This document discusses techniques for broadbanding microstrip patch antennas. It describes how patch antennas have a narrow bandwidth due to their high quality factor Q. Various techniques are presented to decrease Q and increase bandwidth, including increasing the substrate height and lowering the dielectric constant, using multiple resonators coupled electromagnetically in one plane or stacked vertically, and electromagnetically coupled patch antennas. The document concludes by noting the ongoing search for an ideal wideband printed microstrip antenna.

1. BROADBANDING TECHNIQUES FOR
MICROSTRIP PATCH ANTENNAS
NAME-ASHIT TOMAR
BRANCH-ECE
SEC-A
SEM-6th
ROLL NO.-0922231022

2. BRIEF INTRODUCTION OF PATCH ANTENNA
•Microstrip antennas are planar resonant cavities that leak from
their edges and radiate
•Microstrip consists of a metal strip on a dielectric substrate
covered by a ground plane on the other side.
•It is fabricated by etching the antenna element pattern in metal
trace bonded to an insulating dielectric substrate, such as
a printed circuit board , with a continuous metal layer bonded to
the opposite side of the substrate which forms a ground plane.

3. NEED OF BROADBANDING OF PATCH ANTENNA
•The main limitation of printed patches is the
Narrow Bandwidth availability.
WHY BW OF PATCH ANTENNA IS LIMITED?
• The operating bandwidth of a single linearly
polarized patch antenna is limited by its input
VSWR(Standing Wave Ratio) and it is inversely
proportional to the Q factor of the patch
resonator.

4. What Does Broadbanding Means
 Broadbanding concern with the increment of the
operating Bandwidth *of the patch antenna.
 Bandwidth of patch antenna may be define as –
The frequency range over which the radiated power is
within 3dB of the incident power and the radiation
pattern is essentially the same.

5. Techniques For Broadbanding
1-Decreasing the Q factor of patch by increasing
substrate height & decreasing the dielectric
constant.
2-Use the multiple resonator located in one plane.
3- Electromagnetically coupled patch Antenna.
4-Use of multilayer configuration with multilayer
resonators stacked vertically.

6. Decreasing the Q factor of the patches by increasing the
substrate height & lowering the dielectric constant
Bandwidth of patches can be given by the expression-
BW= s-1/Q*s^(12)
For s=2, & substituting for Q in terms of energy stored &
power radiated we can write
BW=√2hGe/πc √ εre εo be……………….(a)
Where Ge is the edge conductance
be is the effective width ,h is the substrate thickness
εr is the effective dielectric constant.

7. Performance & Limitations
 From equation (a) we can conclude that the BW
increases linearly with increase of “h”.
 Also BW increases when εr is reduced.
BUT IT HAVE CERTAIN LIMITATIONS-
1-For probe -fed patch antenna an increase in the thickness of
substrate causes an increase in probe inductance which in
turn creates input matching problems.
2-For microstrip fed patches,increased substrate thickness
causes an increase junction reactance,which creates spurious
radiation as well as input match problem.

8. CONTINUED ……
3-Thick substrates make it mechanically
difficult to have antenna arrays conformal to
curved surfaces(of aircraft,space craft,
missile etc.).
4-Many of the analysis and design techniques
used (cavity model etc.) become inaccurate
for thick substrate.

9. Use the multiple resonator located in
one plane.
•This configuration consist of 4
triangular patches as shown in
the figure.
•The central patch “A” is probe fed
, the lower patch “B” is gap
coupled & other two patches are C
and D are coupled by short
sections of microstrip lines.

10. Performance & Limitations-
 A bandwidth which is 5.4 times the bandwidth of
single rectangular patch antenna has been reported.
But there are two problems associated with
this configuration-
1-Larger area requirement & consequent difficulty in using
these configurations as array element.
2-Variations of the radiation pattern over the impedance
bandwidth of the configuration.

11. Multiple-Resonator Configuration with
Patches Stacked Vertically
 In this approach two or more then two layers of dielectric
substrate are used .
Resonant patches are located on the top of each of the substrate
layers & are stacked vertically.Two-layer configurations are most
common but three dielectric layers have also been used.
It may be work in two ways
1-When smaller patch is on the top,edges of both of the smaller &
larger patches becomes as the source of radiation with the effective
aperture shifting from the bigger patch to the smaller patch as the
frequency of operation is incresed.

12. Continued…..
2-When the larger patch is on the top the upper patch
constitutes the radiating aperture.The lower patch helps in
the broadband excitation of the upper patch and is termed
as the Feeder patch.
 If two patches have identical dimension in that condition
the distinction between the Feeder & Radiator patches
disappear s and the two functions merged.
 In most of these two patch configuration,the lower patch is
fed via a probe or a microstrip line.
 For upper patch excitation capacitive coupling can be
done.

13. Electromagnetically coupled patch
Antenna(ECPA)
As shown in the figure this
configuration consist of the three
layers namely cover, patch & ground
plane
Patch is sandwiched in between
the other two layers
The antenna is fed by the ground
plane which is an advantage of the
ECPA.

14. ADVANTAGES OF ECPA
 The whole feed structure for the single antenna or array is
located more closely to the ground so the radiation pattern
that we get is less disturbed.
 Spacing to the patch and the ground plane is increased
which causes in return of the enhanced bandwidth.
 The cover layer of ECPA is very useful in case of the
Environmental protection which is further an advantage of
the patch antenna.

15. CONCLUDING REMARK
The bandwidth of patch antenna can be increased by
the height of the substrate or by decreasing the value
of the dielectric constant of substrate.
The problems that are faced in above method is over
come by the introduction of the Electromagnetically
coupled patch antenna.
Between the two different method of constructing the
multiresonator coupled patch configuration the
vertically stacked patches require small area and does
not suffer from pattern degradation with frequency.

16. Continued….
The search for “ ideal” wideband printed microstrip
antenna is still on.Perhaps a combination of various
approaches discussed in this paper would lead to an
optimum broadband configuration.
We can look forward to continued research in this
area.