Why is the bowtie antenna broadband?

Like the biconical antenna it derives from, the bowtie's broadband behavior comes from its tapered geometry. A standard half-wave dipole is narrowband because its impedance varies rapidly with frequency around its resonance. The bowtie's triangular arms provide a gradual impedance transition from the feed point outward, creating a smoother impedance variation over frequency. The flare angle (half-angle of the triangle) controls the impedance: wider flare angles produce lower impedance and broader bandwidth. For a 60-degree half-angle, the input impedance is approximately 100-150 ohms with 2:1 VSWR bandwidth of about 3:1. Resistive loading at the tips can further extend the bandwidth at the cost of reduced efficiency.

How is a bowtie antenna designed?

Key design parameters: (1) Arm length: approximately lambda/4 at the lowest operating frequency, setting the overall antenna size. (2) Flare angle: 30-90 degrees. Wider angles give broader bandwidth but larger physical size. 60 degrees is a common compromise. (3) Feed gap: typically 1-2 mm, affects impedance matching and acts like the apex gap of a bicone. (4) Substrate: for printed bowties, the substrate dielectric constant and thickness affect the radiation efficiency and resonant frequency. High-permittivity substrates reduce size but increase surface wave losses. (5) Ground plane: a ground plane at lambda/4 spacing creates a unidirectional pattern, improving gain by 3 dB. (6) Balun: the bowtie is a balanced antenna requiring a balun for coaxial feed. Microstrip-to-slotline or tapered baluns are common.

Where are bowtie antennas used?

(1) Ground-penetrating radar (GPR): printed bowtie arrays operating at 200 MHz to 2 GHz for subsurface imaging of utilities, rebar, and geological features. The wideband pulse fidelity of the bowtie preserves the short radar pulse needed for range resolution. (2) UWB communications: IEEE 802.15.4a/z uses wideband signals from 3.1 to 10.6 GHz; bowties provide the necessary bandwidth. (3) EMC testing: alternative to log-periodic antennas for radiated emissions measurement. (4) Phased arrays: printed bowties are used as wideband array elements in connected/tightly-coupled arrays (TCDA) achieving decade bandwidth. (5) Radio astronomy: bowtie dipoles in the SKA-Low telescope cover 50-350 MHz.

Broadband Antennas

Bowtie Antenna

/boh-ty an-ten-uh/ (bow-tie dipole)

A Bowtie Antenna is a wideband planar dipole formed by two triangular conductors in a bowtie shape. The planar equivalent of a bicone, it achieves 2:1 to 3:1 bandwidth through tapered geometry. Its flat profile enables PCB integration, conformal arrays, and phased array elements. Used in GPR, UWB communications, EMC testing, and radio astronomy (SKA-Low).

Category: Broadband Antennas

Bandwidth: 2:1 to 3:1

Gain: 2-5 dBi

Understanding Bowtie Antennas

Take a biconical antenna and flatten it. The result is a bowtie: two triangles, apex-to-apex, fed at the gap. Like the bicone, the tapered geometry provides smooth impedance variation across a wide bandwidth. Unlike the bicone, the bowtie can be printed directly on a PCB, integrated into conformal surfaces, and tiled into large phased arrays. It has become the element of choice for wideband antenna arrays in radar, radio astronomy, and next-generation communications.

Bowtie Antenna Design

Bowtie Antenna:
A Bowtie Antenna is a wideband planar dipole formed by two triangular conductors in a bowtie shape. The planar equivalent of a bicone, it achieves...

Key specifications:
500 MHz | 150 mm | 3 dB | -5 dB | -12 dB | -8 dB

Gain: G = η_ap×4πA/λ²

Wideband Planar Antenna Comparison

Antenna	BW Ratio	Gain	Profile	Application
Bowtie dipole	2:1 to 3:1	2-5 dBi	Planar	GPR, UWB, arrays
Vivaldi (TSA)	10:1+	5-12 dBi	Endfire, planar	UWB arrays, imaging
Patch (standard)	1.05:1	5-8 dBi	Planar, low	Cellular, GPS, Wi-Fi
Stacked patch	1.2:1	5-8 dBi	Planar, medium	Wideband comms
TCDA (connected bowtie)	10:1+	5-8 dBi	Planar	Wideband phased array

Key Equations

Friis transmission:
P_r = P_tG_tG_r(λ/4πd)²

Antenna gain:
G = η_ap × 4πA_eff/λ²

Beamwidth (3 dB):
θ ≈ 70λ/D degrees

Comparison

Aspect	Bowtie Antenna Spec	Typical Range	Impact	Design Note
Primary function	A Bowtie Antenna is a wideband planar di...	Application-dep.	Critical	Verify in sim
Operating range	The planar equivalent of a bicone, it ac...	Application-dep.	Critical	Verify in sim
Performance	Its flat profile enables PCB integration...	Application-dep.	Critical	Verify in sim
Integration	Used in GPR, UWB communications, EMC tes...	Application-dep.	Critical	Verify in sim
Trade-off	Understanding Bowtie Antennas Take a bic...	Application-dep.	Critical	Verify in sim

Common Questions

Frequently Asked Questions

Why is it broadband?

Tapered triangular arms provide gradual impedance transition vs. abrupt resonance of standard dipole. Flare angle controls impedance: wider = lower Z, broader BW. 60-degree half-angle: ~100-150 ohms, 3:1 BW. Resistive loading or connected-array topology extends further.

Design parameters?

Arm length: lambda/4 at lowest frequency. Flare angle: 30-90 degrees. Feed gap: 1-2 mm. Ground plane at lambda/4: +3 dB gain, unidirectional. Substrate: high-permittivity reduces size but increases losses. Requires balun for coax feed.

Applications?

GPR (200 MHz-2 GHz subsurface imaging). UWB comms (3.1-10.6 GHz). EMC testing. Phased array elements (TCDA for decade bandwidth). Radio astronomy (SKA-Low: 50-350 MHz). Flat profile enables PCB printing and conformal mounting.

Related Terms

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