## 3 Antenna Implementation  
Based on the aforementioned design methodology, a broadband circularly polarized (CP) filtering magnetoelectric dipole antenna (ME) was designed, fabricated, and  
Figure 6: Surface current distribution of the proposed antenna when t = 0 and t = T/4 at the CP radiation frequencies. (**a**) 3.65 GHz. (**b**) 4.45 GHz. Figure 7: Frequency control of the dual CP moods at (**a**) 3.65 GHz with \(w\) varies, (**b**) 4.45 GHz with \(d_{3}\) varies, and (**c**) 4.45 GHz with \(w_{1}\) varies. tested, as shown in Figure 8a. The S parameters were measured using an Agilent N5227A (Keysight, Santa Rosa, CA, USA) vector network analyzer, while the axial ratio (AR), gain, and radiation patterns were obtained using a Satimo measurement system (Microwave Vision Group, Paris, France). Figure 8b-d present the simulated and measured S parameters, the realized gain, and the AR, respectively. Figure 8: _Cont._  
The measured results show good agreement with the simulated ones, as illustrated in Figure 8b-d except for minor discrepancies. These variations primarily stem from practical fabrication limitations in PCB production, including but not limited to etching tolerances, dielectric constant variations, and assembly alignment precision. In simulations, the antenna achieves a \(-10\) dB impedance bandwidth of 46.2% (3.06 GHz-4.90 GHz) and a 3 dB axial ratio (AR) bandwidth of 31.9% (3.53 GHz-4.87 GHz), with a relatively stable in-band gain of 6.6 dBi. In measurements, the fabricated antenna exhibits an (\(S_{11}\)) bandwidth of 66.4% (2.87 GHz-5.05 GHz) and an AR bandwidth of 31.9% (3.32 GHz-4.58 GHz), with an average in-band gain of 5.5 dBi. Compared to simulations, the measured impedance bandwidth is significantly broadened by approximately 20.2%. Three radiation nulls are observed at around 2.45 GHz, 6.8 GHz, and 7.5 GHz. Although the out-of-band suppression level in the lower stopband is slightly reduced, the upper stopband maintains a high radiation suppression level. However, the in-band gain decreases by approximately 1.1 dB, which can be attributed to fabrication and measurement tolerances. While the measured AR bandwidth shifts slightly toward lower frequencies compared to simulations, its fractional bandwidth remains nearly unchanged. Figure 9 presents the normalized radiation patterns at 3.5 GHz and 4.35 GHz. As expected, stable radiation patterns with over 20 dB cross-polarization levels are observed within \(\pm 30^{\circ}\). Moreover, in the phi = \(90^{\circ}\) plane, the power difference be  
Figure 8: The proposed ME antenna (**a**) prototype, (**b**) measured reflection coefficients, (**c**) measured realized gains, (**d**) measured AR, and (**e**) measured radiation efficiency. tween the main polarization (LHCP) and the cross-polarization (RHCP) is further enhanced, confirming the antenna's effective left-hand circular polarization characteristics. To highlight the merits of the proposed work, Table 1 provides a comparative analysis of relevant CP antennas. The proposed antenna demonstrates superior wideband performance. In [10; 11; 12], metallic patches serve as radiators, and filtering circuits are employed to achieve CP filtering functionality. However, their operational bandwidths are inherently limited (7.10% in [10], 11.40% in [11], and 21.60% in [12]). In references [16; 17; 22], bandpass filtering characteristics were achieved in circularly polarized patch antennas through relatively simple modifications including loading parasitic elements, etching slots, or incorporating open-circuited stubs on the microstrip feedline. More advanced approaches in [19; 21] combined these slotting or stub-loading techniques with additional filtering methods such as introducing parasitic patches, loading shorting probes, or implementing shorted patches. In [18; 20], although relatively wide operating bandwidths were achieved, these designs suffer from several drawbacks including excessive antenna profile height, unstable in-band gain, and poor out-of-band suppression performance.