Progress In Electromagnetics Research Letters, Vol. 75, 33–38, 2018
An Omnidirectional Printed Collinear Microstrip Antenna Array
Davoud Zarifi1, * and Ali Ahmadi2
Abstract—An omnidirectional antenna array is proposed in this paper. The antenna unit of the array
is composed of ten radiation patches and the associated microstrip feeding network. Some gaps between
top and back patches are introduced in the antenna to improve matching, ease of feeding and enhance the
bandwidth. Microwave experiments and numerical simulations are performed to demonstrate antenna
functionalities. The fabricated antenna exhibits a bandwidth of 14% (1–1.15 GHz) for VSWR ≤1.5,
with a gain around 6 dBi. The results are valuable for the design and evaluation of omnidirectional
planar antenna arrays with good impedance matching, which are important for airborne and navigation
applications.
1. INTRODUCTION
Antennas with light weight, compact size and low profile are required in modern wireless communication
systems. In recent years, the need for omnidirectional antennas with narrow beams in the elevation
plane is increased considerably. Omnidirectional antennas are used in many frequency bands from 0.8
to 6 GHz in different applications such as local area network (WLAN) access points, positioning and
satellite communication. The omnidirectionality is often obtained using omnidirectional elements, such
as dipoles, monopoles, and magnetic loops.
As shown in Fig. 1, different collinear-array configurations are designed using radiating elements
with an intrinsic omnidirectional pattern. These arrays are based on in-phase feeding of radiating
elements that lie in a straight line, and the radiation pattern is typically broadside. The coaxial
collinear antenna, introduced by Judasz and Balsley firstly [1], and it has been widely used due to
its compact, simple and cheap structure. Several researches further implemented this principle in
either coaxial or microstrip antenna technology [2–11]. In applications where the sidelobe level and
bandwidth of omnidirectional pattern are critical, some collinear arrays have been presented [12]. All
mentioned collinear antenna arrays have nearly omnidirectional radiation pattern due to the more or
less longitudinal axis symmetry.
In this paper, we present a simple and low-cost printed collinear antenna with omnidirectional
radiation. Design considerations of collinear array of patches fed by microstrip feed networks are
described for operating in the 1 GHz band. An array of 10 radiating elements is designed, simulated
and fabricated. The main advantage compared to other similar arrays is that this antenna can keep a
simple structure with a simple feeding network, good impedance matching and broadband performance
compared to coaxial collinear dipole arrays. Furthermore, the proposed antenna has a narrow width
comparable to that of coaxial antennas and shows good omnidirectional radiation across the operating
band.
Received 25 February 2018, Accepted 28 March 2018, Scheduled 11 April 2018
1School of Electrical and Computer Engineering, University of Kashan, Kashan, Iran. 2Department of Electrical Engineering, Imam
Hossein University, Tehran, Iran.
