Increased bandwidth patch antenna

An increased bandwidth patch antenna which includes first and second arms spaced by an air gap. The first and second arms are electrically connected by a bridge. A ground plane, which is approximately parallel to the first and second arms, is separated from the first and second arms by a dielectric substrate. In one embodiment of the present invention, the first arm is a radiating arm and the second arm is a tuning arm. By varying the length of the tuning arm, the bandwidth of the antenna is increased. The second arm, which also acts as a parasitic arm of the first arm, increases the gain of the antenna. A signal unit is electrically coupled to the bridge. The signal unit transmits and/or receives signals having a selected frequency band. The antenna resonates at the selected frequency band.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
The present invention relates generally to antennas and, more specifically, 
to an increased bandwidth patch antenna. 
II. Description of the Related Art 
Antennas are an important component of wireless communication systems. 
Although antennas may seem to be available in numerous different shapes 
and sizes, they all operate according to the same basic principles of 
electromagnetics. An antenna is a structure associated with a region of 
transition between a guided wave and a free-space wave, or vice versa. As 
a general principle, a guided wave traveling along a transmission line 
which opens out will radiate as a free-space wave, also known as an 
electromagnetic wave. 
In recent years, with the rise in use of personal communication devices, 
such as PCS phones, cellular phones and other communication devices, the 
need for small antennas that are suitable for use in personal 
communication devices has increased. An important factor to be considered 
in designing antennas for personal communication devices is the radiation 
pattern. In most applications, the communication device must be able to 
communicate in all directions. Therefore, the device must receive and 
transmit signals effectively in all directions. Consequently, in personal 
communication devices, it is essential that the antenna has an 
omnidirectional radiation pattern. Furthermore, the antenna must be 
compact in size in order to be suitable in a personal communication 
device. 
One antenna commonly used in personal communication devices is the whip 
antenna. There are, however, several disadvantages associated with the 
whip antenna. Often, the whip antenna is subject to damage by catching on 
things. Even when the whip antenna is designed to be retractable in order 
to prevent such damage, it consumes scarce interior space. This results in 
less interior space being available for advanced features and circuits. 
Also, as personal communication devices such as cellular phones become 
smaller, the ability to use the whip antenna efficiently is being 
challenged. 
Another antenna which may also be suitable for use in personal 
communication devices is the patch or microstrip antenna. The patch 
antenna was originally developed in the late 1960's for use with aircraft, 
missiles and other military applications requiring a thin or low-profile 
antenna. These applications required that the antenna neither disturb the 
aerodynamic flow nor protrude inwardly to disrupt the mechanical 
structure. The patch antenna satisfied these requirements. 
The bandwidth of a patch antenna is proportional to the thickness of the 
dielectric substrate used. The thicker the substrate, the wider the 
antenna's bandwidth. In order to maintain desired bandwidth of personal 
communication devices, current patch antennas must have relatively thick 
substrates, which make them relatively bulky for personal communication 
devices. Since antennas in personal communication devices are required to 
be quite small in size, they would typically have thin substrates. 
Consequently, they would also have narrow bandwidth. Unfortunately, a 
narrow bandwidth restricts the utility of the antenna to a narrow 
frequency band. An increased bandwidth would allow personal communication 
devices to operate over a wider frequency band. 
SUMMARY OF THE INVENTION 
The present invention is directed to an increased bandwidth patch antenna. 
According to the present invention, the patch antenna includes a conductor 
plate having first and second arms. The first and second arms are spaced 
by an air gap. A bridge connects the first and second arms. A ground plane 
which is approximately parallel to the conductor plate is separated from 
the conductor plate by a dielectric substrate. 
According to one embodiment of the present invention, the first arm is a 
radiating arm and the second arm is a tuning arm. The length of the 
radiating arm is set in relation to the wavelength .lambda. associated 
with the resonant frequency f.sub.0. Commonly used lengths are .lambda., 
.lambda./.sub.2 and .lambda./.sub.4, although other lengths are possible. 
The length of the second arm is longer or shorter than that of the first 
arm. By varying the length of the second arm, the bandwidth of the antenna 
is increased. Furthermore, the second arm acts as a parasitic arm of the 
first arm, which increases the gain of the antenna. The parasitic arm also 
increases the bandwidth of the antenna by increasing its overall volume. 
