A conical quad-mode antenna excited through four orthogonal transverse electromagnetic modes is presented. The radiation characteristics of each mode are validated through measurements, illustrating the complimentary nature of the four far-field radiation patterns through which near-hemispherical field-of-view coverage can be achieved

Ivashina, Marianna

Maaskant, Rob

Meyer, P.

Prinsloo, D. S.

Prinsloo, D.S,

Meyer, P.,

Maaskant, Rob,

Ivashina, Marianna,

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Quad-Mode Antenna for Wide-Scan Sparse Arrays [Elektronisk resurs]

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Quad-Mode Antenna for Wide-Scan Sparse Arrays
This document has been downloaded from Chalmers Publication Library (CPL). It is the author´s
version of a work that was accepted for publication in:
2015 IEEE International Symposium on Antennas and Propagation & USNC/URSI National
Radio Science Meeting
Citation for the published paper:
Prinsloo, D. ; Meyer, P. ; Maaskant, R. et al. (2015) "Quad-Mode Antenna for Wide-Scan
Sparse Arrays". 2015 IEEE International Symposium on Antennas and Propagation &
USNC/URSI National Radio Science Meeting pp. 1516-1517.
http://dx.doi.org/10.1109/APS.2015.7305147
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Quad-Mode Antenna for Wide-Scan Sparse Arrays
D.S. Prinsloo and P. Meyer
Dept. Electrical and Electronic Engineering
Stellenbosch University
Stellenbosch, Western Cape, South Africa
email:{16238087,pmeyer}@sun.ac.za
R. Maaskant and M.V. Ivashina
Dept. Signals and Systems, Antenna Group
Chalmers University of Technology
Gothenburg, Sweden
email:{rob.maaskant, marianna.ivashina}@chalmers.se
Abstract—A conical quad-mode antenna excited through four
orthogonal transverse electromagnetic modes is presented. The
radiation characteristics of each mode are validated through
measurements, illustrating the complimentary nature of the four
far-field radiation patterns through which near-hemispherical
field-of-view coverage can be achieved.
I. INTRODUCTION
The authors recently proposed the use of multi-mode an-
tennas to extend the Field-of-View (FoV) coverage of phased-
array antenna elements implemented in sparse configurations
[1], [2]. These antennas utilize multiple orthogonal Trans-
verse Electromagnetic (TEM) modes to excite integrated, and
co-located, dipole and monopole elements through a multi-
conductor transmission line. In [3], the authors introduce a
conical quad-mode antenna and illustrate the improved FoV
coverage with respect to gain, sensitivity and polarimetric
performance that can be obtained through judicious use of
the four available TEM excitation modes.
This paper presents the measured multi-mode response of
a conical quad-mode antenna design. The presented results
affirm the complimentary nature of the four orthogonal exci-
tation modes that enables the quad-mode antenna to achieve
near-hemispherical FoV coverage.
II. CONICAL QUAD-MODE ANTENNA DESIGN
The conical quad-mode antenna design presented in this
paper operates at a center frequency of 950 MHz with an op-
erating frequency bandwidth of approximately 35%. As shown
in Fig. 1, the antenna comprises two perpendicularly oriented
bow-tie antennas printed on a FR-4 substrate positioned above
a 2 mm thick aluminium conical monopole sleeve connected
to the ground shield of a quadraxial transmission line at the
apex. The conical monopole element extends downward up to
a distance (h1) from the ground plane. To excite the antenna,
four coaxial connectors are positioned below the ground plane,
where the center conductor of each connector is connected to
one of the brass inner conductors of the air-core quadraxial
feed – each with a diameter of 5 mm. As shown in Fig. 1(b),
the four inner conductors of the feed are each terminated in one
of the bow-tie arms. Table I summarizes the design dimensions
indicated in Fig. 1.
To illustrate the radiation characteristics of the quad-mode
antenna consider the simulated field distributions of the four
(a)
(b)
Fig. 1. Conical quad-mode antenna design (a) side view showing inner
conductor of quadraxial feed (b) top view of printed bow-tie antennas.
TABLE I
CONICAL QUAD-MODE ANTENNA DESIGN PARAMETERS
Parameter Value [mm] Description
w1 26.15 Ground shield outer diameter
w2 4 Reduced inner conductor diameter
w3 3.3 Bow-tie inner edge width
t1 3 Aluminium feed short thickness
t2 4 Bottom Teflon spacer thickness
t3 1 Top Teflon spacer extrusion above cone
t4 1.6 FR-4 substrate
t5 2 Top Teflon spacer feed extrusion depth
l1 96 Conical monopole bottom length
l2 40 Conical monopole top length
l3 150 Bow-tie dipole length
h1 11 Conical monopole - ground plane separation
h2 70 Quadraxial feed height
h3 75 Dipole height
s1 14.15 SMA feed center separation
