1 

Finiteness effects in wideband connected arrays: Analytical models to highlight the effects of the loading impedances
Most phased arrays are designed using infinite array theory, which does not account for edge effects. However, this approximation might not be adequate for the design of wideband arrays, for which truncation effects are more significant than in traditional narrowband arrays. In particular, edge effects can be very severe in broadband connected arrays, since the interelement connection facilitates the propagation of edgeborn waves that can become dominant over large portions of the arrays. This paper presents a formulation based on Green's function for the analysis of finite connected arrays. We first rigorously derive the electric current distribution on the array with an efficient numerical solution. Later on, the introduction of a few simplifying assumptions allows the derivation of an analytical approximation for the current distribution. This latter provides meaningful insights in the induced dominant edgewave phenomena.

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2 

Truncation effects in connected arrays: Analytical models to describe the edgeinduced wave phenomena
This paper presents a Green's function based procedure to assess edge effects in finite wideband connected arrays. Truncation effects are more severe in broadband arrays, since the interelement mutual coupling facilitates the propagation of edgeborn waves that can become dominant over large portions of the arrays. As a consequence, the overall behavior of a finite wide band array can be dramatically different with respect to the designs based on infinite array analysis. Here, we first rigorously derive the electric current distribution on the finite connected array with an efficient numerical solution. Later on, the introduction of a few simplifying assumptions allows the derivation of an analytical approximation for the current distribution. This latter provides meaningful insights in the induced dominant edgewave phenomena.

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3 

Edgeborn waves in connected arrays: A finite × infinite analytical representation
Connected arrays constitute one of the most promising options for wideband phased arrays. Like most phased arrays, they are designed using infinite array theory. However, when finiteness is included, edge effects perturb their behavior. These effects are more severe when the arrays are designed to operate over very broad frequency ranges, since the mutual coupling between the elements facilitates the propagation of edgeborn waves that can become dominant over large portions of the arrays. Finite array simulations, which would predict these behaviors, are computationally unwieldy. In this paper we present a Green's function based procedure to assess edge effects in finite connected arrays. First the electric current distribution on the array is rigorously derived. Later on, the introduction of a few simplifying assumptions allows the derivation of an analytical approximation for the current distribution. This latter provides meaningful insights in the induced dominant edgewave mechanism. The efficiency of connected arrays as a function of their dimension in terms of the wavelength and of the loading feed impedances is investigated.

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4 

Analysis of commonmode resonances in arrays of connected dipoles and possible solutions
A prototype array of dual polarized connected dipoles has been manufactured. The feed structure is composed by two orthogonal 8x8 elements for each polarization (128). The operational frequency ranges from 6 to 9 GHz (40% relative bandwidth). Preliminary measurements highlighted the presence of unpredicted commonmode resonances excited in the vertical feeding lines. An analysis of the commonmode excitation is carried out and exit strategies for a design of a resonancefree connected array are presented.

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5 

A wideband (3 to 5 GHz) widescan connected array of dipoles with low cross polarization
A wideband, widescan prototype phased array of connected dipoles has been manufactured and tested from 3 to 5 GHz. The array comprises 7 × 7 elements, each fed by a loopshaped transformer to avoid commonmode resonances. Such resonances typically affect this type of arrays, with consequent degradation of the polarization performance. The commonmode rejection implemented by the loop transformers allows to maintain the crosspolarization levels to values lower than 10 dBs over a 30% relative bandwidth, for elevation angle up to 45° in all azimuth planes. The array exhibits a measured voltage standingwave ratio (VSWR) lower than 2.5 from 3 to 5 GHz for broadside radiation. © 2012 IEEE.

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6 

Analytical Description and Design of Printed Dipole Arrays for Wideband WideScan Applications
Wideband arrays of printed dipoles with interelement loads are investigated. A closedform expression for the active input impedance of the array element is derived with a spectral domain approach. The procedure is based on an extension of the Green's function formulation for arrays of connected dipoles to the case of dipoles coupled via loads. The accuracy of the formulation is investigated with the aid of parametric analyses. The model can be used in the preliminary design of wideband printed dipoles for the dimensioning of the radiating elements. The procedure remains accurate also for arrays of dipoles that are not tightly coupled, for which and the current along the element assumes a resonantlike sinusoidal distribution.

