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Journal ArticleDOI

Artificial magnetic conductor surfaces and their application to low-profile high-gain planar antennas

TL;DR: In this article, a ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines, and the bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated.
Abstract: Planar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate and they introduce a zero degrees reflection phase shift to incident waves. In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. A ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines. The bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated. Planar AMC surfaces are used for the first time as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface as superstrate. A significant reduction of the antenna profile is achieved. A ray theory approach is employed in order to describe the functioning of the antenna and to predict the existence of quarter wavelength resonant cavities.

Summary (2 min read)

Introduction

  • OVER the last few years the electromagnetic band gap(EBG) properties of passive metallodielectric arrays have been studied [1]–[4].
  • In practice, the reflection phase of AMCs crosses zero at just one frequency (for one resonant mode).
  • Full-wave analysis and measurements of both the AMC alone and the antenna are used to validate the assertions of the cavity model.
  • A full-wave study on the AMC performance of square patch arrays is presented and the ray model predictions are validated.

II. ANALYSIS

  • A simple geometrical optics model can be used to describe the function of resonant cavities.
  • This analysis can be carried over to the design of high-gain microwave antennas.
  • The analysis is briefly outlined in this section.
  • Following the paths of the direct and the reflected waves and taking into account the various phase shifts introduced to them, the resonance condition of the cavity can be easily derived.
  • The PRS introduces a phase shift equal to the phase of its transmission coefficient, .

III. PLANAR AMC SURFACES

  • In this section the resonant cavity model is initially employed to provide with guidelines on the design of AMCs.
  • Full-wave Floquet modal analysis [3] of periodic metallodielectric PRS surfaces and AMC structures without vias is carried out in order to validate the conclusions obtained from the approximate cavity model.
  • The bandwidth of AMC surfaces is studied and the effect of the substrate thickness is presented.

B. Bandwidth Considerations

  • According to (5), for a wideband AMC, an optimum PRS would require its transmission coefficient phase to linearly increase with frequency with a gradient of [8].
  • This would result in a wideband cavity that would satisfy the resonance condition (5) for all frequencies.
  • While increasing transmission phase with frequency is not feasible for a capacitive screen, this conclusion suggests that among two screens with equal reflectivity, greater AMC bandwidth will be observed for the one with slower varying transmission phase.
  • This is demonstrated using full wave results in the example mentioned above (Fig. 5).
  • PRS1 has slower transmission phase variation with frequency compared to PRS2 [Fig. 5(a)].

C. Effect of Substrate Thickness

  • The resonant cavity AMC model predicts that for a fixed capacitive screen with an approximately frequency independent phase, the AMC frequency decreases as the dielectric thickness increases.
  • Therefore, in general, with increasing , the AMC frequency decreases and the bandwidth is improved.
  • This is also consistent with the analysis of reflectarray antennas [16].
  • The effect of substrate thickness is demonstrated here in Fig. 6, using full-wave analysis.
  • A parametric study of the AMC response for a fixed square patch PRS is presented.

IV. PROFILE REDUCTION OF HIGH-GAIN ANTENNA

  • The application of AMC surfaces to low-profile high-gain antennas is presented in this section.
  • A broadband AMC surface is designed based on the methodology of the previous section and is used as the ground plane of a microstrip patch antenna with a PRS superstrate.
  • According to the analysis in Section II the AMC ground plane in conjunction with a highly reflective PRS superstrate are expected to produce a low-profile (about quarter wavelength) high-gain planar antenna.
  • Full wave simulations of the antenna have been carried out prior to the fabrication stage and are in good agreement with measured results.

A. Design of AMC Substrate and PRS Superstrate

  • A broadband AMC surface has been designed with a center frequency (zero degrees phase) at about 14 GHz.
  • The simulated reflection phase response as obtained from Floquet modal analysis is shown in Fig.
  • Closely packed square patches were used with unit cell dimensions , [Fig. 3(a)].
  • The measured complex reflection coefficient of the fabricated surface has been obtained with reference a solid metal plate at the position of the array and is shown in Fig.
  • The reflection coefficient at 14 GHz is about 0.43 dB.
  • Following (3) of the ray model a maximum antenna directivity of about 20.5 dBi is expected.

