What Are Microstrip Antenna Arrays?

Microstrip antenna arrays are planar antenna systems composed of multiple microstrip patch elements arranged on a dielectric substrate and fed by a common network to produce a combined radiation pattern with higher gain and directional control than any single element alone. Each element radiates through fringing fields at the edges of its conducting patch, and the collective pattern of the array emerges from the superposition of those individual contributions. The array architecture is central to phased-array radar, 5G base stations, satellite communication terminals, and millimeter-wave imaging systems.

The technology builds on the established properties of individual microstrip antennas: low profile, light weight, compatibility with planar fabrication, and straightforward integration with printed RF circuitry. Forming an array multiplies the effective aperture, increasing directivity in proportion to the number of elements, and introduces the ability to steer the beam electronically by controlling the relative phase or amplitude of each element's excitation.

Array Configuration and Feeding

Microstrip antenna arrays are organized as linear, planar, or conformal arrangements depending on the desired scan coverage and aperture geometry. In a linear array, elements are spaced at roughly half a wavelength along a single axis; planar arrays extend this arrangement into two dimensions to enable steering in both azimuth and elevation. The feed network delivers the required amplitude and phase to each element through a corporate feed (a tree of power dividers), a series feed (elements connected along a transmission line), or a space-feed (where a separate source illuminates the array from behind). Corporate feeds offer good amplitude uniformity, while series feeds are more compact but introduce beam squinting with frequency. The design and analysis of these configurations is covered in detail in the ACS Omega study on microstrip patch antenna arrays for space applications, which evaluates directivity and half-power beamwidth across multiple array geometries.

Beam Steering and Pattern Control

Phase-controlled microstrip arrays achieve electronic beam steering by adjusting the progressive phase shift applied across elements. A Butler matrix is a widely used passive feed network that generates orthogonal fixed beams through a set of hybrid couplers and crossover connections, requiring no active phase shifters. For continuous beam steering, active phase shifters or time-delay units are inserted in each element's feed path. The IEEE Xplore paper on two-dimensional beam-steering phased arrays using BST thick-film phase shifters demonstrates how ferroelectric materials can provide low-loss phase control suitable for compact planar arrays at centimeter-wave frequencies.

Array factor analysis defines the directivity, sidelobe level, and null positions that result from a given amplitude and phase excitation. Sidelobe suppression often uses amplitude tapering, such as Taylor or Chebyshev weighting, at the cost of some broadening of the main beam. Mutual coupling between adjacent elements perturbs the active input impedance of each element from its isolated value, requiring compensation in the feed design to maintain pattern fidelity.

Bandwidth and Mutual Coupling

Individual microstrip patches are inherently narrowband, with impedance bandwidths typically in the range of 1 to 5 percent of the center frequency. Array bandwidth can be extended through aperture-coupled feeds, stacked patches, or U-slot loading, which are techniques that reduce the sensitivity of the resonant structure to frequency. As detailed in the IEEE Xplore paper on phased-array reconfigurable antennas for ground-penetrating radar, wideband array designs must manage both the element bandwidth and the frequency-dependent squinting of the feed network simultaneously.

Applications

Microstrip antenna arrays have applications in a range of fields, including:

• 5G base stations and user equipment, providing high-gain beamforming at sub-6 GHz and millimeter-wave bands
• Synthetic aperture radar (SAR) and surveillance radar, forming large apertures with electronically scanned beams
• Satellite communication terminals, enabling low-profile flat-panel dish replacements for mobile users
• Automotive radar at 77 GHz, offering compact phased arrays for adaptive cruise control and collision avoidance
• Medical microwave imaging, arranging arrays around the body for diagnostics and hyperthermia treatment