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7 

Green's function based equivalent circuits for connected arrays in transmission and in reception
Connected arrays constitute the only family of antenna arrays for which the spectral Green's Functions have been derived analytically. This formalism is extended here to the receiving case. When the arrays are assumed to be infinitely extended and periodically excited, rigorous equivalent networks can be derived to represent the electromagnetic field distribution in transmission and/or reception. These equivalent networks are based on Green's functions, thus each components can be associated with a specific physical wave mechanism. Moreover, all components are evaluated analytically. The total power transmitted, received and/or scattered by a connected array with and without backing reflector is discussed. The full efficiency of an array with backing reflector is demonstrated and explained. Finally, measurements from a dualband connected array prototype validate the equivalent circuit representation.

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8 

Performance of wide band connected arrays in scanning : The equivalent circuit and its validation through a dualband prototype demonstrator
Connected array antennas are planar radiators in which the mutual coupling between the neighboring elements is so high that the antenna elements are effectively touching each other. Physically touching connected arrays have been formally introduced by R. Hansen [1] and were then developed for wideband through the foliage observations by J.J. Lee [2]. Similarly, wideband antenna concepts were also developed by B. Munk [3], who did not refer to the name connected arrays, but essentially realized the connection by means of capacitive loading at the edges of the dipoles.

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9 

Commonmode resonances in ultra wide band connected arrays of dipoles: Measurements from the demonstrator and exit strategy
A 69 GHz prototype array of dualpolarized connected dipoles has been manufactured. The array is composed by two orthogonal sets of 8×8 elements for each polarization (128), arranged in an eggcrate configuration. Preliminary measurements highlighted the presence of unpredicted commonmode resonances excited in the vertical feeding lines. An analysis of the commonmode excitation is carried out and exit strategies for a design of a resonancefree connected array are presented.

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10 

PCB Slot Based Transformers to Avoid CommonMode Resonances in Connected Arrays of Dipoles
The scanning performances of connected arrays are degraded by the excitation of commonmode resonances that are compatible with balanced feeding lines. Here, a strategy to avoid these resonances is outlined. The strategy involves feeding the dipoles via printed circuit board (PCB) based transformers and significantly reducing the feeding periods in the direction of the dipoles. The number of transmit/receive (T/R) modules does not have to be increased as a consequence of the increased sampling of the dipoles. Full wave simulations that validate the procedure are presented

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11 

A 10.514.5 GHz widescanning connected array of dipoles with commonmode rejection loops to ensure polarization purity
Wideband, widescanning phased arrays with low crosspolarization across the entire bandwidth are increasingly desired for many applications. Although tapered slot antennas have very broad bandwidth (BW), they are known to radiate strongly crosspolarized fields, especially in the diagonal plane (ψ = 45°), [1]. On the other hand, conventional phased array based on printed resonant elements can achieve only moderate BW (∼25%), [24]. A novel trend in this field is the use of planar arrays of long dipoles or slots periodically fed. This concept was originally proposed by Hansen, [5], and further theoretically developed in [6], proving the wideband behaviour of such arrays. Besides broad bandwidth, low cross polarization (Xpol) over a wide scanning volume is another important feature of such antenna solutions. In [7], scanning performance of connected array was investigated and a theoretical design of a dipole array was presented, with 40% relative BW and wide scan capability, up to 45° for all azimuths. © 2010 IEEE.

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12 

Connected phased array antennas for ultrawide band radar applications
The constantly increasing demand of advanced sensors and communications systems aboard of military platforms (ships, UAVs, aircraft, land vehicles, etc.) requires a high number of antennas, covering a very wide frequency spectrum. An interesting and significant example is given by typical RF functions on board of multifunction frigates. These range from 200 MHz up to 18 GHz. The complete band in between these two frequencies is allocated to several functions, including among the others: UHF communication, Electronic warfare Support Measure (ESM), Electronic Counter Measure (ECM), radar, navigation, Identification Friend or Foe (IFF), Joint Tactical Information Distribution System (JTIDS), SHF Satcom etc.

