Development of a Receive Phased Array Antenna for High Altitude Plat-

form Stations using Integrated Beamformer Modules

Will Theunissen 1, Vipul Jain 2, Gaurav Menon 2 1 Facebook Connectivity Labs, Menlo Park, CA, 2 Anokiwave, Inc., San Diego, CA

Abstract— This paper describes the development and test of an electrically steerable phased array antenna designed for imple-mentation in multilayer circuit board architecture. The arrays

were designed for use in high altitude platform stations (HAPS) demonstrations to support RF links to mechanically steered cus-tomer premises equipment (CPE) terminals. Measured perfor-

mance results are shown for K-band 256 element receive arrays using Anokiwave 0102 QFN packaged beamformer modules.

Index Terms—5G mobile communication, internet of things,

satcom, phased arrays, HAPS

I. INTRODUCTION

A K-band receive phased array antenna was developed to

provide full electronic beam steering for an airborne platform

for broadband wireless applications. The antenna is designed to

provide service to a 50km radius service area with four sectors.

One Tx/Rx antenna pair serves each sector. Fig. 1 shows a

steerable focused beam radiation pattern and a phase only con-

tour beam used in acquisition of CPE terminals. The contour

beams are range compensated for uniform power flux density.

The DC power consumption, G/T, radiated power (EIRP) and

spatial isolation of the communications link drive the size of the

array.

II. ARRAY DESIGN CONSIDERATIONS

The arrays are based on MLB and surface mount packaging

and assembly that have been in common use since starting to

appear about a decade ago [1]. Receive apertures are formed

with 256 element tiles. The tiles can be arbitrarily added and

arranged based on electrical G/T requirements for the receive

chain taking into account achievable tile performance. The tile

performance in turn is determined by receive module noise fig-

ure (NF) of the LNA. The array triangular grid is sized to pro-

vide grating lobe free scan performance to 65° from boresight.

Radiating elements were designed to provide 27% VSWR

bandwidth with 2 GHz instantaneous bandwidth. An array

friendly stacked patch radiating element compatible with the

multilayer board stackup shown in Fig. 2 was used with suffi-

cient performance over the required bandwidth. The patch radi-

ator model is shown in Fig. 3. The dual input of the module

R = 18km

Range rings at 10km intervals

CPEs

Focused / Contoured beam

Peak 15.5 dBi 1dB interval

Peak 29 dBi 3dB interval

Figure 1. Focused and contoured beam radiation patterns and footprints.

Fig. 2. Multilayer board cross section.

Fig. 3. Radiating element model, return loss and isolation.

Fig. 4. Layout of beamforming modules and patches.

allows switchable left- and right-handed circular polarization.

The patches couple directly to the RF layer of the multilayer

board with plated through hole (PTH) vias. A sequential rota-

tion of the radiating elements provides low axial ratio. Power

Control and DC power are supplied mostly using layers 2 and

3 of the seven layer MLB. The RF power divider network di-

viders are connected by PTH vias to surface mount resistors.

Fig. 4 shows the leadframe footprint of the 7x7mm module with

some detail of coupling to the radiating elements, DC power

and digital control.

III. RECEIVE BEAMFORMER MODULE

The receive beamformer module incorporates two receive

channels (H/V) for each antenna element served. With inde-

pendent complex weighting in each channel the module can

correct for maximum gain, regardless of receive polarization.

The schematic of the beamformer module is captured in Fig. 5.

Complex weighting is achieved using a 5-bit phase shifter and

5-bit VGA with 15.5dB of range. Each receive channel can be

disabled independently which is useful for calibration and test

purposes. The module achieves a NF of 3.5dB with a total

power consumption of only 36mW per channel. The module

consists of a single Silicon IC wire bonded within a 7x7mm

QFN.

Fig. 5. Schematic diagram of the beamforming module.

IV. ASSEMBLY AND TEST

Array boards were assembled in a high volume assembly facil-

ity. Figs. 6 and 7 show the front and back of the receive array.

Array control software is integrated into the antenna range

measurement control software so that multiple beamstates can

be measured over the frequency band at each look vector over

a spherical scan volume. This allows rapid evaluation of tile

performance over the whole scan volume of the array. Results

of a single tile measurement are shown in Fig. 8 where the array

performance is measured and displayed as a function of scan in

volumetric pattern plots. The assembled arrays were also meas-

ured in a planar near-field measurement. Automated array cali-

bration provides correction tables. The goal was to have a sys-

tem that would not have to be calibrated in field use. Fig. 9

shows a directly measured excitation with a 4 dB peak variation

in the uncalibrated state.

Fig. 6. Front View of the Array.

Fig. 7. Backside view of the array.

Fig. 8. Measured volumetric radiation patterns in the Ø=45° plane using inte-

grated array control in the antenna range measurement control system.

Fig. 9. Uncalibrated measured aperture excitation.

As a demonstration of the versatility of arrays, a sector beam

was synthesized with phase only excitation. Fig. 10a shows the

synthesized 90 degree sector. The beamstate was loaded to the

array and the resulting volumetric pattern measurement is

shown in Fig. 10b. A cell based hexagonal footprint was also

loaded and measured as shown in Fig. 11. The resulting radia-

tion pattern footprint is also shown in the figure. Two dimen-

sional array pattern control from HAPS platforms allows the

possibility of precise sectoring and high isolation between cells,

minimizing handover overhead and interference.

Fig. 10a. Phase only synthesized 90 degree sector beam.

Fig. 10b. Measured radiation pattern of phase only synthesized 90 degree sec-

tor beam.

Fig. 11. Contour beam generation example for a cell based system showing

measured radiation pattern of phase only synthesized beams and resulting pat-

tern footprints for HAPS platforms.

Transmit and receive arrays were finally tested in an airborne

test campaign from aircraft to test tracking to mechanically

steered reflector antennas on the ground, and the resulting link

throughput to modems and routers on the ground in simultane-

ous up- and downlinks.

V. CONCLUSION

The development of an electrically steerable receive K-band

phased array antenna was successfully demonstrated with test-

ing in both the antenna test range and on an airborne platform.

Measured RF results are shown for a 256 element receive array.

REFERENCES

[1] Theunissen, W.H. et al; Development of an X-band phased

array antenna using multilayer circuit board architecture, 2010

IEEE International Symposium on Phased Array Systems and

Technology (ARRAY), Digital Object Identifier: 10.1109/AR-

RAY.2010.5613367, 2010, Page(s): 211 - 218