Array Feed Network Research Articles

A Large Microstrip Patch Array With a Simplified Feed Network: A low cross-polarized design

Discontinuities in the feed lines are one of the major sources of spurious radiation that results in high cross-polarized (XP) radiation in microstrip-line-fed large arrays. This limits the use of the arrays in satellites where frequency is reused by means of polarization diversity. But for low-profile and lightweight designs, microstrip arrays are very useful. In this article, the design aspects of a simpler topology for the array feed network are discussed in detail. The purpose is to realize an array with high XP isolation by reducing the number of discontinuities. In addition, this topology reduces the length of the feed network of 2 × 2 subarrays by approximately 20%, as well as reducing the amount of the mutual coupling. A rectangular array with 32 × 16 elements has been realized at 10.7 GHz using this concept, for transmission of satellite telemetry data. The measured results of the array indicate more than 35 dB of XP isolation, even in the diagonal planes. The aperture efficiency of the array is found to be approximately 27%, which is very good for a microstrip-fed array.

Improved Model for Inclined Coupling Slots in the Feed of a Planar Slot Array

The conventional design equations for centered-inclined slots of a planar array feed network rely on certain assumptions regarding the phase relationship between the elements of the scattering parameters of coupling junctions, and do not account for higher-order coupling between tilted slots. Phase variations between S-parameters give rise to excitation errors in the radiating branches, and discounting the effects of higher-order coupling causes the input reflection coefficient minimum to deviate from the design frequency. In this communication, we derive new design relations which accommodate phase differences between individual scattering parameters and compensate for higher-order coupling. Compensation is achieved with the addition of closed-form terms in the expression for the equivalent impedance of the coupling slots. The effectiveness of the proposed procedure is demonstrated by means of an illustrative design example.

Analytical Evaluation of an Antenna Array System and Adaptive Cell Densification Technique for Energy Efficient LTE Network

This paper will propose a cost effective antenna array system and an adaptive cell densification technique for energy efficient Long Term Evolution mobile radio network. The antenna array system is designed to control the elevation half power beam width and elevation electrical beam down tilt angle by using a low loss novel antenna array feed network. The paper will also propose a novel sectorisation order control technique, which is the amalgamation of horizontal and modified vertical sectorisation with the improved and novel features. The proposed sectorisation order control technique can efficiently deal with uniform and non-uniform angular traffic loads in the dense urban region and therefore the proposed solution is more pragmatic. The results show that the capacity of the mobile radio network can be controlled with the highest possible flexibility by using the proposed cost effective antenna array system and adaptive sectorisation order control technique. The results also show that the 40 % energy can be saved when the traffic load of the base station is less than or equal to the minimum threshold value.

TFSIW-Excited Dual-Polarized Array Antenna With 30° Beam-Pointing for Millimeter-Wave Applications

This communication presents a dual-polarized series-fed array antenna with 30° beam-pointing for millimeter-wave (MM-Wave) applications. The 45° and −45° polarized subarrays share the aperture in an interdigital shape. The spacing between subarrays with the same polarization orientation is set to $0.56\lambda _{0}$ through the use of narrower T-type folded substrate integrated waveguide (TFSIW) instead of substrate integrated waveguide (SIW). The substrate integrated coaxial line (SICL) is adopted to design the array feeding network. To validate the proposed design, a $4 \times 6$ (single polarization) dual-polarized array antenna operating at 28 GHz with 30° beam-pointing is fabricated. Based on the measurement, the return losses are lower than −10 dB from 27.5 to 28.5 GHz, the isolations between the two polarization ports are higher than 30.0 dB in the frequencies mentioned above, the maximum gain at the center frequency is 15.7 dBi, and the cross-polarization levels are lower than −18.5 dB. The proposed antenna only needs one-step processing with the standard PCB technology without additional stitching assembly. Simulated and measured results of the proposed antennas were compared.

