Keywords

1 Introduction

Wireless communication has become an essential part of modern era. Microstrip patch antenna consists of a dielectric substrate with a ground plane on other side. A reconfigurable microstrip patch array antenna which is simple, low cost and high gain has been demonstrated in this paper with suitable feeding technique and dielectric substrate for GHz frequency range applications. Single microstrip patch antenna comes up with many advantages like low cost, low weight, low profile and conformal, etc. But it has certain limitations as well like low gain, low directivity, low efficiency, and narrow bandwidth. To overcome these limitations, implementation of multiple patches has been proposed in the array configuration. Because of the advancement of technology in the present scenario, there is a need for antenna which can satisfy changing operating requirements. Reconfigurable antennas are used to maximize antenna performance in a changing scenario. So, in this paper we have designed array of microstrip patch antenna and developed reconfigurability in it so that we can get all benefits together like low profile, low weight, low cost, high gain, high directivity, and different operating capability. PIN diodes are used to achieve reconfigurability. Diodes basically changes the path of current flow and thereby achieve reconfigurability. The desired antenna because of its multi-band operation capability can be widely used in Mobile Broadband Wireless Access (MBWA) protocols based on standards specifications such as IEEE 802.20 or ATIS/ANSI HC-SDMA(such as iBurst) operate between 1.6 and 2.3 GHz to give mobility and in-building penetration characteristics similar to mobile phones but with vastly greater spectral efficiency, amateur radio, amateur satellite operator and amateur television repeaters that operates in S band at 3.4 GHz. 1.260–1.270 GHz band is used for amateur satellite up-links, and 4.9 GHz is used for 802.11j public safety WLAN and 6 and 7 GHz spectrum band for point-to-point microwave backhaul links.

2 Array Design

2.1 Design of 1 × 1 Array

The geometrical structure of the antenna and the radiating element including dimensions is shown in Fig. 1. The antenna is based on a 40 mm × 40 mm FR4-epoxy substrate with a dielectric constant of 4.4, loss tangent 0.02 and a thickness of 1.6 mm. The patch, which is square-shaped, is fed using a 3 mm wide microstrip feed line. The width of feed is chosen according to best impedance matching. Antenna is printed on non-grounded part of substrate. The antenna inhabits an area of 35 mm × 37.5 mm. Reconfigurability is achieved by using a PIN diode. Simulated design of antenna when diode is OFF and when diode is ON is shown in Figs. 1 and 2 respectively.

Fig. 1
figure 1

Simulated Design of 1 × 1 reconfigurable antenna when the diode is OFF (front view and back view respectively.)

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Fig. 2
figure 2

Simulated design of 1 × 1 reconfigurable antenna when the diode is ON (front view and back view respectively.)

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2.2 Design of 2 × 1 Array

Here 2 × 1 reconfigurable array antenna has been designed with above-said dimensions. In this design, as shown in Fig. 3, two patches are joined together with a common feed. PIN diodes are used to achieve reconfigurability.

Fig. 3
figure 3

Simulated design of 2 × 1 reconfigurable antenna. a When diode is OFF, b When diode is ON

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3 Simulation and Study Results

3.1 Simulation and Results of 1 × 1 Antenna

Return loss characteristics of 1 × 1 antenna is displayed in Fig. 4. When diode is in OFF state, then it radiates on frequencies 1.786, 3.484 and 6.136 GHz (green color curve in Fig. 4) and when diode is in ON state, it radiates on frequency 6.61 GHz (red color curve in Fig. 4). In this design with the application of PIN diode reconfigurability is developed in frequency.

Fig. 4
figure 4

Return loss of 1 × 1 antenna in OFF and ON condition of diode

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Gain and Directivity characteristics of 1 × 1 antenna is displayed in Fig. 5 when diode is in OFF state and in Fig. 6 when the diode is in ON state. It is clearly inferred from Figs. 5 and 6 that when diode is in OFF condition Gain and Directivity of 1 × 1 antenna at resonant frequency 6.136 GHz is 5.76 dBi and 8.674 dBi, respectively and when diode is in ON condition Gain and Directivity of 1 × 1 antenna at resonant frequency 6.61 GHz is 5.248 dBi and 6.263 dBi, respectively. Simulation and Results of 1 × 2 array.

Fig. 5
figure 5

Gain and directivity curve of 1 × 1 antenna when diode is in OFF state

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Fig. 6
figure 6

Gain and Directivity curve of 1 × 1 antenna when diode is in ON state

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3.2 Simulation and Results of 2 × 1 Array

Return loss characteristics of 2 × 1 array antenna is displayed in Fig. 7. When diode is in OFF state, then it radiates on frequencies 4.075, 4.991, 6.44, and 6.943 GHz (red color curve in Fig. 7) and when diodes are in ON state, it radiates on frequencies 1.266, 3.878, 4.971, and 6.681 GHz (blue color curve in Fig. 7). In this design with the application of PIN diode reconfigurability is developed in frequency.

Fig. 7
figure 7

Return loss of 2 × 1 array antenna in OFF and ON condition of diode

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Gain and Directivity characteristics of 2 × 1 array antenna are displayed in Fig. 8 when diode is in OFF state and in Fig. 9 when the diode is in ON state. It is clearly inferred from Figs. 8 and 9 that when diode is in OFF condition Gain and Directivity of 2 × 1 array antenna at resonant frequency 6.44 GHz is 6.78 dBi and 9.97 dBi respectively and when diode is in ON condition Gain and Directivity of 2 × 1 array antenna at resonant frequency 6.681 GHz is 5.572 dBi and 9.53 dBi, respectively.

Fig. 8
figure 8

Return loss of 1 × 4 array antenna in OFF and ON condition of diode

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Fig. 9
figure 9

Gain and Directivity curve of 2 × 1 array antenna when diode is in ON state

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4 Comparative Study of All the Designs

As we can see in Table 1 when there is single Patch Antenna with no diodes, then it radiates on frequencies 1.786, 3.484 and 6.136 GHz, and Gain and Directivity at max resonant frequency as 5.76 dBi and Directivity as 8.764 dBi. On applying diode, resonant frequency changed to 6.61 GHz with return loss as −49.927, and Gain and Directivity as 5.248 dBi and 6.263 dBi resp. Similarly, we can clearly see from Table 1, as numbers of patches in the array are increased, Gain and Directivity are also getting increased. In this paper, we have obtained maximum gain and directivity as 6.780 dBi and 9.970 dBi resp. when diode is OFF and 5.572 dBi and 9.53 dBi resp. when diode is ON.

Table 1 Operating frequency, and return loss, gain and directivity of the antenna for each condition
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5 Conclusion

In this paper, we have proposed 1 × 1 and 2 × 1 array antennas and developed reconfigurability for all the proposed structures. In this design, we have used PIN diodes to achieve reconfigurability, which acts as a switch. From above, it is clear that with the increase of the no. of elements, antenna parameters like gain and directivity are getting improved. As future work, we can simulate 4 × 1 and 8 × 1 microstrip array antenna with different diode configurations to achieve better radiation characteristics like more gain, directivity and bandwidth, and reduced return loss. The designed antennas operate in L band, S band, and C band and can be used in multiple applications like WLAN, Satellite, Radio applications, etc.