Frequency domain sweeps of array antennas are well-known to be time-intensive, and different surrogate models have been used to improve the performance. Data-driven model order reduction algorithms, such as the Loewner framework and vector fitting, can be integrated with adaptive frequency sampling algorithms, in an iterative scheme, to reduce the number of full-wave simulations required to accurately capture the requested frequency behavior of multiport array antennas. In this work, we propose two novel adaptive methods exploiting a block matrix function which is a key part of the Loewner framework generating system approach. The first algorithm leverages an inherent matrix parameter freedom in the block matrix function to identify frequency points with large errors, whereas the second utilizes the condition number of the block matrix function. The first method effectively provide a frequency domain error estimator, which is essential for improved performance. Numerical experiments on multiport array antenna S-parameters demonstrate the effectiveness of our proposed algorithms within the Loewner framework, where the proposed algorithms reach the smallest errors for the smallest number of frequency points chosen.

This paper introduces a novel filtering approach that employs integrated periodic structures with a conventional Vivaldi antenna to achieve a fully integrated bandpass filtering antenna. The approach results in a wide out-of-band suppression, high passband selectivity, adjustable operational bandwidth, and low insertion loss. The proposed filtering approach maintains the original size of the conventional Vivaldi antenna (base antenna) without requiring additional modifications. To validate the approach, we present two filtering Vivaldi antennas: filtering antenna I (center frequency: 18GHz, fractional bandwidth: 21%, insertion loss: 0.32dB) and filtering antenna II (center frequency: 6.5GHz, fractional bandwidth: 12%, insertion loss: 0.6dB). Their wide out-of-band gain suppression (typically >= 15dB) covers the conventional Vivaldi antenna's frequency range (4-24GHz). A prototype of the filtering antenna I is manufactured. Its measurement results validate the proposed approach and show good agreement with the simulated reflection coefficient, realized gain, and radiation patterns. The features of the proposed filtering antenna approach, make it suitable for various applications requiring efficient frequency filtering.

A convex optimization program is presented for wideband arrays. Constraints are imposed on the frequency variation of excitation coefficients to ensure that the optimal solution can be realized in a wideband active electronically scanned array (AESA). AESA implementation with true time delays (TTDs) and phase shifters are handled separately. We also discuss the general case of combining TTDs and phase shifters. Contrary to single-frequency optimization, the wideband optimization method presented here ensures that the computed excitation is optimal over a specified bandwidth. It is shown that there is a tradeoff between instantaneous bandwidth and sidelobe level. The proposed method works for both narrow and wideband arrays, as illustrated with examples. In addition to regular arrays, the method is also applicable to monopulse arrays. The optimization program is implemented in terms of embedded element patterns (EEPs) to account for and compensate for mutual coupling, radome, and platform effects.

The near-field contribution in the high-frequency method Shooting and Bouncing Rays (SBR) is investigated for installed antenna performance. Three SBR solvers, the in-house solver SIENT and two commercial solvers, are compared to a commercial full-wave solver. SIENT and one commercial solver have an option to disable near-field effects, which allows the strength of these effects to be investigated. The last solver also includes near-field effects. The results indicate an increase in accuracy when including near-field effects. The most notable difference in the far-field phase and the induced surface current are obtained for the in-house solver. Improvements for the surface current density is seen close to the antenna. On the tested platform, the difference in gain is not as notable but it is overestimated for both the in-house solver and the commercial solvers when excluding near-field terms.

This paper presents a novel active integrated antenna unit cell for millimeter-wave (mmW) active array designs. With the co-design of the electromagnetics and circuits, a 47% power added efficiency has been achieved over a 5 G band around 28 GHz. The direct matching network is simple and compact, which is easy to be allocated in the antenna unit cell. Moreover, the impedance bandwidth is also stable versus beam scanning in various directions. Hence, the investigated deep integration and direct matching technologies have significantly enhanced the system power efficiency, paving the way for high efficiency mmW communication systems.