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13 

Design of a lowprofile printed array of loaded dipoles with inherent frequency selectivity properties
This work presents the design of a lowprofile array of printed dipoles with inherent filtering properties for radar applications. The antenna and the bandpass filter are integrated in a single module, which is small enough to fit within the array unit cell (with period of about 0.4 ? at the highest operational frequency). The array element may be viewed as a threepole Tchebychev filter in which the load resistance and the first resonator are implemented by means of the radiating dipole and the backing reflector. Results obtained via infinite array simulations are presented. A 23% relative bandwidth (S11 < 10 dB) is achieved for broadside radiation and for scanning up to 45 on the Hplane.

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14 

Integrated filtering in a planar array of connected dipoles including a commonmode rejection module
A smart design strategy for a planar Xband phasedarray antenna of connected dipoles with inherent filtering properties is described. As shown in previous works, the use of a commonmode rejection module is necessary in order to suppress undesired resonances excited when scanning on the Eplane. In the present solution, part of the filtering function is performed by the dipole, acting as first resonator, while the other part is integrated in the commonmode rejection module consisting in a planar hybridring. As shown in the simulation results, scanning capabilities up to 45° in the Hplane and up to 30° for the Eplane are achievable with a fractional bandwidth of 21%. © 2012 EUROPEAN MICROWAVE ASSOC.

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15 

Compact design of a planar filtering antenna array including a frequency selective commonmode rejection module
A new compact design of a planar phasedarray antenna with inherent frequency selectivity properties is presented. In previous works, starting from an array of connected dipoles, the design of a filtenna structure and a strategy for the suppression of commonmode resonances have been addressed. In the present approach, a compact design solution has been obtained by the integration of part of the filtering function in the commonmode rejection module, consisting in a planar hybridring. As proved by simulation results, scanning up to 45 ° for the Hplane and up to 30 ° for the Eplane is achieved with a relative bandwidth of 21%. © 2012 IEEE.

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16 

Integrated filtering in a planar array of connected dipoles including a commonmode rejection module
A smart design strategy for a planar Xband phasedarray antenna of connected dipoles with inherent filtering properties is described. As shown in previous works, the use of a commonmode rejection module is necessary in order to suppress undesired resonances excited when scanning on the Eplane. In the present solution, part of the filtering function is performed by the dipole, acting as first resonator, while the other part is integrated in the commonmode rejection module consisting in a planar hybridring. As shown in the simulation results, scanning capabilities up to 45 ° in the Hplane and up to 30 ° for the Eplane are achievable with a fractional bandwidth of 21%. © 2012 EUROPEAN MICROWAVE ASSOC.

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17 

A dualband planar array of connected dipoles: Experimental validation based on bistatic RCS measurements
Rigorous equivalent networks representing connected arrays in transmission and reception are derived in this paper. These equivalent networks are not based on reciprocity but on Green's functions. Thus, all components have well identified and physically meaningful roles. A dualband connected array demonstrator is then presented to validate the theory. The matching properties of the array are characterized via Radar Cross Section (RCS) measurements without resorting to lossy and expensive feeding networks.

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18 

A Novel PrintedCircuitBoard Feeding Structure for CommonMode Rejection in WideScanning Connected Arrays of Dipoles
A novel PrintedCircuitBoard (PCB) solution to avoid commonmode resonances in connected arrays is proposed in this paper. It consists in a loopshaped circuit that rejects commonmode current propagation over more than an octave bandwidth. The use of such commonmode rejection loop allows the design of linear and dual polarized array of connected dipoles, with crosspolarization levels lower than 17 dBs for elevation angles in the range ±45° and for all azimuths, over more than 30 % relative bandwidth. Fullwave simulations are presented to validate the design..

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19 

Connected arrays of dipoles for broad band, wide angle scanning, dual polarized applications : A novel solution to the common mode problem
Wideband connected arrays of dipoles are a very promising solution for broadband, wideangle scanning phased arrays. Unlike tapered slot antennas, connected arrays can operate over wide bandwidth maintaining polarization purity. However, an open issue for the practical implementation of these arrays is the propagation of commonmode currents along the differential feeding lines. A solution for this problem is here proposed and is constituted by a loopshaped transformer that acts as commonmode rejection circuit. Simulated results are presented for connected arrays of dipoles for both linear and dual polarization, with 30% relative bandwidth (from 10.7 to 14.5 GHz) and scanning capability up to 45° for any azimuth. © 2010 IEEE.

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20 

On the Potentials of Connected Array Technology for Wide Band, Wide Scanning, Dual Polarized Applications

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