Machine learning enabled dual to wideband frequency agile $$\:_S_\:$$ ceramic-based dielectric MIMO antenna for 5G new radio applications

The several advantages of Frequency Reconfigurable (FR) antennas have contributed to their increasing popularity. By employing several techniques, these antennas can automatically transition between frequencies, radiation patterns, and polarisations, which allows them to replace several antennas^1,2,3. The rapid expansion of wireless communications systems, higher data transmission rates, and larger channel capacities are becoming increasingly required to support the maximum number of users within a coverage area and provide continuous access to high-definition video streaming. However, fading becomes a significant challenge in a multipath environment due to surrounding objects or obstacles emphasising the significance of this issue^4,5,6.

The development of the multiple-input multiple-output (MIMO) system has been caused by its ability to accommodate higher capacities and quicker data rates without consuming more channel capacity. A MIMO antenna system may meet every modern wireless communication system’s needs. MIMO technology increases system capacity and data throughput by using many antennas on the transmitter and receiving sides without consuming more radio spectrum or power. The MIMO system’s requirements include a compact size, high efficiency, and a minimum level of mutual coupling between ports within the operational frequency range^7,8. One popular type of MIMO antenna that improves wireless communication is the Microstrip Patch Antenna (MPA). This is a result of the MPA’s low cost and small size. However, the MPA has a very low radiation efficiency due to its significant conductor loss. Alternatively, a dielectric resonator antenna (DRA) is a suitable technique that provides a large bandwidth and high radiation efficiency. Other methods that can be employed to excite DRAs include coaxial feed probes, microstrip feed lines, co-planar waveguides, and aperture coupling^{9,10,11,12,13,14}.

Limited research papers regarding DRA-based MIMO dual or triple bands operating in the lower frequency bands are available^{4,5,6,7,8,10,11,14}. In⁴, a MIMO DRA allows smartphone multi-band LTE MIMO operation and provides an impedance bandwidth of more than 24% in all frequency bands. In⁷, In all frequency bands, a cylindrical DRA triple-band hybrid MIMO antenna may achieve isolation of more than 25 dB and give an impedance bandwidth of more than 20%. In⁸, cylinder DRA and annular ring produce a two-port dual-band MIMO system. This configuration provides a strong isolation of more than 20 dB for the frequency bands of 1.75 to 2.4 GHz and 3.5 to 5.5 GHz. In¹⁰, by adjusting the permittivity values, a rectangular MIMO antenna was created that can function in the quad bands of 4.70–4.90 GHz, 3.79–4.04 GHz, 2.83–3.07 GHz, and 5.72–5.86 GHz. In¹⁴, a dual-band MIMO DRA with permittivity values. The comparative analysis of the suggested FR MIMO antenna with other MIMO antennas is given in Table 1. The flowchart for the DR-based FR antenna is illustrated in Fig. 1.

The layout of the suggested DR-based FR MIMO antenna is illustrated in Fig. 2. and Fig. 3. The attractive characteristics of the suggested DR-based FR MIMO antenna are as follows: a FR MIMO antenna based on DR for 5G Sub 6 GHz applications has been presented. It provides dual-band to wideband characteristics in ON-ON and OFF-OFF configurations, respectively. The isolation and gain are achieved by 20 dB and 4.3 dBi, respectively. The antenna can operate and is adaptable across many frequencies due to its 49.36 tuning range (TR). It is simple in design and easy to fabricate.

Table 1 Comparative Analysis of Proposed Work with Other Existing Work.

Table of Contents

Antenna configuration and analysis

Single Port FR antenna

The layout of the single port FR antenna is illustrated in Fig. 4. The single port is created on the FR-4 epoxy substrate ($\:S_=4.4)\left(tan\delta\:=0.02\right).$ The size of the FR-4 epoxy is 50 × 40 $\:S^$. The ground plane is printed below the substrate. The dimension of the ground plane is 18 × 40 $\:^{2}$. The dielectric resonator (DR) is made of $\:{Al}_{2}{O}_{3}({\in\:}_{r}=9.8)$ ceramic material. DR is placed above the feed structure. The microstrip patch behaves as a feed for DR. It is created above the substrate. By adding a small quantity of low-loss adhesive material to the dielectric resonator’s contact surface and carefully positioning it in the correct place on the radiator, the RDRs have been securely attached on the radiator’s surface in the suggested configuration. The dimensions of the layout parameters are given in Table 2.

Step evaluation of single Port antenna

The effect of $\:{|S}_{11}|$ due to various design steps is illustrated in Fig. 5. In the initial Stage-1, The rectangular patch with half ground is created and resonates at 2.4 GHz. In the next Stage-2, a T-shape is created inside the Stage-1. The resonant frequency is shifted to the left side, and it.

Table 2 Dimensions of the layout parameters.

resonant at 2.2 GHz. In Stage 3, the rectangular patch’s corner edges are truncated, providing a narrow band and wideband. In Stage 4, the annular ring structure is created above the T-shape, and it also provides the narrowband and wideband, but the resonant frequency is shifted to the left side. In the last Stage-5, DR is placed above Stage-4, providing a narrow band and wideband with improved bandwidth and impedance mapping. The frequency range, bandwidth, percentage of impedance bandwidth, and bandwidth ratio of various stages are given in Table 3.

Table 3 Stage by stage parameter analysis.