B. Antenna Performance

  • A microstrip patch antenna (6 mm 4.5 mm) has been designed as the primary feeder of the resonant cavity and fabricated using the AMC ground plane .
  • The patches of the AMC are surrounding the patch antenna which is printed on the same dielectric substrate.
  • A full-wave simulation of the antenna was carried out in Microstripes.
  • The gain of the low-profile antenna is shown in Fig. 10(a).
  • In both planes highly directive pattern is obtained and the sidelobe level is below 15 dB.

V. CONCLUSION

  • A resonant cavity model has been proposed in order to describe the functioning of AMC surfaces.
  • Full wave results validated the trends predicted from the ray model, with regard to the bandwidth and the center frequency.
  • A new application of AMC ground planes to low-profile highgain planar antennas with PRS superstrate has been presented.
  • A ray model has provided valuable insight into the function of the antenna as a resonant cavity and moreover predicted the existence of quarter wavelength PEC-PMC resonant cavities.
  • Measured and simulated results have been presented and are in good agreement.

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 1, JANUARY 2005 209
Artificial Magnetic Conductor Surfaces and Their
Application to Low-Profile High-Gain Planar
Antennas
Alexandros P. Feresidis, Member, IEEE, George Goussetis, Member, IEEE, Shenhong Wang, and
John (Yiannis) C. Vardaxoglou, Member, IEEE
Abstract—Planar periodic metallic arrays behave as artificial
magnetic conductor (AMC) surfaces when placed on a grounded
dielectric substrate and they introduce a zero degrees reflection
phase shift to incident waves. In this paper the AMC operation of
single-layer arrays without vias is studied using a resonant cavity
model and a new application to high-gain printed antennas is pre-
sented. A ray analysis is employed in order to give physical insight
into the performance of AMCs and derive design guidelines. The
bandwidth and center frequency of AMC surfaces are investigated
using full-wave analysis and the qualitative predictions of the ray
model are validated. Planar AMC surfaces are used for the first
time as the ground plane in a high-gain microstrip patch antenna
with a partially reflective surface as superstrate. A significant re-
duction of the antenna profile is achieved. A ray theory approach
is employed in order to describe the functioning of the antenna and
to predict the existence of quarter wavelength resonant cavities.
Index Terms—Arrays, Artificial magnetic conductors, electro-
magnetic bandgap structures, high-gain antennas, low-profile an-
tennas.
I. INTRODUCTION
O
VER the last few years the electromagnetic band gap
(EBG) properties of passive metallodielectric arrays have
been studied [1]–[4]. The presence of band gaps similar to those
obtained from dielectric photonic crystals [5] has been demon-
strated. Metallodielectric EBG (MEBG) structures have been
used for suppression of surface waves and performance en-
hancement of printed antennas and circuits. In addition, MEBG
arrays have been utilized as partially reflective superstrate
layers for the gain enhancement of simple radiating sources,
such as microstrip patches and waveguide apertures [6]–[8].
Similar implementations using dielectric EBG structures have
also been presented and novel explanations have been given
[9]–[11].
Recently metallic arrays printed on a grounded dielectric sub-
strate and connected to the ground through vias have been pre-
sented as artificial magnetic conductors (AMCs) [12]. Such sur-
faces fully reflect incident waves with a near zero degrees reflec-
tion phase. AMC surfaces have also been produced from sim-
Manuscript received January 15, 2004; revised July 23, 2004. This work was
supported by the Engineering and Physical Sciences Research Council (EPSRC)
of the U.K., under research grant GR/R42580/01.
The authors are with the Wireless Communications Research Group, De-
partment of Electronic and Electrical Engineering, Loughborough University,
Loughborough, LEll 3TU, U.K. (e-mail: a.feresidis@ieee.org).
Digital Object Identifier 10.1109/TAP.2004.840528
ilar structures in the absence of vias, which eases the fabrication
process [13], [14]. Assuming no losses and exactly 0
reflection
phase, the surface is referred to as a perfect magnetic conductor
(PMC), which is complementary to a perfect electric conductor
(PEC). In practice, the reflection phase of AMCs crosses zero
at just one frequency (for one resonant mode). The useful band-
width of an AMC is in general defined as
to on ei-
ther side of the central frequency, since these phase values would
not cause destructive interference between direct and reflected
waves.
Metallic arrays have also been placed over a ground plane in
order to significantly enhance the directivity of simple radiating
sources positioned between the array and the ground [6]–[8].
The structure is based on the formation of a resonant cavity be-
tween the ground plane and the array that acts as a partially re-
flective surface (PRS). While high gain planar antenna designs
have been produced, the antenna profile, which is determined
by the resonance condition of the cavity, has always been close
to half wavelength.
In this paper, a novel resonant cavity approach to the anal-
ysis of AMCs is initially presented using ray theory. This pro-
vides design guidelines and a physical insight into the function
of AMCs. Subsequently, a novel high-gain microstrip patch an-
tenna with PRS superstrate is presented, where an AMC is uti-
lized as ground plane to reduce the antenna profile. The antenna
is also studied using a resonant cavity model with the source
internal to the cavity. By virtue of the AMC ground plane the
resonance condition changes and the thickness of the cavity is
reduced to approximately half. The AMCs considered are com-
prised of a single layer array of patches (in the absence of vias)
printed on a grounded dielectric substrate. Full-wave analysis
and measurements of both the AMC alone and the antenna are
used to validate the assertions of the cavity model.
The organization of the paper is as follows. In Section II a
brief outline of the ray analysis is given and the existence of
quarter wavelength resonant PEC-PMC cavities is predicted.
The ray model for an AMC cavity is also described. In Sec-
tion III, an explanation of AMC surfaces as resonant cavities
is given. Using the ray model, the AMC response is related to
the transmission characteristics of the array alone. A full-wave
study on the AMC performance of square patch arrays is pre-
sented and the ray model predictions are validated. The AMC
bandwidth and the effect of substrate thickness are studied. Sec-
tion IV presents a new application of AMC ground planes to
low profile high-gain antennas. The existence of a quarter wave-
0018-926X/$20.00 © 2005 IEEE

