Miniaturised folded-short patch antenna designs for compact platforms: CubeSats and UAVs

Abstract

The increasing demand for compact platforms such as unmanned aerial vehicles (UAVs) and small satellites, particularly CubeSats, has necessitated the need for innovative compact antenna solutions offering high performance at a low cost. Therefore, the increasing demand for compact, lightweight, and high-performance antennas has driven significant research in miniaturised designs suitable for modern communication systems. However, implementing antennas for compact platforms has many challenges, mainly relating to size, weight, and power limitations, making it a crucial yet intricate aspect of these compact platforms. Researchers have investigated novel methods to enhance compact antennas, addressing size and weight challenges through techniques such as folding, shorting, and miniaturisation to decrease both dimensions and mass. Furthermore, employing additive manufacturing techniques like 3-D printing can enhance manufacturing efficacy. Moreover, these techniques help to facilitate the low-cost realisation of such non-deployable and compact antennas, which might be favourable when compared to more conventional manufacturing solutions and deployable antenna designs.

It is also important that these compact platforms employ circularly polarised (CP) antennas and beam steering arrays. Having CP capability is crucial for supporting reliable as well as resilient communication links and connectivity in dynamic and multipath environments. CP also reduces polarisation mismatch losses, improving signal reception when sending and receiving antennas are not perfectly aligned and can mitigate depolarisation effects when signals are propagating through the Earth’s atmosphere. This capability is especially beneficial for compact platforms, where platform rotation or misalignment frequently occurs. Therefore, broad angle radiation and link coverage (enabled by wide angle half-power beamwidths) guarantee more robust signal connectivity, and this enhances link reliability. Furthermore, beam-steering functionality is essential for dynamic and adaptive communication systems, as it allows the antenna phased array to redirect its primary radiation beam towards the intended target without the need for physical movement of the platform. This increases tracking precision, signal strength, and angular coverage for UAVs and small satellites. Integrating beam-steering into compact antennas also facilitates real-time modifications to sustain optimal communications with ground stations or other airborne and spaceborne systems, enhancing both data flow and system adaptability.

In this thesis, the main goal is to address these needs for small and compact antennas to be integrated on said compact platforms. In addition, this thesis presents an extensive study of the design and development of miniaturised folded-short patch (FSP) antennas for compact ground planes while also minimising the space and weight requirements for the antennas and arrays. Furthermore, this work studies dual-band functionality, dual-circularly polarised (DCP) radiation, and beam steering functionality while also employing new and innovative additive manufacturing techniques.

Followed by Introduction and Background Chapters, the first contribution of this thesis (in Chapter 3) presents a new FSP array that provides dual-band functionality and DCP radiation, suitable for communications, geolocation, and other wireless applications. The proposed 2 × 2 FSP array design with a total size of 50 mm x 50 mm, operates at about 1:1 and 2:4 GHz and offers good radiation performance. In addition, this approach achieves high efficiency and stable radiation properties while maintaining a compact footprint. In Chapter 4, a 3-D metalprinted dual-band compact antenna array is reported with a total size of 268 mm x 66 mm. The 1x4 compact linearly polarised array can offer beam-steering capabilities with dual-band operation; i.e. in the L-band at 1.15 GHz and the S-band at 2:38 GHz. In addition, the measured peak realised gain is 4.7 dBi at 1.15 GHz and 4.2 dBi at 2.38 GHz. This array design can offer beam-steering and can improve the communications link as well as reliability in dynamic circumstances. This design has shown promise for 3D metal printing by additive manufacturing (AM) techniques, for such aerospace and airborne applications. The third contribution in Chapter 5 examines AM-inspired compact and lightweight antenna designs, exploring hybrid methods; i.e. AM, more conventional subtractive manufacturing, and, printed circuit board (PCB) material integration. This hybridisation of the different fabrication methods achieves structural effectiveness as well as new antenna functionalities, in particular, design tunability. The proposed 2x2 compact array operates in the lower frequency band (UHF/VHF) with a total size of 90 mm x 90 mm. This demonstrates the compactness of the antenna design, as the operating wavelength can be approximately 1 metre. The array also offers CP radiation. Moreover, the study demonstrates how advanced AM techniques may be employed, along with more conventional assembly approaches, to offer further miniaturisation, reduce mass by introducing air-holes (AH), and enhance antenna efficiency while still maintaining antenna performances. In summary, the various antennas designed and measured in this final contribution demonstrate the feasibility of reduced mass and controllable operating frequency by the hybridisation of the aforementioned manufacturing techniques. For example, the structure can be tuned to operate between 300 MHz and 600 MHz, while not changing the physical antenna footprint of 90 mm x 90 mm.

All in all, this PhD research can enhance next-generation compact antenna technology, specifically when considering placement on small satellites (i.e., CubeSats), UAVs, and other related compact platforms, in terms of mass reduction and selective antenna performances.