co-polar patterns. Contrary to common patch array antennas, this design does not require a continuous grounded substrate. This diminishes the surface wave propagation along the ground plane. Efficient techniques, applied to the element design, isolate the two polarizations from each other. Higher than 40 dB port isolation is achieved within the entire frequency range of 2.7–3.0 GHz in principal plane scanning. In order to preserve the symmetry of the array antenna, a mirrored arrangement in both orthogonal directions is applied to the array configuration. This enhances the co- to cross-polarization levels to better than 45 dB in scanning up to ±45° in the principal planes. The proposed phased array antenna with enhanced polarization purity can potentially improve polarimetric performance.

A Multiband antenna using plus‐shaped fractal‐like elements and stepped ground plane

A multiband planar symmetrical plus-shaped fractal monopole antenna with stepped ground plane is presented in this study. Measured results show that the proposed antenna operates with 10 dB return loss bandwidths from 1.630 to 1.88 GHz and from 4.5 to 8.5 GHz covering The Global System for Mobile Communications (GSM) 1800 MHz 2G spectrum band, 4400 to 4900 MHz 5G spectrum band adopted by Japan and China for future 5G communication in sub-6 GHz band, 5.15 to 5.925 GHz LTE band 46, WLAN IEEE 802.11 y/a/h/j/n/P bands, and 5.8 to 7.707 GHz military band. The antenna gain varies between 1.73 and 1.97 dB in lower band and 3.6 to 5.05 dBi in upper band with radiation efficiencies more than 90% in lower band and more than 80% in upper band. The antenna has more than 64 and 28 dB isolations between the copolar and cross-polar radiation patterns in the lower and upper bands, respectively.

An Ultra-Compact X-Band Dual-Polarized Slotted Waveguide Array Unit Cell for Large E-Scanning Radar Systems

A design of an X-band dual-polarization slotted waveguide antenna (SWGA) array for high polarization performance over 200 MHz bandwidth and wide scan in the azimuth plane, ideal for high-power dual-polarized radar system, is presented. The proposed design uses a compact array unit cell where the overall dimensions are reduced to 50% in comparison with that of the dual-polarization slotted waveguide array antenna using the conventional rectangular waveguides. The new design overcomes the fundamental limitation of zero electronically scanning, due to the large element spacing (1.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> ), when conventional waveguides are used. Reducing the element spacing to 0.6λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> (in the azimuth plane), based on a partial H-plane waveguide, enables a 1D e-scanning range up to 84°(±42°) in the azimuth plane perpendicular to the waveguide axis. An active sub-array panel of 8×8 elements, excited with 8 high-power transmit and receive modules, is proposed. This active sub-array can be scaled to obtain a large array without any constraints in size and power. The proposed design uses longitudinal shunt slots on the partial H-plane waveguide for V-polarization antenna and non-inclined edge wall slots on the conventional waveguide for H-polarization antenna. The proposed design offers stable impedance, gain, cross-polarization isolation and excellent copolar pattern mismatch over the whole frequency band of interest. Having a cross-polarization isolation better than -60 dB and co-polar pattern mismatch around ± 0.12 dB across the scanning range, make this array unit cell (8 × 8 elements) a perfect candidate for high power e-scanned dual-polarized phased array radar for weather observations.

A Method for Radiation Pattern Reconstruction of Phased-Array Antenna

In this letter, we propose an approach for reconstructing the radiation pattern of a phased-array antenna by application of the minimum norm least-square solution. Compared with conventional methods, our construction process only requires fewer beam patterns and distortion is also largely mitigated by compensating the mutual coupling between the elements in the antenna. Our approach has low reconstruction error for the copolar and cross-polar patterns while being valid for a large scanning range. Moreover, we design a dual-polarization microstrip patch array antenna to test the effectiveness of the proposed method.

Developer Design of Hybrid Plasmonic Nano Patch Antenna with Metal Insulator Metal Multilayer Construction

Hybrid plasmonic nanopatch antenna with metal-insulator-metal (HMIM) multilayer has been investigated for operation at the frequency of 125–250 THz using the finite element method (FEM) implemented in Ansoft High Frequency Structure Simulator (HFSS). The proposed antenna exhibits a wide bandwidth of 49.5 THz (151.5 THz–201 THz) for the slots thicknesses Wg = 50 nm and Ws = 100 nm and dual bandwidth for Ws = 20 nm. The obtained results show the input impedance of 50.3 Ω input resistance (real part) and 2.3 Ω reactance (imaginary part) occurring at (near) the operation frequency. The maximum gain of 23.98 dB has been observed for resonant frequencies of 176 THz, and the maximum directivity remains above 6.73 dB and 7.46 dB at resonant frequencies of 170 THz and 190 THz, respectively. Our proposed antenna performance is compared to previously reported designs. The copolar and cross-polar radiation patterns are simulated at different resonant frequencies of 160 THz and 197 THz for planes Φ=90° and Φ=0°. The arrays of a proposed antenna are designed in one and two dimensions in order to appropriate high-gain applications.

