Feature: Communications design
every antenna element. This coverage means a significantly high loss and challenging to fit into a given antenna spacing. Having a 6-bit phase PS resolution with the given coverage would bring some design challenges, along with the many delay stages to be placed into TTD. If resolution is preserved and the coverage is reduced to
mitigate these drawbacks, then we would have to wrap back through zero when the coverage is exceeded (by calculating phase equivalent using Equation 4), but then, ironically, the beam squint feature would be lost. This quick analysis shows that using PSs at every antenna
element followed by TTDs at the common legs of subarrays can be useful even when cross-polarisation is not required. TTDs in Figure 1 would again need the same coverage, but this time the resolution requirement is relaxed compared with the case of a TTD at every antenna element, since now they are used to align relatively larger time delays between subarrays. Breaking down a phased array into subarray partitions
reduces the cost and complexity of a system at the expense of higher scan loss and lower beam-steering resolution. By having wider beamwidth, subarrays are more tolerant to beam squint effects. It is apparent that beam squint and beamwidth targets are important metrics affecting subarray size.
Design planning True time delays behind every antenna element are required for broadband squint-free operation, and phase shifters behind
every V and H feed of each antenna element are required for a broadband cross-polarisation operation. If cross-polarisation is not required and fully squint-free operation is targeted, then TTD-based design should be followed. As the frequency increases, adding PSs could help meet the QSLL target, in return for a compromised squint-free operation. If cross-polarisation is required, then each polarisation feed
of the antenna should be followed by separate yet identical PSs with a tight 90° difference above the operational bandwidth. Adding TTDs on the common leg of PSs could help to mitigate the beam squint. Whether cross-polarisation is required or not, a subarray
architecture with PSs behind antenna elements followed by TTDs at the common legs of subarrays can be a cost-effective solution. Note that TTD functionality can be implemented in a digital domain and all digital design can eliminate both TTDs and PSs at the expense of higher system cost. Before diving into the countless challenges of ESA design,
understanding the differences in using either TTDs or PSs vs. using them in tandem is an essential part of planning a system-level beamforming architecture that meets system requirements for better size, weight, power and cost. Analog Devices has a huge portfolio of solutions,
platforms and products for all analogue, digital and hybrid beamforming ESAs in a wide range of applications, along with the capability to provide tailored power solutions for the complete signal chain.
M 26 September 2022
www.electronicsworld.co.uk
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