The astronomical progress in miniaturising and integrating electronic circuits in the past decade has recently crerated a positive demand for a new generation of antenna systems. In principle, microstrip antennas are thin planar configurations that are leightweight, low cost, easy to manufacture and can be made conformal with the surfaces of vehicles, missiles etc. The compatibility of microstrip antennas with integrated electronics is another great advantage. However, the microstrip wavetrapping effects inhibit the radiation mechanism and must be taken into account in antenna design. Wave-trapping effects in substrates involve the study of surface waves and discontinuities in open waveguide structures. The microstrip antenna designer must therefore encompass many more effects than previously considered by microstrip circuit designers. It is for these reasons that the scope of this monograph is necessarily somewhat wider than the title may suggest.
The design of an ultra-wideband microstrip patch antenna with a small coplanar capacitive feed strip is presented. The proposed rectangular patch antenna provides an impedance bandwidth of nearly 50%, and has stable radiation patterns for almost all frequencies in the operational band. Results presented here show that such wide bandwidths are also possible for triangular and semiellipse geometries with a similar feed arrangement. The proposed feed is a very small strip placed very close to the radiator on a substrate above the ground plane. Shape of the feed strip can also be different, so long as the area is not changed. Experimental results agree with the simulated results. Effects of key design parameters such as the air gap between the substrate and the ground plane, the distance between radiator patch and feed strip, and the dimensions of the feed strip on the input characteristics of the antenna have been investigated and discussed. As demonstrated here, the proposed antenna can be redesigned for any frequency in the L-, S-, C-, or X-band. A design criterion for the air gap has been empirically obtained to enable maximum antenna bandwidth for all these operational frequencies.
A class of antennas that has gained considerable popularity in recent years is the microstrip antenna. There are many different varieties of microstrip antennas, but their common feature is that they basically consist of four parts:
A typical microstrip element is illustrated in Fig. 1. Microstrip elements are often made by etching the patch (and sometimes the feeding circuitry) from a single printed-circuit board clad with conductor on both of its sides.
Applied Electromagnetics. Research interests at present include microstrip antennas and circuits, leaky-wave antennas, leakage and radiation effects in microwave integrated circuits, periodic structures, and electromagnetic compatibility and interference.
Implementing microstrip antennas for some wearable purposes, such as smart clothing [3], also calls for the antenna to be quite thin, flexible, and thermally robust, and to have a good moisture repellence.
This paper contributes with the following: it offers a more comprehensive, sufficiently argued, and verifiable report on our experience with the design, optimization, fabrication, and measurement of and IRMA using Pyralux as a microstrip antenna substrate, both by full-wave simulations and measurements on fabricated models. Second, sizing of the inset gap width was found to be quite tricky at the combination of this frequency band and this ultra-thin a substrate, which makes it relevant to report on.
Unlike antennas manufactured with a standard substrate, such as FR4, which show a wider feasible range of the inset gap width values, this thin a substrate exhibited a very small range of acceptable values of wf/g to make good impedance matching, at least in this frequency range. In the first designs, we hoped that wf/g=5 was an adequate ratio and searched for some other reasons that would have explained the unsatisfactory impedance matching. The CAD models also required mesh refinement until more confident results were achieved. The reason stems from the fact that Pyralux AP9131R is about 20 times thinner than typical substrates such as FR4 or RT/duroid. Ultimately, when the wf/g ratio was sufficiently increased, a satisfactory reflection coefficient was achieved, as shown in Figure 2b.
The frequencies used by these different applications are spread over the frequency range [1GHz- 5.8GHz] (Gautam, A, et al., 2016). So to get all these devices connected to each other it is necessary to use compact and easy to integrate antennas into the objects. The patch antenna is one of the best solutions used by many engineers because it gives good results in terms of parameters such as directivity, gain, return loss, VSWR (Voltage Standing Wave Ratio), bandwidth, etc (Gupta, N., et al., 2016). In order to improve it further, we need to make some changes to traditional antennas to make them multi-band and broadband with high performance (Huang, Y., et al., 2008).
The concept of patch antenna appeared in 1950, but the real development has been involved in 1970. It can be used alone or as part of a network (Jmes, J. R., et al., 1989). Similarly, it can be integrated closer to the electronic circuits by occupying a reduced volume and conforming to different types of surfaces (Kaur, N. et al., 2017). For the microstrip line shown in Fig. 2 (a), the field lines are inside, and some of them are extended to outer space. For this, an effective dielectric constant (reff) is introduced to account for fringing and the wave propagation in the line. When an antenna is energized by a microstrip line or other power mode, this generates negative charges around the feed point and positive charges of the other part of the radiator. This charge difference creates electric fields in the antenna; these electric fields are the main cause of the radiation in the printed antenna (Fig 1).
Several feeding techniques are available such as coaxial feed, proximity coupled feed, microstrip inset feed etc, (Nornikman, H., et al., 2012), (Nornikman, H., et al., 2018), (Orik, N., 2008). to excite the patch. Here, the feed is applied through a microstrip inset feed having the width Wf. The patch antenna is completely designed using FEKO Slover. Here, FR4 epoxy is the substrate as discussed earlier (?r=4.4), and the parameters characterize our patch antenna (Figure 2) are presented in the following table:
The following table represents a comparison between the performances of the antennas found in indexed works and our antenna, we note that our work has an improvement in performances Compared to existing works.
In the future works, the antenna design can be improved by adding the N-number circular slot or define the other new slot into the microstrip patch design, also we can study the effect of the ground plane.
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