Why is the bow-tie wideband?

The triangular element shape provides a gradual impedance transition from the feed point to the outer edges. Unlike a thin wire dipole (which resonates at a single frequency), the bow-tie's width supports multiple current modes simultaneously. The flare angle (typically 60-90 degrees) controls the impedance bandwidth: wider angles give broader bandwidth but lower impedance. It is the 2D planar equivalent of a biconical antenna.

Typical specifications?

Bandwidth: 3:1 to 10:1 depending on flare angle and loading. Gain: 2-5 dBi (single element), 8-12 dBi with reflector. Impedance: 100-300 ohms (depends on flare angle). Polarization: linear. Pattern: dipole-like (omnidirectional in H-plane). Can be printed on PCB for low-cost mass production. Adding resistive loading extends bandwidth at the cost of efficiency.

Ground-penetrating radar (GPR): wideband for range resolution. UWB communications (3.1-10.6 GHz): FCC-compliant antenna. EMC testing: wideband probe. Microwave imaging: array element. RFID reader: wideband coverage. The planar PCB form factor makes it popular for integrated sensor systems. Bow-tie arrays with ground planes are used in radio astronomy (e.g., SKA low-frequency aperture array).

Antenna Technology

Bow-Tie Antenna

A Bow-Tie Antenna is a planar wideband dipole consisting of two triangular conductors arranged symmetrically with their tips meeting at the feed point. The triangular flare provides a gradual impedance transition that supports 3:1 to 10:1 bandwidth. It is the 2D planar equivalent of the biconical antenna, easily fabricated on PCB, and widely used in GPR, UWB communications, EMC testing, and radio astronomy aperture arrays.

Category: Antenna Technology

Bandwidth: 3:1 to 10:1

Understanding Bow-Tie Antennas

The flare angle α (half-angle of each triangle) determines the input impedance: wider flare = lower impedance, broader bandwidth. At α=90° (flat plate), the impedance approaches that of a biconical antenna (~188 Ω for infinite bow-tie). Practical finite bow-ties with α=60° have ~150 Ω impedance. A balun transforms this to 50 Ω.

Adding a ground plane or reflector behind the bow-tie creates a unidirectional pattern with 5-8 dBi gain, useful for GPR and imaging arrays. Resistive loading (Wu-King profile) at the triangle edges absorbs reflections, extending bandwidth beyond 10:1 at the cost of 3-5 dB efficiency loss.

Bow-Tie Parameters

Lower frequency: f_L ≈ c / (2·L)
L = triangle length (tip to base)
Upper frequency: limited by feed gap

Input impedance (infinite):
Z ≈ 120·ln(cot(α/4)) Ω
α=90°: Z ≈ 188 Ω
α=60°: Z ≈ 150 Ω

Wideband Antenna Comparison

Antenna	BW Ratio	Gain (dBi)	Form Factor
Bow-Tie	3:1-10:1	2-5	Planar (PCB)
Vivaldi	10:1+	5-12	Planar endfire
Log-periodic	10:1+	6-10	3D structure
Spiral	10:1+	2-5	Planar (circular)

Common Questions

Frequently Asked Questions

Why wideband?

Triangular flare gives gradual impedance transition. Multiple current modes. Flare angle controls BW: wider = broader. 2D biconical equivalent.

Specs?

BW: 3:1-10:1. Gain: 2-5 dBi (8-12 with reflector). Z: 100-300 Ω. Linear polarized. PCB-fabricable.

Applications?

GPR (range resolution), UWB comms, EMC probes, microwave imaging arrays, SKA radio astronomy aperture arrays.

Related Terms

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Antenna Design

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