The computer-aided design of rectangular microstrip antennas

229 Pages·2016·10.11 MB·English

by  Noel Maxwell Martin

of
The computer-aided design
rectangular microstrip antennas
by
Noel Maxwell Martin,
M.Sc., B.Eng., C.Eng.
A theais submitted to the f)epartment of Electrical and Electronic
Engineering, the University of Adelaide, to meet the requirements
for the award of the degree of Doctor of Philosophy
December, 1984
aJmmo?y
SI'MMARY
A computer-aided desigu progr:un has been developed for use with probe or trans-
mission line fed rectangular microstrip antennas and arrays. The antenna is modelled
using both a single mode leaþ reeonatrt cavity and a transmiesion line with radiating
apertures at each end, where in both c:Ees a series reactance is used to repreaent the
effects of the feed probe. The cavity model is used to specifically define and calculate
the resouaut frequencies to withiu 2% of measurements, where the effective electrical
dimensions of the antenna are empirically determined. The accuracy of the transmis-
sion line model in determining input impedances is greatly improved through,the use
of empirical equations for the effective admittances located at each eud of the antenna.
Ï)pical errors of 17% and 2% are obtained for the resonant resistances and impedance
resonaut frequencies respectively. In the case of probe fed antennas, the succeEE of
both the resonant frequency and input impedance calculations dependa on the accurate
determination of the equivalent eeries reactance of the probe. Eere a coalcial trans-
nlission line with an empirical taper is used as a model. The resultatrt reactances are
within *3O of the transformationg in the measured input impedance loci. The near
field distributions of the two apertuies at each end of the antenna are exa-ined using a
liquid crystal film, aud leads to the conclusion that the respective far field patterns are
tilted off the broadside direction and emanating at different power levels. The far ûeld
radiation pattern ie calculated to within 2dB of me:¡auremente using :ur array of two
uniformly illuminated apertures, where the separation takes into account the effective
length to which the fields fringe at each end of the antenna. A space radiation model
for the power transfer betweeu two apertures is used to calculate the mutual coupling
to within 3dB of measurements, where the antennas ane separated by at least 0.75À0.
The definition of bandwidth used for resonant cavities is proposed ¡rs a more appro-
priate quantity for comparative studies between microatrip antennas whether they are
i
tlmnu?J
matched or not; a¡d is used in au investigation into the bandwidth performance of a
novel hexagonal element, which is shown to exhibit wider ba¡dwidth and greater gain
performance than a rectangular antenna. All of the models are tested on typical geome-
tries operating up to a frequency of 5GEr, and are shown to provide reaults of sufrcient
¡rccur¡rcy for moet design purpoEeE without requiring octensive computations.
u
Sto/eme¡l
STATEMENT
This thegir contains Bo material which has beeu accepted for the awa¡d of any
other degree or diploma in any Univeraity and to the best of the candidate's knowledge
and belief, contains no material proriously published or written by auother person,
except where due reference is made in the text.
Also the author cousents to the theais being made avzilable for photocopyiug and
loan if accepted for the award of the degree.
'ì
Noel Martin
ut
Acksoolalgemeslo
ACtr,NOWLEDGEMENTS
The guidatrce of the author's supenisor, Dr.D.Iff.Griffin, is gratefully acknowl-
edged. Eis balanced practical and theoretical approach to problems in electromaguetics
has been invaluable to this research progrâmme.
The author's wife, Kathleen, is also thanked for her constant support aud eucour-
agement, for without it this candidature would have never gtarted. She ie also thanked
for typing the thesie. The author is also grateful for the regular encouragement of Mr.
and Mrs. P. Budimir.
Messrs G.\lV.Pook and G.L.Allison are thanked for their skilled technical assis-
tance,
The author also acknowledges the financial support from the University of Ade-
laide through a URG scholarship.
¡v
Lict of pritcípal qøbolo
