1 Introduction

Antennas are the essential constituents of wireless communication systems. They are the uniting links between transmitter and receiver [1]. Low profile antennas are required in mobile phones, aircraft or spacecraft operations, where the size, weight, cost, and performance are the basic requirements. The microstrip patch antenna satisfies all the above necessities. In [2], a planar E-shaped antenna operating in single frequency band (5–6 GHz) is presented for wireless communication. In [3], the author proposed a quarter wavelength slotted rectangular patch antenna. For many applications, it is appropriate to have a patch antenna resonating at one or more frequencies. The various ways of achieving dual band in the design of the patch antenna are suggested in [4] and [5]. In [4], it is shown that dual or triple bands can be obtained in the design of planar multi-band antenna by making U-shaped slots in its radiator. Similarly, in [5] dual-band characteristics are obtained by Gemini-shaped microstrip patch antenna.

The proposed antenna size and dual band operating frequencies are compared with the antennas available in the literature. It can be observed from Table 1, the size of the antenna is very small and the results of the proposed antenna are better.

Table 1. Size and bandwidth comparison of proposed antenna
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This article deals a dual band slotted ground plane planar antenna. The antenna is targeted for the devices of WLAN and satellite downlink communication. WLAN (IEEE 802.11b), and functions at 2.4–2.484 GHz [6, 7]. The proposed antenna exhibits a high gain in WLAN band.

X-band offers frequencies ranging between 7.25–7.75 GHz for satellite downlink applications [8, 9]. This paper proposes an annular ring patch antenna with appreciable gain and desired VSWR in WLAN and in satellite downlink applications. Commercially available EM software, FEKO software is employed for simulation of the proposed antenna.

2 Antenna Design

Figure 1 shows the proposed slotted ground plane annular ring antenna is designed with compact dimensions (35 mm × 45 mm) on FR4 substrate. It consists of an annular ring radiator with one horizontal strip attached to the feed line. The ground plane has partially defected with a circular slot. The slot helps in providing capacitance. A 50 Ω impedance microstrip feed line is used to match impedance of the antenna with SMA connector.

Fig. 1.
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Proposed antenna design with (a) front and (b) rear views

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In the course of designing the proposed antenna, initially, a circular patch radiator is used as shown in Fig. 2(a). In the next stage, a circular slot is made in the patch to form an annular ring-shaped patch radiator as shown in Fig. 2(b). However, this change didn’t generate the required dual frequency operation. In the next stage, a horizontal strip is added to the ring structure as in Fig. 2(c). This produced the dual frequency bands, but the return loss was not enough. In the final stage, a circular slot was made in the back plane caused to great improvement in the S11 in the operating bands. Figure 3 shows the S11 plots of different stages of the proposed antenna (Table 2).

Fig. 2.
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Design steps of the proposed antenna.

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Fig. 3.
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S11 curves of proposed antenna in different stages.

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Table 2. Structural parameters of the proposed antenna
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3 Parametric Analysis

3.1 Influence of the Slot in Ground Plane

A circular slot is embedded in the ground plane that improves the S11 and gain of the proposed antenna at resonant frequencies. In the absence of this circular, poor return loss characteristics are obtained at both resonant frequencies. Figure 4 clearly shows the impact of the circular slot on return loss characteristics.

Fig. 4.
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Effect of ground plane slot on S11.

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3.2 Influence of the Horizontal Strip

A horizontal strip is attached to the feed line caused to dual band response. In the absence of the horizontal strip, the frequency bands are shifted to higher frequencies as compared to the proposed antenna. The effect of the horizontal strip on S11 is clearly observed in Fig. 5.

Fig. 5.
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Effect of horizontal strip on S11.

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4 Results

The proposed patch antenna is designed in FEKO software. The simulation and measured results of the antenna are analyzed and presented here. The simulated antenna design is successfully fabricated using LKPF 105 prototype machine. The fabricated antenna is shown with its top and bottom views in Fig. 6. The S11 measurements of the fabricated prototype are measured with Agilent Network Analyzer.

Fig. 6.
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Fabricated prototype of the proposed antenna.

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A comparison of S11 of simulated and fabricated antennas are presented in Fig. 7. The bandwidths of the antenna in simulation and measurement are found to be almost the same with little shift in the resonating frequencies. The fabricated antenna exhibits dual resonances at 2.53 GHz and 7.66 GHz. The antenna obtained the first resonance at 2.457 GHz in 2.41–2.51 GHz frequency band. And the second resonance at 7.57 GHz in the frequency band 7.43–7.83 GHz. In this band, the antenna is found to obtain a bandwidth of 400 MHz. In Fig. 8, H-plane and E-plane radiation patterns of the proposed antenna are presented at dual resonant frequencies.

Fig. 7.
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Comparison of simulated and measured S11.

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Fig. 8.
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Radiation patterns of the proposed antenna (a) H-plane, (b) E-plane.

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5 Conclusion

A dual band antenna with slotted ground plane is presented for dual band wireless applications. The presented antenna obtained return losses below −10 dB at the two frequencies at 2.45 and 7.57 GHz. The employment of slot in the ground plane has resulted in dual band, 2.41–2.51 GHz and 7.43–7.83 GHz with appreciable gain values at the resonating frequencies. The proposed antenna convincingly outperformed the existing antenna designs in the literature. Hence, the antenna can be used for the wireless communication in WLAN and satellite downlink communications.