s2 8 Bow-tie arm inner edge separation
𝜃 72 Bow-tie arm flare angle
+
+ _
_ +
+ _
_
+
+
+ + + +
_
_
(a) (b) (c) (d)
(e) (f) (g) (h)
Fig. 2. Field distribution of port excitation modes (a) MM1, (b) MM2, (c)
MM3, (d) MM4 and corresponding radiated far-field patterns of modes (e)
MM1, (f) MM2, (g) MM3, and (h) MM4.
orthogonal TEM port excitation modes with their correspond-
ing radiated far-field patterns [c.f. Fig. 2], as simulated in CST
Microwave Studio over an infinite ground plane. As shown
in Fig. 2, excitation modes MM1 and MM2 result in two
orthogonal dipole-over-ground far-field patterns, mode MM3
radiates in a typical monopole fashion and excitation mode
MM4 radiates power diagonal to the orientation of the bow-
tie antennas. It is noted from Figs. 2(e)–(h) that, collectively,
these four excitation modes allow for a hemispherical scan-
range.
III. MEASURED RESPONSE
(a) (b)
Fig. 3. Manufactured quad-mode antenna (a) side view showing four SMA
connectors (b) top view of printed bow-tie antennas.
To verify the simulated response of the quad-mode antenna,
the manufactured design is placed on a circular ground plane
with a diameter of 450 mm. Figure 3 shows the measured
conical quad-mode antenna design as well as the four coaxial
connectors through which the antenna is excited.
As reported in [4], the multi-mode response of the quad-
mode antenna can be obtained from conventional Single-
Ended (SE) radiated far-field pattern measurements where each
SE far-field is measured by individually exciting each port
with the remaining three ports terminated in a matched load.
Figure 4 compares the multi-mode co-polar gain, transformed
from SE far-field measurements, to the co-polar gain simulated
in CST using the multi-mode port excitations illustrated in
Figs. 2(a)–(d). Given the symmetrical design, only the 𝜙 = 0∘
plane measurements are shown.
The measurements in Fig. 4 are seen to be in close
correspondence to the radiation characteristics of the four
−100 −50 0 50 100−20
−15
−10
−5
0
|d
B|
θ, deg
[Phi = 0, f = 0.8 GHz]
−100 −50 0 50 100−20
−15
−10
−5
0
|d
B|
θ, deg
[Phi = 0, f = 0.9 GHz]
MM1 − CST
MM2 − CST
MM3 − CST
MM4 − CST
MM1 − Measured
MM2 − Measured
MM3 − Measured
MM4 − Measured
(a) (b)
−100 −50 0 50 100−20
−15
−10
−5
0
|d
B|
θ, deg
[Phi = 0, f = 1 GHz]
−100 −50 0 50 100−20
−15
−10
−5
0
|d
B|
θ, deg
[Phi = 0, f = 1.1 GHz]
MM1 − CST
MM2 − CST
MM3 − CST
MM4 − CST
MM1 − Measured
MM2 − Measured
MM3 − Measured
MM4 − Measured
(c) (d)
Fig. 4. Measured and simulated co-polar gain (normalized) in the 𝜙 = 0∘
plane at (a) 800 MHz, (b) 900 MHz, (c) 1 GHz, and (d) 1.1 GHz.
orthogonal excitation modes observed in the simulated results
illustrated in Fig. 2. Furthermore, the measurements are seen
to agree with the co-polar gain of each mode simulated in
CST over the finite circular ground plane. Modes MM1 and
MM2 are seen to radiate dipole-over-ground patterns across
the frequency band with mode MM3 radiating in a typical
monopole fashion. Note that the lower measured gain of mode
MM4 can be attributed to the mismatch of this mode observed
within the operating frequency band [3].
IV. CONCLUSION
This paper presents the design of a conical quad-mode an-
tenna for wide scan-range irregular phased array applications.
The radiation characteristics of the four orthogonal excitation
modes that collectively allow for hemispherical FoV coverage
are introduced and validated through measurements.
ACKNOWLEDGEMENT
This research was supported by a MCA International Re-
search Staff Exchange Scheme Fellowship within the Euro-
pean FP7 Programme, contract no. 612599. The authors would
also like to acknowledge SKA SA, the South African Research
Chairs Initiative of the DST, the NRF, as well as the Swedish
VR and VINNOVA agencies for funding this work.
REFERENCES
[1] D. Prinsloo, P. Meyer, M. Ivashina, and R. Maaskant, “A quad-mode
antenna for accurate polarimetric measurements over an ultra-wide field-
of-view,” in 8th European Conf. on Antennas and Propag. (EuCAP), April
2014, pp. 3794–3797.
[2] D. Prinsloo, R. Maaskant, M. Ivashina, and P. Meyer, “Mixed-mode
sensitivity analysis of a combined differential and common mode active
receiving antenna providing near-hemispherical field-of-view coverage,”
IEEE Trans. Antennas Propag., vol. 62, no. 8, pp. 3951–3961, Aug. 2014.
[3] D. Prinsloo, M. Ivashina, R. Maaskant, and P. Meyer, “Beamforming
strategies for active multi-mode antennas: Maximum gain, signal-to-noise
ratio, and polarization discrimination,” in Int. Conf. on Electromagnetics
in Advanced Applicat. (ICEAA), Sep. 2014, pp. 507–510.
[4] P. Meyer and D. Prinsloo, “Generalized mixed-mode scattering parame-
ters and antenna far-field conversions,” IEEE Trans. Antennas Propag.,
submitted for publication.


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