In this design, metamaterials are used to reject unwanted bands. Two metamaterial unit cells, M1 and M2, are positioned above the ground (see Figure 4, Step 3). Equation 1 determines the center frequency of the band-notch for a given effective dielectric constant and Equation 2 determines εeff:

Equation 1


Where:

Lm is the length of the resonator

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C is the speed of light

εr is the dielectric constant of the substrate.

Figure 6b shows -4 dB |S11| at the center frequency (fn1) of the first unwanted band (5.2 to 5.8 GHz); however, the integration of metamaterials in Step 3 introduces a noticeable degradation in antenna matching, particularly above 7 GHz. To address this effectively, two rectangular stubs are added (see Figure 4, Step 4) and |S11| is reduced to under -10 dB.

Finally, in Step 5, two additional unit cells, M3 and M4, are integrated. This results in significant rejection over the second targeted band (7.2 to 7.8 GHz). |S11| reaches approximately -4 dB at the center frequency of fn2 = 7.6 GHz.

Figure 7

Figure 7 Prototype UWB antenna.

Figure 8

Figure 8 Measurement setup.


PROTOTYPE FABRICATION AND MEASUREMENT RESULTS

An antenna prototype, shown in Figure 7, is fabricated to verify the simulations experimentally. Measurements of |S11| are made using a Keysight N5224A vector network analyzer, as shown in Figure 8. Figure 9 compares simulated and measured results, showing a close correspondence.

Figure 9

Figure 9 Simulated and measured antenna reflection coefficients.

Figure 10

Figure 10 Simulated antenna current distributions at the notch center frequencies.


To provide a more comprehensive illustration of the characteristics associated with the dual band-notch features, Figure 10 shows simulated current distributions at frequencies fn1 and fn2. It reveals a concentration of current around metamaterial unit cells M1 and M2 within the WLAN band. Within the satellite data link band, current clusters around metamaterials M3 and M4.

Radiation patterns are measured in both the E-plane (YZ-plane) and H-plane (XZ-plane) at 4.3, 6.6 and 9 GHz, with the results shown in Figure 11. The results show bidirectional characteristics in the E-plane and omnidirectional characteristics in the H-plane for all frequencies of interest. Minimal changes at high frequencies are attributed to substrate power loss.

Figure 11

Figure 11 Simulated and measured antenna radiation patterns at 4.3 (a), 6.6 (b) and 9 (c) GHz.

Figure 12

Figure 12 Simulated and measured antenna peak gain.


Figure 12 shows the measured and simulated peak gain, demonstrating close agreement. Gain remains stable across the entire UWB range, reaching a maximum of 3.7 dBi at 10.3 GHz. This is accompanied by a significant decrease at fn1 (-3.8 dBi) and fn2 (-3.7 dBi). It validates the effectiveness of the metamaterials technique for rejecting radiation within the two undesired frequency bands.

A comprehensive comparison of this with other related works is shown in Table 2, highlighting distinctive aspects such as dimensions, frequency range, rejected bands, employed techniques, complexity and design technology. This design is compact and features a simple rejection technique based on metamaterials. The use of a single-faced CPW configuration not only simplifies its construction but also enhances practicality and ease of integration into diverse antenna systems.

Table 2


CONCLUSION

A novel approach to the design of a compact UWB patch antenna with improved rejection capabilities integrates a dual-ellipse structure in the patch geometry fed by CPW. It also employs four open-loop resonators to selectively target undesirable frequency bands, specifically WLAN (5.2 to 5.8 GHz) and the satellite downlink band (7 to 8 GHz). Experimental results closely align with the simulation, verifying the effectiveness of the open-loop resonators in enhancing rejection. The final design, incorporating metamaterials, demonstrates UWB performance with dual-band rejection. The use of metamaterials to reject radiation in undesirable frequency bands provides insight into the development of compact UWB antennas for applications in wireless communication systems.

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