On completion of this module, you will be able to:

• Understand filter design
• Explain microwave amplifier design
• Explain microwave mixer design
• Explain microwave oscillator
• Explain different types of microwave antennas like Parabola, Horn and Slot antenna.

Microwave Filter Design

• A filter is a two port network used to control the frequency response at a certain point in microwave system by providing transmission at frequencies within the pass band and attenuation in the stop band.
• Filter can be classified into four different categories of characteristics; It include Lowpass frequency (LPF), Highpass frequency (HPF), Bandpass frequency (BPF), Bandstop Frequency (BSF).
• There are some main classes of amplitude response such as Butterworth, Chebyshev, Elliptic, Gaussian ans so forth.
• The insertion method can be used to characterise a filter response in microwave. It is defined as the ratio of power available from source to power delivered to load.

Butterworth Filter

• A Butterworth filter is a type of filter designed to have a frequency response as flat as possible in the passband. Hence the Butterworth filter is also known as maximally flat magnitude filter.
• The frequency response of the Butterworth filter is flat in the passband and roll-offs towards zero in the stopband. The rate of roll-off response depends on the order of the filter.
• The inductor and capacitor are reactive elements used in filters. But in the case of Butterworth filter only capacitors are used. So, the number of capacitors will decide the order of the filter.
• The frequency response of the Butterworth filter for various orders of the filter is shown below.


Fig. : Frequency Response of Butterworth Filter

Fixed attenuator

• It provides only fixed amount of attenuation. It consists of dissipative element called pad and it is placed in a waveguide
• Pad is placed in such a way that its plane is parallel to the electric field. For this two thin metal rods are used.

• The pad is tapered, which provides a gradual transition from waveguide medium to absorbing medium of pad. It also reduces reflection
• The amount of power that a fixed attenuator can absorb depends on Strength of dielectric field, Location of pad within waveguide, Frequency of operationArea of pad and pad material used for power absorption

Variable Attenuator

• It provides continuous attenuation
• The amount of attenuation is controlled by depth of insertion of absorbing plate inside the waveguide
• For this a knob and gear assembly is used. Knob can be calibrated suitably. The maximum attenuation will be offered when the pad extends all the way across the guide
• Types of variable Attenuators -
  1. Rotary attenuator
  2. Electronically controls( PIN diode , FET attenuator)