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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 46, NO. 11, NOVEMBER 1998 1757

A Novel Integrated Antenna for Millimeter-Wave

Personal Communications Systems

K. Hettak, G. Delisle, and M. Boulmalf

Abstract This paper presents the design and experimental resultsof a coplanar waveguide (CPW) aperture-coupled patch antenna for

the extremely high frequency (EHF) band around a center frequency

of 37 GHz. The antenna is implemented on a high dielectric constantsubstrate ( "

r

= 9 : 9 ) , which is close to the dielectric constant of GaAs anddemonstrates the feasibility of integration of such an antenna structureinto monolithic circuits. The major advantage of this configuration isthat the reverse side of the antenna can be used for the active and feedcomponents. The antenna structure combines the advantages of CPWwith the those of the aperture-coupled microstrip antenna and simplifiesthe structure of the antenna by reducing the number of metallization level,from three down to two. In addition, this type of coupling is advantageouswhen applied to millimeter-wave monolithic phased arrays. A unique feed

design eliminates the competition for surface space between the antennaelements and the feed network. In addition, the ground plane shieldsthe antenna half-space from spurious radiation emitted by feed lines

and active devices. Finally, aperture coupling avoids problems associatedwith probe feeds at millimeter-wave frequencies, such as complexity ofconstruction and large probe self reactances. This new type of antennaopens the ways to a large number of a new possibilities such as active

antennas for millimeter-wave personal communications using monolithicmicrowave integrated circuits (MMICs) on the same substrate and acombination of optical and radio transmission.

Index TermsCoplanar waveguides, microstrip antennas.

I. INTRODUCTION

The development of appropriate antennas and associated technol-

ogy will be important to the success of millimeter-wave wireless

personal communication systems. Research in these areas and also

on the processes of indoor propagation has been carried out [1] with

particular emphasis on integrating antennas with multifunction GaAs

monolithic microwave integrated circuits (MMICs). The choice

between antenna and circuit type depends on many factors such

as the intented application, the type of device being used andconsiderations involving unwanted radiation from the circuit elements

and the significance of substrate surface modes. As it is well known,

planar antennas consisting of patches, dipoles or slots, fed by a

microstrip transmission line, are extremely useful due to their low

cost, light weight, and flexibility of design. In general, a combination

of slot and patch antennas lead to convenient geometries. Of these

the most likely candidate for integration with GaAs MMICs is the

coplanar waveguide (CPW) aperture-coupled patch antenna that uses

a single substrate. Indeed, for components including active devices, in

particular, MMICs, the popularity of CPW has increased significantly

in recent years because the advantages of CPW like wider bandwidth,

smaller mutual coupling between two adjacent lines, and easier

integration with solid-state active devices on one side of the planar

substrate, thus avoiding via hole connections. Over the past few years,a considerable number of studies have been carried out on the linearly

polarized antennas, loop antennas, and slot antennas [2], but only a

few attempts have so far been made at realizing antenna patch fed

by CPW in the millimeter-wave region. In light of this, considering

Manuscript received November 4, 1997; revised July 13, 1998.The authors are with the Personal Communication System Group, INRS-

Telecommunications, Ile des Soeurs, Quebec, H3E 1H6 Canada.Publisher Item Identifier S 0018-926X(98)08904-2.

Fig. 1. Layout of the test-patch antenna and feeder network.

the recent development that shows that microstrip patch antennas can

be coupled with CPW transmission lines [3][7] via a slot in the

ground plane, a new structure of the printed antenna fed by CPW

that conjugates the advantage of aperture-coupled microstrip antenna

and the wide range of flexibility is proposed using the innovationthat uniplanar technology offers.

