Keywords

1 Introduction

A communication system is said to be a wide band system when its bandwidth significantly exceeds the coherence band width of the system. One such system has been designed in this work as well. Wideband Antennas have a wide number of applications. Military requires a wideband antenna for system agility or multifunctionality of the system. Communication systems having high gain require wideband. One of the latest applications of wideband antenna is the 4G LTE technology. The antennas used here are generally Multiple Input Multiple Output antennas. The designed antenna is a Microstrip Patch Antenna which gives the desired results at 5 GHz frequency. The results have been found to be compatible for the 5 GHz Wireless LAN applications. This LAN has got several advantages as compared to the 2.45 GHz LAN networks. The problem of interference and airtime challenges has been resolved, more over it offers a much higher data rate as compared to the 2.45 GHz Wifi LAN. The 5 GHz ISM Band was initially for about 150 MHz which was further extended to 725 MHz of spectrum. Therefore, two designs of Microstrip Patch Antenna applicable for wideband applications have been proposed in this paper. The S11 parameter is below −10 dB along with wide band characteristics, which makes them suitable for many wireless networking applications such as Wifi, WiMax.

1.1 Related Work

In [1] designing of a Dual Band patch antenna with circular slots operating at Wifi frequency was done. Gain of 3.93 dB was obtained at the lower band and a gain of 3.73 dB was obtained for the upper band. The Microstrip Patch Antenna was designed at 2.4 GHz and 3.5 GHz frequency. The main purpose was to cater to the Zigbee and WiMax applications. The concept of IOT has been implemented on the designed antenna [2]. The designed antenna is implemented by cutting ‘L’ shaped slots on the main patch of the antenna. This showed better return loss and gain along with the dual band characteristics [3]. In [4] the insight of a novel rectangular finite grounded Microstrip Patch antenna with DGS. The designed antenna has the bandwidth of 31% due to the contribution of the DGS. Similarly, size reduction of the Microstrip Patch Antenna is due to the cutting of the slots on the patch of the antenna. The dual band frequency of the Microstrip Patch Antenna was achieved by using the capacitive value which was also used in the structure of artificial magnetic conductor [5]. The two Microstrip Patch Antenna designs have been implemented for the S Band (2 GHz–3 GHz) and C Band (4 GHz–8 GHz). The designs have been implemented using inverted ‘E’ slot and ‘U’ slot to obtain the desired gain and reflection coefficient [6]. The proposed antenna was found to be suitable for compact wireless devices and their various applications. It has a very compact size because of high dielectric constant of the substrate that is 10.2 and loss tangent of 0.0002. The desired resonance was obtained by the removal of the diagonal edges of the patch [7]. The design proposed in [8] has been simulated at 2.45 GHz and 3.5 GHz using the DGS technique. The bandwidth percentage of 13.56% at 2.45 GHz and 10.36% at 3.5 GHz was obtained. [9] proposes a dual band Microstrip Patch Antenna having a wide band of 180 MHz for mobile applications. The obtained results are compatible for devices involving WiMax, Wifi, Bluetooth and WLAN. The proposed design is a dual band antenna working at 3.5 GHz and 5.2 GHz for WiMAx and Wifi applications respectively. The designed antenna has two parallel slots on the ground plane and a ‘C’ shaped slot on the patch. The results obtained showed low profile, high gain and wide bandwidth for the entire range of frequency [10].

1.2 Contribution

This research work will contribute towards designing and implementation of a Wideband Microstrip Patch Antenna using the inset feed technique. The ‘U’ slot on the patch and the ‘G’ shaped defect on the ground have led to the desired results which are applicable for various wireless applications.

1.3 Organization of Paper

The paper has been divided into total four parts. Section 1 containing the Introduction. Section 2 comprises of the proposed Antenna design with the specifications. Section 3 providing the results and discussions obtained from the design and finally Sect. 4 concluding the paper.

2 Proposed Antenna Design

Microstrip antenna is one of the most common and the most widely used antennas in the communication domain. The main reason behind its popularity is the ease of fabrication and low cost. The microstrip antenna is also very compact and gives efficient results at the desired frequencies. The length of the Microstrip Patch Antenna depends upon the dielectric constant of the substrate. If the dielectric constant of the substrate increases the length of the Microstrip patch Antenna decreases. The resonant length of the antenna is slightly less than the actual length of the antenna. The reason behind this difference is the extended electric fringe fields which increase the electrical length of the antenna.

The dimensions of the substrate, ground, patch and the microstrip feed line were calculated using the standard Microstrip Patch Antenna equations. Patch Antenna was designed using RT Duroid as the substrate with dimensions equal to [−W, W] and [−L, L], Copper (annealed) as the ground with dimensions as [−(W + 6 h), (W + 6 h)] and [−(L + 6 h), (L + 6 h)]. The patch was cut on the substrate along with the microstrip line using copper (annealed). The dimensions of the patch and the microstrip feed line were [−W/2, W/2], [−L/2, L/2] and [−Wf/2, Wf/2], [(L/2 − Fi), (Lf + L/2 − Fi)] respectively. W and L are the width and length of the patch, Wf and Lf are the width and length of the feed line and Fi is the inset depth. The frequency and the dielectric constant were taken as 5 GHz and 2.2 respectively. The thickness of the substrate was taken as 3.175 mm. First, a simple Microstrip Patch Antenna was simulated by using the dimensions given in Table 1.