Synthesizing Uniform Amplitude Sparse Dipole Arrays With Shaped Patterns by Joint Optimization of Element Positions, Rotations and Phases

This paper presents a novel method for synthesizing sparse dipole arrays with shaped patterns by joint optimization of element positions, rotations and phases. Such joint optimization exploits maximum available degrees-of-freedom under the assumption of uniform amplitude excitations to improve the shaped power pattern synthesis performance, and it leads to a reduced number of elements and simpler feeding network without using unequal power dividers for the array. The copolarization (COP) and cross-polarization patterns for a rotated dipole array are derived in a 2-D case, and then the vectorial shaped pattern synthesis problem is formulated as finding the optimal solution by maximally approaching the desired COP pattern shape under multiple constraints on the sidelobe level (SLL) and cross-polarization level (XPL). In addition, an asymmetric mapping method is incorporated into the proposed joint optimization, so that the minimum element spacing constraint can be also used for the synthesis of planar sparse dipole arrays. The comprehensive learning particle swarm optimization (CLPSO) algorithm is adopted to optimize the element positions, rotation angles and phases. A set of synthesis experiments including linear and planar rotated dipole arrays with a different pattern shape requirements are conducted to validate the effectiveness and robustness of the proposed approach. Synthesis results show that the proposed approach can save about 17.24% – 55.86% elements as well as many unequal power dividers for test cases.

Mutual Coupling Reduction for a UWB Coplanar Vivaldi Array by a Truncated and Corrugated Slot

This letter reports mutual coupling reduction in an ultrawideband coplanar Vivaldi array (CVA) by incorporating truncated and corrugated slot at the border between adjacent elements. An examination of CVAs shows that mutual coupling in the E-plane is more significant than in the H-plane. Subsequently, arrays using exponential and rectangular corrugated slot are compared with those without a slot structure through the simulation of a surface current distribution. A novel exponential corrugated truncated (ECT) structure is implemented to improve a mutual coupling performance, while maintaining or even improving copolar field patterns. The results of simulation and measurement indicate that mutual coupling and return loss performance can be improved by controlling the length of corrugated structure and the distance of the slot structure from the center of the Vivaldi's tapered slot. The CVA achieves bandwidth ratio of 5:1, i.e., from 2 to 10 GHz. The ECT-CVA structure reduces mutual coupling to below −20 dB in a large portion of the whole band, shows 3.9–10.2 dBi gain over the entire band, increases a sidelobe level performance at 4–9 GHz compared to the CVA without slot structure.

Effective XPD and XPI Optimization in Reflectarrays for Satellite Missions

Crosspolar requirements for space-borne antennas are very stringent. In some missions, such as direct broadcast satellite, these requirements are specified in terms of crosspolar discrimination (XPD) and crosspolar isolation (XPI), usually with values higher than 33 dB. In this regard, the most common approach for crosspolar optimization for reflectarray antennas is to set up a crosspolar template with certain values, improving the XPD and XPI indirectly. In this letter, it is proposed to directly optimize the XPD and XPI in reflectarray antennas with the aim of obtaining better results than the usual crosspolar optimization. For this purpose, the generalized intersection approach is employed, for which the forward projection is improved to include XPD and XPI templates. Three optimization strategies are compared: optimizing the crosspolar pattern, the XPD, and the XPI. The direct optimization of the XPD and XPI achieves better results in less iterations than the common approach of the crosspolar pattern optimization while keeping the copolar pattern within requirements.

Octagonal Sierpinski band-notched super-wideband antenna with defected ground structure and symmetrical feeding

A microstrip line-fed octagonal Sierpinski super-wideband antenna is presented. It comprises a microstrip line-fed second-iterative fractal radiating patch and symmetric miniaturized defected ground plane. It has an operating bandwidth of 3.68–31.61 GHz with band rejection function for the frequency range of 7.86–11.08 GHz. The difference between the co-polar and cross-polar patterns is observed to decrease from 20 to 0 dB with increase in frequency. Omni- and bidirectional patterns are observed at lower frequencies, and distorted patterns at higher frequencies. The experimental and simulated results are observed to be in good agreement with each other. The designed antenna is superior to other SWB antenna structures in terms of its wide bandwidth, miniaturized dimensions, and band-notched characteristic.