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A power-detecting, null-scanning, retrodirective antenna array for CubeSat platforms is presented. The system utilizes several hardware and software enhancements over previous retrodirective array architectures to address the size, weight, and power limitations of the CubeSat structure. Full-duplex retro-directivity is reported at 9.59 and 9.67 GHz for transmit and receive, respectively.

An interleaved, interelement phase-detecting/phase-shifting retrodirective antenna array for interference reduction is presented. This system uses two independent retrodirective subarrays to form a null in one direction while retrodirecting a beam in another direction, while also eliminating the R4 path loss of previous interleaved architectures. Retrodirectivity as well as null steering is reported at 2.4 GHz.

A liquid-metal reconfigurable Yagi-Uda monopole array is presented. The three-element array consists of driven and parasitic elements whose lengths can be tuned with pressure-driven liquid metal, resulting in an array in which directors can be transformed into reflectors, and in which elements can be tuned to different frequencies. The measured radiation patterns demonstrate single-axis beam steering at multiple operational frequencies from 1.95 to 4.11 GHz.

An overview of the progress made in the RDA field has been presented. The reflect-type architecture that is perhaps most useful for communication purposes is likely to be the phase-conjugating Pon array; this architecture is capable of handling nonuniform wavefronts though it suffers from a large path loss. To correct the path loss issue associated with reflect type arrays, RDAs based on phase- and power-detection were developed. The power-detecting array offers the advantage that it may be readily miniaturized, as well as adding the benefit of measuring the direction of arrival. Phase-detecting/phase-shifting architectures were found to be ideal if phase detectors were used between adjacent element pairs, as the extra phase information permitted retrodirecting nonuniform wavefronts. The next steps in RDA development involve reducing their size, while optimizing the efficiency of the components that make up their hardware.

This paper described the miniaturization challenges in implementing an RDA architecture for a heavily resource-constrained CubeSat platform; by demonstrating this, a transition towards implementation on other highly mobile platforms can be accelerated. Addressing size, weight, and power in RDAs can be achieved through downsizing of circuitry through PCB design while reducing power consumption in each of the operating states, most importantly the prevalent static state.

It has been shown that PCAs suffer from performance variability due to changes in the phase difference and incident angle of interrogating sources. This performance instability can be mitigated by increasing the number of elements in the array.

A full-duplex self-steering array using power detection and phase shifting is presented. The system utilizes two sub-arrays to autonomously steer its beam toward an interrogating signal. A two-element null-scanning array is used for power detection where the interrogator direction is determined by the location where minimum power is detected. Retrodirectivity is reported for angles of 0°, −30°, and +10° at a receive frequency of 7.31 GHz and a transmit frequency of 7.33 GHz.

The performance of a phase-conjugating array (PCA) in a multiple-interrogator environment is investigated. The PCA demonstrates the ability to properly retrodirect signals toward multiple interrogators to varying degrees, dependent on phase, angle of incidence, and amplitude differences between the interrogators. The effect of the three parameters is demonstrated for the 6-GHz array at interrogating angles of ±10° and ±20°. Agreement between the experimental results and theoretical simulations confirm the validity of the measurements; extrapolation of the simulations for additional cases is also presented.

A retrodirective array designed to respond to nonuniform wavefronts is presented. The design overcomes the limitations of existing phase-detection-based retrodirective array architectures by measuring the phase difference between adjacent element pairs to increase array resolution. The transmit and receive frequencies are 2.45 and 2.4 GHz, respectively. Measurements demonstrate the ability to retrodirect to both single and multiple interrogators.