Saturday, August 27, 2011

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

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

b2s² +b1s + bо

here increase of frequency makes the gain extremely low .

  1. 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.

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

a2s²+

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

b2s² +b1s+bo

Their characteristic is shown in the figure

MICROWAVE BANDPASS FILTER : filter Types

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)

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