In another embodiment of the present invention, dual band operation is 
achieved by exciting the second arm by a second frequency band while the 
first arm is also being excited by a first frequency band. In this 
embodiment, the first and second arms are each excited with separate 
frequency bands. The first arm acts as a first active radiator and the 
second arm acts as a first tuning arm. Likewise, the second arm acts as a 
second active radiator and the first arm acts as a second tuning arm. The 
length of the first arm is set in relation to the first frequency band, 
while the length of the second arm is set in relation to the second 
frequency band. 
One advantage of the present invention is that it provides an increased 
bandwidth and increased gain over conventional patch antennas. Another 
advantage of the present invention is that it provides dual frequency band 
operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
1. Overview and Discussion of the Invention 
As discussed earlier, the patch antenna was originally developed in the 
late 1960's for use with aircraft, missiles and other military 
applications requiring a thin or low-profile antenna. These applications 
required that the antenna neither disturb the aerodynamic flow nor 
protrude inwardly to disrupt the mechanical structure. The patch antenna 
satisfied these requirements. 
These characteristics that make the patch antenna suitable for use in 
aircraft and missiles also make it suitable for use in hand-held and 
mobile personal communication devices. For example, the patch antenna can 
be built on the top surface of a personal communication device such as a 
cellular phone, or to a surface of a vehicle carrying a personal 
communication device, or built or mounted on some other device. This means 
that it can be manufactured with increased automation and decreased manual 
labor of installation. This decreases costs and increases reliability. 
Also, unlike the whip antenna, the patch antenna is less susceptible to 
damage by catching on things because it has a very low profile. 
Furthermore, since the patch antenna can be built on the personal 
communication device's top surface, it will not consume interior space 
which is needed for advanced features and circuits. 
In addition, the patch antenna possesses other characteristics which make 
it suitable in personal communication devices. For example, the 
quarter-wave patch antenna, which is a version of a patch antenna, 
radiates an omnidirectional pattern into space above the ground plane, 
which makes it suitable in personal communication devices. Also at the 
frequency band over which the personal communication devices operate, the 
length of the quarter-wave patch antenna is quite short. 
The bandwidth of the patch antenna is proportional to the thickness of the 
dielectric substrate used. The thicker the substrate, the wider the 
antenna's bandwidth. In order to maintain desired bandwidth of personal 
communication devices, current patch antennas must have relatively thick 
substrates, which make them relatively bulky for personal communication 
devices. Since antennas in personal communication devices are required to 
be quite small in size, they typically have thin substrates. Consequently, 
they have narrow bandwidth. Unfortunately, a narrow bandwidth restricts 
the utility of the antenna to a narrow frequency band. An increased 
bandwidth would allow the personal communication devices to operate over a 
wider frequency band. 
The present invention provides a solution to this problem. The present 
invention allows a patch antenna to have increased bandwidth without 
requiring an increase in the thickness of its dielectric substrate. This 
allows the patch antenna to have a relatively small overall size, which 
makes it suitable in personal communication devices. 
According to the present invention, the patch antenna includes a conductor 
plate having first and second arms. The first and second arms are 
approximately planar to each other and are spaced by an air gap. A bridge 
connects the first and second arms. A ground plane which is approximately 
parallel to the conductor plate is separated from the conductor plate by a 
dielectric substrate. 
In one embodiment of the present invention, the first arm is a radiating 
arm and the second arm is a tuning arm. By varying the length of the 
tuning arm, the bandwidth of the antenna is increased. The second arm acts 
as a parasitic arm of the first arm, which increases the gain of the 
antenna. The parasitic arm also increases the bandwidth of the antenna by 
increasing the overall volume of the antenna. 
The length of the radiating arm is set in relation to the wavelength 
.lambda. associated with the resonant frequency f.sub.0. Commonly used 
lengths are .lambda., .lambda./2 and .lambda./4, although other lengths 
are possible. 
The present invention is described in connection with a patch antenna 
having a length of .lambda./4, also known as a quarter-wave patch antenna. 
Although the present invention is described in connection with the 
quarter-wave patch antenna, its utility is not restricted merely to the 
quarter-wave patch antenna. In fact, those skilled in the art will 
recognize that the present invention may be utilized in a patch antenna 
having any length, such as a full-wave, half-wave or n.lambda./4, where n 
is an integer. 
2. Example Environment 
Before describing the invention in detail, it is useful to show an example 
environment in which the invention can be implemented. In a broad sense, 
the invention can be implemented in any personal communication device. One 
such environment is a portable telephone, such as that used for cellular, 
PCS or other commercial service. 