210 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 1, JANUARY 2005
Fig. 1. Resonant cavity formed by (a) PEC and PRS, (b) PMC and PRS, with
excitation inside the cavity.
length resonant cavity antenna predicted by the ray model is
conrmed by full-wave analysis and measurements.
II. A
NALYSIS
A simple geometrical optics model can be used to describe
the function of resonant cavities. The ray optics analysis is
widely used in the description of the FabryPerot interfer-
ometer, which consists of two highly reective surfaces that
form a resonant cavity [15]. This analysis can be carried over
to the design of high-gain microwave antennas. In the past,
highly-directive planar antennas consisting of a ground plane, a
simple radiating source and a partially reective surface (PRS)
as superstrate have been studied using this method [6][8]. In
these studies, surfaces of innite extent have been assumed
(i.e., no edge effects) and higher order mode coupling has
been ignored. Although an approximate analysis, it gave a
valuable insight to the function of highly-directive antennas
as resonant cavities and produced guidelines for successful
designs. The analysis is briey outlined in this section. It is
then used to theoretically predict the existence of a low-prole
highly-directive antenna as a quarter wavelength (instead of
half wavelength) resonant cavity by using a PMC (instead of
PEC) ground plane. In addition, the same ray model is used
in order to obtain an explanation of the function of an AMC
structure as a resonant cavity. For the rst case the excitation
source is considered inside the resonant cavity whereas for the
second case the source is outside the cavity.
The structure shown in Fig. 1(a) is considered. A cavity is
formed by a PEC ground plane and a PRS placed at a distance
. The PRS is assumed to be a homogeneous surface in the anal-
ysis. The antenna function can be described by following the
paths of the waves undergoing multiple reections inside the
cavity. Phase shifts are introduced by the path length, the PEC
and the phase of the reection coefcient of the PRS. The
transmitted power can be derived by considering the interfer-
ence of waves partially transmitted through the PRS. Hence, the
directivity of the cavity at boresight is given by [6][8]
(1)
Fig. 2. Resonant cavity formed by PEC and PRS with excitation outside the
cavity.
where is the complex reection coefcient of the PRS,
, is the free-space wavelength, is the trans-
mitted power and
the power of the excitation source. The res-
onance condition can be easily derived by imposing the phase
difference of the transmitted waves to be zero,
, and
is written
(2)
At resonance maximum boresight directivity is obtained and it
can be derived by substituting (2) into (1)
(3)
This equation expresses the maximum directivity as a function
of the magnitude of the reection coefcient of the PRS. From
the above analysis it can be derived that for a highly reective
surface used as the PRS, with reection phase close to
, the
thickness of the resonant cavity is close to
. For this cavity,
the directivity as obtained from (3) will be very high, since
will be close to 1.
If the PEC in the cavity is now replaced by another cti-
tious ground plane which introduces a phase shift
to inci-
dent waves, the resonance condition becomes
Hence, if the ground plane is a PMC [Fig. 1(b)], i.e., if ,
the resonance condition becomes
(4)
Therefore, a PMC surface with reection phase zero and a
highly reective PRS (with
) would result in a resonant
cavity of thickness approximately
. The above analysis thus
predicts the prole reduction of resonant cavity antennas to
half, by means of replacing the PEC with a PMC ground plane.
Consider now the case where a radiating source is placed out-
side the cavity adjacent to the PRS array (Fig. 2). Following
the paths of the direct and the reected waves and taking into
account the various phase shifts introduced to them, the reso-
nance condition of the cavity can be easily derived. The PEC
introduces a phase shift of
. The PRS introduces a phase shift
equal to the phase of its transmission coefcient,
.If