Table 1. Optimized parameters
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The results of this antenna were then enhanced by the implantation of the ‘U’ shaped slot on the surface of the patch of the antenna. Various slot parameters such as the slot position, width and length were optimized to obtain the wideband characteristics. The position of the slots was chosen according to the areas having maximum surface current density on the surface of the patch. The distance of 5.6 mm from the center of the patch to the vertical slots was optimized for the enhanced bandwidth of the antenna. The width of the slot has to be small with respect to the length of the slot. Since it is a ‘U’ shaped slot, three slots had to be cut on the surface of the patch as shown in Fig. 1.

Fig. 1.
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‘U’ shaped slots and the patch of the antenna and the ‘G’ shaped defect on the ground

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Two slots were cut parallel to each other in the vertical plane and the third one was cut horizontally with respect to the patch. Optimization for the width of the slot was carried out between 0.5–3 mm. The broadest bandwidth was obtained at 2 mm width of the slot along with the desired gain. The length of the slot was not found to be such a significant parameter for increasing the bandwidth of the antenna. The optimized ‘U’ slot is shown in Fig. 2. The obtained bandwidth after this implementation was 450 MHz.

Fig. 2.
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Measurements of the ‘U’-shaped slot on the patch

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The DGS technique was implemented to further enhance the bandwidth. This technique is known for improving various antenna parameters such as bandwidth, low gain, and cross polarization. When a defect is made on the ground of the antenna, the current distribution on the ground gets altered and hence other parameters also change. Thus, the ‘G’ shaped slot as shown in Fig. 3 was cut on the ground of the antenna. The width, length and the position of the defect were optimized to obtain the required improvement in bandwidth. The dimensions of the defect are shown in Fig. 3. The integration of the two techniques led to the design of the wideband antenna.

Fig. 3.
figure 3

Measurements of the G shaped DGS

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3 Result

The desired results were obtained from the implemented design of the Microstrip Patch Antenna with ‘U’ slots on the surface of the patch and ‘G’ shaped DGS. According to the bandwidth obtained the wide band antenna can be used for various wide band applications.

3.1 Reflection Coefficient

The graph given in Figs. 4 and 5 has been plotted between the frequency of simulation and the S11 parameter. Since the S11 parameter is below -10 dB for the frequencies lying in C band, the obtained design can be used for C band applications.

Fig. 4.
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S11 of the antennas operating without DGS

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Fig. 5.
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S11 of the antenna operating with DGS

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The S11 parameter of the antenna having only ‘U’ shaped slot on the patch of the antenna was found to be below −10 dB from 4.94 GHz to 5.39 GHz and the bandwidth was found to be 450 MHz as shown in Fig. 4. The plot shows the minimum value of −24.832 dB at 5.228 GHz.

The S11 parameter of the antenna with the ‘U’ shaped slot on the patch along with the ‘G’ shaped DGS was found to be below −10 dB from 4.82 GHz to 5.52 GHz and the bandwidth was found to be 700 MHz as shown in Fig. 5. The plot shows the minimum value of −27.9 dB at 5.32 GHz.

3.2 Gain

Gain defines the transmission power of the antenna. This gain has been enhanced by cutting the U-Shaped Slot on the Patch.

Figure 6 shows the gain of the antenna at 5 GHz frequency. The gain obtained for the antenna having only the ‘U’ shaped slots was found to be 8.621 dB.

Fig. 6.
figure 6

Gain of the antenna without DGS

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Figure 7 shows the gain of the antenna at 5 GHz frequency. The gain obtained for the antenna based on the DGS technique was found to be 7.356 dB.

Fig. 7.
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Gain of the antenna with DGS

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3.3 Surface Current

The Surface Current is defined as the flow of current on the patch. Surface Current Density is generally higher at the places where the slots are cut on the surface of the patch. Figures 8 and 9 shows the graph obtained for surface current density for the non DGS antenna and DGS antenna respectively.

Fig. 8.
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Surface current of the antenna without DGS

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Fig. 9.
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Surface current of the antenna with DGS

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With the implementation of DGS technique the surface current density on the surface of the antenna increased.

Table 2 shows the gain and the bandwidth obtained at 5 GHz frequency for the antenna having the DGS slot and the one without the DGS slot.

Table 2. Gain and bandwidth of the simulated antennas
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4 Conclusion

The designing and simulation of the wideband Inset-Fed Microstrip Patch Antenna has been successfully completed. The bandwidth of 450 MHz was obtained by cutting the ‘U’ shaped slot on the patch of the antenna and this bandwidth was then enhanced by using the DGS technique. A bandwidth gain of 250 MHz was obtained by the implementation of the ‘G’ shaped DGS along with the ‘U’ shaped slot on the patch leading to the final bandwidth of 700 MHz. Due to this the antenna becomes more suitable for various C Band applications, such as Wifi, WLAN, WiMax and various other wireless applications.