Rod lens antenna design

The second lens antenna is a rod lens antenna. Figure5.37shows the cross section of the AiP with rod lens. Given the success of hemisphere lens, further improvement can be achieved when the hemisphere lens extends to a rod antenna. The value ofRhemi is same as hemisphere lens – 5 mm.

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Figure 5.34: Photo of eWLB AiP test board with hemisphere lens. c2012 IEEE [168]

(a) E-plane (b) H-plane

Figure 5.35: Measured and simulated radiation pattern of hemisphere lens on eWLB AiP – FD with cavity: (a) E-plane and (b) H-plane. c2012 IEEE [168].

(a) (b)

Figure 5.36: EIRP of hemisphere lens on AiP: (a) folded dipole with cavity and (b) dual patch.

c 2012 IEEE [168].

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The other parameter is the height of the rod lens, which influences the antenna gain. The simulated gain of the AiP in the broadside direction for different values of hcly is shown in Figure 5.38. In general, for a fixed mode behavior, a greater h_cly has optimal gain at lower frequencies, while a smaller hcly has optimal gain at higher frequencies (see Figure 5.38(a)).

Figure5.38(b)presents the average gain and gain variation from 71 GHz to 82 GHz. Here, the measured frequency points are from 71 GHz to 82 GHz, with 1 GHz step. The average gain and gain variation are defined as follows:

Average Gain= 1 12

82GHz

X

fi=71GHz

Gf_i (5.5)

Gain V ariation=max(Gf_i)−min(Gf_i) (5.6) whereGfi is the gain atfi GHz frequency.

hcly is chosen as 5.5 mm since this results in optimal gain between 78 GHz and 80 GHz.

Furthermore, this yields a good trade-off between the average gain and the gain variation in the frequency range from 71 GHz to 82 GHz.

Enhanced model simulation The reflection coefficient S11 of the enhanced model simulation exhibits a similar behavior for a simplified model, as shown in Figure 5.39. In the enhanced model simulation, the rod lens and the MMICs are also included.

The reflection coefficientS11 of the enhanced model simulation exhibits a similar behavior for a simplified model, as shown in Fig. 5.39. In the enhanced model simulation, the rod lens and the MMICs are also included.

Measurement results

The rod lens were fabricated and measured with AiP test board. Here, the AiP-DP test board is used as primary antenna. Figure 5.40shows the photo of the test board as well as the rod lens.

Figure 5.37: Cross section of the eWLB package and the rod antenna. c2013 IEEE [172].

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(a) Simulated gain of the AiP for different heights hclyof the rod lens at single frequency.

(b) The average (avg.) gain and gain variation (var.) between 71 GHz and 82 GHz.

Figure 5.38: Simulated gain of the AiP for different heights h_cly of the rod lens at single frequency (a) and the average (avg.) gain and gain variation (var.) between 71 GHz and 82 GHz (b). c2013 IEEE [172].

Figure 5.39: Simulation ofS11 with the enhanced model. The AiP and the rod lens have the dimensionsLp=1.72 mm,Wp=0.52 mm,Rhemi=5 mm,Lm=6 mm,hcly=5.5 mm,hm=0.5 mm, hb=0.2 mm, and the MMIC is 2×2×0.45 mm³. c2013 IEEE [172].

The measurement configuration is similar as in Figure 5.13(a). The AiP was measured as a device under test (DUT). The LOin signal was generated by an Agilent signal source (Ag.

E8257D). The RF signal was transmitted by the AiP and received by an E-band standard 20 dBi gain horn antenna. The distance between DUT and horn antenna (d) was 1.6 m. The received signal was measured by a signal analyzer (R&S FSQ40) combined with a harmonic mixer (R&S FSZ90). Figure5.41shows photographs of the measurement setup in the absorber chamber and of the AiP with lens mounted.

First, the gain of the antenna in package was measured over the frequency. The test board was measured both with and without rod lens. The effective isotropic radiated power (EIRP) of the package was calculated using the Friis Transmission Equation. The measured EIRP of the AiP with lens is over 16 dBm from 71.4 GHz to 81.7 GHz (see Figure5.42). The maximum EIRP is 18.5 dBm at 79.2 GHz. The power output of the chip is also plotted for comparison.

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Figure 5.40: Photo of AiP-DP test PCB with rod lens. c2013 IEEE [172].

