Tri resonance multi slot patch antenna

© The Author(s) 2020. Published by ARDA. Abstract In this work, tri resonance multi slot microstrip patch antenna which operates at three center frequencies of 11 GHz, 11.9 GHz, 15.7 GHz is designed and simulated. As a commercial simulation tool, Sonnet Suites, a planar 3D electromagnetic simulator was used. Details of the simulation results are presented and discussed. As a result, an input match of -6.88 dB at the resonance frequency of 11 GHz, an input match of -37.12 dB at the resonance frequency of 11.9 GHz, an input match of -29.49 dB at the resonance frequency of 15.7 GHz were observed. The gain was observed as 8.25 dB at 11 GHz and 4.82 dB at 11.9 GHz. Also, the gain was observed as 7.07 dB at 15.7 GHz. The patch has several symmetric slots and it’s well known that slots change the current distribution of the patch antenna.


Introduction
Microstrip patch antenna has been studied in use for a long time. The demand for conformability, portability, low cost, light weight has increased. Microstrip antennas are attracting attention in broad range of multifunctional wireless communication systems [1]. The patch and the ground plane may have various geometric configurations and input impedances are usually 50 Ω or 75 Ω. Thus, antennas that can operate at more than one frequency are desired. A single wide-band antenna may fulfill the requirement but on account of receiving more than one frequency band at the same time and consequently is prone to interference [2]. They have some limitations, especially narrow bandwidth. So different antennas that are needed for different applications will cause a limited space problem. Re-searchers think that multiband antennas provide solutions. A multi-band antenna can be made by changing the antenna shape [3]. There are numerous and well-known methods to increase the bandwidth of antennas, including increase of the substrate thickness, the use of a low dielectric substrate matching and feeding techniques, and the use of slot antenna geometry. Many techniques have been reported to reduce the size of microstrip antennas at a fixed operating [4]. These periodic structures would allow a single patch antenna to resonate at multiple frequencies, so that by adjusting their number, shape, width and their positions with respect to each other within the patch, the selection of the desired set of bands is easily achieved. The main purpose is to design a microstrip patch antenna system in the range of 11 to 22GHz [5]. These different studies have been reported in the literature studies of antennas with different frequency and bandwidths.

Antenna design
In this section we will introduce the design of our antenna [6]. The effective dielectric constant has values in the range of 1 < , where the dielectric constant of the substrate is much greater than the unity ( ≫ 1), the value of will be closer to the value of the actual dielectric constant of the substrate. The various design equation for the conventional patch antenna is as written below [7].
The most desirable substrate for good antenna performance is normally thick substrate whereby the dielectric constant is at the lower end. This is due to the fact that this range provides better performance compared to thin substrate [8]. The width (W) and the length (L) of Antenna 1 are calculated from conventional equations: where, where, ffective length of the patch, ∆ ℎ is normalized extension of patch length, is effective dielectric constant [9].
For efficient radiation, the width W is given as: where, c is the speed of light and W is width of patch antenna [10]. The geometry of the slot antenna is shown in Figure 1. The size of the antenna is 48x64 mm. A dielectric substrate with dielectric permittivity " of 4.3 and thickness h1 of 1mm has been used in this design [11]. The antenna consists of square slots and rectangle slots. Also, the slot made on the ground helps in the reduction of overall weight and size of proposed antenna [12]. The position of the coaxial cable can be obtained by using the following equation: where, is the desire input impedance to match the coaxial cable

Analysis results
The simulation and analysis are completed for tri resonance multi slot patch antenna by sonnet lite software. The model was designed to match 50 Ohm of the corporate feed [14]. The input match is another way of expressing mismatch. It is a logarithmic ratio measured in dB that compares the power reflected by the antenna to the power that is fed into the antenna from the transmission line.
The first important parameter which is helpful to calculate the bandwidth of the antenna structure is its S11 in decibel versus frequency. During this antenna feeding has been done at the point where the input match is minimized [16]. Input match as a result of simulations performed was observed as in Figure 2. The simulated radiation patterns of the antenna at its resonance in the elevation-cut plane (ϕ = 0° and ϕ = 90°) have been illustrated [17]. In frequency of 11 GHz, as it can be seen in Figure 3, 8.25 dB directional gain at ϴ =∓60° was obtained in the electric field ϴ polarization. Cross polarization level is less than -5 dB. In frequency of 11.9 GHz with an input match value of -37.12 dB, as seen in Figure 4, 4.82 dB directional gain was obtained in the electric field ϴ polarization at ϴ = 45°. Cross polarization level is less than -7 dB.  In frequency of 15.7 GHz with an input match value of -29.49 dB, as seen in Figure 5, there was a 7.077 dB directional gain at ϴ = 0° in the electric field ϕ polarization. Cross polarization level is less than -9 dB. A parametric study was conducted in order to see the fabrication tolerances of the antenna. The changes which are slot size, dielectric thickness, dielectric(air) thickness and dielectric constant, made in the patch geometry helped to improve design parameters such as return loss, gain, resonance frequency and impedance [18]. The optimization of the air layer thickness results is seen in Table 1. The values in Table 2 were found by changing the thickness of the dielectric material.  Table 3 has the results when slots sizes were changed. The dielectric constant was changed to see the effect on S11 and gain. The results are shown in Table 4.

Conclusion
In this paper a tri resonance multi slot patch antenna has been presented [19]. Different methods for miniaturization of a square microstrip patch were studied and a novel fractal patch with multiple-slots was developed [20]. In this design, a microstrip patch antenna that is desired to run between 11-22 GHz frequency values has been realized. Gains were observed in 3 frequencies. At 11 GHz, the gain of the antenna is 8.25 dB, at 11.9 GHz the gain of the antenna is 4.82 dB, and at 15.7 GHz the gain of the antenna is 7.07 dB. However, a supplementary use of such modifications will certainly help in antenna size reduction with a further improved performance [21]. Future developments could be based on the fabrication of the antenna.