Phase-Only Antenna Array Reconfigurability with Gaussian-Shaped Nulls for 5G Applications

This paper presents a fast iterative method for the synthesis of linear and planar antenna arrays of arbitrary geometry that provides pattern reconfigurability for 5G applications. The method enables to generate wide null regions shaped according to a Gaussian distribution, which complies with recent measurements on millimeter-wave (mmWave) angular dispersion. A phase-only control approach is adopted by moving from the pattern provided by a uniformly excited array and iteratively modifying the sole phases of the excitations. This allows the simplification of the array feeding network, hence reducing the cost of realization of 5G base stations and mobile terminals. The proposed algorithm, which is based on the method of successive projections, relies on closed-form expressions for both the projectors and the null positions, thus allowing a fast computation of the excitation phases at each iteration. The effectiveness of the proposed solution is checked through numerical examples compliant with 5G mmWave scenarios and involving linear and concentric ring arrays.

Design and Fabrication of Wideband Millimeter-Wave Directional Couplers With Different Coupling Factors Based on Gap Waveguide Technology

A class of wideband directional couplers suitable for achieving different coupling levels are proposed in this paper. The proposed couplers have been implemented using the double-layer groove gap waveguide at the millimeter-wave frequency range. They are composed of two parallel groove gap waveguide parts placed on top of each other in such a way that the coupling between the two waveguide sections can be achieved via the coupling structures placed in the common wall. Usually, the coupling layer consists of two rows of holes and depending on the number of holes the coupling levels can be controlled. The manifest and applicable property of the proposed directional coupler is that the coupling level can be simply changed using the different coupling layers without changing the top and bottom groove waveguides and transitions. As another significant advantage of the proposed coupler, there is no requirement of good electrical contact among different metallic parts of the structure, which considerably simplifies the manufacturing processes and mechanical assembly at millimeter-waves applications. For verification purpose, three sample couplers with coupling levels of 10, 20, and 30 dB have been designed, fabricated, and measured. To make the device accessible and measurable using the standard rectangular waveguides, two types of transitions from the groove gap waveguide to standard WR-15 are designed. The simulation and experimental results are in good agreement and show that the proposed couplers have large bandwidth for return loss level of 20 dB, coupling level of 10±1, 20±1, and 30±1 dB, and isolation level of 30, 35, and 40 dB over the desired frequency band of 50-70 GHz. The proposed directional couplers can be used as good candidates at millimeter-wave frequencies for probing and the design of compact integrated microwave circuits and systems, such as antenna array feeding networks.

Air-Filled Substrate Integrated Waveguide Fed Magneto-Electric Dipole Antenna Array for Millimeter-Wave Applications

A substrate integrated magneto-electric (ME) dipole antenna array with an improved radiation efficiency is presented in the 28-GHz band. A novel full-corporate air-filled substrate integrated waveguide (SIW) feed network with low losses is designed and realized by utilizing the low-cost printed circuit board (PCB) facilities. Different from most previous millimeter-wave planar arrays consisting of 2 × 2 subarrays, an SIW fed sub-array with a larger size of 2 × 4 is investigated to simplify the configuration of the major portion of the array feed network, which is of importance to the successful realization of the air-filled SIW feed network. An 8×8 array prototype with a four-layered geometry is fabricated and measured to verify the design. The array has an impedance bandwidth of 25.9%, a gain up to 26 dBi and stable radiation patterns over the operating band. Benefitted from the absence of the significant dielectric loss in the feed network, a high antenna efficiency of 80% is also achieved. The proposed design provides an effective method to improve the achievable gain and efficiency characteristics of the substrate integrated arrays with a large size that are attractive for millimeter-wave wireless applications.

A Novel Multifunctional EBG-Based Coupled-Line-Defect Directional Coupler Based on Layered Dielectric Substrates

In this paper, a novel multifunctional coupler based on line-defect layered electromagnetic bandgap (EBG) waveguides is proposed and studied. Extensive full-wave simulations are used to establish the critical nature of the coupling region for the realization of different functionalities of the coupler. Changing the separation between the rings or orientation of the rings in the coupling and/or channel regions leads to very interesting and unique coupling mechanisms, such as forward-wave, through-wave, and/or backward-wave quasi-0- and 3-dB couplers that distinguish the proposed topology from conventional proximity directional couplers. In the final analysis, one can switch between configurations by changing the orientation of the rings in the coupling region. These configurations with coplanar-slot-line feeding structures are fabricated and tested at X-band for demonstration purposes. Measurement results validated the design procedure and confirmed the general trends in simulations. The proposed EBG coupler is promising for beamforming matrix and antenna array feeding networks.

