Microstrip patch antenna array

A microstrip patch antenna array incorporating a plurality of spaced-apart patch radiating elements electromagnetically coupled to a microstrip line conductively coupled to a source of signals. Both the spaced-apart patch radiating elements and the microstrip line are located on the same side of an adjacent conductive substrate. The microstrip patch radiating elements are arranged in a linear co-planar array electromagnetically excited by the field created by the air substrated microstrip line passing adjacent thereto.

FIELD OF THE INVENTION 
The present invention relates to antennas and more particularly to 
microstrip patch antenna arrays for use in wireless antenna 
telecommunications. 
BACKGROUND OF THE INVENTION 
Microstrip patch antennas are desirable structures for use in wireless 
telecommunications, particularly in view of their compactness, 
conformability, and general ease of fabrication. One major disadvantage of 
such structures has been a narrow bandwidth. A variety of approaches have 
been utilized in an effort to expand the bandwidth of such structures. 
For example, it is known that bandwidth can be increased by increasing the 
thickness of the microstrip antenna patch substrate, or by introducing 
parasitic elements of varying size above and/or below the driven element. 
The addition of parasitic elements stacked above and/or below the driven 
element to increase the bandwidth is less desirable in some cases because 
of the physical structure that is required. 
It would be desirable therefore to produce a microstrip antenna structure 
that would provide the desired broad bandwidth without the disadvantage of 
having a physical structure that creates a problem respecting the ability 
to mount it on various support structures or becomes too large in size. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is disclosed a microstrip 
patch antenna array incorporating a plurality of spaced-apart patch 
radiating elements which are electromagnetically coupled to a microstrip 
line which is connected to a source of signals through an appropriate 
cable connection. Both the spaced-apart patch radiating elements and the 
microstrip line are located on the same side of an adjacent conductive 
substrate. The microstrip patch radiating elements are arranged in a 
linear co-planar array electromagnetically excited by the field created by 
the air substrated microstrip line passing adjacent thereto. 
By utilizing the electromagnetic coupling between the microstrip line and 
the microstrip patch radiating elements, the configuration and structure 
of the antenna array incorporating the present invention can be 
considerably simplified, and the cost of construction reduced. 
In an antenna array incorporating the present invention, a microstrip line, 
conductively connected to a feed line such as a coaxial cable, is disposed 
on one side of a conductive substrate which typically acts as a ground 
plane element and is spaced therefrom. An array of microstrip patch 
radiating elements are spaced apart one from the other and disposed on the 
opposite side of the microstrip line from the ground plane and spaced 
therefrom. The microstrip patch elements are electromagnetically excited 
by the fringing field produced by the microstrip line and are not 
conductively connected thereto. 
Typically, each of the spaced-apart radiating elements is rectangular in 
shape. A generally central U-shaped slot formed in each of the microstrip 
patch radiating elements separates each radiating element into a radiating 
portion, and a coupling portion. The microstrip line passes on one side of 
each of the patch radiating elements, and directly beneath the inner 
coupling portions of each microstrip patch element. 
The patches can be configured to be excited for 90.degree. azimuth 3 db 
beam width or 60.degree. azimuth 3 db beam width. For a 90.degree. azimuth 
3 db beam width, the sides of each rectangular patch element oriented 
generally parallel to the microstrip line and disposed on either side 
thereof are longer than the sides interconnecting them and traversing the 
microstrip line. For a 60.degree. azimuth 3 db beam width, the sides of 
each rectangular patch element oriented generally parallel to the 
microstrip line are shorter than the sides interconnecting them and 
traversing the microstrip line. 
More specifically, the antenna array incorporating the present invention 
utilizes a co-planar array of a plurality of radiating elements each 
divided into a generally centrally disposed coupling portion and an outer 
radiating portion surrounding the coupling portion. The two portions are 
formed and separated by a generally U-shaped slot with the boundary 
therebetween extending between the free ends of the U-shaped slot. The 
base of the U-shaped slot is oriented transverse to the microstrip line 
and extends thereover with the microstrip line passing under and generally 
bisecting the coupling portion of each radiating patch element. 
The width of the coupling portion, the distance from the boundary area to 
the adjacent edge of the radiating element, the spacing between the 
microstrip line and the ground plane all contribute to defining the 
characteristic input impedance for each of the radiating elements and the 
antenna array. 