In Internet of Things (IoT) applications the antennas are often electrically small at their radiation frequency. This makes it hard to design antennas that meet desired bandwidth requirements. It is therefore interesting to consider the trade-off between antenna size and antenna position within the terminal with respect to its available bandwidth, as characterized by the Q-factor bound. To determine these quantities are associated with solving a non-trivial optimization problem. Recent development of model order reduction techniques can include parametric dependencies. Here we apply the data-driven Loewner framework to the Q-factors as a function of size and position parameters, to investigate how well these methods work for the Q-factor bounds in IoT applications. We show that the Loewner framework can deliver a reduced-order model of the bound. Properties of the reduced model can be used to indicate how well the reduced order interpolates the parametric dependence.

This paper investigates the number of required data points to accurately represent the vector far-field information over the radiation sphere and its frequency variation for array antennas. The method needs to be explicit in terms of the excitation of the elements. We compare representations of far-field data on the sphere with two different approaches to spherical wave expansion representations and apply a data-driven model-order reduction to find a small-size representation. As is well known, a spherical wave expansion strongly reduces the number of required data points. Here, we show that accounting for the phase center of the elements further strongly reduces the number of required coefficients in the tested cases. The Loewner framework datadriven model-order reduction shrinks the required far-field data by an additional factor of 8-14 per mode coefficients, depending on the acceptable level of error. This reduction works well for the two investigated cases.

A new wide-scan active direct-integrated phased array antenna (AIPAA), designed for Tx/Rx mm-Wave applications, is introduced in this paper. This novel AIPAA offers seamless switching performance between transmitting (Tx) and receiving (Rx) modes without the need for lossy intermediate RF components, such as RF switches, circulators, and duplexers. The unitcell of the AIPAA consists of three miniaturized tapered slot elements operating in the K-band frequency range. In the Tx mode, a GaN high electron mobility transistor serves as the power amplifier (PA), while in the Rx mode, a GaAs MMIC low noise amplifier (LNA) is employed. The unticell's center antenna element is reshaped to match closely to the optimal load impedance of the PA ( Zopt=6+j36Ω ) while the other elements are tuned to maintain a 50Ω input impedance suitable for the LNA. This direct integration approach enhances system efficiency and reduces the cost and size by eliminating the need for any intermediate impedance matching networks and RF switching components. The proposed Tx/Rx AIPAA achieves a matching at both the PA (optimum load) and LNA ( 50Ω ) ports with a 6% and 16% fractional bandwidth over ±50° scan coverage, respectively. The switching capability is incorporated by utilizing the ON/OFF modes of the PA and LNA DC-biasing. The proposed AIPAA's cell size is 9.2×6.5×1.8 mm3(0.67×0.5×0.13λ3) .

This paper presents a novel method for analyzing and reducing the total coupled power in the Active Highly Integrated Phased Array Antennas (AIPAA), incorporating both the nonlinear impacts of the power amplifier (PA) transfer functions and the normalized scattering matrix. The proposed method introduces a new degree of freedom to reduce the coupling level utilizing two key factors: (i) the balance between the PAs’ transfer function gain and the coupled power difference to the PAs’ gate and drain/antenna ports, and (ii) the out-of-phase sum based on PAs’ transfer function phase response. The proposed method is theoretically demonstrated by accounting for all tones and also is subsequently simplified for the main tone. The method is practically validated by applying the method to a 1 × 5 AIPAA structure to reduce the total coupled power at its drain/antenna port. The results demonstrate a coupling reduction of −5 dB as an average with a maximum reduction of −20 dB, over a scan coverage of ±30∘ and 10% fractional bandwidth at 22 GHz for the center cell.

Circular polarization is an essential feature for small antennas designed to connect with satellite navigation systems. Here, a Q-factor optimization problem constrained with a circular polarization radiation requirement is formulated and solved. The constrained problem is shown to be solvable as fast as calculating the Q-factor bound without the constraint. Two antenna models are designed to assess the bounds. One aims for bandwidth, and the other for circular polarisation. The well-known relation between the Q-factor and the available bandwidth is used to evaluate the designs. The circularly polarised antenna is close to the bound and has a wide field of view. The Q-factor bound provides insight into desirable antenna positions on the small device.