# Proof-of-Concept of a Millimeter-Wave Integrated Heterogeneous Network for 5G Cellular
## 3 mmWave Beamforming Antenna and Backhaul
### Highly Directional Steerable mmWave Antennas  
Phased antenna arrays are a well-established and proven technology for electronically-steerable antennas. However, highly directional arrays with large apertures may encounter a range of implementation problems, such as heat dissipation, feeding line losses and placement/installation difficulties. These are especially critical for small-form factor millimeter wave antennas. In [21], two novel solutions were proposed: the modular antenna array (MAA) architecture and the lens array antenna (LAA). The first allows the creation of a large aperture, high gain antenna array from small-phased antenna array (PAA) modules (see Figure 2b). Hybrid beamforming [61] can be realized in the MAA [62] through coarse analog phase-shifting in the RFIC circuits and fine digital beamforming in the baseband (BB) (see Figure 7a). In this design, an arbitrary number of single modules (eight in this case) is connected to a single baseband and control block. Figure 5: Static backhaul solution based on reflectarray technology. Figure 6: Prototype of the backhaul link installed on a lamp post. This proposed design may substantially decrease the feeding line power losses, as they are of a short length in each subarray, and the common feeding is performed at an intermediate frequency (IF). Mass production of unified inexpensive modules further reduces the cost of the large-aperture antenna. The total output power is equal to the sum of the individual single modules and can therefore be scaled according to the specific needs. The LAA architecture uses a different approach to achieve high directivity with a phased antenna array. The array aperture is increased by using a dielectric lens with a special geometry [63; 64; 65] that focuses the single module phased array beam into a single plane (the elevation, for example), allowing steering in another plane (the azimuth). For efficient azimuth plane beamsteering, a lens array antenna with an elliptic-toroidal geometry is proposed [21] with the emitting-phased antenna array module placed on the backside (Figure 7b). In this antenna design, the antenna aperture is determined by (a) the vertical dimension of the lens and (b) the horizontal dimension of the phased antenna array. The number of array elements in the vertical plane may be significantly lower than is required for a phased antenna array of the same gain. Effective heat dissipation may be achieved by placing a radiator on the back of the lens array antenna. The LAA prototype developed in the framework of the MiWEBA project has an aperture (lens height) of 112 mm and a gain of up to 27 dBi. To demonstrate the feasibility of the proposed LAA in access and backhaul applications, real packet transmissions with different MCSs were performed under field conditions. Three experimental scenarios were investigated: device to device (D2D) linking (single PAA module to single PAA module transmission), access linking (LAA to single PAA module) and long-range backhaul (LAA to LAA). The use of single modules without lenses (D2D) allowed transmissions with the highest data rate in SC mode (MCS #12: 4.7 Gbps physical layer rate, 16-QAM with coding rate \(\frac{3}{4}\); see Table 1) at distances up to 15 m. The application of a lens at the transmitter side achieved the maximum data rate (4.7 Gbps), making 16 QAM modulation practical for outdoor communications at distances of about 30-35 m, which can be appropriate for millimeter wave access links. A second experiment investigated the backhaul link on the base of the two LAA antennas. Figure 8 gives a screenshot of the constellation diagrams obtained for MCS #12 transmissions at 100, 150 and 200 m. It was demonstrated that the backhaul link with two LAA gave the highest data transmission rate of 4.7 Gbps at distances up to 200 m, with a negligible packet error rate.