A feed cable, such as a coaxial cable, is connected to the elongated 
microstrip line at a feed point located intermediate its ends. When the 
orientation of the microstrip patch radiating elements on one side of the 
feed point is opposite to the orientation of the microstrip patch 
radiating elements on the other side of the feed point, the microstrip 
patch radiating elements are spaced from the feed point by distances 
generally equal to an odd number of quarter wavelengths for the center 
frequency at which the antenna array is intended to operate so as to 
produce signals in phase. When the orientation of the microstrip patch 
radiating elements on one side of the feed point is the same as the 
orientation of the microstrip patch radiating elements on the other side 
of the feed point, the microstrip patch radiating elements are spaced from 
the feed point by distances generally equal to an odd number of half 
wavelengths for the center frequency at which the antenna array is 
intended to operate so as to produce signals in phases. The exact 
positions may vary depending upon a number of factors, including the size 
and/or shape of the patch radiating elements. 
By electromagnetically coupling the microstrip line to the radiating 
elements, the entire structure can be disposed internally of the ground 
plane and enclosed therein. A minimum amount of direct electrical 
connections and components requiring such connections are utilized. The 
relative position of the components can be defined relative to the feed 
point along the length of the microstrip line. An additional impedance 
matching element can be attached to the microstrip line intermediate one 
or more pairs of the microstrip patches in order to provide for any 
necessary impedance adjustment. 
A microstrip patch antenna array incorporating the present invention 
operating in the 1.6-2.1 GHz frequency range exhibits at a VSWR below 
1.3:1 over a bandwidth of about 200-300 Mhz and a twenty percent (20%) 
bandwidth for VSWR below about 1.5:1. An antenna having such a bandwidth 
is particular suitable for use in the new personal communication 
applications operating at these frequency ranges and is capable of 
providing and interacting with signals over a desired bandwidth. 
Antennas incorporating the present invention are capable of operating at a 
total power of 200-250 watts in the 1.6-2.1 GHz frequency range, and can 
be readily mounted on any suitable support structure such as a mast or the 
surface of any structure. The utilization in antennas incorporating the 
present invention of electromagnetic coupling and the location of 
substantially all of the components thereof on the same side of the ground 
plane provides for a compact efficient structure capable of a wide range 
of uses. 
Numerous other features and advantages of the present invention will become 
readily apparent from the following detailed description of the invention 
and an embodiment thereof, from the claims, and from the accompanying 
drawings in which the details of the invention are fully and completely 
disclosed as a part of this specification.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A microstrip patch antenna array 10 incorporating the present invention 
includes a conductive substrate 12 which acts as a ground plane for the 
array. The conductive substrate 12 includes a generally rectangular base 
portion 14, a pair of raised side walls 16 extending up from the opposite 
sides thereof, and a pair of raised end walls 18 extending up from the 
opposite ends thereof. 
The antenna array 10 includes a generally rigid, elongated microstrip line 
20 extending substantially the length of the conductive substrate 12 and 
which is spaced away from the base portion 14 by conductive spacers 22 
located at either end thereof. Suitable fasteners 24 passing through the 
base of the conductive substrate or ground plane and the spacers 22 retain 
the microstrip line 20 in place. 
The microstrip line 20 is centered between the side walls 16 and extends 
generally along the center line of the conductive substrate 12. The 
antenna array 10 is connected to a suitable transceiver (not shown) by 
means of an appropriate cable such as a coaxial cable. The cable may pass 
directly through the base of the conductive substrate 12 for connection to 
the microstrip line 20 or may be connected to a coaxial connector 25 
having an outer or shield contact or conductor 26 attached to and 
electrically connected to the conductive substrate and a center contact or 
conductor 28 passing through and insulated from the conductive substrate 
12 and connected to the microstrip line 20 at feed point 30. 
A plurality of microstrip patch radiating elements 32 are disposed along 
the length of the microstrip line 20 and are centered with respect 
thereto. Each of the microstrip patch radiating elements 32 is formed as a 
rectangle having a generally centrally located coupling portion 34 defined 
by a U-shaped slot 36 having legs 36a and a base 36b, and an outer 
radiating portion 38 surrounding the coupling portion 34. The boundary 40 
between the coupling portion 34 and the radiating portion 38 extends 
between the free ends of the legs 36a of the U-shaped slot 36. 
The coupling portion 34 of each of the patch radiating elements 32 is 
located and centered over the microstrip line 20 and is generally bisected 
thereby. The base 36b of the U-shape cut-out 36 traverses the microstrip 
line 20, and the legs 36a extend parallel thereto on either side thereof 
and are equally spaced therefrom. 
The microstrip patch radiating elements 32 are disposed on the opposite 
side of the microstrip line 20 from the conductive substrate 12 and are 
supported in position by suitable insulated spacers 42, there being a pair 
of spacers for each patch radiating element 32. An impedance adjusting 
component or tuning member 44 is attached to the microstrip line 20 
between the feed point 30 and an adjacent one of the patch radiating 
elements 32. 