FERESIDIS et al.: AMC SURFACES AND THEIR APPLICATION TO LOW-PROFILE HIGH-GAIN 211
Fig. 3. (a) Unit cell of square patch array and (b) typical equivalent circuit for
capacitive screen consisting of rectangular patches.
Fig. 4. Transmission/reection phase and magnitude for PRS equivalent
circuit (Fig. 3).
is the phase difference between direct and reected waves, the
resonance condition is written as follows:
(5)
This resonant cavity behaves as a PMC (at normal incidence)
since it reects normal incident waves with zero phase shift.
Consequently, placing a simple point source in close proximity
to the PRS would result in constructive interference between
direct and reected waves at the cavity resonance.
III. P
LANAR AMC S
URFACES
In this section the resonant cavity model is initially employed
to provide with guidelines on the design of AMCs. Full-wave
Floquet modal analysis [3] of periodic metallodielectric PRS
surfaces and AMC structures without vias is carried out in
order to validate the conclusions obtained from the approxi-
mate cavity model. The bandwidth of AMC surfaces is studied
and the effect of the substrate thickness is presented.
A. AMC as Resonant Cavity
A homogenised model for a capacitive PRS screen [Fig. 3(a)]
is employed here to facilitate the analysis. The equivalent cir-
cuit representation of the PRS is shown in Fig. 3(b), where the
conducting element is represented by the inductor
and the
inter-element capacitance by the capacitor
. The complex re-
ection and transmission coefcients obtained from the equiv-
alent circuit are shown in Fig. 4. Similar responses are obtained
Fig. 5. (a) Simulated transmission magnitude and phase of PRS1 and PRS2 (b)
AMC reection responses for same cavity with PRS1 and PRS2, respecively.
from full-wave Floquet modal analysis of innite periodic ar-
rays of conducting elements. While this model does not account
for all the geometrical parameters of the PRS, it is a good rep-
resentation for a wide range of geometries.
According to the ray model presented in Section II (Fig. 2),
a cavity formed by a PEC and a PRS and having external ex-
citation performs as AMC when the resonance condition (5) is
met. Hence, considering (5) as the condition for AMC opera-
tion (normal incidence), a relationship between the transmis-
sion phase of the PRS, the substrate thickness and the center (or
PMC) operating frequency is obtained.
The relation between the PRS characteristics and the func-
tioning of the AMC cavity is demonstrated by means of an ex-
ample which shows that two different PRSs having same reec-
tion and transmission characteristics at frequency
are inter-
changeable in an AMC cavity that operates at
. Fig. 5(a) shows
the reection coefcient (magnitude and phase) of two capaci-
tive screens consisting of square patch arrays [Fig. 3(a)]. The ge-
ometries of the two arrays are:
, for
the rst screen named PRS1 and
,
for the second screen named PRS2. PRS1 resonates at 60.5 GHz
and PRS2 at 26.0 GHz. The reectivity and transmission phase
at 21.7 GHz is identical for the two screens. Fig. 5(b) shows the
full wave simulation results for two AMC cavities of the same
thickness
employing PRS1 and PRS2, respecively. The thick-
ness
has been determined from (5) so that the AMC cavities
operate at 21.7 GHz. In order to have good agreement between

