MICROWAVE BANDPASS FILTER HISTORY AND INVENTION

HISTORY AND INVENTION

The existence of electromagnetic waves was predicted by James Clerk Maxwell in 1864 from his equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF region. The design necessarily used horse-and-buggy materials, including a horse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter whose parabolic cross-section worked as a reflection antenna. In 1894 J. C. Bose publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves.putting the lower boundary at 1GHz (30cm), and the upper around 100GHz (3mm).

MICROWAVE BANDPASS FILTER : filter Types

FILTER

Filter is an electrical network that can transmit signals within a specified frequency range . This frequency range is called pass band and other frequency band where the signal are suppressed is called stop band .The frequency that separates the pass and stop band is known as cut off frequency .

TYPES OF FILTER : Filters are of four types . These are as follows -

1. Low pass filter : In low pass filter the transfer function is

aо

H(s) = ----------------------- where s = jw H(jw) = gain

b2s² +b1s + bо

here increase of frequency makes the gain extremely low .

2. High pass filter : In high pass filter transfer function is

a2s²

H(s) = ---------------------- s=jw H(jw) = gain

b2s² + b1s + b0

Here at low frequency gain is low but at high frequency gain become constant.

3. Band pass filter : In band pass filter transfer function is

aıs

H(s) = -------------------------

b2s² + b1s +bo

here at a middle frequency range H(s) remains constant.

4. Band stop(or rejected) filter : In band stop filter transfer function is

a2s²+ aо

H(s) = ------------------------------

b2s² +b1s+bo

Their characteristic is shown in the figure

MICROWAVE BANDPASS FILTER :Micro wave filter & microwave BPF

MICROWAVE FILTER :

Filter which are designed at microwave frequency is called microwave filter. Microwave filter uses distributed elements . If lumped elements are used for filter design at microwave frequency ,microwave filter design becomes identical to low frequency filter design .

MICROWAVE BANDPASS FILTER

Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter down to as short as one millimeter, or equivalently, with frequencies between 300MHz (0.3 GHz) and 300 GHz. This is an extremely broad definition including both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30GHz, or 10 to 1cm) at minimum, with RF engineering often putting the lower boundary at 1GHz (30cm), and the upper around 100GHz (3mm).

MICROWAVE BANDPASS FILTER :Microwave frequency bands

Microwave frequency bands

The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. Microwave frequency bands, as defined by the Radio Society of Great Britain (RSGB), are shown in the table below:

Microwave frequency bands
Letter Designation	Frequency range	Application
L band	1 to 2 GHz	Military, world space satellite radio, optical communication, GSM mobile phone.
S band	2 to 4 GHz	Weather radar, surface ship radar and some Communication satellite used by NASA .
C band	4 to 8 GHz	Satellite television broadcasts, wifi devices, Cordless phone .
X band	8 to 12 GHz	Satellite communication , radar, space Communication motion detection .
Ku band	12 to 18 GHz	Military , traffic speed detector
K band	18 to 26.5 GHz	Satellite communication ,radar, traffic speed Detector.
Ka band	26.5 to 40 GHz	Radar and experimental communication .
Q band	30 to 50 GHz	Radar and signal processing ,radio astronomy Studies such as telescope, automotive radar .
V band	50 to 75 GHz	High capacity terrestrial millimeter wave Communication system, scientific research.
E band	60 to 90 GHz	Wireless technology
W band	75 to 110 GHz	Millimeter wave radar search , military radar targeting , tracking application .

MICROWAVE BANDPASS FILTER :MICROWAVE FILTER

MICROWAVE FILTER:

Filter which are designed at microwave frequency is called microwave filter. Microwave filter uses distributed elements . If lumped elements are used for filter design at microwave frequency ,microwave filter design becomes identical to low frequency filter design .

MICROWAVE BANDPASS FILTER

Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter down to as short as one millimeter, or equivalently, with frequencies between 300MHz (0.3 GHz) and 300 GHz. This is an extremely broad definition including both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30GHz, or 10 to 1cm) at minimum, with RF engineering often putting the lower boundary at 1GHz (30cm), and the upper around 100GHz (3mm).

There are different types of microwave filter .Among these we are focusing on microwave bandpass filter . It has

Different topologies :->

1. Hair pin

2. comb line

3. Ideal lumped

4. Ideal distributed

5. Inter digital

6. Edge coupled

7. stepped impedance

8. Tubular Waveguide

EDGE coupled filter: The topology consists of asymmetric coupled-slot pairs that symmetric about the center of CPW line. Experimental results are given for a 20GHz filter printed on high-resistivity silicon. As microstrip ,CPW filters may be comprised of coupled lines. Operating principle is based on propagation of two orthogonal modes on the coupled slot geometry and magnetic-wall symmetry is maintained along the center of the line.

Ø Equivalent circuit for an individual for individual coupling section in the bandpass filter (phi=∏/2)