Waveguides, Fibres and Antennas

Syllabus: Rectangular and circular waveguides, light propagation in optical fibers, dipole and monopole antennas, linear antenna arrays.

9 hand-picked visual resources on this topic, 3 of them little-known gems — under each card, look for See it. Every link is checked against the live site before it ships.

Rectangular waveguide

A hollow guide is a high-pass filter: nothing below the cutoff of its lowest mode propagates. With $a>b$ , the dominant mode is $\mathrm{TE}_{10}$ and its cutoff depends only on the broad wall.

$f_c=\dfrac{c}{2\sqrt{\mu_r\varepsilon_r}}\sqrt{\left(\dfrac{m}{a}\right)^2+\left(\dfrac{n}{b}\right)^2}$

Where marks are lost

Below cutoff the mode is evanescent, not absorbed: $\gamma$ is purely real, the field decays exponentially and no power flows. That is different from attenuation by loss.

See it

Optical fibre

Light is trapped by total internal reflection between a core of index $n_1$ and a slightly lower cladding $n_2$ . Numerical aperture measures how wide a cone the fibre accepts.

$\mathrm{NA}=\sqrt{n_1^2-n_2^2}=n_1\sqrt{2\Delta}$

Dipoles, monopoles and the link budget

Four numbers carry most antenna questions: a half-wave dipole has $R_r=73\,\Omega$ and $D=1.64$ ; the quarter-wave monopole over a ground plane has half of each. Everything else is Friis.

$R_r=80\pi^2\left(\dfrac{dl}{\lambda}\right)^2$

Below: on the syllabus, but no past question for it in this bank.

Linear arrays
syllabus

The pattern of $N$ identical elements is the element pattern multiplied by the array factor. The progressive phase shift $\alpha$ steers the beam: zero points it broadside, $\alpha=-\beta d$ points it endfire.

$\mathrm{AF}=\dfrac{\sin(N\psi/2)}{N\sin(\psi/2)},\qquad \psi=\beta d\cos\theta+\alpha$

← Transmission Lines and Matching

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Waveguides, Fibres and Antennas

Syllabus: Rectangular and circular waveguides, light propagation in optical fibers, dipole and monopole antennas, linear antenna arrays.

9 hand-picked visual resources on this topic, 3 of them little-known gems — under each card, look for See it. Every link is checked against the live site before it ships.

Rectangular waveguide

A hollow guide is a high-pass filter: nothing below the cutoff of its lowest mode propagates. With $a>b$ , the dominant mode is $\mathrm{TE}_{10}$ and its cutoff depends only on the broad wall.

$f_c=\dfrac{c}{2\sqrt{\mu_r\varepsilon_r}}\sqrt{\left(\dfrac{m}{a}\right)^2+\left(\dfrac{n}{b}\right)^2}$

Where marks are lost

Below cutoff the mode is evanescent, not absorbed: $\gamma$ is purely real, the field decays exponentially and no power flows. That is different from attenuation by loss.

See it

Optical fibre

Light is trapped by total internal reflection between a core of index $n_1$ and a slightly lower cladding $n_2$ . Numerical aperture measures how wide a cone the fibre accepts.

$\mathrm{NA}=\sqrt{n_1^2-n_2^2}=n_1\sqrt{2\Delta}$

Dipoles, monopoles and the link budget

Four numbers carry most antenna questions: a half-wave dipole has $R_r=73\,\Omega$ and $D=1.64$ ; the quarter-wave monopole over a ground plane has half of each. Everything else is Friis.

$R_r=80\pi^2\left(\dfrac{dl}{\lambda}\right)^2$

Below: on the syllabus, but no past question for it in this bank.

Linear arrays
syllabus

$\mathrm{AF}=\dfrac{\sin(N\psi/2)}{N\sin(\psi/2)},\qquad \psi=\beta d\cos\theta+\alpha$

Waveguides, Fibres and Antennas

Rectangular waveguide

Optical fibre

Dipoles, monopoles and the link budget

Linear arrayssyllabus

Waveguides, Fibres and Antennas

Rectangular waveguide

Optical fibre

Dipoles, monopoles and the link budget

Linear arrayssyllabus

Linear arrays
syllabus

Linear arrays
syllabus