Mathematical modelling

The single port antenna consists of two dielectric layers: FR4 epoxy and alumina ($\:{Al}_{2}{O}_{3}).$ According to⁴, The effective permittivity $\:{\:(\in\:}_{reff})\:$and effective height $\:{(H}_{eff}$), are given by Eqs. (1)-(2):

$$\:{\text{H}}_{eff}=\:\text{H}+{\text{H}}_{\text{S}}$$

(1)

$$\:{\in\:}_{reff}=\frac{{H}_{eff}}{\frac{H}{{\in\:}_{r\:RDRA}}+\frac{{H}_{S}}{{\in\:}_{rSub}}}$$

(2)

In³, states that the resonance frequency of the fundamental $\:{{TE}_{111}}^{Z}$ is given by

$$\:{k}_{z}\text{tan}\left({k}_{z}\frac{d}{2}\right)=\sqrt{{(\in\:}_{reff-1}){{k}^{2}}_{0}-{{k}^{2}}_{z}}$$

(3)

Where, $\:{k}_{x},{k}_{y},$and $\:{k}_{z}$ are wave numbers, they fulfil the subsequent formula.

$$\:{{\:k}^{2}}_{x}+{{k}^{2}}_{y}+{{k}^{2}}_{z}={(\in\:}_{reff}){{k}^{2}}_{0}$$

(4)

$$\:\text{W}\text{h}\text{e}\text{r}\text{e},\:{k}_{x}=\frac{\pi\:}{b}\:\text{a}\text{n}\text{d}\:{k}_{y}=\frac{\pi\:}{b}$$

According to¹, Tuning Range (TR) and Total Spectrum (TS) are calculated through the Eqs. (5) and (6):

$$\%TR = \frac{2(f_{oh}-f_{ol})} {(f_{0h}+f_{0L})}\: \times \:100$$

(5)

Where $\:{f}_{oh}=highest\:resonance\:frequency$, and

$$\:{f}_{ol}=lowest\:resonance\:frequency$$

$$\:TS=\frac{2({f}_{max}-{f}_{min})}{({f}_{max}+{f}_{min})}$$

(6)

Where $\:{f}_{max}=highest\:\:frequency$, and

$$\:{f}_{min}=lowest\:frequency$$

Parametric analysis

The effect of the dielectric constant ($\:{\in\:}_{r})$ on DR and substrate is illustrated in Fig. 6. The dielectric constant of DR varies from 9.2 to 10.2 with a fixed FR-4 epoxy substrate. The $\:{Al}_{2}{O}_{3}$ with FR4 epoxy substrate provides better bandwidth and impedance matching than the others. Similarly, the dielectric constant of the substrate varies from 2.2 to 5.5 with a fixed $\:{Al}_{2}{O}_{3}$ DR. The FR4 epoxy substrate with $\:{Al}_{2}{O}_{3}$ DR provides better bandwidth and impedance matching than the others. The parametric analysis achieves the optimum values of DR’s length, width, and height are illustrated in Fig. 7. The DR’s length, width, and height vary from 15 to 18 mm,15 to 18 mm, and 5 to 8 mm, with a step size of 1 mm, respectively. The L = 16 mm, W = 16 mm, and H = 8 mm achieves better impedance matching and bandwidth than the others. The feed width varies from 2 to 3 mm, with a step size of 0.25 mm. T shape width varies from 1 to 1.5 with a step size of 0.1 mm.

Reconfigurable single Port DR

The single-port DR antenna acts as a reconfigurable due to inserting the PIN Diode switches inside the feed structure of DR, as illustrated in Fig. 4. The equivalent circuit of the PIN diode is illustrated in Fig. 8. When the PIN diode is in “ON” state it acts as a series of resistance and inductance. When the PIN diode is “OFF,” it acts as a parallel combination of resistance with capacitance and a series of inductances. PIN diodes have several benefits, including low resistance and lower capacitance values. Additionally, their compact shape minimizes their influence on antenna performance. We used RLC linear components for our simulations even though a PIN diode is a nonlinear element. It should be mentioned that the datasheet is based on actual tests carried out using packaged samples. Even though a diode is a nonlinear device, actual tests are used to get the lumped model. Instead of using a non-linear diode, we can apply a lumped model, and the result will be unchanged¹⁵. When both the PIN Diode switches are “ON” state, it provides the narrow band. The $\:{TE}_{111}$ mode is generated at 2.6 GHz inside the DR, as illustrated in Fig. 9(a). The wide band is provided when both the PIN Diode switches are in an “OFF” state. The $\:{TE}_{111}$ and $\:{TE}_{211}\:$mode is generated inside the DR at 3.38 GHz and 5.02 GHz, respectively, as illustrated in Fig. 9(b).

Two Port DR-based FR MIMO antenna

The single port DR-based FR antenna is converted into a two port DR-based FR MIMO antenna with an extended substrate. The substrate size is increased to $\:50\:\times\:85\:{mm}^{2}$. The parallel and orthogonal are the two ways to design the MIMO antenna. The comparative analysis between parallel and orthogonal configurations of the proposed antenna is illustrated in Fig. 10. The isolation comparison between the two configurations is illustrated in Fig. 11. The parallel configurations provide an isolation of less than 10 dB, and orthogonal configurations achieve the isolation of 20 dB. To create the Dual port FR antenna, PIN diodes are inserted in the orthogonal configurations, as illustrated in Fig. 2. and Fig. 3. The total numbers of PIN Diodes are increased to four.