The feed point 30 is spaced from the center 32a of each of the patch 
radiating elements 32 by an odd integral number of quarter-wave lengths to 
provide correct phase coupling between the microstrip line 20 and each of 
the patch radiating elements 32. In the embodiment shown in the drawing, 
the bases 36b of the U-shaped slots 36 for each of the patch radiating 
elements on either side of the connection point are oriented closest to 
the feed point 30. In this configuration, the distance between the feed 
point 30 and the center 32a of each of the patch radiating elements 32 is 
an odd number of quarter-wave lengths; and the difference between the 
distance on either side of the connection point differing by one-half 
wavelength in order that all of the patch radiating elements are excited 
in phase. 
Thus, the distance between the center 32a of the closest patch radiating 
element and the feed point 30 is approximately one-quarter of a 
wavelength, and the distance between the feed point 30 and the center 32a 
of the closest patch radiating element on the other side of the feed point 
is about three-quarters of a wavelength. The inter-element spacing between 
the patch radiating elements, the distance between the centers 32a, on 
each side of the connection point is approximately one wavelength. 
It should be appreciated if either pair of the patches is reversed so that 
all the boundaries are in the same relative position, the positions would 
have to be adjusted by a half wave-length in order to maintain the proper 
phase. 
The input impedance of the antenna array can be slightly adjusted by an the 
adjusting or tuning member 44 which is shown as a metal plate 
approximately one inch square disposed between the feed point 30 and one 
of the adjacent patch radiating elements 36. The impedance is adjusted by 
bending the plate 44 towards and away from the conductive substrate 12 
until the proper tuning can be achieved. Typically, the plate is oriented 
at about a 45.degree. angle on either side of the microstrip line although 
the location and angle does not appear to be critical. 
All of the components of the antenna array 10 can be enclosed by a suitable 
non-conductive cover 46, typically made of plastic, which may also serve 
the purpose of protecting the antenna array and its components from the 
effects of exposure to weather after installation. The shape of the cover 
is not critical and can be selected to provide a pleasant and decorative 
appearance. 
In one embodiment of a microstrip patch antenna array incorporating the 
present invention adapted for use in the frequency range of between about 
1.6 GHz and about 2.1 GHz, the components were constructed with the 
following dimensions. 
The microstrip line 20 was constructed from a 0.19 inch square metal rod 
and had a length of about 23.3 inches. The feed point 30 was located about 
10 inches from one end and about 13.3 inches from the other. 
Each of the rectangular patch radiating elements 32 was constructed from a 
metal sheet having a thickness of about 0.062 inch and a dimension of 
about 2.60 inches by about 4.0 inches, with the shorter sides extending 
parallel to the microstrip feed line 20. The width of the coupling portion 
of each of the rectangular patch radiating elements 32 was about 0.875 
inch and the distance between the boundary 40 and the adjacent edge of the 
radiating element was about 0.8 inch. The spacing between the boundaries 
40 of the patch radiating elements was about 6.6 inches. 
The spacing between the microstrip feed line and the conductive substrate 
12 was about 0.335 inch and the spacing between each of the patch 
radiating elements 32 and the conductive substrate 12 was about 0.675 
inch. 
An antenna so constructed for use in the frequency range set forth above 
exhibited a VSWR less than 1.5:1 over a bandwidth of at least about twenty 
percent (20%) and a VSWR less than 1.3:1 over bandwidth in excess of 200 
MHz or in excess of about sixteen percent (16%). 
Thus, there has been disclosed a microstrip patch antenna array in which 
all of the components are disposed internally of the structure and can be 
protected from the elements by virtue of an appropriate cover in which a 
single conductive connection is provided for coupling the transceiver to 
the antenna array and in which the radiating microstrip patch elements are 
electromagnetically excited by the fringing field created by the air 
substrated microstrip line running between and extending between the 
patches and the adjacent conductive substrate. 
The excited patch radiating elements produce and radiate the energy into 
free space with the desired bandwidth characteristics to enable the 
antenna incorporating the present invention to be used in a variety of 
applications. For example, the microstrip patch antenna array 
incorporating the present invention is particularly useful for operation 
in conjunction with personal communications networks (PCN), in the 1.6-2.1 
frequency range, or for cellular wireless mobile communications in the 
800-1000 MHz frequency range. 
From the foregoing, it will be observed that numerous modifications may be 
effected without departing from the true spirit and scope of the novel 
concept of the invention. It should be understood that no limitation with 
respect to the specific apparatus illustrated herein is intended or should 
be inferred. It is, of course, intended to be covered by the appended 
claims, and all such modifications as fall within the scope of the 
appended claims.