Indeed, the patch antenna is an extremely useful configuration for

millimeter-wave wireless applications. When the patch is excited

by CPW, a CPW to slotline junction is required to ensure the

antenna works at high efficiency. The paper proposes the use of

the CPW stub patterned on the center conductor to obtain optimum

matching. It is important to note that the design of CPW coupled

microstrip patch antenna with the CPW series stub within the center

conductor leads to greater field confinement resulting in suppression

of spurious radiation emitted by this stub and provides both low

loss and longitudinal symmetry whose eliminates the need for air

bridges. This arrangement provides additional degrees of freedom

compared to classical topologies resulting in extremely compact con-

figuration. The feasibility of integrating this novel antenna topologyon high-dielectric constant substrate

( "

r

= 9 : 9 )

, which is close to

the dielectric constant of GaAs in millimter wave region is also

demonstrated. The measured results shows the usefulness of the

proposed antenna configuration and the effectiveness of uniplanar

technology both in terms of performance and cost.

II. ANTENNA TOPOLOGY

As the popularity of the CPW transmission line has increased

significantly in recent years, antenna elements that are suitable for

CPW feed configuration have also become important. In light of

this, design guidelines for the CPW-fed patch antenna is presented

herein. The configuration of the proposed slot-coupled planar antenna

is illustrated in Fig. 1. A rectangular microstrip patch is placed on oneside of the substrate, while a slot fed by a coplanar line is arranged

opposite to the patch in the ground plane on the other side of the

substrate. A CPW stub patterned in the ground plane is used as

matching network. Furthermore, the design of the aperture-coupled

patch elements involves the following steps: first, the dimensions

of the antenna patch are determined by a cavity model [2] to be

resonant at the operational frequency of 38 GHz. The side length

of the squared patch is found to be 1.1 mm. The width of the

aperture (slot) is chosen to be 0.1 mm. It has to be large enough to

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1758 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 46, NO. 11, NOVEMBER 1998

Fig. 2. Experimental results for CPW-fed microstrip antenna with CPW stub patterned in the center conductor.

enable good electromagnetic coupling through the slot. The length

has been chosen to be less than s = 2

( s

is the wavelength in

the slot) in order to get a low level of back radiation because

the radiation due to the slot increases as its lengthL s

approaches

s

= 2

. For maximum coupling, the patch should be centered over theslot on one side and, on the other, the feed should be positioned

perpendicular to the slot at its center. The tuning stub with a CPW

open circuited stub patterned in the center conductor is used to

tune the excess reactance of the slot-coupled patch [2]. The stub

length is approximately 0.25 g

. The length of the CPW opened

stub is found to be 0.8 mm. The proposed antenna is optimzed

using electromagnetic simulator (momentum tools from Hewlett-

Packard).

The antenna structure developed in the paper combines the ad-

vantages of CPW with the advantages of aperture-coupled microstrip

antenna and simplifies the structure of the antenna by reducing the

number of metallization level, from three down to two, thereby

making easier the integration of the active devices. The proposed

feeding system has been experimentally investigated and the couplingbetween of a CPW feed line and radiating element is accomplished

with slotline resonator. This type of coupling is advantageous when

applied to millimeter-wave monolithic phased arrays. This feed

design eliminates the competition for surface space between the

antenna elements and the feed network. In addition, the ground

plane shields the antenna half-space from spurious radiation emit-

ted by feed lines and active devices. Finally, aperture coupling

avoids problems associated with probe feeds at millimeter-wave

frequencies, such as complexity of construction and large probe

self-reactances. In the past, electromagnetic coupling was achieved

through an aperture in the common ground plane separate the

microstrip feed-line and patch-antenna circuits [2]. This required

separate substrates, which led to more complex construction, heavier

circuits, and difficulty in MMIC implementation, which typically usesonly one GaAs substrate.

III. EXPERIMENTAL RESULTS

The circuit was implemented on high-dielectric constant substrate

"

r

= 9 : 9

,h = 0 : 2 5 4

mm and to demonstrate the feasibility of

integrating this antenna structure into monolithic circuits. The novel

CPW-fed patch antenna operates at 36.84 GHz. The measured return

loss and normalized input impedance as a function of the frequency of

this structure are shown in Fig. 2. A fairly good matching is obtained,

namelyS

1 1

= 0 4 2

dB atf

1

= 3 6 : 8 4

GHz. The bandwidth at the

resonance frequency is around 1 GHz forV S W R