LIST OF PRINCIPAL SYMBOLSI
a radius of a circula¡ patch or the inner conductor of a coanial transmission line.
c, effective radius of a circular patch.
Á¡ length of a rectangular aperture.
rl¡
separation between two apertures in a broadside array.
r{¿.¡ width of a rectangular aperturc.
ö radius of the outer conductor of a coanial transmission line.
Ba input susceptance of a radiating aperture.
B¿ input susceptance of a slot antenna.
.B[7 bandwidth.
c velocity of electromagnetic waves in free sp:rce.
d diameter of the feed probe.
D inset distance: distance between the feed probe and the nearest end of a rectan-
gular patch antenna.
.E electúc ûeld intensity vector.
lp0ploEerqEO spherical comPonents of .8.
/ frequency iu hertz.
/¿ resonant frequency.
.fm,n resonant frequency of the m, n mode.
v
Líot of príæipal oynbole
reoonant frequeucy of an ideal unloaded cavity.
/¿,¿
/¿¡ frequency at which the input impedance of an antenna is real.
G6 input conductance of a radiating aperture.
G ra¿ radiation conducta¡ce.
l¡ thickness of a dielectrically ñlled substrate.
Jo(r), J"(x) Bessel functions.
/t-,r. wave number of the m, n mode.
le electrical length.
l¿
nhysical length.
leugth of a transmission line or a rectangular patch antenna.
^t
Ç¿¿ quality factor due to ohmic losses.
Q¿;, euality factor due to dielectric losses.
Q¿3¡ quality factor that includes only the e>cternal load.
Q¿ quality factor that includes internal and external losEes.
Qo quality factor of an ideal unloaded cavity.
Qro¿ euality factor due to radiation loeses.
r
aspect r:atio W lL.
.B¿ resonant resistance: input resista¡rce rt Íot.
l?s¡ equivalent resistance due to ohmic losses.
.B¿;, equirralent resistance due to losses in the dielectric.
.Bro¿ radiatiou resista¡ce.
YI
Liú ol pñneipal oymbob
sll¡ s2l tst2t322 scattering matrix parameters.
TEM
transverse electromaguetic
t thickness of copper cladding.
tan ó loss tangeut of a dielectric material.
gy.z,þtltetS.
lt- unit vector iu the ¡-di¡ection; similarly
vph phase velocity.
w width of a microstrip transmigsion line or a rectaugular microstrip patch ¿ntenna.
we effective width of a microstrip transmission line or a rectangular microstrip patch
antenna.
x. (:
seriee reacta¡ce used to model the antenna'e feed probe wLt).
Ya input admittance of a radiating aperture.
Yom characteristic admittance of a microstrip liue.
za input impedance of a radiating aperture.
Z;n input impedance of an antenna.
Zo characteristic impedance of a microstrip line.
zo characteristic impedance of an air ûlled transmission line.
z1 impedance located at the receiving end of a transmission line.
zo input impedance of slot or apertune A.
Z6 input impedance of slot or aperturc B.
d atteuuation constant.
þo phase conatant in free sp:ìce.
vii
Lllt ol2titcí9al rydolo
p¿ phæ const¡urt in the substrate.
6.t edge octension.
6¡ ekin depth.
e¿ effective relative dielectric coustaût.
er relative dielectric constant of a dielectric substrate.
'J propagation constant.
7¿ iutrinsic impedance iD a vacuum (l20r0).
4 antenua efrciency.
7¿ intrinsic impedance of a dielectrically ûlled medium.
)¡
wavelength in a dielectúcally ñlled medium.
À¿ waveleugth in fiee space.
ø conductivity.
O ohm.
U mho.
ø
angular frequency.
vru
Litt of lúlet and plotet
LIST OF Tâ,BLES
Table Title
Page
2.1 Parameters for the large cavity transmission line model 2.19
2.2 Measured series reactance at SGHz for.a large cavity 2.23
2.3 Series reactance measured using the shorted transmission line method 2.26
2.4 Comparison between the series reactance calculated by the tapered transmission line
model and measured by the locus transformation method 2.43
3.1 For the formulas of various authom, a comparison between the percentage difference in
the calculated and measured cavity resonant frequency 3.7
3.2 Calculated and measured resonant frequenciea 3.16
5.1 Calculated and measured resonant resistances and impedance nesonant frequencies 5.22
structures
8.1 A summarJr of the bandwidth characteristics of microstrip antenna 8.7
LIST OF PLATES
Plate Title
Page
patch
6.1 Liquid crystal display of the fields around the periphery of a rectangular 6.5
6.2 Liquid crystal display of the fields off the end of a rectangular patch 6.5
tx