FIG. 1 illustrates a portable phone 100. Specifically, FIG. 1 includes a 
patch antenna 104, a speaker 108, a microphone 112, a display 116 and a 
keyboard 120. 
Antenna 104 is built into the top surface of portable phone 100. Since 
antenna 104 has a very low profile, it is not subject to damage by 
catching on things. Also, unlike a retractable whip antenna, antenna 104 
does not consume interior space in portable phone 100. This results in 
more interior space being available for advanced features and electronics. 
The present invention is described in terms of this example environment. 
Some specific application examples are discussed in terms of cellular and 
PCS frequencies. Description in these terms is provided for convenience 
only. It is not intended that the invention be limited to application in 
this example environment. In fact, after reading the following 
description, it will become readily apparent to a person skilled in the 
relevant art how to implement the invention in alternative environments, 
such as, for example, in automobiles, truck-trailer, other types of 
vehicles and hand-held devices. 
3. A Conventional Quarter-Wave Patch Antenna 
FIG. 2 illustrates a conventional quarter-wave patch antenna 200. 
Specifically, FIG. 2 includes a conductor plate 204, a dielectric 
substrate 208, a ground plane 212 and a signal unit 216. 
The length l of antenna 200 determines its resonant frequency. As a general 
rule, quarter-wave patch antenna 200 having a length l resonates at a 
frequency of c/(4l), where c is the speed of light. Thus, the resonant 
frequency of quarter-wave patch antenna 200 can be selected by selecting 
l. At or near the resonant frequency, quarter-wave patch antenna 200 
radiates most effectively. Consequently, quarter wave patch antenna 200 is 
designed to operate at or near the resonant frequency. For example, at an 
operating frequency of approximately 1.9 GHz (PCS frequency), the 
wavelength .lambda. of the radio signal is approximately 7 inches. Thus, 
the length of antenna 200 is approximately 1.75 inches. 
The height of antenna 200 is determined by the thickness t of dielectric 
substrate 208. The selected value of t is based on the bandwidth over 
which antenna 200 must operate. In addition, there are other factors which 
impact the value of t. If t is too large, the overall size of antenna 200 
becomes too large, which makes antenna 200 undesirable for personal 
communication devices. Also, if t is too large, surface wave modes are 
excited which degrades the performance of antenna 200. If, on the other 
hand, t is too small, conductor plate 204 is too close to ground plane 
212. This causes the surface current induced in ground plane 212 to be too 
strong which causes high ohmic loss. As a result, the efficiency of 
antenna 200 is degraded. In practice, the thickness t of dielectric 
substrate 208 is held at less than or equal to one-tenth of the wavelength 
in dielectric substrate 208 or .lambda..sub.g /.sub.10, where 
.lambda..sub.g =.lambda..sub.0 /.sqroot..epsilon..sub.eff, .lambda..sub.0 
is the wavelength in air and .epsilon..sub.eff is the dielectric constant 
in dielectric substrate 208. 
The width w of antenna 200 should be less than a wavelength so that 
higher-order modes will not be excited. Moreover, in order to make the 
antenna suitable for a personal communication device, the width is usually 
kept relatively small. 
Ground plane 212 is typically made of a conductive material such as gold, 
silver, copper, aluminum or brass. Other conductive materials may also be 
used. Ground plane 212 is separated from conductor plate 204 by dielectric 
substrate 208 and is approximately parallel to conductor plate 204. One 
end of conductor plate 216 is electrically connected to ground plane 212. 
A probe is electrically connected to conductor plate 212. The probe, which 
may be a coaxial cable, passes through ground plane 212 and meets 
conductor plate 204 near an end. The probe couples signal unit 216 to 
conductor plate 204. Signal unit 216 provides a signal of a selected 
frequency band to conductor plate 204, which creates a surface current in 
conductor plate 204. The density of the surface current is high near the 
region of conductor plate 204 where the probe meets conductor plate 204 
and decreases gradually along the length of conductor plate 204 in the 
direction away from the point where the probe meets conductor plate 204. 
In fact, the surface current is concentrated in the first half of 
conductor plate 204 and is negligible in the second half. 
As discussed earlier, an increase in bandwidth of the quarter-wave patch 
antenna is desired. An increase in bandwidth of the antenna would enable a 
personal communication device to operate at a wider range of frequency. 
