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I’m designing a bidirectional antenna for an H-plane sector, but my main lobes are lopsided. What are the key design principles for achieving perfect symmetry in the radiation pattern?

My project requires a simple, planar antenna that radiates equally in two opposite directions (±x) in the H-plane. I've tried a basic dipole and a patch, but the main lobes are always uneven in gain and beamwidth, which ruins my link budget symmetry. Is this an inherent limitation of single-feed structures, or are there specific geometries (like a properly fed bow-tie, a slot antenna, or a two-element array) and substrate/ground plane configurations that enforce pattern symmetry in practice?

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By Deep Answered 1 year ago

For rapid prototyping, I rely on these semi-empirical starting points, remembering they assume an infinite ground plane. For a circular disc monopole, the dominant relationship is between the lowest frequency f_L and the effective radius a: f_L ≈ c / (4*a), where c is the speed of light. For 3.1 GHz, this gives a ≈ 24mm. The ground plane length should be > a. For a rectangular monopole, height h is roughly λ/4 at f_L, so h ≈ 24mm. For elliptical dipoles, the major axis is similar. The feed gap is critical; start with 0.3-0.5mm. These are starting points; UWB operation hinges more on creating multiple, overlapping resonances and smoothing impedance transitions. I then use a parametric sweep in my solver on 2-3 key dimensions (height, feed gap, taper angle) to quickly widen the bandwidth from this initial narrowband resonance.

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