28 GHz Taylor feed network for sidelobe level reduction in 5G phased array antennas

AbstractThis paper presents a design procedure for a phased array feed network. The procedure is validated by designing and fabricating a set of 28 GHz 8‐element beam steerable antennas. Within the feed, a Taylor n‐bar amplitude taper is implemented using unequal power dividers. At boresight, the taper reduced the sidelobe level by 2.84 dB to −15.2 dB. Beam steering from 0° to 48° is achieved using meanders. An empirical formula for the meander widths is proposed, enabling independent control of amplitude and phase. Empirical formulae for the initial parameters of the unequal dividers are also proposed. The wide transmission lines in this feed network are compatible with low‐cost PCB fabrication techniques.

A Compact Highly Efficient Hybrid Antenna Array for W-Band Applications

A W -band hybrid array with a compact size and a high efficiency is presented. With the aid of the joint design of the series-shunt feeding network and substrate integrated waveguide (SIW) blocked slots array, the array with 16 × 56 slots can be divided into eight areas, and then the bandwidth of impedance, gain, and radiation pattern can be improved effectively. Moreover, it has both the advantages of low profile over traditional SIW planar array and low loss over traditional air-filled rectangular waveguide (ARW) slot array. Due to the utilization of back-feeding technology of the proposed hybrid array instead of planar SIW divider, it could save a lot of area for radiating energy and lowering the insertion loss, thus resulting in the gain values higher than 30.7 dBi during the entire operational frequency coverage. It is corresponding to the total efficiency of 26.5%, which is higher than the traditional W -band SIW array due to the usage of the back feeding to conserve the radiation acreage and reduce the insertion loss. By designing the SIW slots array and series-shunt feeding network simultaneously, low sidelobe level characteristics of −16 and −20 dB in E - and H -planes have been successfully accomplished, respectively.

Synthesis of the Sparse Uniform-Amplitude Concentric Ring Transmitting Array for Optimal Microwave Power Transmission

Beam capture efficiency (BCE) is one key factor of the overall efficiency for a microwave power transmission (MPT) system, while sparsification of a large-scale transmitting array has a practical significance. If all elements of the transmitting array are excited uniformly, the fabrication, maintenance, and feed network design would be greatly simplified. This paper describes the synthesis method of the sparse uniform-amplitude transmitting array with concentric ring layout using particle swarm optimization (PSO) algorithm while keeping a higher BCE. Based on this method, uniform exciting strategy, reduced number of elements, and a higher BCE are achieved simultaneously for optimal MPT. The numerical results of the sparse uniform-amplitude concentric ring arrays (SUACRAs) optimized by the proposed method are compared with those of the random-located uniform-amplitude array (RLUAA) and the stepped-amplitude array (SAA), both being reported in the literatures for the maximum BCE. Compared to the RLUAA, the SUACRA saves 32% elements with a 1.1% higher BCE. While compared to the SAA, the SUACRA saves 29.1% elements with a bit higher BCE. The proposed SUACRAs have higher BCEs, simple array arrangement and feed network, and could be used as the transmitting array for a large-scale MPT system.

Numerical Optimization of Compressive Array Feed Networks

Compressive antenna arrays reduce the number of beamforming controls by taking a limited number of weighted combinations of the element signals. A compressive array sidelobe level (SLL)-minimization algorithm, inspired by coherence-optimization algorithms, is presented. Optimized compressive arrays are shown to obtain better SLLs than existing weighted thinned arrays and completely overlapped subarrays. The design of a compressive array with arbitrary sidelobe requirements shows that increasing the number of elements for a given number of beamforming controls improves the array performance over a conventional array. A compressive array with a hard null is proposed to suppress the interference before sampling. Where beamforming controls are the main cost drivers, the proposed approach promises to increase the array performance without a significant increase in cost.