4. Increased Bandwidth Patch Antenna 
The present invention achieves an increase in bandwidth over conventional 
patch antennas while retaining characteristics that are desirable for 
personal communication devices. The present invention is now described 
with reference to FIG. 3. FIG. 3 illustrates an increased bandwidth patch 
antenna 300 in accordance with one embodiment of the present invention. 
The embodiment illustrated in FIG. 3 is a quarter-wave patch antenna. 
Specifically, the embodiment illustrated in FIG. 3 comprises a conductor 
plate 304 having first and second arms 308 and 312, a ground plane 316, a 
dielectric substrate 320, a bridge 324, a probe 328 and a signal unit 332. 
Note that signal unit 332 is used herein to refer to the functionality 
provided by a signal source and/or a signal receiver. Whether signal unit 
332 provides one or both of these functionalities depends upon how antenna 
300 is configured to operate. Antenna 300 described herein could, for 
example, be configured to operate solely as a transmitter, in which case 
signal unit 332 operates as a signal source. Alternatively, signal unit 
332 operates as a signal receiver when antenna 300 is configured to 
operate solely as a receiver. Signal unit 332 provides both 
functionalities (e.g., a transceiver) when antenna 300 is configured to 
operate as both a transmitter and receiver. Those skilled in the art will 
recognize the various ways in which the functionality of generating and/or 
receiving signals might be implemented. 
Conductor plate 304 is comprised of first and second arms 308 and 312. 
First arm 308 is a radiating arm (a radiating element) and second arm 312 
is a tuning arm (a tuning element). By varying the length of second arm 
312, the bandwidth of antenna 300 is increased. Also, by varying the 
length of second arm 312, the input impedance of antenna 300 can be 
matched with an input circuit. Thus, second arm 312 provides a convenient 
way to increase the bandwidth and match the input impedance of patch 
antenna 300 with an input circuit. This allows the added flexibility of 
being able to closely match the impedance of antenna 300 with particular 
circuits. 
Furthermore, second arm 312 acts as a parasitic arm of first arm 308 due to 
a field effect. By acting as the parasitic arm of first arm 308, second 
arm 312 increases the gain of antenna 300. The parasitic arm also 
increases the bandwidth of antenna 300 by increasing the overall volume of 
antenna 300. 
Because first arm 308 is the radiating arm of quarter-wave patch antenna 
300, its length is set at approximately a fourth of a wavelength. 
Depending on a particular application, the length of second arm 312 may be 
longer or shorter than that of first arm 308. 
First and second arms 308 and 312 are approximately planar to each other 
and are separated by an air gap of a distance d. If d is too small, first 
and second arms 308 and 312 are too close to each other, and there is 
excessive coupling between first and second arms 308 and 312. As d 
approaches zero, first and second arms 308 and 312 act like a single 
antenna. This prevents second arm 312 from functioning as a tuning arm as 
well as a parasitic arm of first arm 308. On the other hand, if d is too 
large, coupling between first and second arms 308 and 312 is negligible. 
Consequently, second arm 312 ceases to be a parasitic arm. In practice, d 
is kept small because it makes the antenna small in size which is 
desirable in a personal communication device. 
Ground plane 316 is made of a conductive material such as, for example, 
aluminum, copper, gold, silver or brass. Ground plane 316 is separated 
from conductor plate 304 by dielectric substrate 320 and is approximately 
parallel to conductor plate 304. One end of conductor plate 304 is 
electrically connected to ground plane 316. The overall length of antenna 
300 can be reduced in size by bending a portion of ground plane 316 near 
the edge at a 90 degree angle. 
In one embodiment of the present invention, air is selected as dielectric 
substrate 320. Air has a dielectric constant of approximately 1 and it 
produces a negligible dielectric loss. Because the personal communication 
devices are typically powered by batteries that have limited energy 
storage capability, it is important to reduce dielectric loss in antenna 
300. Thus, air is selected as a preferred dielectric substrate because it 
produces a negligible dielectric loss. 
Probe 328 couples signal unit 332 to bridge 324. Signal unit 332 provides 
antenna 300 with a signal having a selected frequency band. In a PCS 
phone, the frequency band is generally 1.85-1.99 GHz. In a cellular phone, 
the frequency band is generally 824-894 MHz. First arm 308 (the radiating 
arm) receives the signal because it is sized appropriately for the 
selected frequency band, and it resonates at the selected frequency band. 