212 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 1, JANUARY 2005
the ray model and the full-wave results, we are working at the
second
rather than the rst resonant mode of
the cavity [see (5)]. As predicted by the ray model, the full wave
AMC responses are centred at the same frequency 21.7 GHz,
where the transmission phase values are common. For different
cavity thickness, each PRS results in different AMC center fre-
quency.
It is worth noting that according to (5), the second resonant
mode of the AMC cavity lies at a frequency approximately three
times that of the rst resonant mode. Thus, the resonant cavity
model provides a new explanation for the large separation be-
tween the rst and second AMC frequencies of grounded square
patch arrays that has also been studied in [14]. Moreover, the low
reection magnitude observed at the second AMC frequency
can be explained by the fact that for increasing
the sidelobes
of the resonant cavity radiation pattern increase, as described in
[6], [7].
B. Bandwidth Considerations
According to (5), for a wideband AMC, an optimum PRS
would require its transmission coefcient phase to linearly in-
crease with frequency with a gradient of
[8]. This would
result in a wideband cavity that would satisfy the resonance
condition (5) for all frequencies. While increasing transmission
phase with frequency is not feasible for a capacitive screen, this
conclusion suggests that among two screens with equal reec-
tivity, greater AMC bandwidth will be observed for the one with
slower varying transmission phase. This is demonstrated using
full wave results in the example mentioned above (Fig. 5). PRS1
has slower transmission phase variation with frequency com-
pared to PRS2 [Fig. 5(a)]. The AMC bandwidth for PRS1 is
30% wider than that of PRS2, for the same substrate thickness
[Fig. 5(b)].
C. Effect of Substrate Thickness
The resonant cavity AMC model predicts that for a xed ca-
pacitive screen with an approximately frequency independent
phase, the AMC frequency decreases as the dielectric thickness
increases. Furthermore, from Fig. 4 it is evident that away from
the array resonance, the PRS phase variation with frequency is
slower, which in turn corresponds to broader AMC bandwidth.
Therefore, in general, with increasing
, the AMC frequency
decreases and the bandwidth is improved. This is also consis-
tent with the analysis of reectarray antennas [16].
The effect of substrate thickness is demonstrated here in
Fig. 6, using full-wave analysis. A parametric study of the
AMC response for a xed square patch PRS is presented. The
dielectric constant of the substrate is 2.2. The trends predicted
from the approximate model are veried. The frequency of the
AMC operation is reduced and the bandwidth is improved with
thicker dielectric substrates.
IV. P
ROFILE REDUCTION OF HIGH-GAIN ANTENNA
The application of AMC surfaces to low-prole high-gain an-
tennas is presented in this section. A broadband AMC surface is
designed based on the methodology of the previous section and
is used as the ground plane of a microstrip patch antenna with
Fig. 6. Parametric study of AMC performance with thickness t of dielectric
slab.
Fig. 7. Reection magnitude and phase of AMC ground plane (normal
incidence).
a PRS superstrate. According to the analysis in Section II the
AMC ground plane in conjunction with a highly reective PRS
superstrate are expected to produce a low-prole (about quarter
wavelength) high-gain planar antenna. Full wave simulations of
the antenna have been carried out prior to the fabrication stage
and are in good agreement with measured results.
A. Design of AMC Substrate and PRS Superstrate
A broadband AMC surface has been designed with a center
frequency (zero degrees phase) at about 14 GHz. The simulated
reection phase response as obtained from Floquet modal anal-
ysis is shown in Fig. 7. Closely packed square patches were
used with unit cell dimensions
,
[Fig. 3(a)]. The patches were printed on a grounded dielectric
slab of thickness
and . The measured
complex reection coefcient of the fabricated surface has been
obtained with reference a solid metal plate at the position of the
array and is shown in Fig. 7. The measured reection magni-
tude is close to 1 as expected from an AMC surface. The simu-
lation is in good agreement with the measured phase response.
A broadband AMC operation is obtained with a
to
bandwidth of more than 30% (about 4.5 GHz).
A highly reective PRS has been produced using a square
patch array printed on a similar dielectric substrate as the AMC
(without the ground plane). The unit cell dimensions are
, . The complex reection coefcient of
the PRS obtained from modal analysis is shown in Fig. 8. High
reectivity values are obtained for a wide range of frequen-
cies. Moreover, the slow variation of the reection phase con-

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  • ...Recently metallic arrays printed on a grounded dielectric substrate and connected to the ground through vias have been presented as artificial magnetic conductors (AMCs) [12]....

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Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of placing a partially reflecting sheet in front of an antenna with a reflecting screen at a wavelength of 3.2 cm and showed that large arrays produce considerably greater directivity but their efficiency is poor.
Abstract: Multiple reflections of electromagnetic waves between two planes are studied, and the increase in directivity that results by placing a partially reflecting sheet in front of an antenna with a reflecting screen is investigated at a wavelength of 3.2 cm. The construction and performance of various models of such arrays is discussed. Thus, for example, a "reflex-cavity antenna" with an outer diameter of 1.88 \lambda and an over-all length of only 0.65 \lambda is described which has half-power beamwidths of 34\deg and 41\deg in the E and H planes, respectively, and a gain of approximately 14 db. It is shown that larger systems produce considerably greater directivity but that their efficiency is poor.