Line Defect-Layered EBG Waveguides in Dielectric Substrates

A dielectric-based multilayer structure composed of U-shaped rings (ML-UR) is used to develop a class of novel electromagnetic band gap (EBG) slab waveguide. The structure has two band gaps that narrow down as dielectric constant is increased. The EBG slab waveguide is created by embedding a single-layer line defect inside the 3D crystal of the EBG slab guide. Unlike our previously published foam-based EBG structure, the use of dielectric spacer in the EBG waveguides offers significant advantages in terms of overall size, structure reliability, and design flexibility. The waveguide structures reported in this paper are designed to operate at X-band (8–12 GHz) while being fed by coplanar-slotline transitions. Prototypes were fabricated and characterized experimentally. The insertion loss decreases by decreasing the number of full lattices of ML-UR surrounding the channels. The proposed waveguide has potential in microwave components such as directional couplers, phase shifters, and antenna array feeding networks.

D-Band High-Gain Circular-Polarized Plate Array Antenna

This paper represents a low-profile large-scale circular-polarized (CP) plate array antenna in the D-band. To achieve the high gain, high efficiency, and wideband at the same time, a CP $2 \times 2$ subarray antenna is proposed at first, consisting of integrated horns, complementary phase shifters, and a dual-polarized power divider (PD). The complementary phase shifter includes a parallel capacitance phase shifter and a parallel inductance phase shifter. Phase shifts generated by inductance and capacitance structures present opposite tendencies versus frequency. Therefore, an appropriate combination of them will make the phase shift almost constant over a wideband, which is important to generate a wideband CP beam. Besides, the capacitance phase shifter can be implemented by inserting irises at waveguide broadsides, while the inductance phase shifter can be achieved by inserting irises at the waveguide narrow side. Such a simple configuration can guarantee the element spacing limitation and the fabrication accuracy. The dual-polarized PD consists of an octagon cavity with rotated symmetrical coupling slots for wideband equal-amplitude and in-phase outputs. In addition, some matching layers and matching ridges in the octagon cavity are introduced to achieve wideband matching. Finally, a wideband array feeding network is used to build a $16 \times 16$ -element left-handed CP array antenna. The $S_{11}$ below −10 dB bandwidth is about 15.1%, and the co-gain is more than 30 dBi from 130 to 149 GHz. The radiation efficiency is higher than 65% and a 3 dB axial ratio can be satisfied over the whole band.

Synthesis of Reconfigurable Antenna Array Using Differential Evolution Algorithm

ABSTRACTPresently certain applications demand two or more radiation patterns by using a single antenna array due to miniature and cost effective measures of the device. Hence, reconfigurable array is suitable for this purpose. This paper presents differential evolution (DE) algorithm based design of a reconfigurable antenna array. This method effectively obtains the optimum phase weights for efficient antenna performance in dual mode. The problem attempted is to find an optimal common amplitude weight distribution with minimum amplitude range ratio. 4-bit discrete amplitudes and 5-bit discrete phases have been considered to simplify the design of the array feed network. Based on simulation results, it is established that DE-based reconfigurable antenna array design provides better performance in terms of side lobe levels and null steering.

Single layer CPSSA array with change polarization diversity in broadband application

The present study proposes a novel broadband circularly polarized (CP) multiple-input multiple-output antenna array designed for C-band applications. The first step was the introduction of a reconfigurable circularly polarized square slot antenna (CPSSA) capable of changing polarization diversity, which could cover impedance bandwidth (BW) from 4.48 to 8.21 GHz with 1.9 GHz of −3 dB axial ratio (AR) BW. Then, a feed network composed of 90° and 180° couplers, a crossover, and delay lines was presented. The CPSSA with two metalized via-holes adopted with two ports polarization diversity fed the networks. A number of reconfigurable CP array antennas using the polarization diversity technique have been presented so far. However, given that the proposed layout designed in a single layer had advantages of reduced antenna size and increased antenna gain and ARBW, this approach has received due attention over recent years. Another promising feature of this approach is its capability to change the polarization diversity by rotation of phases in the array feed network using PIN diodes.

Reconfigurable wide band circularly polarized antenna array for WiMAX, C-Band,a and ITU-R applications with enhanced sequentially rotated feed network

In this article, a wide-band circularly polarized slot antenna array with reconfigurable feed-network for WiMAX, C-Band, and ITU-R applications is proposed. Different novel methods are used in proposed array to improve antenna features such as impedance matching, 3 dB axial-ratio bandwidth (ARBW), gain, and destructive coupling effects. Miniaturized dual-feed square slot antenna, with one attached L-shaped strip and a pair of T-shaped strip at ground surface for improving impedance matching and circular polarization (CP) purity, is presented. For further enhancement of CP attributes, reconfigurable sequentially rotated feed network is utilized to obtain wider 3 dB ARBW. Furthermore reconfigurable property of network gives controlling Right and Left handed CPs, respectively. Finally, a special form of Electromagnetic Band gap structure is employed on top layer of substrate that provides high isolation between radiating elements and array feed network to enhance overall performance of antenna. The measured results depict 3 dB ARBW from 4.6 to 7.2 GHz, impedance bandwidth from 3.3 to 8.8 GHz for VWSR<2, and peak gain of 10 dBi at 6 GHz. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:825–833, 2015.

