mmWave Antenna-in-Package Design With RFICs

Antenna-in-package design has become the approach of choice for RF systems implementing mmWave functionality, including beamforming with MU-MIMO. Although it would appear that antenna-in-package is a semiconductor design modality, it extends across a range of power levels and frequencies. Antenna-in-package designs span from SiP designs in smartphones up to assemblies for base stations and everywhere in between. Automotive radar designers are likely familiar with antenna-in-package designs as small radar modules implemented in vehicles.

Antenna-in-package offers multiple design approaches with placement of a range of RFICs. As RF designs push up to higher frequencies with more power output in smaller packages, systems designers should know the packaging options available for these systems at each level of the mmWave design hierarchy. This article will examine these packaging options and some important antenna-in-package design approaches used in commercial products.

Antenna-in-Package Design Approaches

Antenna-in-package designs take several forms, depending on the size of the system and its power demands. For example, at the 5G base station level, antenna in-package designs are not necessarily implemented on the same PCB as the host controller or other peripherals, but rather as subsystems bundling antennas with some of the core RFIC elements needed to implement RF functionality. Antenna-in-package designs and form factors include all of the following products:

• Smartphones or small mmWave sensor arrays
• Small and large radar arrays, such as in UAVs and vehicles
• Repeaters for telecom systems
• Base station equipment, both small-cell and large arrays

A typical antenna-in-package architecture implementing an RFIC for signal conditioning and a phased array on a PCB is shown below. In this architecture, the RX and TX signals are brought in through a controller-facing interface, and the RF-front-end is integrated into the chip. The switch on the front-end implements TDD and outputs broadcast signals to antennas in the phased array, resulting in a steered beam being directed to each user accessing the system.

Example antenna-in-package design functionality.

Within this architecture, we have the typical approach to packaging that is required, including RF PCB design, but we also have to consider the IC architecture and technology being used to implement the RF front-end.

IC Architecture

The primary RF components implemented in the baseband and system controller are dominantly built from Si with CMOS processing. Discrete RF components (amplifiers, filters, oscillators, etc.) are typically built from GaAs or GaN. Challenges in scaling GaN technology have limited the material’s usage in RFICs for the RF front-end, rather than as the beamforming controllers operating in the upconverted RF band. The beamforming controller, switching controller, and any other RF components between the baseband and front-end are typically hybrid III-V components, such as GaAs or SiGe (BiCMOS processing).

Antenna Arrays

The antenna array built for an mmWave capable device will vary in size and arrangement depending on the end device. In devices that will be used for scanning or imaging (e.g., advanced radar), the antenna will be constructed as a phased array from multiple antennas. Patch arrays can also be constructed and branched into separate arms. For handheld devices like smartphones, antenna arrays might be included in SiPs that are implemented in the device.

As power, resolution, and range requirements increase, the number of antennas also starts to increase, and the architecture must change accordingly. The table below outlines some application areas and the in-package array types that support these applications.

Patch Arrays Within Phased Arrays

Since advanced RF functionality is needed in mmWave systems implementing antenna-in-package architectures, an appropriate antenna design that offers high gain is needed in the packaging for the overall assembly. Patch arrays are one type of array being implemented to provide high-gain transmission over long distances.

Patch arrays are simple to design: a set of patch antennas are linked together with feedlines and power dividers such that the input signal is phase-matched across all antennas in the array. Parallel-fed patch antennas are hardest to work with in antenna-in-package systems because they also require phase matching across at least one power divider. However, the result is a set of broadcast antennas that provide high-gain emission that is independent of frequency. The alternative approach is to use a series-fed patch antenna, which is common in PCBs for small radar modules.

Example series-parallel patch array antenna.

Patch arrays can also be used in phased arrays. Large groups of patch array antennas can be used in phased arrays to produce very highly directional emission with beam steering along particular directions. When broken into sub-arrays in a MIMO system, multiple users can be served with a single antenna-in-package design. An example array is shown below:

Example phased array with 16 elements, where each element is a 4x2 patch array. Beamforming is achieved by coordinating signal transmission into the 16 array elements.

Working with patch arrays and antenna arrays requires some simulation and evaluation to ensure a design operates at peak performance. Verification is needed at multiple levels:

• Full-wave 3D EM solutions to determine antenna performance
• System-level design and simulation
• Component-level simulation

Whenever you need to place antennas, route feedlines, and develop matching networks, use the complete set of system analysis tools from Cadence. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity. For system-level simulation, users can use best-in-class electromagnetics simulations and CFD simulations to evaluate system functionality. To learn more about antenna-in-package design flows using system-level models in Cadence, read the whitepaper, AiP/AiM Design for mmWave Applications - Advanced RF Front-End Design Flows from Concept to Signoff.

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