Microstrip Patch Antenna Array Gain

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Microstrip patch antenna array design

  1. The patch structure is the most common type of microstrip antenna.This kind has been selected owing to its small size, light weight, low cost and ease of fabrication as well as integration with complex circuitry. However, the conventional microstrip patch antenna inherently has a narrow bandwidth and low gain. For this reason, there are.
  2. In addition to providing more than 6-dB gain compared to a conventional microstrip antenna, these metamaterial-equipped antenna designs also feature increased bandwidth (from 3.64% to 4.68%) when compared to a conventional microstrip design.
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Gain Enhancement of a Microstrip Patch Antenna Using a Reflecting Layer

1Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia
2Department of Electrical and Electronic Engineering, Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia
3Wireless and Photonic Network Research Center, Department of Computer and Communication Systems Engineering, Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia

A microstrip antenna array is one of the simplest forms of antennas available. The antenna consists of a single printed circuit board with an RF connector and perhaps an absorptive load. Microstrip antennas can be manufactured very inexpensively now that reasonably priced, closely controlled substrate materials are available.

Received 20 December 2014; Revised 5 March 2015; Accepted 5 March 2015

Academic Editor: Giampiero Lovat

Copyright © 2015 Anwer Sabah Mekki et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A low profile, unidirectional, dual layer, and narrow bandwidth microstrip patch antenna is designed to resonate at 2.45 GHz. The proposed antenna is suitable for specific applications, such as security and military systems, which require a narrow bandwidth and a small antenna size. This work is mainly focused on increasing the gain as well as reducing the size of the unidirectional patch antenna. The proposed antenna is simulated and measured. According to the simulated and measured results, it is shown that the unidirectional antenna has a higher gain and a higher front to back ratio (F/B) than the bidirectional one. This is achieved by using a second flame retardant layer (FR-4), coated with an annealed copper of 0.035 mm at both sides, with an air gap of 0.04 as a reflector. A gain of 5.2 dB with directivity of 7.6 dBi, F/B of 9.5 dB, and −18 dB return losses () are achieved through the use of a dual substrate layer of FR-4 with a relative permittivity of 4.3 and a thickness of 1.6 mm. The proposed dual layer microstrip patch antenna has an impedance bandwidth of 2% and the designed antenna shows very low complexity during fabrication.

1. Introduction

Microstrip patch antennas have been of interest for a long time due to their low profile, low cost, easy printability, and fabrication, as well as the capability of being embedded within other devices. However, there are many disadvantages, such as low gain and narrow bandwidth [1, 2]. The gain of an antenna refers to the ratio of its radiation power in a specific direction to its power in the isotropic direction [3]. Many researchers are working to enhance the gain of the patch antennas using different designs, ideas, and materials [4–11]. On the other hand, narrow bandwidth system implementation improves system selectivity in a number of applications, including military, security, digital enhanced cordless telecommunications, and low power systems [12]. At the same time, due to the new technologies, most designers tend to reduce the size and increase the efficiency of the devices.

Microstrip Patch Antenna Array

One of the common methods to enhance the gain and directivity is the use of reflector planes. In [13], using the concept of complementary antennas, a planer antenna is presented with a U-shaped metal reflector to achieve a unidirectional propagation; the resultant antenna has a low profile, high F/B, and high gain along the operating frequency range. Moreover, in [14], a multiple metal back reflector is proposed for a wideband slot antenna. In [15], using a metallic cavity shaped as a reflector with a magnetoelectric dipole antenna, the proposed antenna exhibits a high gain with high F/B in the operating frequency range with relatively large dimensions.

But in [16], using a substrate rather than metal as a reflector is introduced to enhance the F/B radiation with aperture coupled antennas. In [17], a high impedance surface (HIS), in the shape of arrays of square cells, is used to reduce the back lobe propagation. The design shows an enhancement in the gain along the frequency range and high F/B. In [18], a dual band, unidirectional coplanar waveguide fed antenna (DB-CPWFA) is proposed. The reflector contains the ground plane, dielectric material, and artificial magnetic conductor. However, the dimensions of the antennas in the previous works are considered relatively large [13–18]. Therefore, achieving high gain while minimizing the size of the antenna is crucial.

In this paper, a new microstrip patch antenna is designed, simulated, and fabricated. The effect of the reflector layer on the gain and directivity is studied and evaluated. Furthermore, the air gap thickness between the two layers of the substrates is investigated. By tuning and optimization, the desired characteristics are achieved and the effect of the multigeometrical shapes is shown. The simulation results are compared to the DB-CPWFA [18] and the conventional microstrip patch antenna [19]. The simulated results are validated by the measurements and the effect of the reflector layer is verified. The measurement results demonstrate that the gain, directivity, and F/B ratio of the antenna have been significantly improved.

Array

2. Proposed Antenna

The proposed dual-layer microstrip patch antenna design was developed by taking the design of the conventional square patch antenna, then changing it by removing symmetrical parts from the left and right sides, changing the right angles to curves, and finally introducing a circular slot in the ground plane. Finally, the proposed design is accomplished using a second layer of FR-4, which is coated with a copper film at both sides, spaced 0.04 from the ground layer.

In order to make the patch antenna operate at the desired characteristics, a tuning and optimization technique is introduced. Therefore, in order to make the design more flexible and workable during this procedure the proposed antenna contains multigeometrical details. In antenna designs, sacrificing some parameters is compulsory in order to enhance others [20].

Microstrip Patch Antenna Array Gain Calculator

Figure 1 illustrates the dimensions of the proposed antenna. The overall dimensions are 60 mm × 55 mm × 8.3 mm. The substrate is FR-4, with a permittivity of 4.3 and loss tangent of 0.025, coated with annealed copper of 0.035 mm thickness at both sides. Four spacers are used, which are made of Teflon PTFE (polytetrafluoroethylene), which is a lossy material, with 2.1 relative permittivity. A second FR-4 layer, which is coated with annealed copper of 0.035 mm thickness at both sides, is placed at a distance of 0.04 from the first FR-4 layer. The second FR-4 layer acts as a reflector to redirect the propagation density from the back lobe to the main lobe. Hence, for the same radiation efficiency, increasing the directivity, , means increasing the gain, , as follows [3]:where is the radiation efficiency.

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