Figure 5.41: Photographs of the measurement setup in the absorber chamber and the AiP with lens mounted. c2013 IEEE [172].

The gain of the antenna with and without lens is shown in Figure 5.43. The measured gain of the AiP with lens is greater than 12 dBi from 71 GHz to 82 GHz and thus, except around 79 GHz, slightly lower than in the simulation. The difference between measurement and simulation may be because of the assembly tolerances and underestimation of the loss tangent of the material. The lens greatly improves the gain of the AiP. On average, it increases the antenna gain from 5.9 dBi to 13.7 dBi. This implies twice the dynamic range in radar applications. The gain variation is 2 dB.

The antenna radiation patterns are measured also at different frequencies. The measured radiation patterns at 78.3 GHz are shown in Figure 5.44.

The radiation patterns exhibit symmetric behavior in both the E-plane and the H-plane.

The side lobe levels in the E-plane and the H-plane are -16 dB and -13 dB, respectively. The cross-polarization (X-pol) is 18 dB lower than the co-polarization (Co-pol) in the E-plane and 117

5. DIFFERENTIAL ANTENNA IN EWLB PACKAGE

Figure 5.42: Measured EIRP of AiP with (wt) and without (wo) lens and power output of the chip. c2013 IEEE [172].

Figure 5.43: Simulated and measured gain of AiP with (wt) and without (wo) lens. c 2013 IEEE [172].

20 dB lower in the H-plane. The simulation X-pol in the H-plane is too small to plot. The measurements and the simulation are in good agreement.

Without the lens, a big notch around 30^◦ appears in the H-plane. It is caused by the mold size and conductivity of MMIC. Adding the lens eliminates this notch. The 3 dB beamwidths of the E-plane (Θ_3dB,E) and the H-plane (Θ_3dB,H) are 24.5^◦ and 17^◦, respectively. Table 5.1 shows a comparison of the rod lens AiP with hemisphere lens AiP [168]. The rod lens AiP achieves a much narrower beamwidth. Some other types of AiP solution are also listed in Table 5.1. The beamwidth of rod lens antenna AiP is comparable to that of various types of array antennas.

Figures5.45and5.46plot the measured radiation patterns at 72 GHz and 81 GHz, respec-tively. They exhibit behaviors similar to that at 78.3 GHz. Thus, we verified that the antenna 118

(a) Measured and simulated E-plane radiation pat-tern at 78.3 GHz.

(b) Measured and simulated H-plane radiation pat-tern at 78.3 GHz.

Figure 5.44: Measured and simulated radiation pattern of AiP rod lens at 78.3 GHz: (a) E-plane and (b) H-plane. c2013 IEEE [172].

(a) Measured and simulated E-plane radiation pat-tern at 72 GHz.

(b) Measured and simulated H-plane radiation pat-tern at 72 GHz.

Figure 5.45: Measured and simulated radiation pattern of AiP rod lens at 72 GHz: (a) E-plane and (b) H-plane. c2013 IEEE [172].

(a) Measured and simulated E-plane radiation pat-tern at 81 GHz.

(b) Measured and simulated H-plane radiation pat-tern at 81 GHz.

Figure 5.46: Measured and simulated radiation pattern of AiP rod lens at 81 GHz: (a) E-plane and (b) H-plane. c2013 IEEE [172].

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Table 5.1: Half power beam width comparison Θ_3dB,E Θ_3dB,H freq. antenna type this work 24.5^◦ 17.0^◦ 78.3 GHz patch+rod lens

[168] 38^◦ 53^◦ 76.5 GHz dipole+hemisphere lens [173] 20^◦ 20^◦ 60.0 GHz 4×4 patch array [153] 20^◦ 20^◦ 60.5 GHz 4×15 grid array

radiation pattern is stable over a wide frequency range.

This section presented lens antenna for AiP performance enhancement. Two lens – hemi-sphere and rod lens –are designed and verified. For the rod lens antenna, measurement results show that the proposed antenna has more than 12 dBi gain in the frequency range from 71 GHz to 82 GHz. The measured 3 dB beamwidth at 78.3 GHz is 24.5 degrees for the E-plane and 17 degrees for the H-plane. The dimensions of the whole antenna are 10×10×10.5 mm³.