The height of antenna 300 is determined by the thickness t of dielectric 
substrate 320. As before, if t is too small, conductor plate 304 is too 
close to ground plane 316. As a result, a surface current induced in 
ground plane 316 tends to be very strong which results in high ohmic loss 
in ground plane 316. Consequently, the efficiency of antenna 300 is 
degraded. If on the other hand, t is too large, surface wave modes are 
excited which degrades the antenna's performance. 
Also, the bandwidth of antenna 300 is proportional to the thickness t of 
dielectric substrate 320. The thicker the substrate, the wider the 
antenna's bandwidth. While increasing t may seem like an easy way to 
increase the bandwidth of antenna 300, practical considerations dictate 
that t be small. A small t allows antenna 300 to have a low profile, which 
makes it suitable for portable devices such as a personal communication 
device. Thus, antenna designers have in the past reluctantly settled for a 
narrow bandwidth in order to make the antenna smaller in size. 
The present invention allows increased bandwidth without increasing t. As 
noted before, in the present invention, the bandwidth of antenna 300 can 
be increased by adjusting the length of second arm 312 (the tuning arm). 
Also, as noted before, second arm 312 acts as a parasitic arm which 
increases the overall volume of antenna 300. Consequently, the bandwidth 
of antenna 300 is increased even further. 
Additionally, the present invention allows dual frequency band operation 
when second arm 312 is excited with a second frequency band while first 
arm 308 is also being excited by a first frequency band. In this mode, 
first and second arms 308 and 312 are each excited with separate frequency 
bands. First arm 308 acts as a first active radiator and second arm 312 
acts as a first tuning arm. Likewise, second arm 312 acts as a second 
active radiator and first arm 308 acts as a second tuning arm. 
The length of first arm 308 is approximately a fourth of a wavelength of 
the first frequency. Likewise, the length of second arm 312 is 
approximately a fourth of a wavelength of the second frequency. Thus, the 
lengths of first and second arms 308 and 312 are sized appropriately for 
the first and second frequency bands, respectively. 
The length of second arm 312 may be longer or shorter than the length of 
first arm 308. If, for instance, the second frequency band is higher than 
the first frequency band, the length of second arm 312 is shorter than the 
length of first arm 308. If, on the other hand, the first frequency band 
is higher than the second frequency band, the length of second arm 312 is 
longer than the length of first arm 308. 
Bridge 324 electrically connects probe 328 to first and second arms 308 and 
312. Bridge 324, thus, provides a convenient way to connect the signal 
source to first and second arms 308 and 312. 
Signal unit 332 provides antenna 300 with two signals: a first signal 
having the first frequency band, and a second signal having the second 
frequency band. In operation, first arm 308 receives the first signal and 
resonates at the first frequency band. First arm 308 resonates at the 
first frequency band because it is sized appropriately (a fourth of a 
wavelength of the first frequency). Likewise, second arm 312 resonates at 
the second frequency band because it is sized appropriately for the second 
frequency band. 
As noted before, the present invention allows antenna 300 to have a wider 
bandwidth than a conventional quarter-wave patch antenna of the same 
volume. For example, a conventional quarter-wave patch antenna having a 
length of 1.3 inches, a thickness of 0.25 inches and a width of 0.5 inches 
has a 2% bandwidth. In contrast, the present invention allows antenna 300 
having generally the same dimensions to have a 7% bandwidth. 
In one example embodiment of the present invention, antenna 300 has the 
following dimensions: the length of first arm 308 is 1.30 inches; the 
length of second arm 312 is 1.10 inches; the overall width w is 0.5 
inches; the thickness t is 0.25 inches; the length of ground plane 316 is 
2.0 inches with a portion of the length (0.25 inches) being bent at a 
right angle; and the air gap d is 0.2 inches. First arm 308 is the 
radiating arm and second arm 312 is the tuning arm. FIG. 4 depicts a 
computer simulated frequency response of the example embodiment. Antenna 
300 has a 10 dB response at 1.9 GHz and 2.04 GHz (PCS frequencies). Thus, 
antenna 300 has a 7% bandwidth. 
While various embodiments of the present invention have been described 
above, it should be understood that they have been presented by way of 
example only, and not limitation. Thus, the breadth and scope of the 
present invention should not be limited by any of the above-described 
exemplary embodiments, but should be defined only in accordance with the 
following claims and their equivalents.