977 citations


"Artificial magnetic conductor surfa..." refers background or methods in this paper

  • ...In addition, MEBG arrays have been utilized as partially reflective superstrate layers for the gain enhancement of simple radiating sources, such as microstrip patches and waveguide apertures [6]–[8]....

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  • ...Metallic arrays have also been placed over a ground plane in order to significantly enhance the directivity of simple radiating sources positioned between the array and the ground [6]–[8]....

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  • ...Moreover, the low reflection magnitude observed at the second AMC frequency can be explained by the fact that for increasing the sidelobes of the resonant cavity radiation pattern increase, as described in [6], [7]....

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  • ...In the past, highly-directive planar antennas consisting of a ground plane, a simple radiating source and a partially reflective surface (PRS) as superstrate have been studied using this method [6]–[8]....

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  • ...Hence, the directivity of the cavity at boresight is given by [6]–[8]...

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Journal ArticleDOI
01 Dec 2001
TL;DR: In this paper, a high gain planar antenna with an optimized partially reflecting surface (PRS) placed in front of a waveguide aperture in a ground plane was investigated, where the antenna performance was initially related to the reflection characteristics of the PRS array following an approximate analysis.
Abstract: A high gain planar antenna has been investigated, using an optimised partially reflecting surface (PRS) placed in front of a waveguide aperture in a ground plane. The antenna performance is initially related to the reflection characteristics of the PRS array following an approximate analysis. The array geometry is optimised using an analytical formula. The optimisation results are verified using a full wave model taking into account the edge effects. The array size for maximum antenna efficiency has also been investigated.

611 citations


"Artificial magnetic conductor surfa..." refers background or methods in this paper

  • ...In addition, MEBG arrays have been utilized as partially reflective superstrate layers for the gain enhancement of simple radiating sources, such as microstrip patches and waveguide apertures [6]–[8]....

    [...]

  • ...Metallic arrays have also been placed over a ground plane in order to significantly enhance the directivity of simple radiating sources positioned between the array and the ground [6]–[8]....

    [...]

  • ...tributes toward a good bandwidth performance for the antenna according to the ray model in Section II and in [8]....

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  • ...According to (5), for a wideband AMC, an optimum PRS would require its transmission coefficient phase to linearly increase with frequency with a gradient of [8]....

    [...]

  • ...In the past, highly-directive planar antennas consisting of a ground plane, a simple radiating source and a partially reflective surface (PRS) as superstrate have been studied using this method [6]–[8]....

    [...]

Journal ArticleDOI
TL;DR: The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles, and the bandwidth limitation of the method is discussed.
Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

594 citations


"Artificial magnetic conductor surfa..." refers background in this paper

  • ...Similar implementations using dielectric EBG structures have also been presented and novel explanations have been given [9]–[11]....

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Frequently Asked Questions (9)
Q1. What contributions have the authors mentioned in the paper "Artificial magnetic conductor surfaces and their application to low-profile high-gain planar antennas" ?

In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. 

According to (5), for a wideband AMC, an optimum PRS would require its transmission coefficient phase to linearly increase with frequency with a gradient of [8]. 

Following the paths of the direct and the reflected waves and taking into account the various phase shifts introduced to them, the resonance condition of the cavity can be easily derived. 

A ray model has provided valuable insight into the function of the antenna as a resonant cavity and moreover predicted the existence of quarter wavelength PEC-PMC resonant cavities. 

The reflection coefficient at 14 GHz is about 0.43 dB. Following (3) of the ray model a maximum antenna directivity of about 20.5 dBi is expected. 

A microstrip patch antenna (6 mm 4.5 mm) has been designed as the primary feeder of the resonant cavity and fabricated using the AMC ground plane . 

Ifis the phase difference between direct and reflected waves, the resonance condition is written as follows:(5)This resonant cavity behaves as a PMC (at normal incidence) since it reflects normal incident waves with zero phase shift. 

the directivity of the cavity at boresight is given by [6]–[8](1)where is the complex reflection coefficient of the PRS, , is the free-space wavelength, is the transmitted power and the power of the excitation source. 

from Fig. 4 it is evident that away from the array resonance, the PRS phase variation with frequency is slower, which in turn corresponds to broader AMC bandwidth.