Arbitrary-Angle Squint-Free Beamforming in Series-Fed Antenna Arrays Using Non-Foster Elements Synthesized by Negative-Group-Delay Networks

Beamforming in series-fed antenna arrays can inherently suffer from beam-squinting. To overcome the beam-squinting problem, low-dispersion, fast-wave transmission lines can be employed. Such transmission lines can be designed by loading a regular transmission line with non-Foster reactive elements (e.g., negative capacitors and inductors). As a result of a recent development, these non-Foster reactive elements can be implemented using loss-compensated negative-group-delay (NGD) networks, providing a solution to the stability issues associated with conventional non-Foster networks. In this work, transmission lines augmented by loss-compensated NGD networks, representing the non-Foster reactive-element loading, are employed for designing wideband fast-wave, low-dispersion transmission lines. This work consolidates this non-Foster reactive element loading method with earlier efforts where NGD networks were used to implement zero-degree phase shifters for beamforming at the broadside direction, and generalizes these methods for arbitrary-angle beamforming from backfire to endfire including the broadside direction. Experimental results are presented for a wideband linear four-element transmitting array feed network for beamforming at 30° with respect to the broadside direction in the frequency range 1-1.5 GHz. By connecting this feed network to four wideband tapered-slot antennas, the beamforming performance is experimentally verified inside an anechoic chamber. Moreover, the antenna array is experimentally tested for transmission of a narrow pulse, where low distortion is observed at the beamforming angle over the entire operating bandwidth. The physical length of the feed network is realistic and is 0.96 wavelengths long at the center of this frequency range. In addition, switched-line phase shifters are employed for squint-free beamforming in three other angles: 60°, 0°, and $-30^{\circ}$.

Physically symmetric wideband waveguide T‐junction with equal‐phase and unequal‐power division

ABSTRACTAn H‐plane wideband rectangular waveguide T‐junction divider with an equal‐phase and an unequal‐power‐division is proposed. This T‐junction has an intrinsic hallmark of symmetry, namely, the lengths of two output branches being maintained equally with reference to the input port. Numerical analysis results are compared with the measured ones to verify the design idea. This device has a potential application in array feeding network designs where equal‐phase and unequal‐power division are to be achieved by equal‐length feeding lines. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1216–1219, 2015

Substrate Integrated Waveguide Directional Couplers for Compact Three-Dimensional Integrated Circuits

A class of directional couplers based on the substrate integrated waveguide (SIW) technique for compact three-dimensional (3-D) integrated circuits is proposed and studied in this work. Backward and forward couplers as well as strong coupling-defined forward couplers are presented and developed. They are composed of two joined SIW sections such that the common wall between them is made of a portion of the broad side of the first SIW and the narrow side of the second SIW. This perpendicular topology is arranged and formed through the use of a LEGO-like interconnect between the two SIW structures. Different coupling geometries developed with a low-cost printed circuit board process are studied. Design considerations and measured results at $Ka$ -band are presented and discussed. To achieve respectively weak backward and forward directional couplings, Schwinger and multihole-type directional couplers are introduced first of all, which make use of coupling slots arranged around the center of the SIW broad wall. For each of those structures, a wideband 20-dB directional coupler is fabricated and measured for demonstration purposes. To achieve a strong coupling, a Riblet-type directional coupler is proposed and examined. Subsequently, a 3-dB coupler is demonstrated together with a 0-dB coupler, offering a wideband and very efficient transition between the perpendicularly arranged SIWs. The proposed directional couplers can be used at millimeter-wave frequencies for probing and the design of compact 3-D integrated circuits and systems such as polarimetric imaging radiometer or antenna array feeding networks.