Performance Analysis of Novel Multi-band Monopole Antenna for Various Broadband Wireless Applications

The star patch design is combined from the iteration of the triangle patch shape. Therefore, the equations below have been applied to compute the resonant frequency of this star monopole antenna [24], where \(S_{1}\) is the length of the triangle side in (mm) as revealed in Fig. 1. All major dimensional parameters of the novel structure are listed in Table 2.

As demonstrated from Fig. 2, the dimensions of the proposed design are 20 × 15 mm² which is printed on the cheap dielectric substrate (FR4) having thickness (h) of 1 mm with loss tangent (\(\delta\)) and dielectric constant (\(\varepsilon r\)) of 0.02 and 4.4 separately. The compact configuration consists of a star patch with slit etched on the center of the radiating patch. A coplanar waveguide (CPW) feeding transmission line (50 \(\varOmega\)) is used to excite the compact antenna with a strip line of width 1.8 mm and length 8.3 mm. Several antenna parameters, in particular the antenna reflection characteristics can be controlled by the proper impedance of the feed line [25]. The radiating patch is bordered by a U-shaped line of width 0.1 mm which connects both the ground planes on the substrate material. There is a gap distance of 0.3 mm between both radiating materials. The main idea behind of the adding dual square-shape slots (1 × 1 mm²) on the ground plane, in order to produce a new resonant frequency. The copper material with a thickness of 0.035 has been used to design the patch and ground plane of the antenna. Consequently, a star shaped slot with a radius of 3 mm is designed on the center of the radiating patch.

Form Fig. 3, the design stages of the novel five-band antenna are depicted and described step by steps. First of all, a star monopole antenna with the slot method is created as illustrated in the design “A1” of Fig. 3. As can be observed in Fig. 4, this antenna operates only at two bands with less value of reflection parameter S₁₁. A slot star is etched on the radiating patch to improve the parameters of the antenna “A1”, as indicated in configuration “A2” of Fig. 3. So that, the antenna “A2” operates at extra bands, the U-shaped copper material is printed on the border of star monopole as presented in configuration “A3” of Fig. 4. The introduction of U-shaped material leads the antenna to resonate at 11.8 GHz for wireless computer networks and International Telecommunication Union (ITU) band, as revealed in Fig. 4. To insert another operating band for the antenna “A3”, dual square shaped slots are designed on the ground conductive surface of the star monopole structure as demonstrated in configuration “A4” and “A5” of Fig. 3. The effects of the dual square shaped slots make the antenna to operate at 17.7 GHz (Ku-band), as revealed in Fig. 4.

A strip-shaped slot is etched on the top star monopole to further increase the operating skills of antenna “A5”, as indicated in configuration “A6” of Fig. 4. A discontinuity in the radiating element of the monopole antenna is created due to the proposal of strip shaped slot. Because of the discontinuity, the long path of the surface electrical current rises [26]. This increase in the length of current path impacts the input impedance of the star monopole. As a result of this effect, the antenna adds extra resonant frequency at 4.9 GHz for a wide collection of wireless broadband applications, as indicated in Fig. 4. The design of the novel monopole antenna “A6” is illustrated in detail in the figure of the antenna geometry part as mentioned in advance.

The result of the theoretical S₁₁ of the design is obtained using Ansoft HFSS and CST software. The electronic device of (VNA) Vector Network Analyzer (N9918A) is used to measure this simulated S₁₁. This study shows that the antenna resonates at 4.9 (WLAN (802.11j)), 5.9 (upper WiMAX), 8.2 (Satellite TV), 11.8 (X-band), and 17.7 GHz (Ku-band) under simulation and at 4.69, 6.03, 7.99, 11.88, and 17.53 GHz in measurement testing, respectively. The simulated bandwidth S₁₁ less than − 10 dB of the prototype model is about 4.41 GHz (4.1–8.51 GHz), 0.99 GHz (11.27–12.26 GHz), and 0.84 GHz (17.26–18.1 GHz), and about 5.08 GHz (3.56–8.64 GHz), 1.01 GHz (11.45–12.46 GHz), and 1.2 GHz (17.18–18.38 GHz) in measurement, respectively.

In addition, the simulated values of the VSWR is achieved which is about 1.04, 1.01, 1.15, 1.10 and 1.26 at 4.9, 5.9, 8.2, 11.8 and 17.7 GHz, and about 1.02, 1.04, 1.19, 1.19 and 1.12 at 4.69, 6.03, 7.99, 11.88, and 17.53 GHz in the measured values, respectively. The screenshots of the VSWR and the return loss of the fabricated multiband monopole antenna are measured using analyzers as appeared in Fig. 7.

The comparison between the obtained studies of the measurement and simulation of S₁₁ and VSWR parameters of the novel antenna is further demonstrated in Fig. 8. A good matching in the obtained results of the theory and experiment is observed for the proposed design. The slight difference may be because of the use of the VNA cable, fabrication tolerance, and point connection of SMA connector and cables applied for the measurement of the configuration. However, the obtained bandwidth of the novel design is enough to fulfill the necessities of WLAN, WiMAX, Satellite communication, ITU-band, and Ku-band applications.

The results of surface current distribution was also simulated in HFSS at all resonant frequencies of the proposed multiband antenna as illustrated in Fig. 9 respectively. From the figure has been revealed that current is uniformly distributed on the radiating patch and ground planes at all the resonance bands of the proposed antenna. The surface current has a maximum value at resonant frequency of 11.8 GHz and a minimum magnitude at resonance band of 5.9 GHz for the antenna loaded with U-shape material.

Theoretical and experimental far-field radiation characteristics of the monopole star-shape patch antenna are illustrated in Fig. 10. The radiation pattern of the fabricated prototype model is measured from 0 to 360 degree with step of 30 degree, at the resonance bands 4.69, 6.03, 7.99, 11.88, and 17.53 GHz, both in E-plane (co and cross) and H-plane (co and cross), respectively. As can be clearly revealed from Fig. 10, the proposed design has an almost omnidirectional pattern in E-plane (Y–Z) and bi-directional pattern in H-plane (X–Z). For both the cases, the achieved results of the measurement and simulation are in close agreement with a slight deviation because of alignment errors, measurement, and electromagnetic interference from the nearby devices.

The experimental and simulated peak gain along the operational frequencies for the compact structure has been depicted in Fig. 10. The figure shows that fluctuated gain along the desired bands is obtained. The simulated results of achieved gain of each operating frequency at 4.9, 5.9, 8.2, 11.8 and 17.7 GHz are about 1.8, 2.4, 3.6, 4.7 and 4.9 dBi, and the measured peak gain of approximately 1.95, 2.55, 3.56, 4.48, and 5.24 dBi are observed for 4.69, 6.03, 7.99, 11.88, and 17.53 GHz, respectively. As the results, the average gain of the simulated and measured results is about 3.51 and 3.56 dBi, respectively. The gain value enhances with operational resonances because of the raised effective area of the designed prototype model at shorter wavelengths.

The HFSS software has been used to find the radiation efficiency characteristics of the multiband antenna. The operating band efficiencies are about 94, 94, 84, 87 and 77% at the simulated operating bands of 4.9, 5.9, 8.2, 11.8 and 17.7 GHz, respectively. The star monopole antenna acts as a transmission line instead of radiating part at higher frequencies. Therefore, the magnitude of radiation efficiency decreases at higher resonances as revealed in simulations and Fig. 11. The summarization of the antenna results is listed in Table 3.