The microstrip bi-Yagi and quad-Yagi array antennas have been simulated using MicroStripes 7.0, a 3D full-wave simulator that solves for the electric and magnetic fields via the transmission line matrix (TLM) method. After an optimized design was obtained, the two antennas were fabricated by Prototron Circuits, as shown in Fig.4. The simulated return loss versus frequency is presented in Fig. 5 compared to that of the original (one branch) microstrip Yagi array design. The bandwidths of the three designs are as follows: microstrip Yagi: 8.1%, bi-Yagi: 7.1%, and quad-Yagi: 5.0%. In comparing the three designs, it seems that the bandwidth tends to decrease as more microstrip Yagi arrays are added to produce a larger array. The smaller bandwidth of the quad-Yagi array may be due to the shift of the lower resonance of the driven element to a higher frequency. The measured return loss plots versus frequency of the antennas are also displayed in Fig. 5. The measured bandwidths of the bi-Yagi and quad-Yagi designs are 6.9% and 5.2%, respectively. Although, the lower and higher resonances of the measured designs occur at similar frequencies, the return loss of the quad-Yagi array is higher than that of the bi-Yagi array, resulting in a smaller bandwidth.
The simulated (normalized) 2D radiation patterns comparing the three Yagi designs at 5.2 GHz are presented in Fig. 6. From this plot, it is observed that the F/B ratio tends to decrease as more Yagi arrays are included to produce the larger array. At some frequencies close to 5.2 GHz, the F/B ratio can be increased as the cost of a lower gain (by 0.5 dB); hence, there is a tradeoff. Table 1 and 2 show how the gain and F/B ratio varies with frequency. The angle of maximum radiation for all the designs is between 35º-45º, while the beamwidth coverage is approximately 40º. Figs. 7 and 8 display the measured (normalized) 2D radiation
patterns of the microstrip bi-Yagi and quad-Yagi arrays at 5.2 GHz. A good agreement is observed between the simulated and measured results in the bi-Yagi array, although, the measured design has a slightly lower F/B ratio (10 dB) in comparison to simulation. The gain is 13.0 dBi and the cross-polarization is below -25 dB. The quad-Yagi array also exhibits a good agreement between the simulations and measurements. For this design, a gain of 15.6 dBi can be obtained with a cross-polarization below -18 dB. Considering that these structures use a highly conductive metal (Cu) that was printed on a low loss dielectric, the efficiencies of all the Yagi designs presented are greater than 89%.
The microstrip bi-Yagi and quad-Yagi array antennas have been simulated using MicroStripes 7.0, a 3D full-wave simulator that solves for the electric and magnetic fields via the transmission line matrix (TLM) method. After an optimized design was obtained, the two antennas were fabricated by Prototron Circuits, as shown in Fig.4. The simulated return loss versus frequency is presented in Fig. 5 compared to that of the original (one branch) microstrip Yagi array design. The bandwidths of the three designs are as follows: microstrip Yagi: 8.1%, bi-Yagi: 7.1%, and quad-Yagi: 5.0%. In comparing the three designs, it seems that the bandwidth tends to decrease as more microstrip Yagi arrays are added to produce a larger array. The smaller bandwidth of the quad-Yagi array may be due to the shift of the lower resonance of the driven element to a higher frequency. The measured return loss plots versus frequency of the antennas are also displayed in Fig. 5. The measured bandwidths of the bi-Yagi and quad-Yagi designs are 6.9% and 5.2%, respectively. Although, the lower and higher resonances of the measured designs occur at similar frequencies, the return loss of the quad-Yagi array is higher than that of the bi-Yagi array, resulting in a smaller bandwidth.
The simulated (normalized) 2D radiation patterns comparing the three Yagi designs at 5.2 GHz are presented in Fig. 6. From this plot, it is observed that the F/B ratio tends to decrease as more Yagi arrays are included to produce the larger array. At some frequencies close to 5.2 GHz, the F/B ratio can be increased as the cost of a lower gain (by 0.5 dB); hence, there is a tradeoff. Table 1 and 2 show how the gain and F/B ratio varies with frequency. The angle of maximum radiation for all the designs is between 35º-45º, while the beamwidth coverage is approximately 40º. Figs. 7 and 8 display the measured (normalized) 2D radiation
patterns of the microstrip bi-Yagi and quad-Yagi arrays at 5.2 GHz. A good agreement is observed between the simulated and measured results in the bi-Yagi array, although, the measured design has a slightly lower F/B ratio (10 dB) in comparison to simulation. The gain is 13.0 dBi and the cross-polarization is below -25 dB. The quad-Yagi array also exhibits a good agreement between the simulations and measurements. For this design, a gain of 15.6 dBi can be obtained with a cross-polarization below -18 dB. Considering that these structures use a highly conductive metal (Cu) that was printed on a low loss dielectric, the efficiencies of all the Yagi designs presented are greater than 89%.
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