Global deployments of 5G networks are on a rapid pace and are expected to deliver a 100x increase in network capacity compared to 4G. To expand network capacity, the 5G NR air interface enables diverse spectrum in both the sub-6 GHz and mmWave frequency bands. The additional spectrum enabled by 5G brings new challenges for product design and global deployment, particularly in the mmWave frequency range. Customer premise equipment (CPE) solutions that operate in the mmWave frequency band are required to bring 5G fixed wireless access (FWA) to urban and suburban landscapes. To achieve the high data rates and low latencies promised by 5G, the antenna system becomes a crucial component in the overall system design. The Antenna Company is developing mmWave active antenna arrays for CPE applications that utilize novel materials and advanced antenna design strategies to address the performance limitations of conventional printed circuit board (PCB) solutions. This article discusses the performance benefits of utilizing a 64-element dielectric resonator antenna (DRA) array.
DRA BENEFITS FOR 5G
The new generation of 5G wireless communications is designed to provide mobile users with fiber-like data speeds, low latency and high signal fidelity. Industry-wide development efforts to enable these performance breakthroughs include advanced channel coding techniques, massive MIMO and mobile mmWave. Breakthroughs in antenna system design are crucial for the global use of mmWave spectrum. In addition to providing radio coverage, antenna systems must be able to reconfigure the radiation pattern characteristics to meet the dynamics in 5G wireless communications.1
Figure 1 Magnitude of the input reflection coefficient of the individual DRA element (the illustration shows the configuration of the radiating structure).
Advances in material science and manufacturing make DRA technology a valid solution for the development of commercial array antennas. DRAs share several features with their counterpart, patch antennas; they are compact and are easy to integrate with active electronics. However, DRAs are more efficient than patch antennas at mmWave frequencies due to the high conduction loss. In addition, DRAs can provide more design freedom, compared to patch antennas, in relation to the geometry and materials forming the basic dielectric resonating structure. Different feeding techniques, design procedures and DRA structures can be found in review papers.2-3 Long et al. systematically studied the radiation characteristics of different DRAs and their potential for mmWave applications.4 It is shown that DRAs are compact, lightweight, cost-effective and feature broader bandwidth (BW) characteristics and large scanning angles up to ±60 degrees and beyond, as compared to patch antennas.5-6
The BW of phased array antennas is mostly determined by the active reflection coefficient during beam steering that affects the scan-loss characteristics of the antenna array. In addition, the shape of the embedded element pattern plays an important role. The mutual coupling can degrade the pattern by modifying the embedded pattern shape and the realized excitation coefficients.
An 8x8 array of dielectric resonator antennas fed by slot antennas is proposed for mmWave 5G wireless communications. The total radiation efficiency is modeled as a function of frequency and beam steering. It is shown that the total radiation efficiency is higher than 80 percent over the frequency band from 26 to 34 GHz and for scan angles up to 60 degrees. The DRA can perform beam steering over wide BW with a scan-loss comparable to the array factor of an ideal source. In addition, the DRA array is 20 percent smaller in size compared to conventional half-wavelength spaced antenna arrays.
In this article, attention is given to the optimal design of hybrid DRA/slot antennas. It will be shown that the antenna impedance BW can be easily tuned in such a way as to synthesize a wide- or multi-band frequency response.
ANTENNA ARRAY DESIGN
Individual Antenna Element Design
A single array antenna element consists of a slot antenna fed by proximity coupling via a microstrip transmission line. The dielectric material for the transmission line is RO4308 with relative permittivity (εr) of 3.6. The slot then feeds a square dielectric rod, as illustrated in Figure 1. In this design a dielectric material with εr = 11.3 is used in the analysis. With a proper selection of dimensions similar to Keyrouz and Caratelli,5 the slot antenna radiates properly and excites the proper modes in the dielectric rod (Transverse Magnetic modes). A detailed mode analysis can be found in Long et al.4
Figure 2 Antenna element feeding structure.
By using a fork-like microstrip line to feed the aperture slot (see Figure 2), the impedance can be well matched to 50 Ω with a broadband reflection coefficient better than −10 dB over the frequency range from 26 to 30 GHz (see Figure 1). In particular, the antenna element is fitted with a suitable mini-SMP connector, as shown in Figure 3. Notice that the considered DRA element displays a radiation pattern that is mostly confined in the half-sphere above the relevant ground plane.
Figure 3 Integration of mini-SMP connector to the individual DRA element.
Figure 4 Three-dimensional view of an 8x8 array of uniformly spaced DRA elements.
